Interconnect structure for multi-thickness semiconductor device

Interconnect structure includes conductive features that connect two or more circuit elements (such as transistors, power source, signal input, etc.) together electrically. Interconnect structure includes both on-chip interconnect of integrated circuits and off-chip interconnect in heterogeneous system integration. In interconnect design, geometric dimensions (width, thickness, spacing, aspect ratio, pitch), materials, process control and design layout are critical to proper interconnect function, performance, power efficiency, reliability, and fabrication yield.

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1 A- 1 D illustrate a series of layout and cross-sectional views of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process.

FIG. 2 illustrates a process flow diagram of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process.

FIGS. 3 A- 3 B illustrate layout and cross-sectional views of some embodiments of an interconnect structure having a staggered via.

FIGS. 4 A- 4 B illustrate layout and cross-sectional views of some additional embodiments of an interconnect structure having a staggered via disposed on a boundary region of an underlying metal line.

FIGS. 5 A- 5 B illustrate layout and cross-sectional views of some additional embodiments of an interconnect structure having multiple staggered vias with different heights.

FIGS. 6 A- 6 B illustrate layout and cross-sectional views of some additional embodiments of an interconnect structure having a staggered via and a second via of smaller height and aligned upper surface.

FIGS. 7 A- 11 B illustrate a series of layout and cross-sectional views of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process.

FIGS. 12 A- 15 B illustrate a series of layout and cross-sectional views of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process at a corner region of a metal line.

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples for similar features. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Fabricating semiconductor devices involves depositing and patterning various materials such as semiconductor, dielectric, and metal to form circuit elements. The circuit elements then need to be electrically connected to function properly. An interconnect structure includes conductive features that connect two or more circuit elements (such as transistors, power source, signal input, etc.) together. Interconnect structure can be either an on-chip interconnect of integrated circuits or off-chip interconnect in heterogeneous system integration. In interconnect design, geometric dimensions (width, thickness, spacing, aspect ratio, pitch), materials, process control and design layout are critical to proper interconnect function, performance, power efficiency, reliability, and fabrication yield.

In some applications, a semiconductor device has a non-uniform thickness, or multiple semiconductor devices with different thicknesses are integrated on one substrate. For example, MEMS devices may comprise gaps with multiple heights; acoustic devices may require different distances from respective flexible and fixed plates, or optical devices may have cavities of different lengths. One way of forming a multi-thickness structure is to form and pattern a first dielectric layer on a first region requiring a greater thickness followed by forming a second dielectric layer globally. Still, it could be challenging to form the interconnect structure to connect a metal line from bottom to top of the multi-thickness structure. Deeper vias may result in a less reliable connection and greater contact resistance with underlying metal. Also, a separate masking and patterning process may be needed to form the deeper vias in order to reduce over-etching damage to other via regions with a smaller dimension.

Accordingly, some embodiments of the present disclosure relates to a new method to form an interconnect structure for multi-thickness semiconductor device, and the associated interconnect structure. In the method, a first via may be formed by a two-step process, where a lower portion of the first via is formed when patterning a first dielectric layer for raising height in a first region, and an upper portion of the first via is subsequently formed by forming and patterning a second dielectric layer overlying the patterned first dielectric layer and concurrently forming a second via in a second region absenting the first dielectric layer. Thus, no additional patterning process is needed for forming the first via and the second via with different thicknesses. In some embodiments, the first via is formed with a bottom lateral dimension of the upper portion greater than a top lateral dimension of the lower portion, and therefore results in a staggered via shape with a ledge between the upper portion and the lower portion. Since the step height for filling the first via is reduced by having the staggered via shape with a ledge in the middle, reliability and contact resistance of the first via can be improved.

FIGS. 1 A- 1 D illustrate a series of layout and cross-sectional views of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process. Although FIGS. 1 A- 1 D are described in relation to a method, it will be appreciated that the structures disclosed in FIGS. 1 A- 1 D are not limited to such a method, but instead may stand alone as structures independent of the method.

As shown in the layout and cross-sectional views of FIG. 1 A , a first metal line 106 A and a second metal line 106 B are provided. In some embodiments, the first metal line 106 A and the second metal line 106 B may be arranged one next to another and may be arranged repeatedly in arrays. To form a greater height above the first metal line 106 A, in some embodiments, a first dielectric layer 108 is firstly deposited over the first metal line 106 A and the second metal line 106 B and then patterned to be removed from the second metal line 106 B. A through-hole 110 is formed from the patterning process exposing a first contact region of the first metal line 106 A. In some embodiments, the through-hole 110 may have a square shape as shown, or another polygon or circle shape alternatively, from the layout view. The through-hole 110 may be arranged at one or more various locations above the first metal line 106 A, such as a boundary region of the first metal line 106 A as shown in FIGS. 1 A- 1 D . In some alternative embodiments, the through-hole 110 may be arranged at one or more of a central region, a corner region, or other applicable locations.

As shown in the layout and cross-sectional views of FIG. 1 B , a second dielectric layer 112 is formed over the first dielectric layer 108 overlying the first metal line 106 A and also overlying the second metal line 106 B absenting the first dielectric layer 108 . Thus, the first dielectric layer 108 and the second dielectric layer 112 collectively build a greater height directly above the first metal line 106 A than a height directly above the second metal line 106 B. The second dielectric layer 112 may extend into the through-hole 110 reaching the first contact region of the first metal line 106 A. In some embodiments, the second dielectric layer 112 may be deposited globally. In some alternative embodiments, the second dielectric layer 112 may also be patterned but still left to cover at least portions of the first dielectric layer 108 and the second dielectric layer 112 .

As shown in the layout and cross-sectional views of FIG. 1 C , the second dielectric layer 112 is then patterned to concurrently form a first via-hole 116 A directly above the lower through-hole 110 and a second via-hole 116 B exposing a second contact region of the second metal line 106 B. The through-hole 110 and the first via-hole 116 A collectively form a via-hole for a first via 118 A (see FIG. 1 D ). The second via-hole is for a second via 118 B (see FIG. 1 D ) with a depth smaller than the first via 118 A. In some embodiments, the first via-hole 116 A or the second via-hole 116 B may have a square shape as shown, or another polygon or circle shape alternatively, from the layout view. The first via-hole 116 A may be arranged concentric with the through-hole 110 . In some embodiments, a bottom lateral dimension of the first via-hole 116 A is greater than a top lateral dimension of the through-hole 110 , and therefore results in a staggered shape with a ledge between the first via-hole 116 A and the through-hole 110 . The second via-hole 116 B may be arranged at one or more various locations above the second metal line 106 B, such as a boundary region as shown in FIGS. 1 C- 1 D . In some alternative embodiments, the second via-hole 116 B may be arranged at one or more of a central region, a side region within the boundary of the second metal line 106 B, a corner region, or other applicable locations, as discussed in more detail later on. In some embodiments, the second via-hole 116 B may have a top or bottom lateral dimension, such as a diameter or a side length, that is between those of the first via-hole 116 A and the through-hole 110 .

As shown in the layout and cross-sectional views of FIG. 1 D , the first via 118 A and the second via 118 B are respectively formed within the first via-hole 116 A and the through-hole 110 and the second via-hole 116 B. In some embodiments, the first via 118 A extends along a first upper surface 112 u 1 of the second dielectric layer 112 , and the second via 118 B extends along a second upper surface 112 u 2 of the second dielectric layer 112 . A first device 128 may be formed on the first via 118 A above the first upper surface 112 u 1 and electrically connected to the first metal line 106 A. Similarly, a second device 130 may be formed on the second via 118 B above the second upper surface 112 u 2 and electrically connected to the second metal line 106 B. As an example, control signals may be provided from a logic circuit to the first device 128 and the second device 130 respectively through the first metal line 106 A and the second metal line 106 B. A first vertical distance from a bottom surface of the first device 128 to the first metal line 106 A is greater than a second vertical distance from a bottom surface of the second device 130 to the second metal line 106 B.

By forming the through-hole 110 when patterning the first dielectric layer 108 and then forming the first via-hole 116 A and the second via-hole 116 B together by patterning the second dielectric layer 112 , no additional patterning process is needed for patterning the first via 118 A and the second via 118 B with different thicknesses. In addition, since the step height for filling the first via 118 A is reduced by having the staggered via shape with a ledge in the middle, reliability and contact resistance of the first via 118 A are improved.

FIG. 2 illustrates a process flow diagram of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process. While method 200 is illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

At act 202 , in some embodiments, a first metal line and a second metal line are provided overlying a substrate. A first dielectric layer is formed over the first metal line and the second metal line. FIGS. 7 A- 7 B illustrate some examples corresponding to act 202 .

At act 204 , in some embodiments, the first dielectric layer is patterned overlying the first metal line and absent from the second metal line. A lower through-hole is patterned in a first region when patterning the first dielectric layer overlying the first metal line. FIGS. 1 A, 8 A- 8 B , and 12 A- 12 B illustrate some examples corresponding to act 204 .

At act 206 , an second dielectric layer is formed over the first dielectric layer in the first region and also overlying a second metal line in a second region absenting the first dielectric layer. The second dielectric layer may extend into the through-hole reaching a first contact region of the first metal line. The second dielectric layer may be formed directly on the second metal line. FIGS. 1 B, 9 A- 9 B, and 13 A- 13 B illustrate some examples corresponding to act 206 .

At act 208 , the second dielectric layer is then patterned to concurrently form a first via-hole directly above the lower through-hole in the first region and a second via-hole in the second region. As a result, the lower through-hole and the first via-hole collectively form a via-hole exposing a first contact region for the first via, and the second via-hole exposes a second contact region for a second via with a depth smaller than the first via. FIGS. 1 C, 10 A- 10 B, and 14 A- 14 B illustrate some examples corresponding to act 208 .

At act 210 , a first via is formed on the first contact region extending along the first via-hole, and a second via is formed on the second contact region along the second via-hole. The first via and the second via may respectively extend along a first upper surface and a second upper surface of the second dielectric layer. FIGS. 1 D, 11 A- 11 B, and 15 A- 15 B illustrate some examples corresponding to act 210 .

FIGS. 3 A- 3 B illustrate a layout view 300 A and a cross-sectional view 300 B of some embodiments of an interconnect structure having a first via 118 A disposed in a first region 132 and a second via 118 B disposed in a second region 134 . The first via 118 A may be a staggered via disposed on a first contact region 106 c 1 of a first metal line 106 A, and the second via 118 B may be disposed on a second contact region 106 c 2 of a second metal line 106 B.

The first metal line 106 A and the second metal line 106 B may be surrounded by an adjoining dielectric 104 and disposed over a substrate 102 . In some embodiments, the first metal line 106 A and the second metal line 106 B are respectively connected to semiconductor devices (not shown) disposed within the substrate 102 through one or more additional interconnect features including metal lines and vias. As an example, the first metal line 106 A and the second metal line 106 B may be connected to logic circuit within the substrate 102 to respectively transmit control signals to a first device 128 and a second device 130 .

In some embodiments, a first dielectric layer 108 is disposed over the first metal line 106 A. A through-hole 110 extends through the first dielectric layer 108 and overlies the first contact region 106 c 1 of the first metal line 106 A. A second dielectric layer 112 may be disposed over the first dielectric layer 108 and the first and second metal lines 106 A, 106 B. A first via-hole 116 A and a second via-hole 116 B extend through the second dielectric layer 112 . The first via-hole 116 A connects to the through-hole 110 and overlies the first contact region 106 c 1 . The second via-hole 116 B overlies the second contact region 106 c 2 of the second metal line 106 B. The first via 118 A extends along the through-hole 110 , the first via-hole 116 A, and a first upper surface 112 u 1 of the second dielectric layer 112 . The second via 118 B extends along the second via-hole 116 B and a second upper surface 112 u 2 of the second dielectric layer 112 .

In some embodiments, the first via-hole 116 A has a bottom lateral dimension greater than a top lateral dimension of the through-hole 110 . The first via 118 A may comprise a ledge 1181 lining an upper surface of the first dielectric layer 108 and connecting sidewalls of the first dielectric layer 108 and the second dielectric layer 112 . In some embodiments, the first via-hole 116 A has the entire sidewall 116 s smoothly extending from the second dielectric layer 112 to the first dielectric layer 108 .

The first device 128 may be disposed on a first lateral portion of the first via 118 A and electrically connected to the first metal line 106 A by the first via 118 A. Similarly, the second device 130 may be disposed on a second lateral portion of the second via 118 B and electrically connected to the second metal line 106 B by the second via 118 B. A first vertical distance t 1 from a bottom surface of the first device 128 to the first metal line 106 A is greater than a second vertical distance t 2 from a bottom surface of the second device 130 to the second metal line 106 B, and thus may provide gaps or cavities of different lengths between the first metal line 106 A and the first device 128 and between the second metal line 106 B and the second device 130 .

Referring to FIG. 3 A for the layout view, in some embodiments, the second via-hole 116 B has a square shape with a side length between a side length of the through-hole 110 and a side length of the first via-hole 116 A. The through-hole 110 and the first via-hole 116 A may both be a square shape as well. In some alternative embodiments, the through-hole 110 , the first via-hole 116 A, or the second via-hole 116 B may have another polygon or circle shape. The first via-hole 116 A may be arranged concentric with the through-hole 110 . As an example, the through-hole 110 may have a side length of from about 50 nm to about 300 nm, the the first via-hole 116 A may have a side length of from about 300 nm to about 1000 nm, while the second via-hole 116 B may have a side length of from about 200 nm to about 500 nm. In some embodiments, the second via-hole 116 B may have a top or bottom lateral dimension, such as a diameter or a side length, that is between those of the first via-hole 116 A and the through-hole 110 . The first via-hole 116 A may have a lateral dimension shifted a constant value from that of the first via-hole 116 A. By setting the layout shapes and dimensions as discussed above, the maximum use of layout areas is achieved while providing sufficient contact areas and ledges for better via fillings.

In various embodiments, the substrate 102 may comprise any type of semiconductor body (e.g., silicon/CMOS bulk, SiGe, etc.) such as a semiconductor wafer or one or more die on a wafer, as well as any other type of semiconductor and/or epitaxial layers formed thereon and/or otherwise associated therewith. The adjoining dielectric 104 may comprise silicon dioxide and/or other low-k dielectric material, for example. The first metal line 106 A and the second metal line 106 B may comprise conductive materials, such as aluminum (Al), copper (Cu), titanium nitride (e.g., TiN), tantalum nitride (e.g., TaN), platinum (e.g., Pt), titanium (e.g., Ti), tantalum (e.g., Ta) tungsten (e.g., W), iron (e.g., Fe), nickel (e.g., Ni), some other suitable metal(s), or any alloy or combination of the foregoing. For example, the first metal line 106 A and the second metal line 106 B respectively has a thickness of about 15 nanometers, about 15-500 nanometers, or some other suitable thickness. The first dielectric layer 108 or the second dielectric layer 112 may comprise a dielectric material such as silicon dioxide, silicon nitride, and/or alumina for example. The first via 118 A and the second via 118 B may comprise TiN or other suitable conductive materials.

FIGS. 4 A- 4 B illustrate a layout view 400 A and a cross-sectional view 400 B of some additional embodiments of an interconnect structure having a first via 118 A disposed in a first region 132 and a second via 118 B disposed in a second region 134 . The first via 118 A may be a staggered via disposed on a first contact region 106 c 1 of a first metal line 106 A, and the second via 118 B may be disposed on a second contact region 106 c 2 of a second metal line 106 B. In some embodiments alternative to what is shown in FIG. 3 A- 3 B , the first via 118 A and the second via 118 B may be respectively disposed at a corner region of the first metal line 106 A and the second metal line 106 B (as shown in FIGS. 4 A- 4 B for example) or a boundary region of the first metal line 106 A and the second metal line 106 B (as shown in FIGS. 1 A- 1 D for example).

In some embodiments, the first metal line 106 A and the second metal line 106 B each comprises a barrier layer 120 surrounding bottom and sidewall surfaces of a metal body 122 . The first via 118 A and the second via 118 B each contacts the barrier layer 120 and the metal body 122 . In some embodiments, the barrier layer 120 includes a material with less native oxide formation on top, and thus is easier to clean and provides better contact resistance for the first via 118 A and the second via 118 B. For example, the barrier layer 120 may comprise TaN, and the metal body may comprise AlCu. The native oxide of the barrier layer 120 , TaO, is easier to be removed than alumina. Thus, interconnect reliability and contact resistance are improved by forming the first contact region 106 cl and the second contact region 106 c 2 at the corner regions of the first metal line 106 A and the second metal line 106 B contacting the barrier layer 120 .

In some embodiments, as shown in FIGS. 4 A- 4 B for example, the first dielectric layer 108 may be removed from one or multiple sides of the first via-hole 116 A when patterning the first via-hole 116 A. Thus, a first sidewall portion 116 s - 1 smoothly extends from the second dielectric layer 112 to the first dielectric layer 108 . A second sidewall portion 116 s - 2 closer to the second region 134 may be lower than the first sidewall portion 116 s - 1 . The first via 118 A may comprise a first ledge 118 l - 1 lining an upper surface of the first dielectric layer 108 . In some embodiments, the first via 118 A further comprises a second ledge 118 l - 2 lining an upper surface of the barrier layer 120 and connecting a surface of the first metal line 106 A and a recessed upper surface of the adjoining dielectric 104 . Similarly, the second via 118 B comprises a ledge lining an upper surface of the barrier layer 120 and connecting a surface of the second metal line 106 B and a recessed upper surface of the adjoining dielectric 104 .

FIGS. 5 A- 5 B illustrate layout and cross-sectional views of some additional embodiments of an interconnect structure having multiple staggered vias with different heights. For example, the interconnect structure may have a first via 118 A disposed in a first region 132 connecting a first metal line 106 A, a second via 118 B disposed in a second region 134 connecting a second metal line 106 B, and a third via 118 C disposed in a third region 136 connecting a third metal line 106 C. The vias 118 A, 118 B, 118 C are formed by a series of upper via-hole patterning processes. In some embodiments, the via-holes may have a square shape as shown, or another polygon or circle shape from the layout view as alternatives. The via-holes may have a lateral dimension shifted a constant value for the maximum use of layout areas while providing sufficient contact areas and ledges for easier via fillings. For example, a first dielectric layer 108 may be patterned directly above the first metal line 106 A with a through-hole 110 disposed therethrough. A second dielectric layer 112 may be patterned directly above the first metal line 106 A and the second metal line 106 B with a first via-hole 116 A and a second via-hole 116 B disposed therethrough. A third dielectric layer 124 may be patterned directly above the first metal line 106 A, the second metal line 106 B, and the third metal line 106 C with a first upper via-hole 126 A, a second upper via-hole 126 B, and a third upper via-hole 126 C disposed therethrough.

Thus, the first via 118 A may be a staggered via disposed along three concentric holes connected by ledges between one another: the first upper via-hole 126 A extending from the third dielectric layer 124 to a first upper surface of the second dielectric layer 112 , the first via-hole 116 A extending from the second dielectric layer 112 to an upper surface of the first dielectric layer 108 , and the through-hole 110 connected to the first via-hole 116 A by the upper surface of the first dielectric layer 108 . The second via 118 B may be a staggered via disposed along two concentric holes: the second via-hole 116 B and the second upper via-hole 126 B, connected by a ledge on a second upper surface of the second dielectric layer 112 . The second upper surface is lower than the first upper surface of the second dielectric layer 112 . At last, the third via 118 C is disposed along the third upper via-hole 126 C reaching on the third metal line 106 C.

Referring to FIG. 5 A for the layout view, in some embodiments, the first upper via-hole 126 A and the first via-hole 116 A may be arranged concentric with the through-hole 110 . In some embodiments, the second via-hole 116 B may be arranged concentric with the second upper via-hole 126 B. By setting the layout shapes and dimensions as discussed above, the maximum use of layout areas is achieved while providing sufficient contact areas and ledges for better via fillings.

FIGS. 6 A- 6 B illustrate layout and cross-sectional views of some additional embodiments of an interconnect structure having a staggered via and a second via of smaller height. Alternative to all discussed above, in some embodiments, the second metal line 106 B may be disposed with an upper surface located above an upper surface of the first metal line 106 A, and thus a smaller height between the second metal line 106 B and the second dielectric layer 112 may exist even the first via 118 A and the second via 118 B have upper lateral portions aligned. The upper lateral portions of the first via 118 A and the second via 118 B may both be disposed on a planar upper surface of the second dielectric layer 112 . Similarly as discussed above, the first via 118 A and the second via 118 B may be formed by forming the through-hole 110 when patterning the first dielectric layer 108 and then forming the first via-hole 116 A and the second via-hole 116 B together by patterning the second dielectric layer 112 . Thus, no additional patterning process is needed for forming the first via 118 A with a greater thickness than that of the second via 118 B. In addition, the through-hole 110 and the first via-hole 116 A may have a lateral dimension shift at the place of connecting, and thus forming a ledge therebetween. As a result, the step height for filling the first via 118 A is reduced by having the staggered via shape, and thus reliability and contact resistance of the first via 118 A can be improved.

FIGS. 7 A- 11 B illustrate a series of layout and cross-sectional views of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process. Although FIGS. 7 A- 11 B are described in relation to a method, it will be appreciated that the structures disclosed in FIGS. 7 A- 11 B are not limited to such a method, but instead may stand alone as structures independent of the method.

As shown in the layout view 700 A and cross-sectional view 700 B of FIGS. 7 A- 7 B , in some embodiments, a first metal line 106 A and a second metal line 106 B are provided. A first dielectric layer 108 is formed over the first metal line 106 A and the second metal line 106 B. A process for forming the first dielectric layer 108 may be or be comprised of depositing an oxide or other applicable dielectric layer by physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), some other suitable deposition process, or any combination of the foregoing.

As shown in the layout view 800 A and cross-sectional view 800 B of FIGS. 8 A- 8 B , in some embodiments, the first dielectric layer 108 is patterned to be removed from the second metal line 106 B. The patterning may, for example, be performed by a photolithography/etching process and/or by some other suitable process. During the patterning, a through-hole 110 is formed exposing a first contact region of the first metal line 106 A. In some embodiments, the through-hole 110 may have a square shape as shown, or another polygon or circle shape alternatively, from the layout view. The through-hole 110 may be arranged at one or more various locations above the first metal line 106 A, such as a boundary region as shown in FIGS. 1 A- 1 D . In some alternative embodiments, the through-hole 110 may be arranged at one or more of a central region, a corner region, or other applicable locations.

As shown in the layout view 900 A and cross-sectional view 900 B of FIGS. 9 A- 9 B , in some embodiments, a second dielectric layer 112 is formed over the first dielectric layer 108 overlying the first metal line 106 A and also overlying the second metal line 106 B absenting the first dielectric layer 108 . A process for forming the second dielectric layer 112 may be or be comprised of depositing an oxide or other applicable dielectric layer by PVD, CVD, ALD, some other suitable deposition process, or any combination of the foregoing. Thus, the first dielectric layer 108 and the second dielectric layer 112 collectively build a greater height directly above the first metal line 106 A than a height directly above the second metal line 106 B. The second dielectric layer 112 may extend into the through-hole 110 reaching the first contact region 106 c 1 of the first metal line 106 A. In some embodiments, the second dielectric layer 112 may be deposited globally. In some alternative embodiments, the second dielectric layer 112 may also be patterned but still left to cover at least portions of the first dielectric layer 108 and the second dielectric layer 112 .

As shown in the layout view 1000 A and cross-sectional view 1000 B of FIGS. 10 A- 10 B , in some embodiments, the second dielectric layer 112 is then patterned to concurrently form a first via-hole 116 A directly above the lower through-hole 110 exposing a first contact region 106 c 1 of the first metal line 106 A and a second via-hole 116 B exposing a second contact region 106 c 2 of the second metal line 106 B. The through-hole 110 and the first via-hole 116 A collectively form a via-hole for a first via 118 A (see FIGS. 11 A- 11 B ). The second via-hole is for a second via 118 B (see FIGS. 11 A- 11 B ) with a depth smaller than the first via 118 A. In some embodiments, the first via-hole 116 A or the second via-hole 116 B may have a square shape as shown in FIG. 10 A , or another polygon or circle shape alternatively, from the layout view of FIG. 10 A . The first via-hole 116 A may be arranged concentric with the through-hole 110 . In some embodiments, a bottom lateral dimension of the first via-hole 116 A is greater than a top lateral dimension of the through-hole 110 , and therefore results in a staggered shape with a ledge 1181 between the first via-hole 116 A and the through-hole 110 . In some embodiments, the second via-hole 116 B may have a top or bottom lateral dimension, such as a diameter or a side length, that is between those of the first via-hole 116 A and the through-hole 110 .

In some embodiments, a hard mask layer 114 may be formed on the second dielectric layer 112 and used as a mask for patterning the second dielectric layer 112 accordingly. The hard mask layer 114 may be formed by one or more deposition or spin-on processes of various polymer, dielectric, and/or metal materials. The hard mask layer 114 may comprise TiN for example. Though the hard mask layer 114 is shown in some figures (e.g., FIGS. 10 A- 11 B, 14 A- 15 B ) and not shown in other figures (e.g., FIGS. 1 A- 6 B ), it is appreciated that the hard mask layer 114 may be used or omitted for various embodiments and may or may not be left in the final device above the second dielectric layer 112 .

As shown in the layout view 1100 A and cross-sectional view 1100 B of FIGS. 11 A- 11 B , in some embodiments, the first via 118 A and the second via 118 B are respectively formed within the first via-hole 116 A and the through-hole 110 and the second via-hole 116 B. In some embodiments, a pre-clean process is performed to prepare the first contact region 106 cl and the second contact region 106 c 2 . For example, an ion bombardment process such as an Ar bombardment process may be performed to remove native oxide (ex. Al2O3). Then, a conductive feature is formed along the first via-hole 116 A, the through-hole 110 , and the second via-hole 116 B and extended along a first upper surface 112 u 1 of the second dielectric layer 112 and a second upper surface 112 u 2 of the second dielectric layer 112 lower than the first upper surface 112 u 1 . For example, the conductive feature may be formed conformally and by DC sputtering, PVD, CVD, ALD, some other suitable deposition process, or any combination of the foregoing. As an example, the conductive feature may be formed with a thickness in a range of 10 nm to 50 nm, in order to balance a low wire resistance and reliable electrical connection with the process cost.

The conductive feature is then patterned to form the first via 118 A with a first lateral portion extending along the first upper surface 112 u 1 and the second via 118 B with a second lateral portion extending along the second upper surface 112 u 2 . The hard mask layer 114 can be patterned together with the conductive feature. In this case, the hard mask layer 114 may have sidewalls vertically aligned with those of the first via 118 A and the second via 118 B. In some embodiments, the hard mask layer 114 may comprise the same metal material as the conductive feature and thus may merge as a seamless integral with the first via 118 A and the second via 118 B in the final device. A first device 128 may be formed on the first lateral portion of the first via 118 A and electrically connected to the first metal line 106 A. Similarly, a second device 130 may be formed on the second lateral portion of the second via 118 B and electrically connected to the second metal line 106 B. As an example, control signals may be provided from a logic circuit within the substrate 102 to the first device 128 and the second device 130 respectively through the first metal line 106 A and the second metal line 106 B. A first distance from a bottom surface of the first device 128 to the first metal line 106 A is greater than a second distance from a bottom surface of the second device 130 to the second metal line 106 B, and thus may provide cavities of different lengths t 1 , t 2 , respectively between the first metal line 106 A and the first device 128 and the second metal line 106 B and the second device 130 .

FIGS. 12 A- 15 B illustrate a series of layout and cross-sectional views of some embodiments of a method for forming an interconnect structure having a staggered via formed by a two-step process at a corner or boundary region. Although FIGS. 12 A- 15 B are described in relation to a method, it will be appreciated that the structures disclosed in FIGS. 12 A- 15 B are not limited to such a method, but instead may stand alone as structures independent of the method.

As shown in the layout view 1200 A and cross-sectional view 1200 B of FIGS. 12 A- 12 B , in some embodiments, a first dielectric layer 108 is formed on a first metal line 106 A with a through-hole 110 exposing a first contact region 106 c 1 of the first metal line 106 A. In some embodiments, a process for forming the first dielectric layer 108 may comprise depositing an oxide or other applicable dielectric layer by physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), some other suitable deposition process, or any combination of the foregoing. Then, the first dielectric layer 108 is patterned to be removed from the second metal line 106 B and the first contact region 106 c 1 of the first metal line 106 A. The patterning may, for example, be performed by a photolithography/etching process and/or by some other suitable process. In some embodiments, the through-hole 110 may have a square shape as shown, or another polygon or circle shape alternatively, from the layout view. The through-hole 110 may be arranged at one or more various locations above the first metal line 106 A, such as a corner region with one or more sides of interfaces of the first and second metal lines 106 A, 106 B and adjoining dielectric 104 exposed. In some embodiments, the first metal line 106 A and the second metal line 106 B each comprises a barrier layer 120 surrounding bottom and sidewall surfaces of a metal body 122 . The through-hole 110 exposes the barrier layer 120 and the metal body 122 . As an example, the barrier layer 120 may comprise TaN, and the metal body may comprise AlCu.

As shown in the layout view 1300 A and cross-sectional view 1300 B of FIGS. 13 A- 13 B , in some embodiments, a second dielectric layer 112 is formed over the first dielectric layer 108 overlying the first metal line 106 A and also overlying the second metal line 106 B absenting the first dielectric layer 108 . A process for forming the second dielectric layer 112 may be or be comprised of depositing an oxide or other applicable dielectric layer by PVD, CVD, ALD, some other suitable deposition process, or any combination of the foregoing. Thus, the first dielectric layer 108 and the second dielectric layer 112 collectively build a greater height directly above the first metal line 106 A than a height directly above the second metal line 106 B. The second dielectric layer 112 may extend onto portions of the barrier layer 120 and the metal body 122 within the through-hole 110 . In some embodiments, the second dielectric layer 112 may be deposited globally. In some alternative embodiments, the second dielectric layer 112 may also be patterned but still left to cover at least portions of the first dielectric layer 108 and the second dielectric layer 112 .

As shown in the layout view 1400 A and cross-sectional view 1400 B of FIGS. 14 A- 14 B , in some embodiments, the second dielectric layer 112 is then patterned to concurrently form a first via-hole 116 A directly above the lower through-hole 110 exposing a first contact region 106 c 1 of the first metal line 106 A and a second via-hole 116 B exposing a second contact region 106 c 2 of the second metal line 106 B. The through-hole 110 and the first via-hole 116 A collectively form a via-hole for a first via 118 A (see FIGS. 15 A- 15 B ). In some embodiments, the second dielectric layer 112 is completely removed from a sidewall of the first dielectric layer 108 as shown in the figure. In some alternative embodiments, the second dielectric layer 112 may have a left over portion disposed on the sidewall of the first dielectric layer 108 . The second via-hole is for a second via 118 B (see FIGS. 15 A- 15 B ) with a depth smaller than the first via 118 A. In some embodiments, the first via-hole 116 A or the second via-hole 116 B may have a square shape as shown in FIG. 14 A , or another polygon or circle shape alternatively, from the layout view of FIG. 14 A . The first via-hole 116 A may be arranged concentric with the through-hole 110 . In some embodiments, a bottom lateral dimension of the first via-hole 116 A is greater than a top lateral dimension of the through-hole 110 , and therefore results in a staggered shape with a ledge between the first via-hole 116 A and the through-hole 110 (more details discussed with reference to FIGS. 15 A- 15 B below). In some embodiments, the second via-hole 116 B may have a top or bottom lateral dimension, such as a diameter or a side length, that is between those of the first via-hole 116 A and the through-hole 110 .

As shown in the layout view 1500 A and cross-sectional view 1500 B of FIGS. 15 A- 15 B , in some embodiments, the first via 118 A and the second via 118 B are respectively formed within the first via-hole 116 A and the through-hole 110 and the second via-hole 116 B. In some embodiments, a pre-clean process is performed to prepare the first contact region 106 cl and the second contact region 106 c 2 . For example, an ion bombardment process such as an Ar bombardment process may be performed to remove native oxide (ex. TaO, Al2O3). By using a layout design of the first via 118 A and the second via 118 B at corners of the metal lines 106 A, 106 B, the barrier layer 120 is at least portions of the contact regions 106 c 1 , 106 c 2 . The barrier layer 120 may have a native oxide softer to etch than that of the metal body 122 . Thus, the pre-clean process takes less time and can be finished more completely, such that interconnect reliability and contact resistance are improved.

Then, a conductive feature is formed along the first via-hole 116 A, the through-hole 110 , and the second via-hole 116 B and extended along a first upper surface 112 u 1 of the second dielectric layer 112 and a second upper surface 112 u 2 of the second dielectric layer 112 lower than the first upper surface 112 u 1 . For example, the conductive feature may be formed conformally and by DC sputtering, PVD, CVD, ALD, some other suitable deposition process, or any combination of the foregoing. As an example, the conductive feature may be formed with a thickness in a range of 10 nm to 50 nm, in order to balance a low wire resistance and reliable electrical connection with the process cost.

The conductive feature is then patterned to form the first via 118 A with a first lateral portion extending along the first upper surface 112 u 1 and the second via 118 B with a second lateral portion extending along the second upper surface 112 u 2 . In some embodiments, a first sidewall portion 116 s - 1 smoothly extends from the second dielectric layer 112 to the first dielectric layer 108 . A second sidewall portion 116 s - 2 closer to the second region 134 may be lower than the first sidewall portion 116 s - 1 . The first via 118 A may comprise a first ledge 118 l - 1 lining an upper surface of the first dielectric layer 108 . In some embodiments, the first via 118 A further comprises a second ledge 118 l - 2 lining an upper surface of the barrier layer 120 and connecting a surface of the first metal line 106 A and a recessed upper surface of the adjoining dielectric 104 . Similarly, the second via 118 B comprises a ledge lining an upper surface of the barrier layer 120 and connecting a surface of the second metal line 106 B and a recessed upper surface of the adjoining dielectric 104 . The hard mask layer 114 can be patterned together with the conductive feature. In this case, the hard mask layer 114 may have sidewalls vertically aligned with those of the first via 118 A and the second via 118 B. In some embodiments, the hard mask layer 114 may comprise the same metal material as the conductive feature and thus may merge as a seamless integral with the first via 118 A and the second via 118 B in the final device.

Therefore, the present disclosure relates to a new method of forming an interconnect structure that eliminates a separate deep via patterning process to simplify the fabrication process. A staggered via is therefore formed to provide for improved connection reliability and contact resistance.

Accordingly, in some embodiments, the present disclosure relates to a method of forming an interconnect structure for a semiconductor device. The method comprises depositing a first dielectric layer over a first metal line and a second metal line overlying a substrate and patterning the first dielectric layer to be removed from the second metal line and to form a through-hole exposing a first contact region of the first metal line. The method further comprises depositing a second dielectric layer over both the first metal line and the second metal line, where the second dielectric layer extending into the through-hole reaching the first contact region of the first metal line and over the second metal line. The method further comprises patterning the second dielectric layer to form a first via-hole connecting to the through-hole vertically and concentric with the through-hole from a layout view. The first via-hole and the through-hole expose the first contact region of the first metal line, and a second via-hole exposes a second contact region of the second metal line. The method further comprises forming a first via on the first contact region extending along the through-hole, the first via-hole, and a first upper surface of the second dielectric layer, and a second via on the second contact region extending along the second via-hole and a second upper surface of the second dielectric layer.

In other embodiments, the present disclosure relates to a method of forming an interconnect structure for a semiconductor device. The method comprises forming a first metal line and a second metal line over a substrate and forming a first dielectric layer over the first metal line and absent from the second metal line. A through-hole is patterned within the first dielectric layer to expose a first contact region of the first metal line. The method further comprises forming a second dielectric layer over both the first metal line and the second metal line. A first via-hole is patterned through the second dielectric layer to be connected to the through-hole and exposes the first contact region of the first metal line. A second via-hole is concurrently patterned through the second dielectric layer with the second via-hole exposing a second contact region of the second metal line. The method further comprises forming a first via on the first contact region extending along the through-hole, the first via-hole, and a first upper surface of the second dielectric layer, and forming a second via on the second contact region extending along the second via-hole and a second upper surface of the second dielectric layer. The first upper surface is higher than the second upper surface.

In yet other embodiments, the present disclosure relates to an interconnect structure for a semiconductor device. The interconnect structure comprises a first metal line and a second metal line surrounded by an adjoining dielectric and disposed over a substrate. A first dielectric layer is disposed over the first metal line with a through-hole extending through the first dielectric layer and overlies a first contact region of the first metal line. A second dielectric layer is disposed over the first dielectric layer and the first and second metal lines with a first via-hole and a second via-hole extending through the second dielectric layer. The first via-hole connects to the through-hole and overlies the first contact region. The second via-hole overlies a second contact region of the second metal line. A first via is disposed on the first contact region and extending along the through-hole, the first via-hole, and a first upper surface of the second dielectric layer. A second via is disposed on the second contact region and extending along the second via-hole and a second upper surface of the second dielectric layer. The first via comprises a first ledge lining an upper surface of the first dielectric layer and connecting sidewalls of the first dielectric layer and the second dielectric layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.