Semiconductor process

1. Field of the Invention

The present invention relates generally to a semiconductor process, and more specifically, to a semiconductor process in which only one photomask is used to form layers of different depths, such as metal layers, in two recesses.

2. Description of the Prior Art

In a complementary metal-oxide semiconductor (CMOS) device, a dual work function metal gate is used for both an NMOS device and a PMOS device. Integration and process controls for the dual work function metal gate are more complicated, while thickness and composition controls for materials used when fabricating the dual work function metal gate are more precise. Fabrication of the conventional dual work function metal gate can be categorized into gate first processes and gate last processes. In a conventional gate first process for fabricating a dual work function metal gate, both an annealing process for forming a source/drain ultra-shallow junction and a silicide process are performed after forming the metal gate. After performing the annealing process with a strict heat budget, a flat band voltage (V fb ) does not increase or decrease linearly with decreasing EOT of a high-K gate dielectric layer; instead, roll-off is observed. The gate last process is developed to improve the V fb roll-off issue, prevent leakage current generation due to re-crystallization of the high-K gate dielectric layer during high-temperature processes, and widen material choices for the high-K gate dielectric layer and the metal gate in the gate first process.

In the conventional gate last process, a sacrificed gate or a replacement gate is provided, followed by performing processes used to construct a normal MOS transistor. Then, the sacrificed/replacement gate is removed to form a gate recess. Metals are filled into the gate recess depending upon electrical needs. For example, a work function metal layer, a barrier layer and a main electrode layer are sequentially filled and formed in the gate recess.

In a current CMOS transistor process, if a work function metal layer of a PMOS transistor is formed and then a work function metal layer of an NMOS transistor is formed, a work function metal layer of a PMOS transistor cover the recesses of the PMOS transistor and the NMOS transistor. Then, two photomasks are used to remove the work function metal layer in the recess of the NMOS transistor. However, using two photomasks is complicated and costly.

The present invention provides a semiconductor process, which can improve the complicated process of the two photomasks.

The present invention provides a semiconductor process including the following steps. An interdielectric layer is formed on a substrate, and the interdielectric layer has a first recess and a second recess. A metal layer is formed to cover the surface of the interdielectric layer, the first recess and the second recess. Partially fills a sacrificed material in the first recess and the second recess to respectively cover a portion of the metal layer in each of the recesses. The uncovered metal layer is removed in each of the recesses. The sacrificed material is removed. An etching process is performed to remove the remaining metal layer in the first recess and reserve the remaining metal layer in the second recess.

The present invention provides a semiconductor process including the following steps. An interdielectric layer is formed on a substrate and the interdielectric layer has a first recess and a second recess. A metal layer is formed to cover the surface of the interdielectric layer, the first recess and the second recess. Partially fills a sacrificed material in the first recess and the second recess to respectively cover a portion of the metal layer in each of the recesses. An etching process is performed to remove the sacrificed material in the first recess. The uncovered metal layer in the first recess, the second recess and on the interdielectric layer is removed. The remaining sacrificed material is removed in the second recess while the remaining metal layer is reserved in the second recess.

The present invention provides a semiconductor process, which entirely removes a metal layer in a recess while reserves a desired metal layer in the other recess by merely performing one time of a photolithography process; in other words, just using one photomask. Therefore, the present invention can simplify the complicated process of the prior art. Besides, due to the present invention does not using two photomasks, the scoring would not happen at the junction of the two photomasks, that leads to the material of the gate metal filling into the scoring and causing short circuit.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

FIGS. 1-6 schematically depict a cross-sectional view of a semiconductor process according to the first preferred embodiment of the present invention.

FIGS. 7-10 schematically depict a cross-sectional view of a semiconductor process according to the second preferred embodiment of the present invention.

A CMOS transistor is used as an example in the two following embodiments, but the semiconductor process of the present invention can be also applied to other semiconductor components that are not described herein.

A gate-last for high-k first process is performed in the following example. FIGS. 1-6 schematically depict a cross-sectional view of a semiconductor process according to the first preferred embodiment of the present invention. As shown in FIG. 1 , a substrate 110 is provided. A desired sacrificed gate (not shown) is formed, which may include an interlayer 130 being formed, a gate dielectric layer 140 being formed, a gate material layer (not shown) being formed and a cap layer (not shown) being formed, then the cap layer, the gate material layer, the gate dielectric layer 140 , and the interlayer 130 being patterned to form the sacrificed gate. Then, a spacer 150 is formed, and a source/drain region 160 is formed beside the spacer 150 in the substrate 110 . An interdielectric layer 120 is formed on the substrate 110 covering the sacrificed gate. The gate dielectric layer 140 may be a dielectric layer having a high dielectric constant, and the material of the gate dielectric layer 140 may be selected from the group comprising hafnium oxide (HfO 2 ), hafnium silicon oxide (HfSiO 4 ), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al 2 O 3 ), lanthanum oxide (La 2 O 3 ), tantalum oxide (Ta 2 O 5 ), yttrium oxide (Y 2 O 3 ), zirconium oxide (ZrO 2 ), strontium titanate oxide (SrTiO 3 ), zirconium silicon oxide (ZrSiO 4 ), hafnium zirconium oxide (HfZrO 4 ), strontium bismuth tantalite (SrBi 2 Ta 2 O 9 , SBT), lead zirconate titanate (PbZr x Ti 1-x O 3 , PZT) and barium strontium titanate (Ba x Sr 1-x TiO 3 , BST). Due to performing the gate-last for high-k first process, the gate dielectric layer 140 has a “-”-shaped profile structure.

After the interdielectric layer 120 is planarized, the gate material layer of each of the sacrificed layers (not shown) is removed to form a first recess R 1 and a second recess R 2 in the interdielectric layer 120 . In this embodiment, a barrier layer (not shown) may be selectively formed on the gate dielectric layer 140 for protecting the gate dielectric layer 140 from being damaged by etching while the gate material layer of each of the sacrificed layers (not shown) is removed.

A barrier layer 170 may be selectively formed on the gate dielectric layer 140 . The barrier layer 170 may be a single-layer or a multi-layers structure composed of tantalum nitride (TaN) or titanium nitride (TiN) etc. A metal layer 180 is formed to entirely cover the surface of the interdielectric layer 120 , the first recess R 1 and the second recess R 2 . The metal layer 180 may be a work function metal layer, which may be a single-layer or a multi-layers structure composed of metals having a desired work function value for a transistor such as tantalum nitride (TaN), titanium carbide (TiC), tantalum carbide (TaC), tungsten carbide (WC), titanium aluminide (TiAl), aluminum titanium nitride (TiAlN) or titanium nitride (TiN) etc. The work function metal layer may be a titanium nitride metal layer suited to forming a PMOS transistor (its work function value is between the range of 4.8 eV and 5.2 eV). The work function metal layer may also be an aluminum titanium metal layer suited to forming an NMOS transistor (its work function value is between the range of 3.9 eV and 4.3 eV). Furthermore, work function metal layers suitable for NMOS transistor A and PMOS transistor B are both needed to form a CMOS transistor 100 . In this embodiment, a function metal layer paired with the PMOS transistor B is first filled into the first recess R 1 of the NMOS transistor A and the second recess R 2 of the PMOS transistor B, and the function metal layer filled into the first recess R 1 is removed. Then, a work function metal layer paired with the NMOS transistor A is filled. The steps of the process may be rearranged.

In another realization of the first embodiment, by performing the gate-last for high-k last process, for example, the gate material layer (not shown) and the gate dielectric layer 140 are removed first for forming the first recess R 1 and the second recess R 2 in the interdielectric layer 120 . Then, a dielectric layer having a high dielectric constant (not shown) is refilled into the first recess R 1 and the second recess R 2 . In this process, because the gate dielectric layer 140 is removed, the material of the gate dielectric layer 140 can be selected from a wide range of materials, without restriction to the aforementioned material of the dielectric layer having a high dielectric constant. The dielectric layer having a high dielectric constant filled subsequently thereafter (not shown) has a U-shaped profile structure. A barrier layer may be selectively formed after the dielectric layer having a high dielectric constant is formed for use as an etching protective layer of the dielectric layer having a high dielectric constant, and then a metal layer may be formed thereon.

As shown in FIG. 1 , after the first recess R 1 and the second recess R 2 are formed, a sacrificed material 190 is partially filled into the first recess R 1 and the second recess R 2 to cover the metal layer 180 in the lower portion of the first recess R 1 and the second recess R 2 , so that the metal layer 180 in the upper portion of the first recess R 1 and the second recess R 2 is exposed. In more detail, the sacrificed material 190 may be formed entirely on the interdielectric layer 120 and filled into the first recess R 1 and the second recess R 2 . An etching back process is performed to remove a portion of the sacrificed material 190 on the interdielectric layer 120 and in the first recess R 1 and the second recess R 2 . The method of removing the portion of the sacrificed material 190 may be performing a dry etching process, performing a wet etching process, or performing a plasma bombardment process. In this embodiment, the sacrificed material 190 may be a material suited for filling gaps, which may be photoresist material, dielectric anti-reflection coating (DARC), light absorbing oxide (DUO), bottom anti-reflective coating (BARC), sacrificial light absorbing material (SLAM) or spin-on glass (SOG) etc, and the sacrificed material 190 may be formed by spin coating.

As shown in FIG. 2 , an etching back process is performed to remove the uncovered metal layer 180 in the first recess R 1 and the second recess R 2 . Therefore, the metal layer 180 a in the lower portion of the first recess R 1 and the metal layer 180 b in the lower portion of the second recess R 2 remain. As shown in FIG. 3 , the sacrificed material 190 is removed. So, the metal layer 180 a in the bottom of the first recess R 1 and the metal layer 180 b in the bottom of the second recess R 2 are exposed.

As shown in FIGS. 4-6 , an etching process is selectively performed to remove the metal layer 180 a in the first recess R 1 and preserve the metal layer 180 b in the second recess R 2 . For example, the etching process may be forming a patterned photoresist P 1 to at least cover the second recess R 2 and expose the first recess R 1 as shown in FIG. 4 . Then, as shown in FIG. 5 , the metal layer 180 a in the first recess R 1 is removed. As shown in FIG. 6 , the patterned photoresist P 1 is removed. In this way, the metal layer 180 b having a U-shaped profile structure is formed in the second recess R 2 without leaving the metal layer 180 a in the first recess R 1 . Thereafter, an N-type work function metal layer (not shown) may be formed in the first recess R 1 and barrier layers (not shown) and a low resistance main conductive layer (not shown) may be formed in the first recess R 1 and the second recess R 2 , respectively, concluding the metal gate process.

Only one iteration of the etching process is needed in this embodiment. In other words, the metal layer 180 a in the first recess R 1 is removed, while the metal layer 180 b in the lower portion of the second recess R 2 is preserved by using only one photomask in this embodiment. Thus, the present invention can simplify the complex process of the prior art. Due to the two lithography etching processes of the prior art not being needed in this embodiment, scoring caused by over-etching does not happen at the junction D of the two photomasks, which would lead to the material of the metal gate, such as aluminum, filling into the scoring while filling into the first recess R 1 and the second recess R 2 . Therefore, short circuiting is avoided, since it is hard to remove the material of the metal gate in a chemical mechanical polishing (CMP) process once the material of the metal gate fills into the scoring. Height of the metal layer 180 b remaining in the lower portion of the second recess R 2 can be controlled by adjusting the height of the partially filled sacrificed material 190 , thereby solving the problem of bad trench filling of depositing films. In one case, the vertical height of the sidewall of the metal layer 180 b can be 5%˜95% of the depth of the second recess R 2 .

In addition, a semiconductor process in the following can also be performed to achieve the purpose of the present invention. FIGS. 7-10 schematically depict a cross-sectional view of a semiconductor process according to the second preferred embodiment of the present invention.

As shown in FIG. 1 , a substrate 110 is first provided. A flat interdielectric layer 120 is formed on the substrate 110 by performing a gate-last process, and the interdielectric layer 120 has a first recess R 1 and a second recess R 2 . Details of the gate-last process are described in the first embodiment, and not described again here. The second embodiment may also be applied to a gate-last for high-k first process or a gate-last for high-k last process.

As shown in FIGS. 7-9 , an etching process is selectively performed to remove the sacrificed material 190 in the first recess R 1 . The steps of the etching process may include forming a patterned photoresist P 2 at least covering the second recess R 2 and exposing the first recess R 1 as shown in FIG. 7 . Then, as shown in FIG. 8 , the sacrificed material 190 in the first recess R 1 is removed. As shown in FIG. 9 , the patterned photoresist P 2 is removed.

As shown in FIG. 10 , an etching back process is performed to remove the uncovered metal layer 180 on the interdielectric layer 120 and in the first recess R 1 and the second recess R 2 . The sacrificed material 190 remaining in the second recess R 2 is removed while the metal layer 180 b remaining in the lower portion of the second recess R 2 is preserved. Finally, an N-type work function metal layer (not shown) may be formed in the first recess R 1 and barrier layers (not shown), and a low resistance main conductive layer (not shown) may be formed in the first recess R 1 and the second recess R 2 , respectively, completing the metal gate process. The semiconductor process of the second embodiment achieves the capability of the semiconductor process of the first embodiment, and likewise the common structure of the first embodiment as shown in FIG. 6 .

The first embodiment and the second embodiment are both applied to fabrication of a CMOS transistor as an example, and the metal layer 180 a in the first recess R 1 of the NMOS transistor is entirely removed, while the metal layer 180 b in the second recess R 2 of the PMOS transistor is partially preserved. The processing steps may also be performed in a different order. The present invention can also be applied to fabrication of other semiconductor components by removing a portion of layers in recesses and preserving different amounts of layers in two recesses depending upon the processing requirements.

The present invention provides a semiconductor process that entirely removes a metal layer in a recess while preserving a metal layer in the other recess by performing a photolithography process once, namely by using only one photomask. Therefore, the present invention simplifies the complicated process of the prior art. Also, due to the present invention not using two photomasks, the scoring caused by over-etching does not occur at the junction of the two photomasks, which would lead to the material of the metal gate (such as aluminum) filling into the scoring while filling into recesses, thereby avoiding short circuit. Furthermore, the present invention controls the height of the metal layer remaining in a recess by adjusting the height of the sacrificed material filled into the recess, thereby solving the problem of difficulty in trench filling of depositing films.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.