Fabrication of semiconductor device including chemical mechanical polishing

The present application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-099259 filed on Apr. 24, 2012, with the Japanese Patent Office, the entire contents of which are incorporated herein by reference.

The embodiments described herein relate to fabrication of a semiconductor device.

Chemical mechanical polishing is a technology of planarizing a metal film or insulation film on a semiconductor wafer by way of polishing and is used extensively in fabrication of various semiconductor devices.

Patent Document

Patent Reference 1 Japanese Laid-Open Patent Application 2002-252194

In an aspect, there is provided a method of fabricating a semiconductor device that includes forming a first insulation film over a semiconductor substrate, the semiconductor substrate including an outer region and an inner region located at an inner side of the outer region, forming a first wiring over the first insulation film in the inner region, forming a second insulation film over the first wiring and over the first insulation film, decreasing a film thickness of the second insulation film in the inner region with regard to a film thickness of the second insulation film in the outer region, and polishing the second insulation film after the decreasing of the film thickness of the second insulation film.

The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

FIG. 1 is a cross-sectional diagram of a reflection-type liquid crystal display device to which the fabrication method of the first embodiment is applied;

FIG. 2 is a plan view diagram representing a silicon wafer to which the first embodiment is applied;

FIGS. 3A-3O are cross-sectional process flow diagrams representing the process of fabricating the semiconductor device according to a first embodiment;

FIG. 4 is an oblique view diagram explaining the exposure process in the step of FIG. 3J ;

FIG. 5 is a cross-sectional diagram representing a semiconductor device according to a comparative example;

FIGS. 6A-6C are cross-sectional process flow diagrams representing the process of fabricating the semiconductor device according to a second embodiment;

FIGS. 7A-7C are cross-sectional process flow diagrams representing the process of fabricating the semiconductor device according to a third embodiment;

FIGS. 8A and 8B are cross-sectional process flow diagrams representing the process of fabricating a semiconductor device according to a modification of the third embodiment.

In the following, embodiments will be described with reference to the accompanying drawings.

[First Embodiment]

In the case a chemical mechanical polishing process is applied to a semiconductor wafer, there can be a situation in which a sloped surface, inclined toward the wafer edge, is formed in the wafer peripheral region in view of the absence of a layer to be polished outside the wafer edge and resultant tendency of increase of the polishing rate toward the wafer edge.

For example, when a multilayer wiring structure is formed over a semiconductor wafer by a damascene process or dual damascene process, there may be formed such an inclined or sloped surface in the interlayer insulation film of lower layer level as a result of the chemical mechanical polishing process, while such an inclined surface formed in a lower layer level works to enhance the slope of an inclined surface formed in an interlayer insulation film of an upper layer level and causes the problem of the area of the inclined surface extending toward the inner region of the wafer. When such an inclined surface is formed in the interlayer insulation film, there may be caused a problem of incomplete via-hole formation at the time of forming via-holes by using high-resolution optical exposure technology due to insufficient focal depth of the optical system used in such high-resolution exposure technology. When this incomplete via-hole formation occurs, there arises a problem that the desired electric contact may not be attained.

FIG. 1 is a cross-sectional diagram representing the construction of a reflection type liquid display device 20 as an example of the semiconductor device fabricated with a first embodiment. It should be noted, however, that the present embodiment is never limited to the fabrication of such a reflection type liquid display device 20 .

Referring to FIG. 1 , the reflection type liquid display device 20 is constructed over a silicon substrate 21 formed with a device isolation region 21 I such that there are formed device regions 21 A 1 , 21 A 2 , 21 A 3 . . . on the silicon substrate 21 in correspondence to the respective pixel regions in a state defined with the device isolation region. In each of the device regions 21 A 1 , 21 A 2 , 21 A 3 . . . , there is formed a gate electrode 23 on the silicon substrate 21 via a gate insulation film 22 in a state of carrying sidewall insulation films, and the silicon substrate 21 is formed with a drain extension region 21 a and a source extension region 21 b to oppose with each other across a channel region (not illustrated) right underneath the gate electrode 23 . Further, a drain region 21 c and a source region 21 d are formed at respective outer sides of the sidewall insulation films to overlap with the drain extension region 21 a and the source extension region 21 b , respectively. The gate electrode 23 , the source extension region 21 b , the drain extension region 21 a , the source region 21 d and the drain region 21 c constitute together a drive transistor that drives a corresponding pixel.

Hereinafter, the explanation will be made only for the device region 21 A 1 and the explanation for other device regions 21 A 2 , 21 A 3 . . . will be omitted in view of the fact that the construction of the reflection-type liquid display device 20 is similar also in these device regions.

Referring to FIG. 1 , again, it can be seen that the gate electrode 23 is covered with an insulation film 24 formed over the silicon substrate and there is formed a via-plug 24 V in the insulation film 24 in contact with the drain region 23 c.

Over the insulation film 24 , there is formed a first interlayer insulation film 25 , and wiring patterns 25 A and 25 B of Cu, for example, are formed in the first interlayer insulation film 25 by way of a damascene process. The wiring pattern 25 A is formed over the via-plug 24 V and makes an electric contact with the drain region 21 c via the via-plug 24 V.

Over the first interlayer insulation film 25 , there is formed a second interlayer insulation film 26 , and a wiring pattern 26 A of Cu, for example, including a via-plug 26 V is formed in the interlayer insulation film 26 by a dual damascene process such that the via-plug 26 V makes a contact with the Cu wiring pattern 25 A.

Over the second interlayer insulation film 26 , there is formed a third interlayer insulation film 27 , and a via-plug 27 V of W, for example, is formed in the third interlayer insulation film 27 by a damascene process in contact with the Cu wiring pattern 26 A.

Further, there is formed a connection pad of Al, for example, over the third interlayer insulation film 27 in contact with the via-plug 27 V, and a fourth interlayer insulation film 28 is formed to cover the connection pad 28 A. Further, a via-plug 28 V of W, for example, is formed in the fourth interlayer insulation film 28 in contact with the connection pad 28 A.

Over the interlayer insulation film 28 , there is formed an optical reflection layer 29 B of Au or Al, for example, in contact with the via-plug 28 V via an adhesion layer 29 A of a Ti/TiN stacked structure, and a first alignment layer 29 is formed over the optical reflection layer 29 B for aligning the orientation of the liquid crystal molecules. The adhesion layer 29 A and the optical reflection layer 29 B forms together a pixel electrode 29 P of the liquid crystal display device 20 in the respective device regions 21 A 1 , 21 A 2 , 21 A 3 . . . .

Over the silicon substrate 21 , there is disposed a glass substrate 31 carrying thereon a transparent electrode 32 and a second alignment layer 33 such that the second alignment layer 33 faces the first alignment layer 29 via a spacer 34 of a predetermined diameter, and the space between the alignment layers 29 and 33 is filled with a liquid crystal layer 35 . Further, a polarizer 40 is disposed over the glass substrate 31 .

When a drive voltage is applied to the pixel electrode 29 P in the device region 21 A 1 , for example, via a corresponding drive transistor in such a reflection type liquid crystal display device 20 , there is induced a change of alignment of liquid crystal molecules in the liquid crystal layer 35 by the electric field formed between the pixel electrode 29 P and the opposing electrode 32 . Thus, an incident light entered into the glass substrate 31 after passing through the polarizer 40 undergoes modulation as it passes through the liquid crystal layer 35 before being reflected by the optical reflection layer 29 B and further as it passes through the liquid crystal layer 35 again. With this, it becomes possible to display the desired image or data visually.

In the cross-sectional diagram of FIG. 1 , it should be noted that the silicon substrate 21 , the source extension region 21 b and the drain extension region 21 a , the source region 21 d and the drain region 21 c , the interlayer insulation films 24 - 28 , the via-plugs 24 V, 26 V, 27 V and 28 V, the Cu wiring patterns 25 A and 26 A, the connection pad 28 A, the adhesion layer 29 A and the optical reflection layer 29 B constitutes together a semiconductor device 20 S.

FIG. 2 is a plan view diagram representing a silicon wafer 40 used for the fabrication of the reflection type liquid crystal display device 20 and is formed with the semiconductor device 20 S.

Referring to FIG. 2 , there are defined a large number of chip regions 40 1 , 40 2 , 40 3 . . . on the silicon wafer 40 by scribe lines 40 L, wherein the semiconductor device 20 S noted before is formed in each of the chip regions 40 1 , 40 2 , 40 3 . . . , on the silicon substrate 21 , and each of the semiconductor devices 20 S includes the device regions 21 A 1 , 21 A 2 , 21 A 3 . . . .

As explained previously, such formation of the semiconductor device 20 S on the silicon wafer 40 includes a damascene process or dual damascene process, and associated therewith, the silicon wafer 40 experiences chemical mechanical polishing process repeated a plurality of times.

Referring to FIG. 2 , it will be noted that the silicon wafer 40 has an edge 40 E, beyond which there exists no material to be polished. Thus, when a chemical mechanical polishing process is applied to such a silicon wafer, 40 , there is a tendency of formation of inclined or sloped surface inclined or sloped toward the edge 40 E in view of the fact that there occurs an increase of polishing rate in a peripheral part 40 B adjacent to the edge 40 E. Now, when the chip regions 40 1 , 40 2 , 40 3 . . . have included such an inclined surface, there is formed a corresponding inclined surface in the interlayer insulation films 24 - 48 , and there arises a problem that via-plugs, formed by using high-resolution optical exposure technology, may not be able to attain the desired electrical contact because of incomplete via-hole formation. A high-resolution optical system used for minute via-hole formation tends to suffer from the problem of shortage of focal depth. Thus, the via-plugs 24 V, 26 V, 27 V and 28 V in the interlayer insulation films 24 and 26 - 28 may fail to attain the desired electrical contact in the illustrated example. Further, when the optical reflection layer 29 B is formed on such an inclined surface, the exit direction of the reflection light may be offset from the nominal direction, leading to the problem of defective image display.

Thus, in the case of forming such a semiconductor device 20 S on the silicon wafer 40 , it is preferable to reduce the proportion of the peripheral part 40 B as much as possible and increase the proportion of an inner region 40 A at an inner side of the peripheral region 40 B as much as possible. In the description hereinafter, the peripheral part 40 B will be designated also as outer region 40 B.

Hereinafter, the present embodiment will be explained with reference to the process flow cross-sectional diagrams of FIGS. 3A-3O . It should be noted that the process flow cross-sectional diagrams of FIGS. 3A-3O represent a cross-section taken along a line A-A′ of the silicon wafer 40 of FIG. 2 . In FIGS. 3A-3O , those parts explained before are designated by the same reference numerals and the description thereof will be omitted.

Referring to FIG. 3A , the device isolation region 21 I defines the device regions 21 A 1 , 21 A 2 , 21 A 3 . . . on the silicon substrate 21 , wherein it should be noted that the silicon substrate 21 corresponds to a part of the silicon wafer 40 . In FIG. 3A , it can be seen further that each of the device regions is formed with the gate electrode 23 via a gate insulation film 22 and that the gate electrode 23 carries sidewall insulation films 23 S A and 23 S B on the respective, mutually opposing sidewall surfaces. Further, the drain extension region 21 a and the source extension region 21 b are formed in the silicon substrate 21 at the respective sides of the sidewall insulation films 23 S A and 23 S B so as to oppose across the channel region right underneath the gate electrode 23 . Further, the drain region 21 c and the source region 21 d are formed respectively in overlapping with the drain extension region 21 a and the source extension region 21 b at the respective outer sides of the sidewall insulation films 23 S A and 23 S B .

Next, in the step of FIG. 3B , the insulation film 24 is formed on the structure of FIG. 3A , and the via-plug 24 A is formed in the insulation film 24 in the step of FIG. 3C by a damascene process in each of the device regions 21 A 1 , 21 A 2 , 21 A 3 . . . . More specifically, a via-hole is formed in the insulation film 24 to expose the drain regions 21 c in the respective device regions 21 A 1 , 21 A 2 , 21 A 3 . . . by a photolithographic process, and the via-plug 24 A is formed by filling the via-hole with a tungsten (W) layer and subsequent removal of unnecessary W layer by a chemical mechanical polishing process. In the step of FIG. 3C , it will be noted that there is formed an inclined surface 24 S slightly inclined toward the wafer edge 40 E on the surface of the insulation film adjacent to the wafer edge 40 E as a result of the chemical mechanical polishing process such that the inclined surface surrounds a flat region 24 F of the interlayer insulation film 24 .

Next, in the step of FIG. 3D , the interlayer insulation film 25 is formed on the insulation film 24 and the interlayer insulation film is formed with the Cu wiring patterns 25 A and 25 B with a damascene process. More specifically, there is formed an opening in the interlayer insulation film 25 in correspondence to the Cu wiring patterns 25 A and 25 B, followed by filling the opening with a Cu layer. Further, unnecessary Cu layer is removed by a chemical mechanical polishing process, and the Cu wiring patterns 25 A and 25 B are formed in the interlayer insulation film 25 in a state in which the top surface is flush with a top surface of the interlayer insulation film 25 .

In the step of FIG. 3D , the interlayer insulation film 25 is formed to cover the inclined surface 24 S of the insulation film 24 adjacent to the wafer edge 40 E, wherein interlayer insulation film 25 thus formed includes an inclined surface inclined further as a result of the chemical mechanical polishing process of the interlayer insulation film 25 as a result of decrease of film thickness associated with the chemical mechanical polishing process of the interlayer insulation film 25 . As a result, an inclined surface 25 S is formed in the interlayer insulation film 25 with increased inclination as compared with the inclined surface 24 S adjacent to the wafer edge 40 E. In the step of FIG. 3D , the extent of the inclined surface 25 S is expanded as compared with the inclined surface 24 S underneath, and with this, a flat region 25 F of the interlayer insulation film 25 located at the inner side of the included surface 25 S is reduced as compared with the flat region 24 F of the underlying interlayer insulation film 24 .

Further, in the step of FIG. 3E , the next interlayer insulation film 26 is formed over the interlayer insulation film 25 and the Cu wiring pattern 26 A including the Cu via-plug 26 V is formed in the interlayer insulation film 26 by a dual damascene process. More specifically, the interlayer insulation film is formed with a via-hole corresponding to the Cu via-plug 26 V and an opening corresponding to the wiring pattern 26 A, followed by filling the via-hole and the opening with a Cu layer. Further, by removing unnecessary Cu layer by a chemical mechanical polishing process, the Cu wiring pattern 26 A is formed in the interlayer insulation film 26 accompanied with the Cu via-plug 26 V, such that a top surface thereof is coincident with the top surface of the interlayer insulation film 26 .

In the step of FIG. 3E , the interlayer insulation film 26 is formed to cover the inclined surface 25 S of the insulation film 25 adjacent to the wafer edge 40 E, wherein the interlayer insulation film 26 thus formed includes an inclined surface inclined further as a result of decrease of the film thickness associated with the chemical mechanical polishing process applied to the interlayer insulation film 26 . As a result, an inclined surface 26 S is formed in the interlayer insulation film 26 with increased inclination as compared with the inclined surface 25 S adjacent to the wafer edge 40 E. In the step of FIG. 3E , the extent of the inclined surface 26 S is increased as compared with the inclined surface 25 S lying underneath, and with this, the extent of a flat region 26 F of the interlayer insulation film 26 located at the inner side of the inclined surface 26 S is reduced as compared with the flat region 25 F of the underlying interlayer insulation film 25 .

Further, with the step of FIG. 3F , the next interlayer insulation film 27 is formed over the interlayer insulation film 26 , and the W via-plug 27 V is formed in the interlayer insulation film 27 . More specifically, there is formed a via-hole in the interlayer insulation film 27 in correspondence to the W via-plug 27 V, followed by filling the via-hole with a W layer. Further, unnecessary W layer is removed by a chemical mechanical polishing process, and the W via-plug 27 V is formed in the interlayer insulation film 27 in a state in which the top surface is coincident with a top surface of the interlayer insulation film 27 .

In the step of FIG. 3F , the interlayer insulation film 27 is formed to cover the inclined surface 26 S of the insulation film 26 adjacent to the wafer edge 40 E, wherein interlayer insulation film 27 thus formed includes an inclined surface inclined further as a result of the chemical mechanical polishing process applied to the interlayer insulation film 27 . As a result, an inclined surface 27 S is formed in the interlayer insulation film 27 with increased inclination as compared with the inclined surface 26 S adjacent to the wafer edge 40 E. In the step of FIG. 3F , the extent of the inclined surface 27 S is increased as compared with the inclined surface 26 S lying underneath, and with this, the extent of a flat region 27 F of the interlayer insulation film 27 located at the inner side of the included surface 27 S is reduced as compared with the flat region 26 F of the underlying interlayer insulation film 26 .

In the step of FIG. 3G , an Al film 28 M is formed over the interlayer insulation film 27 by a sputtering process, for example, with a thickness larger than the thickness of the interlayer insulation films 25 - 27 to cover the flat surface of the interlayer insulation film 27 corresponding to the inner region 40 A and further the inclined surface 27 S of the interlayer insulation film 27 corresponding to the outer region 40 B. Further, the Al film 28 M is pattered in the step of FIG. 3H , and the connection pads 28 A are formed on the flat region 27 F of the interlayer insulation film 27 in correspondence to each of the device regions 21 A 1 , 21 A 2 , 21 A 3 . . . .

Next, in the step of FIG. 3I , the interlayer insulation film 28 is formed on the interlayer insulation film 27 to cover the connection pad 28 A of FIG. 3H with a thickness sufficient to cover the connection pad 28 A such as a thickness exceeding twice as large as the height of the connection pad 28 A, by a CVD process, for example, with a shape conformal to the underlying layer. The interlayer insulation film 28 thus formed includes, in a top surface thereof, a projection 28 P corresponding to the connection pad 28 A and further an inclined surface 28 S corresponding to the inclined surface 27 S of the interlayer insulation film 27 . Because there is no chemical mechanical polishing process is included after the step of FIG. 3F until the step of FIG. 3H , it should be noted that the boundary between the flat region 27 F and the inclined surface 27 S of the interlayer insulation film 27 remains the same as in the case of FIG. 3F .

Next, in the step of FIG. 3J , a resist pattern R 1 is formed to cover the inclined surface 28 S of the interlayer insulation film 28 by using a negative type resist. It should be noted that such a resist pattern R 1 can be formed by applying the resist film uniformly on the structure of FIG. 3I and by locally exposing the resist film by an optical beam 2 of an optical source 1 to expose the outer peripheral part of the wafer while rotating the wafer 20 as represented in FIG. 4 . It should be noted that the inclined surface 28 S of the interlayer insulation film 28 corresponds to the outer region 40 B in the plan view diagram of FIG. 2 and the flat region 28 F of the interlayer insulation film 28 corresponds to the inner region 40 B of the plan view diagram of FIG. 2 . It should be noted that the interlayer insulation film 28 covers the connection pad 28 A in the inner region 40 A.

Next, in the step of FIG. 3K , the present embodiment etches back the top surface of the interlayer insulation film 28 by an anisotropic etching process working generally perpendicularly to the surface of the silicon substrate 21 while using the resist pattern R 1 as a mask, to reduce the film thickness of the interlayer insulation film 28 in the inner region 40 A to the extent that the connection pad 28 A is not exposed. In the case the interlayer insulation film 28 is formed to a film thickness exceeding twice the height of the connection region 28 A, it is possible to avoid the exposure of the connection pad 28 A out from the interlayer insulation film 28 when the etchback is applied to decrease the film thickness of the interlayer insulation film 28 to one half or less. As a result of such an etch back process, there is formed a step S in the interlayer insulation film 28 at the boundary between the outer region 40 B and the inner region 40 A in correspondence to the amount of the etchback.

Next, in the step of FIG. 3L , the resist pattern R 1 of FIG. 3K is removed and the interlayer insulation film 28 is planarized in the step of FIG. 3M by a chemical mechanical polishing process. In this process of FIG. 3M , the polishing of the interlayer insulation film 28 proceeds generally uniformly in the outer region 40 B as well as in the inner region 40 A in view of the fact that there is formed a projection having an inclined surface 28 S in the interlayer insulation film 28 as represented in FIG. 3L along the entire periphery of the wafer 40 in correspondence to the outer region 40 B of the wafer 40 . As represented in FIG. 3L , the projection thus formed forms a step S at the boundary between the outer region 40 B and the inner region 40 A. As a result, there occurs shrinkage in the inclined surface 28 S as represented in FIG. 3M and there is formed a planarized surface 28 f in the top surface of the interlayer insulation film 40 B such that the planarized surface 28 f extends into the outer region 40 B.

Next, in the step of FIG. 3N , there are formed W via-plugs 28 V in the interlayer insulation film 28 by a damascene process respectively in the device regions 21 A 1 , 21 A 2 , 21 A 3 . . . . Further, in the step of FIG. 3O , a pixel electrode 29 is formed on the planarized surface 28 f of the interlayer insulation film 28 in the form of stacking of a Ti/TiN adhesion layer 29 A and an optical reflection layer 29 B of Au or Al. With this, the semiconductor device 20 S is obtained.

With such a semiconductor device 20 S thus formed, it should be noted that the formation of the via-plugs 28 V is conducted to the planarized surface 28 f of the interlayer insulation film 28 , and because of this, it becomes possible to form all the via-plugs 28 V with certainty even in such a case of using a high-resolution optical system of characteristically shallow focal depth at the time of the photolithography. Further, because the pixel electrode 29 B, which includes the optical reflection layer 29 B therein, is formed on such a planarized surface 28 f , there occurs no such a problem that the direction of the exit light is deflected from the desired direction at the time of reflection of the incident light, and it becomes possible to improve the yield of production of the semiconductor device.

FIG. 5 is a cross-sectional diagram of a semiconductor device 20 T fabricated by a fabrication process according to a comparative example in which the etchback process of FIG. 3K is omitted. For the same of comparison, those parts of FIG. 5 explained before are designated by the same reference numerals and the description thereof will be omitted.

Referring to FIG. 5 , the present comparative example applies a first chemical mechanical polishing process to the structure of FIG. 3I for the planarization and a second chemical mechanical polishing process for forming the via-plugs 28 V. Because of this, there is formed an inclined surface 28 S 1 having an angle steeper as compared with the angle of the inclined surface 27 S in connection with the edge 40 E of the wafer 40 , wherein inclined surfaces 28 S 2 and 28 S 3 of less steep angles may follow consecutively and continuously in the inner side of the inclined surface 28 S 1 with consecutively reducing inclination angles. Thereby, it should be noted that, contrary to the structure of FIG. 3O , the inclined surfaces 28 S 2 and 28 S 3 extend to and reach the device regions 21 A 1 and 21 A 2 , respectively, and the pixel electrodes 29 P 1 and 29 P 2 thus formed on the inclined surfaces 28 S 2 and 28 S 3 are inevitably inclined as compared with other pixel electrodes 29 P. Thus, with the semiconductor device according to the comparative example of FIG. 5 , the incident lights are reflected by the pixel electrodes 29 P 1 and 29 P 2 in the directions offset from the desired direction.

Further, with the comparative example of FIG. 5 , it will be noted that the via-plugs 28 V marked up by the broken lines are formed on the inclined surface 28 S 2 or 28 S 3 and thus at the levels lower than a horizontal line H, which is an extension of the planarized surface 28 f of the interlayer insulation film 28 . Because of this, there arises a problem that sufficient exposure dose is not attained at the time of lithography for forming the via-plugs 28 V and the formation of the corresponding via-holes tend to become incomplete. Thus, the semiconductor device of the comparative example tends to suffer from low yield of production.

The semiconductor device 20 S of the present embodiment may be formed as discrete semiconductor chips by dicing the silicon wafer 40 , after formation on the silicon wafer 40 , along the scribe lines 40 L represented in FIG. 2 . Alternatively, the semiconductor device 20 S may also be sold or used while in the form of the silicon wafer 40 .

[Second Embodiment]

FIGS. 6A-6C are cross-sectional process flow diagrams representing the fabrication process of a semiconductor device according to a second embodiment, which is implemented subsequent to the step of FIG. 3G .

Referring to FIG. 6A , the present embodiment not only forms the connection pads 28 A on the flat region 27 F of the interlayer insulation film 27 by patterning the Al film 28 M of the structure of FIG. 3G but forms an Al pad 28 B also on the inclined surface 27 S with the same thickness.

Next, in the step of FIG. 6B , the interlayer insulation film 28 is deposited upon the interlayer insulation film 27 in conformity with the shape of the underlying layer by a CVD process, for example, so as to bury the connection pads 28 A and further the Al pad 28 B. As a result, not only the projections 28 P are formed in the interlayer insulation film 28 in a part corresponding to the flat region 27 F of the underlying interlayer insulation film 27 in correspondence to the connection pads 28 A but there is also formed a projection 28 Q in the part covering the inclined surface 27 S of the interlayer insulation film 27 in correspondence to the Al pad 28 B.

Thus, when the interlayer insulation film of FIG. 6B is planarized by a chemical mechanical polishing process in the next step of FIG. 6C , the increase of the polishing rate in the outer region 40 B is canceled out more or less by the increase of the polishing time for polishing the projection 28 Q. Note that the projection 28 Q is formed in the interlayer insulation film 28 in correspondence to the outer region 40 B in the vicinity of the wafer edge 40 E. Thus, a structure represented in FIG. 6C is obtained such that the planarized surface 28 f of the interlayer insulation film has expanded to the outer region 40 B.

By forming the pixel electrode 29 P having such a planarized principal surface similarly to the process of FIGS. 3N and 3O , it becomes possible to form the desired semiconductor device with high yield.

In the present embodiment, the Al pad 28 B is formed on the inclined surface 28 S of the interlayer insulation film 28 . Even so, there arises no problem of incomplete pattern formation as the Al pad 28 B has a much larger size as compared with minute via-plugs and thus can be exposed with a low-resolution optical system having much larger focal depth.

It should be noted that the Al pad 28 B may also constitute a part of the wiring layer of the Al connection pads 28 A.

It should be noted that, in those chips having a part extending into the outer region 40 B as represented in FIG. 2 by a broken line, there may be a possibility that the Al pad 28 B remains at one of the four corners.

[Third Embodiment]

FIGS. 7A-7C are cross-sectional process flow diagrams representing a part of the fabrication process of a semiconductor device according to a third embodiment, which is implemented subsequent to the step of FIG. 3I .

Referring to FIG. 7A , the present embodiment applies an optical beam 2 in the exposure step of FIG. 4 in such a manner that there occurs no exposure in a band-like region 28 R formed in a part of the inclined surface 28 S adjacent to the wafer edge 40 E with a width of 0 mm-1 mm, for avoiding peeling of the resist film when forming the resist pattern R 1 in the step of FIG. 3J . Here, it should be noted that the width of 0 mm of the band-like region 28 R means that the outer edge of the resist film is in coincident with the wafer edge 40 E. In such a case, the resist film extending beyond the wafer edge 40 E is removed. As a result, the resist pattern R 1 is formed, in the present embodiment, at an inner side with regard to the band-like region 28 R in a manner to avoid the band-like region 28 R as represented in FIG. 7A .

In the case the resist film R coated upon the interlayer insulation film 28 is formed to extend beyond the wafer edge 40 E as in the example of FIG. 8A , there is a tendency that the resist film R peels off easily. Contrary to the foregoing, the resist pattern R 1 of FIG. 7A is obtained by irradiating the optical beam 2 such that there occurs no exposure in the band-like region of a width of 1 mm, for example, formed adjacent to the wafer edge 40 E at the time of forming the resist pattern R 1 by patterning of the resist film R.

As represented in FIG. 8B , there may be obtained a structure in which the band-like region has the width of 0 mm in the case only the part of the resist film R that has extended out from the wafer edge 40 E is removed by exposure and development.

In the present embodiment, it should be noted that, while the inner region 40 A of the silicon wafer 40 is defined as corresponding to the inner region of the inclined surface 27 S similarly to the previous embodiments, the outer region 40 B is defined as being located at the inner side of an outermost peripheral region 40 C that corresponds to the band-like region 28 R. Thus, in the present embodiment, the outermost peripheral region 40 C is formed at the outer side of the outer region 40 B as represented in FIG. 7A .

The structure represented in FIG. 7B is obtained by etching back the structure of FIG. 7A by an anisotropic etching process working generally perpendicular to the principal surface of the silicon substrate 21 .

In the example of FIG. 8B , too, the part of the resist pattern R 1 corresponding to the inner region 40 A is removed similarly to the first embodiment.

Further, by planarizing the interlayer insulation film 28 by chemical mechanical polishing after removing the resist pattern R 1 in the structure of FIG. 7B , the semiconductor device 20 S represented in FIG. 7C is obtained similarly to the case of FIG. 3O by forming the pixel electrode 29 P on the planarized surface 28 f of the interlayer insulation film 28 .

Because the resist pattern R 1 is not formed adjacent to the wafer edge 40 E in the present embodiment, peeling off of the resist pattern R 1 occurs less easily and the production yield of the semiconductor device 20 S is improved.

While explanation has been made heretofore with regard to a semiconductor device used with the reflection-type liquid crystal display device 20 of FIG. 1 , the various embodiments are useful for improving the production yield in general semiconductor devices having a multilayer wiring structure formed by damascene process or dual damascene process.

In the structure of FIG. 3O or FIG. 7C , it should be noted that the pixel electrode 29 P is formed on the planarized surface 28 f of the interlayer insulation film 28 . Thus, it becomes possible to attain secure via-connection also in the case of forming a general electrode of Al or Au in place of the pixel electrode 29 P and forming a next interlayer insulation film and a next wiring layer thereon as compared with the comparative example of FIG. 5 . With this, it becomes possible to improve the yield of production of the semiconductor device as compared with the case of comparative example of FIG. 5 .

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.