JPH03265121A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the resolution and dimension accuracy in exposure of photolithography by forming films of nearly the same thickness, respectively, on the obverse and the reverse of a substrate, and stacking a protective layer on the obverse, and etching the film at the reverse so as to expose the flat face, and then installing a vacuum chuck. CONSTITUTION:SiO2 films and films 3 are formed, in nearly the same thicknesses, on each of the obverse and the reverse of an Si substrate, and further a resist to become a protective film is stacked on the obverse side, and the films 2 and 3 on the reverse side are etched until the flat face is exposed. Next, the film 4 is removed, and an organic photosensitive film 5 is applied, and then a vacuum chuck 6 is installed, and by photolithography method the film 5 is exposed and baked to form a pattern. By this method, the partial thickness value 13 becomes large synthetically without polishing the reverse, and the resolution and dimension accuracy in exposure is elevated, and minute pattern is made.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for manufacturing a semiconductor device, particularly regarding a method for forming a fine pattern when photolithography is applied to a semiconductor wafer, the wafer can be efficiently processed to prevent abrasives and dust from adhering to the back surface of the wafer. To provide a method in which stable resolution and dimensional accuracy of a transferred pattern can be obtained by flattening the back surface, suppressing the LTV of the exposure area to a small value, and preventing shifts in exposure focus and non-uniform exposure due to unevenness on the back surface of the wafer. A film is formed on a first main surface of a semiconductor substrate, a photosensitive resist film is formed on the film, and a second main surface opposite to the first main surface of the semiconductor substrate is formed. According to a method of manufacturing a semiconductor device in which exposure is performed while the semiconductor substrate (1) is in close contact with the flat surface of the support, the second main surface of the semiconductor substrate (1) is
forming at least one layer of a film having a substantially uniform thickness on the main surface and the first main surface; and forming a protective film (4) on the film formed on the first main surface. a step of selectively etching away the film on the second main surface until a surface as flat as that of the semiconductor substrate is exposed; and then, after removing the protective film (4), The film (3) adhered and formed on the main surface side of
) A step of forming a photosensitive resist film (5) on the semiconductor substrate (1) and performing exposure while holding the second main surface side of the semiconductor substrate (1) in close contact with the flat surface of the support (6). Configure it to include.

[Industrial Field of Application] The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of forming a fine pattern when photolithography is applied to a semiconductor wafer.

With the recent demand for higher integration in semiconductor device manufacturing methods,
There is a need for a photolithography process that can form fine patterns on semiconductor wafers. Among these steps, the exposure step of printing a predetermined pattern on a photosensitive resist film coated on the wafer surface is a particularly important step for improving pattern accuracy. In the exposure process, a pattern is baked by focusing on the wafer surface, but if there are irregularities on the surface, it becomes difficult to focus. In wafer processes in which various films are grown on the surface of a semiconductor wafer on which semiconductor elements are to be formed, CV
When the D film is grown, since the flow rate of the gas that goes around the back surface of the wafer cannot be made constant, the in-plane distribution of the film tends to be uneven and abnormal growth tends to occur around the wafer. Therefore, in particular, as the process progresses, the variation in film thickness of the film formed on the back surface of the wafer becomes larger than that on the front surface of the wafer. In addition, dust generated when various films are grown on the wafer surface is also attached to the back surface of the wafer, so unevenness is more likely to occur. This situation is shown in FIG. 2(a). In the figure, the top side is the wafer front surface 10, and the bottom side is the wafer back side 11. In this figure, the interior of the semiconductor wafer is omitted, and a cross-sectional view showing the surface state is shown. In the photolithography process, the wafer is transported onto a flat vacuum chuck, and the wafer is vacuum-adsorbed for exposure. When adsorbing the wafer,
The unevenness on the back side of the wafer is transferred to the front side of the wafer. Therefore,
Even if the film is deposited on the front side of the wafer to a uniform thickness, the unevenness on the back side of the wafer will be reflected on the front surface of the wafer, resulting in an uneven surface. Of course, if there are any irregularities on the wafer surface, the irregularities on the wafer surface will become even larger. For example, when approximately 4,000 CVD polysilicon films are grown on the wafer surface, the absolute value of the difference between the unevenness representing the film thickness distribution on the wafer surface side in FIG. 2(a) before being fixed to the vacuum chuck 6, LTV (
Loca I Th1ckness Value)
13 is about 0.8 μm, whereas when the back surface of the wafer is attracted to the vacuum chuck 6 as shown in FIG. 2(b), the LT
V13 is about 1.8 μm, which makes the wafer surface even more uneven. When the unevenness of the wafer surface becomes severe in this way, the LTV cannot be kept within the allowable range of the depth of focus within the exposure area, that is, the depth of field is 1.5 μm, and out-of-focus areas are created within the exposure area. Exposure will cause scratches. Therefore, the resolution of the transferred pattern decreases,
Furthermore, since the dimensions of the transferred pattern become non-uniform, it becomes difficult to form fine patterns on the wafer. This becomes a problem in advancing the miniaturization of elements, and some kind of solution is desired.

[Prior Art] For this reason, conventionally, a method has been proposed in which the back surface of the wafer is polished and flattened before exposure (Japanese Patent Laid-Open No. 62-26814).

[Problems to be Solved by the Invention] However, since this method uses an abrasive when polishing the back side of the wafer, this abrasive adheres to the back side of the wafer, and furthermore, the dust generated secondary to this polishing is transferred to the wafer surface. There was an inconvenience that it would stick to the surface. Therefore, it is necessary to clean the wafer surface to remove the abrasive and dust, and furthermore, depending on the degree of unevenness of each wafer, it takes time to polish each wafer one by one, resulting in poor throughput.

The present invention efficiently flattens the back surface of the wafer to prevent abrasives and dust from adhering to the back surface of the wafer, and improves the LTV of the exposed area.
It is an object of the present invention to provide a method in which stable resolution and dimensional accuracy of a transferred pattern can be obtained by suppressing the exposure to a small value and preventing deviations in exposure focus and non-uniformity of exposure due to irregularities on the back surface of a wafer.

[Means to solve the problem]

The present invention includes forming a film on a first main surface of a semiconductor substrate, forming a photosensitive resist film on the film, and forming a second main surface opposite to the main surface of the semiconductor substrate. In a method for manufacturing a semiconductor device in which exposure is performed in close contact with a flat surface of a support, a semiconductor substrate +F! having a flat second principal surface is used. , the second of (1)
forming at least one layer of substantially uniform thickness on the main surface and the first main surface; and forming a protective film (4) on the film formed on the first main surface. a step of selectively etching the film on the second main surface until a surface as flat as that of the semiconductor substrate is exposed; and then, after removing the protective film (4), Film (3) adhered and formed on the main surface side of 1
A photosensitive resist film (5) is formed on the semiconductor substrate (
1) of holding the second main surface side in close contact with the flat surface of the support (6) and performing exposure.

[Operation] In the present invention, the film on the back surface of the wafer is removed using an etching method before the pattern is printed. Therefore, compared to the conventional method in which the back surface of the wafer is flattened by polishing, abrasives and dust do not adhere to the wafer surface. That is, it is possible to expose a flat surface on the back surface of the wafer using a method that does not involve dust generation, eliminate the influence of variations in the back surface of the wafer on the LTV of the back surface of the wafer, and suppress the LTV of the front surface of the wafer to a small value. Therefore, the LTV falls within the range of the depth of field in the minimum exposure area, and defocus is eliminated.

Furthermore, in the present invention, there is no need to planarize the back surface of each wafer one by one depending on the degree of unevenness of each wafer (because the film on the back surface of the wafer can be selectively removed by using the difference in etching speed, - Several tens of wafers can be processed at a time. Also, since no dust is generated, there is no need for cleaning. Therefore, the present invention has a good throughput and can realize flattening of the back surface of the wafer.

〔Example〕

FIG. 1 is a sectional view of a main part for explaining the present invention in detail.

See Figure 1(a).

Thermal acid growth (silicon dioxide, SiO2) 2 is formed to a thickness of, for example, about 200 to 300 on both sides of a silicon (Si) substrate 1 having a thickness of, for example, about 600 μm as a semiconductor substrate. At this time, since the thermal oxide film 2 grows uniformly on the Si substrate 1, the in-plane distribution number of the thermal oxide film 2 is constant and kept flat. Next, films 3 are formed on both sides of the thermal oxide film 2 depending on the purpose. Various examples can be given for the membrane 3. For example, CVD (Chem j a c a ) in a gas atmosphere containing silane (SiH) and ammonia
A nitride film such as silicon nitride (Si, N4) is formed to a thickness of about 1,000 mm using a vapor deposition method. Moreover, instead of this nitride film, polysilicon is formed to a thickness of about 1.5 μm using the same CVD method in a gas atmosphere containing silane. Other examples of this film 3 include forming 5iOz to a thickness of about 2,500 to 3,000 Å using the same CVD method in a gas atmosphere containing silane (SIH4) and N20, or
The SG film may be formed to a thickness of about 1.0 um. in this way,
The film 3 is formed by appropriately selecting the material, thickness, etc. according to each purpose. However, in any case, the film 3 is CVD
Since the film is formed by a sputtering method or a sputtering method, there are irregularities on both the front and back surfaces of the wafer, and the irregularities on the back surface of the wafer are particularly large and the in-plane distribution is not uniform. For example, in the case of polysilicon, LTV13 on the wafer surface
Gi is about 0.8 μm. At this point, when the wafer is fixed on a vacuum chuck, the LTV of the wafer surface is
will expand. This situation is shown in Figure 3.

FIG. 3(a) shows the state before the wafer is attracted to the vacuum chuck, and FIG. 3(b) shows the state after the wafer is attracted to the vacuum chuck. As shown in (b), (a)
If the wafer is attracted to the vacuum chuck 6 in this state, the unevenness on the back side of the wafer will be transferred to the front side of the wafer, and the LTV will be 1.8.
Expand to about μm. When the organic photoresist film 5 is applied to this surface, the difference between the parts where the organic photoresist film 5 is thick and the parts where it is thin becomes large, and the depth of field during exposure increases.
V will not settle down and the resolution will drop.

This causes loss of dimensional accuracy of the transferred pattern.

See Figure 1(b).

Next, in order to prevent the adhesion of dust that would occur during the subsequent etching removal of the backside of the wafer, a resist layer 4 was applied only to the front surface of the wafer.
Apply.

See Figure 1(c).

Then, wet etching or dry etching is performed to remove the film 3 on the back surface of the wafer using the thermal oxide film 2 as an etching stopper. Here, when dry etching is performed, if the film 3 is polysilicon, the etching rate ratio with the thermal oxide film 2 is about 20, and if the film 3 is a nitride film, the etching rate ratio with the thermal oxide film 2 is about 3. It will be about 4. Further, if the film 3 is PSG, the etch rate ratio with respect to the thermal oxide film 2 will be about 1 to 2. Therefore, the film 3 is a nitride film or a PS film.
In the case of G, wet etching is preferable to dry etching because it provides a better etch rate ratio. If a nitride film is wet-etched using an aqueous solution containing phosphoric acid, an etch rate ratio of several hundred can be obtained with respect to the thermal oxide film 2, and if a PSG film is wet-etched using an aqueous solution containing hydrofluoric acid or a so-called buffered hydrofluoric acid. If wet etching is performed in an aqueous solution, an etch rate ratio of several hundred to the thermal oxide film 2 can be obtained, and only the film 3 can be selectively removed. Note that when the Si○2 film 3 is formed on the film 3, the film 2 is also 5i02.
Since the film is a film, the film 3 and the Si○2 film 2 are etched at the same time, and the Si substrate is exposed on the back side of the wafer as shown in FIG. 1 (C). In any case, the backside of the wafer is covered with thermal oxide film 2 or S.
Since the i-substrate 1 is in an exposed state, it is flattened. However, if the thermal oxide film 2 remains, it is possible to prevent the back surface of the wafer from being scratched. In this case, the thermal oxide film 2 may be a nitride film. That is, it is sufficient if the film 2 serves as an etching stopper when removing the film 3 by etching. In that case, as described above, the back surface of the wafer may be flattened by dry etching or wet etching so that only the film 3 can be selectively removed. Incidentally, during this etching removal, there is a possibility that dust may adhere to the resist film 4 on the wafer surface. However, in the next step shown in FIG. 1(d), the resist film 4 is removed and the organic photoresist film 5 is recoated instead, so that the dust attached to the resist 1-M4 is removed at this time.

See Figure 1(d).

Finally, the resist film 4 on the wafer surface is removed by a conventional method, and an organic photoresist film 5 is reapplied in its place. This removes the dust adhering to the resist film 4 that was generated when the back surface of the wafer was flattened, that is, when the film 3 on the back surface of the wafer was removed, and a new organic photoresist film can be formed. In addition, if the process shown in Figure 1 (C゛) is taken, the process shown in Figure 1 (d''
)become that way.

The wafer is then attracted to a vacuum chuck and a pattern is printed on it. With this, the back surface of the wafer is attached to the vacuum chunk in a flattened state, so that the unevenness on the back surface of the wafer will not be transferred to the front surface of the wafer during suction and the unevenness on the wafer surface will not be amplified. Therefore, if polysilicon is selected as the film 3, the initial L shown in FIG.
Exposure can be performed at TV O.about 8 μm. That is, since the organic photoresist film 5 can be formed with an even thickness without forming it thickly as shown in FIG. 3(b), the LTV has a depth of field of 1.
It is within 5 μm, so there is no need to reduce the resolution. Therefore, a fine pattern can be clearly printed, and the dimensional accuracy of the transferred pattern is improved compared to the conventional method.

〔Effect of the invention〕

As described above, according to the present invention, stable resolution and dimensional accuracy of a transferred pattern can be obtained during exposure in photolithography technology, so that fine patterns of semiconductor elements can be easily printed. Therefore, it greatly contributes to the miniaturization of semiconductor devices.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a main part for explaining the present invention in detail, Fig. 2 is a cross-sectional view of a semiconductor wafer, and Fig. 3 is a cross-sectional view of a wafer fixed on a vacuum chuck without removing the back side of the wafer. FIG. In the figure: 1: Semiconductor substrate 2: Thermal oxide film 3: Film 4 Resist film 5: Organic photoresist film 6: Vacuum chuck 10: Wafer front side 11: Wafer back side 12: Semiconductor wafer 13: LTV: $-Metal process I'm here, and I'm in the second place.
Table 1 Diagram 1 (: f 1) Key points for explaining and reciting the technical merits of the present invention 1
Diagram (Part 2)

Claims (1)

[Claims] A film is formed on a first main surface of a semiconductor substrate, a photosensitive resist film is formed on the film, and a second main surface opposite to the first main surface of the semiconductor substrate is formed on a flat surface of a support. In a method of manufacturing a semiconductor device in which exposure is performed in close contact with a surface, the thickness is substantially uniform on the second main surface and the first main surface of a semiconductor substrate (1) whose second main surface is flat. forming a protective film (4) on the film formed on the first main surface; and forming the film on the second main surface to the same extent as the semiconductor substrate. A process of selectively etching and removing until a flat surface is obtained, and then, after removing the protective film (4), a photosensitive layer is applied to the film (3) deposited and formed on the first main surface side. forming a resist film (5) and performing exposure while holding the second main surface side of the semiconductor substrate (1) in close contact with the flat surface of the support (6); A method for manufacturing a featured semiconductor device.