JP2002025974A - Method of manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a semiconductor device from deteriorating in manufacturing yield due to the fact that a large number of pinholes occur in a titanium film which is formed through a sputtering method so as to be used as a metal mask for manufacturing the semiconductor device. SOLUTION: A titanium film 1 is formed on a substrate which is kept at a temperature of 200 deg.C or above. The crystallinity of the titanium film 1 is changed from unidirectional to bidirectional orientation by heating, and the titanium film 1 is increased in crystal density and improved in barrier properties to anisotropic etchant such as KOH used for etching a semiconductor substrate 10. The deposit rate of particles that are generated in a sputtering device by heating and deposited on the titanium film 1 is increased, and pinholes 2 opening up due to the separation of the particles are decreased in number. The titanium film 1 is used as a masking material, by which a semiconductor device can be manufactured with a high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor in which a mask material for patterning is formed of a metal film such as a titanium sputtered film.

[0002]

2. Description of the Related Art Conventionally, an organic photoresist is generally used for patterning in a semiconductor device manufacturing process. In addition, a silicon substrate is tapered by anisotropic etching. Forming a concave shape,
There are devices that use this as a part of a semiconductor element. For example, a semiconductor pressure sensor, a specific photodiode array, a device incorporating a laser diode or a phototransistor, or the like.

[0003] In the anisotropic etching step in the manufacture of the above devices, an alkaline etchant is mainly used. In this case, however, the photoresist used as an etching mask usually has no resistance. Therefore, a silicon oxide film, a silicon nitride film, and a metal thin film such as titanium having alkali resistance are used as a mask material when using such an etching solution. However, a silicon oxide film or a silicon nitride film is often used as a part of a device as an interlayer film or a protective film of a semiconductor device, and therefore, it is difficult to use the same material as a mask material.
On the other hand, the titanium film is less frequently used as a component of a semiconductor device in the above-listed devices, and can be formed and etched relatively easily.
In particular, it is widely used as a mask material for alkaline liquids.

In order to form the titanium film, electron beam evaporation is often used. However, recently, in order to improve the step coverage of the device surface and increase the number of processed titanium films per unit time, sputtering is performed. The law is increasingly used.

Hereinafter, a process for forming a titanium film formed by a conventional sputtering method will be described. The sputtering method used here may be a magnetron sputtering method or other methods, and a flat target or a target having a conical inner surface can also be used.

In forming a titanium film, for example, RF
The power is 1 kW, the pressure is 8 mTorr, the thickness of the titanium film to be formed is 0.5 μm, the substrate temperature is 25 ° C., and the diameter of the silicon wafer is 125 mm. Under these conditions, when a titanium film was formed on 25 silicon wafers, the number of pinholes per wafer was measured and is shown in FIG. As a result, it was found that an average of 165 pinholes were formed per wafer.

Next, a case where etching is performed with an alkaline etchant using a titanium film formed by the sputtering method as a mask material will be described. FIG. 1 (a)
(D) are cross-sectional views of the semiconductor device, each showing a conventional etching process of a silicon substrate using a titanium sputtered film as a mask material. 1A to 1D, reference numeral 1 denotes a titanium film formed by a sputtering method, 2 denotes a pinhole formed in the titanium film 1, 3 denotes a photoresist, 4 denotes an opening window of the titanium film 1, and 5 denotes a window. An etch hole formed by the pinhole 2 of the titanium film 1, an etch hole 6 formed by the opening window 4 of the titanium film 1, and a silicon substrate 10. In addition, there is a region where a semiconductor element is formed outside the drawing.

First, as shown in FIG. 1A, a titanium film 1 is first formed on a silicon substrate 10 by the sputtering method under the above-mentioned sputtering conditions. At this time, as shown in FIG. 5, many titanium films 1 are unintentionally formed with pinholes 2. Next, as shown in FIG. 1B, after applying a photoresist 3 on the titanium film 1, normal patterning is performed. Using a hydrofluoric acid solution for patterning, the pattern formed by the photoresist was transferred to the titanium film 1, and then the resist was removed.
An opening window 4 is formed as shown in FIG. Finally, FIG.
As shown in FIG. 1D, the silicon substrate 10 is anisotropically etched with a KOH solution using the titanium film 3 as a mask to form an etch hole 6 in the silicon substrate 10. This etching depends on the type of device,
m to several hundred μm.

[0009]

However, FIG.
As clearly shown in (d), not only the etch hole 6 formed by the opening window 4 of the titanium film 1 but also the etch hole 5 by the pinhole 2 are formed by anisotropic etching using KOH. You. Etch hole 5 by pinhole 2
Is not intentionally formed, and an etch hole 5 is formed up to an unnecessary portion on the semiconductor device, and in some cases, a region where another semiconductor element is formed. In this case, the semiconductor device itself is not formed. It may not work.

As described above, the titanium film formed by the conventional sputtering method has many pinholes 2 and the titanium film 1 does not function effectively as a mask material, so that the production yield of a semiconductor device using the same is not sufficient. .

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a method of manufacturing a semiconductor device capable of suppressing generation of pinholes in a titanium sputtered film.

[0012]

According to a method for manufacturing a semiconductor device of the present invention, the temperature of a crystalline semiconductor substrate is set to 200 ° C. or higher, and a metal film is formed on the semiconductor substrate by sputtering. , Forming a pattern by selectively removing the metal film, and etching the semiconductor substrate using the metal film as a mask.

For example, the metal film is made of titanium, and is etched with KOH in the step of etching the semiconductor substrate. By setting the temperature of the semiconductor substrate to 200 ° C. or higher in the process of the present invention, a metal film such as a sputtered titanium film grows in a two-directional orientation and a dense crystal is formed, thereby improving the etching barrier property. In addition, since the particles and the titanium particles react and fuse, the falling off of the particles is suppressed. For these reasons, the generation of pinholes in the titanium film is suppressed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have examined in detail the fine structure of a titanium film formed by a conventional sputtering method. First, the titanium film formed by electron beam evaporation, which has been used before the sputtering method, has almost near-crystalline crystallinity, whereas the titanium film formed by the sputtering method is oriented almost unilaterally. Grow into polycrystalline
It was found that one crystal grain had good crystallinity, but on the other hand, the arrangement density of the crystal grains was low. Therefore, a portion such as a crystal grain boundary easily becomes a pinhole, and K
When an etchant such as an alkaline solution such as OH is used, it is considered that the film easily passes through the film, that is, the barrier property against wet etching is low.

In electron beam evaporation in which titanium is deposited on a silicon substrate by increasing the temperature to 1725 ° C., which is the melting point of titanium, the incident energy of titanium particles when reaching the substrate is lower than that of the sputtering method. Although the temperature of the particles themselves is low, the radiation temperature to the substrate due to evaporation of the titanium source is very high. For this reason, the particles adhering to the substrate react with the titanium film, and even if etching or the like is performed after film formation, these particles rarely fall off the titanium film.

On the other hand, in the sputtering method, in principle, the energy of titanium particles incident on the substrate is higher than that of electron beam evaporation and the temperature of the particles themselves is higher, but these particles are generated by plasma. Therefore, the radiation temperature to the substrate does not increase so much. Therefore, it is clear that the particles and the titanium film rarely react and fuse on the substrate, and the probability of the particles falling off after the film formation is high. Then, a portion where the particles fall off from the surface of the titanium film becomes a pinhole, and passes through an etchant of wet etching.

As described above, it has been clarified that sputtered titanium films often generate pinholes and do not function effectively as a mask material in terms of the crystal structure of the titanium film and the reaction between the titanium film and particles.

According to the present invention, based on the above findings, a semiconductor device is manufactured as follows. In other words, the manufacturing process of the semiconductor device is the same as the conventional process shown in FIG. 1 in view of the cross-sectional shape, but the titanium film 1 in the process of FIG. In the case where the same sputtering apparatus as that formed in the above was used, the RF power was 1 kW, the pressure was 8 mTorr, and the thickness of the titanium film was 0.5.
μm, but the substrate temperature is set to 300 ° C. different from the conventional one. As described above, it is a feature of the present invention that the substrate is formed by raising the substrate temperature by sputtering, and the substrate heating temperature range is suitably 200 ° C. to 400 ° C. At this time, the diameter of the silicon wafer is 125 mm.

Thereafter, as shown in FIG. 1C, the titanium film 1 is etched to form a pattern of the opening window 4, and this is used as a mask in the same manner as in FIG.
Silicon substrate 10 having a crystal plane is anisotropically etched using KOH to form an inverted trapezoidal concave portion.

FIG. 2 shows a change in the number of pinholes per wafer when a titanium film 1 serving as a mask for anisotropic etching is formed on 25 silicon wafers (silicon substrate 10) by the above method. It is a thing. When the results are averaged, the number of pinholes formed in the titanium film 1 is 5 per wafer, and the number of pinholes can be significantly reduced as compared with the conventional manufacturing method.
Thus, when this sputter-formed titanium film is used as a mask material, the frequency of unnecessary formation of etch holes on the substrate due to pinholes can be suppressed.

The film structure of the titanium film 1 formed by the conventional method and the sputtering method of the present invention was examined.
FIG. 3 is a spectrum analysis result by X-ray diffraction showing a difference in crystallinity of the titanium film 1. Silicon substrate 1 of the present invention
The crystal orientation of the titanium film 1 formed by forming a titanium film by heating 300 ° C. to 300 ° C. is (00)
It can be seen that the single orientation of 2) was remarkable, whereas the orientation in two directions (002) and (101) became remarkable by heating at 300 ° C.

From the above, the film formed by the conventional forming method has a substantially linear fine crystal grain gap reaching from the film surface to the bottom surface because the crystal grows columnar upward from the base in one direction. It is considered that a pinhole was formed, through which the etching solution could easily pass.

On the other hand, in the titanium film 1 formed by the method of the present invention, since there are at least two types of crystal growth directions, it is difficult to form a linear gap between crystal grains, which is a phenomenon of reducing pinholes. It is thought that it appears.
Thereby, it is considered that the barrier property against the etchant is excellent.

When the heating temperature of the silicon substrate 10 is higher than room temperature but lower than 200 ° C., the single orientation of (002) is remarkable as in the prior art.
No decrease in pinholes could be confirmed.

Although the pinholes were found to decrease in the heating temperature of the silicon substrate 10 up to 400 ° C. due to facility restrictions, even if the heating temperature is around 400 ° C., no problem occurs. It is considered that the pinholes can be reduced even when the heating is performed at a temperature of not less than C.

Next, FIG. 4 shows the result of observing the surface of the titanium film 1 by a foreign matter inspection apparatus by forming the titanium film 1 by the conventional method and the method according to the present invention. It can be seen that the residual ratio of particles on the substrate is increased by 20.9% as compared with the conventional one by applying the sputtering method of heating the substrate of the present invention. Therefore, foreign substances are less likely to fall off the titanium film 1, and the formation of pinholes that are formed thereafter is suppressed.

As described above, according to the method of the present invention, the adhesion of particles to the titanium film 1 can be increased by changing the crystal structure itself of the titanium film 1 by increasing the substrate temperature. Pinholes for the wet etch used can be reduced.

In this embodiment, the silicon substrate 10 is used as a substrate and KOH is used as an etchant. However, other substrates such as a compound semiconductor, another etching solution, and another etching method such as dry etching may be used. The same is true. Further, a metal film other than the titanium film 1 can be used as an etching mask.

[0029]

As described above, according to the present invention, when a metal film such as titanium is used as a mask material in a semiconductor device manufacturing process, the temperature of the crystalline semiconductor substrate is set to 200.
By forming a metal film on the semiconductor substrate by a sputtering method after the temperature is raised to not less than ° C., it is possible to suppress the occurrence of pinholes in the sputtered film, thereby contributing to an improvement in yield.

[Brief description of the drawings]

FIGS. 1A to 1D are process cross-sectional views each showing a manufacturing process of a semiconductor device using a titanium film.

FIG. 2 is a diagram showing the number of pinholes per wafer of a titanium film in the embodiment of the present invention.

FIG. 3 is a view showing an X-ray analysis spectrum of titanium film crystallinity in the same embodiment.

FIG. 4 is a diagram showing a particle residual ratio on a titanium film.

FIG. 5 is a diagram showing the number of pinholes per wafer by a conventional titanium film forming method.

[Explanation of symbols]

 Reference Signs List 1 titanium film (metal film) 2 pinhole 3 photoresist 4 opening window 5 etch hole formed by pinhole 6 recess 10 silicon substrate (semiconductor substrate)

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4K029 AA06 AA24 BA17 BD01 CA05 EA08 GA00 4M104 AA01 BB14 DD21 DD37 DD71 4M112 AA01 DA04 DA09 EA02 EA11 5F043 AA02 BB01 CC05 GG10 5F103 AA08 DD28 HH03 NN01 PP06 PP06

Claims (3)

[Claims] A step of forming a metal film on the semiconductor substrate by sputtering at a temperature of 200 ° C. or higher, and a step of forming a pattern by selectively removing the metal film on the semiconductor substrate. And a step of etching the semiconductor substrate using the metal film as a mask. 2. The method according to claim 1, wherein the metal film is titanium, and the semiconductor substrate is etched with KOH in the step of etching. 3. The method for manufacturing a semiconductor device according to claim 1, wherein in the step of etching the semiconductor substrate, the semiconductor substrate is anisotropically etched.