JPH0529306A - Method of forming insulating film by plasma cvd - Google Patents

Abstract

PURPOSE:To lessen the dispersion between each board and improve the uniformity between faces by specifying the structure of the rear and the margin of the surface of a substrate to be processed when forming an insulating film, using a hot wall type plasma CVD device. CONSTITUTION:A low-resistance regions 12 or 21 is provided at the rear of a substrate 10 or 20 to be processed, and besides the low-resistance region 12 or 21 is turned in, at least, to the vicinity of the surface of the substrate to be processed. The substrate to be processed, which has such structure, is supported with parallel planar electrodes, and plasma is generated to form an insulating film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming an insulating film by plasma CVD, and more specifically, it forms an insulating film by a multi-layer parallel plate type plasma CVD apparatus capable of large-scale batch processing, so-called hot wall type PE-CVD apparatus. It is about the method.

[0002]

2. Description of the Related Art When forming a passivation film or the like of a semiconductor device, film formation by plasma CVD is often used. For example, when silicon nitride (Si ₃ N ₄ ) is formed on the surface of a semiconductor substrate, the semiconductor substrate is placed between electrodes, a high frequency power source is connected between the electrodes, and silane (SiH ₄ ) and ammonia (NH ₃ ) are used. ₃ ) is introduced and plasma is generated to form an insulating film of Si ₃ N ₄ on the surface of the semiconductor substrate.

A multi-layer parallel plate type plasma CV is used as a device capable of large-scale batch processing by such a plasma CVD device.
There is a D device, a so-called hot wall type PE-CVD device. As shown in FIG. 9, a flat plate electrode 3 on which a semiconductor substrate 2 is previously supported is inserted into a quartz tube 1 and a process gas such as SiH ₄ or NH ₃ is introduced into the quartz tube 1 to form a flat plate. A high frequency power from a high frequency power source 4 is applied to the electrode 3, and at the same time, the quartz tube 1 is heated by the heater 5. In this way, plasma is generated in the quartz gap 1 and a layer of Si ₃ N ₄ is formed on the surface of the semiconductor substrate 2.

The plate electrode 3 is composed of a carbon disk, and high frequency power is applied to the plate electrode 3 by applying a pair of bus bars 6 to each other.
And 7 are connected to the positive and negative terminals of the high frequency power source 4, respectively, and the plate electrodes 3 are alternately connected from the busbars 6 and 7. Therefore, a high frequency electric field is formed between the adjacent flat plate electrodes 3, and plasma can be generated.

[0005]

In such a hot-wall type PE-CVD apparatus, the film thickness is likely to vary between the end portion and the center portion of the plate electrode 3, and the plasma is not generated uniformly. However, there is a problem that the film thickness easily varies between adjacent semiconductor substrates. For example, when the above Si ₃ N ₄ is used as a passivation film, if the thickness is large, the stress becomes large, and if it is thin, the effect as the passivation film decreases, so that the film thickness uniformity,
In particular, it is important to improve the film thickness uniformity between the substrates in the same batch.

Various attempts have been made to solve the above problems. For example, in Japanese Patent Laid-Open No. 60-202929 and Japanese Patent Publication No. 58-46057, it is necessary to independently control the power source for each plate electrode. Show that the uniformity of the film thickness is improved by making the electric field strength between the flat plate electrodes constant or by aligning the phases. However, in the above device, the variation in the film thickness between the end portion and the central portion can be suppressed, but it is not sufficient to suppress the variation between the semiconductor substrates.

In view of the above points, the present invention is plasma CVD.
It is an object of the present invention to provide a forming method for improving the uniformity of the thickness of an insulating film by the method.

[0008]

According to the present invention, a plurality of plate electrodes for supporting a substrate to be processed are arranged in parallel, and the arranged plate electrodes are alternately connected to a pair of bus bars. In the method of forming an insulating film on the surface of the substrate to be processed by supplying high frequency power to the substrate to generate plasma between the electrodes, a low resistance region is formed on the back surface of the substrate to be processed supported by the electrodes. It is characterized in that it is provided and the low resistance region extends around at least the periphery of the surface of the substrate to be processed. The low resistance region preferably has a resistance of 1 × 10 ⁻³ Ωcm or less, such as polycrystalline silicon (Polysilicon).
-Si) may be formed on the back and front surfaces of the semiconductor substrate and doped with phosphorus or the like to lower the resistance, or the semiconductor substrate itself may be doped with phosphorus or the like to lower the resistance on the back and front surfaces. May be. The semiconductor substrate itself is 1 × 10 ^-3 Ωcm
The back surface and the periphery of the surface may be used as the low resistance region by using the following low resistance materials.

[0009]

According to the present invention, variations among semiconductor substrates,
It is possible to improve the so-called surface-to-surface uniformity and
It is possible to reduce variations in film thickness within a single semiconductor substrate.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. 1A and 1B are cross-sectional views showing pretreatment of a semiconductor substrate used in the method for forming an insulating film by plasma CVD according to the present invention, which is processed as shown in FIGS. 1A and 1B. The substrates to be processed were placed on both sides of the flat plate electrode 3 of the CVD apparatus shown in FIG. 9 to form a Si ₃ N ₄ film.

2A to 2E are sectional views of a preprocessed semiconductor substrate as a comparative example. The conditions of each Example and Comparative Example are as follows. Process gas SiH ₄ 780 [cc / min] NH ₃ 7 [l / min] Pressure 2.20 [torr] RF power 2.1 [kW] 430 [kHz]

[0012]

Example 1 FIG. 1A shows that a thin oxide film 11 is formed on the periphery of the back surface and the front surface of a semiconductor substrate 10 as a pretreatment for forming a Si ₃ N ₄ film, and a low oxide film is formed on the oxide film 11 as a layer. A polycrystalline silicon layer 12 having a resistance is formed. The semiconductor substrate 10 is made of N-type silicon and has a thickness of 8 to 12 Ωcm, and the oxide film 11 formed by thermal oxidation is about 5
It has a thickness of 00Å, and the polycrystalline silicon layer 12 has a thickness of 3700.
Doped with phosphorus to the thickness of Å, 7.4
It is set to × 10 ⁻⁴ Ωcm.

FIG. 3 shows the film thickness when a Si ₃ N ₄ film is formed using the semiconductor substrate thus pretreated. The vertical axis represents the film thickness of the Si ₃ N ₄ film, and the horizontal axis represents the position number of the semiconductor substrate mounted on the plate electrode, that is, the position from the end. As shown in the figure, there is little variation in film thickness

[0014]

[Equation 1]

Then, it was about 3.8%. In addition,
No special treatment is required for the pretreatment in the actual LSI manufacturing process as described above, and when a polycrystalline silicon layer used as a gate electrode or wiring is formed on the back surface and the periphery of the surface, It is only necessary to remove the insulating film such as the provided oxide film and expose the doped polycrystalline layer.

[0016]

Second Embodiment FIG. 1B shows a low resistance region 21 formed around the back surface and front surface of the semiconductor substrate 20 itself as a pretreatment for the formation of the Si ₃ N ₄ film. The semiconductor substrate 20 is made of N-type silicon and has a thickness of 4 to 6 Ωcm and is doped with phosphorus to have a density of 1 × 10 ⁻³ Ωcm or less.

FIG. 4 shows the film thickness when a Si ₃ N ₄ film is formed using the semiconductor substrate thus pretreated. As shown in the figure, in this case as well, the variation in the film thickness was small, and the in-plane uniformity was about 3.8%. In this embodiment, the product pattern 22 is provided on the front surface of the semiconductor substrate 20, and the polycrystal layer and the oxide film layer on the back surface and around the front surface are removed before phosphorus doping into the polycrystal silicon to remove the semiconductor substrate. When 20 is exposed and phosphorus is doped, the above structure is obtained.

The same effect can be obtained if the semiconductor substrate 20 is 1 × 10 ⁻³ Ωcm or less and the back surface and the periphery of the surface are exposed.

[0019]

Comparative Example 1 FIG. 2A shows an example in which a semiconductor substrate 30 is used as a substrate to be processed to form a Si ₃ N ₄ film. The semiconductor substrate 30 is N-type silicon and has a thickness of 8 to 12 Ωcm. FIG. 5 shows the film thickness when a Si ₃ N ₄ film was formed using this semiconductor substrate. As shown in the figure, in this case, the variation in the film thickness was large, and the inter-plane uniformity was 7.9%.

[0020]

[Comparative Example 2] FIG. 6 shows the case where the substrates to be processed shown in FIGS. 2A, 2B and 2C are used as the substrates to be processed and Si ₃ N ₄ is inserted into the same quartz tube. It is a figure which shows the film thickness when a film is formed. FIG. 2B shows that the substrate to be processed is 2.5
Using an N-type silicon substrate 40 of ~ 3.5 Ωcm,
(C) is a processed substrate of 0.008 to 0.018 Ωcm
The N-type silicon substrate 50 is formed with an epitaxial growth layer 51 of 4 to 6 Ωcm.

It can be seen that when the Si ₃ N ₄ film is formed using these substrates to be processed, the substrate to be processed shown in FIG. 2C has a high growth rate. However, it is understood that the variation in the film thickness is large in all the substrates to be processed, and that forming the low resistance region only on the back surface is not effective.

[0022]

Comparative Example 3 In FIG. 7, an N-type silicon substrate 60 of 9 to 12 Ωcm as shown in FIG.
It is a figure which shows the film thickness at the time of using what used the product pattern 61 formed on the surface and exposed the back surface and the surface periphery. Similarly, the variation in film thickness is large.

[0023]

COMPARATIVE EXAMPLE 4 In FIG. 8, as a substrate to be processed, a product pattern is formed on the front surface as shown in FIG. 2E, and on the rear surface, a polycrystalline silicon layer used for wiring, an interlayer insulating film, etc. are left as they are. it is a diagram showing a film thickness when was an Si ₃ N ₄ film in the case of using those were. The substrate to be processed shown in FIG. 2E uses an N-type silicon substrate 70 of 4 to 6 Ωcm, and an oxide film 71 formed as a gate insulating film on the upper layer thereof,
Phosphorus-doped polycrystalline silicon layer 72 formed as a gate electrode and oxide film 7 formed as an interlayer insulating film
3 and a second phosphorus-doped polycrystalline silicon layer 74
And an oxide film 75 formed as an insulating film are provided around the back surface and front surface of the silicon substrate 70. The polycrystalline silicon layers 72 and 74 have a resistance of approximately 7.
It is 4 × 10 ⁻⁴ Ωcm.

As shown in FIG. 8, this comparative example also has a large variation, and the surface-to-plane uniformity is about 11.4%. The oxide film 75, the polycrystalline silicon layer 74, and the oxide film 7 of this comparative example were used.
3 is removed, the substrate becomes equivalent to the substrate to be processed in FIG. 1A. Therefore, if the above three layers are removed and the film is grown, the variation in film thickness will be reduced.

[0025]

As described above, according to the present invention, it is possible to improve the variation between the semiconductor substrates, that is, the so-called face-to-face uniformity, and reduce the variation in the film thickness within one semiconductor substrate. be able to.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a pretreatment of a semiconductor substrate used in a method for forming an insulating film by plasma CVD according to the present invention.

FIG. 2 is a cross-sectional view showing pretreatment of a semiconductor substrate of a comparative example.

FIG. 3 is a diagram showing a film thickness according to Example 1 of the present invention.

FIG. 4 is a diagram showing a film thickness according to a second embodiment of the present invention.

5 is a diagram showing a film thickness according to Comparative Example 1. FIG.

6 is a diagram showing a film thickness according to Comparative Example 2. FIG.

7 is a diagram showing a film thickness according to Comparative Example 3. FIG.

FIG. 8 is a diagram showing a film thickness according to Comparative Example 4.

FIG. 9 is a diagram showing a configuration of a hot wall type plasma CVD apparatus.

[Explanation of symbols]

 2 substrate to be processed 3 plate electrode 4 high frequency power supply 6, 7 bus bar 10, 20 semiconductor substrate 12, 21 low resistance region

Claims (1)

Claim: What is claimed is: 1. A plurality of flat plate electrodes for supporting a substrate to be processed are arranged in parallel, the arranged flat plate electrodes are alternately connected to a pair of bus bars, and a high frequency wave is applied to the pair of bus bars. In the method of forming an insulating film on the surface of the substrate to be processed by supplying electric power to generate plasma between the electrodes, a low resistance region is provided on the back surface of the substrate to be processed supported by the electrodes. And the low resistance region wraps around at least the surface periphery of the substrate to be processed.
A method of forming an insulating film by D.