JPH01276754A - Manufacture of cmos semiconductor device - Google Patents

Abstract

PURPOSE:To enable a substrate and an inverse conductive type CMOS semiconductor, device with a deep diffusion layer to be produced with improved yield by removing only oxide film on the surface by HF vapor. CONSTITUTION:An inverse conductive type deep diffusion layer is formed on low impurities concentration silicon substrate 2 of low-concentration silicon epitaxial film which is formed on high impurities concentration silicon substrate 1. It is placed on a turntable and etching is performed by HF steam. Then, only an oxide film 4a on the front surface is removed and no oxide film 4b on the rear surface is removed, Thus, the surface is nearly in non-contact status and the CMOS semiconductor device where the outer diffusion of impurities on the substrate 1 was prevented by the film 4b does not allow the film 4b to be subject to photoresist treatment and can be produced easily with improved yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a high speed, highly integrated MO3 semiconductor device.

[Summary of the invention]

CM using a silicon substrate with a low impurity concentration silicon epitaxial layer grown on a high impurity concentration silicon substrate
When manufacturing an OS semiconductor device, it is necessary to always cover the surface of the substrate with an oxide film or a nitride film. If the backside of the silicon is exposed, impurities will diffuse outward from the highly concentrated silicon substrate during heat treatment in a diffusion furnace, enter the surface of other silicon substrates, change the substrate resistivity, or adhere to everywhere in the furnace. This is because it becomes a source of pollution. This phenomenon is particularly strong when boron is used as an impurity in the silicon substrate.

In the present invention, in order to always cover the back surface of the silicon substrate with an insulating film, after forming a deep diffusion layer of the opposite conductivity type to the substrate, the oxide film removal process is performed using an HF vapor etcher, and only the oxide film on the surface is selected. It is intended to be removed.

[Conventional technology]

Figure 3 shows CMOS fabrication using a P/P' type silicon substrate in which a P-type low-concentration silicon epitaxial film using boron as an impurity is provided on a conventional P-wall high-concentration silicon substrate using boron as an impurity. A cross-sectional view of the process order is shown.

FIG. 3 (al indicates a state in which a relatively deep N-type well 3 is formed in a P/P" type silicon substrate by diffusion.

This uses a P/P" type silicon substrate with approximately 5,000 oxide films deposited on the back side by chemical vapor deposition (CVD) to prevent outward diffusion from the P/P" type silicon substrate. First, an oxide film of 5,000 to 6,000 layers is grown by oxidation, then the photoresist is patterned by a photolithography process, and the oxide film above the area that will later become an N-type well is removed by wet etching. Next, apply an oxide film to a thickness of approximately 10 mm on the exposed silicon area.
00 people, and 1 to 5 x 10' of phosphorous ions are added using ion implantation method! /ci input, 110
It is formed by diffusion in a non-oxidizing atmosphere at a temperature of 0°C to 1200°C for 5 to 15 hours. Up to this point, the oxide film on the back side of the P/P" type silicon substrate had grown from 5,000 to about 10,000 due to initial oxidation, 1,500 to 2,000 due to oxide film wet etching, and 2,000 to 2,500 due to oxidation before ion implantation. The back surface of the P/P' type silicon substrate is always covered with an oxide film with a thickness of 1000 Å or more, so that impurities do not diffuse outward from the back surface of the P/P' type silicon substrate.

Next, the thermal oxide film 4a on the surface of the P/P" type silicon substrate is removed, but the oxide film thickness on the area other than the N type well is 6000.
~6500 people, and the oxide film thickness on the back side is 2000~25
00, so if the oxide film is removed by sheft etching, the silicon on the back surface of the P/P'' type silicon base Fi will be exposed, and the outward diffusion of impurities will occur in the next oxidation process. As shown in b), photoresist 6 is coated on the back surface of the P/P" type silicon substrate,
Only the surface oxide film 4a is removed by wet etching.

Next, photoresist 6 was applied using a mixture of sulfuric acid and hydrogen peroxide.
3 (C1), proceed to the next step of oxidation. Thereafter, the back surface is always covered with an oxide film or other insulating film, so there is no fear that impurities will diffuse outward during heat treatment or oxidation steps.

[Problem to be solved by the invention]

However, when coating the back side of a P/P" type silicon substrate with photoresist, the surface on which elements will be formed comes into contact with the conveyor belt of the coater and the vacuum chuck, resulting in contamination or scratches on the surface, which reduces yield. This is a factor that lowers the amount.

[Means to solve the problem]

In order to solve the above problems, the present invention uses an HF vapor etcher to perform the oxide film removal step after forming the U-shaped well.

[Effect]

According to the above, only the surface oxide film can be selectively removed,
The oxide film remains on the back side, reducing the number of steps.
Furthermore, outward diffusion of impurities during the heat treatment process can be prevented. Furthermore, the surface is always non-contact, so there is no reduction in yield.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1st
The figure shows how a P/P" type silicon substrate is placed in a HF 77-gas etcher chamber after forming an N-type well 3. Examples of the HF steam etcher include Excalibur manufactured by FSI, USA, etc. Since the wafer is placed on a turntable and the HF vapor is introduced from above, even after removing the oxide film 4a on the front surface, the oxide film placed on the turntable on the back side oxide film 4b is removed. There is no decrease at all, and the area not on the turntable is HF.
It decreases somewhat due to the circulation of steam. When a 6-inch diameter wafer is used to grow a thermal oxide film of 6,000 layers and the surface oxide film is removed, the backside oxide film thickness will be approximately 500 to 1,000 layers depending on the wafer edge, and 1.
About 3,000 people remain at 0n, and 6,000 people remain at the center.Figure 2 shows this situation. Therefore, most of the back surface is covered with an oxide film of 2000 Å or more, and the outward diffusion of boron can be almost completely suppressed in the subsequent heat treatment process.

〔Effect of the invention〕

As explained above, the present invention uses HF vapor etcher to remove the oxide film after N-well formation when using a P/P'' type silicon substrate, thereby reducing the resist coating process and keeping the surface clean. Since it is a contact, there is no drop in yield.Also, since most of the back surface of the substrate is covered with a thick oxide film, outward diffusion of impurities does not occur.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the condition of a silicon substrate during HF vapor etching to explain the present invention, FIG. 2 is a cross-sectional view showing the amount of oxide film remaining on the back side of the substrate after the HF vapor etching process, and FIG. fal ~ (C1 is a cross-sectional view of a conventional manufacturing method in the order of steps. 1... High impurity concentration silicon substrate 2... Low impurity concentration silicon epitaxial film 3...
・N-type wells 4a, 4b...Oxide film 5...Photoresist and above Suppliers Seiko Electronics Co., Ltd. Kokyo MO5 Hand guide na position a belly Calculating zero Oni Elephant / Top surface view Figure 3

Claims (1)

[Claims] In a method for manufacturing a CMOS semiconductor device using a silicon substrate in which a low impurity concentration silicon epitaxial film is provided on a silicon substrate containing high impurity concentration, oxide film removal after forming a deep diffusion layer of conductivity type opposite to that of the substrate. HF process
A method for manufacturing a CMOS semiconductor device, characterized in that only a surface oxide film is selectively removed using a steam etcher.