JPH043917A - Method of diffusing impurity - Google Patents

Abstract

PURPOSE:To obtain gettering action with excellent reproducibility without adding the usage and process of a special semiconductor substrate by introducing a semiconductor substrate having a phosphorus diffusion layer in high concentration on one surface side into a diffusion furnace besides a semiconductor substrate. CONSTITUTION:One hundred epitaxial wafers 10, in which n<-> epitaxial layers 2 are laminated on substrates 1 and boron atoms 3 are introduced into the specified regions of surfaces, are loaded upright on a boat, and ten dummy wafers for preventing the entrainment of the outside air or stabilizing the flow of nitrogen gas passed in a furnace at the flow rate of 5-8l/min are erected on both sides respectively. n-type collector diffusion wafers having n<+> layers by phosphorus diffusion on the whole surfaces are used as the dummy wafers. A p region 4 is formed through a driving process. The p region is utilized as the source-drain regions of a MOS device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an impurity diffusion method for forming a region having a predetermined impurity concentration and conductivity type in a semiconductor substrate.

[Conventional technology]

When heating in a diffusion furnace to diffuse impurities into a semiconductor substrate, contamination occurs due to undesirable impurities from the heater, quartz tube, or atmospheric gas, and the semiconductor properties are affected. Gettering is performed to prevent this. As a gettering method, a polycrystalline silicon film is formed on the back surface of the semiconductor substrate opposite to the surface where the regions necessary for the elements are formed, and impurities are adsorbed to the porous polycrystalline silicon film, or sandblasting is performed on the back surface. Alternatively, by causing damage through Ar ion implantation and attracting impurities, contamination is trapped in places that can be called crystal defects on the back side of the semiconductor substrate.
There is a method to electrically stabilize the surface side. There are also methods to prevent contamination by optimizing the temperature distribution in the furnace during diffusion or by mixing a halogen element such as hydrochloric acid into the atmospheric gas.

[Problem to be solved by the invention]

Among the above gettering methods, the substrate with a polycrystalline Si film is expensive. Methods that damage the substrate require more manufacturing steps, which also leads to higher costs.Methods that prevent contamination by optimizing temperature distribution or incorporating halogen elements have poor reproducibility and require complicated equipment. There is a problem with becoming.

The purpose of the present invention is to solve the above-mentioned problems and provide an impurity diffusion method that can be carried out using a normal semiconductor substrate in a conventional diffusion furnace while preventing contamination on the surface side of the substrate. It's about doing.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an impurity diffusion method in which impurities are heated in a diffusion furnace to diffuse impurities from one side of a semiconductor substrate to a predetermined depth into the substrate. A semiconductor substrate having a diffusion layer is placed in a diffusion furnace in addition to the semiconductor substrate described above.

[Effect]

A semiconductor substrate with a high concentration phosphorus diffusion layer on one side has
Some are used in the manufacture of power transistors and the diffusion layer is used as a collector electrode contact layer, and are easily available. Such a Si substrate, called a collector diffusion wafer, has the best gettering effect in the diffusion process among the various 81 substrates. This gettering effect is due to phosphorus and the oxygen contained in the substrate, which is used when diffusing phosphorus. This gettering effect of impurities in the diffusion furnace by phosphorus and oxygen also helps to prevent contamination of semiconductor substrates in the furnace that do not have a phosphorus diffusion layer.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. Figure 1 shows an epitaxial wafer used to create an MO3 device, with a 50mm
The epitaxial wafer was made by stacking n-epitaxial layers 2 with a thickness of fm, and the diameter of the wafer was 4 inches, of which only a portion is shown. , boron atoms 3 are introduced into a predetermined region of the surface (Fig. 1 ta1), 100 such epitaxial wafers 10 are placed on a boat, and outside air is spread on both sides to the position where the epitaxial wafers are located. Ten dummy wafers were set up for each wafer in order to prevent crowding or to stabilize the flow of nitrogen gas that was returned inside the furnace at a flow rate of 5 to 81/min. As this dummy wafer, an n-type collector diffusion wafer having a diameter of 4 inches and having an n layer formed by phosphorus diffusion on one surface was used. and 1100-11
A drive step of heating at 50° C. for about 1 hour was performed to form a p8M region 4 as shown in FIG. 1('b). This p
The H1 region 4 is used as the source/drain region of the MO3 element. The effectiveness of such a diffusion method was confirmed as follows. For comparison, several n-type epitaxial wafers shown in FIG. 1 (8) and n-type collector diffusion wafers similarly implanted with boron ions were separately prepared in a diffusion furnace contaminated with heavy metals, etc. Diffusion was carried out.

After diffusion, electrodes were deposited on the p-type diffusion regions on the back and front surfaces of each wafer, and the reverse leakage current of the diode formed by the boron diffusion was measured. The result is that the reverse leakage current of the epitaxial wafer diode is 200
In contrast, the reverse leakage current of the collector diffusion wafer diode was as small as 20 nA to 60 nA. Electrodes were attached to the back surface of the substrate 1 and the surface of the pH range 4 of the epitaxial wafer 10 shown in the first diode obtained in the above example, and the reverse leakage current of the diode was measured, and it was found to be 100 nA to 300 n^
The value was lower than that in the case without the collector diffusion wafer, and the variation was also reduced.

This indicates that the electrical characteristics of the epitaxial layer 2 are stable due to the gettering effect of the collector diffusion wafer.

〔Effect of the invention〕

According to the present invention, during the diffusion process, by coexisting a semiconductor substrate having a high concentration phosphorus diffusion layer on one surface that is easy to handle in the diffusion furnace, the desired diffusion is achieved by the gettering effect of phosphorus and oxygen. It was possible to prevent contamination of the semiconductor substrate that is subjected to this process. That is, it has become possible to perform an impurity diffusion process including a gettering effect with good reproducibility without the need for using a special semiconductor substrate or adding a process.

[Brief explanation of the drawing]

FIG. 1 shows the impurity diffusion process carried out in the present invention.
(These are cross-sectional views shown in the order of bl. 1: n゛substrate 2!ll-epitaxial layer, 3: boron, 4: pm region, 10: luneum during epitaxy.

Claims (1)

[Claims] 1) In an impurity diffusion method in which impurities are heated in a diffusion furnace to diffuse impurities from one side of the semiconductor substrate to a predetermined depth into the substrate, a semiconductor substrate having a high concentration phosphorus diffusion layer on one side of the semiconductor substrate is used. Another impurity diffusion method is characterized by placing the impurity in a diffusion furnace.