JPH01315144A - Silicon wafer of excellent gettering capacity and its manufacture - Google Patents

Abstract

PURPOSE:To enhance a gettering capacity by forming a polycrystalline silicon layer on a single-crystal silicon substrate via a silicon oxide film having a specified thickness. CONSTITUTION:This silicon wafer is composed of the following: a single-crystal substrate; a silicon oxide film, with a thickness of 1 to 8Angstrom , formed on one surface of the substrate; a polycrystalline silicon layer formed on the silicon oxide film. In order to form the silicon oxide film on the surface of the singlecrystal silicon substrate, the substrate is heated in a gas containing molecular oxygen or in an atmosphere of steam. A thickness of the polycrystalline silicon layer formed on this silicon oxide film is 1000Angstrom to 5mum; its crystal particle is not amorphous and is 2mum or lower. When the single-crystal substrate is heated under a reduced pressure or under normal pressure in an atmosphere of gaseous silanes diluted by nitrogen gas or the like, the polycrystalline silicon layer of an excellent close contact force can be formed in a uniform thickness. By this setup, it is possible to obtain the silicon wafer whose gettering capacity is excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a silicon wafer with excellent gettering ability used for electronic devices such as integrated circuits, and a method for manufacturing the same.

PRIOR ART AND PROBLEM TO BE SOLVED BY THE INVENTION During the manufacture of integrated circuit devices on silicon wafers, the presence or introduction of defects, contaminants, or impurities near the device-forming surface of the wafer can cause excessive current flow. leakage, which greatly affects the yield of usable devices obtained.

It is recognized in the art that these harmful defects, contaminants, and impurities can, to some extent, relocate from the device forming region to benign regions in the substrate material. The methods and processes for diffusing and trapping defects, contaminants, and impurities from active device regions both before and during device formation are referred to in the electronics industry as gettering.

In order to provide such gettering ability, a method is known in which a polycrystalline silicon layer is grown in a vapor phase on the back surface of a silicon wafer by, for example, thermal decomposition of silane gas (
JP-A-58-138.035, JP-A No. 59-186, 3
No. 31 and No. 1977-120.777).

By the way, gettering by the polycrystalline silicon layer is performed by trapping impurities in the single crystal silicon at the crystal grain boundaries of the polycrystalline silicon. Therefore, in order to improve the gettering ability, it is required that the polycrystalline silicon layer be formed in close contact with the single crystal silicon substrate and that the polycrystalline silicon layer has a large area of crystal grain boundaries. In order to increase the area of this crystal grain boundary, it is desirable to make each crystal grain small (and to make the grain size uniform).

However, in the silicon wafer disclosed in JP-A-52-120,777, in Example 1, one half of the oxide film on the back side of the silicon wafer is etched off to a thickness of 2,700 mm. Back side 12 of silicon wafer
A 1.6 micron polycrystalline silicon film is deposited and the MOS
The results of evaluating the gettering effect by reducing the leakage current of the capacitor showed that the leakage current was reduced by about two orders of magnitude on the side where the oxide film was etched off.

This Example 1 clearly states that the absence of an oxide film between the silicon substrate and the polycrystalline silicon film is a necessary condition for imparting the gettering effect.

The present inventors re-tried the above-mentioned example through the following experiment. That is, the silicon wafer was immersed in 1% hydrofluoric acid to etch off the oxide film on the surface of the silicon wafer, exposing the surface of the silicon single crystal. This wafer was heated with nitrogen gas for 20 minutes at room temperature to prevent an oxide film from growing on the surface.
Reduced pressure chemical vapor flowing at ρ/min
After that, the pressure was reduced to 40 Pa and the temperature was raised from room temperature to 650° C. while flowing nitrogen gas at Q and 5 Ω/min. When the temperature reached 650° C., a polycrystalline silicon film was deposited on the surface of the silicon wafer for 120 minutes by flowing silane gas at 0.35 ρ/min together with a flow of nitrogen gas as a carrier gas at 0.5 fJ/min. Ta. When the surface of the silicon wafer after the deposition process was examined using a metallurgical microscope and a scanning electron microscope, it was found that no polycrystalline silicon film had grown on the surface of the silicon wafer, or even if it had grown, it was only partial. In addition, when we carefully examine the parts where it has grown, we find that polycrystalline silicon is found in areas where particles generated in the low-pressure CVD furnace have adhered, or where particles in the solution have adhered when the oxide film is etched off with hydrofluoric acid. It was found that a film was growing. This fact can be understood as follows. In other words, on the surface of a silicon wafer where the oxide film on the surface has been etched off and the surface of the silicon single crystal is exposed, the CVD reaction becomes an epitaxial reaction, so a polycrystalline silicon film does not grow, but only where there are particles, etc. serves as a growth nucleus, and the polycrystalline silicon film around it grows in an island shape.

Furthermore, in the method described in JP-A-58-138,035, the polycrystalline silicon layer is formed directly on the back surface of the single-crystal silicon substrate, so the gettering ability as described above is not yet sufficient.

Furthermore, in the method of JP-A-59-186,331, the polycrystalline silicon layer formed on the back surface of the single crystal silicon base is doped with oxygen;
This actually impairs the gettering effect of the polycrystalline silicon layer.

Therefore, one object of the present invention is to provide a silicon wafer with excellent gettering ability and a method for manufacturing the same.

(Means for Solving the Problems) The above object includes a single crystal silicon substrate, a silicon oxide film formed on the -h'' surface of the substrate to a thickness of 1 to 8, and a silicon oxide film formed on the silicon oxide film. This is achieved using a silicon wafer with excellent gettering ability made of a polycrystalline silicon layer.

[The purpose of this article is to oxidize at least one surface of a single crystal silicon substrate to form a silicon oxide film with a thickness of 1 to 8, and to contact the silicon oxide film with a gaseous silane under heating. This is achieved by a method for manufacturing a silicon wafer with excellent gettering ability, which is characterized by forming a polycrystalline silicon layer on the silicon oxide film.

(Function) The silicon wafer with excellent gettering ability according to the present invention includes a single crystal substrate, a silicon oxide film with a thickness of 1 to 8 formed on one surface of the substrate, and a silicon oxide film formed on the silicon oxide film. It consists of a polycrystalline silicon layer.

The single-crystal silicon substrate used in the present invention is surface-polished by lapping the surface of the single-crystal substrate, followed by chemical etching to remove the surface layer of several tens of microns or less. The thickness of the subsequent substrate is between 200 and 2000 microns, preferably 3
00-1. 000 microns.

The thickness of the silicon oxide film formed on the surface of this single-crystal silicon substrate is 1 to 8 thick, preferably 1 to 58 thick. In other words, when a silicon oxide film with a thickness greater than I is formed on the surface of a single-crystal silicon substrate, the polycrystalline silicon layer formed thereon has uniform and high adhesion over the entire surface of the single-crystal silicon substrate. It is formed. If the thickness of this silicon oxide film is less than 18 cm, the polycrystalline silicon layer formed on it will be formed non-uniformly, the adhesion will be reduced, and the crystal grains of the polycrystalline silicon layer will become large ( On the other hand, if the thickness of the silicon oxide film exceeds 88 mm, the silicon oxide film becomes an obstacle when the impurities in the single crystal silicon substrate move into the polycrystalline silicon layer, reducing the gettering ability. From this point of view, the thickness of the silicon oxide film is preferably 1 to 8 Å.

In order to form a silicon oxide film on the surface of a single crystal silicon substrate, first remove oxides and contaminants adhering to the surface of the single crystal silicon substrate with dilute hydrofluoric acid, and then rinse with deionized water. and further dry. Next, a silicon oxide film is formed by heating this single crystal silicon substrate in a molecular oxygen-containing gas or water vapor atmosphere.

Examples of the molecular oxygen-containing gas include pure oxygen gas, a mixed gas of oxygen gas and an inert gas, air, and oxygen-rich air. Further, a silicon oxide film can also be formed by placing a single crystal silicon substrate in oxygen plasma.

Furthermore, a silicon oxide film can be formed by immersing a single crystal silicon substrate in an oxidizing chemical or by anodic oxidation. Examples of oxidizing chemicals include nitric acid, dichromic acid or its salts, permanganic acid or its salts, perchloric acid or its salts,
There are hydrogen peroxide solutions, etc.

The thickness of the silicon oxide film depends on the oxidation conditions. For example, when forming a silicon oxide film by heating a single crystal silicon substrate in air at a pressure of 1 atm, the thickness of the oxide film and the single crystal silicon depend on the growth rate of the oxide film and the The relationship with the substrate temperature is as follows.

Substrate temperature (°C) 0.1 0.14 0.22 0.33 0.4
6 speed (8/m1n) Therefore, to form an oxide film in air, 300
2 to 700°C, preferably 300 to 500°C.
It is heated for 100 minutes, preferably 2 to 50 minutes.

Note that the measured value of the film thickness of the silicon oxide film in the present invention is a value measured with an ellipsometer.

That is, the measurement was performed using an ellipsometer immediately after the single crystal silicon substrate was oxidized, that is, before the polycrystalline silicon layer was formed. At this time, the zero point determined as shown above was subtracted from the displayed value of the ellipsometer. After immersing a single crystal silicon substrate in 1% hydrofluoric acid to remove the natural oxide film on the substrate surface, rinsing with deionized water, then spin drying, and immediately measuring with an ellipsometer, the value obtained is taken as the zero point. did. Note that the refractive index of the oxide film is 1.460.
And so.

A polycrystalline silicon layer is formed on this silicon oxide film. The thickness of the polycrystalline silicon layer is 1°0008~5.
μm1 is preferably 5.0OOA to 1°5 μm,
Its crystal grains are not amorphous, but less than 2 microns,
Preferably it is 0.05 to 0.5 microns.

In order to form a polycrystalline silicon layer on the silicon oxide film, the single crystal substrate is heated to a temperature of 570 to 800 nm in an atmosphere of gaseous silane diluted with nitrogen gas, argon gas, etc.
The reaction is carried out by heating at a temperature of 580 to 700°C for 0.1 to 7 hours, preferably 0.3 to 2 hours under reduced pressure or normal pressure. Such a method includes, for example, a low pressure CVD method. Silanes used in the present invention include monosilane (S I H4), dichlorosilane (SiH2C12), and monochlorosilane (SiH2C12).
H3c1) etc.

In the silicon wafer according to the present invention, a silicon oxide film having a specific thickness is formed on the surface of a single crystal silicon substrate, so that a polycrystalline silicon layer is formed with excellent adhesion and a uniform thickness. Moreover, since the silicon oxide film provides countless growth nuclei necessary for the growth of the polycrystalline silicon layer, in the case without the silicon oxide film, the polycrystalline silicon layer would grow in island shapes using dirt etc. as nuclei. The growth rate cannot be determined unconditionally; in the case of island-like growth, the growth rate is several tens of minutes per minute, and in the case of no growth, it is almost zero (unmeasurable), whereas in the case of silicon oxide films, In this case, the growth rate of the polycrystalline silicon layer increases to 150 A/min. In addition, if there is no silicon oxide film,
The crystal grain size of polycrystalline silicon in the island-like grown part is 3~
10 microns, whereas in the present invention, the crystal grain size is as small and uniform as about 0.1 to 0.4 microns (as a result of cross-sectional TEM observation). Furthermore, even if there is slight contamination on the surface of the single-crystal silicon substrate, no contamination pattern will appear after the polycrystalline silicon film is formed.

Further, when using the silicon wafer according to the present invention, the silicon oxide film condenses into islands and disappears due to heat treatment at 900°C or higher performed at the beginning of the IC manufacturing process, and the single crystal substrate and polycrystalline silicon film are removed. come into direct contact with.

In the present invention, gettering ability was measured as follows.

In a silicon wafer in which a silicon oxide film and a polycrystalline silicon layer are formed on one surface of a single crystal silicon substrate, and the other surface is polished to a mirror surface,
The mirror surface is oxidized in pure oxygen gas heated to 1,000°C to form an oxide film with a diameter of about 300 mm, and then a disk with a diameter of 1 mm and a thickness of 5,000 mm is formed on the oxide film. A shaped aluminum electrode is formed by vapor deposition. The regettering ability is evaluated by measuring the generation lifetime of minority carriers of the MOS capacitor thus formed on the substrate. For measurement of generation lifetime of fractional carriers, E, H, N1 collian
and J, R, Brewers MOS Physi
cs and Technology (John Wi
ley & 5ons).

When a silicon substrate becomes contaminated with metal impurities, the generation lifetime of minority carriers is shortened. Once the metal impurities are gettered, the lifetime is restored and extended.

Normally, it is impossible to prevent extremely small amounts of metal impurities from being naturally introduced from the surrounding atmosphere during the oxidation process used to manufacture MOS capacitors.

Therefore, if a plurality of silicon substrates having different gettering abilities are processed simultaneously, there will naturally be a difference in the generation lifetime of fractional carriers, so the gettering abilities can be compared relatively.

(Example) Next, the present invention will be described in further detail by giving examples.

Examples 1 to 4 A single crystal silicon substrate with a thickness of 600 microns was immersed in 1% hydrofluoric acid to remove the native oxide film attached to the surface, then rinsed with deionized water, and further dried with a spin dryer. did. Immediately after drying, the single crystal substrate was placed in an electric furnace in an air atmosphere at 400°C for 7 minutes, 22 minutes, 36 minutes, and 4 minutes.
Silicon oxide films were formed for 1 person, 3A, 5A, and 6 for 3 minutes, respectively. Next, by low pressure CVD method, silicon (SiH4) gas is thermally decomposed at 650°C using nitrogen gas as a carrier, and 1-
A layer of polycrystalline silicon was deposited to a thickness of about 1 micron.

In this way, since the polycrystalline silicon layer and the silicon oxide film are deposited on both sides of the structure in which the polycrystalline silicon layer is deposited, the polycrystalline silicon layer and the silicon oxide film underneath are polished. The film was removed to expose the single-crystal silicon substrate, which was then polished to a mirror surface. On the mirror surface side of the silicon wafer manufactured in this way, the M
An OS capacitor was formed and the gettering ability was evaluated based on the lifetime value of the decimal carrier. The results are shown in Table 1.

In addition, when these silicon wafers were observed using a metallurgical microscope, a scanning electron microscope, and a transmission electron microscope, the growth rate of the polycrystalline silicon layer was 1508/min, and the crystal grain size was 0.1 to 0.4 microns. Met. Furthermore, when this silicon wafer was viewed in a dark room using a condensing light in the dark field and using scattered light, no white pattern was observed.

Comparative Example 1 A silicon wafer was obtained in the same manner as in Example 1 except that a silicon oxide film was not formed on the surface of the single crystal silicon substrate in the method of Examples 1 to 4. The gettering ability of the silicon wafer formed by forming a polycrystalline silicon layer on the surface of this single crystal silicon substrate was evaluated by the same method as in Examples 1 to 4. The results are shown in Table 1.

Furthermore, when these silicon wafers were examined using a metallurgical microscope, a scanning electron microscope, and a transmission electron microscope, it was found that polycrystalline silicon layers were growing at a growth rate of several tens of six directions in the areas where the island-like growth occurred. It is almost zero in the areas where it is not exposed, and since the polycrystalline silicon layer grows using dirt and the like as nuclei, it was not possible to specify the growth rate for -ta.

Further, the crystal grain size was 3 to 10 microns in the island-shaped portion. Furthermore, when this silicon wafer was viewed in a dark room using a condensing light in the dark field and using scattered light, white patterns that looked like stars, islands, or flowing liquid could be seen. Star-shaped particles are particles generated in a low-pressure CVD furnace as growth nuclei, and a polycrystalline silicon layer has grown around them. Island-shaped particles are a collection of star-shaped particles or a silicon wafer. This is a polycrystalline silicon layer that has grown from the point of contact with the boat (a quartz jig that holds the wafer). This is a polycrystalline silicon layer that grows using particles left on the surface of the substrate when it is rinsed and pulled out of the rinsing bath as growth nuclei. 100 sheets were charged in the low pressure CVD furnace, and 95 sheets had some kind of white pattern. Wafers on which no white pattern was observed did not have a polycrystalline silicon layer deposited on them.

Comparative Example 2 A silicon wafer was obtained in the same manner as in Example 1 except that the thickness of the silicon oxide film was changed to 108 in the method of Examples 1 to 4, and the gettering ability was evaluated in the same manner. I did it. The results are shown in Table 1.

1st surface Silicon oxide film Gettering ability thickness (8) (mS) Comparative example 1 0 1. 0-1,4 Example 1 1 3.0-8.5 Example 2
3 3.3-6.7 Example 3 5
2.6-5.2 Example 4 6 1
．． 8-3.7 Comparative Example 2 10 1.2-1
．． 6 As is clear from Table 1, the silicon wafers according to the present invention (Examples 1 to 4) are different from the conventional silicon wafers (Comparative Example 1).
It can be seen that the lifetime of generation of a small number of carriers is longer than that of the conventional method, and the gettering ability is significantly superior. In addition, in the wafer of Comparative Example 1 in which no silicon oxide film was provided, there were regions where polycrystalline silicon crystal grains grew and regions where they did not grow on the single crystal silicon substrate, and the crystal grain size was on average 3 microns or more. Some of them are 10 microns or more.
They are also producing H. On the other hand, in the case of the wafers of Examples 1 to 4 in which the silicon oxide film has a thickness of 18 or more, polycrystalline silicon crystal grains grow over the entire surface of the single crystal silicon substrate, and the crystal grain size is 0.1~0.
It has a uniform diameter of 4 microns.

Reference Example A silicon wafer having a silicon oxide film with a thickness of 5 mm and a polycrystalline silicon layer with a thickness of 1 micron obtained in Example 3 was oxidized in a steam atmosphere at 900° C. for 2 hours. Later, when the cross section was observed using a transmission electron microscope and the composition was analyzed, no continuous oxide film was found at the interface between the single crystal silicon substrate and the polycrystalline silicon layer, but an island-like film like a grain of rice was found. Scattered oxides were observed.

The single crystal silicon substrate and the polycrystalline silicon layer were in close contact with each other at most of the interface, and a portion of the polycrystalline silicon layer was grown by solid phase epitaxial growth.

For example, in an IC manufacturing process, a nitride film is used as a mask to form a well or to insulate and isolate an element region with a thick oxide film, and an oxide film is usually formed under the nitride layer 11m. This oxide film is called a pad oxide film, and in the IC manufacturing process, the process of forming this pad oxide film often occurs immediately after the first wafer cleaning process. Typical pad oxidation is, for example, 1 hour in a dry oxygen atmosphere at 1,000°C or 2 hours in a steam atmosphere at 900°C. Under these conditions, a pad oxide film approximately 500 mm thick is formed.

As is clear from the reference example, in the silicon wafer according to the present invention, such a pad oxide film is formed by forming oxide films 1 to 8 between the single crystal silicon substrate and the polycrystalline silicon layer. disappears, and the single-crystal silicon substrate and polycrystalline silicon layer come into close contact.

(Effects of the Invention) According to the present invention, since a polycrystalline silicon layer is formed on a single crystal silicon substrate via a silicon oxide film having a specified thickness, the adhesion of the polycrystalline silicon layer is improved. Furthermore, since the crystal grain size of the polycrystalline silicon layer is uniform, the area of the grain boundaries is smaller than that of conventional polycrystalline silicon layers. It has a large size and excellent gettering ability. Therefore, it can be used as a material with high yield as a device for high-density integrated circuits.

Claims (2)

[Claims] (1) Gettering ability consisting of a single crystal silicon substrate, a silicon oxide film with a thickness of 1 to 8 Å formed on one surface of the substrate, and a polycrystalline silicon layer formed on the silicon oxide film. Superior silicon wafer. (2) Oxidizing at least one surface of a single crystal silicon substrate to form a silicon oxide film with a thickness of 1 to 8 Å, and contacting the silicon oxide film with a gaseous silane under heating to form the silicon oxide film. A method for manufacturing a silicon wafer with excellent gettering ability, characterized by forming a polycrystalline silicon layer thereon.