JPH0648686B2 - Silicon wafer having excellent gettering ability and method of manufacturing the same - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon wafer having excellent gettering ability used for electronic devices such as integrated circuits and a method for manufacturing the same.

(Prior Art and Problems to be Solved by the Invention) During manufacture of an integrated circuit device on a silicon wafer, if a defect, a contaminant or an impurity is present or introduced near the device forming surface of the wafer, excessive current leakage occurs. And these greatly affect the yield of usable devices obtained. It is recognized in the art that this deleterious defect, contaminant, and impurity can, to some extent, be relocated from the device formation region to a harmless region in the substrate material. The method and process of diffusing and trapping this defect, contaminants and impurities from the active device region, both before and during device formation, is referred to in the electronics industry as gettering.

In order to provide such gettering ability, a method of vapor-depositing a polycrystalline silicon layer on the back surface of a silicon wafer by thermal decomposition of silane gas, for example, is known (Japanese Patent Laid-Open No. 58-138,035). 59-186,
331 and 52-120,777).

By the way, the gettering by the polycrystalline silicon layer is performed by trapping the impurities in the single crystalline 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 is formed in close contact with the single crystal silicon substrate and has a large grain boundary area. In order to increase the area of this crystal grain boundary, it is desired to reduce the size of each crystal grain and to make the grain size uniform.

However, in the silicon wafer disclosed in Japanese Unexamined Patent Publication No. 52-120,777, one half of the oxide film having a thickness of 2,700 Å on the back surface of the silicon wafer is etched off in Example 1 to remove the silicon wafer. Backside of wafer 1
Deposit 21.6 micron polycrystalline silicon film
As a result of evaluating the effect of gettering by reducing the leak current of the S capacitor, it is shown that the leak current is reduced by about two digits on the side where the oxide film is etched off. In the first embodiment, it is clearly stated that the absence of an oxide film between the silicon substrate and the polycrystalline silicon film is a necessary condition for giving the gettering effect.

The present inventors repeated the above-mentioned example by the following experiment. That is, the silicon wafer was dipped in 1% hydrofluoric acid to etch off the oxide film on the surface of the silicon wafer to expose the surface of the silicon single crystal. This wafer is exposed to nitrogen gas at room temperature for 20 times so that an oxide film does not grow on the surface.
/ Min Flowed under reduced pressure Chemical vapor deposition (CV
D) It was put in a furnace, and then the pressure was reduced to 40 Pa while flowing nitrogen gas at 0.5 / min to raise the temperature from room temperature to 650 ° C. When the temperature reaches 650 ° C, silane gas
A polycrystalline silicon film was deposited on the surface of the silicon wafer for 120 minutes by passing 0.35 / minute with a flow of 0.5 / minute of nitrogen gas as a carrier gas.
When the surface of the silicon wafer after the deposition process was examined by a metallographic microscope and a scanning electron microscope, the polycrystalline silicon film was not grown on the surface of the silicon wafer or was partially grown. Also, a close examination of the partially grown portion revealed that polycrystalline silicon was found in the part where the particles generated in the low pressure CVD furnace adhered, or in the part where the particles in the liquid adhered when the oxide film was etched off with hydrofluoric acid. It was found that the film was growing. This fact can be understood as follows. That is, since the CVD reaction becomes an epitaxy reaction on the surface of the silicon wafer in which the surface oxide film is etched off and the surface of the silicon single crystal is exposed, the polycrystalline silicon film does not grow, and only in the presence of particles, etc. Becomes a growth nucleus, and the polycrystalline silicon film around it grows like an island.

Further, in the method described in JP-A-58-138,035, the polycrystalline silicon layer is directly formed on the back surface of the single crystal silicon substrate, and thus the gettering ability as described above is still insufficient.

Further, in the method of Japanese Patent Laid-Open No. 59-186,331, the polycrystalline silicon layer formed on the back surface of the single crystal silicon base is doped with oxygen. This oxygen doping is a getter by the polycrystalline silicon layer. The ring effect is rather spoiled.

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

(Means for Solving the Problems) The above object is to provide a single crystal silicon substrate, a silicon oxide film having a thickness of 1 to 8Å formed on one surface of the substrate, and a multi-layered silicon oxide film formed on the silicon oxide film. It is achieved by a silicon wafer having a gettering ability which is composed of a crystalline silicon layer.

The above object is to oxidize at least one surface of a single crystal silicon substrate to form a silicon oxide film having a thickness of 1 to 8Å, and to contact the silicon oxide film with gaseous silanes under heating. This is achieved by a method for producing a silicon wafer having an excellent gettering ability, which is characterized by forming a polycrystalline silicon layer on the film.

(Function) A silicon wafer having excellent gettering ability according to the present invention is formed by a single crystal substrate, a silicon oxide film having a thickness of 1 to 8Å formed on one surface of the substrate, and a silicon oxide film formed on the silicon oxide film. And a polycrystalline silicon layer.

The single crystal silicon substrate used in the present invention is obtained by lapping the surface of the single crystal substrate, and then chemically polishing the surface layer by etching to remove the surface layer having a thickness of several tens of microns or less. The substrate has a thickness of 200-2,000 microns, preferably 300
~ 1,000 microns.

The thickness of the silicon oxide film formed on the surface of the single crystal silicon substrate is 1 to 8Å, preferably 1 to 5Å. That is, when a silicon oxide film having a thickness of 1Å or more is formed on the surface of a single crystal silicon substrate, a polycrystalline silicon layer formed thereon is formed uniformly and with high adhesion over the entire surface of the single crystal silicon substrate. To be done. If the thickness of this silicon oxide film is less than 1 Å, the polycrystalline silicon layer formed thereon will be nonuniformly formed, the adhesion will be reduced, and the crystal grains of the polycrystalline silicon layer will be large. On the other hand, if the thickness of the silicon oxide film exceeds 8 Å, the silicon oxide film becomes an obstacle when the impurities in the single crystal silicon substrate move into the polycrystalline silicon layer, and the gettering ability is deteriorated. From this point, 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, oxides and contaminants attached to the surface of the single crystal silicon substrate are removed with diluted hydrofluoric acid, and then rinsed with deionized water. And further dry. Then, the single crystal silicon substrate is heated in a molecular oxygen-containing gas or water vapor atmosphere to form a silicon oxide film. Examples of the molecular oxygen-containing gas include pure oxygen gas, mixed gas of oxygen gas and inert gas, air, and oxygen-rich air. Further, the silicon oxide film can be formed by placing the single crystal silicon substrate in oxygen plasma. Further, the silicon oxide film can be formed by immersing the single crystal silicon substrate in an oxidizing chemical or by anodizing. Examples of the oxidizing agent include nitric acid, dichromic acid or its salt, permanganic acid or its salt, perchloric acid or its salt, and hydrogen peroxide solution. The film thickness of the silicon oxide film depends on the oxidation conditions. For example, when a single crystal silicon substrate is heated in air at a pressure of 1 atm to form a silicon oxide film, the growth rate of the oxide film and the single crystal silicon The relationship with the substrate temperature is as follows.

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.

In addition, the measured value of the film thickness of the silicon oxide film in the present invention is a value measured by an ellipsometer. That is, it was measured by an ellipsometer immediately after the oxidation treatment of the single crystal silicon substrate, that is, before the formation of the polycrystalline silicon layer. At this time, the zero point determined as follows was subtracted from the display value of the ellipsometer. 1 single crystal silicon substrate
% Of hydrofluoric acid to remove the natural oxide film on the surface of the substrate, rinse with deionized water, spin dry and immediately measure with an ellipsometer. The value obtained was the zero point. The refractive index of the oxide film was 1.460.

A polycrystalline silicon layer is formed on this silicon oxide film. The thickness of the polycrystalline silicon layer is 1,000 Å ~
It is 5 μm, preferably 5,000 Å to 1.5 μm, and its crystal grains are not amorphous and are 2 μm or less, preferably 0.05 to 0.5 μm.

In order to form a polycrystalline silicon layer on a silicon oxide film, the single crystal substrate is grown in an atmosphere of gaseous silanes diluted with nitrogen gas, argon gas, etc.
C., preferably 580 to 700.degree. C., for 0.1 to 7 hours, preferably 0.3 to 2 hours by heating under reduced pressure or normal pressure. As a method like this,
For example, there is a low pressure CVD method. The silanes used in the present invention include monosilane (SiH ₄ ), dichlorosilane (SiH ₂ Cl ₂ ), monochlorosilane (SiH ₃ C).
l) etc.

In the silicon wafer according to the present invention, since the silicon oxide film having a specific thickness is formed on the surface of the single crystal silicon base, the polycrystalline silicon layer is formed to have a uniform thickness with excellent adhesion. Moreover, since the silicon oxide film gives an infinite number of growth nuclei necessary for growing the polycrystalline silicon layer, without the silicon oxide film, the polycrystalline silicon layer grows like islands with stains as nuclei. The growth rate cannot be specified unconditionally, the growth rate is several tens of liters / minute in the island-shaped portion, and it is almost zero (not measurable) in the case of no growth, whereas the silicon oxide film exists. In this case, the growth rate of the polycrystalline silicon layer is improved to 150 Å / min. If there is no silicon oxide film,
The crystal grain size of polycrystalline silicon is 3 to
On the other hand, in the present invention, the crystal grain size is as small as about 0.1 to 0.4 micron (result of cross-sectional TEM observation) and is uniform. Further, even if the surface of the single crystal silicon substrate is slightly contaminated, no stain pattern occurs after the polycrystalline silicon film is formed.

Further, when the silicon wafer according to the present invention is used, the silicon oxide film is condensed and disappears in an island shape by heat treatment at 900 ° C. or higher performed at the beginning of the IC manufacturing process, so that the single crystal substrate and the polycrystalline silicon film are separated from each other. You will come into direct contact.

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

In a silicon wafer in which a silicon oxide film is formed on one surface of a single crystal silicon substrate and a polycrystalline silicon layer is formed on the film, and the other surface is mirror-polished,
The mirror surface is oxidized in pure oxygen gas heated to 1,000 ° C. to form an oxide film of about 300 Å, and then a disc-shaped aluminum film having a diameter of 1 mm and a thickness of 5,000 Å is formed on the oxide film. The electrodes are formed by vapor deposition. The gettering ability is evaluated by measuring the generation lifetime of the minority carriers of the MOS capacitor thus formed on the substrate. EH Nicollian and JR Brews for measuring lifetime of minority carriers
MOS Physics and Technology (John Wiley & So
ns). When the silicon substrate is contaminated with metal impurities, the generation lifetime of minority carriers is shortened. When the metal impurities are gettered, the lifetime is recovered and lengthened. In general, it is impossible to prevent a very small amount of metal impurities from being naturally introduced from the surrounding atmosphere in the oxidation process for manufacturing a MOS capacitor. Therefore, if a plurality of silicon substrates having different gettering abilities are processed at the same time, the generation lifetimes of the minority carriers are naturally different, so that the gettering abilities can be relatively compared.

(Examples) Next, the present invention will be described in more detail with reference to Examples.

Examples 1 to 4 A 600 μm thick single crystal silicon substrate was immersed in 1% hydrofluoric acid to remove the natural oxide film adhering to the surface, followed by rinsing with deionized water and further spin drying. Dried. Immediately after drying, the single crystal substrate is heated to 400 ° C.
It was placed in an electric furnace in the air atmosphere for 7 minutes, 22 minutes, 36 minutes and 43 minutes to form 1Å, 3Å, 5Å and 6Å silicon oxide films, respectively. Then, by a low pressure CVP method, silicon (SiH ₄ ) gas was thermally decomposed at 650 ° C. using nitrogen gas as a carrier to deposit a polycrystalline silicon layer on the silicon oxide film by 1 micron.

In this way, since the polycrystalline silicon layer and the silicon oxide film are deposited on both sides of the wafer on which the polycrystalline silicon layer is deposited, one surface of the wafer is polished to polish the polycrystalline silicon layer and the underlying silicon oxide film. Was removed to expose the single crystal silicon substrate, which was then mirror-finished. A MOS capacitor as described above was formed on the mirror surface side of the silicon wafer thus manufactured, and the gettering ability was evaluated by the value of the lifetime of the minority carrier. The results are shown in Table 1.

When these silicon wafers were observed with a metallographic microscope, a scanning electron microscope and a transmission electron microscope, the growth rate of the polycrystalline silicon layer was 150Å.
/ Min, the crystal grain size was 0.1 to 0.4 micron. further,
When this silicon wafer was viewed in the dark field with a condenser lamp in a dark room and scattered light was observed, no white pattern was observed.

Comparative Example 1 A silicon wafer was obtained in the same manner as in Example 1 except that the silicon oxide film was not formed on the surface of the single crystal silicon substrate in the methods of Examples 1 to 4. The gettering ability of the silicon wafer obtained 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.

When using a metallographic microscope, a scanning electron microscope, and a transmission electron microscope for these silicon wafers, the polycrystalline silicon layer was grown at a growth rate of several tens of Å in the island-shaped portion. The growth rate could not be defined unconditionally because the polycrystalline silicon layer grows with stains and the like as nuclei in the non-exposed area. Also, the crystal grain size is 3 to 3 in the island-shaped grown portion.
It was 10 microns. Furthermore, when this silicon wafer was viewed in the dark field with a concentrating lamp in the dark field and scattered light was observed, star-shaped, island-shaped, or star-shaped objects with a white pattern like liquid flowing were found in the low-pressure CVD furnace. Polycrystalline silicon layer grows around the generated particles as growth nuclei, and island-shaped ones are a collection of star-shaped ones or silicon wafers and boats (quartz jig for mounting wafers). ) Is a polycrystalline silicon layer that has grown from the contact point, and the pattern in which the fluid has flowed is that when the oxide film on the wafer surface is etched off, it is rinsed with deionized water and then lifted from the rinse tank. It is a polycrystalline silicon layer grown using particles left on the surface as growth nuclei. After charging 100 sheets in the low pressure CVD furnace, some white pattern was observed in 95 sheets. No polycrystalline silicon layer was deposited on the wafer in which no white pattern was observed.

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 10 Å in the method of Examples 1 to 4, and the gettering ability was evaluated by the same method. I did. The results are shown in Table 1.

As is clear from Table 1, the silicon wafer according to the present invention (Examples 1 to 4) has a long generation life of a small number of carriers and is extremely excellent in gettering ability as compared with the conventional wafer (Comparative Example 1). You can see that Further, in the wafer of Comparative Example 1 in which the silicon oxide film is not provided,
On the single crystal silicon substrate, there are a portion where polycrystalline silicon crystal grains grow and a portion where polycrystalline silicon does not grow, and the average crystal grain size is 3 microns or more, and some of them are 10 microns or more. On the other hand, in the case of the wafers of Examples 1 to 4 in which the thickness of the silicon oxide film is 1 Å or more, the crystal grains of polycrystalline silicon grow over the entire surface of the single crystal silicon substrate, and the crystal grain size is 0.1. Uniformity of ~ 0.4 micron.

Reference Example A silicon wafer having a silicon oxide film having a thickness of 5Å and a polycrystalline silicon layer having a layer thickness of 1 micron obtained in Example 3 was oxidized in a steam atmosphere at 900 ° C. for 2 hours, and then, When the composition was analyzed by observing the cross section with a transmission electron microscope, no continuous oxide film was observed at the interface between the single crystal silicon substrate and the polycrystalline silicon layer, and island-like dots were seen like rice grains. Oxides were found.
The single crystal silicon substrate and the polycrystalline silicon layer were in close contact with each other at most of the interface, and part of the polycrystalline silicon layer was solid phase epitaxially grown.

For example, in the IC manufacturing process, a nitride film is used as a mask in order to form a well or to insulate the element region with a thick oxide film. Normally, an oxide film is formed under the nitride film. This oxide film is called a pad oxide film,
In the IC manufacturing process, the pad oxide film is often formed immediately after the first wafer cleaning process. A typical example of 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 having a thickness of about 500Å is formed. As is apparent from the reference example, in the silicon wafer according to the present invention, the oxide film of 1 to 8 Å between the single crystal silicon substrate and the polycrystalline silicon layer is formed by the process of forming such a pad oxide film. It disappears and the single crystal silicon substrate and the polycrystalline silicon layer come into close contact with each other.

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Araki 3434 Shimada, Hikari City, Yamaguchi Prefecture, Hikari Plant, Nittetsu Electric Co., Ltd. (56) References JP-A-60-89932 (JP, A) JP-A-61 -159741 (JP, A)

Claims (2)

[Claims] 1. A gettering comprising a single crystal silicon substrate, a silicon oxide film having a thickness of 1 to 8Å formed on one surface of the substrate, and a polycrystalline silicon layer formed on the silicon oxide film. A silicon wafer with excellent capability. 2. A surface of at least one side of a single crystal silicon substrate is oxidized to form a silicon oxide film having a thickness of 1 to 8Å, and the silicon oxide film is brought into contact with gaseous silanes under heating to perform the oxidation. A method for producing a silicon wafer having excellent gettering ability, which comprises forming a polycrystalline silicon layer on a silicon film.