JPH05121415A - Production of semiconductor substrate - Google Patents

Abstract

PURPOSE:To reduce the warpage even if a wafer is subjected to the specular grinding and suppress the reduction of device characteristics and yield when forming a polycrystalline silicon film on a semiconductor wafer. CONSTITUTION:When a wafer composed of Si (silicon) single crystal is processed to produce a semiconductor substrate, the surface to form semiconductor elements is a mirror surface, and its rear side is provided with a polycrystalline Si film. The Si film is formed by using a material gas whose composition is mainly 10-100wt.% SiH4 (monosilane) and an invent gas for remaining part, whereas its reaction temperature is 600-700 deg.C and the pressure is within 0.01-0.3 Torr during reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer (hereinafter referred to simply as "wafer") made of Si single crystal for manufacturing a semiconductor device (hereinafter referred to as "device"), which is provided on a surface opposite to a surface on which a semiconductor element is formed. The present invention relates to a method for manufacturing a semiconductor substrate having an extrinsic gettering effect by forming a polycrystalline Si film.

[0002]

2. Description of the Related Art A semiconductor substrate is subjected to various heat treatments in a device manufacturing process. In this heat treatment process,
Carbon and metal impurities existing in the substrate, or metal impurities that contaminate the surface of the substrate during the device manufacturing process, are deposited on the substrate and cause various crystal defects. These defects also occur on the surface of the semiconductor substrate and in the vicinity thereof, increasing the leak current and decreasing the lifetime of the substrate, which adversely affects the characteristics and yield of the device manufactured.

On the other hand, minute crystal defects and strains formed on the back surface or inside of the wafer trap impurities that have a harmful effect on device characteristics, fix them, or remove point defects that are involved in the generation of defects. It has an effect. This action is called gettering, the former is called extrinsic gettering (EG) and the latter is called intrinsic gettering (IG).

As one of the EGs, a method of forming a polycrystalline Si film on the back surface of a wafer and using a strain field generated at a grain boundary of the polycrystalline Si film or a strain field due to lattice mismatch as a gettering source. Is known (Japanese Patent Application Laid-Open No. 52-1207).
77, JP-A-55-113318, JP-A-57-133331, etc.).

The wafer used here is usually one obtained by etching a disk sliced from a silicon single crystal ingot after polishing. Further, to form a polycrystalline Si film on the wafer surface, there is a CVD method utilizing a thermal decomposition reaction of a Si-containing gas such as SiH ₄ or a hydrogen reduction reaction of SiH _x Cl _4-x (chlorosilane). However, in any method, when forming a Si polycrystalline film on the wafer surface, in order to prevent the deformation of the wafer that occurs when only one surface is applied, the entire surface should be as uniform as possible. A semiconductor substrate is manufactured by forming a film having quality and thickness, and then removing the Si polycrystal on one surface and performing mirror polishing. However, the semiconductor substrate obtained in this manner also causes a warp in which the mirror surface side is concave, and if it exceeds a certain value, it becomes an obstacle in device manufacturing. Further, even if the substrate does not warp in the initial stage, a new warp may occur due to heat treatment or the like in the subsequent device manufacturing process, which may deteriorate the quality of the device and the manufacturing yield.

[0006]

According to the present invention, when a polycrystalline silicon film is formed on a wafer, warpage is less likely to occur even if the wafer is subjected to mirror polishing treatment, resulting in a decrease in device characteristics and yield. It is an object of the present invention to provide a method for manufacturing a semiconductor substrate that does not include the above.

[0007]

In order to solve the above-mentioned problems, in the method for manufacturing a semiconductor substrate of the present invention, the surface on which a semiconductor element is formed is a mirror surface and the back surface side of the wafer made of Si single crystal. In manufacturing a semiconductor substrate having a structure in which a polycrystalline Si film is formed, the formation of the polycrystalline Si film is performed by changing the composition of the source gas to SiH ₄ 10
The balance is 100% by weight and the balance is an inert gas, the reaction temperature is 600 to 700 ° C., and the reaction pressure is 0.01 to 0.3 T.
It is within the range of orr.

If the composition of the monosilane gas is less than 10% by weight, the reaction rate of forming a polycrystalline Si film under the low pressure condition of the present invention is remarkably reduced, and the film thickness can be controlled when a large number of parallel wafers are simultaneously processed. It will be difficult. Again 1
When the amount is 00% by weight, the effect of preventing warpage of the present invention is exhibited at all. However, since the film thickness control becomes somewhat difficult when a large number of wafers are simultaneously processed, an inert gas for dilution is also used. However, it is preferable to operate by controlling the gas pressure and the gas flow rate.

When the reaction temperature is 600 ° C. or lower, the thermal decomposition rate of monosilane decreases, and as a result, the production efficiency of film formation deteriorates and the warpage tends to increase. Again 70
At a temperature of 0 ° C. or higher, the thermal decomposition rate increases, and as a result, it becomes difficult to control the film thickness to be uniform when a large number of parallel wafers are simultaneously processed.

The most significant feature of the method of the present invention is that the reaction pressure is extremely low as compared with the conventional method, that is, 0.01 to 0.3 Tor.
That is r. The pressure condition in the low pressure pyrolysis CVD method of SiH ₄ is usually 1.0 Torr or less to 0.5
It is in the range of Torr, and it is considered that the main reason for this is to maintain a predetermined productivity. However, under these conditions, a semiconductor substrate with a large warp is often generated. In a semiconductor substrate, at the same time as the flatness of the substrate,
The requirement is that there be no deformation such as warpage, and especially the higher density of device integration makes this requirement even more stringent, and semiconductor substrates that do not meet this requirement are out of specification, and as a result, semiconductor substrate manufacturing It causes a decrease in yield.

Further, the present invention relates to a plurality of wafers, in which the entire surface is uniformly arranged at a predetermined interval so as to come into contact with the raw material gas, and the raw material gas is introduced from one side of the wafer arrangement and the other side. In the method of forming a polycrystalline Si film to be discharged from the side, the reaction temperature is increased stepwise in the flow direction of the raw material gas in a row of wafers to increase the thickness of the polycrystalline Si film for all wafers. Can be made uniform. The central temperature and temperature gradient in this case cannot be specified because they are determined by various conditions such as the structural dimensions of the entire apparatus, the size and number of wafers to be processed, the composition flow rate of the raw material gas, etc. Is preferably within ± 20 ° C.

A reactor used in carrying out the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 2 is a vertical reactor for carrying out the present invention. The reaction furnace 2 has a double wall structure of an outer tube 4 and an inner tube 6 made of quartz, and a plurality of wafers W are set on a susceptor 8 installed at the center.

The reaction gas introduced into the furnace from the gas inlet 10 provided in the lower part of the reactor 2 is sucked and exhausted from the gas outlet 12 by a vacuum pump (not shown). In addition, H is a heater.

Since the reaction gas flows from the lower part to the upper part in the reaction furnace 2, when the reaction gas is introduced only from the lower gas introduction port 10, the concentration of the reaction gas inside the reaction furnace 2 is the introduction port 10. The lower part close to is thicker, and the concentration of the reaction gas becomes thinner as it goes to the upper part. In this state, if the temperature in the reaction furnace is set to be the same in the upper and lower sides, a thick polycrystalline silicon film is formed on the lower wafer and a thin polycrystalline silicon film is formed on the upper wafer.

In order to eliminate this inconvenience, the temperature of the upper part of the reaction furnace 2 is set higher than the temperature of the lower part to accelerate the reaction rate of the upper part, and when the reaction gas is thin, the reaction rate is increased.
When the reaction gas is rich, the film thickness of the polycrystalline silicon film produced can be made uniform without increasing the reaction rate.

Using the reaction furnace 2 shown in FIG. 1, when the reaction gas composition is 80% SiH ₄ and 20% SiH ₄ and the reaction pressure is changed to 0 to 0.6 Torr, The change in value is shown in FIG. This warp change amount is
For a wafer on which a polycrystalline silicon film is formed, the warp after mirror-polishing and the wafer before the formation of the polycrystalline silicon film are measured by an optical interference fringe warpage measuring machine, and the difference, that is, the warp change amount (μm) = mirror surface It shows the warp (μm) of the wafer after the polishing treatment-the warp (μm) of the wafer before the formation of the polycrystalline silicon film.

Although the above-mentioned technique for making the thickness of the polycrystalline silicon film uniform has been described for the vertical reaction furnace 2 shown in FIG. 1, it is needless to say that it can be similarly applied to a horizontal reaction furnace.

That is, the reaction temperature is increased stepwise with respect to the direction of flow of the reaction gas flow along the wafer, whereby the thickness of the polycrystalline silicon film produced can be made uniform. ..

Since the wafers W set in the susceptor 8 of the reaction furnace 2 are usually set one by one, the polycrystalline silicon film is formed on the entire surface of the wafer W. By mirror-polishing one surface of the wafer with the polycrystalline silicon film, the polycrystalline silicon film remains on the back surface of the wafer, and the EG function described above is achieved.

As means for forming a polycrystalline silicon film,
In addition to the above-mentioned means, two wafers may be superposed and set to form a polycrystalline silicon film.
In this case, since the polycrystalline silicon film is formed on only one surface of each of the two wafers, the mirror-polishing process can be easily performed. Moreover, in this case as well, it has been confirmed that the warp deformation of the semiconductor substrate is small as compared with the conventional method.

[0022]

The warpage of the semiconductor substrate is considered to be caused by the stress generated in the Si polycrystal formed by the CVD method or at the interface between the polycrystal and the Si single crystal of the wafer.

During the heat treatment, this stressed portion causes dislocations and stacking faults at the substrate boundary, and acts as an EG source for the semiconductor substrate of the present invention. By the way, when such a Si polycrystalline film is covered with a uniform film thickness and crystallinity on the entire surface of the wafer, since these stresses act uniformly on the entire surface, the wafer deformation in appearance does not occur. Although it does not occur, in a semiconductor substrate in which the Si polycrystalline film on one side surface is removed and mirror processing is performed, the stress balance due to the film is lost and the mirror surface side is deformed in a concave state. As a result of studying the prevention of deformation, the present inventors have completed the present invention by finding that an increase in wafer warpage is prevented by reducing the reaction pressure to a predetermined pressure range as in the present invention. Is.

Upon further studying the reason for this, under the low pressure condition of the present invention, the crystal grains observed in the concavo-convex state of the Si polycrystal surface under the microscope sometimes grow large. That is, the causal relationship between the occurrence of warpage and the occurrence of warpage was confirmed. That is, when the growth of the crystal grains is large, the contact area between the crystal grains and the Si single crystal surface of the wafer is small, and the stress between the crystal grains is reduced, but the crystal grains are small as in the conventional condition. In this case, it is estimated that the stress increases and warpage of the wafer increases. The crystal grains become larger as the concentration of the reaction raw material gas and the reaction temperature increase, but in this case, S formed.
The film thickness distribution of i-polycrystal begins to be disturbed, and as a result, the quality and manufacturing yield of the semiconductor substrate are reduced.

However, the method of the present invention in which the pressure of the raw material gas is made extremely low reduces the occurrence of warpage of the semiconductor substrate and consequently improves the production yield thereof, so that it is industrially possible even if some productivity is sacrificed. The use effect of is fully demonstrated.

[0026]

EXAMPLES Next, examples of the present invention will be described together with comparative examples. In the examples,% means% by weight. Example 1 A reaction furnace similar to that shown in FIG. 1 was used, 80 wafers having a diameter of 150 mm were set in the furnace, the reaction temperature was 635 ° C., the entire area was soaked, the degree of vacuum was 0.18 Torr, and the reaction gas composition was SiH.
₄ 20%, balance helium gas, gas flow 0.50 l /
Under the condition of min, the polycrystalline silicon film generation reaction was performed with the thickness of the polycrystalline silicon film set at 0.8 μm at the bottom of the reaction furnace.

The thickness of the produced polycrystalline silicon film was measured by an ellipsometer, and the relationship with the set position of the wafer in the furnace is shown in FIG. In FIGS. 3 to 7 below, the left end of the wafer position on the horizontal axis indicates the bottom (BTM) and the right end indicates the top (TOP). From the result of FIG. 3, the value of the amount of change in warp was within 35 μm, and it was confirmed that the warp of the wafer was improved.

Comparative Example 1 A polycrystalline silicon film formation reaction was performed in the same manner as in Example 1 except that the degree of vacuum was 0.50 Torr, and the film thickness and the amount of change in warpage were measured and shown in FIG. From the results shown in FIG. 6, it can be seen that the amount of change in warp exceeds 60 μm and the warp of the wafer is large.

Example 2 A vacuum degree of 0.10 Torr and a reaction gas composition of SiH ₄ 80
% Balance helium gas, gas flow 0.24 l / min
5A and 5B, the polycrystalline silicon film formation reaction was performed in the same manner as in Example 1 except that the above was used, and the film thickness and the amount of change in warpage were measured.
It was shown to. From the result of the figure, the value of the warp change amount is 40 to 5
It was about 5 μm, and it was confirmed that the warp of the wafer was improved.

Comparative Example 2 A polycrystalline silicon film formation reaction was performed in the same manner as in Example 2 except that the degree of vacuum was 0.50 Torr, and the film thickness and the amount of change in warpage were measured and shown in FIG. From the result of FIG. 5, the value of the amount of change in warpage increases to 60 to 120 μm.

Example 3 The bottom (BTM) and the center (CT) of the reactor shown in FIG.
R) and the temperature of the top (TOP) are 640 ° C. and
A polycrystalline silicon film formation reaction was performed in the same manner as in Example 1 except that the temperatures were set to 650 ° C. and 665 ° C., and the film thickness and the amount of change in warpage were measured and shown in FIG. From the result of the figure,
It was confirmed that the amount of change in warpage was uniform in the range of 10 to 20 μm in all of the bottom, center and top, and the film thickness was also uniform.

[0032]

As described above, according to the present invention, when a polycrystalline silicon film is formed on a wafer, warpage does not increase even if the wafer is subjected to mirror polishing, and the device characteristics and It is possible to prevent the yield from decreasing.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an example of a vertical reactor used in the method of the present invention.

FIG. 2 is a graph showing the relationship between reaction pressure and the amount of change in warp when one embodiment of the method of the present invention is carried out.

FIG. 3 is a graph showing the relationship between the wafer position and the film thickness and the amount of change in warpage in Example 1.

FIG. 4 is a graph showing a relationship between a wafer position and a film thickness and a warp change amount in Comparative Example 1.

FIG. 5 is a graph showing the relationship between the wafer position and the film thickness and the amount of change in warpage in Example 2.

FIG. 6 is a graph showing a relationship between a wafer position and a film thickness and a warp change amount in Comparative Example 2.

FIG. 7 is a graph showing the relationship between the wafer position and the film thickness and the amount of change in warpage in Example 3.

[Explanation of symbols]

 2 Reactor 4 Outer tube 6 Inner tube 8 Susceptor 10 Gas inlet 12 Gas outlet

Claims (2)

[Claims] 1. A wafer made of Si (silicon) single crystal, a surface on which a semiconductor element is formed is a mirror surface, and a back surface side thereof has a structure in which a polycrystalline Si film is formed. The formation of the polycrystalline Si film is performed by changing the composition of the source gas to SiH ₄ (monosilane) 10-1.
The reaction temperature is 6
00-700 ° C., pressure during reaction 0.01-0.3 To
A method of manufacturing a semiconductor substrate, characterized in that it is within the range of rr. 2. The plurality of wafers are uniformly arranged at a predetermined interval so that the entire surface of the plurality of wafers comes into contact with the raw material gas, and the raw material gas is introduced from one side of the wafer row,
The method for forming the polycrystalline Si film to be discharged from the other side, wherein the reaction temperature is raised stepwise with respect to the flow direction of the raw material gas in a row of wafers. The method described in 1.