JPH03184345A - Silicon wafer and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application 1] The present invention relates to a silicon wafer that has stable oxygen precipitation properties and is less likely to be defective due to surface defects, and a method for manufacturing the same.

[Prior Art] Various methods have been known for growing silicon single crystals for manufacturing devices such as ICs and LSIs. Among them, the Czochralski method (which grows a single crystal rod by pulling up a seed crystal attached to a silicon melt in a quartz crucible)
Hereinafter, this will be referred to as the C2 method.

) has become industrially popular due to the fact that silicon wafers manufactured using this method do not warp easily even after repeated heat treatments, and are resistant to heavy metal contamination from the device manufacturing process due to their intrinsic gettering effect. It is widely used. The above-mentioned advantages of the silicon wafer obtained by the CZ method are all due to the oxygen contained in the crystal. However, - this oxygen, on the other hand, causes heat treatment-induced crystal defects. When crystal defects appear in the active region of a device, device characteristics are significantly degraded.

The precipitation of oxygen has been studied in detail, and 60
It is known that precipitation nuclei are formed at temperatures between 0 and 700°C. During the single crystal manufacturing process, as the crystal is pulled up, it passes through a temperature range of 600 to 700°C due to natural cooling of the crystal, where precipitate nuclei are formed, and this is a major factor in the growth of precipitates during the device manufacturing process. However, since the persimmon crystal side of the single crystal pulled in this way takes a long time to cool down, many precipitation nuclei are generated.
Oxygen precipitability in silicon wafers produced from each part of the single crystal varies greatly due to differences in thermal history during the production of the single crystal, such as shorter cooling time and fewer precipitation nuclei on the bottom side. Met.

[Problem to be solved by the invention] By the way, it is known that carbon atoms residing in a silicon single crystal promote the precipitation of interstitial oxygen (for example, VLSI technology 7 Process basics Semiconductor research 20
, published by Kogyo Kenkyukai, pp. 225-229).

Therefore, if a silicon single crystal is prepared by containing carbon at a predetermined concentration, such carbon atoms promote the precipitation of interstitial oxygen and easily form precipitation nuclei, so that the thermal history of the silicon single crystal increases. It is considered that the oxygen precipitability in the silicon single crystal can be stabilized without being affected by differences or slight fluctuations in the oxygen concentration in the silicon single crystal.

However, in a wafer made from a silicon single crystal grown with carbon at a predetermined concentration, a large number of oxygen precipitation nuclei are naturally formed not only inside the wafer but also in the surface layer. Become. Therefore, during heat treatment in the device manufacturing process, oxygen is further precipitated around these precipitation nuclei, and there is a high possibility that defects will eventually be formed in the surface layer, resulting in device failure.

Therefore, an object of the present invention is to provide a silicon wafer that has stable oxygen precipitability and is less likely to be defective due to surface defects, and a method for manufacturing the same.

[Means for solving the problem] In other words, the inside of the silicon wafer is 0. 1-50
The silicon wafer contains carbon at a predetermined concentration within the ppma range to form a carbon-containing layer, while the surface layer on at least one side of the silicon wafer forms a decarburized layer that does not substantially contain carbon. This is achieved using a silicon wafer characterized by the following characteristics.

In the above terms, a silicon wafer containing a certain predetermined concentration of carbon is heated to 1,000 to
This can also be achieved by a silicon wafer manufacturing method characterized by forming a decarburized layer on the surface layer of the silicon wafer by heat treatment at a temperature of 1200°C.

[Function] As described above, the silicon wafer of the present invention contains a sufficient amount of carbon inside. Since carbon in the silicon single crystal promotes oxygen precipitation and easily forms precipitation nuclei, the oxygen precipitation in this region is stable and the quality of the wafer, such as gettering effect and strength, is good and stable. Become. On the other hand, since the surface layer of the silicon wafer of the present invention is a decarburized layer and does not substantially contain carbon, oxygen precipitation does not occur in this region even if it is subjected to heat treatment in the device process. Defects are less likely to occur.

In this way, a sufficient amount of carbon is contained inside,
On the other hand, in order to manufacture a silicon wafer having a structure in which carbon is not substantially contained in the surface layer, the present inventors further grew a silicon single crystal containing carbon at a certain predetermined concentration. We have discovered a method of heat-treating the obtained wafer under predetermined temperature conditions to cause the carbon in the silicon wafer to diffuse outward and form a decarburized layer on the surface layer. Conventionally, for example, heat treatment for the purpose of decarburization has been carried out to diffuse oxygen in the silicon wafer outward to form a denuded zone in the intrinsic gettering process. has not been carried out before, and is introduced for the first time in the manufacturing method of the present invention.

Hereinafter, the present invention will be explained in more detail based on embodiments.

FIG. 1 schematically shows the structure of one embodiment of the silicon wafer of the present invention.

As shown in FIG. 1, in the silicon wafer of the present invention,
A carbon-containing layer 1 containing a predetermined concentration of carbon is formed inside the carbon-containing layer 1, while a decarburized layer 2 that does not substantially contain carbon is formed on the surface thereof.

In the silicon wafer of the present invention, the concentration of carbon contained in the carbon-containing layer 1 is set to an optimum value required for controlling oxygen precipitation in the silicon wafer/X, and the silicon wafer is used in the device process. Although it depends on the heat treatment conditions etc., it is generally 0.11) pm.
It is within the range of a to 50 ppma. That is, if the carbon concentration is less than 0.1 ppma, it is thought that controlling the formation of oxygen precipitated nuclei will be a national problem and the amount of oxygen precipitated will become unstable, whereas if it exceeds 5 Q ppma,
This is because carbon precipitation occurs during crystal growth, making it difficult to grow dislocation-free single crystals.

Further, in the silicon wafer of the present invention, the thickness of the decarburized layer 2 formed on the surface layer portion is preferably about 20 to 60 μl, more preferably about 35 to 45 μm. That is, if the M of the decarburized layer 2 is less than 20 μm, it becomes a national problem to create the active region of the device within the decarburized layer 2, whereas if it exceeds 60 μm, the formation becomes technically and economically difficult. This is because not only is this a national disaster, but also there is a risk that the gettering ability, strength, etc. of the wafer will be reduced. In the embodiment shown in FIG. 1, the decarburized layer 2 is formed on both sides of the wafer, but the decarburized layer 2
may be formed only on one side forming the device. Furthermore, it is most desirable that this decarburized layer 2 contains no carbon at all, but if the carbon concentration is 0.05 pp.
If it is less than ma, it is considered that there is substantially no effect of the carbon component, so it is acceptable.

When the silicon wafer of the present invention having such a configuration is subjected to a predetermined heat treatment in a device process, a large number of micro defects, for example, about 109 to 1010/Cm3, are formed inside the silicon wafer due to the carbon present at a desired concentration. On the other hand, since there is no carbon in the surface layer, interstitial oxygen does not precipitate, and no microdefects occur. Therefore, the reliability of the obtained device is increased, excellent gettering properties are obtained in the device manufacturing process, and the device strength is also sufficient.

A silicon wafer having such a configuration can be manufactured from a silicon single crystal containing carbon at a predetermined concentration as described above.

First, such a silicon single crystal containing carbon at a predetermined concentration is obtained, for example, as follows. FIG. 2 schematically shows the configuration of an example of a single crystal pulling apparatus used in the production of such silicon monolithic products in use.

In the silicon single crystal pulling apparatus shown in Figure 2,
A raw material supply pipe 5 capable of supplying raw materials from the peripheral edge side of the quartz crucible 4 in which the silicon melt 3 is formed is arranged. In the pulling device having such a configuration, first, a polycrystalline silicon raw material and an impurity as a dopant are loaded into the crucible 4, and the polycrystalline silicon raw material and dopant are melted by heating with a cylindrical heater 6. As a result, a melt 3 is formed. When forming the melt 3 or immediately before pulling the silicon single crystal, carbon, silicon carbide, or silicon containing carbon is added to the melt 3 in the crucible 2.
It is added so that the carbon concentration C6° in it becomes the following value.

Cc0=Cc-, +/k (where, in the formula, C(s, I are the target concentrations of carbon to be included in the silicon single crystal, and k is the segregation coefficient of carbon with respect to silicon.) and , pulling wire 7
A silicon single crystal 9 is grown on the tip of the seed crystal 8 by dipping the seed crystal 8 fixed at the tip of the seed crystal 8 into the melt 3 and pulling it at a predetermined speed. Here, since the segregation coefficient of carbon with respect to silicon is 0.07, if no operation is applied to the silicon melt 3, the carbon in the melt 3 will increase as the silicon single crystal 9 grows. Concentration Cc.

It is concentrated at a different rate, and the carbon concentration C6 in the obtained single crystal 9 varies greatly. Accordingly, as the silicon single crystal 9 is pulled, a carbon component is supplied from the raw material supply pipe 5 into the crucible 9 along with the silicon raw material and, if necessary, an impurity as a dopant, depending on the amount of the single crystal pulled. For example, this supplementary raw material contains, in addition to a granular or powdered polycrystalline silicon raw material and an impurity as a dopant, also granular or powdered carbon, silicon carbide, or silicon containing carbon, and a carbon concentration Cc in this supplementary raw material. may be prepared by blending them to the following values.

CCm" CCs, 1 This reduces the amount of carbon that is taken in as a single crystal from the melt 3 in the crucible 4 during delivery, and the amount of carbon in the supplementary raw material that is replenished into the melt 3 from the raw material supply pipe 5. The carbon content is balanced, and the carbon concentration C in the resulting single-linked 1'irI body 9 is kept constant at a desired value C6,1 in the axial direction.

However, as a method for growing a silicon single crystal containing a predetermined concentration of carbon, the above-mentioned aspect is not specified at all, and the method involves pulling a silicon single crystal in a crucible in a single crystal pulling operation. In the area to be raised,
Depending on the amount of single crystal pulled, an operation is performed to continuously or intermittently replenish the carbon component together with the silicon raw material, and the carbon concentration Cc0 in the melt is adjusted to a predetermined carbon concentration C68□ as the segregation coefficient of carbon with respect to silicon. Any method may be used as long as it can control the concentration within a certain range, preferably within ±10%, from the divided value through a pulling operation.

Once a silicon single crystal containing carbon at a predetermined concentration is obtained in this manner, the silicon single crystal is sliced to prepare a wafer using a conventional method, and the wafer is subjected to rough surface polishing and other treatments.

Accordingly, in the manufacturing method of the present invention, heat treatment is performed to form a decarburized layer on the surface layer of the silicon wafer. For example, as shown in FIG. 3, this heat treatment is carried out in a heating furnace 12 which is heated in advance by a heater 10 and maintained at a predetermined temperature, and which is maintained at a predetermined atmosphere by flowing a predetermined gas from a gas supply device 11. This is done by inserting the silicon wafer 13 into a jig 14 made of quartz or silicon carbide, and taking it out from the heating furnace 12 again after a predetermined period of time has elapsed. The temperature conditions for this heat treatment are approximately 1000°C to 1200°C, more preferably approximately 11°C.
A temperature of 50°C to 1200°C is suitable. In other words, if the heat treatment temperature is less than 1000°C, the diffusion rate of carbon from the silicon wafer 13 is slow and it takes a long time to form a decarburized layer of a desired thickness, which is not only impractical but also takes a long time. This is because there is a risk that decarburization for 1 minute will not be achieved even if heat treatment is applied, and on the other hand, if the heat treatment temperature exceeds 1200° C., there is a high risk that slip dislocations and the like will occur within the wafer surface. The heat treatment time is about 12 to 36 hours, although it depends on the heat treatment temperature and the thickness of the decarburized layer to be formed. Furthermore, the atmosphere in the furnace in this heat treatment may be any carbon-free atmosphere, for example, dry 02 atmosphere, wet 02 atmosphere, etc.
An atmosphere, N2 atmosphere, Ar atmosphere, etc. may be formed.

The silicon wafer with the decarburized layer formed on the surface layer in this way is then subjected to lapping, polishing, etc., as necessary, to be manufactured into a product.

[Example code] Hereinafter, the present invention will be explained in more detail with reference to Examples.

In a crucible 4 of a pulling device having the configuration shown in FIG. 2, a polycrystalline silicon raw material and a predetermined amount of boron as a dopant are first melted to form a melt 3. Further, carbon was added in an amount corresponding to a concentration of 14.0 ppma based on the amount of melt 3 in crucible 4. Then, while pulling a single crystal with a diameter of 5 inches based on a conventional method, a layer-shaped polycrystalline silicon containing a carbon component at a concentration of 1.0 ppma and a dopant at a predetermined concentration is supplied from the raw material supply pipe 5 according to the amount of pulling. The raw material was continuously supplied into the crucible 4 and the single crystal was grown to a length of about 80 cm.

The silicon single crystal obtained in this way was sliced and the wafer 13 obtained by surface polishing was heated at a temperature of 1150°C.
, heat treatment was carried out for 24 hours in a heating furnace 12 as shown in FIG. 3 which was maintained in a dry 02 atmosphere.

Thereafter, this silicon wafer was analyzed using a secondary ion mass spectrometer, and it was confirmed that a decarburized layer of about 40 μm was formed on the surface layer.

Further, this wafer was heat-treated in a heating furnace 12 as shown in FIG. 3 at 1000° C. for 16 hours in an N2 atmosphere.

When we etched a cross section of the silicon wafer after oxygen precipitation treatment and observed it with an optical microscope, we found that
In the region approximately 40 μm deep from the surface, that is, in the decarburized region, no precipitated defects are observed, whereas in the inner region, an average of 1010 defects/cm
There were 3. It should be noted that no significant difference was observed in the occurrence of precipitation defects among the wafers obtained from each part of the single suspended body, and it was considered that the characteristics were uniform.

[Effects of the Invention] As described above, according to the present invention, the inside of the silicon wafer contains carbon at a predetermined concentration within the range of 0.1 to 50 ppma, while the surface layer of at least one side of the silicon wafer contains carbon at a certain concentration within the range of 0.1 to 50 ppma. Since a decarburized layer that contains virtually no carbon is formed in the surface layer, the internal oxygen precipitation is stabilized, while oxygen precipitation in the surface layer is avoided, resulting in fewer surface defects. It also has excellent gettering properties, strength, and other qualities, and its product value is extremely improved.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view schematically showing the structure of the silicon wafer of the present invention, and Figures 2 and 2 are schematic diagrams showing the configuration in use of an example of a single crystal pulling apparatus used in manufacturing the silicon wafer of the present invention. FIG. 3 is a schematic diagram showing the configuration of an example of a heating furnace used in the production of silicon wafers of the present invention in a state of use. 1... Carbon-containing layer, 2... Decarburized layer, 3... Melt,
4... Crucible, 5... Raw material supply pipe, 6... Cylindrical heater 7... Draw wire, 8... Weighed product, 9...
...Single hanging body, 10...Heater 1...Gas supply device, 12...Heating furnace, 13...Silicon wafer\, 14...Jig.

Claims (2)

[Claims] (1) The inside of the silicon wafer contains carbon at a certain concentration within the range of 0.1 to 50 ppma to form a carbon-containing layer, while the surface layer on at least one side of the silicon wafer is substantially free of carbon. A silicon wafer characterized by forming a decarburized layer containing no carbon. (2) Silicon characterized by forming a decarburized layer on the surface layer of the silicon wafer by heat-treating the silicon wafer containing a certain predetermined concentration of carbon at a temperature of 1000 to 1200°C in a carbon-free atmosphere. Wafer manufacturing method.