JPH05319987A - Production of silicon single crystal - Google Patents

Abstract

PURPOSE:To improve the quality by forming an Si ingot having a necked tail composed of a neck part which is the middle of the tail converging from the terminal end of a straight drum part into a conical form, a conical part following the neck part and the rear end part and treating the resultant ingot at a specific temperature. CONSTITUTION:A neck part is formed into >=10mm diameter and a conical part is formed into a diameter of >= (neck part diameter + 8mm) so as to prevent an Si ingot from falling off during the heat treatment at a high temperature. The dislocation is caused by plastic deformation with the resistance supporting the ingot weight by the neck part 3 and the conical part 4 during the heat treatment. The diameter of the neck part is regulated to <=1/5 that of the straight drum part so as to prevent the dislocation from propagating to the interior of the straight drum part 1. Furthermore, the conical angle (alpha) of the conical tail 2 is regulated to an acuter angle than 90 deg.C so as to make the propagation region of the dislocation stay in the conical tail 2. The Si ingot of this shape is then held with a suspending jig of a heat-treating furnace, nearly vertically hung and heat-treated at 1150-1400 deg.C. After completing the heat treatment, the ingot is cooled to <=1150 deg.C in the furnace and then taken out of the furnace to afford the objective Si single crystal without containing crystal defects.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing single crystal silicon by the Czochralski method (hereinafter, CZ).

[0002]

2. Description of the Related Art A silicon wafer, which is a substrate of a semiconductor device represented by a silicon integrated circuit, is usually manufactured by slicing and polishing a cylindrical silicon ingot pulled by the CZ method into a disk shape. In a device manufacturing process, a silicon wafer is subjected to complicated heat treatment, and if crystal defects such as precipitation, dislocations, and stacking faults occur in the vicinity of the device element as a result, the operation of the device becomes defective.
Therefore, it is required that no defects occur on the surface of the wafer on which the device is processed. The wafer surface is also required to be free from harmful impurities such as heavy metal elements, and residual contaminant elements that could not be removed in the device manufacturing process are not limited to the wafer surface but are taken in and fixed inside the wafer or on the back surface. The so-called gettering characteristic is also an important performance required for the wafer. It is crystal defects such as precipitates, dislocations, and stacking faults that serve as gettering sites for heavy metal elements inside the wafer. As described above, since crystal defects have both harmful and useful effects, a wafer in which the generation characteristics of crystal defects during heat treatment are strictly controlled is required.

By the way, in the CZ method, a high-purity polycrystalline silicon melt melted in a quartz crucible is impregnated with a seed crystal, and the seed crystal is pulled up while rotating the crucible and the crystal, and a single crystal ingot having the same orientation as the seed crystal. Is a way to get. The crystal diameter is controlled by adjusting the heating temperature of the silicon melt and the crystal pulling rate. For example, in order to grow a crystal from a dislocation-free seed crystal having an outer diameter of about several mm to a predetermined ingot diameter of 100 mm or more, the pulling speed is gradually reduced while the melt temperature is lowered, and a so-called conical shoulder portion is formed. To increase the crystal diameter. At the end of pulling, conversely, the pulling speed is accelerated, the crystal diameter is gradually reduced, and a conical tail is formed to finish. The CZ silicon crystal contains supersaturated solid solution oxygen taken in at the time of pulling, a trace amount of impurity elements such as carbon, atomic vacancies, and self-interstitial atoms. These impurities and defects diffuse and agglomerate during the cooling process during crystal production to form clusters. Such clusters serve as nuclei for crystal defects generated during heat treatment in the device manufacturing process. The type and amount of clusters in a crystal depend on the crystal production conditions, especially the cooling heat history from solidification during crystal production. Therefore, the crystal pulling conditions have to be strictly controlled in order to obtain the crystal defect generation characteristics required from the device manufacturing process.

Even so, it is not easy to make the thermal history the same for the head and the bottom of the same ingot, for example. To obtain almost the same thermal history, continue heating the bottom even after pulling the crystal.
A method such as pulling up a short ingot or making the characteristics of the ingot uniform by heat treatment of the wafer must be taken. However, bottom heating or short ingot pulling has the drawback of reducing productivity. Further, although it is possible to match the wafer heat treatment to the side having a high defect density by low temperature heat treatment, a high temperature heat treatment of 1150 ° C. or higher is necessary to adjust to the side having a low defect density, and such a high temperature heat treatment tends to occur. It is difficult to completely prevent the introduction of dislocations due to deformation. Therefore, there is a limit to the method using the wafer heat treatment. In the first place, strictly controlling the heat history during crystal pulling is almost impossible due to the change with time of the pulling furnace, and it depends largely on skilled operation techniques and evaluation of product crystals. If the ingot can be heat-treated as it is in another furnace after pulling up the ingot, the above problems will be solved. However, when the ingot is placed on a flat table in the furnace and heat-treated, dislocations occur over the entire ingot regardless of the horizontal vertical installation direction, and it cannot be used as a wafer material for integrated circuits. The major challenge was to first establish a technology for producing dislocation-free single crystals by ingot heat treatment.

The heat treatment of an ingot itself has been proposed so far, for example, JP-A-2-263792.
In the publication, a single crystal silicon ingot produced by the CZ method is subjected to high temperature treatment at 1200 to 1300 ° C., and then 400 to
Although it has been proposed to perform heat treatment at a low temperature of 550 ° C., neither the above problems associated with the ingot heat treatment nor the solution thereof are mentioned. Also, Japanese Patent Laid-Open No. 3-2088
Although Japanese Patent Publication No. 79 also proposes ingot heat treatment, it is similar to the fact that only the heat treatment temperature is described, and the above problems associated with the ingot heat treatment, and therefore no solution thereof, are described. Alternatively, JP-A-3-9
Japanese Patent No. 3700 proposes a heat treatment apparatus provided with a mechanism for suspending and holding a silicon single crystal and a heating means arranged around the single crystal, but in the embodiment, heat treatment is performed in a CZ furnace with an ingot pulled up. Only an example is given, and no method for suspending heat treatment of an ingot in another heat treatment furnace is proposed. In the end, high-temperature heat treatment of an ingot having an outer diameter of 100 mm or more and a weight in a heat treatment furnace different from the pulling furnace has not been put into practical use because there is no technology for preventing the generation of dislocations that easily occur due to thermal strain or the like.

[0006]

In view of the above-mentioned problems of the prior art, the present invention pulls an ingot of a silicon single crystal out of a furnace without generating dislocations at a portion to be processed on a wafer, and a heat treatment furnace outside the furnace. The present invention provides a method for manufacturing a silicon single crystal which enables high temperature heat treatment at 1150 ° C. or higher according to the above, and easily and economically obtains a silicon single crystal containing almost no defect nucleus.

[0007]

In order to achieve the above object, the present inventors have carefully observed the dislocation generation behavior when a large outer diameter ingot is subjected to high temperature heat treatment by various methods,
No dislocations occurred at the ingot production site.
We have found a method that makes it possible to perform heat treatment at a high temperature of 50 ° C. or higher.

That is, according to the present invention, when a silicon single crystal is manufactured by the Czochralski method, an outer diameter of 10 mm or more and a diameter of the straight body portion are formed between the end of the straight body portion of the silicon ingot and the middle of the ingot tail portion which converges in a cone shape. A silicon ingot having a neck portion of 1/5 or less, a cone portion that follows the neck portion and a diameter of 8 mm or more in diameter, and a tail portion with a neck that continues in a cone shape from the cone portion is formed, and the silicon ingot is formed in a heat treatment furnace. A gist is a method for producing a silicon single crystal, characterized in that the neck is suspended and held so that the ingot is suspended substantially vertically, and heat treatment is performed at a temperature of 1150 ° C. or higher and 1400 ° C. or lower.

At the end of the heat treatment, it is preferable that the silicon ingot is cooled to a temperature of 1150 ° C. or lower in the furnace and then the ingot is taken out of the furnace. Also,
Further, in order to make the present invention effective, it is preferable that the cone angle of the conical tail extending from the end of the straight body of the ingot to the neck is 90 ° or less.

[0010]

Function: About 10 in the Si single crystal pulled by the CZ method.
^When about ¹⁸ atoms / cm ³ of oxygen is in solid solution, when the crystal temperature is cooled to 1100 ° C. or less and the solid solution limit of oxygen to Si is reduced to about 2 × 10 ¹⁷ atoms / cm ³ , the solid solution Oxygen collects and begins to precipitate. Precipitation proceeds especially below 1000 ° C, but the volume of the precipitate is the same as Si.
Since the number of atoms is more than twice that of the Si crystal, a considerable elastic strain is accompanied around the precipitate. Therefore, when the CZ crystal is heat-treated at 1150 ° C. or higher, the solid solubility limit of oxygen at 1150 ° C. is 4 × 10 ¹⁷ atoms / cm ³ , but almost all of the crystals precipitated at 1100 ° C. or lower are released to release elastic strain energy. The precipitate re-dissolves within 30 minutes. 1
The time for reprecipitation of oxygen to the solid solution limit at 150 ° C. requires 100 hours or more, and there is almost no reprecipitation during heat treatment within a practical several hours. When the heat treatment temperature is set to 1250 ° C. or higher, which is the solid solution limit temperature of oxygen, the precipitates are completely solid-dissolved in a shorter time. The upper limit of the heat treatment temperature is, in principle, the melting point of silicon, but since a sufficient effect can be obtained at 1400 ° C. or lower, conversely, even if a part of the ingot is melted, a dislocation-free single crystal cannot be obtained. Is 1400 ° C.

In addition to oxygen, there are 10 ¹⁷ point defects such as atomic vacancies and self-interstitial atoms in the Si single crystal pulled by the CZ method.
The number of particles / cm ^{3 is} present, and these cluster together during the crystal cooling process to form oxygen precipitation nuclei and dislocation / stacking fault generation nuclei. The heat treatment at 1150 ° C. or higher re-dissolves the oxygen precipitates and at the same time decomposes the clusters. The supersaturated point defects diffuse out of the crystal during the heat treatment and disappear. The residual point defect concentration is equal to the thermal equilibrium concentration at the heat treatment temperature, and the temperature at which the crystal is taken out of the furnace is 115 after the heat treatment is completed.
Below 0 ° C, this is less than 1/100 of the point defect concentration introduced during pulling. Therefore, the number of clusters formed by re-aggregation of point defects during cooling after the heat treatment is extremely smaller than that of the as-pulled crystal.

As described above, the heat treatment at 1150 ° C. or more causes the oxygen precipitates to form a solid solution, and the number of point defect clusters serving as nuclei for precipitation centers or dislocations / stacking defects is significantly reduced. This does not depend on the parts such as the head and bottom of the ingot, and it does not depend on the crystal pulling conditions. The thermal history of crystal pulling is completely erased. The controlled oxygen precipitation properties required for CZ crystals can be imparted by low-temperature heat treatment at, for example, 700 ° C. or lower after processing a wafer from an ingot.

In the heat treatment, the ingot is
As shown in FIG. 3, the neck portion 3 of the conical tail portion 2 and the cone portion 4 that follows the pyramidal tail portion 2 are held by the suspension jig of the heat treatment furnace and are suspended almost vertically. In order to prevent the ingot from falling off during heat treatment, the neck diameter is required to be 10 mm or more and the cone diameter is required to be the neck diameter +8 mm or more. The reason is that if the neck diameter is less than 10 mm, the neck portion may not support the weight of the ingot and may be broken during the heat treatment at 1400 ° C. Also, the diameter of the cone that follows the neck is the neck diameter +
If it is less than 8 mm, the cone portion supporting the weight of the ingot may be deformed by the softening of the crystal in the same heat treatment at 1400 ° C., and the ingot may fall out of the jig.

The neck portion and the cone portion are plastically deformed and dislocations are generated during the heat treatment due to the drag force supporting the weight of the ingot.
In order to prevent the dislocation from propagating into the straight body portion, it is first required to limit the diameter of the neck portion to ⅕ or less of the straight body portion so that the dislocations are locally generated. The neck diameter is 1 / the straight body diameter
If it exceeds 5, dislocations generated in the neck may propagate in the conical tail and reach the straight body. Furthermore, as shown in FIG. 3, if the cone angle of the conical tail is more acute than 90 °, the propagation region of this dislocation remains within the conical tail. The sharper the cone angle, the more reliably the dislocation propagation region is limited. During the heat treatment, the straight body and the lower part (the head when the crystal is pulled) of the ingot are completely unrestrained, so dislocations do not occur from the straight body and the lower part. Naturally, thermal expansion of about 5 mm per 1 m does not affect at all. Therefore, according to the heat treatment of the present invention, dislocations are not introduced into the straight body of the ingot where the wafer is processed, and the oxygen precipitates formed in the ingot pulling step and the nuclei of dislocation / stacking faults are re-dissolved. Or it can be made to disappear, and the whole length of the ingot straight body part can be made into a healthy and homogeneous crystal.

[0015]

EXAMPLES Next, the present invention will be described with reference to examples. In the first embodiment, the straight body length is about 1 by the CZ method.
m, the diameter of the straight body part is 158 mm, and when the crystal is pulled up and the terminal part is formed, the cone angle of the pyramidal tail portion from the straight body part to the neck part is approximately 45.
The necked tail was formed so that the neck diameter was 15 mm and the cone diameter following the neck was 25 mm. The pulling speed of the straight body part is 0.8 mm / min, and the oxygen amount is 9.6 × 10 ¹⁷ atom.
s / cm ³ . Of the five ingots pulled up under these conditions, one is 800 ° C x 4hr + 10 after wafer processing.
The precipitation heat treatment was performed at 00 ° C. for 16 hours, the amount of dissolved oxygen before and after the heat treatment was measured by an infrared absorption method, and the oxygen precipitation amount was calculated from the difference. Separately, steam oxidation treatment was performed at 1100 ° C. for 1 hour, and after selective corrosion with Wright's solution, crystal defects were observed by an optical microscope. The other four are each 1100 ° C., 1150 ° C., 1200 in Ar atmosphere.
The ingot was heat-treated at 1250C for 2 hours. In this heat treatment, as schematically shown in FIG. 1, the neck of the ingot was supported by a U-shaped jig, and the head of the ingot was suspended downward. With respect to each heat-treated ingot, the wafer was processed in the same step as the ingot as it was pulled, and after the heat treatment, the amount of oxygen precipitation was measured or the crystal defect was observed. As a result, as shown in FIG. 2, when the as-pulled crystal was subjected to the above-mentioned precipitation heat treatment, it showed different oxygen precipitation behavior depending on the original ingot position where the wafer was sampled.
Specifically, the oxygen precipitation amount of the wafer taken from the ingot head is about 80% of the total oxygen amount, whereas the oxygen precipitation amount at the bottom of the ingot is only about 30%. Regarding the ingot heat-treated at 1100 ° C, the amount of oxygen deposited after the deposition heat treatment is 50% for the ingot head wafer and 25% for the bottom.
Therefore, the behavior of oxygen precipitation differs depending on the ingot position. On the other hand, regarding the ingot having the heat treatment temperature of 1150 ° C. or higher, the oxygen precipitation amount after the precipitation heat treatment was constant regardless of the ingot position, and was 30% or less of the total oxygen amount. The ingot wafer that was heat-treated at a temperature of 1150 ° C. or higher was further subjected to a heat treatment of 650 ° C. × 24 hr, and then the above precipitation heat treatment was performed to investigate the oxygen precipitation state. As a result, 60% for 1150 ° C material, 120%
The 0 ° C material was 55% and the 1250 ° C material was 48%, and the amount of this precipitation did not depend on the position of the ingot where the wafer was sampled. The number of wafers taken from the above five types of ingots is 1
The crystal defect generation state due to the 100 ° C. steam oxidation heat treatment was also different. For a wafer sampled from an ingot as it is pulled up, the radius is about 50 to 5 from the center of the wafer regardless of the sampled position.
Many stacking faults were distributed in the area on the ring of 7 mm. No stacking fault occurred in the 1100 ° C heat-treated ingot, but the radius from the wafer center was about 50 to 57 mm.
A large number of minute pits were observed in the same area. On the other hand, no defects could be observed in the ingot subjected to the heat treatment at 1150 ° C. or higher even by steam oxidation. As a result, it was confirmed that the crystal defect nuclei generated during the pulling were eliminated by the ingot heat treatment at 1150 ° C. or higher and that the oxygen precipitation characteristic did not depend on the ingot position.

In the second embodiment, an ingot having a straight body portion length of 0.8 m and a straight body portion diameter of 210 mm is fixed with a neck portion diameter of 20 mm and a cone diameter of 30 mm following the neck portion, and a pyramidal angle from the straight body portion to the neck portion is fixed. Variously (70 °, 80 °, 90 °, 10
0 °, 110 °) and the same ingot heat treatment (temperature 1350 ° C.) as in the first embodiment was performed to see the effect of the cone angle on the dislocation distribution. After the heat treatment, a vertical section of the ingot including the axis of the ingot was cut from the tail portion to the straight body portion, and a wafer having a thickness of 3 mm was cut out. After removing the processed layer on the cut surface by corrosion with a mixed solution of hydrofluoric acid and nitric acid, this longitudinal cross-section wafer was observed by X-ray topography to investigate the dislocation distribution. As a result, as shown in FIG. 3, the cone angle is 90 °.
In the following cases, it can be seen that the propagation range of the dislocations generated in the neck portion remains within the conical tail portion, while the dislocations propagate to the straight body portion when the cone angle exceeds 90 °.

In the third embodiment, three ingots each having a straight body length of 1.2 m, a straight body diameter of 131 mm, a tail pyramid angle of 45 °, and a neck diameter of 10 mm are subjected to suspension heat treatment at 1400 ° C. and then each in a furnace. After cooling to 1200 ° C., 1150 ° C. and 1100 ° C., it was taken out of the furnace, allowed to cool in the atmosphere, and the effect of cooling after heat treatment was investigated. This result shows that for materials with a take-out temperature of 1150 ° C. and 1100 ° C., the amount of precipitated oxygen after the precipitation heat treatment was 20% of the total amount of oxygen regardless of the ingot position.
Below, there were no defects generated by the steam oxidation treatment. On the other hand, when the extraction temperature was 1200 ° C., the amount of oxygen precipitated after the precipitation treatment was 27% of the total amount of oxygen, and about ² to 3 stacking faults / cm ² were observed after steam oxidation. Regardless of the oxygen precipitation characteristic, the occurrence of stacking faults in the latter case is not preferable because it is small, and it was confirmed that it is suitable to take out at a temperature of 1150 ° C or lower.

[0018]

As described above, according to the present invention, it is possible to reliably and easily obtain a crystal having a uniform oxygen precipitation characteristic without defects over the entire length of the straight body of the ingot. Further, as shown in Example 1, even if the as-pulled ingot contains defective nuclei, the defective nuclei are erased by the present invention, so the effect of the present invention is not affected by the ingot pulling conditions. .. Therefore, the conditions required for pulling up the ingot are that it is a dislocation-free single crystal with a predetermined outer diameter, that the dopant concentration and oxygen concentration are within a predetermined range, that carbon and other impurities are below a predetermined amount, etc. There are no restrictions on the cooling conditions of the ingot. This reduces the load on the pulling furnace,
Brings significant improvements in productivity, yield and quality.

[Brief description of drawings]

FIG. 1A is a schematic view of a tail portion with a neck, and FIG. 1B is a schematic view showing a method of vertically suspending an ingot using the neck portion.

FIG. 2 Ingot as pulled, and 1100 ° C., 1
It is a figure which shows the oxygen precipitation amount at the time of carrying out precipitation heat treatment of the wafer cut out from the head part, middle part, and bottom part of the ingot heat-processed at 150 degreeC, 1200 degreeC, and 1250 degreeC for 2 hours.

FIG. 3 shows the relationship between the distance between the dislocation tip generated and propagated in the ingot neck due to ingot heat treatment and the end of the ingot straight body and the cone angle of the conical tail, from the end of the straight body to the neck side.
It is a figure which shows the straight body part side in a negative direction.

[Explanation of symbols]

 1 Silicon ingot straight body part 2 Conical tail part 3 Neck part 4 Cone part 5 Terminal part α Conical angle of conical tail part

Claims (3)

[Claims] 1. When manufacturing a silicon single crystal by the Czochralski method, the outer diameter is 10 mm between the end of the straight body of the silicon ingot and the middle of the tail of the ingot that converges in a cone shape.
A necked tail portion having a neck portion having a diameter of ⅕ or less of the diameter of the straight body portion and a cone portion having a diameter of neck portion +8 mm or more following the neck portion, and a terminating portion which continues from the cone portion in a cone shape. A silicon ingot is formed, and the neck is suspended and held in a heat treatment furnace so that the ingot is suspended substantially vertically.
A method for producing a silicon single crystal, which comprises performing heat treatment at a temperature of 150 ° C. or higher and 1400 ° C. or lower. 2. The method for producing a silicon single crystal according to claim 1, wherein after the heat treatment at a temperature of 1150 ° C. or more and 1400 ° C. or less, cooling is performed to a temperature of 1150 ° C. or less in the heat treatment furnace. 3. The method for producing a silicon single crystal according to claim 1, wherein the pyramidal tail portion from the straight body portion of the silicon ingot to the neck portion has a cone angle of 90 ° or less.