JP2006213582A - Method and apparatus for manufacturing silicon crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for manufacturing a silicon crystal being grown by the Czochralski method, wherein the crack of a silicon crystal having a large diameter can be effectively suppressed. <P>SOLUTION: The silicon crystal is manufactured by a method, wherein use is made of an apparatus for manufacturing a silicon crystal where a heat shielding body and a cooling body are provided around a crystal being pulled, and the thermal stress of a growing crystal at 1,100-900°C is less than 40 MPa in Mises's equivalent stress. When a silicon crystal is grown by using the apparatus and a dislocated and thus polycrystalline portion is formed, the silicon crystal portion is separated from a molten liquid as a portion having a length of (1/D)×3×10<SP>4</SP>(mm) or less, where D (mm) represents the diameter of the crystal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for manufacturing a silicon crystal by the Czochralski method (hereinafter abbreviated as “CZ method”), and more particularly, generation of cracks in a large-diameter silicon crystal grown by the CZ method. The present invention relates to a silicon crystal manufacturing method and a manufacturing apparatus to which the method can be applied.

  The most widely adopted method for manufacturing a silicon single crystal used for a semiconductor material silicon wafer is a method of pulling and growing a single crystal by the CZ method.

  In this CZ method, a seed crystal is dipped in a molten silicon in a quartz crucible and pulled up to grow a single crystal. With respect to this silicon single crystal, not only the reduction of defects corresponding to high integration of semiconductor devices but also the increase of crystal diameter in response to cost reduction and improvement of productivity is demanded. The product is shifting from a product having a diameter of 300 mm to a diameter of 400 mm.

  When the diameter of the single crystal to be grown increases, the surface area with respect to the volume of the crystal decreases, so that it becomes difficult to sufficiently remove the latent heat of solidification by solidification of the melt, and the pulling speed must be lowered. For this reason, a heat shield is usually installed around the single crystal to prevent the side surface of the single crystal being pulled up from being heated by the radiant heat from the melt surface, the inner wall of the crucible, or the heating element for melting and heating. It is well known that measures to do this are adopted.

  Furthermore, as disclosed in, for example, Patent Documents 1, 2, or 3, an annular cooling body that is forcibly cooled, such as water cooling, is placed near the surface of the single crystal inside the thermal shield, It has also been proposed to further increase the cooling speed by increasing the cooling speed.

  Further, in Patent Document 4, etc., the surface cooling conditions are changed by the combination of the heat shield and the cooling body, the temperature distribution inside the single crystal immediately after solidification is controlled, and oxygen precipitation, atomic vacancies and interstitial atoms are controlled. There is also disclosed a manufacturing method that attempts to suppress the occurrence of grown-in defects or the like of a wafer grown from a single crystal by changing the distribution of the above.

  When forced cooling using a cooling body is performed in order to improve the pulling speed, especially in large-diameter crystals having a diameter of 300 mm or more, cracks are likely to occur during crystal growth, and tend to dislocation and polycrystallize. In contrast, Patent Document 5 discloses an invention relating to a manufacturing method as a countermeasure.

  Specifically, in the invention disclosed in Patent Document 5, when the forced cooling is performed and the high-speed pulling is performed, it is assumed that the cause of cracks occurring in the single crystal is an increase in thermal stress at the solid-liquid interface. This is a method for forcibly cooling the crystal lower part and forcibly heating the lower part of the crystal below the cooling part.

JP-A 63-256593 JP-A-8-239291 JP 11-292684 A JP 2001-220289 A JP 2003-165791 A

  When a silicon crystal is grown by the CZ method, a cooling body is arranged around the crystal being pulled to speed up the cooling, thereby improving the pulling speed and controlling the generation of defects inside the crystal. Yes. The means for disposing the cooling body and actively removing heat from the crystal becomes essential and important as the diameter of the crystal to be pulled increases. However, if the cooling is not performed appropriately, not only the pulling speed can be improved, but also there is a risk of crystal cracking.

  This crystal cracking is presumed to be caused by thermal stress generated inside the crystal being grown, but it is often confirmed that it occurs before the crystal is grown and cut into blocks. Further, it may occur during the pulling of the crystal, and in the worst case, if it occurs during the pulling or taking out from the apparatus and it is broken, there is a risk of leading to a serious accident.

  The present invention has been completed in view of such a situation, and a silicon crystal manufacturing method and a manufacturing apparatus thereof capable of effectively suppressing cracking of a large-diameter silicon crystal manufactured by the CZ method. The purpose is to provide.

  In order to solve the above-mentioned problems, the inventors of the present invention, when growing a silicon crystal having a diameter of about 300 mm or more, have a pulling speed by installing a cooling body close to the single crystal being pulled. Various studies were conducted on improvement.

  By installing the cooling body, the lifting speed can be increased. However, when a cooling body is installed with a large-diameter crystal and pulled up, it was often found that the crystal was cracked when it was cut into blocks after the completion of the pulling.

  In the worst case, if this crack occurs during the pulling, not only can the pulling not continue, but depending on the situation, the cooling body may be damaged and the cooling water will flow into the furnace, resulting in a serious accident such as a steam explosion. There is a risk of connection. Moreover, even if it occurs after the end of the pulling, there is a risk that productivity may be lowered, such as ensuring the safety of the worker and reducing the yield of non-defective products due to the progress of cracks.

  According to Patent Document 5, when the crystal diameter is 300 mm or more in single crystal growth by the CZ method, the thermal stress at the solid-liquid interface of the crystal increases when forced cooling is performed by installing a cooling body to increase the pulling speed. This causes dislocation or crystal cracking. And as a countermeasure, a manufacturing method has been proposed in which a heating body is placed under the cooling section along with the installation of the cooling body to keep the lower part of the crystal warm.

  When the cause of this crystal cracking is investigated further in detail, all the cracked crystals are dislocated and polycrystallized during or at the end of the pulling, and the crack changes from a single crystal to a polycrystal. It turns out that it has a starting point in the area. In particular, after the completion of the growth, the occurrence of cracks became apparent upon removal.

  In Patent Document 5, cracking is prevented during crystal growth, and attention is paid to thermal stress at the solid-liquid interface. However, the occurrence of crystal cracking after the completion of the growth is caused by thermal stress in the crystal. If the thermal stress state is changed by changing the temperature distribution inside the crystal being pulled by changing the shape or installation position of the cooling body, the heat in the temperature range of 1100 to 900 ° C. during the pulling It was found that the frequency of cracking tends to increase as the stress increases. In particular, in a crystal having a high thermal stress in this temperature range, even if no crack is found immediately after pulling, the crack is caused by a slight impact during transportation.

  The reason why the thermal stress in the temperature range of 1100 to 900 ° C. greatly affects the occurrence of cracking can be estimated as follows. Thermal stress is generated by thermal contraction during the cooling process, and its magnitude is determined from the elastic modulus, thermal expansion coefficient, crystal size, Poisson's ratio, etc. of silicon at that temperature due to the temperature distribution or temperature gradient of the growing single crystal.

  In general, the yield strength of metal materials decreases at high temperatures and plastically deforms before cracking occurs.However, in the case of a silicon single crystal, dislocations increase and dislocation density increases when plastic deformation occurs. Cooling is performed so that the thermal stress caused by the heat shrinkage does not exceed the yield strength at which plastic deformation begins. Since the yield strength is low at high temperatures, plastic deformation occurs even if the temperature gradient is large, so that thermal stress that causes cracking does not occur.

  However, with silicon single crystals, the yield strength increases at temperatures below about 1000 ° C. For this reason, since the yield strength of the single crystal portion is large, the strain is resolved immediately when it is added without plastic deformation, but the polycrystalline portion is easily plastically deformed at a temperature higher than 1000 ° C., and creep is reduced when stress is added. Due to the phenomenon, distortion decreases with time.

  However, since the plastic deformation cannot be easily performed at a temperature lower than 1000 ° C. and the strain remains, the strain generated at around 1000 ° C. remains as the temperature is lowered. Distortion also increases. Further, although the strain is formed so as to be balanced at the high temperature portion, if the strain does not return to its original state, the balance cannot be balanced after cooling, and stress is generated as a residual stress.

  At this time, since the single crystal part and the polycrystalline part in which the remaining strain greatly differs in the vicinity of the dislocation are adjacent to each other, the stress increases due to the difference in strain. From this point of view, the deformation behavior of the dislocation portion and the single crystal portion are greatly different, and the generated thermal stress is not increased in the temperature range around 1000 ° C. where the thermal stress due to thermal shrinkage increases. We thought that it would be possible to prevent the occurrence of cracks, and we proceeded with experiments and studies.

  As a result, it has been found that if the thermal stress generated in the crystal at 900 to 1100 ° C. is regulated to a value equal to or less than the equivalent stress indicated by the Mises yield condition formula, the occurrence of cracks in the grown crystal can be greatly reduced. It is.

  It was found that the cracked crystals were dislocated and polycrystallized in the middle or at the end of the pulling, and were polycrystallized, and there was a crack initiation point in the transition region from single crystal to polycrystal. In the transition region, it is presumed that the shear stress due to the difference in thermal shrinkage between the upper single crystal portion and the lower polycrystalline portion acts to cause cracks.

  Therefore, when dislocations occur, if the polycrystalline part is shortened, it is considered that the shear stress generated in the transition region is relaxed and the occurrence of cracks can be reduced. Even if the starting point of the crystal crack is in the transition region, the crack propagates to the single crystal portion, and the sampling rate of the healthy portion is lowered.

  Therefore, after the occurrence of dislocations, after growing the polycrystal for a while and then separating it from the melt, growing the crystals with various lengths of the polycrystal part and examining the occurrence of cracks, It becomes clear that the frequency of occurrence of cracks can be greatly reduced if the thickness is reduced to some extent.

The present invention has been completed based on the above examination results, and the gist thereof is the following silicon crystal manufacturing method and silicon crystal manufacturing apparatus.
(1) When pulling up a silicon crystal by the CZ method, the value of thermal stress in the temperature range of 1100 to 900 ° C. of the crystal being grown is raised to less than 40 MPa in Mises' equivalent stress, It is a manufacturing method.
(2) A crystal manufacturing apparatus for pulling up a silicon crystal by the CZ method, wherein the crystal being grown is being pulled so that the thermal stress in the temperature range of 1100 to 900 ° C. is less than 40 MPa at Mises equivalent stress. The silicon crystal manufacturing apparatus is characterized in that a heat shield and a cooling body are arranged around the crystal.
(3) When a silicon crystal is grown by the CZ method, when dislocations are formed during pulling, the length of the polycrystalline portion from the dislocation position is (1 / D) × with respect to the crystal diameter D (mm). The silicon crystal production method is characterized in that the silicon crystal is separated from the melt as 3 × 10 ⁴ (mm) or less.
(4) In the silicon crystal manufacturing method of (1) above, when dislocations are formed during pulling, the length of the polycrystalline portion from the dislocation position is (1 / D) relative to the crystal diameter D (mm). ) × 3 × 10 ⁴ (mm) or less, wherein the silicon crystal is separated from the melt.
(5) The method for producing a silicon crystal according to (1), (3) or (4) above, wherein the crystal to be grown has a large diameter, for example, a diameter of 300 mm or more.

  According to the method and apparatus for manufacturing a silicon crystal of the present invention, it is effective in suppressing the occurrence of crystal cracking during and after pulling in the manufacture of silicon crystal by the CZ method. As the diameter of the silicon crystal that is pulled up increases, the risk of cracking increases, but not only can the occurrence of defective products due to crystal cracking be reduced, but also the occurrence of accidents due to cracking during the pulling can be suppressed, reducing costs. And greatly contribute to the improvement of safety.

  The silicon crystal manufacturing method and manufacturing apparatus of the present invention have been clarified by limiting conditions based on the above examination results, and have been completed. The contents thereof will be described below. First, in the present invention, when pulling up a silicon crystal by the CZ method, the value of the thermal stress in the temperature range of 1100 to 900 ° C. of the crystal being grown is pulled as less than 40 MPa in Mises equivalent stress.

  The reason why the value of the equivalent stress of Mises in this temperature range is limited to less than 40 MPa is that the occurrence of cracks increases when the value is 40 MPa or more. The smaller the value of the equivalent stress is, the more cracking can be reduced. However, there is a limit to lowering the value of the equivalent stress, and for that purpose, during the pulling, the cooling of the crystal is relaxed and the pulling rate is greatly slowed, resulting in a decrease in productivity. It is good to do it. Desirable is 30 to 36 MPa.

  Thermal stress is generated by thermal contraction during the cooling process. The magnitude of the heat shrinkage can be obtained from the temperature distribution in the crystal, and the temperature distribution in the crystal can be estimated by a commonly used computer simulation such as comprehensive heat transfer analysis software.

The equivalent stress of Mises specified in the present invention is, for example, the stress in each direction by computer simulation generally used, such as general-purpose structural analysis software by a finite element method, etc. The elastic modulus at 1100 ° C. is 190 GPa, the coefficient of linear expansion is 4 × 10 ⁻⁶ / K, the density is 2.33 kg / m ³ , the Poisson's ratio is 0.23, and the obtained stress is obtained by converting it into principal stress. be able to. Specific examples of general-purpose structural analysis software using the finite element method include ABAQUS (ABAQUS), ANSYS (CYBERNET SYSTEM), and the like.

  The reason why the equivalent stress of Mises is less than 40 MPa only in a temperature range of 900 to 1100 ° C. during pulling is that, as described above, only polycrystals are plastically deformed in a high temperature range of 900 to 1100 ° C. This is because plastic deformation does not occur on the side regardless of a single crystal portion or a polycrystalline portion.

  FIG. 1 is a diagram showing a schematic structure of a silicon crystal manufacturing apparatus including a heat shield and a cooling body to which the present invention can be applied. The silicon crystal manufacturing apparatus in which the equivalent stress of Mises inside a single crystal in the temperature range of 900 to 1100 ° C. of the present invention is less than 40 MPa is the structure shown in FIG. As long as it has a structure in which the cooling body 10 is installed so as to surround the crystal 7 being pulled up.

  The cooling body 10 has a distance from the single crystal surface to the cooling body surface in the range of 30 to 80 mm, a length in the pulling axis direction of 50 to 180 mm, and a distance between its lower end and the melt surface of 170 to 300 mm. Thus, the temperature of the surface facing the crystal may be 50 to 220 ° C. The shape, position, and surface temperature of the cooling body 10 are adjusted, and the pulling rate is controlled so that the equivalent stress at the 900 to 1100 ° C. portion of the crystal is less than 40 MPa.

  In the present invention, the thermal stress is defined by the equivalent stress of Mises, but is not limited to this, and can be defined by, for example, the equivalent stress of Tresca or the stress in the slip direction. When the thermal stress value obtained by the above corresponds to the Mises equivalent stress defined in the present invention, the range is defined in the present invention.

In the present invention, when a silicon crystal is grown by the CZ method, when dislocation occurs during the pulling and the growth is interrupted, the length of the polycrystalline portion from the dislocation position is set to the crystal diameter D ( mm), it is assumed to be (1 / D) × 3 × 10 ⁴ (mm) or less and separated from the melt.

  This is because the progress of dislocation formation depends on the thermal stress at the solid-liquid interface. For example, if the crystal has a diameter of 300 mm, the polycrystalline portion is within 100 mm, and if the diameter is 400 mm, the polycrystalline portion is within 75 mm. Means to. In this way, when dislocations and polycrystals occur during the growth of a single crystal, the length of the portion is limited, but if it is long, cracks are likely to occur, but if it is short, the transition region between the single crystal portion and the polycrystalline portion This is because the generation of crack starting points is suppressed and cracks do not occur.

  This limiting condition from the dislocation position is effective in preventing cracking even in the case of large-diameter crystal growth in the normal CZ method, but is equivalent in the temperature range of 900 to 1100 ° C. which is the production method of the present invention. It is more effective if applied to a silicon crystal manufacturing method in which stress is limited.

  Moreover, although the specified contents of the present invention are described for a silicon crystal having a diameter of 300 mm, these limiting conditions are effective even when applied to a crystal having a larger diameter of 400 mm or more. Not too long.

Example 1
Using the silicon crystal manufacturing apparatus having the structure schematically shown in FIG. 1 provided with a heat shield and a cooling body, the pulling rate from the melt of 420 kg is 0.6 mm / min, the diameter is 300 mm, and the length of the straight body A test was conducted in which four 550 mm crystals were repeatedly grown under the same conditions.

  As the growth conditions, the distance from the melt surface at the lower end of the heat shield 11 is fixed to 60 mm, the length of the cooling body 10 arranged around the crystal 7 at a distance of 120 mm from the surface, and the melt surface at the lower end. The temperature distribution in the crystal 7 was changed by changing the position from the surface and the surface temperature of the cooling body. These cooling body conditions are shown in Table 1.

  The temperature distribution in the crystal is estimated using comprehensive heat transfer analysis software, and the stress component in each direction within the range of 900 to 1100 ° C. obtained by that is numerically analyzed, and the stress component is converted into Mises equivalent stress. Asked. The maximum equivalent stress in this temperature range causes crystal cracking. The obtained stress values are shown together in Table 1.

  In either case, during the pulling, when the length of the cylinder reached 400 mm, a minute quartz piece was dropped on the melt surface to cause dislocation. After the completion of the pulling, it was cut into blocks, and a crystal in which cracking occurred or a crack was detected was regarded as a crystal in which cracking occurred. Table 1 shows the number of cracked crystals.

As is apparent from the results in Table 1, when the equivalent stress of Mises generated in the crystal at 900 to 1100 ° C. is 40 MPa or more, four out of four cracks are generated.
(Example 2)
Using the manufacturing apparatus with the cooling body condition of test number 2 in Example 1, changing the pulling speed and the distance between the lower end of the heat shield 11 and the melt surface, crystals having a diameter of 300 mm and a length of 550 mm were set to the same conditions. The test which raises 4 pieces repeatedly was done.

  Table 2 shows the pulling speed and the distance between the lower end of the heat shield and the melt surface. The equivalent stress of Mises at 900 to 1100 ° C. was obtained in the same manner as in Example 1, and after making the dislocation at 400 mm, the results of examining the number of occurrence of cracks are shown in Table 2.

As is clear from the results in Table 2, even when the equivalent stress was changed by changing the pulling speed and the position of the heat shield, cracks occurred up to three out of four when the equivalent stress was 40 MPa or more. If the stress is less than 40 MPa, it can be seen that no cracks have occurred.
(Example 3)
Using the manufacturing apparatus of the cooling condition of test number 7 of Example 1, a single crystal having a diameter of 300 mm was grown up to a length of 800 mm at a pulling rate of 0.6 mm / min, and at that time, a minute crystal was formed on the melt surface. The quartz piece was dropped on the melt surface to cause dislocation, and after changing the length of the polycrystallized portion from the position, the crucible was lowered and separated from the melt. In this case as well, as in the previous example, the growth was repeated 4 times under the agreed conditions, and the number of cracks was investigated.

The results are shown in Table 4, and cracking occurs if there is a polycrystalline portion. Even under the growth conditions where the equivalent stress at 900 to 1100 ° C. is 40 MPa, the length of the polycrystalline portion is the crystal diameter D ( It is clear that cracks do not occur if (1 / D) × 3 × 10 ⁴ (mm) or less, that is, 100 mm or less, and cracks tend to occur if the thickness exceeds 100 mm.

  According to the method and apparatus for manufacturing a silicon crystal of the present invention, it is effective in suppressing the occurrence of crystal cracking during and after pulling in the manufacture of silicon crystal by the CZ method. As the diameter of the silicon crystal that is pulled up increases, the risk of cracking increases, but not only can the occurrence of defective products due to crystal cracking be reduced, but also the occurrence of accidents due to cracking during the pulling can be suppressed, reducing costs. It can greatly contribute to the improvement of safety and can be widely used in the field of manufacturing semiconductor wafers.

It is the figure which showed the typical structure of the manufacturing apparatus of the silicon crystal provided with the heat shielding body and cooling body which can apply this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Heat insulating material 2: Support shaft 3: Heating heater 4: Crucible tray 5: Quartz crucible 6: Silicon melt 7: Silicon growth crystal 8: Pulling shaft 9: Seed crystal chuck 10: Cooling body 11: Heat shield

Claims (5)

  Production of silicon crystal characterized by raising the value of thermal stress in the temperature range of 1100 to 900 ° C. of the crystal being grown to less than 40 MPa at Mises equivalent stress when pulling up the silicon crystal by the Czochralski method Method.   A crystal manufacturing apparatus for pulling up a silicon crystal by the Czochralski method, wherein the crystal being pulled is such that the thermal stress in the temperature range of 1100-900 ° C. of the crystal being grown is less than 40 MPa at Mises equivalent stress. An apparatus for producing a silicon crystal, characterized in that a heat shield and a cooling body are arranged around the substrate. When growing a silicon crystal by the Czochralski method, when dislocations are formed during pulling, the length of the polycrystalline portion from the dislocation position is (1 / D) × 3 with respect to the crystal diameter D (mm). The manufacturing method of the silicon crystal characterized by cut | disconnecting from a melt as x10 < ⁴ > (mm) or less. In the method for producing a silicon crystal according to claim 1, when dislocations are formed during the pulling, the length of the polycrystalline portion from the dislocation position is (1 / D) × with respect to the crystal diameter D (mm) × The method for producing a silicon crystal, wherein the silicon crystal is separated from the melt as 3 × 10 ⁴ (mm) or less. The diameter of the crystal to grow is 300 mm or more, The manufacturing method of the silicon crystal of Claim 1, 3 or 4 characterized by the above-mentioned.

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