JP2001106591A - Method for producing cz silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high quality single crystal having a large diameter and a long size, which is almost free from Grown-in defects such as COP or dislocation cluster. SOLUTION: This method of producing a single crystal comprises pulling up the single crystal under the condition such that, when the temperature T( deg.C) at the center part of the single crystal being pulled up is in the range of >=1,230 deg.C, the Gc/Gp satisfies formulas: Gc/Gp>=-0.007T+10.62 (when T is >1,360 deg.C) and Gc/Gp>=1 (when T is in the range of 1,230 to 1,360 deg.C), wherein Gc ( deg.C/mm) is the temperature gradient in the direction of a pulling-up shaft at the center part of a plane perpendicular to the pulling-up shaft and Gp ( deg.C/mm) is the temperature gradient in the direction of the pulling-up shaft at the peripheral part of the plane perpendicular to the pulling-up shaft, at the temperature T. Such temperature condition is realized by arranging a heat shielding material, whose inner diameter becomes larger toward the upper direction, at the peripheral part of the single crystal being pulled up in such a manner that a space is provided between the lower end of the heat shielding material and the surface of a melt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a silicon single crystal for a silicon wafer used as a semiconductor material, and more particularly to a method for producing a silicon single crystal for a wafer grown by the Czochralski method (hereinafter referred to as CZ method).

[0002]

2. Description of the Related Art The most widely adopted method for producing a silicon single crystal used for a silicon wafer of a semiconductor material is a pulling and growing method of a single crystal by a CZ method.

In the CZ method, a seed crystal is immersed in molten silicon in a quartz crucible, pulled up, and a single crystal is grown. Large single crystals are being manufactured. A semiconductor device is manufactured as a substrate using a wafer obtained from a single crystal as a substrate and passing through many processes. In the process, the substrate is subjected to a number of physical, chemical, and thermal treatments, including treatments in harsh thermal environments, such as high-temperature treatments exceeding 1150 ° C. For this reason, defects such as oxygen precipitates that become apparent during the device manufacturing process and reduce the performance thereof are formed during crystal growth, as well as defects such as oxygen precipitates.
Fine defects that greatly affect device performance, namely Gr
Own-in defects are a problem.

[0004] The distribution of typical Grown-in defects is observed, for example, as shown in FIG. This is because a wafer is cut out of a single crystal just after growth, immersed in an aqueous solution of copper nitrate, and
FIG. 7 is a diagram schematically showing the result of observing a minute defect distribution by X-ray topography after adhering u and heat treatment. This wafer has a ring-shaped distribution of oxygen-induced stacking faults-OSF (Oxygen induced Stacking Fault)
The inner part of the ring has a COP (Crystal Originated) of about 0.1 μm in size.
Particles) are detected at about 10 ⁵ to 10 ⁶ defects / cm ³ . There is an oxygen precipitation region immediately outside the ring-shaped OSF, where an oxygen precipitate is liable to be formed. However, outside the oxygen precipitation region, there is an oxygen precipitation suppression region where oxygen precipitation hardly occurs. Outside thereof, there are about 10 ³ to 10 ⁴ defects / cm ³ called dislocation clusters having a size of about 10 μm. These COPs and dislocation clusters are called Gronn-in defects.

[0005] The position where the above-mentioned defect is generated is largely affected by the pulling speed in the normal single crystal pulling. For example, when a single crystal grown while gradually lowering the pulling speed is examined for the distribution of various defects in a cross section cut in the longitudinal direction along the pulling axis at the center of the crystal, it is schematically shown in FIG. Results are obtained. After forming the shoulder portion to obtain the required single crystal diameter and then lowering the pulling speed, when looking at the surface of the plate-shaped test piece cut out perpendicular to the pulling axis, first, the ring-shaped OSF is formed from the crystal periphery. appear. The diameter of the ring-shaped OSF appearing in the peripheral portion gradually decreases as the lifting speed decreases,
Eventually, the entire surface of the wafer will correspond to the outer portion of the ring-shaped OSF. That is, FIG.
2 shows a single crystal wafer grown at the position A in FIG. 2 or at this pulling speed.

It is well known that dislocations in a silicon single crystal cause deterioration of characteristics of a device formed thereon. The OSF deteriorates electrical characteristics such as an increase in leakage current, and the ring-shaped OSF exists at a high density. Therefore, for ordinary LSIs at present, single crystals are grown at a relatively high pulling rate such that the ring-shaped OSF is distributed on the outermost periphery of the single crystal. Thereby, the generation of dislocation clusters is avoided by setting the majority of the wafer inside the ring-shaped OSF. This is because the inner portion of the ring-shaped OSF has a greater gettering effect on heavy metal contamination generated during the manufacturing process of the device than the outer portion.

In recent years, as the degree of integration of LSIs has increased, the gate oxide film has been thinned, and the temperature in the device manufacturing process has been lowered. For this reason, OSF, which is likely to be generated by high-temperature treatment, is reduced, and the problem of OSF such as a ring-shaped OSF as a factor for deteriorating device characteristics has been reduced due to low oxygen content of the crystal. Also, a ring-shaped OS
In order to reduce the COP density in the F inner portion, a method of gradually cooling a temperature region near 1100 ° C. where the defect is formed is also adopted. However, the slow cooling reduces the defect density but increases the size of the defect. The existence of COP
It is said that the withstand voltage characteristic of the thinned gate oxide film is greatly deteriorated. However, it is said that, particularly when the device pattern becomes finer, the effect becomes large and it becomes difficult to cope with high integration. In order not to generate such COP,
By lowering the pulling speed and growing at the position shown in FIG. 2B or at the pulling speed, the ring-shaped OSF can be eliminated at the center of the wafer, but dislocation clusters occur instead. come.

In the defect distribution shown in FIG. 1, the ring-shaped OSF region, the oxygen precipitation region, and the oxygen precipitation suppression region are regions in which no Grown-in defect exists. Wafer or a single crystal may be obtained. For example, in Japanese Patent Application Laid-Open No. 8-330316, the pulling speed at the time of growing a single crystal is V (mm / min), and the temperature gradient in the pulling axis direction in the temperature range from the melting point to 1300 ° C. is G (° C. /
mm), V / G is set to 0.20 to 0.22 at the inner position from the outer periphery to 30 mm from the center of the crystal, and the temperature gradient is controlled so as to gradually increase toward the outer periphery of the crystal to generate dislocation clusters. There has been proposed an invention of a method in which only the defect-free region outside the ring-shaped OSF is extended over the entire surface of the wafer and further over the entire single crystal without performing the above operation. In this case, the position of the crucible and the heater, the position of the semi-conical heat radiator made of carbon placed around the grown single crystal,
Various conditions such as the structure of the heat insulator around the heater are examined by comprehensive heat transfer calculation, and the temperature is set to the above condition, and the growth is performed.

Japanese Patent Application Laid-Open No. 11-79889 discloses that the shape of the solid-liquid interface during the growth of a single crystal is within ± 5 mm with respect to the average position of the solid-liquid interface except for 5 mm around the single crystal. When the temperature gradient in the crystal in the pulling axis direction from 1420 ° C. to 1350 ° C. or from the melting point to 1400 ° C. is Gc at the center of the crystal and Ge at the periphery of the crystal, the difference ΔG between these two temperature gradients (= Ge-Gc) is 5
An invention of a manufacturing method by controlling the furnace temperature so as to be within ° C / cm is disclosed. In short, this is a manufacturing method in which the solid-liquid interface during growth is kept as flat as possible and the temperature gradient from the solid-liquid interface inside the single crystal is kept as uniform as possible. By growing a single crystal under such conditions, the defect-free region can be expanded, and
By applying the above horizontal magnetic field to the melt, a single crystal with few Grown-in defects can be obtained more easily.

[0010] It is believed that the COP or dislocation cluster of a Grown-in defect is both derived from a point defect in the crystal. When the melt is solidified at the time of pulling the single crystal, vacancies of point defects and interstitial Si atoms taken into the solid phase disappear by diffusion or bonding in a cooling process after solidification.
However, if they remain supersaturated, the vacancies will
P causes interstitial Si atoms to cause dislocation clusters. That is, the inner region of the ring-shaped OSF is cooled with excess vacancies, the outer region is cooled with excess interstitial Si atoms, and the above region is reduced to a region where the number of vacancies and the degree of supersaturation of interstitial Si atoms are reduced. A defect-free area occurs. Therefore, it is necessary to diffuse and eliminate these point defects as quickly as possible after solidification, and to reduce the degree of supersaturation.At the same time, the number of vacancies and the number of interstitial Si atoms are balanced as widely as possible, and during the cooling process, Eliminating the bond is also considered effective in expanding the defect-free region.

The above-mentioned method for controlling the distribution in the crystal from the melting point to 1300 ° C. with respect to the temperature gradient in the pulling axis direction,
A method to make the temperature gradient as uniform as possible between 20 ° C and 1350 ° C seems to control the behavior of such vacancies and interstitial atoms, but it is not necessarily stable.
In defects have not been reduced to the whole crystal.

[0012]

SUMMARY OF THE INVENTION The present invention provides a COP by controlling a temperature gradient in a pulling axis direction of a single crystal.
It is an object of the present invention to provide a single crystal production method capable of stably producing a large-diameter, long, high-quality single crystal capable of collecting a wafer with as few Grown-in defects as possible, such as crystal and dislocation clusters.

[0013]

SUMMARY OF THE INVENTION In pulling a single crystal, in order to accelerate cooling and increase the pulling speed,
In order to prevent the single crystal surface immediately after solidification from receiving heat radiation from the crucible wall surface or the melt surface, a method of surrounding the single crystal with a heat shielding material has been adopted. The temperature distribution inside the single crystal changes depending on how the heat shield is used. The present inventors have found that the difference in the temperature gradient in the single crystal pulling axis direction depending on the location inside the single crystal affects the behavior of the vacancies and interstitial Si atoms taken in, which causes the expansion of the defect-free region of the single crystal. Since it is considered possible, various possibilities for reducing the Grown-in defects by covering the periphery of the single crystal immediately after pulling with a heat shield were examined.

When a heat shielding material is used, it is considered that the distance from the single crystal surface, the thickness, the height, the distance from the melt surface, the shape, the material, and the like variously affect the temperature distribution. Therefore, first, a thermocouple was embedded in the single crystal during the pulling, and the temperature change accompanying the pulling was measured. In this case, a single crystal in the middle of pulling is prepared by cutting the lower part perpendicularly to the pulling axis, and through-holes are provided in the central part, intermediate part, peripheral part, etc. in the axial direction parallel to this, and this hole is used for the quartz glass protective tube The inserted thermocouple was inserted so that the tip thereof protruded about 50 mm from the lower surface, and the thermocouple was set in a single crystal pulling apparatus, allowed to blend in with the melt, then pulled, and the temperature was detected.

[0015] Along with the actual measurement by embedding the thermocouple,
Normally, the temperature is obtained by a comprehensive heat transfer calculation method used for predicting the temperature distribution during the pulling of such a single crystal, and the temperature is compared with the actually measured value to correct the difference between the actually measured value and the calculated temperature indication value, The calculated prediction was made to match the measured value. At the same time, the heat shield was also installed with its size, shape, and position changed, and the change in the temperature distribution in the single crystal due to the change was investigated. From these results, it was confirmed that the temperature distribution in the single crystal during the pulling can be estimated almost accurately by calculation. Furthermore, the temperature distribution in the single crystal caused by the structure of the pulling device, the heating method, the heat shielding material, etc. However, it was found that the same state was maintained even when the single crystal was growing, and that it did not change significantly even when the pulling speed was different.

Based on these results, since a healthy single crystal cannot be obtained by inserting a thermocouple, the size, shape, and shape of the heat shielding material are checked while confirming the temperature distribution inside the single crystal by thermal calculation.
The single crystal was pulled while the pulling speed was continuously changed while changing the installation position, and the distribution of each defect was investigated in a longitudinal section including the pulling axis of the single crystal.

Although there are various ways of expressing the temperature distribution inside the single crystal during pulling, it is point defects of vacancies and interstitial Si atoms that are related to the generation of Grown-in defects. Influencing is the temperature and the vertical temperature gradient. Therefore, on the surface perpendicular to the pulling axis, that is, on the surface equivalent to the wafer, the relationship between the temperature at the center and the temperature gradient in the vertical direction of the center and the periphery was determined, and the relationship with the defect occurrence was determined. . In this case, the peripheral part for which the temperature gradient is to be calculated is not the single crystal surface but the surface
The outer peripheral position of the final product as a wafer, which is within about 5 mm.

FIG. 3 shows an example of the examination result. this is,
The temperature T at the center of the single crystal being pulled is taken on the horizontal axis, and the vertical axis represents the vertical temperature gradient Gc at the center and the vertical temperature gradient Gp at the position showing the same temperature as the center of the peripheral portion. The ratio, Gc / Gp, is taken.

The line A in the figure indicates that the cylindrical heat shield material concentric with the vertical axis disposed around the single crystal during pulling is brought close to the single crystal, and the lower end thereof is brought as close as possible to the melt surface. This is a case where the heating by the heat radiation from the crucible wall is suppressed. In this case, in a high temperature range of 1360 ° C. or more, the value of Gc / Gp is 1.
It is lower than 0, indicating that in this temperature range, the periphery is more cooled than the crystal center. However, at a temperature lower than this, the value of Gc / Gp is larger than 1.0, and it can be seen that the peripheral part is harder to cool than the central part. This is because the heat-shielding material is nearby, so the heat retention effect is considered to have been achieved. In this state of temperature distribution in the crystal, the pulling speed was increased from 1.0 mm / min to 0.3 mm / min.
FIG. 4 shows the result of investigation of the defect distribution in the vertical cross section after the temperature was gradually lowered. This result is not significantly different from the result shown in FIG. 2 when the lifting is performed without using any heat shielding material or the like.

Next, the same heat shielding material is used, and the distance between the lower end and the melt is increased so that the single crystal surface immediately after the pulling is heated by heat radiation. An example of the value of Gc / Gp is shown in FIG. In this case, at a temperature higher than 1340 ° C., the value of Gc / Gp is larger than that of A, but at around 1300 ° C., the value of Gc / Gp is less than 1.0. It seems that the effect of cooling by the material appeared.
As described above, the value of the temperature gradient ratio Gc / Gp with respect to the crystal center temperature can be variously changed depending on the position of the heat shielding material. However, in the temperature distribution of FIG. Also, the results of the investigation of the distribution did not greatly differ from the results shown in FIG.

However, by changing the distance of the heat shield from the single crystal surface, the distance from the melt surface at the lower end, and the shape of the heat shield, Gc / Gp for T is variously changed, and the pulling speed is increased. As a result of attempting to pull down a single crystal gradually, it has become clear that the distribution of defects may be greatly changed. Therefore, as a result of further studying the possibility that the wafer surface can be free of a Grown-in defect, the value of Gc / Gp in FIG. 3 is always set to be higher than the broken line shown in FIG. It turns out that it can be realized.

Whether the value of Gc / Gp is substantially the same as the broken line in FIG.
FIG. 5 shows an example of a defect distribution of a single crystal which is pulled up while its speed is reduced in a state slightly above. In this case, it is impossible to obtain a wafer in which the ring-shaped OSF completely disappears and in which no dislocation cluster is generated. However, since no Grown-in defect is generated on the ring-shaped OSF, the ring-shaped OSF remains at the center portion by selecting a pulling speed between w and x in FIG. Can be no wafer. Furthermore, if the value of Gc / Gp can be made sufficiently larger than the broken line, a defect-free wafer without OSF can be obtained.

This dashed line indicates that when T exceeds 1360 ° C., G
c / Gp = -0.007T + 10.62, Gc / Gp =
1.0. Therefore, in FIG. 3, Gc / Gp is above the broken line when T> 1360 ° C. Gc / Gp ≧ −0.007T + 10.62... When T = 1230 to 1360 ° C. Gc / Gp ≧ 1.0・ ・ ・ ・ ・

As described above, when the temperature distribution satisfying the above equation is realized, the pulling speed at which a wafer having no Grown-in defect over the entire surface between w and x shown in FIG. It is not clear why it appears.

As described above, it is considered that the regions where the Grown-in defects occur and the regions where these defects do not occur appear due to the balance of the number of vacancies and interstitial Si atoms. When the melt at the time of pulling a single crystal solidifies and changes to a solid crystal, it transitions from a liquid phase with a random atomic arrangement to a solid phase in which atoms are regularly arranged. There are a large number of interstitial Si atoms in which vacancies that should be Si atoms are missing or extra Si atoms have entered between the crystal lattice arrangements of Si. Then, as the portion solidified into a single crystal by pulling away from the solid-liquid interface, the vacancies and interstitial Si atoms disappear due to movement, diffusion, bonding, or the like, and an ordered atomic arrangement is formed.

The number of vacancies and interstitial Si atoms taken in at the solid-liquid interface are different from each other, and the diffusion rates are also different. Further, the temperature gradient in the single crystal immediately after solidification greatly affects the diffusion of these vacancies and interstitial Si atoms. Generally, it is considered that the saturation equilibrium concentration of vacancies or interstitial Si atoms in solid silicon is higher as the temperature is higher, and lower as the temperature is lower. Therefore, when the same amount is present, the lower the temperature, the higher the substantial concentration, and the vacancies and interstitial Si taken in during the solidification process are increased.
In addition to normal diffusion of atoms due to a concentration difference, diffusion from a low temperature side to a high temperature side proceeds against a temperature gradient.
In addition, since these vacancies and interstitial Si atoms disappear when reaching the single crystal surface, the concentration near the surface is low and there is also diffusion from the inside to the surface.

At these high temperatures, the diffusion of various types and the bonding between vacancies and interstitial Si atoms are mainly diffusions that go against the temperature gradient. At low temperatures, bonding and diffusion to the surface proceed in addition to this. It is considered that the higher the temperature, the more active. As described above, by satisfying the expression at a temperature exceeding 1360 ° C. and satisfying the expression below 1360 ° C., a defect distribution as shown in FIG. 5 is obtained. This is probably due to the combination of such diffusion and bonding.

Next, the shape of the heat shield in which such a temperature distribution in the single crystal was stably obtained was examined. Factors to consider are the distance from the single crystal surface to the heat shield, the distance from the melt surface to the lower end of the heat shield, the material and thickness of the heat shield, and the like.

If there is no heat shielding material, or if there is any, the distance from the single crystal surface is too short, the relationship between T and Gc / Gp becomes close to A shown in FIG. Was not obtained at the same time. Assuming that the inner surface of the heat shielding material has a vertical cylindrical shape whose diameter does not change even if the height changes, the distance from the melt surface at the lower end portion is closer to A shown in FIG. Get closer,
This also does not provide a sufficient temperature distribution.

As a result of further study, as shown in FIG. 6, the shape of the heat shielding material is a funnel-like shape which is coaxial with the single crystal pulling axis and becomes larger as the distance from the single crystal surface increases. It has become clear that those having an inner surface of are preferred. This is placed away from the melt surface so that the surface of the single crystal immediately after being pulled up is heated by receiving heat radiation from the crucible wall and the melt surface. That is, the lower end of the heat shield is brought closer to the single crystal surface, the distance between the melt surface and the lower end is further increased, and the heat shield is separated from the single crystal surface as it goes upward. By selecting the lower end position of the heat shield, it is considered that a state in which the expression can be satisfied was obtained, and by moving the heat shield away from the surface, a state in which the expression was satisfied was obtained.

However, even if such a satisfactory state of T and Gc / Gp is obtained, if the pulling speed is not appropriate, a single crystal having no Grown-in defect over the entire surface of the wafer cannot be obtained. The optimal lifting speed without this defect is determined by the thermal conditions of the lifting device such as crucible shape, heater shape, heating conditions, hot zone shape, etc. other than the shape of the heat shielding material. It is necessary to change the selection.

Based on the above examination results, the present invention was completed by further clarifying the limit conditions. The gist of the present invention is as follows. (1) A method for producing a silicon single crystal which is pulled and grown by the Czochralski method (CZ method), wherein a temperature of a central portion of the single crystal during the pulling is T (° C.), and a pulling axis at a position indicating the temperature. Assuming that the temperature gradient with respect to the pulling-up axis direction is Gc (° C./mm) at the center and Gp (° C./mm) at the periphery, the ratio Gc / Gp of the vertical temperature gradient is A method for producing a silicon single crystal, characterized in that pulling is performed in the range of T ≧ 1230 ° C. while satisfying the following and formulas.

When T> 1360 ° C. Gc / Gp ≧ −0.007T + 10.62... When T = 1230 to 1360 ° C. Gc / Gp ≧ 1.0 (2) Czochralski method ( A method for producing a silicon single crystal which is pulled and grown by a CZ method, wherein a cylindrical heat shield coaxial with a pulling axis disposed around the single crystal to be pulled has a height of 200 to 400 mm and an inner surface at a lower end. Has a funnel-like shape whose distance from the single crystal surface is 20 to 60 mm and whose inclination with respect to the vertical direction is 10 ° to 30 °, and which increases as it goes upward, from the melt surface at the lower end surface of this heat shield. The height of
(1) The method for producing a silicon single crystal according to the above (1), wherein the silicon single crystal is pulled up to 50 to 110 mm. (3) By growing the single crystal by continuously changing the pulling speed, a pulling speed range where no Grown-in defect occurs in the cross section perpendicular to the pulling axis is found, and the single crystal is pulled at a speed within the range. The method for producing a silicon single crystal according to the above (1) or (2), wherein

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention is characterized in that, when the temperature at the center of a single crystal during pulling is defined as T (° C.), on a plane perpendicular to the pulling axis at a position indicating the temperature,
The temperature gradient in the pulling axis direction is Gc at the center.
(° C./mm) and Gp (° C./mm) in the peripheral portion, the ratio Gc / Gp of the vertical temperature gradient is in the range of T ≧ 1230 ° C. and the following condition is satisfied. , For pulling a single crystal.

When T> 1360 ° C. Gc / Gp ≧ −0.007T + 10.62... When T = 1230 to 1360 ° C. Gc / Gp ≧ 1.0... Gc / Gp falls within the above range. If it is not satisfactory, it is impossible to produce a single crystal in which almost no entire surface of the wafer surface perpendicular to the single crystal pulling axis has a Grown-in defect even if the pulling speed is changed variously. Gc / Gp may be large as long as the above expression and the expression are satisfied. However, in order to pull up a healthy single crystal, G
c / Gp is desirably up to about 1.5. In addition, the above and the formulas must all be satisfied in a continuous process in which the single crystal solidifies from the melt and cools.Even if only one formula is satisfied, the Grown-in defect is sufficiently reduced. I can't let it.

The temperature distribution inside the single crystal affects the generation of defects in a temperature range of 1230 ° C. or more, and any temperature distribution below this temperature may be used.

Here, the peripheral portion is an outer peripheral position of a final product as a wafer, which is about 3 to 5 mm from the surface of the single crystal. Such a temperature distribution inside the single crystal is obtained using a computer by a comprehensive heat transfer analysis method.
In order to make this estimated value more accurate, it is desirable to embed a thermocouple in a single crystal, measure the temperature, and correct the result by a computer.

In order to realize the above-described temperature distribution inside the single crystal during pulling, a cylindrical heat shield coaxial with the pulling axis is arranged around the single crystal. This heat shield has a height of 200 to 400 mm, the inner surface facing the single crystal has a distance from the single crystal surface at the lower end of 20 to 60 mm, and the inclination with respect to the vertical direction is 10 to 30 degrees. It has a funnel-shaped shape that increases, and the height of the lower end surface from the melt surface is set to 50 to 110 mm. A holding tool for fixing the heat shield at a required position is provided at a position far from the single crystal surface outside the inner diameter at the upper end and does not affect the temperature of the single crystal. It may be of a shape.

FIG. 6 schematically shows a state in which the heat shield is disposed in a lifting device. A dark shielding body 8 having a cylindrical shape and having a larger inner diameter as it goes upward like a funnel is provided coaxially with the single crystal 7 to be pulled, and the distance b between the lower end thereof and the melt surface is set to 50 to 50 mm.
Install as 110mm. If this distance b is less than 50mm,
This is because Gc / Gp cannot satisfy the condition of the above equation. If it exceeds 110 mm, even if Gc / Gp increases on the high temperature side, the equation cannot be satisfied when the single crystal temperature T approaches 1360 ° C.

The distance c of the lower end of the heat shield 8 from the single crystal surface is 20 to 60 mm, and the inner diameter of the lower end of the heat shield 8 is
This distance is added to the outer diameter of the single crystal. This is 60mm
In the following, Gc / Gc / Tc in the temperature range from more than 1360 ° C. to the melting point depends on the combination with the distance from the melt surface.
Gp is important for satisfying the equation. If Gp is larger than this, the condition of the equation cannot be maintained as in the case where b increases. However, if the distance is less than 20 mm, there is a risk of contact with the single crystal due to deformation during pulling.
mm or more.

The inner surface of the heat shield 8 has a funnel shape whose diameter becomes larger as it goes upward, and the diameter is widened with an inclination of 10 ° to 30 ° with respect to the inner surface of the cylinder perpendicular to the lifting axis. . This is because if the inclination is less than 10 ° and the shape is a cylindrical surface or a shape close thereto, the above expression cannot be satisfied and Gc /
This is because Gp may be less than 1, and when it is larger than 30 °, the effect of the heat shield is reduced and the condition (1) cannot be realized.

The reason for increasing the diameter as it goes upward is to gradually reduce the influence of the heat shield.
Such effects can be achieved by making the heat shield thinner upwards.
It can also be obtained by changing the thickness a. However, when the thickness a is changed, the effect is affected by the thermal characteristics of the heat shield. Therefore, it is desirable that the thickness should be sufficiently large, that is, at least 20 mm or more.

The material of the heat shield is not particularly limited as long as it has a large heat insulating effect and does not cause contamination of silicon even when approaching the melt.

The length d of the heat shield is 200 to 400 mm.
If the height is less than 200 mm, the effect of the heat shield is insufficient, and the formula and the condition of the formula cannot be obtained. on the other hand
Even if it is larger than 400 mm, it only affects the temperature range below 1230 ° C., and no significant effect is obtained.

Even if a temperature distribution satisfying the expression and the expression is obtained by using the above-mentioned heat shield, as shown in FIG. Unless the crystal is pulled at the above speed, a single crystal having no defect cannot be obtained. The optimum pulling speed is determined by the shape of the graphite crucible 1b and the quartz crucible 1a fitted inside the crucible 1b.
Since it depends on the thermal environment, such as the shape of the heater 4 and the way of heating, the arrangement of the heat insulating material and cooling members of the entire device,
It differs for each device that actually raises. However, after determining the state of such a device and the shape and position of the heat shield, the found optimum speed shows a substantially constant value unless these conditions are changed.

Therefore, in the production of a single crystal, the above-mentioned heat shield is used, and after the formula and a condition satisfying the formula are satisfied, the pulling speed is continuously changed in advance to grow the single crystal. The range of the pulling speed in which the Gronn-in defect does not occur in the cross section perpendicular to the axis is found. Thereafter, the single crystal is pulled at a speed within the range.

[0047]

EXAMPLE A single crystal was pulled using the single crystal pulling apparatus and the heat shield 8 shown in FIG. The amount of silicon loaded in the crucible 1a is 100 kg and B is used as a dopant.
Was added to make the target specific resistance 13 Ωcm. The heat shield is made of graphite felt covered with a graphite plate.
m, the angle of inclination of the inner surface upward is 20 °, and the height d is 350
mm and the thickness a were 60 mm. The distance b from the lower end of the heat shield to the melt surface was 80 mm, and the diameter of the single crystal was 210 mm.
Therefore, the distance c between the single crystal surface and the single crystal surface at the lower end of the heat shield was 45 mm.

The seed crystal attached to the seed chuck 6 at the tip of the pulling shaft 5 is brought into contact with the silicon melt 3 heated and melted by the heater 4 in the crucible 1 a,
The melt is pulled up while solidifying and growing on the tip of the seed crystal to grow the single crystal 7. The crucibles 1a and 1b can be rotated by the support shaft 2, and the single crystal is also rotated by the pulling shaft 5. First, in order to make the crystal dislocation-free, the single crystal is subjected to seed drawing in which the crystal is grown to be smaller than the initial diameter attached to the seed crystal, and then a shoulder portion is formed, and the shoulder is changed to a constant body diameter.

The single crystal has a target diameter of 210 mm and a body length of 1
000 mm. In this case, the lifting speed is set to 0.6 mm / min when the body length reaches 300 mm, and then gradually decreased almost linearly in accordance with the lifting length. mm / min.
FIG. 7 shows the result of measurement of the temperature T at the center of the single crystal being pulled and the ratio Gc / Gp of the temperature gradient in the vertical direction. The result shown in FIG. I was

The obtained single crystal was vertically divided along the pulling axis, processed into a plate-like sample including the pulling axis, heated at 800 ° C. for 4 hours in an oxygen atmosphere, and further heated at 1000 ° C. for 16 hours. After heat treatment, perform X-ray observation and immersion in an aqueous copper nitrate solution to perform Cu decoration.
After heat treatment at 20 ° C. for 20 minutes, X-ray observation was performed to investigate the distribution of defects.

FIG. 8 shows the distribution of defects. As can be seen, if the pulling speed is selected between y and z, a wafer free of ring-shaped OSF and grown-in defects can be obtained. In this case, the optimal lifting speed difference between y and z is 0.03 mm
/ min.

[0052]

According to the method of the present invention, if a silicon single crystal is pulled by the CZ method, a large-diameter, long-sized high-quality wafer can be obtained with extremely few Grown-in defects such as dislocation clusters and infrared scatterers. A single crystal can be manufactured stably.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an example of a typical defect distribution observed on a silicon wafer.

FIG. 2 is a diagram schematically illustrating an example of a defect distribution in a vertical cross section parallel to a pulling axis of a single crystal pulled at a gradually lowering speed.

FIG. 3 shows a temperature (T) of a central portion of a single crystal during pulling, and a vertical portion of the peripheral portion with respect to a vertical temperature gradient Gc of the central portion in a horizontal section perpendicular to the pulling axis at a position indicating the temperature of the central portion. FIG. 5 is a diagram showing a relationship between a directional temperature gradient Gp and a ratio Gc / Gp.

FIG. 4 is a diagram showing a defect distribution in a vertical cross section of a single crystal pulled up at a different speed in the temperature distribution in the single crystal of A or B in FIG. 3;

FIG. 5 shows a defect distribution in a vertical cross section of a single crystal pulled up at a different speed under a temperature distribution condition in the single crystal where Gc / Gp is slightly above the position shown by the broken line in FIG. FIG.

FIG. 6 is a schematic view showing a cross section of a silicon single crystal pulling apparatus provided with a heat shield.

FIG. 7 is a diagram showing the relationship between Gc / Gp and the temperature (T) at the center of a single crystal pulled up in an example.

FIG. 8 is a diagram showing a defect distribution in a vertical cross section of a single crystal pulled up in an example.

[Explanation of symbols]

 1a. Quartz crucible 1b. Graphite crucible 2. Crucible support shaft 3. Silicon melt 4. Heater 5. 5. Lift shaft Seed chuck 7. Single crystal 8. Heat shield

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G077 AA02 BA04 CF10 EG19 EH09 PE22 PF55 5F053 AA12 BB04 BB13 DD01 FF04 GG01 JJ01 KK03

Claims (3)

[Claims] 1. A method for producing a silicon single crystal, which is pulled and grown by the Czochralski method (CZ method), wherein a temperature of a central portion of the single crystal during the pulling is defined as T (° C.), and at a position indicating the temperature. On a plane perpendicular to the pulling axis, the temperature gradient in the pulling axis direction is Gc (° C./m
m), assuming that Gp (° C./mm) in the peripheral portion, when the ratio Gc / Gp of the vertical temperature gradient satisfies the following expression when the ratio Gc / Gp satisfies T ≧ 1230 ° C. A method for producing a silicon single crystal, the method comprising: When T> 1360 ° C Gc / Gp ≧ −0.007T + 10.62 ・ ・ ・ ・ When T = 1230 ～ 1360 ℃ Gc / Gp ≧ 1.0 ・ ・ ・ ・ ・ ・ ・ 2. A method of manufacturing a silicon single crystal to be pulled and grown by the Czochralski method (CZ method), wherein a cylindrical heat shield coaxial with a pulling axis disposed around the single crystal to be pulled is formed by a high-temperature method. 200 to 400 mm, the inner surface of which has a funnel-like shape whose distance from the single crystal surface at the lower end is 20 to 60 mm and whose inclination with respect to the vertical direction is 10 ° to 30 °, and which becomes larger upward. The method for producing a silicon single crystal according to claim 1, wherein the height of the lower end surface of the shield from the melt surface is raised to 50 to 110 mm, and the shield is pulled up. 3. Growing a single crystal by continuously changing the pulling speed to obtain a Gr in a cross section perpendicular to the pulling axis.
3. The method for producing a silicon single crystal according to claim 1, wherein a pulling speed range in which an own-in defect does not occur is found, and the single crystal is pulled at a speed within the range.