JP4016471B2 - Crystal growth method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crystal growth method for growing a single crystal by a CZ method (Czochralski method), and more particularly, a low speed pulling condition in which an OSF ring is generated inside the outermost peripheral portion of the pulling crystal or disappears at the central portion. Relates to a crystal growth method performed in the above.
[0002]
[Prior art]
Silicon wafers used for manufacturing semiconductor devices are collected from single crystals grown mainly by the CZ method. As is well known, the CZ method involves soaking a seed crystal in a silicon raw material melt contained in a quartz crucible, pulling the seed crystal while rotating the seed crystal and the quartz crucible in the opposite direction, and forming silicon underneath. This is a method for growing a single crystal.
[0003]
It is known that a silicon wafer manufactured through such a growth process by the CZ method generates a ring-shaped oxidation-induced stacking fault called an OSF ring when subjected to a thermal oxidation treatment. The OSF ring itself not only causes deterioration of the characteristics of the semiconductor device, but also has different physical properties on the outside and inside of the ring, and dislocation clusters are generated outside the OSF ring due to aggregation of interstitial atoms. However, the inside of the OSF ring is relatively healthy. On the other hand, it is known that the OSF ring moves to the outer peripheral side of the single crystal as the pulling speed increases.
[0004]
Under these circumstances, single crystals have been grown so far under high-speed pulling conditions in which the OSF ring is distributed in the outermost peripheral portion of the crystal that is excluded from the effective portion during device formation.
[0005]
However, the inside of the OSF ring is not without problems. In this portion, vacancy clusters caused by flocculation are generated. Although this defect appears as a small pit when the wafer surface is etched, it is so small that it has not been particularly regarded as a problem until now. However, since the pattern width has become very fine as the degree of integration has increased remarkably in recent years, even this vacancy cluster has begun to be a problem in high-grade single crystals.
[0006]
This vacancy cluster hardly occurs in a so-called epitaxial wafer in which a silicon single crystal thin film is grown on a wafer. However, since this wafer is very expensive, the vacancy cluster is raised by pulling up the single crystal by the CZ method. From this point of view, it is required to grow fewer crystals. From this point of view, in high-grade crystal growth, the pulling speed is slowed and the OSF ring is pulled inside the outermost periphery of the crystal. Thus, a low-speed pulling method is conceived in which the defective portion is concentrated in the central portion or disappears in the central portion to improve the yield.
[0007]
[Problems to be solved by the invention]
However, with this low speed pulling, it is necessary to reduce the number of dislocation clusters generated outside the OSF ring. This is because even if the OSF ring is generated at the center of the crystal, high quality cannot be ensured if the outer dislocation clusters are left untreated.
[0008]
An object of the present invention is to provide a crystal growth method capable of effectively suppressing the generation of dislocation clusters at the outer periphery of the crystal, which becomes a problem when the vacancy cluster generation region is concentrated at the center of the crystal by low-speed pulling. There is to do.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have conducted a detailed analysis on the cause of the generation of dislocation clusters when the vacancy cluster generation region is concentrated at the center of the crystal by slow pulling. As a result, the following findings could be obtained.
[0010]
It is known that vacancy clusters are generated due to the concentration difference between vacancies and interstitial silicon caused by thermal history during single crystal pulling, and this concentration difference is reduced by lowering the pulling rate.
[0011]
More specifically, out of excess vacancies and interstitial silicon taken in at the solid-liquid interface during pulling, vacancies with a large diffusion coefficient in the high temperature region diffuse due to the difference in equilibrium concentration due to the temperature gradient in the crystal growth direction. It is diffused and moved toward the solid-liquid interface by so-called slope diffusion. In addition, due to the temperature distribution in the radial direction of the crystal and the release of vacancies on the crystal surface, the vacancies have a low concentration on the crystal surface. For these reasons, the concentration of vacancies is high in the center of the crystal where the temperature gradient is small and low in the outer periphery where the temperature gradient is large.
[0012]
On the other hand, interstitial silicon in the high temperature part hardly moves because the diffusion coefficient is as low as 1/100 to 1/1000 of that of vacancies. For this reason, the concentration of interstitial silicon is substantially constant in the crystal radial direction regardless of the thermal history, and a concentration difference between vacancies and interstitial silicon occurs in the crystal radial direction. FIG. 1A shows the vacancy concentration distribution and the interstitial silicon concentration distribution in the case of normal high-speed pulling.
[0013]
As can be seen from FIG. 1A, the concentration of vacancies increases toward the center of the crystal, whereas the interstitial silicon concentration is constant in the crystal radius direction. Then, in the crystal center portion where the temperature gradient is small, the vacancy concentration becomes larger than the interstitial silicon concentration, and when the concentration difference B becomes large, vacancy clusters are generated. On the other hand, at the crystal outer periphery where the temperature gradient is large, the interstitial silicon concentration is higher than the vacancy concentration, and when the concentration difference A increases, dislocation clusters are generated.
[0014]
When the pulling speed is decreased from the high speed pulling shown in FIG. 1A, the thermal history of the high temperature part becomes long and the slope diffusion is promoted as shown in FIG. . However, the distribution form in the crystal radial direction does not change. For this reason, excessive vacancies are reduced at the center of the crystal and the concentration difference B is reduced, but excessive interstitial silicon is increased at the periphery of the crystal, and the concentration difference A is increased. As a result, dislocation clusters are generated from the outer periphery of the crystal, and the generation position expands to the center side from the normal generation position.
[0015]
Thus, the generation of dislocation clusters is inevitable only by reducing the pulling rate. However, as shown in FIG. 1 (c), even if the pulling rate is lowered and the vacancy concentration is lowered, the concentration reduction rate is suppressed at the outer periphery of the crystal and the vacancy concentration distribution is made uniform in the crystal radial direction. If combined, the concentration difference B is reduced without increasing the concentration difference A, and as a result, generation of vacancy clusters can be suppressed without generating dislocation clusters. The suppression of the vacancy concentration decrease rate at the outer periphery of the crystal is realized by making the temperature gradient of the outer periphery close to the central temperature gradient at the high temperature portion of the crystal and lengthening the high temperature thermal history.
[0016]
The crystal growth method of the present invention has been developed based on the above knowledge, and uses the CZ method, and under low-speed pulling conditions in which the OSF ring is formed inside the outermost peripheral portion of the pulling crystal or disappears at the central portion. In the crystal growth method for growing a single crystal, the temperature gradient at the outer periphery of the crystal is suppressed to ± 0.3 ° C./mm or less of the temperature gradient at the center of the crystal at a high temperature portion where the crystal temperature is 1300 ° C. or higher. The feature point.
[0017]
When the temperature gradient difference between the outer peripheral portion and the inner peripheral portion at the high temperature portion of the crystal exceeds ± 0.3 ° C./mm, the concentration difference B at the center portion of the crystal becomes small due to the slow pulling. As a result, the generation of dislocation clusters becomes remarkable. A particularly preferable temperature gradient difference is ± 0.15 ° C./mm or less.
[0018]
Such a temperature gradient difference is, for example, that the liquid surface position of the raw material melt accommodated in the crucible is 1/5 of the heat generating part height with respect to the heat generating part upper end position of the heater arranged outside the crucible. This is achieved relatively easily by holding it down 4/5.
[0019]
When the liquid surface position of the raw material melt is above this range, the temperature gradient difference between the outer peripheral portion and the inner peripheral portion at the high temperature portion of the crystal exceeds ± 0.3 ° C./mm, and the generation of dislocation clusters becomes significant. . On the other hand, if the liquid surface position of the raw material melt is below this range, it becomes difficult to control the temperature of the raw material melt, resulting in unstable crystal diameter control or the occurrence of dislocations. Problems arise. Further, there is a risk that the quartz crucible becomes soft due to an increase in the heating amount and falls down or deforms, so that the crystal cannot be pulled up. A particularly preferable range is 1/4 or more for the lower limit and 3/4 or less for the upper limit.
[0020]
Besides the above-described liquid surface position control of the raw material melt, it is also effective to make the thickness of the heat insulating material arranged outside the heater lower than the thickness of the lower portion of the heater upper end. This has been confirmed by experiments by the present inventors. Specifically, the thickness of the upper part is preferably 1/4 to 3 to 4 of the thickness of the lower part. This is because if the thickness of the upper portion is made extremely thin, the gas generated from the raw material melt is rapidly cooled and solidified, falls into the melt and becomes a foreign substance, and crystal dislocation is easily generated.
[0021]
The pulling speed is preferably a speed at which the OSF ring is generated on the inner side of the ½ position in the crystal diameter direction in order to narrow the generation region of the vacancy cluster, and is a speed at which the OSF ring disappears at the crystal center. Is particularly preferred.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an explanatory diagram of a crystal growth method according to an embodiment of the present invention.
[0023]
The crystal growing apparatus includes a main chamber 1 and a pull chamber 2 connected to the center of the upper surface thereof. These are formed of a substantially cylindrical vacuum vessel whose axial direction is vertical, and has a water cooling mechanism (not shown). Inside the main chamber 1, a crucible 3 is arranged at a substantially central position, and a cylindrical heater 4 and a heat insulating material 5 are arranged outside the crucible 3.
[0024]
The crucible 3 is composed of an inner layer container made of quartz and an outer layer container made of graphite, and is supported by a rotary and elevating support shaft 6. Above the crucible 3, a rotary and liftable lifting shaft 7 is suspended through the pull chamber 2.
[0025]
To perform crystal growth, first, a polycrystalline silicon material of silicon is loaded into the crucible 3 with the chamber disassembled. Next, the chamber is assembled, the heater 4 is operated in a state where the inside of the chamber is evacuated, and the raw material in the crucible 3 is melted.
[0026]
When the silicon raw material melt 8 is generated in the crucible 3 in this way, the seed crystal attached to the lower end of the pulling shaft 7 is immersed in the raw material melt 8, and from this state, the crucible 3 and the pulling shaft 7 are immersed. The lifting shaft 7 is raised while rotating in the reverse direction. As a result, a silicon single crystal 9 is grown below the seed crystal.
[0027]
The pulling speed here is a low speed at which the OSF ring occurs inside the outermost peripheral part of the crystal or disappears at the central part. Moreover, the liquid level of the raw material melt 8 is kept constant by raising the crucible 3 as the single crystal 9 is pulled up. At this time, the liquid level of the raw material melt 8 is lower than the upper end of the heat generating part of the heater 4, and the level difference L from the liquid level to the upper end of the heat generating part is 1/5 to 4/5 of the heat generating part height H.
[0028]
In the grown single crystal 9, the OSF ring is reduced by pulling at a low speed, and the generation region of the vacancy cluster is limited to the crystal center. Further, by controlling the liquid surface level of the raw material melt 8, the high temperature portion having a crystal temperature of 1300 ° C. or higher is efficiently kept from the outside by the heat generated by the heater 4, and the temperature gradient of the outer peripheral portion in the high temperature portion is the central portion. By suppressing the temperature gradient to ± 0.3 ° C./mm or less, the generation of dislocation clusters outside the OSF ring is suppressed.
[0029]
The heating part height H when the heater 4 is divided in the height direction is the distance from the upper end of the uppermost heater to the lower end of the lowermost heater. For example, in the case of a so-called double heater with two upper and lower stages, the upper stage The distance from the upper end of the heater to the lower end of the lower heater is the heating part height H.
[0030]
FIG. 3 is an explanatory diagram of a crystal growth method according to another embodiment of the present invention.
[0031]
Here, in the cylindrical heat insulating material 5 arranged outside the heater 4, the thickness Ta of the portion 5a above the upper end of the heater 4 is made thinner than the thickness Tb of the lower portion 5b . According to the experiments by the present inventors, even with this configuration, a high temperature portion having a crystal temperature of 1300 ° C. or higher is efficiently kept from the outside by the heat generated by the heater 4, and the temperature gradient of the outer peripheral portion in the high temperature portion is the central portion. By suppressing the temperature gradient to ± 0.3 ° C./mm or less, the generation of dislocation clusters outside the OSF ring is suppressed.
[0032]
This configuration is better to combine the liquid level control of the material melt 8, which is adopted in the embodiment of FIG. 2, it is more effective.
[0033]
【Example】
Next, examples of the present invention will be shown, and the effects of the present invention will be clarified by comparing with the conventional examples.
[0034]
When pulling up a 6 inch crystal of (100) orientation from a raw material melt formed by charging 70 kg of polycrystalline silicon raw material in an 18 inch quartz crucible, as a conventional example, from the surface of the raw material melt The level difference L to the upper end of the heat generating part was 50 mm as usual. Since the heater is a single heater and the heat generating portion height H is 400 mm, the ratio (L / H) between the level difference L and the heat generating portion height H is 1/8.
[0035]
The difference in temperature gradient between the outer peripheral portion and the central portion in the high temperature portion where the crystal temperature was 1300 ° C. or higher was 0.52 ° C./mm. Each temperature gradient of the outer peripheral part and the central part was obtained by calculation by heat transfer simulation and temperature measurement by placing a simulator in the furnace.
[0036]
FIG. 4A shows the result of investigating the vacancy cluster generation region and the dislocation cluster generation region when the pulling speed is changed. When the pulling speed is slower than 0.7 mm / min, the void cluster generation region starts to decrease, and at 0.4 mm / min or less, this generation region disappears. However, when the pulling rate is slower than 0.6 mm / min, dislocation clusters start to be generated from the outer periphery. For this reason, even if the generation region of the vacancy clusters is limited to the crystal central portion, dislocation clusters are generated on the entire outer side, so that a high-quality wafer cannot be obtained.
[0037]
As Reference Example 1, the level difference L from the liquid surface of the raw material melt to the upper end of the heat generating part was set to 100 mm larger than the conventional one, and the ratio (L / H) to the heat generating part height H was set to 1/4. The temperature gradient difference between the outer peripheral portion and the central portion in the high temperature portion where the crystal temperature was 1300 ° C. or higher was 0.18 ° C./mm. The result at this time is shown in FIG.
[0038]
When the pulling speed is slower than 0.7 mm / min, the generation area of the hole clusters starts to decrease, and this generation area disappears at 0.4 mm / min or less, which is the same as the conventional example. However, the pulling speed at which dislocation clusters start to be generated from the outer periphery decreases to 0.45 mm / min. As a result, even when the vacancy cluster generation region is limited to the crystal central portion, the dislocation cluster generation region is limited to the crystal outer peripheral portion, and a relatively wide defect-free region is formed therebetween.
[0039]
As Reference Example 2, the level difference L from the liquid surface of the raw material melt to the upper end of the heat generating portion is set to 50 mm as in the conventional case, while the cylindrical heat insulating material disposed outside the heater is a portion above the upper end of the heater The thickness Ta was set to 50 mm, which is thinner than the thickness Tb (150 mm) of the lower part. The difference in temperature gradient between the outer peripheral portion and the central portion in the high temperature portion where the crystal temperature was 1300 ° C. or higher was 0.23 ° C./mm. The result at this time is shown in FIG. Results close to Reference Example 1 were obtained.
[0040]
As Example 1 , the level difference L from the liquid surface of the raw material melt to the upper end of the heat generating part is set to 100 mm larger than the conventional one, and the portion of the cylindrical heat insulating material disposed outside the heater above the upper end of the heater The thickness Ta was set to 50 mm, which is thinner than the thickness Tb (150 mm) of the lower part. The difference in temperature gradient between the outer peripheral portion and the central portion in the high temperature portion where the crystal temperature is 1300 ° C. or higher was reduced to 0.08 ° C./mm. The result at this time is shown in FIG. When the pulling speed at which dislocation clusters begin to be generated is further lower than that in Reference Example 1 and the pulling speed is in the range of 0.35 to 0.4 mm / min, no defect-free and high-quality single crystals are generated. Crystals are produced.
[0041]
As Example 2 , the level difference L from the surface of the raw material melt to the upper end of the heat generating part was 150 mm larger than Reference Example 1, and the ratio (L / H) to the heat generating part height H was 3/8. The difference in temperature gradient between the outer peripheral portion and the central portion in the high temperature portion where the crystal temperature was 1300 ° C. or higher was 0.10 ° C./mm. The result at this time is shown in FIG. The pulling speed at which dislocation clusters begin to occur is lower than that in Reference Example 1, and results close to Example 1 are obtained .
[0042]
【The invention's effect】
As is apparent from the above description, the crystal growth method of the present invention suppresses the generation of dislocation clusters, which is a problem when pulling up at a low speed in order to narrow the generation region of vacancy clusters, thereby reducing the number of defects. Enables production of quality wafers.
[Brief description of the drawings]
FIG. 1 is a concentration distribution diagram for explaining a reason for occurrence of a cluster.
FIG. 2 is an explanatory diagram of a crystal growth method according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram of a crystal growth method according to another embodiment of the present invention.
FIG. 4 is a chart showing a relationship between a pulling speed and a cluster generation area.
FIG. 5 is a chart showing a relationship between a pulling speed and a cluster generation area.
[Explanation of symbols]
1 Main chamber 2 Pull chamber 3 Crucible 4 Heater 5 Insulating material 6 Support shaft 7 Lifting shaft 8 Raw material melt 9 Single crystal

Claims (2)

In a crystal growth method using a CZ method and growing a single crystal under a low-speed pulling condition in which an OSF ring is generated inside the outermost peripheral portion of the pulling crystal or disappears at the center portion,
By raising the crucible with the pulling of the single crystal, the liquid level position of the raw material melt contained in the crucible is maintained constant, and the liquid level position of a heater disposed outside the crucible is maintained. A heat insulating material that is held 1/5 to 4/5 below the height of the heat generating portion with respect to the heat generating portion upper end position, and a cylindrical heat insulating material is disposed outside the heater, and a heat insulating material in a portion above the upper end of the heater. The thickness of the crystal is 1/4 to 3/4 of the thickness of the lower part, and the temperature gradient of the crystal periphery is ± 0.3 ° C. of the temperature gradient of the crystal center in the high temperature part where the crystal temperature is 1300 ° C. or higher. / Mm or less, a crystal growth method characterized by being controlled . Maintaining the liquid surface position of the raw material melt contained in the crucible 1/5 to 4/5 below the height of the heat generating part with respect to the upper end position of the heat generating part of the heater arranged outside the crucible. The crystal growth method according to claim 1, wherein the crystal growth method is characterized.

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