JPH11199364A - Growing of crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce high-quality wafer scarcely containing defect over the whole surface. SOLUTION: A single crystal 9 is grown by CZ method. A pulling up rate in pulling up the single crystal 9 from a raw material melt 8 is kept in low rate at which an OSF ring is produced on inner side than crystal outer periphery or the ring disappears in center part. A distance L from the lower end of effective adiabatic part of a heat-shielding member 6 provided on the outside of a crystal pulling up passage to the liquid level of the raw material melt 8 is kept to >10% of crystal diameter D. Thereby, occurrence of dislocation cluster on the outside of the OSF ring is prevented and pulling up rate is accelerated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a single crystal by the CZ method (Czochralski method), and more particularly, to a method in which an OSF ring is formed inside the outermost peripheral portion of a pulled crystal or at the center. The present invention relates to a crystal growing method performed under a low-speed pulling condition that disappears in a part.

[0002]

2. Description of the Related Art A silicon wafer used for manufacturing a semiconductor device is mainly collected from a single crystal grown by a CZ method. As is well known, the CZ method is a method in which a seed crystal is immersed in a raw material melt of silicon contained in a quartz crucible, and the seed crystal is pulled up while rotating the seed crystal and the quartz crucible in opposite directions. This is a method of growing a single crystal.

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 not only causes deterioration of the characteristics of the semiconductor device itself, but also has different physical properties between the outside and the inside of the ring.
Dislocation clusters are generated outside the ring due to aggregation of interstitial atoms, but the inside of the OSF ring is relatively healthy. On the other hand, about this OSF ring,
It is known that as the pulling speed increases, the single crystal moves toward the outer periphery.

[0004] Under such circumstances, the OSF
Single crystals are grown under high-speed pulling conditions such that the rings are distributed at the outermost peripheral portion of the crystal excluded from the effective portion when forming the device.

[0005] However, there is no problem inside the OSF ring. In this portion, vacancy clusters caused by vacancy aggregation occur. These defects appear as small pits when the surface of the wafer is etched, but are so small that they have not been particularly problematic. However, since the pattern width has become very fine with the remarkable increase in the degree of integration in recent years, even this vacancy cluster has begun to become a problem in high-grade single crystals.

Although this vacancy cluster hardly occurs in a so-called epitaxial wafer in which a silicon single crystal thin film is grown on a wafer, this wafer is very expensive. From this viewpoint, it is required to grow a crystal having a small number of hole clusters. From this viewpoint, in growing a high-grade crystal, the pulling speed is reduced and the OSF ring is pulled up from the outermost periphery of the crystal. A low-speed pulling method has been considered in which a defect portion is generated inside to concentrate the defective portion at the central portion or is eliminated at the central portion to improve the yield.

[0007]

However, in this low-speed pulling, it is inevitably necessary to reduce the number of dislocation clusters generated outside the OSF ring.
Because, even if the OSF ring is generated at the center of the crystal,
This is because high quality cannot be secured if the outer dislocation cluster is left unattended.

SUMMARY OF THE INVENTION It is an object of the present invention to grow a crystal capable of effectively suppressing the generation of dislocation clusters at the outer peripheral portion of the crystal, which is a problem when the vacancy cluster generating region is concentrated at the central portion of the crystal by slow pulling. It is to provide a method.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors conducted detailed analysis on the cause of the generation of dislocation clusters when the vacancy cluster generation region was concentrated at the center of the crystal by slow pulling. Was done. As a result, the following findings were obtained.

It is known that vacancy clusters are generated by the concentration difference between vacancies and interstitial silicon caused by the thermal history during single crystal pulling, and that the concentration difference is reduced by lowering the pulling speed. ing.

More specifically, of the excess vacancies and interstitial silicon taken in at the solid-liquid interface during the pulling, vacancies having a large diffusion coefficient in a high-temperature portion form an equilibrium concentration due to a temperature gradient in the crystal growth direction. Diffusion due to the difference, that is, so-called sloping diffusion, causes diffusion movement toward the solid-liquid interface. Further, due to the temperature distribution in the crystal radial direction and the release of vacancies on the crystal surface, the vacancies on the crystal surface have a low concentration. For these reasons, the concentration of vacancies is
The distribution is high at the center of the crystal with a small temperature gradient and low at the outer periphery with a large temperature gradient.

On the other hand, interstitial silicon in a high-temperature portion hardly moves because its diffusion coefficient is as low as 1/100 to 1/1000 of that of vacancies. Therefore, the concentration of interstitial silicon is
It becomes almost constant regardless of the thermal history in the crystal radial direction, 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 ordinary high-speed pulling.

As can be seen from FIG. 1A, the vacancy concentration increases toward the center of the crystal, while 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 higher than the interstitial silicon concentration, and when the concentration difference B increases, vacancy clusters are generated. On the other hand, in the crystal periphery where the temperature gradient is large,
When the interstitial silicon concentration becomes higher than the vacancy concentration and the concentration difference A increases, dislocation clusters are generated.

When the pulling speed is reduced from the high speed pulling shown in FIG. 1 (a), the heat history of the high temperature part becomes longer and the slope diffusion is promoted as shown in FIG. 1 (b). Decrease. However, the distribution form in the crystal radial direction does not change. For this reason, excessive vacancies decrease in the central portion of the crystal and the concentration difference B decreases, but excessive interstitial silicon increases in the peripheral portion of the crystal and the concentration difference A increases. As a result, dislocation clusters are generated from the outer periphery of the crystal, and the generation position is expanded toward the center from the normal generation position.

As described above, the occurrence of dislocation clusters cannot be avoided only by lowering the pulling speed. But,
As shown in FIG. 1 (c), even when the pulling speed is reduced and the vacancy concentration is reduced, it is necessary to suppress the concentration reduction rate at the outer periphery of the crystal and make the vacancy concentration distribution uniform in the crystal radial direction. If done together, the density difference B becomes smaller without increasing the density difference A, and as a result, it becomes possible to suppress the generation of vacancy clusters without generating dislocation clusters. The suppression of the rate of decrease in the vacancy concentration at the outer periphery of the crystal is achieved by keeping the surface of the high-temperature portion of the crystal immediately after being pulled out of the raw material melt, and bringing the temperature gradient at the outer periphery of the crystal closer to the temperature gradient at the central portion of the crystal. This is achieved by lengthening the high-temperature heat history.

More specifically, in recent crystal growth by the CZ method, an inverted cone-shaped heat shielding member called a cone is arranged outside the crystal pulling path, and heat incident on the pulled crystal from outside is shielded on the way. It has been practiced to increase the pulling speed by promoting heat radiation of the crystal by removing the lower end of the heat shielding member and increasing the amount of heat incident on the surface of the crystal high temperature portion immediately after the pulling. It is an effective and easy to implement technique.

The crystal growing method of the present invention has been developed on the basis of the above findings, and uses the CZ method and the OSF
In a crystal growing method in which a single crystal is grown under a low-speed pulling condition in which a ring is generated inside the outermost peripheral portion of the pulled crystal or disappears at a central portion, an inverted cone-shaped heat shielding member disposed outside the crystal pulling path is provided. A feature of the configuration is that the distance L from the lower end of the effective heat insulating portion to the liquid level of the raw material melt in the crucible is set to be more than 10% of the pulled crystal diameter D.

As a concrete method for setting the distance from the lower end of the effective heat insulating portion of the heat shielding member to the melt surface (hereinafter referred to as heat transmission section length L) to be more than 10% of the crystal diameter D, for example, the following method is used. is there. The effective heat-insulating portion of the heat shielding member refers to a portion having an intended heat-insulating performance, and usually indicates a portion filled with a heat insulating material having a predetermined thickness.

The gap G from the lower end of the heat shielding member filled with the heat insulating material to the melt surface is set to more than 10% of the crystal diameter D. The lower end portion of the heat shielding member filled with the heat insulating material or the thickness of the heat insulating material filled in the lower end portion is made thinner than the thickness of the other portions to increase the heat permeability, and the melt surface is usually formed from the lower end of the thickness portion. Is set to more than 10% of the crystal diameter D. The heat insulating material is removed from the lower end of the heat shielding member to enhance heat permeability, and the distance from the lower end of the heat insulating material to the melt surface is determined by the crystal diameter D.
More than 10%. While removing the heat insulating material from the lower end of the heat shielding member,
An opening is provided in this portion, and a heat-resistant material having high heat permeability is provided in the opening. The distance from the lower end of the heat insulating material to the melt surface is set to more than 10% of the crystal diameter D. The distance from the lower end of the heat shield member filled with the heat insulating material to the melt surface is set to be more than 10% of the crystal diameter D, and an inverted pyramid-shaped auxiliary member having excellent heat permeability is provided below the heat shield member. Add to it.

As described above, the main purpose of the heat shielding member is to limit the heat incident on the pulled crystal, promote cooling of the crystal, and increase the pulling speed.
On the other hand, this heat shielding member has a function of rectifying the gas descending flow around the crystal to improve the crystal yield and the controllability of the oxygen concentration. It is preferable not to increase the gap G to the liquid surface. This is because, when the gap G increases, the flow rate of the gas descending flow decreases, and the function of improving the crystal yield and the controllability of the oxygen concentration decreases. Of the specific methods described above ~
Is preferable in that the heat transmission section length L can be made to be more than 10% of the crystal diameter D without increasing the gap G.

The cooling of the pulled crystal proceeds because the radiation heat from the crystal is larger than the heat incident on the crystal. Assuming that the heat transmission section length L is more than 10% of the crystal diameter D, the heat incident on the crystal increases in the high temperature portion of the crystal immediately after the pulling, and the temperature gradient at the outer peripheral portion of the crystal approaches the temperature gradient at the central portion of the crystal. By making the distribution of the hole concentration in the crystal radial direction uniform, generation of dislocation clusters due to low-speed pulling is suppressed. In addition to this, the pulling speed when the OSF ring is generated at the same position increases. The reason is as follows.
Conventionally, by providing a heat shielding member, a spatial and temporal temperature gradient becomes tight, and in this, the OSF ring is moved inward by lowering the lifting speed.
By increasing the length L of the heat transmission section, the temperature gradient in space and time becomes gentle, so that the OSF ring enters the inside more than the conventional one at the same pulling speed. Therefore,
When the OSF ring is generated at the same position, the pulling speed increases.

The ratio of the heat transmission section length L to the crystal diameter D is preferably large in terms of suppressing generation of dislocation clusters, and is preferably 20% or more, particularly preferably 30% or more. Because of deformation, the upper limit is preferably limited to 60% or less, particularly preferably 50% or less.

On the other hand, the gap G from the lower end of the heat shielding member to the melt surface is expressed by the ratio of the heat transmission section length L to the crystal diameter D in order to ensure the rectification of the gas descending flow around the crystal. % Or less, and particularly preferably 10% or less. However, if the gap G is extremely reduced, the melt surface adheres to the heat shielding member due to the fluctuation of the melt surface or the like. Therefore, the lower limit is preferably limited to 1% or more, particularly 7.5% or more. .

The pulling speed is set such that the position where the OSF ring is generated is one in the crystal diameter direction in order to narrow the vacancy cluster generation region.
It is preferable to select so as to be inside the / 2 position,
It is particularly preferred that the OSF ring be chosen so that it disappears at the center of the crystal.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an explanatory diagram of the crystal growing method according to the embodiment of the present invention.

The crystal growing apparatus has a main chamber 1 and a pull chamber 2 connected to the center of the upper surface. These are composed of a substantially cylindrical vacuum vessel whose axial direction is vertical, and have a water cooling mechanism (not shown). Inside the main chamber 1, the crucible 3 is arranged substantially at the center, and a cylindrical heater 4 and a heat insulating material 5 are arranged outside the crucible 3. Above the crucible 3, an inverted conical heat shield member 6 called a cone is concentrically arranged.

The crucible 3 comprises an inner container made of quartz and an outer container made of graphite, and is supported rotatably and vertically by a support shaft (not shown). Above the crucible 3, a rotary and elevating lifting shaft 7 is suspended through the pull chamber 2. The heat shielding member 6 has a normal structure in which the entire inside is filled with a heat insulating material, but has a height higher than that of the conventional structure so that a heat transmission section length L of 6% or more of the crystal diameter D is secured during pulling. It is designed to be small.

In order to grow a crystal, first, a polycrystalline raw material of silicon is charged into the crucible 3 with the chamber being disassembled. Next, the chamber 4 is assembled, and the heater 4 is operated in a state where the inside of the chamber is evacuated to melt the raw material in the crucible 3.

When the silicon raw material melt 8 is formed in the crucible 3 in this manner, the seed crystal mounted on the lower end of the pulling shaft 7 is immersed in the raw material melt 8 and the crucible 3
While rotating the lifting shaft 7 in the opposite direction.
To rise. As a result, a silicon single crystal 9 is grown below the seed crystal.

The pulling speed here is a low speed at which the OSF ring is generated inside the outermost peripheral portion of the crystal or disappears at the central portion. By raising the crucible 3 as the single crystal 9 is pulled up, the liquid surface level of the raw material melt 8 is maintained constant, but the gap G from the lower end of the heat shielding member 6 to the melt surface has a crystal diameter. Over 10% of D,
This ensures a heat transmission section length L exceeding 10% of the crystal diameter D.

In the grown single crystal 9, the OSF ring is reduced by slow pulling, and the region where vacancy clusters are generated is limited to the crystal center. Further, by setting the heat transmission section length L to more than 10% of the crystal diameter D, the high temperature portion immediately after the pulling is efficiently kept warm from the outside by the radiant heat from the raw material melt 8, and the temperature of the outer peripheral portion in the high temperature portion is increased. As the gradient approaches the temperature gradient at the center, the generation of dislocation clusters outside the OSF ring is suppressed, and the pulling speed is increased.

FIG. 3 is an explanatory view of a crystal growing method according to another embodiment of the present invention.

In FIG. 3 (a), the heat shielding member 6 whose lower end has a thinned portion 6b thinner than other portions and has a reduced heat shielding function is used. Normal thick part 6
The distance from the lower end of a to the melt surface, that is, the heat transmission section length L is more than 10% of the crystal diameter D. Further, the distance from the lower end of the thin portion 6b to the melt surface, that is, the gap G is the same as the conventional one.

In FIG. 3B, the heat insulating material 10 filled in the heat shielding member 6 is removed from the lower end of the heat shielding member 6.
The distance from the lower end of the heat insulating material 10 to the melt surface, that is, the heat transmission section length L is more than 10% of the crystal diameter D. Further, the distance from the lower end of the heat shielding member 6 to the melt surface, that is, the gap G is the same as the conventional one.

In FIG. 3C, the heat insulating material 10 to be filled in the heat shielding member 6 is removed from the lower end of the heat shielding member 6, and an opening is provided in the lower end of the heat insulating member 6. A heat resistant material 11 such as high quartz glass is provided. The distance from the lower end of the heat insulating material 10 to the melt surface, that is, the heat transmission section length L is more than 10% of the crystal diameter D. Further, the distance from the lower end of the heat shielding member 6 to the melt surface, that is, the gap G is the same as the conventional one.

Also in these embodiments, the OSF ring is reduced by slow pulling, and the region where vacancy clusters are generated is limited to the crystal center. Further, by setting the heat transmission section length L to more than 10% of the crystal diameter D, the high temperature portion immediately after the pulling is efficiently kept warm from the outside by the radiant heat from the raw material melt 8, and the temperature of the outer peripheral portion in the high temperature portion is increased. As the gradient approaches the temperature gradient at the center, the generation of dislocation clusters outside the OSF ring is suppressed, and the pulling speed is increased. Furthermore, by setting the gap G from the lower end of the heat shielding member 6 to the melt surface as usual, a conventional flow velocity is ensured in the gas descending flow around the crystal.
Deterioration in yield and deterioration in controllability of oxygen concentration due to the decrease in the flow velocity are avoided.

[0037]

EXAMPLES Next, examples of the present invention will be shown, and the effects of the present invention will be clarified by comparing with the conventional example.

In a quartz crucible, 12 polycrystalline silicon materials were placed.
From the raw material melt produced by charging and dissolving 0 kg, 10
When pulling an 8-inch crystal in the 0 direction, a conventional heat shielding member was used as a conventional example, and the gap G from the lower end of the heat shielding member to the melt surface was set to 20 mm. The heat transmission section length L is also 20 mm.

In Example 1, the lower end of the heat shielding member was removed, and the gap G from the lower end of the heat shielding member to the melt surface was set to 40 mm (see FIG. 2). Heat transmission section length L is also 40m
m.

In Example 2, the lower end of the heat shield was removed, and the gap G from the lower end of the heat shield to the melt surface was set to 60 mm (see FIG. 2). Heat transmission section length L is also 60m
m.

In the third embodiment, the thickness of the lower end portion of the heat shielding member is reduced to の of the thickness of the other portions, the gap G from the lower end of the heat shielding member to the melt surface is set to 20 mm, and the thickness of the normal thick portion is reduced. The heat transmission section length L from the lower end to the melt surface was set to 60 mm (see FIG. 3A).

In Example 4, the heat insulating material was removed from the lower end of the heat shielding member, an opening was provided in this portion, and quartz glass was provided. The gap G from the lower end of the heat shielding member to the melt surface was set to 20 mm, and the length L of the heat transmission section from the lower end of the heat insulating material to the melt surface was set to 60 mm (see FIG. 3C).

In each of the examples, the pulling speed was adjusted so that the OSF ring was generated at a position of a half of the crystal radius.

FIG. 4 shows the pulling speed in each example by the speed ratio when the pulling speed (1.0 mm / min) in the high speed pulling in which the OSF ring is generated at the outermost peripheral portion of the crystal is set to 1. FIG. 5 shows the results of investigation of the radial distribution of the vacancy cluster generation density and the radial distribution of the dislocation cluster generation density for a wafer collected from the grown single crystal. 6 and FIG. 7 show the results of investigating the oxygen concentration distribution in the pulling axis direction of the grown crystal.

In each figure, "low speed pulling" is a conventional example,
"Large gap 1" refers to Example 1, "Large gap 2" refers to Example 2, "tip thinning" refers to Example 3, "tip quartz" refers to Example 4, and "high-speed pulling" refers to the OSF ring at the outermost periphery of the crystal. Represents the pull that occurs in the part.

As shown in FIG. 5, in either case,
The generation of vacancy clusters inside the OSF ring is inevitable. However, dislocation clusters outside the ring are remarkably generated in the conventional example (low-speed pulling), whereas in the present invention in which the length L of the heat transmission section is increased, the generation of dislocation clusters is effectively suppressed. In “Large gap 2” of Example 2, “Thin tip” in Example 3, and “Quartz tip” in Example 4, the occurrence is almost completely prevented.

Regarding the pulling speed, as shown in FIG. 4, in the present invention, the speed was increased despite the occurrence of the OSF ring at the same position. In particular, the effect was great in "thin tip" in Example 3 and "Quartz tip" in Example 4 in which the gap G was maintained as before.

As shown in FIG. 6, in the present invention, the ratio of complete crystallization was improved by increasing the pulling speed in the present invention. In particular, the “tip thinning” of the third embodiment in which the gap G is maintained as before and the fourth embodiment.
The "quartz tip" has a great effect, which is equivalent to high-speed pulling.

Regarding the axial distribution of the oxygen concentration in the crystal,
As shown in FIG. 7, the “thin tip” of the third embodiment and the “quartz tip” of the fourth embodiment, in which the gap G is maintained as before, ensured the same uniformity as the related art.

[0049]

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 at a low speed to narrow the region where vacancy clusters are generated. This enables the production of high quality wafers with few defects. In addition, the pulling speed is increased, thereby improving the productivity and the complete crystallization rate.

[Brief description of the drawings]

FIG. 1 is a density distribution diagram for explaining the reason for the occurrence of clusters.

FIG. 2 is an explanatory diagram of a crystal growing method according to an embodiment of the present invention.

FIG. 3 is an explanatory view of a crystal growing method according to another embodiment of the present invention.

FIG. 4 is a table showing a pulling speed ratio in the embodiment.

FIG. 5 is a table showing a radial distribution of cluster generation density in an example.

FIG. 6 is a table showing a complete crystallization ratio in Examples.

FIG. 7 is a table showing an axial distribution of oxygen concentration in a crystal in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main chamber 2 Pull chamber 3 Crucible 4 Heater 5 Heat insulating material 6 Heat shielding member 7 Pull-up shaft 8 Raw material melt 9 Single crystal 10 Heat insulating material 11 Quartz glass

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masahiko Okui 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd.

Claims (2)

[Claims] 1. A method for growing a single crystal under a low-speed pulling condition in which a CZ method is used and an OSF ring is generated inside an outermost peripheral portion of the pulled crystal or disappears at a central portion thereof. A distance from the lower end of the effective heat-insulating portion of the reverse-conical heat shield member to the liquid surface of the raw material melt in the crucible is set to be more than 10% of the pulled crystal diameter. 2. The heat shielding member has a portion having a high heat permeability below the effective heat insulating portion.
3. The method for growing a crystal according to item 2.