JPH09208360A - Growth of single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a single crystal having uniform resistivity in the length up to the top end of the pulled-up crystal according to the DLCZ process. SOLUTION: A large crucible 2 and a small crucible 3 are filled with polycrystalline silicon and dopant elements and the raw materials for the crystal is molten with the heater 4. As the solid layer 12 is molten in such a state that the molten layer 11 is allowed to coexist with the upper part of the solid layer, a seed crystal 14 is dipped at its bottom end in the molten layer 11 in the small crucible 3 and the lifting shaft 13 is pulled up to allow the single crystal 15 to grow. From the time when the solid layer 12 is judged to completely melt, the granular raw material 9 is fed at a constant rate to the molten layer 11 in the large crucible 2 and the single crystal 15 is continuously pulled up.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for growing a single crystal such as a silicon single crystal used as a semiconductor material.

[0002]

2. Description of the Related Art Generally, the Czochralski method (CZ method) is widely used as a method for producing a silicon single crystal.
In the CZ method, a quartz crucible having a bottomed cylindrical shape is filled with a melt of a crystal raw material, and a seed crystal is immersed in the melt and pulled up to solidify the melt at the lower end of the seed crystal to form a single crystal. This is a method of growing crystals. A heater is arranged in a concentric cylindrical shape outside the crucible so as to melt the raw material for crystallization in the crucible.

When a silicon single crystal is grown by this method, an impurity element is usually added to the melt before pulling in order to adjust the electric resistivity and electric conductivity type of the single crystal. However, there is a problem that the added impurities segregate in the crystal growth direction of the single crystal, and as a result, a single crystal having uniform electric characteristics in the crystal growth direction cannot be obtained. The segregation ratio C _S of the impurity concentration C _L of the melt with impurity concentration C _S in the single crystal in the growth interface between the melt and the single crystal
/ C _L , that is, the effective segregation coefficient K _e is not 1. For example, when K _e <1, the impurity concentration in the melt increases as the single crystal grows, and segregation occurs in the single crystal.

A double-layer pulling method (DLCZ method: Double Layered CZ), that is, a molten layer method is known as a method for suppressing such segregation (Baifukan'Bulk Crystal Growth ').
P.115). The melting layer method, the raw material for crystals in the crucible is melted so that the solid layer on the lower side coexists with the molten layer on the upper side, and the seed crystal is dipped in a state where the impurity concentration in the molten layer is kept constant,
This is a method of pulling this and growing a single crystal. The melt layer method melts the solid layer along with pulling to prevent an increase in the concentration of impurities in the melt layer and prevents the segregation of single crystals.

Further, as another method for suppressing such segregation, a continuous charge method (CCZ method, Continuous Charg method) is used.
ing CZ, published by Maruzen'Semiconductor Silicon Crystal Engineering 'p.73) is known. This method uses a split-type double crucible for C
It has been put to practical use by the Z method (Baifukan issue, 'Bulk crystal length' p.94). After filling the large crucible with the raw material for crystal and melting, the small crucible is placed in the center of the large crucible and The single crystal is pulled up by immersing the seed crystal in the surface of the melt that has flowed in from the flow opening provided on the bottom surface. Then, by supplying the raw material for crystallization to the melt located outside the small crucible, the concentration of impurities in the melt is prevented from increasing and the segregation of the single crystal is prevented.

[0006]

However, in the DLCZ method described above, the resistivity of the single crystal is uniform in the growth direction while the solid layer is present, but after the melting of the solid layer is completed. Similar to the CZ method, the impurity concentration in the melt increases as the single crystal grows, segregation occurs in the single crystal, and the resistivity of the single crystal at the pulling terminal is different from the resistivity at the initial stage of pulling. There was a problem. Further, the CCZ method has a problem that when dislocations occur in the initial stage of pulling a single crystal and the single crystal is redissolved, the impurity concentration of the melt differs from the initial value.

On the other hand, the single crystal pulled by the DLCZ method is supplied with oxygen dissolved from the quartz crucible which is in direct contact with the molten layer. Part of the oxygen dissolved from the crucible is carried to the crystal growth interface by the convection of the melt, and taken into the single crystal. In the DLCZ method, the lower temperature of the molten layer is lower than that of the molten liquid of the CZ method due to the influence of the solid layer, and thermal convection in the molten layer is suppressed. This makes DL
Compared with the CZ method, the CZ method has a lower oxygen concentration (6 × 10 ^{17 to} 12
A single crystal of × 10 ¹⁷ atoms / cm ³ ) can be obtained.

However, in the DLCZ method, the solid layer
After the melting of the
The obtained single crystal has the same medium oxygen concentration (14 × 10¹⁷~ 18
× 10 ¹⁷atoms / cm^Three). Therefore, single crystal oxygen
The concentration becomes non-uniform in the growth direction, and
There was a problem of low yield.

As another method for obtaining a low oxygen concentration single crystal, a magnetic field applied CZ method (MCZ method, Magnetic-field-appli method) is used.
ed CZ, published by Maruzen, 'Semiconductor Silicon Crystal Engineering', p.68), is proposed as a method of applying a magnetic field to a molten liquid in Japanese Patent Laid-Open Nos. 56-104791 and 56-45589. Has been done. By this method, the melt convection in the direction orthogonal to the lines of magnetic force is suppressed, and the effect of suppressing thermal convection is obtained. However, in this method, since a magnetic field is applied to a melt obtained by melting all of the raw materials for crystallization filled in the crucible, that is, a melt of the CZ method, the growth direction of the resistivity due to the segregation of impurities as described above is unbalanced. There is a problem that uniformity occurs.

In addition, the applicant of the present application applies a magnetic field to the molten layer from the initial stage of pulling a single crystal by the DLCZ method,
A method has been proposed for achieving uniform oxygen concentration in the radial direction of a single crystal (Japanese Patent Laid-Open No. 7-267776), but it mentions the oxygen concentration in the growing direction up to the pulling end of the single crystal. Absent.

The present invention has been made in view of the above circumstances, and in the DLCZ method, the raw material for crystallization is supplied to the molten layer from the middle of pulling the single crystal so that it is taken up from the molten layer to the pulling end. An object is to provide a method for growing a single crystal in which the amount of impurity elements is controlled.

Further, in the present invention, in the DLCZ method, the crystal raw material is supplied to the molten layer during the pulling of the single crystal,
By applying a magnetic field to the molten layer, up to the pulling end,
It is an object of the present invention to provide a method for growing a single crystal in which the amount of impurity elements and the amount of oxygen taken in from a molten layer are controlled.

[0013]

A method for growing a single crystal according to a first aspect of the present invention is a solid layer in which a raw material for crystal containing an impurity element is filled and melted in a crucible and the melt is solidified, and a solid layer above the solid layer. Coexisting with the molten layer, while melting the solid layer by heating the heater installed around the crucible, while pulling the crystal from the molten layer to grow while incorporating the impurity element in the molten layer In the growth method, the raw material for crystallization is supplied to the molten layer during the pulling of the single crystal in order to control the amount of the impurity element taken into the single crystal from the molten layer.

The method for growing a single crystal according to the second aspect of the present invention is the first aspect.
In the invention, after the melting of the solid layer, the crystallization raw material is supplied to the molten layer.

In the DLCZ method, while pulling a single crystal, for example, when substantially all of the lower solid layer is melted and the concentration of impurities in the melt is increased, a crystal raw material is supplied to the melt layer. This prevents an increase in the impurity concentration of the molten layer, prevents segregation of the single crystal, and makes the resistivity in the growth direction uniform up to the pulling end of the single crystal.

In the method for growing a single crystal according to the third aspect of the invention, a crucible is filled with a crystal raw material containing an impurity element and melted.
A solid layer obtained by solidifying a melt and a molten layer thereabove coexist, and the solid layer is melted by heating a heater installed around the crucible, and the molten layer is applied while applying a magnetic field to the molten layer. A method for growing a single crystal in which a crystal is pulled up from the melted layer to grow while taking in oxygen in the melted layer, in order to control the amount of impurity elements and the amount of oxygen incorporated in the single crystal from the melted layer, The crystal raw material is supplied to the molten layer and a magnetic field is applied to the molten layer during the pulling process.

The method for growing a single crystal according to the fourth aspect of the present invention is the third aspect.
In the invention, after the melting of the solid layer is completed, the raw material for crystallization is supplied to the molten layer, and a magnetic field is applied to the molten layer.

In the DLCZ method, during the pulling of a single crystal, for example, when the entire solid layer of the lower layer is melted to increase the concentration of impurities in the melt or when the effect of suppressing thermal convection disappears, the melting occurs. A crystal raw material is supplied to the layer and a magnetic field is applied to prevent an increase in the impurity concentration of the molten layer, thereby obtaining an effect of suppressing thermal convection by lines of magnetic force. This prevents the segregation of the single crystal after the solid layer is melted, prevents the increase in the amount of oxygen taken into the single crystal, and makes the resistivity in the growth direction and the oxygen concentration uniform up to the pulling end of the single crystal. To be done.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings showing a first embodiment. FIG. 1 is a schematic cross-sectional view showing the structure of a single crystal growth apparatus used for carrying out the method of the present invention. In the figure, 1 is a chamber. The chamber 1 is a vacuum container having a substantially cylindrical shape, and a large crucible 2 is arranged at a substantially central position of the chamber 1. The large crucible 2 is composed of a bottomed cylindrical quartz inner layer holding container 2a and a bottomed cylindrical outer layer holding container 2b made of graphite and fitted outside the inner layer holding container 2a. A quartz crucible 3 made of quartz and having a bottomless cylindrical shape is arranged substantially in the center of the inner bottom surface of the inner layer holding container 2a. A circular flow passage 3a is opened in the lower part of the peripheral surface of the small crucible 3, and a quartz pipe 3b is wound around the peripheral surface of the small crucible 3 in a single layer. They are connected and the other end is open at the bottom of the inner layer holding container 2a. The pipe 3b allows the contents of the large crucible 2 and the small crucible 3 to flow through each other.

A shaft 7 for rotating and raising and lowering the large crucible 2 is attached to the lower surface of the outer layer holding container 2b, and a resistance heating type heater 4 is vertically movable around the outer periphery of the large crucible 2. ing. The heater 4 has a cylindrical shape concentric with the large crucible 2 and is composed of an upper heater 4a on the upper side of the large crucible 2 and a lower heater 4b on the lower side. A heat insulating cylinder 5 is fixedly provided outside the heater 4 and below the large crucible 2. By adjusting the relative positions of the large crucible 2 and the heater 4 in the vertical direction, the molten layer 11 and the solid layer 12 can be formed in the large crucible 2 by adjusting their respective thicknesses.

On the other hand, a raw material supply device 8 is arranged outside the chamber 1 above the large crucible 2. The raw material supply device 8 is adapted to fill the granular raw material 9 and
Equipped with a supply pipe that penetrates through the
It is adapted to supply the molten layer 11 outside the small crucible 3 therein. A small cylindrical pull chamber 6 is continuously formed above the chamber 1 above the large crucible 2, and a pulling shaft 13 is pierced through the pull chamber 6 so as to be rotatable and vertically movable. And a seed crystal at the lower end of the pulling shaft 13.
14 is to be installed. Then, the lower end of the seed crystal 14 is immersed in the molten layer 11 in the small crucible 3, and then the single crystal 15 is grown from the lower end of the seed crystal 14 by rotating and raising the seed crystal 14. .

A procedure for growing a silicon single crystal using the apparatus configured as described above will be described. First, the large crucible 2 and the small crucible 3 are filled with polycrystalline silicon and an impurity element as a crystallization raw material, and the upper heater 4a and the lower heater 4a.
The raw material for crystallization is melted by 4b. And the upper heater 4
a, by controlling the positions of the lower heater 4b and the large crucible 2 and controlling the power of the upper heater 4a and the lower heater 4b,
The molten liquid is solidified from the bottoms of the large crucible 2 and the small crucible 3 to form a solid layer 12, and the molten layer 11 coexists on the solid layer 12. Next, the large crucible 2 and the small crucible 3 are rotated, and the lower end of the seed crystal 14 is immersed in the molten layer 11 in the small crucible 3 while melting the solid layer 12. The pulling shaft 13 is pulled while rotating, and the single crystal 15 is grown on the lower end of the pulling shaft 13 to manufacture a silicon single crystal.

When it is determined that the solid layer 12 has melted, the raw material supply device 8 supplies the granular raw material 9 to the molten layer 11 of the crucible 2 and then the single crystal 15 from the molten layer 11 continues.
To produce a silicon single crystal. At this time, the granular raw material 9 is melted in the molten layer 11 of the large crucible 2 and the pipe 3b
And the small crucible 3 through the passage port 3a and into the small crucible 3.
The increase in the impurity concentration of the molten layer 11 is suppressed. The supply amount, the supply speed, and the supply timing of the raw material supply device 8 after the completion of melting is determined according to the normal CCZ method,
Here, the description is omitted.

The determination of the completion of melting of the solid layer 12 is made based on a past empirical rule (a time until the melting of the solid layer 12 is judged, which is determined by the resistivity in the growth direction) by the same growth system. However, this determines the time when the melting is substantially completed. Further, when the melting of the solid layer 12 is completed, for example, a rod made of quartz is immersed in the molten layer 11 so that one end is landed on the upper surface of the solid layer 12, and the depth from the one end to the upper surface of the crucible wall is measured. It can also be determined by measuring the thickness of the melted layer 11 by propagating ultrasonic waves or microwaves to the melted layer 11.

Under the conditions shown in Table 1, according to the procedure described above,
From the time when it is determined that the solid layer 12 has melted, the granular raw material 9
Was supplied at a constant rate of 43.4 g / min, a silicon single crystal was grown, and the resistivity of the obtained silicon single crystal was measured. The results are shown in FIG. The pulling rate of the single crystal 15 is
1.0 mm / min. At this time, the φ6 inch single crystal pulls up 43.4 g per minute. The granular raw material 9 is the following formula 1
The impurity element is contained in an amount according to. The crystal length at the time when the melting of the solid layer 12 was determined to be 700 mm.

[0026]

[Table 1]

[0027]

[Equation 1]

FIG. 2 is a graph showing the resistivity of the pulled single crystal in the growth direction. In the graph, "○" indicates the silicon single crystal obtained in the first embodiment, and "□"
Shows a conventional silicon single crystal obtained by the DLCZ method without additionally supplying a crystal raw material. As is clear from the graph, in the conventional example, the resistivity is approximately 9 Ωcm and uniform when the crystal length is 200 mm to 700 mm, but the resistivity decreases to approximately 6 Ωcm at 700 mm or more. On the other hand, in the first embodiment, it was possible to obtain a uniform silicon single crystal having a crystal length of 200 mm to 1000 mm at the pulling end and a resistivity of about 9 Ωcm.

As described above, after the melting of the solid layer 12 is completed, the raw material for crystallization is supplied to the molten layer 11 to obtain the solid layer.
Even after the melting of 12 is completed, a silicon single crystal having a uniform resistivity in the growth direction can be obtained. Further, since the crystal raw material is not supplied in the initial stage of pulling, the impurity element concentration of the molten layer 11 does not change and can be redissolved even when the single crystal has dislocations in the early stage of pulling.

Next, a second embodiment of the present invention will be described below with reference to the drawings showing the same. FIG. 3 is a schematic cross-sectional view showing the structure of a single crystal growth apparatus used for carrying out the method of the present invention. The magnets 10S, 10N are arranged outside the heat insulating cylinder 5 at a height position where the large crucible 2 can move up and down with the opposite poles facing each other. A horizontal magnetic field is applied to the molten layer 11. Other configurations are the same as those of the single crystal growth apparatus shown in FIG. 1, and the same parts are designated by the same reference numerals and the description thereof will be omitted.

A procedure for growing a single crystal using such an apparatus will be described. Until the completion of melting of the solid layer 12 is determined, it is the same as in the first embodiment. Solid layer 12
When it is determined that the melting has been completed, a horizontal magnetic field is applied to the molten layer 11 by the magnetic field application device, and while the granular raw material 9 is supplied from the raw material supply device 8 to the molten layer 11 of the large crucible 2, Subsequently, the single crystal 15 is pulled up from the molten layer 11 to manufacture a silicon single crystal. At this time, the granular raw material 9 is melted in the molten layer 11 of the large crucible 2 and flows into the small crucible 3 through the pipe 3b and the flow port 3a to increase the impurity concentration of the molten layer 11 of the small crucible 3. Is suppressed. Further, in the molten layer 11, the horizontal magnetic force lines suppress thermal convection in a direction orthogonal to the lines of magnetic force, thereby suppressing an increase in the amount of oxygen taken into the single crystal.
The supply amount, the supply speed, the supply timing, and the magnetic field generation intensity of the raw material supply device 8 after the completion of melting is determined according to the usual CCZ method and MCZ method, and the description thereof is omitted here. The determination of the completion of melting of the solid layer 12 is made in the same manner as in the first embodiment.

Under the conditions shown in Table 2, according to the procedure described above,
When the completion of melting of the solid layer 12 was determined, a horizontal magnetic field of 3000 G was applied to the melting layer 11 to grow the silicon single crystal while supplying the granular raw material 9 at a constant rate of 43.4 g / min. The resistivity and oxygen concentration of the silicon single crystal were measured.
The results are shown in FIGS. The pulling rate of the single crystal 15 was 1.0 mm / min, and the granular raw material 9 contained the impurity element in an amount according to the above-mentioned numerical formula 1. Also a solid layer
The crystal length was 700 mm when the completion of melting of 12 was judged.

[0033]

[Table 2]

FIG. 4 is a graph showing the resistivity of the pulled single crystal in the growth direction. In the graph, "○" indicates the silicon single crystal obtained in the second embodiment, and "□"
Does not perform additional supply of crystal raw material and application of magnetic field D
The conventional silicon single crystal obtained by the LCZ method is shown. As is clear from the graph, the crystal length is 20 in the conventional example.
From 0 mm to 700 mm, the resistivity is uniform at about 9 Ωcm,
At 700 mm or more, the resistivity drops to about 6 Ωcm. On the other hand, in the second embodiment, it was possible to obtain a uniform silicon single crystal having a crystal length of 200 mm to 1000 mm at the pulling end and a resistivity of about 9 Ωcm.

FIG. 5 is a graph showing the oxygen concentration in the growth direction of the pulled single crystal. "○" is the second in the graph
The silicon single crystal obtained in the embodiment of
“Δ” represents a silicon single crystal of a comparative example obtained by applying a magnetic field from the initial stage of pulling the single crystal, and “□” was obtained by the DLCZ method in which additional supply of the crystal raw material and application of the magnetic field were not performed. The conventional silicon single crystal is shown. As can be seen from the graph, in the conventional example, the oxygen concentration is approximately 7 × 10 ¹⁷ atoms / cm ³ (low oxygen concentration) and is uniform up to a crystal length of 700 mm, but the oxygen concentration increases significantly above 700 mm. ing.
In the comparative example, the oxygen concentration is approximately 3 × 10 5 up to the crystal length of 700 mm.
¹⁷ atoms / cm ³ (very low oxygen concentration), uniform but 700 mm
As a result, the oxygen concentration has increased to a low oxygen concentration. On the other hand, in the second embodiment, the crystal length of the pulling end is
It was possible to obtain a uniform silicon single crystal with an oxygen concentration of approximately 7 × 10 ¹⁷ atoms / cm ³ (low oxygen concentration) up to 2000 mm.

As described above, after the melting of the solid layer 12 is completed, the raw material for crystallization is supplied to the molten layer 11 and the horizontal magnetic field is applied, so that the resistivity and A silicon single crystal having a uniform oxygen concentration in the growth direction can be obtained. Further, since the crystal raw material is not supplied in the early stage of pulling, even if the single crystal has dislocations in the early stage of pulling, it can be redissolved. Further, since the magnetic field is applied during the pulling, the manufacturing cost can be reduced as compared with the case where the magnetic field is applied from the initial stage of pulling.

In the second embodiment, the case of using the horizontal application system, that is, the horizontal application system as the magnetic field application device has been described, but the present invention is not limited to this, and the vertical application system, that is, the vertical application system. The effect of suppressing thermal convection can be obtained even by using a magnetic field application device such as an application system or a cusp type application system, and the present invention can be applied.

[0038]

As described above, in the present invention, DL
In the CZ method, the concentration of impurities in the melt is prevented from increasing and the segregation of the single crystal is prevented by supplying the raw material for crystallization to the molten layer from the middle of pulling the single crystal, for example, after the melting of the solid layer is completed. As a result, a single crystal in which the resistivity in the growth direction is raised and even up to the end can be obtained, and the yield is improved.

In the DLCZ method, the raw material for crystallization is supplied to the molten layer from the middle of pulling a single crystal, for example, after the melting of the solid layer is completed, and a magnetic field is applied to the molten layer to remove impurities in the molten liquid. The yield can be improved by preventing the increase of the concentration and suppressing the increase of the thermal convection in the molten layer due to the disappearance of the solid layer, and obtaining the single crystal in which the resistivity in the growth direction and the oxygen concentration increase and the end is uniform. Thus, the present invention has excellent effects.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a single crystal growth apparatus according to a first embodiment.

FIG. 2 is a graph showing the resistivity in the growth direction of the single crystal pulled up in the first embodiment.

FIG. 3 is a schematic cross-sectional view showing the structure of the single crystal growth apparatus of the second embodiment.

FIG. 4 is a graph showing the resistivity in the growth direction of the single crystal pulled in the second embodiment.

FIG. 5 is a graph showing the oxygen concentration in the growth direction of the single crystal pulled up in the second embodiment.

[Explanation of symbols]

 1 chamber 2 large crucible 3 small crucible 4 heater 8 raw material supply device 9 granular raw material 10S, 10N magnet 11 molten layer 12 solid layer 15 single crystal

Claims (4)

[Claims] 1. A heater installed around the crucible, in which a raw material for crystallization containing an impurity element is filled in the crucible and melted, and a solid layer obtained by solidifying the molten liquid and a molten layer above the coexisting layer coexist. While melting the solid layer by heating, a method for growing a single crystal in which a crystal is pulled up from the molten layer to grow while incorporating an impurity element in the molten layer, wherein an impurity element incorporated in the single crystal from the molten layer A method for growing a single crystal, wherein the raw material for crystallization is supplied to the molten layer from the middle of pulling the single crystal in order to control the amount. 2. The method for growing a single crystal according to claim 1, wherein the raw material for crystallization is supplied to the molten layer after completion of melting of the solid layer. 3. A heater installed around the crucible, in which a raw material for crystallization containing an impurity element is filled in the crucible and melted, and a solid layer obtained by solidifying the molten liquid and a molten layer above the solid layer coexist. Is a method for growing a single crystal in which the solid layer is melted by heating and a magnetic field is applied to the molten layer, and a crystal is pulled up from the molten layer to grow while taking in oxygen in the molten layer, In order to control the amount of impurity elements and the amount of oxygen taken into the single crystal from the layer, the raw material for crystallization is supplied to the molten layer and a magnetic field is applied to the molten layer during the pulling of the single crystal. And a method for growing a single crystal. 4. The method for growing a single crystal according to claim 3, wherein after the melting of the solid layer, the raw material for crystallization is supplied to the molten layer and a magnetic field is applied to the molten layer.