JP2681115B2 - Single crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a single crystal capable of homogenizing the oxygen concentration in the crystal growth direction and radial direction of a single crystal produced by the Czochralski method (CZ method). Manufacturing method.

[Conventional technology]

In general, a single crystal is manufactured by the Czochralski method (CZ method). For example, a raw material for crystal is put into a crucible arranged in a chamber, heated and melted by a heater, and then a seed crystal is added to the melt. And growing the single crystal at the lower end of the seed crystal by rotating it and pulling it upward.

By the way, for example, when a semiconductor integrated circuit is manufactured using a silicon single crystal substrate, it is suitable for a silicon single crystal substrate in order to obtain a so-called IG (Intrinsic Gettering) effect for purifying a trace amount of heavy metal contamination in the manufacturing process. Oxygen content is required.

Therefore, in the process of manufacturing a silicon single crystal, it is necessary to uniformly contain oxygen in an appropriate concentration in the crystal growth direction and the radial direction of the single crystal. For this purpose, particularly in the melt of the crystal raw material in the crucible, especially in the single crystal. It is necessary to maintain a constant oxygen concentration in the crystal growth region.

By the way, most of the oxygen in the crucible is supplied into the silicon melt from the surface of the quartz crucible during the process of melting polycrystalline silicon, which is a crystal raw material, in the quartz crucible, and the forced convection of the melt by the rotation of the crucible and the inside of the crucible. In addition to being agitated in the melt by heat convection due to the internal temperature difference of the melter and being evaporated from the surface of the melt, a part of it is carried to the growth interface of the single crystal and taken into the single crystal.

Therefore, the amount of melt in the crucible is large, and the contact area with the quartz crucible is large.At the beginning of crystal growth, the oxygen concentration in the melt is high, and the growth of single crystals progresses, and the amount of melt in the crucible decreases. Along with this, the contact area between the melt and the quartz crucible decreases, and the oxygen concentration in the melt tends to decrease, and the oxygen concentration in the single crystal is generally high at the beginning of crystal growth. It decreases as the growth progresses.

However, such relationships are not always centralized,
In addition to the amount of melt in the crucible, the amount of quartz dissolved, the flow of the melt carrying the eluted oxygen, the amount of oxygen evaporated in the form of silicon monoxide, etc. are related, and the amount of quartz dissolved is the reaction temperature, in other words Depending on the heating distribution from the heater to the crucible, and the convection of the melt, the diameter of the single crystal, the melt temperature distribution, or the crucible,
It is known that the evaporation rate of oxygen is further affected by the pressure in the chamber, Ar flow rate, etc. depending on the rotation speed of the single crystal, and the oxygen concentration of the single crystal is determined by the complex combination of these factors. It is extremely difficult to keep this constant from the beginning to the end.

As a countermeasure against this, focusing on the relationship between the rotation speed of the crucible and the oxygen concentration in the single crystal, the rotation speed of the crucible was changed in relation to the amount of the raw material melt, and the relative speed between the quartz crucible and the melt was changed, A method of controlling the oxygen concentration in the melt, in other words, the oxygen concentration in a single crystal, by adjusting the thickness of the oxygen diffusion boundary layer on the surface of the quartz crucible by forced convection to the melt (JP-A-57)
-27996, Japanese Patent Laid-Open No. 57-135796), or a plurality of heaters are arranged around the crucible and the power supply ratio to the heaters is adjusted so that a part of the crystal raw material is in a solid state in the crucible. A method for growing a single crystal while changing the contact area between quartz and the melt and the temperature of the melt has been proposed (JP-A-62-153191).

[Problems to be solved by the invention]

However, although it is recognized that the former method slightly improves the uniformity of the oxygen concentration in the single crystal, the inventor's experiment cannot maintain the fluctuation range of the oxygen concentration in the crystal below a predetermined level.

Further, the latter method has a problem that repeated melting and solidification of the crystal raw material gives a large shear stress to the crucible, which may damage the crucible. In addition, these methods are applied to prevent the silicon oxide from falling into the crucible, to prevent the effect of radiant heat from the crucible melt on the single crystal, and to use a shielding member having a function of rectifying the gas in the chamber. When applied to a crystal manufacturing apparatus, the high temperature region of the molten liquid in the crucible moves upward in the crucible, and the temperature below the quartz crucible relatively decreases, so the amount of oxygen dissolved from the bottom of the quartz crucible decreases and the single crystal There has been a problem that the concentration of oxygen taken in is lowered, and means such as forced convection of the melt cannot control the high oxygen concentration.

Fig. 5 shows the temperature distribution at the contact point between the crucible (quartz crucible) and the melt, with the horizontal axis representing temperature (° C) and the vertical axis representing the position of the quartz crucible in the height direction. , ○ is plotted in the graph when there is a shielding member,
The plot with Δ indicates that there is no shielding member.

As is clear from this graph, when the shielding member is used, the high temperature region in the melt inside the crucible shifts upward, and the temperature at the bottom of the crucible decreases.

The present invention has been made in view of such circumstances, and an object thereof is to precisely control the oxygen concentration in the growth direction of a single crystal in the process from the start to the end of crystal growth even in equipment using a shielding member. It is to provide a method for producing a single crystal that can be manufactured.

[Means for solving the problem]

The method for growing a single crystal according to the present invention, in the process of pulling the single crystal by the CZ method from the crucible in which the heat shielding member is arranged in a manner to cover the other portion except the pulling region of the single crystal, In order to adjust the oxygen concentration, the output of each heating means facing the bottom and the periphery of the crucible is controlled.

[Action]

In the present invention, this makes it possible to finely control the amount of oxygen supplied to the growth region of the single crystal regardless of the pulling rate of the single crystal within that region.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments.

FIG. 1 is a schematic vertical sectional view showing a case where the method of the present invention is applied to the production of a silicon single crystal, in which 1 is a chamber, 2 is a crucible, 3 is a side heater, 4 is a bottom heater,
Reference numeral 5 indicates a heat insulating material, and 6 indicates a shielding member.

A crucible 2 is arranged in the center of the inside of the chamber 1, a side heater 3 is arranged between the crucible 2 and the heat insulating material 5, and a bottom heater 4 is arranged below the crucible 2, respectively, and the crucible 2 and the side heater 3 are further arranged. The shielding member 6 is arranged over the above. The crucible 2 has a double structure in which an outer crucible 2b made of graphite is arranged on the outer periphery of an inner crucible 2a made of quartz, and the upper end of a shaft 2c penetrating the bottom wall of the chamber 1 is connected to the center of the bottom of the crucible 2. The shaft 2c can be rotated and raised and lowered. The side heater 3 is formed in a cylindrical shape and surrounds the side peripheral wall of the crucible 2, and the bottom heater 4
Are formed in an annular shape, and are arranged below the bottom of the crucible 2 at intervals of 10 to 100 mm around the shaft 2c so that the position can be changed in the upward and downward directions, respectively, and the output can be controlled independently. Has become.

FIG. 2 is a schematic plan view of the bottom heater 4, which has an annular shape, and the heater wire 4a is arranged in a meandering manner between the inner and outer peripheral edges.

The shielding member 6 is formed in an inverted truncated cone shape (a supporting frame is not shown), and in this state, covers other portions on the crucible except the pulling region of the single crystal 9 and the side heater 3, and The lower end of the inverted truncated cone portion 6b faces the melt 7 in the crucible 2 to prevent the solidified silicon oxide from falling into the crucible, and to prevent the radiant heat of the crucible 2, the melt, the side heater 3, and the bottom heater 4 from radiating heat. The carrier gas such as Ar, which is cut off and passed through the chamber 1 from above, is guided to the center of the crucible 2 and is caused to flow along the surface of the melt from the center toward the peripheral edge side. The evaporative gas is discharged outward from the peripheral edge of the crucible 2,
The chamber 1 is guided to the exhaust port side (not shown) provided in the lower portion.

At the center of the upper wall of the chamber 1, a single-crystal protective cylinder 1a that doubles as a cylinder for supplying atmospheric gas is erected, and above the protective cylinder 1a is connected to a rotation / elevation mechanism (not shown). The upper end of the pulling shaft 8 is connected. A seed crystal 9 held by a chuck is hung at the lower end of the pulling shaft 8, and the seed crystal 9 is made to adapt to the melt 7 in the crucible 2 and then raised while rotating to make it a seed crystal. A single crystal 10 of silicon is allowed to grow on the lower end of 9.

Thus, in the method of the present invention, first, the crucible 2
After charging the raw material for crystal into the inside and melting it by using the side heater 3 and the bottom heater 4, the seed crystal 9 is immersed in the melt 7.
The seed crystal 9 is raised while rotating, and the growth of the single crystal 10 is started. At the same time when the growth of the single crystal 10 is started, the output control of the side heater 3 and the bottom heater 4 is started and the pulling of the single crystal 10 is completed. To continue.

FIG. 3 is a graph showing the output ratio (%) of the side heater 3 and the bottom heater 4, with the pulling rate of the single crystal on the horizontal axis.
The vertical heater output ratio (%) is plotted on the vertical axis. In the graph, the solid line shows the output ratio of the side heater 3, and the broken line shows the output ratio of the bottom heater 4. As is clear from this graph, the output ratio (%) of the side heater is set to 100% immediately after the start of the growth of the single crystal, and then gradually decreased to a pulling rate of 0.2 to 80%, and a pulling rate of up to 0.6. The rate is reduced to 70%, and after that, the state is maintained until the pulling rate is 0.7, and then the pulling rate is slightly increased at 0.7 or more. On the contrary, the output ratio of the side heater is gradually increased from 0 after the start of growth until the pulling rate is 0.2 and is increased to 20%. Further, the output ratio is gradually increased to 30% until the pulling rate is 0.6. When the pull rate reaches 0.7, the pull rate is gradually decreased from here to 0.8.

(Test example)

Using the equipment shown in FIG. 1 (crucible diameter 16 inches), the oxygen concentration target value in the single crystal was set to 16 × 10 ¹⁷ atm / cm ³ ,
The crucible 2 is rotated at a constant speed to pull up a single crystal having a diameter of 16 inches, and the side heater 3 and the bottom heater 4 placed 20 mm below the bottom of the crucible 2 in an output pattern as shown in FIG. Controls the output distribution of each, and crucible 2
A single crystal was produced while intensively heating a portion of 100 to 300 mm from the rotation center of, and the oxygen concentration in the growth direction of the obtained single crystal was detected.

The results are as shown in FIG. In FIG. 4, the horizontal axis indicates the pulling rate and the vertical axis indicates the oxygen concentration. As is clear from this graph, the oxygen concentration is close to the target value, and the pulling rate is 0.75 ± 3. An oxygen concentration distribution within% was obtained.

In the above-described embodiment, the configuration in which the single side heater 3 and the bottom heater 4 are provided on the peripheral wall and the bottom of the crucible 2 has been described, but the present invention is not limited to this, and a plurality of heaters are provided. Of course, each output may be controlled.

〔effect〕

As described above, in the method of the present invention, since the output of the heating means at the periphery and bottom of the crucible is controlled, the method is applied to a single crystal manufacturing facility using a shielding member, and the target in the growth direction of the single crystal is applied. It has an excellent effect that the oxygen concentration can be obtained without variation.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an implementation state of the method of the present invention, FIG. 2 is a schematic plan view of a bottom heater used for implementing the method of the present invention, and FIG. 3 is a graph showing an output control pattern of a heater in the method of the present invention. FIG. 4 is a graph showing an oxygen concentration distribution in the growth direction of a single crystal according to the method of the present invention,
FIG. 5 is a graph showing the influence of the shielding member on the temperature distribution of the melt in the crucible. 1 ... chamber, 2 ... crucible, 2a ... inner crucible, 2b ... outer crucible, 3 ... side heater, 4 ... bottom heater, 6 ...
… Shielding member, 9 …… Seed crystal, 10… Single crystal

Continuation of the front page (56) Reference JP 62-153191 (JP, A) JP 60-46993 (JP, A) JP 1-93489 (JP, A) JP 59-13695 (JP , A) JP 57-135796 (JP, A) JP 60-239389 (JP, A) JP 63-159285 (JP, A) JP 62-119189 (JP, A)

Claims (1)

(57) [Claims] 1. In the process of pulling a single crystal by a CZ method from a crucible provided with a shielding member so as to cover other portions except a pulled-up region of the single crystal, in order to adjust the oxygen concentration in the single crystal, A method for producing a single crystal, characterized in that the output of each heating means facing the periphery and bottom of the crucible is controlled.