JP2681114B2 - Single crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a single crystal capable of making the oxygen concentration uniform in the crystal growth direction of a single crystal produced by the Czochralski method (CZ method). About.

[Conventional technology]

In general, the Czochralski method (CZ method) is used to manufacture a single crystal. For example, a single crystal raw material is put into a crucible placed in a chamber, and this is heated and melted by a heater, and then melted in this melt. It is carried out by immersing a seed crystal hung on a pulling shaft and pulling it upward while rotating it to grow a single crystal at the lower end of the seed crystal.

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

Therefore, it is necessary to contain oxygen in the silicon single crystal at a uniform concentration in the crystal growth direction. For this purpose, the oxygen concentration in the melt of the single crystal raw material in the crucible, especially in the single crystal growth region, should be controlled. Uniformity is required.

By the way, most of the oxygen in the crucible is melted in the silicon melt and quartz is supplied to the silicon melt in the process of melting polycrystalline silicon, which is a crystal raw material, in the quartz crucible.

Therefore, the amount of molten liquid in the crucible is large, the contact area with the quartz crucible is large, and the oxygen concentration is high at the beginning of the crystal growth, and the growth of the single crystal proceeds and the amount of molten liquid decreases as the amount of molten liquid in the crucible decreases. There is a tendency, and with this,
The oxygen concentration taken into the single crystal also increases while the oxygen concentration in the melt is high, and the oxygen concentration in the single crystal also decreases as the growth of the single crystal progresses.

However, the relationship between the two is not necessarily unitary, and is related to the amount of quartz dissolved in the crucible in addition to the amount of molten liquid, the flow of the molten liquid that carries dissolved oxygen, the amount of evaporated oxygen in the form of silicon monoxide, etc. Moreover, the amount of dissolved quartz depends on the reaction temperature, in other words, the heating distribution from the heater to the crucible, the flow of the melt depends on the crucible and the rotation speed of the single crystal, and the amount of evaporated oxygen depends on the pressure in the chamber, Ar flow rate, etc. It is known to be affected, and it is extremely difficult to maintain a constant concentration from the beginning to the end of the crystal because the oxygen concentration of the single crystal is determined by the complex combination of these factors. ..

[Problems to be solved by the invention]

As a countermeasure against this, a method has been proposed in which the rotational speed of the crucible and the oxygen concentration in the single crystal are focused, and the rotational speed of the crucible is changed according to the decrease in the amount of the raw material melt (JP-A-57-
27996, JP-A-57-135796).

Although it is recognized that the homogeneity in the single crystal is slightly improved by these methods, the fluctuation range of the oxygen concentration in the crystal can be ± 0.5 × 10 (10 ¹⁷ atm / cm ³ ) also by the experiment of the present inventor. There wasn't.

The present inventor has conducted experiments and researches to make the oxygen concentration in the growth direction of such a single crystal uniform, and as a result, the oxygen concentration in the melt in the crucible is closely related to the inner bottom wall temperature of the crucible. I found out that.

FIG. 4 is a graph showing the oxygen concentration on the vertical axis and the solidification rate of the single crystal on the horizontal axis. The circles in the graph are plotted when the output ratio of the bottom heater is 40%. The plots with triangles show the results when the output ratio of the bottom heater is 20%, and the plots with squares show the results when the output ratio of the bottom heater is zero.

As is clear from this graph, it is understood that the oxygen concentration in the single crystal shifts higher when the output ratio of the bottom heater is increased.

The reason for this is not fully understood, but it can be considered as follows. FIG. 5 is an explanatory view showing the dynamics of oxygen in the quartz inner crucible 2a. As described above, the oxygen in the melt in the inner crucible 2a is the melt and the inner crucible made of quartz.
2a is supplied from the contact surface with the wall as shown by the arrow, but since the flow of the molten liquid in the inner crucible 2a is as shown by the white arrow, it was supplied from the side peripheral wall side of the inner crucible 2a. Oxygen flows toward the surface of the melt and is vaporized as it is, whereas oxygen supplied from the bottom wall flows downward toward the growth region of the single crystal 9.
Therefore, as compared with oxygen supplied from the peripheral wall side in the inner crucible 2a, the ratio of oxygen supplied from the bottom wall side into the single crystal becomes large, and the influence of the bottom heater output increases accordingly. Become. Therefore, it is understood that in the initial stage of crystal growth, if the temperature of the bottom wall of the crucible is kept low and the output of the bottom heater is changed so as to increase with the growth, uniform oxygen can be obtained in the growth direction.

The present invention has been made based on such knowledge,
It is an object of the invention to provide a method for producing a single crystal in which the oxygen concentration in the growth direction of the single crystal can be made uniform from the start to the end of the crystal growth.

[Means for solving the problem]

The single crystal growth method according to the present invention, in order to make the oxygen concentration in the single crystal in the pulling direction uniform in the process of pulling the single crystal from the crucible by the CZ method, the temperature of the crucible wall is controlled to a set temperature. The output of each heating means facing the crucible and the bottom of the crucible is controlled, and in addition to this, the rotation speed of the crucible about its axis is controlled.

[Action]

In the present invention, this makes it possible to more precisely control the amount of oxygen supplied to the growth region of the single crystal.

〔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 an embodiment of the method of the present invention, in which 1 is a chamber, 2 is a crucible, 3 is a side heater, 4 is a bottom heater, and 5 is a heat insulating material.

A crucible 2 is arranged at 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. The side heater 3 surrounds the side peripheral wall of the crucible 2 and the bottom heater 4
Are arranged around the shaft 2c so as to face the bottom of the crucible 2 and the output of each can be controlled independently.

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.

A raw material for single crystal, for example, polycrystalline silicon is supplied into the crucible 2 and is heated and melted by the side heater 3 and the bottom heater 4.

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 7 is connected, and the seed crystal 8 held by a chuck is hung at the lower end of the pulling shaft 7. The seed crystal 8 is allowed to adapt to the melt 6 in the crucible 2 and then rotated. The silicon single crystal 9 is grown at the lower end of the seed crystal 8 by raising the temperature while raising the temperature.

Thus, in the method of the present invention, first, the crucible 2
A crystal raw material is charged into the inside, and after melting 7 by using the side heater 3 and the bottom heater 4, the seed crystal 8 is immersed in the melt 6 and the seed crystal 8 is rotated and raised to grow a single crystal 9. However, prior to the start of the growth of the single crystal 9 or at the same time as the start of the growth, the output control of the side heater 3 and the bottom heater 4 is started, and in addition, the rotation speed control of the crucible 2 is started. This is continued until the pulling of the single crystal is completed.

FIG. 2 is a graph showing the control patterns of the side heater 3 and the bottom heater 4, where the horizontal axis represents the solidification rate of the single crystal, the vertical axis represents the oxygen concentration (× 10 ¹⁷ atm / cm ³ ), and the set temperature (° C). ,
The heater output (%) is shown for each. In the graph, the crucible bottom (inner bottom of inner crucible 2a) temperature target profile,
Shows the outputs of the side heater 3 and the bottom heater 4. Is the oxygen concentration in the obtained single crystal.

The crucible bottom temperature profile has been experimentally set in advance so as to keep the oxygen concentration in the single crystal constant, and the side temperature of the crucible 3 and the bottom heater 4 are controlled during the crystal growth to make the crucible low temperature follow the initial target profile. It

[Test Example 1] The oxygen concentration target value in the single crystal was measured by the equipment shown in FIG.
With 16 × 10 ¹⁷ atm / cm ³ and rotating the crucible 2 at a constant speed, each side heater and bottom heater output was controlled in a pattern as shown in FIG. 2, and as a result, the oxygen concentration in the growth direction of the single crystal was 15.5. It was confirmed that it can be accommodated within the range of ~ 16.4 × 10 ¹⁷ atm / cm ³ .

[Test Example 2] In order to achieve this, 16 × 10 ¹⁷ atm / cm ³ and 14 × 10 ¹⁷ atm / cm ³ are set as the target oxygen concentration values in the single crystal in the manner as shown in FIG. The output of the bottom heater with respect to the side heater was controlled as shown in FIG.

In the graph, the target oxygen concentration in the single crystal is 16 × 10 ¹⁷ atm /
It is the bottom heater output at cm ³ , and ′ indicates the oxygen concentration in the single crystal obtained at this time.

Indicates the bottom heater output when the target oxygen concentration in the single crystal is 14 × 10 ¹⁷ atm / cm ³ , and ′ indicates the oxygen concentration in the single crystal obtained at this time.

The rotation speed of the crucible was fixed at 8 rpm in the former case and 10 to 15 rpm in the latter case, which was controlled to increase according to the progress of single crystal growth. 15.8〜16.5 × 10 ¹⁷ atm / cm ³ , 1 respectively
It was confirmed that 3.5 to 14.1 × 10 ¹⁷ atm / cm ³ was obtained, and that the uniformity which could not be obtained by the conventional method was obtained.

〔effect〕

As described above, according to the method of the present invention, the fluctuation range of the oxygen concentration in the growth direction of the single crystal can be significantly reduced, so that the uniformity is high and the high reliability of the product as a semiconductor substrate or the like can be obtained. The present invention has excellent effects such as yield can be obtained.

[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 graph showing control contents in the method of the present invention, FIG. 3 is a graph showing other control contents of the method of the present invention, and FIG. FIG. 5 is a graph showing the relationship between the solidification rate and the output ratio of the bottom heater obtained in the experiment conducted by the inventor, and FIG. 5 is an explanatory diagram showing the dynamics of oxygen in the crucible. 1 ... Chamber, 2 ... Crucible, 2a ... Inner crucible, 2b ... Outer crucible, 3 ... Side heater, 4 ... Bottom heater, 8 ...
… Seed crystal, 9… 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 60- 239389 (JP, A) JP 63-159285 (JP, A) JP 62-119189 (JP, A) JP 59-13695 (JP, A) JP 57-135796 (JP, A) 63-50881 (JP, U)

Claims (2)

(57) [Claims] 1. In the process of pulling a single crystal from a crucible by the CZ method, in order to make the oxygen concentration in the single crystal uniform in the pulling direction, the temperature around the crucible wall is controlled to a set temperature, the surroundings of the crucible, A method for producing a single crystal, which comprises controlling the output of each heating means facing the bottom. 2. In the process of pulling a single crystal from a crucible by the CZ method, in order to make the oxygen concentration in the single crystal uniform in the pulling direction, the rotation speed around the axis of the crucible, and the circumference and bottom of the crucible. A method for producing a single crystal, characterized in that the output of each heating means facing the surface is controlled.