JPH10291891A - Production of single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more exactly estimate an oxygen concn. in the axial direction of an ingot and to cut out a single crystal at which the desired oxygen concn. is obtainable in a process for producing the single crystal. SOLUTION: This process for producing the single crystal consists in storing a melt 7 of polycrystals in a crucible 3 disposed in a hermetic vessel 2 and cutting the ingot 10 of the single crystal pulled up from the melt in the position where the prescribed oxygen concn. is attained. In such a case, the process has a cutting stage for cutting out the single crystal by determining a cutting position in the axial direction of the ingot in accordance with the estimated value of the oxygen concn. calculated by the equation; Oi=axGP+bxCP+cxBt+dxAP+e (a, b, c, d, e, are empirically obtained coeffts.) when the velocity of flow of the inert gas supplied into the hermetic vessel is defined as GP, the liquid level position of the melt as CP, the number of use times of a heater for heating the melt to a prescribed tap. as Bt, the axial position of the ingot as AP and the oxygen concn. in the axial position AP of the ingot as Oi.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal part having an effective oxygen concentration from an ingot of a high-purity silicon single crystal or the like pulled from a melt of Si (silicon) polycrystal by the CZ (Czochralski) method. And a method for producing a single crystal.

[0002]

2. Description of the Related Art In the production of a silicon single crystal by the CZ method, the contact area between a molten metal and a quartz crucible changes as the amount of molten metal (melt) decreases due to crystal pulling, and the amount of oxygen eluted from the crucible changes. . Therefore, the pulled single crystal has a distribution in which the oxygen concentration in the axial direction is not constant but gradually decreases.

However, in recent years, a silicon single crystal as a semiconductor element substrate has strict tolerance standards for oxygen concentration in addition to the quality items such as resistivity and dislocation density. Only a part of the crystal can be used as a semiconductor element, and there is a problem that the yield is reduced unless the cutting position at which a single crystal within the standard is obtained is accurately determined.

[0004] Among the above-mentioned quality items, the criteria for the resistivity and the dislocation density are clear, whereas the criteria for the oxygen concentration are not particularly clear. The cutting position was determined based on the correlation relating to the active gas. That is, for example,
No. 94 discloses a technique for estimating the oxygen concentration from the flow rate of the inert gas supplied into the chamber and the furnace pressure during pull-up growth based on the previous measurement results.

[0005]

However, means for cutting an ingot based on the estimated value of the oxygen concentration based on the flow rate of the inert gas and the furnace pressure to obtain a single crystal having a desired oxygen concentration include the following. Such issues remain.
That is, based on the measurement result of the single crystal, the flow rate of the inert gas and the furnace pressure are used as parameters, and the coefficient of the relational expression applied at the time of the next pull-up growth is calculated, which is calculated by the obtained relational expression. At present, there is still a large error between the theoretical value of the oxygen concentration and the actually measured value of the oxygen concentration of the single crystal. Therefore, in order to determine a more accurate cutting position, it was necessary to more accurately estimate the oxygen concentration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to more accurately estimate the oxygen concentration in the axial direction of an ingot and to cut out a single crystal at a position where a desired oxygen concentration can be obtained. It is an object of the present invention to provide a method for producing the same.

[0007]

The present invention has the following features to attain the object mentioned above. That is, in the method for producing a single crystal of the present invention, a polycrystalline melt is stored in a crucible provided in an airtight container, and the single crystal ingot pulled up from the melt is placed at a position where a predetermined oxygen concentration is reached. In the method for producing a single crystal cut by the method, the flow rate of the inert gas supplied into the hermetic container is GP, the liquid surface position of the melt is CP, and the number of times of using the heater for heating the melt to a predetermined temperature is Bt, when the axial position of the ingot is AP and the oxygen concentration at the axial position AP of the ingot is Oi, the following relational expression: Oi = a × GP + b × CP + c × Bt + d × AP + e (d and e are experimentally obtained coefficients). A technique is provided that includes a cutting step of determining a cutting position in the axial direction of the ingot and cutting a single crystal based on an estimated value of the oxygen concentration calculated by an experimentally obtained coefficient. Adopted.

The method for producing a single crystal includes a cutting step of determining a cutting position in the axial direction of the ingot and cutting the single crystal based on the estimated value of the oxygen concentration calculated by the above relational expression. A multiple regression analysis is performed based on the plurality of variables that have been experimentally found to affect the oxygen concentration, and the oxygen concentration in the axial direction of the ingot is more accurately estimated. Therefore, the cutting position can be determined more accurately than when the cutting position is simply determined based on the oxygen concentration calculated from the flow rate of the inert gas and the furnace pressure.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method for producing a single crystal according to the present invention will be described below with reference to FIG.

FIG. 1 is a schematic diagram showing an example of a silicon single crystal pulling apparatus used in the present embodiment. In this single crystal pulling apparatus 1, a crucible 3 and a heater 4 are arranged concentrically in a chamber 2 which is a hollow airtight container.

The crucible 3 is made of quartz (SiO ₂ ), and is mounted on a susceptor 6 on a shaft 5 vertically erected at the lower center of the chamber 2. It is configured to rotate at a predetermined angular velocity above. Further, in the crucible 3, a melt of Si polycrystal (a raw material of a semiconductor single crystal melted by heating) 7 is stored.

The heater 4 is arranged so as to surround the outer periphery of the crucible 3 and heats and melts the semiconductor raw material in the crucible 3 and keeps the generated melt 7 warm. Usually, resistance heating is used. Further, the inside of the chamber 2 can be evacuated by a vacuum pump or the like, and the inside of the chamber 2 can be supplied with argon (Ar) as an inert gas at a predetermined flow rate from above.

With the single crystal pulling apparatus 1 described above, the crucible 3
A seed crystal 9 is hung on a pulling shaft 8 arranged above and on the axis, and an ingot 10 of Si, which is a semiconductor single crystal, is grown above the melt 7 using the seed crystal 9 as a nucleus.

Next, a description will be given of a cutting step of cutting a single crystal in the axial direction of the ingot 10 of the Si single crystal pulled by the single crystal pulling apparatus 1.

First, in order to determine the cutting position in the axial direction of the pulled ingot 10, the oxygen concentration is estimated using the following relational expression. At this time, the estimation is performed by introducing a plurality of variables that are empirically known to affect the oxygen concentration.

That is, the flow rate of argon supplied into the chamber 2 is GP, the liquid surface position of the melt 7 (distance from the upper end of the heater 4 to the liquid surface of the melt 7) is CP, and the melt 7 is maintained at a predetermined temperature. Number of uses of heater 4 to be heated (heater life)
Is Bt, the axial position of the ingot 10 is AP, and the oxygen concentration at the axial position AP of the ingot is Oi, the following relational expression: Oi = a × GP + b × CP + c × Bt + d × AP + e The oxygen concentration Oi is calculated by multiple regression analysis using d and e, coefficients obtained experimentally.

Based on the estimated value of the oxygen concentration Oi thus calculated, the cutting position in the axial direction of the ingot 10 is determined, and a single crystal is cut out. Each coefficient of the above relational expression is calculated from a previously measured value and varies depending on the type of apparatus, pulling conditions, and the like. In particular, the coefficient e is a value unique to the device, for example, the value of the crucible 3. Different values are introduced depending on the type (difference in material such as manufacturer and raw material (quartz powder)).

The axial position AP of the ingot 10
Sets the position of the ingot 10 from the shoulder to the straight body (where the target diameter is reached) as TOP (position zero). Furthermore, the flow rate GP of argon may be defined as (flow rate of argon) / (furnace pressure) and introduced into the above relational expression.

In this single crystal manufacturing method, the single crystal is cut out by determining the cutting position in the axial direction of the ingot 10 based on the estimated value of the oxygen concentration Oi calculated by the above relational equation. In addition to the above, by performing a multiple regression analysis based on a plurality of variables such as the liquid surface position CP of the melt 7 which has been experimentally found to affect the oxygen concentration, the oxygen concentration in the axial direction of the ingot 10 is obtained. Is estimated with high accuracy. Therefore, the cutting position is determined more accurately than simply the oxygen concentration calculated based on the flow rate of argon and the furnace pressure.

[0020]

EXAMPLE For a single crystal actually obtained by the above method for producing a single crystal, an estimated value of the oxygen concentration at the cutting position by the above relational expression and an estimated value of the oxygen concentration using only the argon flow rate were actually measured. Table 1 shows a comparison with the obtained oxygen concentration.

[0021]

[Table 1]

(The underline in Table 1 is drawn up to the second decimal place (0.01 × 10 ¹⁸ atoms / cm ³ ) in agreement with the actually measured value.) As can be seen from Table 1, only argon is used. The accuracy of the multiple correlation of the present embodiment including the liquid level position CP and the number of times Bt of using the heater is better than the simple correlation with the flow velocity GP. That is, the one that matches up to the second decimal place is
The estimated value [Oi-Ar] based on the argon flow rate GP is 2
/ 8, whereas the estimated value [O
In [i], it was 7/8.

An example of the relational expression used in this embodiment is shown below. Oi = −0.074 × GP + 0.0004 × CP-0.
0014 × Bt + 0.0004 × AP + 1.293

[0024]

As described above, according to the present invention, the cutting step for determining the cutting position in the axial direction of the ingot and cutting the single crystal based on the estimated value of the oxygen concentration calculated by the above relational expression is performed. Since it is provided, it is possible to more accurately estimate the oxygen concentration in the axial direction of the ingot compared to the oxygen concentration calculated simply from the flow rate of the inert gas and the furnace pressure, and easily and accurately determine the cutting position. be able to. Therefore, by improving the accuracy of estimation of the oxygen concentration in the axial direction, the yield is improved and the number of times of re-cutting, that is, the number of times of cutting until the oxygen concentration reaches the standard can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a single crystal pulling apparatus in one embodiment of a method for manufacturing a single crystal according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Chamber (airtight container) 3 Crucible 4 Heater 7 Melt 10 Ingot CP Liquid level position of melt

 ──────────────────────────────────────────────────の Continuing on the front page (72) Koji Hosoda, Inventor 1-5-1, Otemachi, Chiyoda-ku, Tokyo Within Mitsubishi Materials Silicon Co., Ltd. (72) Inventor Yasuo Ito 1-5, Otemachi, Chiyoda-ku, Tokyo No. 1 Mitsubishi Materials Silicon Co., Ltd.

Claims (1)

[Claims] 1. Production of a single crystal in which a polycrystalline melt is stored in a crucible provided in an airtight container, and a single crystal ingot pulled up from the melt is cut at a position where a predetermined oxygen concentration is obtained. In the method, the flow rate of the inert gas supplied into the hermetic container is GP, the liquid surface position of the melt is CP, and the number of times of using the heater for heating the melt to a predetermined temperature is B.
t, the axial position of the ingot AP, the oxygen concentration at the axial position AP of the ingot O
When i is assumed, the following relational expression: Oi = a × GP + b × CP + c × Bt + d × AP + e (a, b, c, d, e are estimated values of oxygen concentration calculated by an experimentally obtained coefficient) A method for determining a cutting position in the axial direction of the ingot based on the above, and cutting a single crystal.