CN112639175A

CN112639175A - Method for growing single crystal silicon

Info

Publication number: CN112639175A
Application number: CN201880095845.XA
Authority: CN
Inventors: 末若良太; 滨田建
Original assignee: Sumco Corp
Current assignee: Sumco Corp
Priority date: 2018-08-23
Filing date: 2018-08-23
Publication date: 2021-04-09
Also published as: WO2020039553A1; KR102461073B1; TWI722480B; TW202014565A; KR20210010583A; JP7036217B2; JPWO2020039553A1

Abstract

The present invention addresses the problem of providing a method for growing a defect-free single crystal silicon that can accurately grow a defect-free single crystal in consideration of the effect of stress acting on the single crystal during growth of the single crystal. The method for growing a silicon single crystal of the present invention uses a single crystal growing apparatus in which a water cooling body (11) surrounding a single crystal (8) being grown is arranged and a heat shield (10) surrounding the outer peripheral surface and the lower end surface of the water cooling body (11) is arranged, and comprises a gap variable control for pulling the single crystal while changing the gap between the liquid surface of a raw material melt (9) and the heat shield (10), and the temperature gradient in the direction of a pulling axis in the vicinity of a solid-liquid interface at the center of the single crystal (8) is G_cAnd a temperature gradient G in the direction of the pulling axis in the vicinity of the solid-liquid interface at the outer periphery of the single crystal (8)_e、A＝0.1769×G_c+0.5462, so as to satisfy 0.9 XA ≦ G_c/G_ePulling the single crystal (8) under a condition of not more than 1.1 xA.

Description

Method for growing single crystal silicon

Technical Field

The present invention relates to a method for growing a silicon single Crystal by a czochralski method (hereinafter, referred to as "CZ" method), and more particularly, to a method for growing a defect-free Crystal which does not cause point defects such as infrared scatterer defects such as OSF (Oxidation Induced Stacking Fault), COP (Crystal Originated Particle), and Dislocation clusters such as LD (Interstitial-type Large Dislocation).

Background

A single crystal silicon which is a substrate material of a semiconductor device is often produced by the CZ method. In the CZ method, a seed crystal is immersed in a silicon raw material melt stored in a quartz crucible in a chamber in which an inert gas atmosphere under reduced pressure is maintained, and the immersed seed crystal is slowly pulled up. Thereby, the single crystal silicon is grown by being connected to the lower end of the seed crystal.

Fig. 1 is a schematic diagram illustrating the generation of various defects according to vornkov theory. As shown in FIG. 1, in the Voronkov theory, when the pull rate is V (mm/min) and the temperature gradient in the pull axis direction in the vicinity of the solid-liquid interface of the ingot (single-crystal silicon) is G (. degree. C./mm), the relationship between V/G and the point defect concentration is schematically shown with the ratio V/G of V/G on the horizontal axis and the concentration of the vacancy-type point defects and the concentration of interstitial silicon-type point defects on the same vertical axis. Further, a case where there is a boundary between the region where the void type point defect occurs and the region where the interstitial silicon type point defect occurs, and the boundary is determined by V/G will be described. Hereinafter, the "temperature gradient in the pulling axis direction" may be simply referred to as a "temperature gradient".

The void type point defect is a point defect originating from voids lacking silicon atoms constituting a crystal lattice, and a typical type of an aggregate of the void type point defects is COP. Interstitial silicon type point defects are based on interstitial silicon in which silicon atoms enter crystal interstitials, and a representative type of an aggregate of the interstitial silicon type point defects is LD.

As shown in FIG. 1, when V/G exceeds the critical point, a single crystal in which void type point defects are dominant is grown. On the contrary, when V/G is lower than the critical point, a single crystal in which interstitial silicon type point defects are dominant is grown. Therefore, when V/G is lower than a critical point (V/G)₁In the range of [ I ], interstitial silicon type point defects are dominant in the single crystal, and a region in which aggregates of interstitial silicon point defects appear [ I ]]And LD is generated. When V/G exceeds a value greater than the critical point (V/G)₂In the range of (1), hollow hole type point defects in a single crystalPredominantly, regions in which aggregates of void-type point defects appear [ V ]]And a COP is produced.

When V/G is at the critical point ~ (V/G)₁In the range of [ B ], a defect-free region [ P ] in which interstitial silicon type point defects do not exist as aggregates appears in the single crystal_I]When V/G is at the critical point ~ (V/G)₂In the range of (1), a defect-free region [ P ] in which a void-type point defect does not exist as an aggregate appears in the single crystal_V]Defects including OSF, COP and LD were not generated. Here, the defect-free region [ P ]_I]And defect-free region [ P_V]Merged to be called a non-defective region [ P]. In the defect-free region [ P_V]Adjacent region [ V ]](V/G in (V/G)₂～(V/G)₃Range) exists the OSF region forming the OSF nucleus.

FIG. 2 is a schematic view showing a relationship between a pulling rate and a defect distribution when a single crystal is grown. The defect distribution shown in fig. 2 shows the results obtained by growing single crystal silicon while gradually lowering the pulling rate V, cutting the grown single crystal along the central axis (pulling axis) to obtain a plate-like sample, adhering Cu to the surface thereof, applying a heat treatment, and observing the plate-like sample by an X-ray topography method.

As shown in FIG. 2, when the single crystal is grown at a high pulling rate, a region [ V ] in which aggregates (COP) having void-type point defects are present is formed over the entire region in a plane perpendicular to the pulling axis direction of the single crystal]. When the pulling rate is gradually decreased, an OSF region appears in a ring shape from the outer periphery of the single crystal. The OSF region has a diameter gradually decreasing with decreasing pulling rate, and when the pulling rate becomes V₁And disappear when the liquid is used. Thus, instead of the OSF region, a defect-free region [ P ] appears](region [ P ]_V]) The whole region in the single crystal plane is composed of a defect-free region [ P ]]And (4) occupation. And, if the pulling speed is reduced to V₂Then, a region [ I ] in which an aggregate (LD) having interstitial silicon type point defects is present appears]Finally, the defect-free region [ P ] is replaced](region [ P ]_I]) The entire region in the single crystal plane is defined by region [ I ]]And (4) occupation.

Recently, as the miniaturization of semiconductor devices progresses, the demand for the quality of silicon wafers is increasing. Therefore, in the production of silicon single crystal as a silicon wafer material, there is a strong demand for a technique for growing defect-free crystal in which various point defects such as OSF, COP, and LD are eliminated and a defect-free region [ P ] is distributed over the entire in-plane region.

In order to satisfy this requirement, when pulling up single-crystal silicon, as shown in fig. 1 and 2, the following control is required: in the hot zone, ensuring that V/G falls into the 1 st critical point (V/G) of the aggregate without generating interstitial silicon type point defects over the entire in-plane region₁Above critical point (V/G) of the aggregate without generating void hole type point defect₂Within the following ranges. In actual operation, the target of the pulling speed is set at V₁And V₂In between (e.g., the median of the two), and falls into V even if the pull rate is changed during the growth₁～V₂Within a range (referred to as "pulling rate limit" or "PvPi limit").

Further, since the temperature gradient G depends on the size of the hot zone in the vicinity of the solid-liquid interface, the hot zone is appropriately designed in advance before growing the single crystal. In general, the hot zone is composed of a water cooling body disposed to surround the growing single crystal and a heat shielding body disposed to surround the outer peripheral surface and the lower end surface of the water cooling body. Here, as a control index in designing the hot zone, the temperature gradient G at the center of the single crystal was used_cAnd temperature gradient G of the outer periphery of the single crystal_e. In order to grow a defect-free crystal, for example, in the technique disclosed in patent document 1, a temperature gradient G is applied to the central portion of a single crystal_cTemperature gradient G with the outer periphery of the single crystal_eDifference Δ G (═ G)_e-G_c) Within 0.5 ℃/mm.

However, in recent years, it has been found that the critical V/G, which is the V/G to be targeted in the growth of defect-free crystals, varies depending on the stress acting on the single crystal during the growth of the single crystal. Therefore, in the technique disclosed in patent document 1, since the effect of the stress is not considered at all, there are cases where a perfect defect-free crystal cannot be obtained.

In this respect, for example, patent document 2 discloses that a single crystal having a diameter of 300mm or more is used as a growth target, and the use of the single crystal is consideredForce effect, temperature gradient G of the central portion of the single crystal_cTemperature gradient G with the outer periphery of the single crystal_eThe ratio of (hereinafter, also referred to as "temperature gradient ratio") G_c/G_eTo greater than 1.8. However, in the technique disclosed in patent document 2, even when stress effect in the single crystal is considered, a perfect defect-free crystal is not necessarily obtained. The reason for this is considered to be that the temperature gradient ratio G_c/G_eThe management range of (2) is not sufficient.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 11-79889

Patent document 2: japanese patent No. 4819833

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for growing a silicon single crystal, which can accurately grow a defect-free crystal in consideration of a stress effect acting on the single crystal when growing the single crystal.

Means for solving the technical problem

In order to achieve the above object, the inventors of the present invention paid attention to the stress acting on a single crystal when growing the single crystal, conducted numerical analysis taking the stress into consideration, and conducted intensive studies repeatedly. As a result, the following findings were obtained.

FIG. 3 is a graph showing stress σ acting on a single crystal_meanGraph of relationship to critical V/G. Critical V/G and mean stress σ were investigated by comprehensive heat transfer analysis with various modifications to the hot zone conditions_meanAs a result of the relationship between them, it was found that (critical V/G) ═ 0.17+0.0013 × σ as shown in fig. 3_mean。

The stress distribution in the vicinity of the solid-liquid interface of the single crystal is regular, and the distribution of the in-plane stress can be grasped by the stress or temperature gradient limited to the central portion of the single crystal. As a result, the temperature gradient at the center of the single crystal or the stress at the center of the single crystal is determined in consideration of the stress effect in the single crystal, whereby the in-plane temperature gradient most suitable for growing defect-free crystals can be graspedThe temperature distribution can be grasped, and the optimal temperature gradient ratio G can be further grasped_c/G_e. And, by optimizing the temperature gradient ratio G_c/G_eThe optimum temperature gradient ratio G is set by designing the appropriate dimension of the hot zone as a management index_c/G_eThe defect-free crystal can be accurately grown within the standard control range.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for growing a silicon single crystal by pulling a single crystal having a diameter of 300mm or more from a molten raw material in a crucible disposed in a chamber by the CZ method, wherein a single crystal growing apparatus is used in which a water cooling body surrounding the single crystal being grown is disposed and a heat shield surrounding an outer peripheral surface and a lower end surface of the water cooling body is disposed, and a single crystal growing apparatus is used in which a water cooling body surrounding the single crystal being grown is disposed and a heat shield surrounding an outer peripheral surface and a lower end surface of the water cooling body is disposed, the method including a gap variable control of pulling the single crystal while changing a gap between a liquid level of the molten raw material and the heat shield disposed above the molten raw material, and when a temperature gradient in a pulling axis direction in the vicinity of a solid-liquid interface in a_cAnd a temperature gradient in the direction of the pulling axis in the vicinity of a solid-liquid interface at the outer periphery of the single crystal is G_e、A＝0.1769×G_c+0.5462, so as to satisfy 0.9 XA ≦ G_c/G_ePulling the single crystal under the condition of less than or equal to 1.1 xA.

In the past, it is considered that in order to widen the pulling rate limit at which a defect-free crystal can be obtained, it is preferable to make the in-plane distribution of the temperature gradient in the crystal uniform. However, according to the new findings of the inventors of the present application, it was found that the pulling rate limit could not be increased unless the in-plane distribution of the temperature gradient in the crystal was set in accordance with the stress state in the crystal. According to the present invention, the temperature gradient ratio G is set appropriately in consideration of the effect of stress in the single crystal_c/G_eSo that a defect-free crystal can be accurately grown from the upper end to the lower end of the single crystal. Further, the single crystal produced by the present invention can be used, whereby efficiency can be improvedHigh quality wafers with a diameter of 300mm or 450mm are produced. Further, when the diameter of the wafer is 300mm, the diameter of the single crystal (straight body portion) is preferably 301mm or more and 340mm or less, and when the diameter of the wafer is 450mm, the diameter of the single crystal (straight body portion) is preferably 451mm or more and 510mm or less.

In the present invention, the variable gap control preferably controls the crucible raising speed using a total value of three values: a quantitative value of a crucible raising speed required for maintaining the gap, which varies as the single crystal is pulled, at a constant distance; a variation value of the crucible lifting speed obtained from the variation amount of the target value of the gap; and a correction value of the crucible lifting speed obtained from a difference between the target value and an actual measurement value of the gap. In this control, the correction value of the crucible raising speed is specialized only for correction for eliminating the deviation between the target value and the measured value of the gap, and therefore, the crucible raising speed amplitude can be prevented from increasing. Therefore, by stabilizing the crystal thermal history of the single crystal silicon from the upper end to the lower end, the variation in the in-plane distribution of crystal defects can be suppressed, and the production yield of high-quality single crystal silicon can be improved.

In the present invention, it is preferable to obtain the amount of change in the target value of the gap from a gap distribution that defines a relationship between the crystal length that changes as the single crystal is pulled and the target value of the gap. Thus, the fluctuation value of the crucible raising speed can be easily and accurately obtained, and the stability of the crucible raising speed can be further improved.

In the present invention, it is preferable that the correction value is obtained from a difference between the target value of the gap obtained from the gap distribution and the measured value of the gap. This makes it possible to easily and accurately obtain a correction value of the crucible raising speed, and further improve the stability of the crucible raising speed.

In the method for producing a single crystal according to the present invention, it is preferable that the volume decrease amount of the melt is determined from a volume increase amount of the single crystal accompanying pulling of the single crystal, and the fixed amount is determined from the volume decrease amount of the melt and an inner diameter of the crucible. Thus, the quantitative value of the crucible raising speed can be simply and accurately obtained.

In the present invention, the gap profile preferably includes at least one gap constant control section that maintains the gap at a constant distance and at least one gap variable control section that slowly changes the gap. In this case, the gap variable control section may be provided after the gap constant control section in the latter half of the main body portion growing process of the single crystal, or may be provided before the gap constant control section in the former half of the main body portion growing process of the single crystal. Preferably, the gap profile includes 1 st and 2 nd variable gap control sections in which the gap is gradually changed, the 1 st variable gap control section is provided before the constant gap control section in the first half of the main body portion growing process of the single crystal, and the 2 nd variable gap control section is provided after the constant gap control section in the second half of the main body portion growing process of the single crystal. This makes it possible to maintain the in-plane distribution of crystal defects from the upper end to the lower end of the single crystal substantially constant, thereby improving the production yield of high-quality single crystals. The first half of the body growth step is a step of dividing the entire length of the body of the single crystal into 2 equal parts to produce a single crystal in the first half of the body, and the second half of the body growth step is a step of producing a single crystal in the second half of the body.

In the method for producing a single crystal according to the present invention, it is preferable that the measured value of the gap is calculated from a mirror image position of the heat shield reflected on the liquid surface of the melt photographed by a camera. Thus, the measurement value of the clearance can be accurately obtained with a simple structure at low cost.

Effects of the invention

According to the method for growing a silicon single crystal of the present invention, the stress effect in the single crystal is taken into consideration, and the temperature gradient ratio G is appropriately set_c/G_eSo that defect-free crystals can be accurately grown.

Drawings

Fig. 1 is a schematic diagram illustrating the generation of various defects according to vornkov theory.

FIG. 2 is a schematic view showing a relationship between a pulling rate and a defect distribution when a single crystal is grown.

FIG. 3 is a graph showing stress σ at the center of a single crystal_meanGraph of relationship to critical V/G.

FIG. 4 is a graph illustrating a temperature gradient G per the central portion of a single crystal_cThe distribution of the optimal in-plane temperature gradient G (r) of (1).

FIG. 5 is a view illustrating a temperature gradient G with respect to the central portion of the single crystal_cCorresponding optimal temperature gradient ratio G_c/G_eA graph of the distribution of (2).

FIG. 6 is a graph illustrating stress σ per single crystal center portion_{mean_c}The distribution of the optimal in-plane temperature gradient G (r) of (1).

FIG. 7 is a graph illustrating stress σ with respect to the center portion of a single crystal_{mean_c}Corresponding optimal temperature gradient ratio G_c/G_eA graph of the distribution of (2).

Fig. 8 is a schematic diagram schematically showing the configuration of a single crystal growing apparatus to which the method for growing single crystal silicon of the present invention can be applied.

FIG. 9 shows the gap H between the heat shield 10 and the liquid surface of the raw material melt 9 and the temperature gradient ratio G_c/G_eA graph of the relationship of (a).

Fig. 10 is a flowchart showing a manufacturing process of single crystal silicon.

FIG. 11 is a schematic cross-sectional view showing the shape of a single crystal silicon ingot.

Fig. 12 is a schematic diagram for explaining a relationship between a gap distribution and a crystal defect distribution in the crystal pulling process, and particularly shows a case of the gap constant control in the past.

FIG. 13 is a schematic view for explaining the relationship between the distribution of the gap and the distribution of crystal defects in the crystal pulling process, and particularly shows the case of the gap variable control of the present invention.

Fig. 14 is a block diagram illustrating a gap variable control function for a method of calculating a crucible raising speed.

Detailed Description

Hereinafter, embodiments of the method for growing a silicon single crystal of the present invention will be described in detail.

1. Critical V/G type introducing stress effect

When a defect-free crystal is grown, it is assumed that a target pull rate (hereinafter, also referred to as "critical pull rate") is V_cri(unit: mm/min) and G (unit: DEG C/mm) as a temperature gradient in the direction of the pulling axis in the vicinity of the solid-liquid interface of the single crystal, the ratio of the temperature gradient to the critical value V_criThe following formula (1) can be used to define the structure of the crystal structure/G, when the stress effect acting on the single crystal during growth of the single crystal is introduced. The vicinity of the solid-liquid interface of the single crystal as referred to herein means a range of the single crystal temperature from the melting point to 1350 ℃.

V_cri/G＝(V/G)σ_mean＝0+α×σ_mean……(1)

(1) Wherein (V/G) σ_mean＝0Is a constant representing the critical V/G when the average stress in the crystal is zero. α is the stress coefficient, σ_meanIs the average stress (unit: MPa) in the single crystal. For example, when a single crystal having a diameter of 310mm is used as the object of growth, (V/G). sigma._mean＝0Is 0.17 and alpha is 0.0013. Here, the mean stress σ is_meanWhich corresponds to the stress of the component that changes in the volume of a single crystal during the incubation and can be grasped by numerical analysis, the average stress σ_meanIs obtained by extracting the vertical component [ sigma ] of the stress acting on each of 3 planes of a plane in the radial direction, a plane in the circumferential direction and a plane orthogonal to the direction of the pulling axis in the micro portion of the single crystal_rr、σ_θθAnd sigma_zzThese are summed up and divided by 3. Here, the mean stress σ_meanIt is tensile and negative that compressive.

Due to (V/G)_σmean＝0Is constant, therefore the above formula (1) is obtained by mixing (V/G)_σmean＝0The substitution ξ is represented by the following formula (2).

V_cri/G＝ξ+α×σ_mean……(2)

The above formula (2) represents the critical V in one dimension_criG and mean stress (σ)_mean) However, in order to grow a defect-free crystal, it is necessary to align the direction of the pulling axis of the single crystal with that of the single crystalThe intersection is considered in-plane.

2. Propagation of critical V/G induced stress effect into the in-plane distribution of a single crystal

In a position of radius r (unit: mm) from the center of the single crystal, with respect to V as a critical pulling rate_criCritical V of the ratio of the temperature gradient G (r) (unit:. degree. C./mm) in the position of the radius r and (unit: mm/min)_criThe formula (1)/G (r) can be defined by the following formula (3) in accordance with the above formula (2) when a stress effect is introduced.

V_cri/G(r)＝ξ+α×σ_mean(r)……(3)

(3) In the formula, σ_mean(r) is the average stress (unit: MPa) in the vicinity of the solid-liquid interface at a position having a radius r from the center of the single crystal, and represents the in-plane average stress distribution in the vicinity of the solid-liquid interface of the single crystal. According to the formula (3), the temperature gradient g (r) at the position of the radius r can be represented by the following formula (4).

G(r)＝V_cri/(ξ+α×σ_mean(r))……(4)

Here, the temperature gradient g (r) represents a temperature gradient distribution in a plane orthogonal to the single crystal pulling axis direction, and therefore, in order to grow a defect-free crystal, it is desired to obtain an optimum in-plane temperature gradient g (r) distribution, but it is difficult to predict the in-plane average stress σ_meanThe (r) distribution becomes a problem. And, in-plane average stress σ thereof_meanThe distribution of (r) is also problematic depending on conditions.

Thus, the in-plane average stress σ was investigated_mean(r) the method of predicting.

2-1 relationship between temperature gradient and average stress (stress) of central portion of single crystal

The temperature gradient G (0) (═ G) of the central portion of the single crystal was investigated_c) Mean stress σ with the center of the single crystal_mean(0)(＝σ_{mean c}) The relationship (2) of (c). The study was conducted as follows. Assuming that a single crystal having a diameter of 310mm is grown, first, the radiant heat of the surface of the single crystal under each hot zone condition is calculated by comprehensive heat transfer analysis with various changes made to the hot zone conditions, and then the calculated radiant heat under each hot zone condition and the variously changed solid-liquid interface shape are used as boundary conditions to newly grow a single crystal having a diameter of 310mmThe temperature within the single crystal under each boundary condition was calculated. Here, as the condition of the hot zone was changed, a gap between the lower end of the heat shield surrounding the single crystal and the liquid surface of the raw material melt in the quartz crucible (hereinafter, also referred to as "liquid surface gap") was changed. Further, as the condition of the solid-liquid interface shape was changed, the height in the pulling axis direction from the liquid surface of the raw material melt to the center portion of the solid-liquid interface (hereinafter also referred to as "interface height") was changed. Then, for each condition, stress (average stress) was calculated from the temperature distribution in the single crystal obtained by recalculation.

From the analysis results, it was found that the average stress σ at the center portion of the single crystal_mean(0)(＝σ_{mean_c}) Independent of the interface height, the temperature gradient G (0) (═ G) in the center of the single crystal_c) In proportion, the following formula (5) is given between the two.

σ_mean(0)＝-15.879×G(0)+38.57……(5)

2-2 normalization of in-plane mean stress

Next, the in-plane average stress σ was analyzed based on the numerical analysis_mean(r) normalization of the distribution the study was carried out. Here, as shown in the following expression (6), the average stress σ at the position of the radius r is expressed_mean(r) mean stress σ with respect to the center of the single crystal_mean(0)(＝σ_{mean_c}) The ratio n (r) is used as the normalized stress ratio.

n(r)＝σ_mean(r)/σ_{mean_c}……(6)

As a result, it was found that the normalized stress ratio n (r) is approximately the same at the position of the radius r even when the liquid surface Gap and the interface height are different, and can be expressed by the following expression (7).

n(r)＝0.000000524×r³-0.000134×r²+0.00173×r+0.986……(7)

However, in the center portion (r ═ 0) of the single crystal, σ is caused_mean(r)＝σ_{mean_c}Thus, n (0) is 1 according to the above formula (6). In the outer peripheral portion of the single crystal (r ═ e (e, for example, 155mm in the case of a single crystal having a diameter of 310 mm), σ represents_meanSince (r) is 0, n (e) is 0 according to the above formula (6).

Thus, the in-plane average stress σ is obtained from the above expressions (6) and (5)_meanThe (r) can be represented by the following formula (8).

σ_mean(r)＝n(r)×σ_{mean_c}＝n(r)×(-15.879×G(0)+38.57)……(8)

According to the equation (8), it is only necessary to know the average stress σ of the central portion of the single crystal_mean(0)(＝σ_{mean_c}) The in-plane average stress σ can be grasped_meanThe distribution of (r), in other words, the temperature gradient G (0) (═ G) at the center of the single crystal can be said to be known_c) The in-plane average stress σ can be grasped_meanDistribution of (r).

3. Derivation of the distribution of the optimal in-plane temperature gradient G (r)

When a single crystal having a diameter of 310mm is to be grown, the in-plane temperature gradient g (r) can be represented by the following expression (9) by substituting the above expression (8) into the above expression (4).

G(r)＝V_cri/(ξ+α×n(r)×(-15.879×G(0)+38.57))……(9)

Here, when the normalized temperature gradient ratio is defined as the ratio (G (r)/G (0)) of the temperature gradient G (r) at the position of the radius r to the temperature gradient G (0) at the center portion of the single crystal, the following expression (10) is derived from the above expression (9), in consideration of the normalization of the distribution of the temperature gradient G (r).

G(r)/G(0)＝[V_cri/(ξ+α×n(r)×(-15.879×G(0)+38.57))]/[V_cri/(ξ+α×n(0)×(-15.879×G(0)+38.57))]

＝(ξ+α×n(0)×(-15.879×G(0)+38.57))/(ξ+α×n(r)×(-15.879×G(0)+38.57))……(10)

According to the formula (10), the in-plane temperature gradient g (r) can be represented by the following formula (11).

G(r)＝[(ξ+α×n(0)×(-15.879×G(0)+38.57))/(ξ+α×n(r)×(-15.879×G(0)+38.57))]×G(0)……(11)

In the above formulae (10) and (11), n (0) is 1 as described above. n (r) is represented by the above formula (7). However, as described above, n (r), that is, n (e), in the single crystal outer peripheral portion (r ═ e) is 0.

Therefore, it can be said that the temperature gradient G at the center of the single crystal is determined₍₀₎(＝G_c) The optimum in-plane temperature gradient g (r) distribution can be grasped by the above equation (11).

When a single crystal having a diameter of 310mm is to be grown, the in-plane temperature gradient G (r) can be expressed by the above expression (4), and the following expression (12) can be derived from the expression (4) as the normalized temperature gradient ratio (G (r)/G (0)).

G(r)/G(0)＝[V_cri/(ξ+α×n(r)×σ_mean(0))]/[V_cri/(ξ+α×n(0)×σ_mean(0))]

＝(ξ+α×n(0)×σ_mean(0))/(ξ+α×n(r)×σ_mean(0))……(12)

According to the formula (12), the in-plane temperature gradient g (r) can be represented by the following formula (13).

G(r)＝[(ξ+α×n(0)×σ_mean(0))/(ξ+α×n(r)×σ_mean(0))]×G(0)……(13)

In the above formulae (12) and (13), n (0) is 1 as described above. n (r) is represented by the above formula (7). However, as described above, n (r), that is, n (e), in the single crystal outer peripheral portion (r ═ e) is 0.

Therefore, it can be said that the average stress at the center of the single crystal, i.e., the stress σ, is determined_mean(0)(＝σ_{mean_c}) The optimum in-plane temperature gradient g (r) distribution can be grasped by the above equation (13).

4. Temperature gradient G in the center of single crystal_cTemperature gradient G with respect to the outer peripheral portion_eRatio G of_c/G_eIn the optimum range of

When a single crystal having a diameter of 310mm is to be grown, the temperature gradient G at the center of the single crystal is determined according to the above expression (11)_cWhen the optimum temperature gradient G (r) corresponding to the position of the radius r from the center of the single crystal is calculated, the distribution of the in-plane temperature gradient G (r) is as shown in FIG. 4, for example.

FIG. 4 is a graph illustrating a temperature gradient G per the central portion of a single crystal_cThe distribution of the optimal in-plane temperature gradient G (r) of (1). As can be seen from fig. 4, the temperature gradient G (0) (═ G) at the center of the single crystal was determined_c) The optimal in-plane temperature gradient G (r) distribution can be grasped.

Here, the temperature gradient G at the center of the single crystal is a main control index for growing defect-free crystals_cTemperature gradient G with the outer periphery of the single crystal_eRatio G of_c/G_e. From the calculation result based on the expression (11), the optimum temperature gradient ratio G is calculated corresponding to the temperature gradient G (0) (═ Gc) of the central portion of the single crystal_c/G_eThe temperature gradient ratio G thereof_c/G_eThe distribution state of (2) is, for example, the distribution state shown in fig. 5.

FIG. 5 is a view illustrating a temperature gradient G with respect to the central portion of the single crystal_cCorresponding optimal temperature gradient ratio G_c/G_eA graph of the distribution of (2). Fig. 5 shows a case where a single crystal having a diameter of 310mm is to be grown, that is, a case where r is 155 mm. From FIG. 5, the temperature gradient G at the center portion of the single crystal is clarified_cRatio to optimum temperature gradient G_c/G_eThere is a correlation between (G (0)/G (150)), and a relationship of a linear expression represented by the following expression (14) is established.

G_c/G_e＝0.1769×G_c+0.5462……(14)

Therefore, by determining the temperature gradient G of the central portion of the single crystal₍₀₎(＝G_c) By using the above equation (14), the optimum temperature gradient ratio G can be grasped_c/G_e. Since the relationship of the expression (14) is established, G satisfying the following expression (a)_c/G_eWhen the single crystal is pulled under the conditions of (1), a defect-free crystal can be grown precisely.

0.9×A≤G_c/G_e≤1.1×A……(a)

In the above formula (a), A is 0.1769 XG_c+0.5462。

If the temperature gradient ratio G_c/G_eIf the value is less than "0.9 XA" or exceeds "1.1 XA", the growth of defect-free crystals becomes unstable. More preferably, the temperature gradient ratio G_c/G_eIs not less than "0.95 × A" and not more than "1.05 × A".

When a single crystal having a diameter of 310mm is to be grown, the stress σ at the center of the single crystal is expressed by the above expression (13)_{mean_c}Calculating andthe distribution of the in-plane temperature gradient G (r) is, for example, the distribution shown in FIG. 6 when the optimum temperature gradient G (r) is located at a position away from the center radius r of the single crystal.

FIG. 6 is a graph illustrating stress σ per single crystal center portion_{mean_c}The distribution of the optimal in-plane temperature gradient G (r) of (1). As can be seen from FIG. 6, the stress σ at the center of the single crystal is determined_mean(0)(＝σ_{mean_c}) The optimal in-plane temperature gradient G (r) distribution can be grasped.

Here, as a main management index for growing defect-free crystals, there is a temperature gradient ratio G_c/G_e. Based on the calculation result based on the above expression (13), the stress σ with respect to the central portion of the single crystal_mean(0)(＝σ_{mean_c}) Correspondingly calculating the optimal temperature gradient ratio G_c/G_eThe temperature gradient ratio G thereof_c/G_eThe distribution state of (2) is, for example, the distribution state shown in fig. 7.

FIG. 7 is a graph illustrating stress σ with respect to the center portion of a single crystal_{mean_c}Corresponding optimal temperature gradient ratio G_c/G_eA graph of the distribution of (2). Fig. 7 shows a case where a single crystal having a diameter of 310mm is to be grown, that is, a case where r is 155 mm. From FIG. 7, the stress σ at the center portion of the single crystal is clarified_{mean_c}Ratio to optimum temperature gradient G_c/G_eThere is a correlation between (G (0)/G (150)), and a relationship of a linear expression represented by the following expression (15) is established.

G_c/G_e＝-0.0111×σ_{mean_c}+0.976……(15)

Therefore, by determining the stress σ of the central portion of the single crystal_mean(0)(＝_{σmean_c}) By using the above equation (15), the optimum temperature gradient ratio G can be grasped_c/G_e. Since the relationship of the expression (15) is established, G satisfying the following expression (b)_c/G_eWhen the single crystal is pulled under the conditions of (1), a defect-free crystal can be grown precisely.

0.9×B≤G_c/G_e≤1.1×B……(b)

In the above formula (B), B is-0.0111 Xsigma_{mean_c}+0.976。

If the temperature gradient ratio G_c/G_eIf the value is less than "0.9 XB" or exceeds "1.1 XB", the growth of defect-free crystals becomes unstable. More preferably, the temperature gradient ratio G_c/G_eIs not less than 0.95 XB and not more than 1.05 XB.

However, in the above formulas (a) and (b), when a single crystal having a diameter of 310mm is to be grown, the temperature gradient G at the center of the single crystal is_cIs set within the range of 2.0-4.0 ℃/mm. This is because if the amount is outside this range, various point defects such as OSF, COP, and LD occur. Temperature gradient G in the center of the crystal_cThe range is more preferably 2.5 to 3.5 ℃/mm.

As described above, the stress σ in the vicinity of the solid-liquid interface of the single crystal_mean(r) regularity in distribution, in-plane stress σ thereof_mean(r) distribution can be based on stress σ confined to the center portion of the single crystal_{mean_c}Or a temperature gradient G_cAnd (5) mastering. As a result, the temperature gradient G in the central portion of the single crystal was determined in consideration of the stress effect affecting the generation of point defects_cOr stress σ of the central portion of the single crystal_{mean_c}Thus, the in-plane temperature gradient G (r) distribution optimum for growing defect-free crystals can be grasped, and the optimum temperature gradient ratio G can be grasped_c/G_e. And, by optimizing the temperature gradient ratio G_c/G_eThe optimum temperature gradient ratio G is set by using the optimum temperature gradient ratio G as a management index to design the appropriate size of the hot zone_c/G_eThe defect-free crystal can be accurately grown within the standard control range.

5. Cultivation of silicon single crystal

Fig. 8 is a diagram schematically showing the configuration of a single crystal growing apparatus to which the method for growing single crystal silicon of the present invention can be applied. As shown in FIG. 8, the outer periphery of the single crystal growing apparatus is constituted by a chamber 1, and a crucible 2 is disposed at the center of the single crystal growing apparatus. The crucible 2 has a double structure including an inner quartz crucible 2a and an outer graphite crucible 2b, and is fixed to an upper end portion of a support shaft 3 that can be rotated and lifted. The rotation and lifting operation of the support shaft 3 are controlled by a crucible driving mechanism 14.

A resistance heating type heater 4 surrounding the crucible 2 is disposed outside the crucible 2, and a heat insulating material 5 is disposed outside the heater 4 along the inner surface of the chamber 1. A pulling shaft 6 such as a wire rod that rotates at a predetermined speed in the opposite direction or the same direction as the support shaft 3 is disposed above the crucible 2. A seed crystal 7 is attached to the lower end of the pulling shaft 6. The movement of the pulling shaft 6 is controlled by a crystal pulling mechanism 15.

A cylindrical water-cooling body 11 surrounding a silicon single crystal 8 being grown above a raw material melt 9 in a crucible 2 is disposed in a chamber 1. The water cooling body 11 is made of a metal having good thermal conductivity, such as copper, and is forcibly cooled by cooling water flowing through the inside thereof. The water cooling body 11 has the following functions: the cooling of the single crystal 8 during the growth is promoted, and the temperature gradient in the direction of the pulling axis in the central portion and the outer peripheral portion of the single crystal is controlled.

A cylindrical heat shield 10 is disposed so as to surround the outer peripheral surface and the lower end surface of the water cooling member 11. The heat shield 10 has the following functions: the temperature gradient of the central portion and the outer peripheral portion of the single crystal is controlled together with the water cooling body 11, while the high-temperature radiation heat from the raw material melt 9 in the crucible 2, the heater 4, or the side wall of the crucible 2 is blocked, and the diffusion of heat to a low temperature is suppressed in the vicinity of the solid-liquid interface which is the crystal growth interface, with respect to the single crystal 8 being grown.

A gas inlet 12 for introducing an inert gas such as Ar gas into the chamber 1 is provided in the upper part of the chamber 1. An exhaust port 13 for sucking and discharging gas in the chamber 1 by driving a vacuum pump, not shown, is provided in a lower portion of the chamber 1. The inert gas introduced into the chamber 1 from the gas inlet 12 descends between the growing single crystal 8 and the water cooler 11, passes through a gap (liquid surface gap) between the lower end of the heat shield 10 and the liquid surface of the raw material melt 9, flows outward of the heat shield 10, further flows outward of the crucible 2, descends outside the crucible 2, and is discharged from the gas outlet 13.

A camera 16 is provided outside the chamber 1, and the camera 16 photographs the vicinity of the solid-liquid interface through an observation window provided in the chamber 1. The image captured by the camera 16 is processed by the image processing unit 17 to determine the crystal diameter, the liquid surface position, and the like. The controller 18 controls the heater 4, the crucible driving mechanism 14, and the crystal pulling mechanism 15 based on the image processing result.

When the silicon single crystal 8 is grown using such an apparatus, a solid raw material such as polycrystalline silicon filled in the crucible 2 is melted by heating the heater 4 while maintaining the chamber 1 in a reduced-pressure inert gas atmosphere, thereby forming a raw material melt 9. When the raw material melt 9 is formed in the crucible 2, the pulling shaft 6 is lowered to immerse the seed crystal 7 in the raw material melt 9, and the pulling shaft 6 is slowly pulled while rotating the crucible 2 and the pulling shaft 6 in a predetermined direction, thereby growing the single crystal 8 connected to the seed crystal 7.

When a single crystal having a diameter of 310mm is grown, in order to grow a defect-free crystal, the temperature gradient ratio G is set so as to be in the vicinity of the solid-liquid interface of the single crystal_c/G_eThe single crystal is pulled by adjusting the pulling rate of the single crystal and the gap (height of the crucible 2) so as to satisfy the conditions of the above-mentioned formula (a) or formula (b). Before growing the single crystal, the optimum temperature gradient ratio G obtained from the above equation (14) or (15) is used_c/G_eThe dimensions and shapes of the hot zones (thermal shield and water cooler) are designed and used. This enables accurate growth of defect-free crystals.

FIG. 9 shows the gap H between the heat shield 10 and the liquid surface of the raw material melt 9 and the temperature gradient ratio 6_c/G_eGraph of the relationship between the gap H and the gap G_c/G_e. In FIG. 9, the triangular plot represents the value of the gap H and the temperature gradient ratio G obtained by the comprehensive heat transfer simulation test for growing a silicon single crystal having a diameter of 310mm using a hot zone having a specific structure_c/G_eAnd A represents G of the formula (a) as 2 straight lines_c/G_eLower limit of 0.9A and upper limit of 1.1A. The range of the region between these 2 straight lines is defined by the formula (a), and a defect-free crystal can be obtained.

As shown in FIG. 9, it can be seen that when the gap H is about 5G is in the range of 8-70 mm_c/G_eSatisfies the formula (a). Thus, by adjusting the gap H, the temperature gradient ratio G can be adjusted_c/G_eThe content is set in the range of 0.9A to 1.1A.

Fig. 10 is a flowchart showing a manufacturing process of the silicon single crystal 8. Fig. 11 is a schematic cross-sectional view showing the shape of a single crystal silicon ingot.

As shown in fig. 10, the manufacturing process of the silicon single crystal 8 according to the present embodiment includes: a raw material melting step S11 of generating a raw material melt 9 by heating and melting the silicon raw material in the crucible 2 by the heater 4; a contact step S12 of lowering a seed crystal attached to the tip end portion of the pulling shaft 6 to make the seed crystal contact the raw material melt 9; and a crystal pulling step (S13-S16) of growing a single crystal by slowly pulling the seed crystal while maintaining the contact state with the raw material melt 9.

In the crystal pulling step, a necking step S13 is sequentially performed to form a neck portion 8a in which the crystal diameter is reduced so as not to cause dislocation; a shoulder growing step S14 of forming a shoulder 8b in which the crystal diameter gradually increases with the growth of the crystal; a body part growing step S15 of forming a body part 8c having a crystal diameter kept constant; and a tail growing step S16 for forming a tail 8d in which the crystal diameter gradually decreases as the crystal grows.

Next, a cooling step S17 is performed to separate the silicon single crystal 8 from the melt surface and promote cooling. By performing the above steps, a silicon single crystal ingot 8I having a neck portion 8a, a shoulder portion 8b, a body portion 8c, and a tail portion 8d as shown in fig. 11 is completed.

As described above, the kind and distribution of crystal defects contained in the single-crystal silicon 8 are strongly influenced by the furnace thermal environment surrounding the crystal, that is, the hot zone, depending on the ratio V/G of the crystal pulling rate V to the temperature gradient G. Therefore, when the hot zone changes as the crystal pulling process proceeds, the Gc/Ge cannot be made within the range of 0.9A to 1.1A even if the gap is maintained at a constant distance, and a desired pulling rate limit may not be secured.

For example, in the intermediate stage of the main body part growing step S15 shown in fig. 11, a single crystal ingot of a sufficient length is present in the space above the silicon melt, but since such a single crystal ingot is not present at the time of starting the main body part growing step S15, the heat distribution in the space is somewhat different even if the heat shield 10 is provided. In addition, at the final stage of the body part growing step S15, the output of the heater 4 is increased to prevent the silicon melt from solidifying as the raw material melt 9 in the crucible decreases, and therefore, the heat distribution around the crystal also changes. When the hot zone changes in this way, the thermal history in the crystal changes even if the gap is maintained at a constant distance, and therefore the in-plane distribution of crystal defects cannot be maintained constant.

Therefore, in the present embodiment, the gap does not always maintain a constant distance in the range from the upper end to the lower end of the ingot, but is changed in accordance with the crystal growth stage. I.e. so as to make the temperature gradient ratio G_c/G_eThe gap is changed so as to satisfy the above expression (a) or (b). By changing the gap in this manner, the in-plane distribution of crystal defects from the upper end to the lower end of the ingot can be controlled as desired, and the production yield of defect-free crystals can be improved by suppressing the drop in the pulling rate limit. The decrease in the pulling rate limit can be suppressed by changing the gap, which varies depending on the hot zone. Therefore, in order to obtain a crystal having a temperature gradient ratio G from the upper end to the lower end_c/G_eThe in-plane distribution of crystal defects is maintained constant while being within the range of 0.9A to 1.1A, and it is necessary to appropriately set the gap distribution in accordance with the crystal growth stage while considering how the hot zone varies with the progress of the crystal pulling process.

Fig. 12 and 13 are schematic diagrams for explaining the relationship between the gap distribution and the crystal defect distribution in the crystal pulling process, fig. 12 shows the case of the conventional constant gap control, and fig. 13 shows the case of the variable gap control of the present invention.

As shown in FIG. 12, in the gap constant control in which the gap is always maintained at a constant distance in the crystal pulling step, the temperature gradient ratio G is changed by the change in the hot zone_c/G_eThe in-plane distribution of crystal defects cannot be maintained constant because of the variation. That is, in the upper end (Top), center (Mid), and lower end (Bot) of the single crystal silicon ingot 8I, the surface is due to crystal defectsInner distribution is different, so G passes through the center of ingot 8I_c/G_eA desired pulling rate limit can be ensured by optimization, but a desired pulling rate limit cannot be ensured at the upper end and the lower end of the ingot 8I.

In contrast, in the present invention, as shown in fig. 13, the gap distribution is set so that the gap is gradually narrowed in accordance with the progress of the crystal pulling step. In particular, in the gap profile according to the present embodiment, the 1 st constant gap control section S1 for maintaining the gap constant from the start of the crystal pulling process, the 1 st variable gap control section S2 provided in the first half of the body portion growing process and gradually decreasing the gap, the 2 nd constant gap control section S3 for maintaining the gap constant, the 2 nd variable gap control section S4 provided in the second half of the body portion growing process and gradually decreasing the gap, and the 3 rd constant gap control section S5 for maintaining the gap constant until the end of the crystal pulling process are provided in this order. Such a gap distribution is set in accordance with the change in the hot zone, and thus the in-plane distribution of crystal defects is maintained constant from the upper end to the lower end of the ingot 8I as shown in the drawing, and the production yield of defect-free crystals can be improved.

The gap distribution is an example, and is not limited to a distribution in which the gap gradually narrows in accordance with the progress of the crystal pulling process. Therefore, for example, the gap may be gradually decreased in the 1 st gap variable control section S2 and gradually increased in the 2 nd gap variable control section S4.

The temperature gradient in the outer peripheral portion of the single crystal 8 is more susceptible to the gap variation than the temperature gradient in the central portion. When the gap is wide, since radiant heat from the heater 4 is easily transmitted to the single crystal 8 through the gap, the temperature gradient G at the outer peripheral portion of the single crystal 8_eRelatively smaller, temperature gradient ratio G_c/G_eBecomes larger. Conversely, when the gap is narrow, since radiant heat from the heater 4 is blocked by the heat shield 10 and is difficult to be transmitted to the single crystal 8, the temperature gradient G at the outer peripheral portion of the single crystal 8_eRelatively larger, temperature gradient ratio G_c/G_eAnd becomes smaller. Therefore, by adjusting the gap, it is possible toEasily adjusting the temperature gradient ratio G_c/G_e。

In the case of performing the gap variable control, if a simple method of changing the gap by correcting the crucible lifting speed is used, there is a possibility that the crucible lifting speed may vibrate greatly. Such a vibration phenomenon may hinder the object of maintaining the in-plane distribution of crystal defects from the upper end to the lower end of the ingot 8I constant by the gap variable control to improve the production yield of defect-free crystals. Therefore, in the present invention, such a vibration phenomenon is prevented to enable the production of high-quality crystals.

Next, a method of calculating the crucible raising speed in the gap variable control according to the present invention will be described with reference to the functional block diagram of fig. 14.

As shown in fig. 14, the gap variable control function includes a crucible raising speed calculation unit 30. The crucible raising speed calculation unit 30 includes: the quantitative value calculating section 31 calculates a quantitative value V of a crucible raising speed required for controlling a liquid surface position and a gap, which change as the silicon single crystal 8 is pulled, to be constant_f(ii) a A variation value calculating part 32 for calculating a variation value V of the crucible rising speed according to the variation of the target gap value_a(ii) a And a correction value calculating part 33 for calculating a correction value V of the crucible lifting speed according to the difference between the target value of the gap and the measured value of the gap_adj(ii) a The crucible driving mechanism 14 outputs the rising speed V of the liquid level_MWhile using the quantitative value V_fVariation value V_aAnd a correction value V_adjThe total value of (a) controls the position of the crucible. And the crystal pulling mechanism 15 outputs the crystal length DeltaL_S(Crystal pulling velocity V_S). The image processing unit 17 measures the gap between the liquid surface of the raw material melt 9 and the heat shield 10 and the crystal diameter based on the image captured by the camera 16.

In the gap variable control, the crucible raising speed V is calculated by using the following expression (16)_CThe crucible raising speed is controlled according to the control period.

V_C＝V_f+V_a+V_adj……(16)

Here, V_fThe quantitative value of the crucible raising speed required for maintaining the gap constant is the crucible raising speed used for the gap constant control. And, V_aThe variation of the crucible lifting speed is obtained from the variation of the target value of the gap. V_adjThe correction value of the crucible lifting speed is obtained according to the difference between the current target value and the actual measured value of the clearance.

Quantitative value V of crucible rising speed_fThis can be obtained from the following equation (17).

V_f＝((P_S×D_S ²)÷(P_L×D_C ²))×(V_S-V_M)+V_M……(17)

P_S: specific gravity of silicon solid (2.33 x 10)^-3)

P_L: specific gravity of silicon melt (2.53 × 10)^-3)

D_S: current crystal diameter

D_C: current inner diameter of quartz crucible

V_S: current crystal pulling rate

V_M: last crucible rising speed (liquid level rising speed)

And the liquid level rising speed V_MThe following formula (18) is shown.

V_M＝-((P_S×D_S ²×ΔL_s)÷(P_L×D_C ²-P_S×D_S ²))+((P_L×D_C ²×ΔL_C)÷(P_L×D_C ²-P_S×D_S ²))……(18)

ΔL_S: amount of crystal movement per 1 control cycle

ΔL_C: amount of crucible movement per 1 control cycle

Thus, the quantitative value V of the crucible raising speed_fIn the calculation of (2), the crystal movement amount (crystal length) Δ L per 1 control cycle from the crystal pulling mechanism 15 is obtained_SAccording to crystal diameter D_SAnd amount of crystal movement DeltaL_CDetermining the increase of crystal volume based on the increase of crystal volume and the inner diameter D of the crucible_CCalculating the reduction of the melt volume, and further calculating the reduction of the melt volume and the inner diameter D of the crucible_CCalculating the quantitative value V of the crucible rising speed_f. With respect to the crystal diameter D_SThe image processing unit 17 processes the single crystal reflected in the captured image of the camera 16. Inner diameter D of crucible_CIs a constant value determined from the design size of the quartz crucible 2 a.

When the liquid level rises at a speed V_MCrystal pulling rate V corresponding to the current crystal pulling rate_SAt equilibrium, the crucible rises at a constant rate V_fBecomes equal to the liquid level rising speed V_MEqual, the gap can be maintained at a constant distance. And, if the liquid level rises at a speed V_MThan the current crystal pulling rate V_SAt a high speed, the quantitative value V of the rise speed of the crucible_fBecomes specific liquid level rising velocity V_MSlow, conversely if the liquid level rises at a speed V_MThan the current crystal pulling rate V_SSlow, constant value V of crucible rising speed_fBecomes specific liquid level rising velocity V_MFast, the gap can be kept constant.

Variation V of crucible rising speed_aThe following formula (19) is shown.

V_a＝(H_{pf_i}-H_{pf_i+1})÷T……(19)

Here, H_{pf_i}Is the current (i-th) gap target value (mm), H_{pf_i+1}Is the target gap value (mm) after 1 control period (i +1 th). The target value of the gap is set, for example, based on the crystal length, and the crystal length after 1 control period can be set based on the current crystal pulling rate V_SThe crystal length increment obtained by multiplying the control period T (min). The control period T is not particularly limited, and may be set to 2 minutes, for example. Thus, the variation V of the crucible raising speed_aCan be based on the current gap target value H_{pf_i}And 1 control period after the target value H_{pf_i+1}The difference between them. When the target value of the gap is kept constant (H)_{pf_i+1}＝H_{pf_i}) When not changed, becomes V _a0. For example, when the gap is set from 50mm to 51mm, the gap needs to be increased by 1mm, but since the amount of change in the target gap value can be known from the gap distribution, the quantitative value V is set_fAdding a variation V of crucible raising speed required for increasing the clearance by 1mm_a。

Correction value V of crucible rising speed_adjThe following formula (20) is shown.

V_adj＝(H_{pf_i}-H_i)÷T×k……(20)

Here, H_iIs the current gap measurement (mm) and is preferably not the latest single value but a moving average. K is a gain, and is preferably 0.001 to 0.1. When k is set to 0.05, for example, the influence of the deviation of the gap measurement value on the crucible raising speed can be controlled to 1/20. When the gap measured value is equal to the gap target value, the crucible rise correction speed V_adj＝0。

As described above, the quantitative value V of the crucible raising speed_fThe calculation of (A) requires the inner diameter D of the quartz crucible 2a_CThe exact value of (c). However, since the quartz crucible 2a softens in the vicinity of the melting point of silicon and may be deformed during pulling, the value of the gap deviates from the target value. The value of the gap deviates from the target value also due to various other main factors. Therefore, in the present embodiment, the gap is actually measured from the mirror image position of the heat shield 10 reflected on the melt surface, the control error of the gap is calculated based on the crucible rising speed calculated from the amount of decrease in the raw material melt 9, and the fixed amount V is calculated_fTo which a correction value V of the rising speed of the quartz crucible 2a for eliminating the control error is added_adjThe gap is controlled with high accuracy.

As described above, the crucible raising speed V_CIs a quantitative value V of the crucible raising speed required for maintaining the clearance constant_fAnd a variation V of the crucible raising speed obtained from the variation of the target value of the gap_aAnd a correction value V of the crucible rising speed obtained from the difference between the target value of the gap and the actual measurement value_adjThe total value of (2) is constituted such that, with respect to the amount of change in the target clearance value that can be obtained from the clearance distribution,the value based on the quantitative value is included in the crucible raising speed in advance regardless of the measured value of the gap, so that the correction value V of the crucible raising speed can be minimized_adjA variation of (c). That is, the correction value V is obtained by correcting the crucible raising speed_adjThe effect is specialized only for correction for eliminating the deviation between the target value and the measured value of the gap, so that the amplitude of the crucible rising speed can be prevented from increasing, and the crucible rising speed can be stably controlled.

As described above, the method for growing a silicon single crystal according to the present embodiment includes the step of variably controlling the gap for pulling the single crystal while changing the gap between the liquid surface of the raw material melt and the heat shield, and the temperature gradient in the vicinity of the solid-liquid interface at the center of the single crystal is G_cG represents a temperature gradient in the vicinity of a solid-liquid interface at the outer periphery of the single crystal_e、A＝0.1769×G_c+0.5462, due to the temperature gradient ratio G_c/G_eSatisfies 0.9 xA ≤ G_c/G_eThe single crystal is pulled while changing the gap under the condition of 1.1 xA or less, so that a defect-free crystal can be accurately grown while considering the stress acting on the single crystal when growing the single crystal.

In the method for growing a silicon single crystal according to the present embodiment, a gap distribution is prepared in which the target value of the gap changes in accordance with the crystal length, and the crucible raising speed V is controlled so that the measured value of the gap follows the gap distribution during the crystal growth_CTherefore, it is possible to prevent the amplitude of the crucible raising rate from increasing, and as a result, it is possible to produce high-quality single-crystal silicon with a small variation in the in-plane distribution of crystal defects from the upper end to the lower end of the single-crystal silicon in high yield.

In the present embodiment, the quantitative value V of the crucible raising speed required for maintaining the gap constant is used_fA variation value V of the crucible lifting speed required for changing the gap according to the variation amount of the target value of the gap_aAnd a correction value V of the crucible lifting speed required for correcting the difference between the target value and the measured value of the gap_adjThe total value of (A) is used as the crucible rising speed V_CThus, the variation of the gap can be improvedThe control of the crucible raising speed is unstable, and the crystal yield can be improved.

While the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

For example, in the above embodiment, the target gap value H is used as the correction value of the crucible raising speed_{pf_i}And the clearance measurement value H_iDifference (H) of_{pf_i}-H_i) The value obtained by multiplying the reciprocal 1/T of the control period and the gain k, but the present invention is not limited to such a value, and a correction value calculated by various calculation methods can be used.

In the above embodiment, the method of growing single crystal silicon is exemplified, but the present invention is not limited thereto, and various single crystals pulled by the CZ method can be targeted.

Industrial applicability

The method for growing a silicon single crystal of the present invention is useful for growing a defect-free crystal which does not cause various point defects such as OSF, COP, LD, and the like.

Description of the reference numerals

1-chamber, 2-crucible, 2 a-quartz crucible, 2 b-graphite crucible, 3-support shaft, 4-heater, 5-thermal insulation material, 6-pulling shaft, 7-seed crystal, 8-single crystal silicon, 8I-single crystal silicon ingot, 8 a-neck, 8 b-shoulder, 8 c-body, 8 d-tail, 9-raw material melt, 10-heat shield, 11-water-cooling body, 12-gas inlet, 13-gas outlet, 14-crucible driving mechanism, 15-crystal pulling mechanism, 16-camera, 17-image processing section, 18-control section, 30-crucible lifting speed calculating section, 31-quantitative value calculating section, 32-variation value calculating section, 33-correction value calculating section.

Claims

1. A method for growing a single crystal silicon by pulling a single crystal having a diameter of 300mm or more from a raw material melt in a crucible disposed in a chamber by a pulling method,

a single crystal growing apparatus is used in which a water cooling body is arranged to surround a single crystal being grown and a heat shield is arranged to surround the outer peripheral surface and the lower end surface of the water cooling body,

including a gap variable control of pulling the single crystal while changing a gap between a liquid surface of the raw material melt and the heat shield disposed above the raw material melt,

when the temperature gradient in the direction of the pulling axis in the vicinity of the solid-liquid interface in the central portion of the single crystal is G_cA temperature gradient in the direction of the pulling axis in the vicinity of a solid-liquid interface at the outer periphery of the single crystal is G_e、A＝0.1769×G_c+0.5462, so as to satisfy 0.9 XA ≦ G_c/G_ePulling the single crystal under the condition of less than or equal to 1.1 xA.

2. The method of growing single crystal silicon according to claim 1,

the gap variable control controls the crucible raising speed using a total value of three values:

a quantitative value of a crucible raising speed required for maintaining the gap, which varies as the single crystal is pulled, at a constant distance;

a variation value of the crucible lifting speed obtained from the variation amount of the target value of the gap; and

and a correction value of the crucible lifting speed obtained from a difference between the target value and an actual measurement value of the gap.

3. The method of growing single-crystal silicon according to claim 2,

the amount of change in the target value of the gap is determined from a gap distribution defining a relationship between a crystal length that changes as the single crystal is pulled and the target value of the gap.

4. The method of growing single-crystal silicon according to claim 3,

the correction value is determined from a difference between the target value of the gap determined from the gap distribution and the measured value of the gap.

5. The method of growing single crystal silicon according to any one of claims 2 to 4, wherein,

the volume reduction amount of the raw material melt is obtained from the volume increase amount of the single crystal accompanying the pulling of the single crystal, and the quantitative value is obtained from the volume reduction amount of the raw material melt and the inner diameter of the crucible.

6. The method of growing single crystal silicon according to any one of claims 1 to 5, wherein,

the gap profile includes at least one gap constant control section that maintains the gap at a constant distance and at least one gap variable control section that slowly changes the gap.

7. The method of growing single-crystal silicon according to claim 6,

the gap variable control section is provided after the gap constant control section in the latter half of the main body growth step of the single crystal.

8. The method of growing single-crystal silicon according to claim 6,

the gap variable control section is provided before the gap constant control section in a first half of a main body growth process of the single crystal.

9. The method of growing single-crystal silicon according to claim 6,

the gap profile includes 1 st and 2 nd gap variable control intervals that slowly change the gap,

the 1 st gap variable control section is provided before the gap constant control section in the first half of the main body growth step of the single crystal,

the 2 nd gap variable control section is provided after the gap constant control section in the latter half of the main body growth step of the single crystal.

10. The method of growing single crystal silicon according to any one of claims 1 to 9, wherein,

the measured value of the gap is calculated from the mirror image position of the heat shield reflected on the liquid surface of the raw material melt photographed by a camera.