WO2020039553A1

WO2020039553A1 - Method for growing silicon single crystal

Info

Publication number: WO2020039553A1
Application number: PCT/JP2018/031164
Authority: WO
Inventors: 良太末若; 建濱田
Original assignee: 株式会社Sumco
Priority date: 2018-08-23
Filing date: 2018-08-23
Publication date: 2020-02-27
Also published as: JPWO2020039553A1; JP7036217B2; TWI722480B; KR20210010583A; KR102461073B1; TW202014565A; CN112639175A

Abstract

[Problem] To provide a method for growing a silicon single crystal, wherein a defect-free crystal can be grown accurately by considering the effect of the stress acting on the single crystal during single crystal growth. [Solution] Provided is a method for pulling a single crystal 8 using a single-crystal growth apparatus comprising: a water-cooled body 11 surrounding a growing single crystal 8; and a heat shield 10 surrounding the outer circumferential surface and the bottom surface of the water-cooled body 11. The method comprises a variable gap control for pulling up the single crystal while changing the gap between the liquid surface of a raw material melt 9 and the heat shield 10. The single crystal 8 is pulled up under conditions satisfying 0.9×A≤G_c/G_e≤1.1×A, where A=0.1769×G_c+0.5462, G_c represents the temperature gradient in the pulling axis direction in the vicinity of the solid-liquid interface at the central portion of the single crystal 8, and G_e represents the temperature gradient in the pulling axis direction in the vicinity of the solid-liquid interface at the outer circumferential portion of the single crystal 8.

Description

Silicon single crystal growth method

The present invention relates to a method for growing a silicon single crystal by the Czochralski method (hereinafter, referred to as a “CZ method”), and particularly to an OSF (Oxidation Induced Stacking Fault), a COP (Crystal Originated Particle) and the like. The present invention relates to a method for growing a defect-free crystal free from point defects such as infrared scatterer defects and dislocation clusters such as LD (Interstitial-type Large Dislocation).

多く Most of silicon single crystals used as substrate materials for semiconductor devices are manufactured 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 maintained in an inert gas atmosphere under reduced pressure, and the immersed seed crystal is gradually pulled up. Thereby, a silicon single crystal is grown continuously from the lower end of the seed crystal.

FIG. 1 is a schematic diagram for explaining a situation in which various defects occur based on the Bornkov theory. As shown in the figure, in the Bornkov theory, when the pulling speed is V (mm / min) and the temperature gradient in the pulling axis direction near the solid-liquid interface of the ingot (silicon single crystal) is G (° C./mm), The relationship between V / G and the point defect concentration is schematically shown by plotting the ratio of V / G, which is their ratio, on the horizontal axis and the concentration of vacancy type point defects and the concentration of interstitial silicon point defects on the same vertical axis. expressing. Further, it is described that there is a boundary between a region where a vacancy type point defect occurs and a region where an interstitial silicon type point defect occurs, and the boundary is determined by V / G. Hereinafter, the “temperature gradient in the pulling-up axis direction” may be simply referred to as “temperature gradient”.

Vacancy-type point defects originate from vacancies lacking silicon atoms that constitute a crystal lattice, and COP is a typical example of an aggregate of the vacancy-type point defects. The interstitial silicon type point defect originates from interstitial silicon in which silicon atoms enter between crystal lattices, and a typical example of the aggregate of the interstitial silicon type point defect is LD.

As shown in FIG. 1, when V / G exceeds the critical point, a single crystal in which vacancy type point defects predominate is grown. On the other hand, when V / G falls below the critical point, a single crystal in which interstitial silicon type point defects predominate is grown. For this reason, in the range where V / G is lower than the critical point (V / G) ₁ , interstitial silicon type point defects are dominant in the single crystal, and aggregates of interstitial silicon point defects are present. An area [I] appears, and LD occurs. In the range where V / G is larger than the critical point (V / G) ₂ , vacancy-type point defects are dominant in the single crystal, and the region [V] where vacancy-type point defect aggregates are present Appears, and COP occurs.

When V / G is in the range of the critical point to (V / G) ₁ , the defect-free region [P _I ] in which the interstitial silicon type point defect does not exist as an aggregate in the single crystal is in the range of the critical point to (V / G) _2. In this range, a defect-free region [P _V ] in which vacancy-type point defects do not exist as aggregates appears in the single crystal, and neither COP nor LD defects including OSFs are generated. Here, the defect-free area [P _I ] and [P _V ] are collectively referred to as a defect-free area [P]. An OSF region forming an OSF nucleus exists in a region [V] (V / G is in the range of (V / G) ₂ to (V / G) ₃ ) adjacent to the defect-free region [P _V ].

FIG. 2 is a schematic diagram showing the relationship between the pulling speed and the defect distribution during single crystal growth. The defect distribution shown in the figure is obtained by growing a silicon single crystal while gradually lowering the pulling speed V, cutting the grown single crystal along a central axis (pulling axis) into a plate-shaped specimen, The figure shows the results of observing the plate-like specimen by X-ray topography after Cu was attached and heat treatment was performed.

As shown in FIG. 2, when the growth is performed at a high pulling speed, the region [V] where the aggregate of vacancy type point defects (COP) exists over the entire surface in a plane orthogonal to the pulling axis direction of the single crystal. ] Occurs. As the pulling speed is reduced, the OSF region appears in a ring shape from the outer periphery of the single crystal. The OSF region is a diameter with decreasing pulling rate gradually reduced, pulling rate disappears and becomes V _1. Accordingly, a defect-free region [P] (region [P _V ]) appears instead of the OSF region, and the entire in-plane region of the single crystal is occupied by the defect-free region [P]. When the pulling speed is reduced to V ₂ , a region [I] in which an aggregate (LD) of interstitial silicon-type point defects is present, and finally a defect-free region [P] (region [P _I ]) Instead, the entire in-plane region of the single crystal is occupied by the region [I].

品質 The quality required for silicon wafers has been increasing more and more recently due to the development of miniaturization of semiconductor devices. For this reason, in the production of a silicon single crystal, which is a raw material of a silicon wafer, various point defects such as OSF, COP, and LD are eliminated, and a defect-free crystal in which a defect-free region [P] is distributed over the entire in-plane region is grown. There is a strong need for a technology that does this.

In order to meet this demand, when pulling a silicon single crystal, as shown in FIGS. 1 and 2, V / G is generated in the hot zone, and aggregates of interstitial silicon type point defects are generated over the entire surface. It is necessary to perform management so as to secure the first critical point (V / G) ₁ or higher and the second critical point (V / G) ₂ or lower where no aggregate of vacancy type point defects is generated. . In actual operation, the aim of the pulling speed is set between V ₁ and V ₂ (for example, the median value of both), and even if the pulling speed is changed during the growth, the range of V ₁ to V ₂ (“pulling speed margin”) ”Or“ PvPi margin ”).

Further, since the temperature gradient G depends on the size of the hot zone near the solid-liquid interface, the hot zone is appropriately designed in advance before growing a single crystal. In general, the hot zone is composed of a water-cooled body arranged to surround the growing single crystal, and a heat shield arranged to surround the outer peripheral surface and lower end surface of the water-cooled body. Here, the management indicators in designing the hot zone, and the temperature gradient G _c of the center portion of the single crystal, the temperature gradient G _e of the outer peripheral portion of the single crystal is used. Then, in order to grow a defect-free crystal, for example, in the technique disclosed in Patent Document 1, the difference between the temperature gradient G _e of the temperature gradient G _c and the single crystal outer peripheral portion of the single crystal center ΔG (= G _e - G _c ) is set to be within 0.5 ° C./mm.

In recent years, it has been found that the V / G to be aimed at in growing a defect-free crystal, that is, the critical V / G fluctuates due to the stress acting on the single crystal during the growth of the single crystal. For this reason, in the technique disclosed in Patent Document 1, the effect of the stress is not taken into consideration at all, so that a situation in which a perfect defect-free crystal cannot be obtained occurs in some cases.

In this regard, for example, Patent Document 2, the diameter is the subject of development over the single crystal 300 mm, taking into account the effect of the stress in the single crystal, the temperature gradient G _c and the single crystal outer peripheral portion of the single crystal center the ratio of the temperature gradient G _e (hereinafter, referred to as "temperature gradient ratio") G _c / G _e to be greater than 1.8 technique are disclosed. However, in the technique disclosed in Patent Document 2, even though the effect of stress in a single crystal is considered, a completely defect-free crystal is not always obtained. This is believed to be due to the management range of the temperature gradient ratio G _c / G _e is not sufficient.

JP-A-11-79889 Japanese Patent No. 4819833

The present invention has been made in view of the above problems, and takes into account the effect of stress acting on a single crystal during single crystal growth, and a method of growing a silicon single crystal capable of growing a defect-free crystal with high accuracy. The purpose is to provide.

In order to achieve the above object, the present inventors focused on stress acting in a single crystal during single crystal growth, and conducted intensive studies by performing numerical analysis taking this stress into account. As a result, the following findings were obtained.

FIG. 3 is a diagram showing the relationship between the stress σ _mean acting in the single crystal and the critical V / G. As a result of investigating the relationship between the critical V / G and the average stress σ _mean by comprehensive heat transfer analysis in which the conditions of the hot zone were variously changed, as shown in FIG. 3, (critical V / G) = 0.17 + 0.0013 × σ _mean was found.

The distribution of stress in the vicinity of the solid-liquid interface of a single crystal has a regularity, and the distribution of in-plane stress can be grasped by a stress or a 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 effect of the stress in the single crystal, so that the distribution of the in-plane temperature gradient optimal for growing a defect-free crystal is determined. further it becomes possible to grasp the optimum temperature gradient ratio G _c / G _e. Then, by using the optimum temperature gradient ratio G _c / G _e as a management indicator, able to operate properly dimensioning of the hot zone, moreover, a reference to its optimum temperature gradient ratio G _c / G _e By setting the control range, it is possible to grow a defect-free crystal with high accuracy.

The present invention has been completed based on the above findings, and is a method for growing a silicon single crystal by the CZ method, in which a single crystal having a diameter of 300 mm or more is pulled from a raw material melt in a crucible disposed in a chamber, Using a single crystal growing apparatus in which a water-cooled body surrounding the growing single crystal is arranged and a heat shield surrounding the outer peripheral surface and the lower end face of the water-cooled body is arranged, the water-cooled surrounding the growing single crystal is used. With the body disposed, using a single crystal growing apparatus in which a heat shield surrounding the outer peripheral surface and the lower end surface of the water-cooled body is disposed, and the liquid surface of the raw material melt and the raw material melt are disposed above the raw material melt. includes a gap variable control pulling the single crystal while changing the gap between the heat shield, the temperature gradient in the pulling axis direction in the solid-liquid interface near the central portion of the single crystal G _c, out of the single crystal The temperature gradient G _e solid-liquid of the pulling axis direction in the vicinity of the interface section, when the A = 0.1769 × G _c +0.5462, a _{0.9 × A ≦ G c / G} e ≦ 1.1 × A The single crystal is pulled under a satisfactory condition.

According to the conventional knowledge, it is considered that it is better to make the in-plane distribution of the temperature gradient in the crystal uniform anyway in order to widen the pulling speed margin for obtaining a defect-free crystal. However, according to the present inventors' new knowledge, it has become clear that the pulling speed margin cannot be widened unless the in-plane temperature gradient in the crystal according to the stress state in the crystal is used. According to the present invention, since the properly setting the control range of the temperature gradient ratio G _c / G _e in consideration of the effects of stress in the single crystal, a defect-free crystals from the top of the single crystal to the bottom of accurately grown It becomes possible. Furthermore, by using the single crystal manufactured according to the present invention, a high-quality wafer having a diameter of 300 mm or 450 mm can be efficiently manufactured. When the diameter of the wafer is 300 mm, it is preferable that the diameter of the single crystal (straight body) is 301 mm or more and 340 mm or less. When the diameter of the wafer is 450 mm, the diameter of the single crystal (straight body) is 451 mm or more. It is preferable to set it to 510 mm or less.

In the present invention, the gap variable control is determined from a quantitative value of a crucible rising speed required to maintain the gap, which changes with the pulling of the single crystal, at a constant distance, and a change in a target value of the gap. Controlling the crucible ascent speed using a total value of the fluctuation value of the crucible ascent speed and a correction value of the crucible ascent speed obtained from a difference between the target value and the actual measurement value of the gap. preferable. In this control, since the role of the correction value of the crucible ascending speed is specialized only to the correction for eliminating the gap between the target value of the gap and the measured value, it is possible to prevent the amplitude of the crucible ascending speed from increasing. Can be. Therefore, stabilization of the crystal heat history from the top to the bottom of the silicon single crystal can be realized, the change in the in-plane distribution of crystal defects can be suppressed, and the production yield of a high-quality silicon single crystal can be increased. .

In the present invention, it is preferable that the change in the target value of the gap is obtained from a gap profile that defines the relationship between the crystal length and the target value of the gap that change with the pulling of the single crystal. As a result, the fluctuation value of the crucible rising speed can be easily and accurately obtained, and the stability of the crucible rising speed can be further improved.

In the present invention, it is preferable that the correction value is obtained from a difference between a target value of the gap obtained from the gap profile and a measured value of the gap. Thereby, the correction value of the crucible rising speed can be easily and accurately obtained, and the stability of the crucible rising speed can be further improved.

The method for producing a single crystal according to the present invention determines the decrease in the volume of the melt from the increase in the volume of the single crystal accompanying the pulling of the single crystal, and calculates the decrease in the volume of the melt and the inner diameter of the crucible. Preferably, the quantitative value is determined. Thus, the quantitative value of the crucible rising speed can be easily and accurately obtained.

In the present invention, it is preferable that the gap profile includes at least one gap constant control section for maintaining the gap at a constant distance and at least one gap variable control section for gradually changing the gap. In this case, the gap variable control section may be provided in the latter half of the single crystal body part growing step and after the constant gap control section, and may be provided in the first half of the single crystal body part growing step. It may be provided before the constant gap control section. Further, the gap profile includes first and second gap variable control sections for gradually changing the gap, and the first gap variable control section is a first half of the single crystal body part growing step. Preferably, the second gap variable control section is provided before the constant gap control section, and the second variable gap control section is provided after the constant gap control section in the latter half of the single crystal body portion growing step. . As a result, the in-plane distribution of crystal defects from the top to the bottom of the single crystal can be made substantially constant, thereby increasing the production yield of high-quality single crystals. The first half of the body part growing step means a step of manufacturing a single crystal of the first half part of the body part by dividing the entire length of the body part of the single crystal into two equal parts. This means a step of manufacturing a single crystal in the latter half of the body part.

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 the position of the mirror image of the heat shield reflected on the liquid surface of the melt taken by a camera. As a result, the measured value of the gap can be easily and accurately obtained with an inexpensive configuration.

According to the method for growing a silicon single crystal of the present invention, taking into account the effect of the stress in the single crystal, since the properly setting the control range of the temperature gradient ratio G _c / G _e, the defect-free crystal accurately It is possible to nurture.

FIG. 1 is a schematic diagram illustrating a situation in which various defects occur based on the Bornkov theory. FIG. 2 is a schematic diagram showing the relationship between the pulling speed and the defect distribution during single crystal growth. FIG. 3 is a diagram showing the relationship between the stress σ _{mean at the} center of the single crystal and the critical V / G. Figure 4 is a diagram illustrating the distribution of the temperature gradient G _c each optimal plane temperature gradient G in the single crystal center (r). Figure 5 is a diagram illustrating the distribution of the optimum temperature gradient ratio G _c / G _e in accordance with the temperature gradient G _c of the single crystal center. FIG. 6 is a diagram exemplifying a distribution state of the optimal in-plane temperature gradient G (r) for each stress σ _{mean_c at the} center of the single crystal. Figure 7 is a diagram illustrating the distribution of the optimum temperature gradient ratio G _c / G _e in accordance with the stress sigma _{Mean_c} monocrystalline center. FIG. 8 is a diagram schematically showing a configuration of a single crystal growing apparatus to which the silicon single crystal growing method of the present invention can be applied. Figure 9 is a graph showing the relationship between the gap H and the temperature gradient ratio G _c / G _e between the liquid surface of the thermal shield 10 and the raw material melt 9. FIG. 10 is a flowchart showing a process for manufacturing a silicon single crystal. FIG. 11 is a schematic sectional view showing the shape of a silicon single crystal ingot. FIG. 12 is a schematic diagram for explaining the relationship between the gap profile and the crystal defect distribution during the crystal pulling step, and particularly shows the case of conventional gap constant control. FIG. 13 is a schematic diagram for explaining the relationship between the gap profile and the crystal defect distribution during the crystal pulling step, and particularly shows the case of the variable gap control of the present invention. FIG. 14 is a block diagram of a variable gap control function for describing a method of calculating a crucible lifting speed.

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

1. Critical V / G formula introducing stress effect The pulling speed (hereinafter also referred to as “critical pulling speed”) aimed at growing a defect-free crystal is _defined as V _cri (unit: mm / min), and a single crystal solid-liquid Assuming that the temperature gradient in the pulling axis direction near the interface is G (unit: ° C./mm), the critical V _cri / G, which is the ratio, can be obtained by introducing the effect of stress acting on the single crystal during single crystal growth. , Can be defined by the following equation (1). Here, the vicinity of the solid-liquid interface of the single crystal means that the temperature of the single crystal ranges from the melting point to 1350 ° C.
V _cri / G = (V / G) _{σmean = 0} + α × σ _mean (1)

In the equation, (V / G) _{σmean = 0} is a constant indicating the critical V / G when the average stress in the crystal is zero. α is a stress coefficient, and σ _mean is an average stress (unit: MPa) in the single crystal. For example, when a single crystal having a diameter of 310 mm is to be grown, (V / G) _{σmean = 0} is 0.17 and α is 0.0013. Here, the average stress σ _mean corresponds to the stress of the component that changes the volume of the single crystal during growth, and can be grasped by numerical analysis. The vertical components σ _rr , σ _θθ , and σ _zz of the stress acting on each of the three surfaces, that is, the surface along the direction and the surface perpendicular to the direction of the pulling axis are extracted, and these are summed and divided by three. . Here, a positive _mean stress σ _mean means a tensile stress, and a negative _mean compressive stress.

Since (V / G) _{σmean = 0} is a constant, the above equation (1) becomes the following equation (2) by replacing (V / G) _{σmean = 0} with ξ.
V _cri / G = ξ + α × σ _mean (2)

The above equation (2) expresses the relationship between the one-dimensional critical V _cri / G and the average stress (σ _mean ). In order to grow a defect-free crystal, it is perpendicular to the pulling axis direction of the single crystal. You need to think in the plane.

2. Expansion of the Critical V / G Equation Introducing the Stress Effect to Single Crystal In-Plane Distribution At a position of radius r (unit: mm) from the center of the single crystal, a critical pulling speed V _cri (unit: mm / min), The critical V _cri / G (r), which is the ratio to the temperature gradient G (r) (unit: ° C./mm) at the position of the radius r, can be obtained by _applying the stress effect according to the above equation (2). It can be defined by the following equation (3).
V _cri / G (r) = ξ + α × σ _mean (r) (3)

In the equation, σ _mean (r) is the average stress (unit: MPa) near the solid-liquid interface at a position of radius r from the center of the single crystal, and the average in-plane near the solid-liquid interface of the single crystal. 3 shows a stress distribution. From the equation, the temperature gradient G (r) at the position of the radius r can be expressed by the following equation (4).
G (r) = V _cri / (ξ + α × σ _mean (r)) (4)

Here, the temperature gradient G (r) indicates the distribution of the temperature gradient in a plane orthogonal to the pulling axis direction of the single crystal. Therefore, in order to grow a defect-free crystal, the optimal in-plane temperature gradient G ( Although it is desired to obtain the distribution of r), it is difficult to predict the distribution of the average stress σ _mean (r) in the plane. Another problem is that the distribution of the in-plane average stress σ _mean (r) varies depending on conditions.

Therefore, a method for predicting the in-plane average stress σ _mean (r) was examined.

2-1. Relationship between the temperature gradient at the center of the single crystal and the average stress (stress) The temperature gradient G (0) (= G _c ) at the center of the single crystal and the average stress σ _mean (0) (= σ _{mean_c} ) at the center of the single crystal Considered the relationship. This examination was performed as follows. Assuming that a single crystal having a diameter of 310 mm is grown, first, the radiant heat of the single crystal surface under each hot zone condition is calculated by comprehensive heat transfer analysis in which the conditions of the hot zone are variously changed. With the radiant heat under the zone conditions and the solid-liquid interface shape changed variously as the boundary conditions, the temperature in the single crystal under each boundary condition was recalculated. Here, the condition of the hot zone was changed by changing the gap between the lower end of the heat shield surrounding the single crystal and the liquid level of the raw material melt in the quartz crucible (hereinafter, also referred to as “liquid level gap”). As the condition change of the solid-liquid interface shape, the height in the direction of the pulling axis from the liquid surface of the raw material melt to the center of the solid-liquid interface (hereinafter, also referred to as “interface height”) was changed. For each condition, the stress (average stress) was calculated based on the temperature distribution in the single crystal obtained by the recalculation.

From the analysis results, the average stress σ _mean (0) (= σ _{mean_c} ) at the center of the single crystal is proportional to the temperature gradient G (0) (= G _c ) at the center of the single crystal, _regardless of the interface height. However, it was found that there was a relationship represented by the following equation (5).
σ _mean (0) = − 15.879 × G (0) +38.57 (5)

2-2. Standardization of In-Plane Average Stress Subsequently, standardization of the distribution of the in-plane average stress σ _mean (r) was examined by the above-described numerical analysis. Here, as shown by the following equation (6), the ratio n () between the average stress σ _mean (r) at the position of the radius r and the average stress σ _mean (0) (= σ _{mean_c} ) at the center of the single crystal. r) was defined as a standardized stress ratio.
n (r) = σ _mean (r) / σ _{mean_c} (6)

As a result, it can be seen that the standardized stress ratio n (r) has almost the same tendency according to the position of the radius r even when the interface height is different from the liquid level Gap, and can be expressed by the following equation (7). Was.
n (r) = 0.000000524 × r ³ −0.000134 × r ² + 0.00173 × r + 0.986 (7)

However, since σ _mean (r) = σ _{mean_c} at the center of the single crystal (r = 0), n (0) is 1 from the above equation (6). At the outer periphery of the single crystal (r = e (e is, for example, 155 mm when a single crystal having a diameter of 310 mm is targeted)), since σ _mean (r) = 0, n (e) is It is 0 according to equation (6).

Then, from the above equations (6) and (5), the in-plane average stress σ _mean (r) can be expressed by the following equation (8).
σ _mean (r) = n (r) × σ _{mean_c}
= N (r) × (-15.879 × G (0) +38.57) (8)

From the equation, the distribution of the in-plane average stress σ _mean (r) can be grasped if the average stress σ _mean (0) (= σ _{mean_c} ) at the center of the single crystal is known. It can be understood that the temperature gradient G (0) (= _Gc ) can be grasped.

3. Derivation of distribution of optimum in-plane temperature gradient G (r) When a single crystal having a diameter of 310 mm is to be grown, the in-plane temperature gradient G (r) is obtained by substituting the above equation (8) into the above equation (4). Then, it can be expressed by the following equation (9).
G (r) = V _cri /(ξ+α×n(r)×(−15.879×G(0)+38.57)) (9)

Here, consideration is given to standardizing the distribution of the temperature gradient G (r), and the ratio (G (0) between the temperature gradient G (r) at the position of the radius r and the temperature gradient G (0) at the center of the single crystal. r) / G (0)) as the standardized temperature gradient ratio, the following equation (10) is derived from the above equation (9).
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)

From the equation, the in-plane temperature gradient G (r) can be expressed by the following equation (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)

中 In the formulas (10) and (11), n (0) is 1 as described above. n (r) is represented by the above equation (7). However, as described above, n (r) at the outer peripheral portion (r = e) of the single crystal, that is, n (e) is 0.

Therefore, by determining the temperature gradient G ₍₀₎ (= G _c ) at the center of the single crystal, it is possible to grasp the optimal distribution of the in-plane temperature gradient G (r) using the above equation (11). It can be said that it can be done.

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

From the equation, the in-plane temperature gradient G (r) can be expressed by the following equation (13).
G (r) = [(ξ + α × n (0) × σ _mean (0)) / (ξ + α × n (r) × σ _mean (0))] × G (0) (13)

中 In the formulas (12) and (13), n (0) is 1 as described above. n (r) is represented by the above equation (7). However, as described above, n (r) at the outer peripheral portion (r = e) of the single crystal, that is, n (e) is 0.

Therefore, by determining the average stress at the central portion of the single crystal, that is, the stress σ _mean (0) (= σ _{mean_c} ), the optimum distribution of the in-plane temperature gradient G (r) can be calculated using the above equation (13). It can be said that it can be grasped.

4. If the optimum range diameter ratio G _c / G _e between the temperature gradient G _e of the temperature gradient G _c and the outer peripheral portion of the central portion of the single crystal is a growing interest for single crystal 310 mm, by the above equation (11), a single When the optimum temperature gradient G (r) corresponding to the position of the radius r from the center of the single crystal is _calculated for each temperature gradient Gc at the center of the crystal, the distribution of the in-plane temperature gradient G (r) is, for example, As shown in FIG.

Figure 4 is a diagram illustrating the distribution of the temperature gradient G _c each optimal plane temperature gradient G in the single crystal center (r). From the figure, it can be seen that by determining the temperature gradient G (0) (= G _c ) at the central portion of the single crystal, the optimum distribution of the in-plane temperature gradient G (r) can be grasped.

Here, the main management indicator for growing a defect-free crystal, it is the ratio G _c / G _e between the temperature gradient G _e of the outer peripheral portion of the temperature gradient G _c and the single crystal in the center portion of the single crystal. When the optimum temperature gradient ratio G _c / G _e is calculated based on the temperature gradient G (0) (= G _c ) at the central portion of the single crystal from the calculation result by the above equation (11), the temperature gradient ratio G _c / distribution of G _e is, for example, as shown in FIG.

Figure 5 is a diagram illustrating the distribution of the optimum temperature gradient ratio G _c / G _e in accordance with the temperature gradient G _c of the single crystal center. The figure shows a case where a single crystal having a diameter of 310 mm is to be grown, that is, a case where r = e = 155 mm. From the figure, there is a correlation between the single crystal center temperature gradient G _c and optimal temperature gradient ratio _{_{G c / G e (= G}} (0) / G (150)), the following (14) It became clear that the relationship of the linear expression represented by the expression holds.
G _c / G _e = 0.1769 × G _c +0.5462 (14)

Therefore, by determining the temperature gradient G in the single crystal center ₍₀₎ (= G _c), using the above equation (14), it is possible to grasp the optimum temperature gradient ratio G _c / G _e. Then, since the relation of the equation (14) holds, if the single crystal is pulled under the condition of G _c / G _e that satisfies the following equation (a), a defect-free crystal can be grown with high accuracy. Become.
0.9 × A ≦ G _c / G _e ≦ 1.1 × A (a)
In the above formula (a), A is 0.1769 × G _c +0.5462.

If the temperature gradient ratio G _c / G _e is less than “0.9 × A” or exceeds “1.1 × A”, the growth of defect-free crystals becomes unstable. More preferably, the temperature gradient ratio G _c / G _e is equal to or greater than “0.95 × A” and equal to or less than “1.05 × A”.

When a single crystal having a diameter of 310 mm is to be grown, the optimum temperature gradient G according to the position of the radius r from the center of the single crystal for each stress σ _{mean_c at the} center of the single crystal by the above equation (13). When (r) is calculated, the distribution of the in-plane temperature gradient G (r) is, for example, as shown in FIG.

FIG. 6 is a diagram exemplifying a distribution state of the optimal in-plane temperature gradient G (r) for each stress σ _{mean_c at the} center of the single crystal. From the figure, it can be seen that the optimum distribution of the in-plane temperature gradient G (r) can be grasped by determining the stress σ _mean (0) (= σ _{mean_c} ) at the central portion of the single crystal.

Here, the main management indicator for growing a defect-free crystal, there is a temperature gradient ratio G _c / G _e. When the optimum temperature gradient ratio G _c / G _e is calculated from the calculation result by the above equation (13) according to the stress σ _{mean —} (0) (= σ _mean — _c ) at the central portion of the single crystal, the temperature gradient ratio G _c / distribution of G _e is, for example, as shown in FIG.

Figure 7 is a diagram illustrating the distribution of the optimum temperature gradient ratio G _c / G _e in accordance with the stress sigma _{Mean_c} monocrystalline center. The figure shows a case where a single crystal having a diameter of 310 mm is to be grown, that is, a case where r = e = 155 mm. From the figure, there is a correlation between the stress σ _{mean_c at the} central portion of the single crystal and the optimum temperature gradient ratio G _c / G _e (= G (0) / G (150)). It has been clarified that the linear relationship represented by
G _c / G _e = −0.0111 × σ _{mean_c} +0.976 (15)

Therefore, by determining the stress sigma _{Mean_} single crystal center ₍₀₎ (= σmean_c), using the above equation (15), it is possible to grasp the optimum temperature gradient ratio G _c / G _e. Then, since the relationship of the formula (15) holds, if the single crystal is pulled under the condition of G _c / G _e that satisfies the following formula (b), a defect-free crystal can be grown with high accuracy. Become.
0.9 × B ≦ G _c / G _e ≦ 1.1 × B (b)
In the above equation (b), B is −0.0111 × σ _{mean_c} +0.976.

If the temperature gradient ratio G _c / G _e is less than “0.9 × B” or exceeds “1.1 × B”, the growth of defect-free crystals becomes unstable. More preferably, the temperature gradient ratio G _c / G _e is not less than “0.95 × B” and not more than “1.05 × B”.

However, in the above formulas (a) and (b), the temperature gradient G _{c at the} central portion of the single crystal is in the range of 2.0 to 4.0 ° C./mm when a single crystal having a diameter of 310 mm is to be grown. Inside. This is because if it is out of this range, various point defects such as OSF, COP and LD occur. A more preferred range of the temperature gradient G _c of the single crystal center is 2.5 ~ 3.5 ℃ / mm.

As described above, the distribution of the stress σ _mean (r) in the vicinity of the solid-liquid interface of the single crystal has a regularity, and the distribution of the in-plane stress σ _mean (r) is the stress σ _{mean_c} limited to the center of the single crystal. or it can be grasped by the temperature gradient G _c. As a result, in consideration of the effect of the impact stress on the generation of point defects, by determining the stress sigma _{Mean_c} temperature gradient G _c or single crystal center portion of the single crystal heart, for growing a defect-free crystal distribution of optimal plane temperature gradient G (r), further it is possible to grasp the optimum temperature gradient ratio G _c / G _e. Then, by using the optimum temperature gradient ratio G _c / G _e as a management indicator, able to operate properly dimensioning of the hot zone, moreover, a reference to its optimum temperature gradient ratio G _c / G _e By setting the control range, it is possible to grow a defect-free crystal with high accuracy.

5. FIG. 8 is a diagram schematically showing the configuration of a single crystal growing apparatus to which the method for growing a silicon single crystal of the present invention can be applied. As shown in FIG. 1, the single crystal growing apparatus has a chamber 1 at its outer periphery, and a crucible 2 is arranged at the center thereof. 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 of a support shaft 3 that can rotate and move up and down. The rotation and elevating operation of the support shaft 3 are controlled by the crucible drive 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 crucible 2 along the inner surface of the chamber 1. Above the crucible 2, a lifting shaft 6 such as a wire that rotates at a predetermined speed in the opposite direction or the same direction coaxially with the support shaft 3 is disposed. A seed crystal 7 is attached to a lower end of the pulling shaft 6. The operation of the pulling shaft 6 is controlled by a crystal pulling mechanism 15.

(4) In the chamber 1, a cylindrical water-cooled body 11 surrounding the silicon single crystal 8 being grown above the raw material melt 9 in the crucible 2 is arranged. The water-cooled body 11 is made of, for example, a metal having good thermal conductivity such as copper, and is forcibly cooled by cooling water flowing inside. The water-cooled body 11 plays a role of promoting cooling of the single crystal 8 during growth and controlling a temperature gradient in a pulling axial direction of a central portion of the single crystal and a peripheral portion of the single crystal.

Furthermore, a tubular heat shield 10 is arranged so as to surround the outer peripheral surface and the lower end surface of the water cooling body 11. The heat shield 10 blocks the raw material melt 9 in the crucible 2 and the high-temperature radiant heat from the heater 4 and the side wall of the crucible 2 with respect to the single crystal 8 being grown, and also forms a solid-liquid interface as a crystal growth interface. In the vicinity of, the diffusion of heat to the low-temperature water-cooled body 11 is suppressed, and the temperature gradient of the central portion of the single crystal and the outer peripheral portion of the single crystal is controlled together with the water-cooled body 11.

ガス A gas inlet 12 for introducing an inert gas such as Ar gas into the chamber 1 is provided at an upper portion of the chamber 1. An exhaust port 13 for sucking and discharging the gas in the chamber 1 by driving a vacuum pump (not shown) is provided below 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-cooled body 11, and the inert gas flows between the lower end of the heat shield 10 and the liquid surface of the raw material melt 9. After passing through the gap (liquid level gap), it flows toward the outside of the heat shield 10 and further to the outside of the crucible 2, then descends outside the crucible 2, and is discharged from the exhaust port 13.

カメラ A camera 16 is provided outside the chamber 1, and the camera 16 photographs the vicinity of the solid-liquid interface through a viewing window provided in the chamber 1. The image captured by the camera 16 is processed by the image processing unit 17, and the crystal diameter, the liquid level, and the like are obtained. The control unit 18 controls the heater 4, the crucible driving mechanism 14, and the crystal pulling mechanism 15 based on the image processing result.

At the time of growing the silicon single crystal 8 using such a growing apparatus, a solid raw material such as polycrystalline silicon filled in the crucible 2 is supplied to the heater 4 while the inside of the chamber 1 is maintained in an inert gas atmosphere under reduced pressure. The material is melted by heating to form a raw material melt 9. When the raw material melt 9 is formed in the crucible 2, the lifting shaft 6 is lowered to immerse the seed crystal 7 in the raw material melt 9, and while rotating the crucible 2 and the lifting shaft 6 in a predetermined direction, the lifting shaft is rotated. 6 is gradually pulled up, thereby growing a single crystal 8 connected to the seed crystal 7.

When growing a single crystal having a diameter of 310 mm, in order to grow a defect-free crystal, the temperature gradient ratio _Gc / _Ge is set near the solid-liquid interface of the single crystal according to the above equation (a) or (b). The pulling speed of the single crystal and the gap (height of the crucible 2) are adjusted so as to satisfy the conditions, and the single crystal is pulled. Further, prior to the growth of a single crystal, the (14) or (15) to conform to the optimum temperature gradient ratio G _c / G _e which is obtained by the formula, the dimensions of the hot zone (thermal shield and a water-cooled body) shape And use this hot zone. Thereby, a defect-free crystal can be grown with high accuracy.

Figure 9 is a graph showing the relationship between the gap H and the temperature gradient ratio G _c / G _e between the liquid surface of the thermal shield 10 and the raw material melt 9, the horizontal axis represents the gap H, the vertical axis G _c / _Ge is shown. In the figure, the triangular plot points represent the value of the gap H and the temperature gradient ratio G _c / G _e obtained by a comprehensive heat transfer simulation in which a silicon single crystal having a diameter of 310 mm is grown using a hot zone having a specific structure. Further, the lower limit of 0.9 C and the upper limit of 1.1 A of G _c / G _{e in} equation (a) are indicated by two straight lines. The region sandwiched between these two straight lines is the range defined by the equation (a), that is, the range in which defect-free crystals can be obtained.

As shown in FIG. 9, it can be seen that G _c / G _e satisfies the expression (a) when the gap H is in the range of about 58 to 70 mm. Thus, by adjusting the gap H, the temperature gradient ratio G _c / G _e can be set within the range of 0.9A to 1.1A.

FIG. 10 is a flowchart showing a process for manufacturing the silicon single crystal 8. FIG. 11 is a schematic sectional view showing the shape of a silicon single crystal 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 in which a silicon raw material in the crucible 2 is heated and melted by the heater 4 to generate a raw material melt 9, A dipping step S12 in which the seed crystal attached to the tip end of the pulling shaft 6 is lowered to be immersed in the raw material melt 9, and the seed crystal is gradually pulled up while maintaining the state of contact with the raw material melt 9 to form a single crystal. A crystal pulling step (S13 to S16) for growing a crystal is provided.

In the crystal pulling step, a necking step S13 for forming a neck portion 8a having a narrowed crystal diameter for eliminating dislocations, and a shoulder growing step S14 for forming a shoulder portion 8b having a crystal diameter gradually increased with crystal growth. And a body part growing step S15 for forming the body part 8c in which the crystal diameter is kept constant, and a tail part growing step S16 for forming the tail part 8d in which the crystal diameter is gradually reduced as the crystal grows. .

(4) Thereafter, a cooling step S17 of separating the silicon single crystal 8 from the melt surface to promote cooling is performed. Thus, 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 type and distribution of the crystal defects contained in the silicon single crystal 8 depend on the ratio V / G of the crystal pulling speed V and the temperature gradient G, and the thermal environment in the furnace surrounding the crystal, that is, the hot zone Strongly influenced by Therefore, when the hot zone changes with the progress of the crystal pulling process, Gc / Ge cannot be kept within the range of 0.9A to 1.1A even if the gap is maintained at a constant distance. In some cases, a desired lifting speed margin cannot be secured.

For example, in the middle stage of the body part growing step S15 shown in FIG. 11, a single crystal ingot having a sufficient length exists in the space above the silicon melt, but at the start of the body part growing step S15. Since there is no single crystal ingot, even if the heat shield 10 is provided, the heat distribution in the space is slightly different. Further, at the end of the body part growing step S15, the output of the heater 4 is increased to prevent the silicon melt from solidifying due to the decrease of the raw material melt 9 in the crucible, thereby changing the heat distribution around the crystal. . When the hot zone changes in this way, even if the gap is maintained at a constant distance, the thermal history in the crystal changes, so that the in-plane distribution of crystal defects cannot be maintained constant.

Therefore, in the present embodiment, the gap is not always kept at a constant distance from the top to the bottom of the ingot, but is changed according to the crystal growth stage. That is, the gap is changed so that the temperature gradient ratio G _c / G _e satisfies the above equation (a) or (b). By changing the gap in this manner, the in-plane distribution of crystal defects from the top to the bottom of the ingot can be controlled as intended, and a reduction in the pulling speed margin is suppressed to improve the production yield of defect-free crystals. be able to. How to change the gap to suppress a decrease in the pulling speed margin depends on the hot zone. Therefore, in order to fix the in-plane distribution range crystal defects contained within the 0.9 A ~ 1.1A temperature gradient ratio G _c / G _e from the top of the crystal to the bottom is the progress of the crystal pulling process It is necessary to appropriately set a gap profile according to the crystal growth stage while considering how the hot zone changes accordingly.

12 and 13 are schematic diagrams for explaining the relationship between the gap profile and the crystal defect distribution during the crystal pulling step. FIG. 12 shows the case of the conventional constant gap control, and FIG. 13 shows the gap of the present invention. Each shows the case of variable control.

Figure 12 As shown, at all times the gap constant control for maintaining a constant distance gap during crystal pulling process, the temperature gradient ratio G _c / G _e is changed by the hot zone is changed, the plane of the crystal defects The distribution cannot be kept constant. That is, the top of the silicon single crystal ingot 8I (Top), the center (Mid), in the bottom (Bot), by in-plane distribution of the crystal defects are different, in the center of the ingot 8I by optimizing the G _c / G _e desired Can be secured, but a desired lifting speed margin cannot be secured at the top and bottom of the ingot 8I.

In contrast, in the present invention, as shown in FIG. 13, the gap profile is set so that the gap gradually narrows as the crystal pulling process proceeds. In particular, the gap profile according to the present embodiment includes a first gap constant control section S1 for maintaining the gap constant from the start of the crystal pulling step, and a first gap provided in the first half of the body part growing step to gradually reduce the gap. A variable control section S2, a second gap constant control section S3 for maintaining a constant gap, a second gap variable control section S4 provided in the latter half of the body part cultivation step to gradually reduce the gap, and until the end of the crystal pulling step. A third constant gap control section S5 for keeping the gap constant is provided in this order. Such a gap profile is set in accordance with the change of the hot zone, thereby maintaining a constant in-plane distribution of crystal defects from the top to the bottom of the ingot 8I as shown in the drawing to increase the production yield of defect-free crystals. Becomes possible.

The above-described gap profile is an example, and is not limited to a profile in which the gap gradually narrows as the crystal pulling process proceeds. Therefore, for example, it is possible to gradually decrease the gap in the first gap variable control section S2 and gradually increase the gap in the second gap variable control section S4.

The temperature gradient at the outer periphery of the single crystal 8 is more susceptible to the change in the gap than the temperature gradient at the center. If the gap is wide, because radiation heat from the heater 4 is easily transmitted to the single crystal 8 through the gap, the temperature gradient G _e of the outer peripheral portion of the single crystal 8 becomes relatively small, the temperature gradient ratio G _c / G _e Becomes larger. Conversely, when the gap is narrow, since the radiant heat from the heater 4 is not easily transmitted to the single crystal 8 is blocked by the thermal shield 10, the temperature gradient G _e of the outer peripheral portion of the single crystal 8 becomes relatively large, the temperature gradient ratio G _c / G _e is small. Therefore, by adjusting the gap, it is possible to easily adjust the temperature gradient ratio G _c / G _e.

When performing the variable gap control, simply correcting the crucible ascending speed and varying the gap may cause a phenomenon in which the crucible ascending speed greatly fluctuates. Such a vibration phenomenon may be an obstacle for the purpose of maintaining a constant in-plane distribution of crystal defects from the top to the bottom of the ingot 8I by the variable gap control and increasing the production yield of defect-free crystals. Therefore, in the present invention, such a vibration phenomenon is prevented, and a high-quality crystal can be manufactured.

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

As shown in FIG. 14, the variable gap control function has a crucible lifting speed calculation unit 30. The crucible rising speed calculating unit 30 includes a quantitative value calculating unit 31 that calculates a quantitative value _Vf of the crucible rising speed necessary to control the liquid level and the gap that change as the silicon single crystal 8 is pulled up. A variation value calculating unit 32 that calculates _a variation value Va of the crucible ascending speed from a change amount of the target value of the gap, and calculates a correction value _Vadj of the crucible ascending speed from a difference between the target value of the gap and the measured value of the gap. and a correction value calculation unit 33, a crucible drive mechanism 14 outputs the liquid level rising speed V _M, the position of the crucible using quantitative value V _f, the total value of the variation value V _a and the correction value V _adj Control. The crystal pulling mechanism 15 outputs a crystal length ΔL _S (crystal pulling speed V _S ). The image processing unit 17 measures a gap between the liquid surface of the raw material melt 9 and the heat shield 10 and a crystal diameter from an image captured by the camera 16.

In the gap variable control controls the crucible lifting speed for each control period based on the crucible lifting speed V _C calculated using shown below (16).

V _C = V _f + V _a + V _adj (16)

Here, _Vf is a quantitative value of the crucible rise speed required to maintain the gap constant, and is a crucible rise speed used for constant gap control. The V _a is a variation value of a crucible lifting speed which is determined from the variation of the gap target value, V _adj is the current correction value of the crucible lifting speed which is determined from the difference between the actual measured value and the target value of the gap.

The quantitative value _Vf of the crucible rising speed is 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 × 10 ^-3 )
P _L : Specific gravity of silicon melt (= 2.53 × 10 ^-3 )
D _S: the current crystal diameter D _C: inner diameter V _S of the current of the quartz crucible: Current crystal pulling speed V _M: increase the speed of the previous crucible (liquid level rising speed)

The liquid level rising speed V _M is given by the following equation (18).

_{_{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 : crystal movement amount per control cycle ΔL _C : crucible movement amount per control cycle

Thus, in the calculation of the quantitative value V _f of the crucible lifting speed, crystal movement amount per one control cycle from the crystal pulling mechanism 15 acquires (crystal length) [Delta] L _S, crystal diameter D _S and the crystal moving amount [Delta] L _C seeking the increase in crystal volume from calculates the decrease of the melt volume from increase and the crucible inner diameter D _C of the crystal volume, further quantitative value V of the crucible lifting speed from decrease and the crucible inner diameter D _C of the melt volume Calculate _f . The crystal diameter D _S is obtained by the image processing unit 17 processing a single crystal appearing in an image captured by the camera 16. Crucible inner diameter D _C is a fixed value determined from the design dimensions of the quartz crucible 2a.

When the liquid level rise velocity V _M is balanced with the current crystal pulling speed V _S, since the quantitative value V _f of the crucible lifting speed becomes equal to the liquid level rising speed V _M, the gap is maintained at a constant distance. The liquid level rising speed V _M of the current crystal pulling speed V _S is greater if the crucible ascent speed of the quantitative value V _f than is smaller than the liquid level rise velocity V _M, contrary to the liquid level rising speed V _M is currently the crystal pulling speed V _S if smaller crucible ascent speed of the quantitative value V _f than is larger than the liquid level rise velocity V _M, it is possible to keep the gap constant.

Variation value V _a of the crucible lifting speed is given by the following equation (19).

V _a = (H _{pf — i} −H _{pf — i + 1} ) ÷ T (19)

Here, _{Hpf_i} is the current (i-th) gap target value (mm), and _{Hpf_i + 1} is the gap target value (mm) after one control cycle (i + 1-th). The gap target value is set, for example, according to the crystal length, and the crystal length after one control cycle can be obtained from the increment of the crystal length obtained by multiplying the current crystal pulling speed V _S by the control cycle T (min). . The control cycle T is not particularly limited, but can be set to, for example, 2 minutes. Thus, variation value V _a of the crucible lifting speed is to be determined from the difference between the current gap target value _H pf_i _{+ 1} after the gap target value H _{Pf_i} and one control period. For certain _{_{(H pf_i + 1 = H pf_i}} ) the target value of the gap is not changed, the V _a = 0. For example, when the cap is changed from 50 mm to 51 mm, the gap needs to be increased by 1 mm. Since the change in the target value of such a gap can be known from the gap profile, it is necessary to increase the gap by 1 mm. adding the variation value V _a of the crucible ascent speed in quantitative value V _f.

The correction value _Vadj of the crucible ascending speed is represented by the following equation (20).

V _adj = (H _{pf —} _i −H _i ) ÷ T × k (20)

Here, _Hi is the current gap measurement value (mm), preferably a moving average value instead of the latest single value. Further, k is a gain, and is preferably 0.001 or more and 0.1 or less. When k is set to, for example, 0.05, the influence of the variation in the measured gap value on the crucible ascending speed can be suppressed to 1/20. When the gap measurement value is equal to the gap target value, the crucible rise correction speed V _adj = 0.

As described above, the calculation of the quantitative value V _f of the crucible lifting speed is required exact value of the inner diameter D _C of the quartz crucible 2a. However, since the quartz crucible 2a softens near the melting point of silicon and may be deformed during pulling, the value of the gap deviates from the target value. The gap value deviates from the target value due to various other factors. Therefore, in the present embodiment, the gap is actually measured from the position of the mirror image of the heat shield 10 reflected on the melt surface, and the gap control error is calculated from the crucible rising speed calculated from the decrease amount of the raw material melt 9. Then, the gap is controlled with high accuracy by adding the correction value _Vadj of the rising speed of the quartz crucible 2a for eliminating this control error to the quantitative value _Vf .

As described above, the crucible ascending speed V _C is determined by the quantitative value V _f of the crucible ascending speed required to maintain the gap constant, and the fluctuation value V _a of the crucible ascending speed obtained from the change in the gap target value. It _consists of the sum of the correction value V _adj of the crucible ascending speed obtained from the difference between the target value of the gap and the actual measurement value, and the change in the gap target value that can be obtained from the gap profile is based on the quantitative value. By including the value in advance in the crucible ascending speed irrespective of the gap measurement value, the fluctuation of the crucible ascending speed correction value _Vadj can be made as small as possible. That is, the role of the correction value V _adj of the crucible ascending speed is specialized only for the correction for eliminating the difference between the target value of the gap and the measured value, so that the amplitude of the crucible ascending speed is prevented from increasing. And stable control of the crucible ascent speed is made possible.

As described above, the method for growing a silicon single crystal according to the present embodiment includes gap variable control for pulling up the single crystal while changing the gap between the liquid surface of the raw material melt and the heat shield, When the temperature gradient near the solid-liquid interface at the center is G _c and the temperature gradient near the solid-liquid interface at the outer periphery of the single crystal is G _e , and when A = 0.1769 × G _c +0.5462, the temperature gradient ratio G _{Since the} single crystal is pulled while changing the gap under the condition that _c / _Ge is 0.9 × A ≦ _Gc / _Ge ≦ 1.1 × A, the stress acting on the single crystal during the growth of the single crystal is reduced. It is possible to grow a defect-free crystal with high accuracy while taking this into consideration.

Further, in the method for growing a silicon single crystal according to the present embodiment, a gap profile in which a gap target value changes according to the crystal length is prepared, and the crucible rising speed V _C is adjusted so that the gap measurement value follows the gap profile during crystal growth. Control, the crucible rise rate amplitude can be prevented from increasing, and as a result, a high-quality silicon single crystal with little change in the in-plane distribution of crystal defects from the top to the bottom of the silicon single crystal can be produced. Can be manufactured well.

Further, in the present embodiment, the quantitative value _Vf of the crucible rising speed required to maintain the gap constant and the variation value _Vf of the crucible rising speed required to change the gap from the change in the target value of the gap. and _a, since using the total value of the correction value V _adj of the crucible increasing speed required in order to correct the difference between the target value and the measured value of the gap as the crucible lifting speed V _C, the crucible lifting speed caused by a gap variable control Control instability can be improved, and thereby the crystal acquisition rate can be improved.

As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It goes without saying that they are included in the range.

For example, in the above embodiment, as the correction value of the crucible lifting speed, the difference between the gap target value H _{Pf_i} and the gap measured value H _i - multiplied by _(H pf_i H _i) the reciprocal 1 / T and the gain k of the control cycle However, the present invention is not limited to such values, and correction values calculated by various calculation methods can be used.

In the above embodiment, the method of growing a silicon single crystal has been described as an example, but the present invention is not limited to this, and can be applied to various single crystals pulled by the CZ method.

The method for growing a silicon single crystal of the present invention is extremely useful for growing a defect-free crystal free of various point defects such as OSF, COP and LD.

1: chamber, 2: crucible, 2a: quartz crucible, 2b: graphite crucible, 軸 3: support shaft, 4: heater, 5: heat insulating material, 6: pull-up shaft, 7: seed crystal, 8: silicon single crystal, 8I: Silicon single crystal ingot, # 8a: neck, # 8b: shoulder, # 8c: body, # 8d: tail, # 9: raw material melt, # 10: heat shield, # 11: water cooled, # 12: gas inlet, # 13: Exhaust port, # 14: crucible drive mechanism, # 15: crystal pulling mechanism, # 16: camera, # 17: image processing section, # 18: control section, # 30: crucible rise speed calculation section, # 31: quantitative value calculation section, # 32: fluctuation value calculation Section, # 33: correction value calculation section

Claims

A method for growing a silicon single crystal by the Czochralski method of pulling a single crystal having a diameter of 300 mm or more from a raw material melt in a crucible disposed in a chamber,
With a water-cooled body surrounding the single crystal being grown, and using a single-crystal growing apparatus with a heat shield surrounding the outer peripheral surface and lower end surface of the water-cooled body,
Gap variable control for pulling up the single crystal while changing the gap between the liquid surface of the raw material melt and the heat shield disposed above the raw material melt,
The temperature gradient in the pulling axis direction near the solid-liquid interface at the center of the single crystal is G c , the temperature gradient in the pulling axis direction near the solid-liquid interface at the outer periphery of the single crystal is G e , and A = 0.1769 × A method for growing a silicon single crystal, comprising: pulling the single crystal under a condition satisfying 0.9 × A ≦ G c / G e ≦ 1.1 × A, where G c +0.5462.
The gap variable control,
Quantitative value of the crucible rise speed required to maintain the gap changing with the pulling of the single crystal at a constant distance,
A variation value of the crucible ascending speed obtained from a change amount of the target value of the gap,
2. The silicon single crystal according to claim 1, wherein the crucible rising speed is controlled by using a total value of a correction value of the crucible rising speed obtained from a difference between the target value of the gap and an actual measurement value. Training method.
The method for growing a silicon single crystal according to claim 2, wherein the amount of change in the target value of the gap is obtained from a gap profile that defines a relationship between a crystal length that changes as the single crystal is pulled and a target value of the gap. .
4. The method of growing a silicon single crystal according to claim 3, wherein the correction value is obtained from a difference between a target value of the gap obtained from the gap profile and a measured value of the gap.
The amount of decrease in the volume of the raw material melt is determined from the amount of increase in the volume of the single crystal accompanying the pulling of the single crystal, and the quantitative value is determined from the amount of decrease in the volume of the raw material melt and the inner diameter of the crucible. 5. The method for growing a silicon single crystal according to any one of 2 to 4.
6. The gap profile according to claim 1, wherein the gap profile includes at least one gap constant control section for maintaining the gap at a constant distance, and at least one gap variable control section for gradually changing the gap. The method for growing a silicon single crystal according to the above item.
7. The method for growing a silicon single crystal according to claim 6, wherein the variable gap control section is provided in a latter half of the single crystal body growing step and after the constant gap control section.
7. The method of growing a silicon single crystal according to claim 6, wherein the variable gap control section is provided in a first half of the body growing step of the single crystal and before the constant gap control section.
The gap profile includes first and second gap variable control sections that gradually change the gap,
The first gap variable control section is provided in the first half of the body part growing step of the single crystal and before the constant gap control section,
The method of growing a silicon single crystal according to claim 6, wherein the second gap variable control section is provided in a latter half of the body growth step of the single crystal and after the constant gap control section.
The method for growing a silicon single crystal according to any one of claims 1 to 9, wherein a measurement value of the gap is calculated from a position of a mirror image of the heat shield reflected on a liquid surface of the raw material melt photographed by a camera. .