JP5145721B2 - Method and apparatus for producing silicon single crystal - Google Patents

Description

  The present invention relates to a method for producing a single crystal for a silicon wafer used as a semiconductor material, and more specifically, infrared scatterer defects (COP) and dislocation clusters grown by the Czochralski method (hereinafter referred to as “CZ method”). The present invention relates to a method and an apparatus for manufacturing a silicon single crystal that is free from Grown-in defects.

  The most widely adopted method for producing a silicon single crystal used for a semiconductor material silicon wafer is a single crystal pulling and growing method by the CZ method. The CZ method is a method of growing a single crystal by immersing a seed crystal in molten silicon in a quartz crucible and growing the single crystal. With the progress of this growth technique, a dislocation-free large single crystal with few defects is produced. It has become like this.

  A semiconductor device is commercialized through a number of processes for forming a circuit using a wafer obtained from a single crystal as a substrate. In that process, many physical treatments, chemical treatments, and thermal treatments are performed, including severe treatments exceeding 1000 ° C. For this reason, the cause is introduced at the time of growing a single crystal, and a fine defect that becomes apparent in the manufacturing process of the device and greatly affects its performance, that is, a grown-in defect becomes a problem.

  FIG. 1 is a view for explaining the distribution of typical grown-in defects present in a silicon single crystal obtained by the CZ method. This figure shows the results of cutting a wafer perpendicular to the pulling axis from a single crystal immediately after growth, immersing it in an aqueous copper nitrate solution, attaching Cu, and observing the distribution of minute defects by X-ray topography after heat treatment. It is shown schematically.

  In this wafer, oxygen-induced stacking faults distributed in a ring shape (hereinafter referred to as “OSF” -Oxidation Induced Stacking Fault-) appear at a position about 2/3 of the outer diameter. , An infrared scatterer defect or a defect called COP (Crystal Originated Particle) appears, and there is a region where a defect composed of a micro dislocation called a dislocation cluster exists outside the ring. This infrared scatterer defect (hereinafter referred to as “COP”) and a dislocation cluster are called Grown-in defects.

  The cause of these defects is not necessarily clear, but is thought to be as follows. That is, in the crystal near the solid-liquid interface when growing a single crystal, vacancies and interstitial atoms diffuse into the crystal from the solid-liquid interface in the axial direction and diffuse to the crystal surface in the radial direction. It disappears when vacancies and interstitial atoms are connected. The diffusion coefficient is larger for interstitial atoms than for vacancies, but the concentration taken in at the time of crystal solidification is considered to be greater for vacancies than for interstitial atoms. When the pulling rate is high, the interstitial atoms diffuse into the crystal from the solid-liquid interface in the process of cooling to the temperature at which COP is formed in the crystal, and the amount of incoming lattice is small. Since the interstitial atoms do not lead to the disappearance of the vacancies that are largely taken in at the solid-liquid interface, the concentration of the vacancies is greater than that of the interstitial atoms. Give rise to On the other hand, when the pulling rate is low, interstitial atoms diffuse into the crystal from the solid-liquid interface during the process of cooling to the temperature at which dislocation clusters are formed in the crystal, and the amount of incoming ions increases. Many trapped vacancies disappear, interstitial atoms have a higher concentration than vacancies, and the interstitial atoms that have predominated coalesce to form dislocation cluster defects. Note that OSF is a stacking fault caused by interstitial atoms generated during the oxidation heat treatment.

  There are very few COPs and dislocation cluster defects in the vicinity of the region where the ring-shaped OSF is generated, and there is an oxygen precipitation promoting region on the outer side in contact with the ring-shaped OSF generation region and depending on the processing conditions. Between the dislocation cluster generation region, there is an oxygen precipitation suppression region where no oxygen precipitation occurs. These oxygen precipitation promoting region and oxygen precipitation suppressing region are both defect-free regions with very few grown-in defects.

  The defect occurrence state described above is usually greatly influenced by the pulling rate during single crystal growth and the temperature distribution in the single crystal immediately after solidification.

  FIG. 2 is a diagram schematically showing a general relationship between the pulling speed and the position of occurrence of crystal defects when pulling a single crystal. This figure shows, for example, that a single crystal grown while gradually reducing the pulling rate is cut along the pulling axis at the center of the crystal, and the cross section of the defect is obtained in the same manner as the result shown in FIG. Can be obtained by examining the distribution of.

  In FIG. 2, when viewed from a plane perpendicular to the pulling axis, at the stage where the pulling speed is high, there is a ring-shaped OSF around the single crystal, and the inside is a region where many COPs are generated. As the pulling speed decreases, the diameter of the ring-shaped OSF gradually decreases, and at the same time, a region where dislocation clusters are generated appears on the outer portion of the ring-shaped OSF. It becomes a dislocation cluster defect generation region.

  FIG. 1 shows a cross section perpendicular to the pulling axis at the position A of the single crystal shown in FIG. 2, or a cross section perpendicular to the pulling axis of the single crystal grown at the pulling speed corresponding to the position A. It is a representation.

  When the OSF is generated and grown on the surface of a wafer serving as an active region of the device, it causes a leakage current and degrades the device characteristics. The same applies to dislocation clusters, which are one of the grown-in defects, and cause the device characteristics to be defective, and COP is a factor to reduce the oxide film pressure resistance.

  For this reason, technological development has been made to obtain a defect-free wafer in which ring-shaped OSF and Grown-in defects are extremely reduced.

For example, in the invention disclosed in Patent Document 1, when the internal temperature gradient in the pulling axis direction in the temperature range from the pulling speed V (mm / min) and the melting point to 1300 ° C. is G (° C./mm), the crystal V / G is set to 0.20 to 0.22 mm ² / (° C./min) between the center position and the position from the outer periphery to 30 mm, and the temperature gradient is gradually increased toward the outer periphery of the crystal. A silicon single crystal wafer is manufactured by controlling the above. In this way, when the pulling is performed, only the COP free region (defect-free region) of the oxygen precipitation promotion region and the oxygen precipitation suppression region outside the ring-shaped OSF is generated within the wafer surface without generating OSF and dislocation clusters. Expand to the whole.

  However, in this method, even if a COP-free single crystal can be grown, the range of conditions is limited, so it is difficult to cope with an increase in pulling speed or an increase in the diameter of the single crystal. In actual production, There are places where it is difficult to easily maintain a stable yield.

In Patent Document 2, when the temperature gradient in the crystal in the pulling axis direction in the temperature range from the melting point to 1400 ° C. is G (° C./mm), the pulling rate F (mm / min) is F / G at the crystal center. Is a manufacturing method of a silicon single crystal wafer in which the crystal is pulled up to 0.112 to 0.142 mm ² / (° C./min), and Patent Document 3 discloses that F / G is 0.119 to 0.142 mm ² / A method for producing a silicon single crystal in which the crystal is pulled up as (° C. min) is described. Each of the manufacturing methods is intended to obtain a silicon single crystal wafer that includes a ring-shaped OSF generation region but does not include a dislocation cluster or a COP generation region. The method described in Patent Document 3 is applied. For example, a wafer having a high gettering capability can be obtained. In order to prevent the ring-shaped OSF from becoming apparent, the oxygen concentration is set to less than 24 ppma and the oxygen crystal is pulled up so that the precipitation of oxygen is difficult to occur, or the growth crystal passes through the temperature range of 1050 ° C. to 850 ° C. Pull up to 140 minutes or less.

  However, in the method described in Patent Document 2 or Patent Document 3, in a normal pulling furnace, the in-crystal temperature gradient (G) in the pulling axis direction changes in the crystal length direction, and the in-plane distribution of G However, since it varies depending on the crystal length, there is a problem in that it is difficult in terms of production technology to mass-produce crystals with no COP or dislocation clusters in the entire crystal length with a high yield.

  Patent Document 4 discloses that the temperature inside the crystal in the pulling axis direction of the single crystal immediately after the pulling is selected by selecting the size and position of the heat shielding material surrounding the single crystal immediately after the pulling and using the cooling member. An apparatus for producing a silicon single crystal in which the gradient is large at the central part and small at the outer peripheral part is presented. With this apparatus, the pulling rate is controlled to an appropriate range around 0.70 to 0.74 mm / min. It is described that the single crystal in which most of the straight body of the single crystal is a defect-free region is obtained by pulling and growing.

JP-A-8-330316 JP-A-11-147786 JP-A-11-157996 JP 2001-220289 A

  The object of the present invention is to produce a silicon single crystal that can be pulled up stably and with good yield over the entire crystal length when growing a single crystal free of grown-in defects such as dislocation clusters and COP by the CZ method, and An object of the present invention is to provide a manufacturing apparatus suitable for carrying out this method.

  In order to achieve the above-mentioned object, the present inventors have examined conditions that can widen the pulling speed range (width) at which a defect-free crystal is obtained when pulling a single crystal. If the range of pulling speed at which defect-free crystals can be obtained is wide, the allowable range of pulling speed is widened, so the number of cases that deviate from the appropriate speed range at the time of pulling is reduced, yield is improved, and stable mass production is possible. It is.

  By the way, the silicon single crystal manufacturing apparatus described in the above-mentioned Patent Document 4 is configured such that the temperature gradient in the crystal in the pulling axis direction of the single crystal immediately after the pulling is large in the central portion and small in the outer peripheral portion. This is because the concentration distribution in the crystal diameter direction of vacancies and interstitial atoms taken in a large amount in the vicinity of the solid-liquid interface during the growth of the single crystal is made uniform.

  The temperature gradient in the crystal in the pulling axis direction is usually large at the outer peripheral portion and small at the central portion because the single crystal being pulled immediately after solidification is cooled by heat dissipation from the surface. That is, Gc <Ge, where Gc is the temperature gradient at the center and Ge is the temperature gradient at the outer periphery. On the other hand, in the apparatus described in the above-mentioned Patent Document 4, the structure of the hot zone, such as the use of a heat shielding material and a cooling member surrounding the single crystal immediately after the pulling, is improved from the melting point to around 1250 ° C. In the temperature range, Gc> Ge can be satisfied. With this temperature distribution condition, the amount of diffusion to the crystal surface in the radial direction of vacancies and interstitial atoms in the periphery of the crystal immediately after pulling and the solid liquid in the axial direction The amount of diffusion from the interface into the crystal is adjusted, and the concentration distribution in the crystal diameter direction of vacancies and interstitial atoms becomes almost equal over the entire surface.

  FIG. 3 shows the crystal defect pulling position in the cross-section including the central axis of the single crystal obtained by pulling the crystal while continuously reducing the pulling rate under such a concentration distribution condition. Although it is a figure which showed the relationship with speed, the ring-shaped OSF, a defect-free area | region, etc. are in the state near horizontal.

  As described above, the apparatus described in Patent Document 4 is pulled up at a pulling speed of about 0.70 to 0.74 mm / min because the defect-free region shown in FIG. This is because a small oxygen precipitation promoting region is included) and the entire crystal length is obtained. If the range of the pulling speed at which this defect-free region appears can be expanded, it can greatly contribute to the improvement of the pulling yield of the defect-free crystal as described above.

  Therefore, a radiant heat shielding screen incorporating a heat shield and a water-cooled body is arranged around the crystal immediately after the pulling, and the distance between the melt surface and the lower end of the radiant heat shielding screen (this distance is referred to below) according to the pulled crystal length. The possibility of expanding the pulling speed range (hereinafter, referred to as “allowable pulling speed width”) in which the defect-free crystal is obtained was investigated by changing the “gap”. The apparatus used is similar to the apparatus described in the above-mentioned Patent Document 4, and the temperature gradient in the pulling axis direction of the single crystal immediately after pulling is Gc> when the central part is Gc and the outer peripheral part is Ge. A device that can be Ge.

As a result, the following findings (a) to (e) were obtained.
(A) In order to make the defect-free region uniform in the crystal diameter direction, it is necessary to satisfy the relationship of Gc> Ge, and the gap must be set within the condition that Gc> Ge is satisfied.
(B) In order to satisfy Gc> Ge, it is effective to increase the gap, but the pulling speed is also reduced.
(C) When the gap is small, the pulling speed is increased, but the allowable pulling speed width on the top side of the pulling crystal is narrowed.
(D) The larger the gap on the top side, the wider the allowable pulling speed range on the top side. However, when the gap is large in the middle part, the allowable pulling speed range is extremely reduced.
(E) Therefore, it is preferable to grow the top portion by increasing the gap and to grow the middle portion and the following by reducing the gap.

  The present invention has been made on the basis of such knowledge, and the gist of the present invention resides in the following method (1) for producing a silicon single crystal and (2) an apparatus for producing a silicon single crystal.

(1) When a silicon single crystal is produced by the CZ method by arranging a radiant heat shielding screen composed of a water-cooled body and a heat shield around the pulling area of the silicon single crystal, the straight body portion of the silicon single crystal is being grown. A method for producing a silicon single crystal in which the gap is changed in accordance with the length of the straight body of the silicon single crystal, wherein the gap is once narrowed during the growth from the top part to the middle part of the straight body part of the silicon single crystal, and then the bottom A method for producing a silicon single crystal, wherein the gap is kept constant by growing a portion.

  The “gap” here is the distance from the lower end of the radiant heat cutoff screen (in this case, the lower end of the heat shield incorporated in the radiant heat cutoff screen) to the melt surface as described above. The “pulled region” refers to a region where a single crystal in a high temperature state (about 1250 ° C. or higher) exists immediately after the pulling. In addition, as described above, it is an accurate expression to write "change the gap according to the length of the straight body part during growth of the straight body part", but replace "straight body part" with "crystal", Or simply “change the gap according to the (pull-up) crystal length”. That is, the “crystal” here refers to the straight body portion of the pulled ingot.

  According to the method for producing a silicon single crystal of the present invention, the grown silicon single crystal can be a defect-free silicon single crystal having no dislocation clusters and no COP.

  Further, in the method for producing a silicon single crystal according to the present invention, the gap is adjusted so that the allowable pulling speed width is wide, and the growth of the straight body portion of the silicon single crystal is started. It is more desirable to grow the silicon single crystal by reducing the gap before reaching the narrowed single crystal pulling length.

  The “allowable pulling speed range” is a pulling speed range in which a defect-free crystal is obtained as described above.

(2) A silicon single crystal manufacturing apparatus using the Czochralski method in which a radiant heat shielding screen composed of a water-cooled body and a heat shield is disposed around a pulling area of a silicon single crystal, and a straight body portion of the silicon single crystal A distance control means for changing a distance (ie, a gap) from the lower end of the radiant heat shielding screen to the melt surface according to the length of the straight body being grown is provided, and the distance control means is a straight body of a silicon single crystal. The silicon single crystal is characterized in that the distance from the lower end of the radiant heat shielding screen to the melt surface is temporarily narrowed during the growth from the top part to the middle part, and the distance is kept constant by the subsequent growth of the bottom part. manufacturing device.

  In this silicon single crystal manufacturing apparatus of the present invention, the distance control means is set and inputted to change the gap according to the measured value of the gap with respect to the straight body length of the growing silicon single crystal and the length of the silicon single crystal. And a control unit that adjusts the gap based on the gap correction amount calculated by the calculation unit. Can do.

  In this case, the gap adjusting means may be constituted by a crucible vertical elevating means and / or a radiant heat blocking screen vertical elevating means.

  According to the method for producing a silicon single crystal of the present invention, it is possible to widen the allowable pulling speed range by changing the gap during crystal pulling. As a result, crystals having no grown-in defects such as COP and dislocation clusters can be pulled stably with a high yield over the entire crystal length, and the yield in mass-producing defect-free crystals can be improved. This method can be preferably carried out using the silicon single crystal production apparatus of the present invention.

  Below, the manufacturing method and manufacturing apparatus of the silicon single crystal of this invention are demonstrated with reference to drawings.

  FIG. 4 is a diagram schematically showing a main configuration of a lifting device suitable for carrying out the manufacturing method of the present invention. The appearance of the pulling device is constituted by a chamber (not shown), and a crucible 1 is disposed at the center thereof. The crucible 1 is fixed to the upper end of a support shaft 6 that can rotate and move up and down, and a heater 2 is arranged substantially concentrically outside the crucible 1. The silicon raw material charged into the crucible 1 is melted to form a melt 3. On the central axis of the crucible 1, a pulling shaft 5 that rotates on the same axis as the support shaft 6 in the reverse direction or in the same direction at a predetermined speed is disposed. Is held.

  Further, in this apparatus, a radiant heat blocking screen 8 is disposed around the pulled up single crystal 4. This radiant heat blocking screen 8 has a longitudinal section that shields between the water-cooled body 8a arranged in parallel with the length direction of the single crystal 4 and the melt 3 and the water-cooled body 8a, and between the quartz crucible 1 and the water-cooled body 8a. It is comprised from the L-shaped heat shield 8b. The heat shield 8 b is a heat insulating material 10 whose surface is covered with high-purity carbon 9.

  As described above, the method for producing a silicon single crystal of the present invention is a method for producing a silicon single crystal by a CZ method by disposing a radiant heat blocking screen around a pulling region of the silicon single crystal. In this method, the gap is changed according to the length of the straight body part during the growth of the straight body part.

  In the manufacturing method of the present invention, as shown in FIG. 4, the radiant heat blocking screen 8 is arranged around the pulling region of the silicon single crystal 4 and the pulling is performed because the temperature in the crystal in the pulling axis direction immediately after the pulling is increased. This is because the gradient is greater at the center than at the outer periphery. That is, the temperature gradient in the crystal immediately after solidification (for example, the temperature range from the melting point to 1300 ° C.) is adjusted so that Gc> Ge (where Gc is the temperature gradient at the center and Ge is the temperature gradient at the outer periphery). This is because the in-plane distribution of the defect-free region in the crystal diameter direction is made uniform. By pulling and growing at such a speed that a uniform surface having no defect is obtained, a single crystal having no grown-in defects can be manufactured.

  Adjustment of the temperature gradient in the crystal in the pulling axis direction is performed by the radiant heat blocking screen 8. That is, the temperature from the surface of the melt of the single crystal being pulled up to the lower end of the heat shield 8b is kept warm by heat radiation from the crucible wall surface or the surface of the melt, and the cooling body 8a and heat Cooling more strongly using the shield 8b, the temperature of the central part is also lowered by the heat conduction from the cooled crystal surface, and the temperature gradient toward the central part becomes relatively large, so that The temperature gradient in the crystal in the pulling axis direction satisfies the condition of Gc> Ge.

  The manufacturing method of the present invention is a method of manufacturing a silicon single crystal by using the pulling apparatus configured as described above, and its feature is that the gap depends on the length of the straight body portion during the growth of the straight body portion of the silicon single crystal. (Distance between the melt surface and the lower end of the radiant heat blocking screen).

  The operation of changing the gap in this way is based on the investigation results on the change of the gap and the increase of the allowable pulling speed range (the range of pulling speed at which defect-free crystals can be obtained) described below.

  That is, the allowable pulling speed range is increased by changing the gap using the pulling apparatus shown in FIG. 4 in which the temperature gradient in the crystal in the pulling axis direction immediately after solidification satisfies the condition of Gc> Ge. We investigated the possibility of. Specifically, the gap is changed between 30 mm and 80 mm, and for each gap, as illustrated in FIG. 5, the pulling speed Vp is 0.90 to 0.60 mm depending on the pulling length of the crystal. A silicon single crystal having a diameter of 200 mm was grown while being gradually lowered or raised within the range of / min.

  Regarding the distribution of crystal defects, the obtained single crystal was vertically divided along the pulling axis, a plate-shaped specimen including the vicinity of the pulling axis was produced, and this specimen was immersed in an aqueous copper nitrate solution to adhere Cu. And subjected to a heat treatment at 900 ° C. for 20 minutes, and then examined by an X-ray topographic method.

  As a result, when the crystal pulling is performed while changing the pulling speed Vp while the gap is controlled to be constant at 45 mm, the width of the pulling speed is within a certain range (this is the allowable pulling speed width and will be collectively displayed later). It was confirmed that a defect-free region free from ring-shaped OSF, COP, and dislocation clusters was obtained on the entire surface in the crystal diameter direction. At the top of the pulling crystal, the in-plane distribution of the defect-free region was non-uniform and the allowable pulling speed range was narrow. In the middle part and the bottom part, in-plane uniformity was better than in the top part, and the allowable lifting speed range was wide.

  When the crystal was pulled in the same manner while the gap was controlled to be constant at 50 mm, the in-plane uniformity of the defect-free region increased as compared with the case where the gap was kept constant at 45 mm. However, in the top portion of the pulling crystal, the in-plane distribution was slightly non-uniform, and the allowable pulling speed range was slightly narrower than that of the middle and bottom portions. The middle part and the bottom part also had good in-plane uniformity.

  When the crystal is pulled in the same manner while the gap is controlled to be constant at 55 mm, in-plane uniformity of the defect-free region and allowable pull-up at the top portion compared to the case where the gap is fixed at 45 mm or 50 mm. Any of the speed ranges increased. However, in the middle part, because the gap was too wide and Gc> Ge was emphasized too much, dislocation clusters were generated from the center of the crystal, a considerable in-plane nonuniformity was observed, and the allowable pulling speed range was also reduced. .

  The above survey results are summarized in Table 1. Furthermore, it showed with the graph in FIG.

  As shown in Table 1 and FIG. 6, when the gap is controlled to 50 mm (constant), the in-plane uniformity is good from the top part to the bottom part, and the allowable pulling speed range is wide. However, in the top portion, when the gap is further enlarged and controlled to 55 mm (constant), the in-plane uniformity is better and the allowable pulling speed range is wider.

Therefore, in order to obtain a defect-free crystal with a high yield by increasing the allowable pulling speed range at each portion of the pulling crystal, it is desirable to perform crystal growth under one of the following pulling conditions.
i) Start pulling up with a gap = 55 mm, gradually increase the gap = 50 mm, and set the gap = 45 mm.
ii) First, the gap is raised at 50 mm, and the gap is gradually narrowed in the middle to make the latter half gap = 45 mm.
iii) First, the gap is raised at 55 mm, and the gap is gradually narrowed in the middle, and the latter half gap is fixed at 45 mm.

  In the manufacturing method of the present invention, the gap is changed according to the length of the straight body portion during the growth of the straight body portion of the silicon single crystal, as described above, depending on the length of the crystal pulled up during the pulling. This is because it is possible to change the in-plane uniformity of the defect-free region and the allowable pulling speed range by performing the operation of changing the gap.

  The adjustment of the gap during the pulling can be performed, for example, as follows. That is, when the gap is kept constant, the lowering of the melt surface level corresponding to the volume of the silicon melt reduced by crystallization is compensated by raising the crucible containing the melt, and the melt in the crucible Control so that the position of the surface does not fluctuate. When changing the gap according to the pulled crystal length, set the gap according to the crystal length, and grasp the height or gap of the melt surface at that crystal length in advance. Adjust the ascending speed of the so that it becomes the set gap.

  According to the method for producing a silicon single crystal of the present invention, the grown silicon single crystal can be a defect-free silicon single crystal in which dislocation clusters do not exist and COP does not exist.

  That is, when implementing the method of the present invention in which the gap is changed according to the pulling length of the silicon single crystal being grown, any desired pulling condition of i) to iii) based on the above-described investigation results is applied. This makes it possible to grow a silicon single crystal having a uniform in-plane distribution of defect-free regions.

  FIG. 7 is a diagram showing a relationship between a desirable gap that can widen the allowable pulling speed range and the pulling crystal length. The desirable pulling conditions of i) to iii) are represented in a graph.

In curves i) to iii) representing desirable pulling conditions displayed in FIG. 7, there is a common tendency that the gap is wide at the top portion and narrower at the middle portion and the bottom portion. Judging from this tendency, as a method of pulling up a defect-free silicon single crystal,
“At the top of the pulling crystal, pulling is started with a wide gap, and the gap is gradually narrowed as the crystal is pulled up. It can be said that a method of pulling up while performing gap control is desirable.

  As a specific example of a desirable crystal pulling method, for example, when growing a single crystal (ingot) having a diameter of 200 mm and a straight body length of 1500 mm or more, a gap of 65 mm to at least up to a crystal length of 200 mm is used. As the range of 50 mm, there is a pulling method in which growth is performed while controlling the gap so that the gap in the range of 50 mm to 45 mm is maintained at least when the crystal length reaches 1500 mm.

  In the method for producing a silicon single crystal of the present invention, an embodiment in which the gap in the middle part and / or bottom part of the straight body part of the silicon single crystal is made smaller than the gap in the top part growth is ( a) When the gap between the middle part and the bottom part of the straight body part of the silicon single crystal is made smaller than the gap during the top part growth, and (b) The gap during the middle part or bottom part growth is grown at the top part. In the case of making it smaller than the gap in the inside, the former (a) is substantially the same as the desirable pulling method derived from FIG.

  On the other hand, in the latter case (b), the gap is made smaller than the gap during the top portion growth either during the middle portion growth or during the bottom portion growth. As long as the portion for reducing the gap is the middle portion or the bottom portion, a wide allowable pulling speed range from the top portion to the bottom portion can be obtained. That is, a large gap of 55 mm and 50 mm is preferable during the top portion growth so that the allowable pulling speed range is widened, and a smaller gap of 50 mm and 45 mm is formed during the middle portion or bottom portion growth. If it is set, for example, a decrease in the allowable pulling speed width in the middle portion seen when the gap is 55 mm can be avoided and the speed width can be widened, which is desirable.

  Further, in the method for producing a silicon single crystal according to the present invention, the gap is adjusted so that the allowable pulling speed width is wide, and the growth of the straight body portion of the silicon single crystal is started. It is more desirable to grow the silicon single crystal by reducing the gap before reaching the smaller single crystal pulling length.

  This is also a more desirable embodiment that can be adopted based on the result of the investigation as shown in FIG. For example, according to the investigation result of FIG. 6, when the lifting is continued with the gap set to 55 mm so that the allowable pulling speed width is increased at the start of the straight body part growth, the allowable pulling speed width is reduced in the middle part. Therefore, by reducing the gap to 50 mm or 45 mm in advance before the crystal pulling length reaches the length corresponding to the middle portion, the growth can be continued while the allowable pulling speed width is always kept wide.

  According to the method for producing a silicon single crystal of the present invention described above, it is possible to maintain a wide allowable pulling speed range by appropriately changing the gap during crystal pulling. By applying this method, it is possible to reduce the case of deviating from the appropriate speed range during pulling, so that the pulling yield can be improved. As a result, there is no crystal having grown-in defects such as COP and dislocation clusters. A single crystal having a uniform in-plane distribution of the defect-free region in the radial direction can be pulled stably with a high yield over the entire crystal length. Since it can be lifted stably, it can cope with mass production.

  Next, the silicon single crystal manufacturing apparatus of the present invention will be described.

  This apparatus is a silicon single crystal manufacturing apparatus by the Czochralski method in which a radiant heat shielding screen is arranged around a pulling area of a silicon single crystal as described above. A silicon single crystal manufacturing apparatus comprising distance control means for changing a gap according to a length of a part.

  In the manufacturing apparatus of the present invention, such a distance control means is provided, and by using this apparatus, as described above, the gap is changed during the pulling according to the length of the pulled crystal. This is because the operation can be performed and the in-plane uniformity of the defect-free region and the allowable pulling speed range can be changed.

  In this silicon single crystal manufacturing apparatus of the present invention, the distance control means is set and inputted to change the gap according to the measured value of the gap with respect to the straight body length of the growing silicon single crystal and the length of the silicon single crystal. And a control unit that adjusts the gap based on the gap correction amount calculated by the calculation unit. Can do.

  FIG. 8 is a diagram schematically showing a schematic configuration example of a main part of the silicon single crystal manufacturing apparatus of the present invention. The pulling device 11 is provided with distance control means 12 for changing the gap according to the length of the straight body portion during the growth of the straight body portion of the silicon single crystal.

  The distance control means 12 includes an ingot length detection means 13 that can always detect the length of the straight body portion of the silicon single crystal that is being grown, and an optical surface position detection means 14 that is attached above the crucible 1. A melt surface position detecting means 15 is provided which can detect the surface position of the melt 3 in the crucible 1 and measure the gap. Furthermore, the measured value of the gap with respect to the length of the silicon single crystal straight body portion, and the set value of the gap set to change the gap according to the length of the silicon single crystal straight body portion (that is, i) to The calculation unit 16 is provided for calculating a gap correction amount by comparing and calculating a gap setting value to which any desired pulling condition of iii) is input, and hereinafter referred to as a “gap setting profile”).

  In this way, the singularity of the configuration in the silicon single crystal manufacturing apparatus of the present invention is that the calculation unit that calculates the gap correction amount by comparing the gap measurement value with respect to the length of the ingot being grown and the gap setting profile. In the gap control means.

  In order to carry out the method for producing a silicon single crystal of the present invention using this apparatus, first, the length of the straight body portion of the silicon single crystal being grown is always detected by the ingot length detection means 13 to grow the single crystal. The surface position of the silicon melt in the crucible 1 inside is detected by the melt surface position detecting means 15. In addition, the length of the single crystal straight body part during the growth can be detected from the rising amount of the pulling wire after the growth of the straight body part is started.

  From the ingot straight body length information from the ingot length detection means 13 and the measurement result of the melt surface position obtained by the melt surface position detection means 15, the gap with respect to the length of the ingot straight body being grown can be obtained.

  As the melt surface position detecting means 15, when the radiant heat blocking screen is a stationary fixed type, an optical surface position detecting means 14 (for example, a two-dimensional CCD camera) provided above the crucible 1 is used. The position of the melt surface in the crucible 1 during the growth of the single crystal ingot can be detected by detecting the fusion ring generated at the growth interface between the ingot and the melt.

  Next, the gap with respect to the calculated ingot length is compared with the gap setting profile, and the calculation unit 16 calculates the deviation (that is, the correction amount) with respect to the gap setting profile.

  Subsequently, a control command for the crucible ascending speed is transmitted from the distance control means 12 to the crucible elevating device 17 so as to cancel out this deviation, the crucible elevating device 17 is operated to move the crucible up and down, and the gap becomes a set value. Adjusted to the street.

  The gap setting profile is input from the pulling condition control PC 18 to the calculation unit 16. When obtaining the gap setting profile, it is desirable to conduct an experiment in which the gap is changed for each lifting device, and to obtain an optimum gap setting profile for each lifting device that increases the allowable lifting speed range. .

  In the silicon single crystal manufacturing apparatus of the present invention, the gap adjusting means may be composed of a crucible vertical elevating means and / or a radiant heat blocking screen vertical elevating means.

  In the above description, the case where the gap is adjusted by raising and lowering the crucible has been described. However, the present invention is not limited to this. The radiant heat cutoff screen can be moved up and down, and the gap can be adjusted by raising and lowering the radiant heat cutoff screen, or the raising and lowering of the crucible and the raising and lowering of the radiant heat cutoff screen can be used in combination.

  When adjusting by raising / lowering the radiant heat cutoff screen, the melt surface position decreases with the growth of the silicon single crystal. If it does, the gap value during single crystal growth can be detected by detecting the amount of up-and-down movement of the radiant heat cutoff screen. Thereafter, in the same manner as described above, the radiant heat shut-off screen can be moved up and down to control a desired gap value so as to cancel out the deviation from the gap setting profile.

  If the silicon single crystal manufacturing apparatus of the present invention described above is used, the method of the present invention can be carried out easily and suitably.

Example 1
A silicon single crystal having a target diameter of 210 mm and a straight body length of 1700 mm was pulled up by the pulling apparatus having the configuration shown in FIG.

  A silicon raw material was charged into the crucible, and p-type dopant boron (B) was added so as to obtain a predetermined electrical resistivity. Subsequently, the inside of the apparatus was placed in a reduced-pressure atmosphere of argon and heated using a heater to melt the raw material to obtain a melt. Next, the seed crystal was immersed in the melt and pulled up while rotating the crucible and the lifting shaft. Note that the crystal orientation of the plane perpendicular to the pulling axis was <100>, and after performing seed drawing, a shoulder portion was formed and the shoulder was changed to the target diameter.

  At the time of pulling, the gap was widened to 55 mm at the top portion, and the crystal was grown with the gap kept constant at 50 mm after the middle portion. This is a desirable pulling method of the present invention described above, and is a method in accordance with the pulling condition of ii) or iii) shown in FIG. As a result, even in the top portion, a wide allowable pulling speed width as large as the allowable pulling speed width when the gap shown in FIG. 6 was 55 mm was obtained.

  By this method, it was confirmed that the allowable pulling speed range could be wider than when the gap was kept constant at 55 mm until the end of the pulling.

(Example 2)
As in the case of Example 1, the silicon single crystal was pulled up. During the pulling, the gap was gradually narrowed so that the gap was widened to 55 mm at the top, the gap = 50 mm at the middle, and the gap = 45 mm at the bottom. This is a growing method corresponding to the pulling condition of i) shown in FIG. As a result, an allowable pulling speed range equivalent to the value indicated by the Δ mark in FIG. 6 at the top portion, the same ● mark at the middle portion, and the same ○ mark at the bottom portion was obtained.

  It has been confirmed that this method can also adopt a wider allowable pulling speed range than when the gap is constant.

(Example 3)
As in the case of Example 1, the silicon single crystal was pulled up. At the time of pulling up, crystal growth was carried out with a gap of 50 mm wide at the top part and a gap of 45 mm (constant) from the middle part. This is a growing method corresponding to the pulling condition of ii) shown in FIG. As a result, a wide allowable pulling speed range as large as the value indicated by the mark ● in FIG. 6 at the top part and the value indicated by the ◯ mark at the middle part and the bottom part was obtained.

  It was confirmed that this method can also widen the allowable pulling speed range as compared with the case where the gap is constant.

  The method for producing a silicon single crystal according to the present invention is a method of changing the gap (distance between the melt and the lower end of the heat shield) according to the crystal pulling length during crystal growth. It is possible to maintain a wide range of pulling speeds obtained. As a result, it is possible to reduce the number of cases that deviate from the appropriate speed range during pulling up, improve the yield, and enable stable pulling that can sufficiently cope with mass production. This method can be preferably carried out using the silicon single crystal production apparatus of the present invention.

  Therefore, the silicon single crystal manufacturing method and manufacturing apparatus of the present invention can be widely used in the field of manufacturing semiconductor materials.

It is a figure explaining the distribution situation of the typical Grown-in defect which exists in the silicon single crystal obtained by CZ method. It is a figure which shows typically the general relationship between the pulling speed | rate and the generation | occurrence | production position of a crystal defect at the time of single crystal pulling. It is a figure which shows typically the relationship between the pulling speed | rate and the generation | occurrence | production position of a crystal defect at the time of single crystal pulling. It is a figure which shows typically the principal part structure of the raising apparatus suitable for implementing the manufacturing method of this invention. It is a figure which shows typically the change of the raising speed used in the investigation regarding the change of the gap in this invention. FIG. 5 is a diagram showing the relationship between the pulling crystal portion and the allowable pulling speed width, with the gap as a parameter, as a result of investigation on the change in gap in the present invention. It is a figure which shows the relationship between a gap desirable for obtaining a defect-free crystal and a pulling crystal length with a wide allowable pulling speed range. It is a figure which shows typically the example of schematic structure of the principal part of the silicon single crystal manufacturing apparatus of this invention.

Explanation of symbols

1: crucible 2: heater 3: molten liquid 4: single crystal
5: Lifting shaft
6: Support shaft
7: Seed crystal
8: Radiant heat blocking screen 8a: Water-cooled body 8b: Thermal shield 9: High purity carbon 10: Heat insulating material 11: Lifting device 12: Distance control means 13: Ingot length detection means 14: Optical surface position detection means 15: Melting Liquid surface position detection means 16: arithmetic unit 17: crucible lifting device 18: pulling condition control PC

Claims (6)

When producing a silicon single crystal by the Czochralski method by disposing a radiant heat shielding screen composed of a water-cooled body and a heat shield around the pulling area of the silicon single crystal,
A method for producing a silicon single crystal, wherein the distance from the lower end of the radiant heat blocking screen to the melt surface is changed according to the length of the straight body part during the growth of the straight body part of the silicon single crystal,
During the growth from the top part of the straight body part of the silicon single crystal to the middle part, the distance from the lower end of the radiant heat cutoff screen to the melt surface is once narrowed, and the distance is kept constant by the subsequent growth of the bottom part. A method for producing a silicon single crystal characterized by
  2. The method for producing a silicon single crystal according to claim 1, wherein the silicon single crystal to be grown is a defect-free crystal having no dislocation cluster and no COP. The distance from the lower end of the radiant heat shielding screen to the surface of the melt is adjusted so that the pulling speed range in which defect-free crystals can be obtained is increased, and the growth of the straight body of the silicon single crystal is started. 3. The silicon single crystal according to claim 1, wherein the silicon single crystal is grown by reducing the distance before reaching a single crystal pulling length in which a pulling speed range in which the pulling speed is obtained becomes small. Method. An apparatus for producing a silicon single crystal by the Czochralski method in which a radiant heat shielding screen composed of a water-cooled body and a heat shield is disposed around a pulling area of the silicon single crystal,
Equipped with a distance control means for changing the distance from the lower end of the radiant heat cutoff screen to the melt surface according to the length of the straight body during the growth of the straight body of the silicon single crystal,
The distance control means temporarily narrows the distance from the lower end of the radiant heat cutoff screen to the melt surface during the growth from the top part of the straight body part of the silicon single crystal to the middle part, and then the distance is obtained by growing the bottom part thereafter. An apparatus for producing a silicon single crystal characterized by maintaining a constant value.
The distance control means melts from the lower end of the radiant heat cutoff screen according to the measured value of the distance from the lower end of the radiant heat cutoff screen to the melt surface with respect to the length of the silicon single crystal straight barrel being grown and the length of the silicon single crystal straight barrel. Comparing and calculating the set value of the distance set and inputted to change the distance to the liquid surface, and calculating a correction amount of the distance, based on the correction amount calculated by the calculation unit The silicon single crystal manufacturing apparatus according to claim 4, wherein the silicon single crystal manufacturing apparatus is a control unit that adjusts the distance with respect to the length of the straight body portion of the silicon single crystal being grown. 6. The silicon single crystal according to claim 5, wherein the means for adjusting the distance from the lower end of the radiant heat cutoff screen to the surface of the melt is composed of a crucible vertical elevating means and / or a radiant heat cutoff screen vertical elevating means. manufacturing device.

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