JP5500138B2 - Method for producing carbon-doped silicon single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon single crystal for cutting a silicon wafer used as a semiconductor device substrate such as a memory or a CPU, and in particular, crystal defects and impurity gettering by doping carbon used in the most advanced field. The present invention relates to a method for producing a silicon single crystal with controlled oxygen precipitation amount and BMD density.

  Silicon single crystals that cut out silicon wafers used as substrates for semiconductor devices such as memories and CPUs are mainly manufactured by the Czochralski (CZ) method. The silicon single crystal produced by the CZ method contains oxygen atoms. When a device is manufactured using a silicon wafer cut out from the silicon single crystal, the silicon atoms and oxygen atoms are combined to form oxygen precipitates. And BMD are formed. These are known to have IG capability that improves device characteristics by capturing contaminating atoms such as heavy metals inside the wafer. The higher the oxygen precipitation amount and BMD density in the bulk part of the wafer, the higher the performance and reliability. High device can be obtained.

In recent years, in order to provide sufficient IG capability while controlling crystal defects in a silicon wafer, a silicon single crystal is manufactured by intentionally doping carbon or nitrogen. As a method for doping carbon into a silicon single crystal, gas doping, high-purity carbon powder, carbon lump, and the like have been proposed.
However, in these methods, re-melting is not possible when the crystal is dislocated with gas dope, and with high-purity carbon powder, high-purity powder is scattered by the introduced gas when the raw material is melted. In addition to being difficult to dissolve, there was a problem that the crystal being grown was dislocated.

  As means to solve these problems, a silicon polycrystalline container containing carbon powder, a silicon wafer formed by vapor deposition of carbon, a silicon wafer baked by applying an organic solvent containing carbon particles, or a predetermined amount of carbon There has been proposed a method of doping carbon into a silicon single crystal by, for example, putting the contained polycrystalline silicon into a crucible. Although these methods can be used to solve the above-mentioned problems, both of them involve processing of polycrystalline silicon and heat treatment of the wafer, and it is not easy to prepare a carbon dopant. There was also a possibility of contamination by impurities during processing for adjustment and wafer heat treatment.

Therefore, in order to solve these problems, a method for producing a carbon-doped single crystal described in Patent Document 1 has been proposed.
On the other hand, Patent Documents 2-7 propose a method for suppressing the occurrence of cracks, dislocations, and the like when a silicon single crystal is pulled up.

JP 2009-222102 A JP 2002-137888 A JP 2003-165791 A JP 2006-213582 A JP 2009-292702 A JP 2010-24129 A JP 2006-306640 A

  However, the methods of Patent Documents 1-7 have also solved the problem of dislocations caused by internal stress that occurs when carbon atoms are taken into the bulk of the silicon single crystal from the solid-liquid interface of the growing silicon single crystal. There wasn't. In particular, with the recent increase in the diameter of silicon single crystals, such a problem has become apparent, making it difficult to eliminate dislocations in carbon-doped silicon single crystals.

  The present invention has been made in view of the above problems, and it is possible to effectively suppress dislocation at the time of pulling up a carbon-doped silicon single crystal, and to improve the yield of the carbon-doped silicon single crystal. An object is to provide a manufacturing method.

  In order to achieve the above object, the present invention provides a method for producing a carbon-doped silicon single crystal that pulls up a silicon single crystal from a silicon-added silicon melt. When the average value of the crystal temperature gradient in the pulling axis direction during C is expressed in G [° C./mm], the value of G is 1.0 to 3.5 [° C./mm at least until the solidification rate is 20%. And the Srcs value (von Mises equivalent stress [Pa] at the center in the radial direction of the solid-liquid interface during the growth of the silicon single crystal is expressed as CRSS (Critical Resolved Shear Stress) [Pa The silicon single crystal is pulled up so that the value obtained by dividing] is 0.9 or less. The law provides.

  By pulling up the carbon-doped silicon single crystal in this way, it can be pulled up efficiently while preventing the occurrence of dislocations. For this reason, a high quality carbon dope silicon single crystal can be manufactured with a sufficient yield.

At this time, in the pulling of the silicon single crystal, it is preferable that the passing time of the silicon single crystal in a temperature range from the silicon melting point to 1300 ° C. in the pulling furnace is 40 minutes or more and 220 minutes or less.
By pulling up in this way, pulling up under the conditions of the present invention can be facilitated, and furthermore, extreme cooling can be prevented and crystals can be pulled up stably without dislocation.

At this time, the carbon concentration of the silicon single crystal to be pulled is preferably set to 1 × 10 ^{16 to} 5 × 10 ¹⁷ atoms / cm ³ (NEW ASTM).
Thus, even a high carbon concentration exceeding 1 × 10 ¹⁶ atoms / cm ³ (NEW ASTM), particularly 5 × 10 ¹⁶ atoms / cm ³ (NEW ASTM), can be easily raised. If it is this invention, it can manufacture with sufficient productivity, suppressing a dislocation conversion effectively.

  As described above, according to the present invention, it is possible to produce a carbon-doped silicon single crystal while effectively suppressing dislocations, and thus it is possible to produce a wafer with sufficient IG capability with high productivity. .

It is the schematic which shows an example of the single crystal pulling machine which can be used when implementing the manufacturing method of the carbon dope silicon single crystal of this invention. It is the schematic which shows the other example of the single crystal pulling machine which can be used when implementing the manufacturing method of the carbon dope silicon single crystal of this invention. It is explanatory drawing of the method of adding carbon to a raw material in the pulling of a carbon dope silicon single crystal. It is the schematic which shows the single crystal pulling machine used in Comparative Example 1-4.

Conventionally, there has been a problem that the yield is deteriorated due to the occurrence of dislocations when the carbon-doped silicon single crystal is pulled.
On the other hand, the present inventors have intensively studied focusing on the dislocation due to internal stress, which is a problem specific to the pulling of the carbon-doped silicon single crystal, and have found the following.

  The present inventors have come up with the idea of using an Srcs value that can numerically express a change in thermal stress due to a change in crystal temperature in the growth direction as an index indicating the magnitude of thermal stress during the growth of a carbon-doped silicon single crystal. Here, the Srcs value is a value obtained by dividing von Mises equivalent stress (hereinafter also simply referred to as “equivalent stress”) by CRSS (Critical Resolved Shear Stress).

  Furthermore, in order to suppress the occurrence of dislocations in the carbon-doped silicon single crystal, it is important to reduce the volume shrinkage stress in the crystal cooling process that further promotes the stress, as well as the thermal stress during growth. The inventors paid attention to the average value G (° C./mm) of the crystal temperature gradient in the pulling axis direction between the silicon melting point and 1400 ° C. as the control parameter. In the case of a carbon-doped silicon single crystal, the shrinkage stress in the crystal cooling process is larger than that of a crystal not doped with carbon. That is, in the case of a carbon-doped silicon single crystal having a diameter of 300 mm, particularly 450 mm or more, it is important that the crystal is not excessively cooled in the crystal cooling process, and the size of G is an index.

  And the present inventors found out the optimal conditions that the Srcs value is 0.9 or less and G is 1.0 to 3.5, and satisfying these conditions at the same time when pulling up the carbon-doped silicon single crystal. It was found that dislocations can be effectively suppressed. Furthermore, since the formation of dislocations is likely to occur up to a solidification rate of 20% at the initial stage of growth, it has been found that pulling without dislocations can be efficiently performed by pulling up at the above conditions at least in the initial stage of growth. The present invention has been completed.

  Here, it is the thermal stress acting on the crystal temperature zone around 1400 ° C. that induces the generation of dislocation due to the internal stress of the silicon single crystal to be grown. If the increase in thermal stress in the vicinity of the solid-liquid interface of the silicon single crystal is large, it will cause cracking of the silicon single crystal to be pulled up, and there is a method disclosed in Patent Document 2-6 as a solution.

However, these methods, in particular, the cooling body for forced cooling of the pulling crystal as described in Patent Documents 3 and 4 are not added to the equipment in the method of the present invention. In particular, in the case of a large-diameter carbon-doped silicon single crystal, eliminating the cooling effect by forced cooling equipment does not promote dislocation during pulling, and pulls up dislocation-free crystals over the entire straight body by the method of the present invention. Good results are obtained.
Patent Document 2 describes a relationship between the internal stress of a silicon single crystal to be grown and the crystal growth interface shape. Certainly, proper control of the convex shape of the crystal growth interface is important, but in the case of carbon-doped silicon single crystal growth, control of the interface shape alone does not lead to a fundamental solution, and relaxation of thermal stress is also important. .

Patent Documents 4-6 have a specific description regarding the magnitude of thermal stress (von Mises equivalent stress) that affects crystal cracking during pulling. However, the thermal stress that generates dislocations during the pulling of the carbon-doped silicon single crystal controlled by the present invention is smaller than the thermal stress of crystal cracking and is less than 2 MPa in the crystal temperature zone near 1400 ° C. Thermal stress (von Mises equivalent stress). In the case of carbon-doped silicon single crystal growth, the present inventors have developed a phenomenon in which dislocations are generated with a high probability even in a very small thermal stress that does not lead to crystal cracking, particularly in the first half of the straight body growth process. I have confirmed.
Although the mechanism of the occurrence of dislocation (slip) is specifically described in Patent Document 7, the dislocation of a carbon-doped silicon single crystal is a region of V-rich crystal, I-rich crystal, Nv crystal, or Ni crystal. However, the generation mechanism described in Patent Document 7 is essentially different.

Hereinafter, the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.
The present invention relates to a method for producing a carbon-doped silicon single crystal in which a silicon single crystal is pulled up from a silicon melt added with carbon, and in the pulling up of the silicon single crystal, a crystal in the pulling axis direction between the melting point of silicon and 1400 ° C. When the average value of the temperature gradient is expressed as G [° C./mm], the value of G is 1.0 to 3.5 [° C./mm] at least until the solidification rate is 20%, and the silicon single crystal The Srcs value (the value obtained by dividing the von Mises equivalent stress [Pa] by CRSS (Critical Resolved Shear Stress) [Pa] at a crystal temperature of 1400 ° C.) at the center in the radial direction of the solid-liquid interface during the growth of 0.1. The silicon single crystal is pulled up to 9 or less.

  In the production of a carbon-doped silicon single crystal, the control such that the value of G is less than 1.0 ° C./mm makes it difficult to increase the crystal growth rate, forcing inefficient production. In addition, control such that the value of G exceeds 3.5 ° C./mm tends to cause dislocation during the growth of the carbon-doped silicon single crystal, and it is difficult to pull up the crystal without dislocation. Therefore, it is necessary to control the pulling conditions so that the G value is 1.0 ° C./mm or more and 3.5 ° C./mm or less, and more preferably, the G value is 2.0 ° C./mm. By controlling so as to satisfy the conditions of mm or more and 3.5 ° C./mm or less, the pulling speed can be increased and the single crystal can be pulled more efficiently.

At the same time, it is necessary that the Srcs value at the central portion in the radial direction of the solid-liquid interface during the growth of the silicon single crystal be 0.9 or less, and more preferably 0.7 or less. . When the Srcs value at the crystal temperature of 1400 ° C. at the center of the solid-liquid interface exceeds 0.9 during the growth of the silicon single crystal, the concentration of internal stress acting on the center in the radial direction of the solid-liquid interface Inhibits the dislocation-free of the carbon-doped silicon single crystal. For this reason, it is difficult to pull up crystals without dislocations.
In addition, CRSS can be calculated | required with the following formula | equation, and by substituting 1400 degreeC (1673.15K) for T, CRSS in the crystal | crystallization temperature of 1400 degreeC used by this invention can be calculated | required.
CRSS [Pa] = 0.1 × 10 ^ (440.08 / T + 4.58)
T: Absolute temperature

Such control of the G and Srcs values of the present invention is performed at least in a growth step in which the crystal growth solidification rate of the carbon-doped silicon single crystal is up to 20% with respect to the total charge amount of the raw material.
Since the silicon-doped silicon single crystal has a characteristic that it is likely to undergo dislocation during the growth of a growth process having a low solidification rate of 20% or less (the initial stage of single crystal growth), the above-described control of the present invention is performed at the initial stage of the growth. Do.

  The control of the G and Srcs values of the present invention may be continued even after the solidification rate exceeds 20%. However, after the solidification rate exceeds 20%, G is set to 3.5 ° C./mm. By controlling it to be larger, the growth rate can be easily increased in the latter half of the crystal growth, which is efficient. Also in this case, it is preferable to maintain the Srcs value to be 0.9 or less.

Moreover, it is preferable that the transit time of the silicon single crystal in the temperature range from the silicon melting point to 1300 ° C. in the pulling-up furnace is 40 minutes or more and 220 minutes or less.
Thus, in the present invention, it is also important to control the cooling rate of the carbon-doped silicon single crystal. By controlling the pulling rate so that the passing time is 40 minutes or more, the carbon-doped silicon single crystal is also rapidly controlled. It is not cooling, and the dislocation can be more effectively suppressed. If the single crystal passage time is 220 minutes or less, excessive slow cooling is not achieved, growth of glow-in defects can be suppressed, and a higher crystal growth rate can be achieved. Therefore, extreme heat outflow is prevented, and further, no dislocation can be achieved stably. Therefore, productivity is good.

  Next, the single crystal pulling machine shown in FIGS. 1 and 2 that can be used in carrying out the method for producing a carbon-doped silicon single crystal of the present invention will be described below.

In the single crystal pulling machine 10 of FIG. 1, a main chamber 11 and a pull chamber 29 constitute a furnace. A quartz crucible 15 for accommodating the molten silicon melt 13 and a graphite crucible 16 for supporting the quartz crucible 15 are provided inside the main chamber 11.
These crucibles 15 and 16 are supported via a tray 30 on a support shaft 14 called a pedestal. A main heater 12 is installed around the crucibles 15 and 16, and a heat insulating material 17 is installed along the inner wall of the main chamber 11 on the outer side. Above the crucibles 15 and 16, a gas rectifying cylinder 18 made of a cylindrical graphite material having a heat insulating collar 31 attached to the lower end portion is installed. A pulling shaft 20 (wire or the like) for pulling up the silicon single crystal 22 while growing it is provided at the lower end of the seed crystal 19.

In the present invention, in order to make a preferable apparatus for controlling the single crystal transit time t of G, Srcs and silicon melting point to 1300 ° C. within the scope of the present invention, the heat insulation property of the furnace upper part (gradual cooling) is as follows. (Effect) is preferably improved.
For example, as shown in FIG. 1, in order to suppress the amount of heat removed from the cooling part and the upper side of the inner wall of the main chamber 11, the position above the silicon melt 13, that is, the upper part of the hot zone may be covered with a heat insulating member 21. it can.

Further, as shown in FIG. 2 (a), in order to suppress heat removal from above the main chamber and further increase the cooling effect, the inner wall of the passage portion of the single crystal pulled up by the pull chamber above the main chamber is insulated. The pulling machine 10 ′ covered with the member 23 can be used.
In addition, as shown in FIG. 2B, in the case of a pulling machine 10 ″ having a water cooling jacket (cooling cylinder) 24 for forced cooling of a single crystal as ancillary equipment, the inner wall of the water cooling jacket 24 is a heat insulating member. 25.
Alternatively, a heating means is provided in the installation part of the gas rectifier cylinder above the silicon melt, the distance from the lower end of the gas rectifier cylinder to the melt surface of the silicon melt, the extension of the heat generating part (slit) of the main heater, or The slow cooling effect can be further enhanced by a method such as upward movement of the heat generation center.

By using the pulling machine as described above, for example, the pulling machine 10 shown in FIG. 1, the Czochralski (CZ) method, particularly the magnetic field applied Czochralski (MCZ) method, and the carbon-doped silicon Crystals can be produced as follows.
For example, the quartz crucible 15 is first filled with a carbon dopant and polycrystalline silicon. At this time, a resistivity controlling dopant such as phosphorus or boron which determines the resistivity of the substrate is also added. The carbon dopant and the doping method used in the present invention can be added by the methods described in Japanese Patent No. 4507690, Japanese Patent Application Laid-Open No. 2008-297139, and the like. For example, as shown in FIG. 3, carbon powder 28 sandwiched between chemically etched wafers 27 can be added together with polycrystalline silicon 26 into quartz crucible 15.

  Next, the vacuum pump is operated, Ar gas is introduced from a gas inlet (not shown) of the pull chamber 29 while exhausting from a gas outlet (not shown) of the main chamber 11, and the inside of the furnace is replaced with an Ar atmosphere. Next, it heats with the main heater 12 arrange | positioned so that the graphite crucible 16 may be surrounded, and melt | dissolves raw materials, such as a polycrystalline silicon, and the silicon melt 13 is obtained. After melting the raw material, the seed crystal 19 is immersed in the silicon melt 13 and pulled up while the seed crystal 19 is rotated by the pulling shaft 20 to grow a rod-shaped silicon single crystal 22. Thus, a silicon single crystal 22 doped with a desired concentration of carbon can be manufactured.

In the manufacture of the present invention, the optimum conditions such as the optimum structure of the hot zone, the melt surface, and the position of the heat generation center installed in the main chamber as shown in FIGS. 1 and 2 are determined by the thermal numerical analysis simulation software FEMAG. It can be calculated and set by calculation.
Furthermore, von Mises equivalent stress [Pa] and CRSS value [Pa] are calculated from the thermal numerical analysis result by FEMAG, Srcs is estimated, and using this as an index, pulling conditions such as pulling speed and heater power are set. The silicon single crystal can be pulled up. That is, as a result of thermal numerical analysis by FEMAG, the Srcs value at the central portion of the solid-liquid interface during the growth of the silicon single crystal is 0, and the G value is in the range of 1.0 to 3.5 [° C./mm]. 9 or less, more preferably, a condition in which the pulling single crystal passage time in the high temperature range from the silicon melting point to 1300 ° C. in the pulling furnace is within the range of 40 to 220 minutes. The silicon single crystal can be pulled up by applying.

  Further, as a control method for increasing G during single crystal growth after exceeding the above solidification rate of 20%, for example, from the lower end of the gas flow straightening cylinder to the melt surface of the silicon melt by shift control of the upper drive of the crucible The distance can be reduced, or the heat generating center can be moved downward by driving the main heater.

The present invention as described above is effective for producing a carbon-doped silicon single crystal having a high concentration of, for example, 5 × 10 ¹⁶ atoms / cc (New ASTM) or more, while effectively suppressing dislocations. The carbon-doped silicon single crystal can be pulled with good yield.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Examples 1 and 2)
In Example 1, the pulling machine of FIG. 2A, and in Example 2, 360 kg of silicon polycrystalline raw material is placed in a quartz crucible having a diameter of 32 inches (800 mm) installed in the main chamber of the pulling machine of FIG. Then, high purity carbon powder sandwiched between chemically etched wafers was filled (see FIG. 3). At this time, the amount of carbon powder was adjusted by calculating so that the carbon concentration in the silicon was 6 × 10 ¹⁶ atoms / cm ³ (New ASTM) at 140 cm of the straight body of the single crystal to be pulled up. Furthermore, the boron dopant for resistance adjustment was filled, and it heated using the heater and fuse | melted the raw material.
Then, using a MCZ (Magnetic Field Applied Czochralski) method, a P-type carbon-doped silicon single crystal having a diameter of 300 mm and a straight body length of 140 cm was grown while applying a horizontal magnetic field having a central magnetic field strength of 3000 G.

Under the above conditions, 10 silicon single crystals were grown. Based on the calculation result by the thermal numerical simulation software FEMAG, the average value G of the crystal temperature gradient in the pulling axis direction between the melting point of silicon and 1400 ° C, the center in the radial direction of the solid-liquid interface during the growth of the silicon single crystal The Srcs value (at a crystal temperature of 1400 ° C.) and the single crystal passage time t in the temperature range from the melting point of silicon to 1300 ° C. were controlled as shown in Table 1.
Table 1 shows the number of dislocation-free crystals pulled up in Examples 1 and 2 and the dislocation-free success rate.
Moreover, about the single crystal pulled up, when the wafer-like sample was extract | collected in the position of the straight cylinder 140cm and the carbon concentration was measured, it confirmed that the carbon concentration was 6 * 10 < ¹⁶ > atoms / cm < ³ > (New ASTM). did.

(Comparative Example 1-4)
In Comparative Example 1, the pulling machine shown in FIG. 4C, in Comparative Example 2, the pulling machine shown in FIG. 4D, in Comparative Example 3, the pulling machine shown in FIG. 4B, and in Comparative Example 4, the pulling machine shown in FIG. ) Pulling machine. A quartz crucible having a diameter of 32 inches (800 mm) installed in the main chamber of this puller was filled with 360 kg of silicon polycrystalline material and high-purity carbon powder sandwiched between chemically etched wafers (see FIG. 3). . At this time, the amount of carbon powder was adjusted by calculating so that the carbon concentration in the silicon was 6 × 10 ¹⁶ atoms / cm ³ (New ASTM) at 140 cm of the straight body of the single crystal to be pulled up. Furthermore, the boron dopant for resistance adjustment was filled, and it heated using the heater and fuse | melted the raw material.
Then, using a MCZ (Magnetic Field Applied Czochralski) method, 10 P-type carbon-doped silicon single crystals having a diameter of 300 mm and a straight body length of 140 cm are grown under the above conditions while applying a horizontal magnetic field with a central magnetic field strength of 3000 G. did. The pulling conditions such as pulling speed, crucible rotation and crystal rotation were set in the same manner as in Example 1.

When the calculation result in each manufacturing condition by the thermal numerical analysis simulation software FEMAG was confirmed, the result shown in Table 1 was obtained. Further, for a single crystal that could be pulled up without dislocation, a wafer-like sample was taken at a position of a straight cylinder of 140 cm and the carbon concentration was measured. The carbon concentration was 6 × 10 ¹⁶ atoms / cc (New ASTM). I confirmed.
Table 1 shows the number of dislocation-free crystals pulled up in Comparative Example 1-4 and the dislocation-free success rate.

As can be seen from Table 1, in Examples 1 and 2, dislocation-free crystals could be pulled at a success rate of 100%. On the other hand, in Comparative Example 1-4, remelting was repeated when dislocations occurred, but in some cases it could not be pulled up without dislocations, and the success rate did not reach 100%, 20-80%.
In Comparative Examples 1 and 3, G was 3.5 or less, but Srcs exceeded 0.9, and the success rate of dislocation-free crystal pulling was 80% or less.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

10, 10 ', 10''... single crystal puller, 11 ... main chamber,
12 ... Main heater, 13 ... Silicon melt, 14 ... Support shaft,
15 ... quartz crucible, 16 ... graphite crucible, 17 ... heat insulating material, 18 ... gas rectifier,
19 ... Seed crystal, 20 ... Lifting shaft, 21, 23, 25 ... Thermal insulation member,
22 ... Silicon single crystal, 24 ... Water-cooled jacket, 26 ... Polycrystalline silicon,
27 ... Chemically etched wafer, 28 ... Carbon powder, 29 ... Pull chamber,
30 ... saucer, 31 ... heat insulation collar.

Claims (3)

A method for producing a carbon-doped silicon single crystal in which the silicon single crystal is pulled up from a silicon melt added with carbon,
In the pulling of the silicon single crystal, when the average value of the crystal temperature gradient in the pulling axis direction between the melting point of silicon and 1400 ° C. is expressed by G [° C./mm], at least the solidification rate is 20%, The Srcs value (von Mises equivalent stress [Pa] of the central portion in the radial direction of the solid-liquid interface during the growth of the silicon single crystal is a crystal having a value of 1.0 to 3.5 [° C./mm]. A method for producing a carbon-doped silicon single crystal, wherein the silicon single crystal is pulled up so that CRSS (Critical Resolved Shear Stress [Pa] at a temperature of 1400 ° C.) is 0.9 or less.   In the pulling of the silicon single crystal, the transit time of the silicon single crystal in a temperature range from a silicon melting point to 1300 ° C. in a pulling-up furnace is set to 40 minutes or more and 220 minutes or less. The manufacturing method of the carbon dope silicon single crystal of description. The carbon concentration of the silicon single crystal to be pulled is set to 1 × 10 ^{16 to} 5 × 10 ¹⁷ atoms / cm ³ (NEW ASTM), and the carbon-doped silicon single crystal according to claim 1 or 2. Production method.

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