JP2007210820A - Method for producing silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the uniformity of resistivity distribution and interstitial oxygen concentration distribution of a silicon single crystal and facilitate cost reduction of a silicon wafer.
A rare gas is caused to flow into a main chamber. Then, the raw material silicon melt 12 is formed in the quartz crucible 13, the seed crystal is deposited, the pulling shaft 19 is rotated in one direction, and the silicon single crystal 15 is pulled at a predetermined pulling speed. Here, the support shaft 17 rotates and is driven upward to maintain the melt surface of the raw material silicon melt 12 at a constant height. In this pulling growth of the silicon single crystal 15, the distance L between the lower end of the radiation shield 16 and the melt surface of the raw silicon melt 12 is set to 60 mm or more. Further, the pulling speed V is set to satisfy 0.55 mm / min ≦ V <0.75 mm / min.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a silicon single crystal by a CZ method (Czochralski Method). More specifically, the present invention relates to a silicon single crystal that improves the uniformity of impurities and interstitial oxygen in the silicon single crystal and facilitates cost reduction of a silicon wafer. The present invention relates to a crystal manufacturing method.

  Currently, many silicon single crystals used for semiconductor devices as silicon wafers are grown by a so-called pulling method called the CZ method. The silicon single crystal ingot grown in this way is made into a sliced silicon wafer through various processes and used as a substrate of a semiconductor device.

  In the CZ method, polycrystalline silicon filled in a quartz crucible of a single crystal manufacturing apparatus is heated and melted by a heater provided around the quartz crucible to form a silicon melt. Then, the seed crystal attached to the seed chuck is deposited on the molten silicon melt, and the seed chuck is pulled up at a predetermined speed by a pulling shaft such as a wire, for example, so that a silicon single crystal having a required diameter and length is obtained. Is nurtured. Here, the seed chuck and the quartz crucible are rotated in the same direction or in the opposite direction.

  In the growth of this silicon single crystal, vacancies that cause crystal defects, interstitial silicon, oxygen, carbon, and the like of foreign atoms are taken into the single crystal. Based on these, crystal defects generated in the silicon wafer greatly affect semiconductor device characteristics, reliability, manufacturing yield, and the like.

  For example, the vacancies are aggregated in a silicon crystal and become a fine void-like, for example, octahedral void defect (hereinafter referred to as LSTD), which deteriorates the oxide film breakdown voltage of the semiconductor device (see, for example, Patent Document 1). ). In addition, when the interstitial silicon also aggregates, crystal defects such as dislocation loops accompanied by stacking faults (Stacking Fault) occur, which causes deterioration such as leakage current or junction depth abnormality in a pn junction constituting the semiconductor device.

Then, oxygen mixed into the silicon melt mainly from the quartz crucible is taken in a considerably large amount as, for example, interstitial oxygen (Oi) of silicon single crystal (10 ¹⁸ atoms / cm ³ level) and processed into a silicon wafer. A minute SiO ₂ precipitate is formed by the heat treatment. Such a precipitate is hereinafter referred to as BMD (Bulk Micro Defect). This BMD is subjected to a heat treatment and has crystal defects such as dislocation loops around it. When this BMD is formed in the active layer of a semiconductor device, the device manufacturing yield is greatly reduced. On the other hand, by using the heavy metal gettering by controlling it to be formed in a region other than the active layer, for example, inside a silicon wafer, the manufacturing yield can be improved. Therefore, in general, in consideration of the gettering effect and the mechanical strength of the silicon wafer, it is grown so that an appropriate interstitial oxygen concentration [Oi] is taken into the silicon single crystal.

In addition, OSF (Oxidation), which is a so-called thermal oxidation-induced stacking fault that occurs in the thermal oxidation of a silicon wafer.
Induced Stacking Fault) is formed in a ring shape on the silicon wafer surface (hereinafter referred to as R-OSF). This R-OSF is an interstitial dislocation loop generated by the thermal oxidation, and causes deterioration of the pn junction described above in the active layer of the semiconductor device.

  Therefore, in order to control and reduce the occurrence of crystal defects as described above, many studies have been made so far on the relationship between the growth conditions of the silicon single crystal and the vacancies, interstitial silicon, interstitial oxygen, and the like. Yes. And various knowledge is obtained empirically.

For example, the amount of vacancies and interstitial silicon taken in has a strong correlation with the pulling rate of the silicon single crystal. When the pulling rate increases, many vacancies are taken into the crystal, and conversely, the pulling rate decreases. A large amount of interstitial silicon is taken into the crystal. Correspondingly, crystal defects due to vacancies or interstitial silicon as described above occur in the silicon wafer.
In addition, the ring radius of the R-OSF increases as the pulling speed increases. When the pulling speed becomes a certain level or more, the R-OSF is distributed on the outer peripheral portion of the silicon wafer that is not used in the semiconductor device. Conversely, when the pulling speed is reduced, the ring radius of the R-OSF is reduced. And since the said hole-type LSTD tends to generate | occur | produce inside R-OSF, the generation | occurrence | production comes to reduce.

  As described above, the growth conditions of the silicon single crystal for reducing the generation of crystal defects are basically contradictory among, for example, the defects due to the vacancies, the defects due to the interstitial silicon, or the R-OSF defects. come. For this reason, there is no growth method that can eliminate all crystal defects.

  For this reason, in the manufacture of silicon single crystals, conventionally, heat treatment in the manufacturing process of semiconductor devices is also taken into consideration, and in order to guarantee the quality of silicon wafers emitted from the semiconductor device side, different silicon single crystals differ from device to device. Various growth conditions are taken. Here, the quality of the silicon wafer is determined based on the final manufacturing yield of the semiconductor device and its long-term reliability.

Alternatively, a silicon single crystal is grown and then processed into a silicon wafer, and a heat treatment (hereinafter referred to as high performance annealing) using a rare gas (helium, argon), hydrogen gas, or a mixed gas thereof as an atmospheric gas is applied to the silicon wafer. And the method of making it high quality is taken. For example, the pulling rate of the silicon single crystal is relatively increased so that the interstitial silicon type dislocation defects and R-OSF are reduced even if the vacancy type LSTD increases relatively. Then, the LSTD generated under the growth conditions is reduced by the high performance annealing to be applied. Such a method utilizes the fact that the high-performance annealing effectively eliminates voids in the crystal.
JP-A-10-152395

However, the method of applying the high performance annealing to the silicon wafer requires a high temperature of about 1200 ° C. The rare gas used in the high-performance annealing is more expensive than nitrogen gas or oxygen gas, and hydrogen gas requires strict safety measures, which increases the production cost of silicon wafers. was there.
On the other hand, the method corresponding to the quality of the silicon wafer emitted from the semiconductor device side has sufficient uniformity of resistivity distribution (equivalent to impurity distribution) or interstitial oxygen concentration distribution in the growth of silicon single crystal. If it can be increased, there is a material that can sufficiently guarantee the quality of the silicon wafer by applying an appropriate heat treatment at a low temperature (for example, 600 ° C. or less) in nitrogen gas or oxygen gas after the processing of the silicon wafer. Here, this low-temperature heat treatment is extremely low in cost as compared with the high-performance annealing. However, no silicon single crystal manufacturing method has been proposed so far that ensures the high uniformity in pulling up the silicon single crystal and ensures the quality of the silicon wafer.

  The present invention has been made in view of the above-described circumstances, and is excellent in uniformity of resistivity distribution and interstitial oxygen concentration distribution in a silicon single crystal or a silicon wafer processed from the silicon single crystal, thereby reducing the cost of the silicon wafer. An object of the present invention is to provide a method for manufacturing a silicon single crystal that is easy.

  In order to achieve the above object, a method for producing a silicon single crystal according to the present invention provides a crucible filled with a raw material silicon melt, a heater for heating the crucible from the surroundings, and a silicon single crystal pulled up from the crucible. In the production of a silicon single crystal by a CZ method provided with a radiation shield for shielding radiation heat from the heater, the distance between the lower end of the radiation shield and the raw material silicon melt surface should not be less than 60 mm, and G is a temperature gradient in the pulling direction at the solid-liquid interface between the liquid and the silicon single crystal, Gmax is the maximum value of the temperature gradient G in the radial direction of the solid-liquid interface, and G is the temperature gradient G in the radial direction. When the minimum value is Gmin, the silicon single crystal is grown so that the value of (Gmax−Gmin) / Gmin is less than 0.18. To have.

  According to the above invention, in the growth of the silicon single crystal, the p conductivity type impurity, the n conductivity type impurity, and the interstitial oxygen are uniformly taken into the silicon single crystal. And the uniformity of the resistivity and the interstitial oxygen concentration of the as-grown silicon single crystal or the silicon wafer processed from the as-grown silicon crystal can be improved very easily.

  In a preferred aspect of the invention, the silicon single crystal is further grown so as to satisfy 0.55 ≦ V <0.75, where the pulling rate of the silicon single crystal is V (mm / min).

  By doing so, in the silicon single crystal or a silicon wafer processed therewith, LSTD which is a vacancy-type crystal defect is reduced, and at the same time, no R-OSF is generated. Further, after the silicon single crystal is processed into a silicon wafer, a low temperature heat treatment is performed in an atmosphere of nitrogen or oxygen at, for example, 600 ° C. or lower. In this way, it becomes possible to supply a silicon wafer that guarantees the quality of the semiconductor device and facilitates cost reduction.

  With the configuration of the present invention, a method for producing a silicon single crystal that is excellent in uniformity of resistivity distribution and interstitial oxygen concentration distribution in a silicon single crystal or a silicon wafer processed from the same, and that can easily reduce the cost of the silicon wafer Can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view schematically showing a state in a single crystal manufacturing apparatus according to the method for manufacturing a silicon single crystal of the present embodiment.

  In the method for producing a silicon single crystal according to the present embodiment, a quartz crucible 13 in which a raw material silicon melt 12 is filled in a cylindrical main chamber 11, a heater 14 for heating the quartz crucible 13 from the surroundings, and the heater A single crystal manufacturing apparatus based on the CZ method, which includes a radiation shield 16 that shields radiation heat to the silicon single crystal 15 pulled up from 14 as a main component, is used.

  In addition to this, the single crystal manufacturing apparatus includes a graphite crucible 13 a disposed in a double structure outside the quartz crucible 13 and a support shaft 17 for rotating and raising and lowering the quartz crucible 13. A heat insulating member 18 is provided between the main chamber 11 and the heater 14. A pulling shaft 19 made of a wire is connected to a seed chuck (not shown) that holds a seed crystal above the neck of the silicon single crystal 15 in FIG. 1, and hangs down from the pull chamber 20 into the main chamber 11 to form silicon. The single crystal is pulled up at a predetermined speed.

  In the silicon single crystal manufacturing method of this embodiment, first, a rare gas is introduced into the main chamber 11 to melt the polycrystalline silicon to form the raw silicon melt 12 in the quartz crucible 13. Next, the seed crystal attached to the seed chuck is deposited on the raw material silicon melt 12. Then, the silicon single crystal 15 is grown by rotating the pulling shaft 19 at a predetermined speed while rotating it in one direction and simultaneously rotating the quartz crucible 13 by the support shaft 17 in the same direction or the reverse direction. Here, the support shaft 17 is driven upward to maintain the melt surface of the raw material silicon melt 12 at a constant height. In this way, the silicon single crystal 15 is grown in the order of the so-called neck portion, shoulder portion, body portion, and tail portion.

  In the pulling growth of the silicon single crystal 15, the distance L between the lower end of the radiation shield 16 and the melt surface of the raw silicon melt 12 shown in FIG. Here, the radiation shield 16 rectifies the flow of the rare gas flowing in from the upper part of the pull chamber 20 with the surface of the silicon single crystal 15 having a cylindrical shape. Further, the radiation shield 16 mainly has a function of shielding radiation heat from the heater 14 and suppressing heat reflection to the pulled silicon single crystal 15. Furthermore, the radiant heat from the raw material silicon melt 12, the quartz crucible 13 and the graphite crucible 13a is controlled.

  Next, referring to FIG. 2, the in-plane distribution of the temperature gradient G in the pulling axis direction at the solid-liquid interface between the raw material silicon melt 12 and the silicon single crystal 15 as shown on the vertical axis, and shown on the horizontal axis. The relationship with the separation distance L will be described. Here, the temperature gradient G was obtained by measuring the solid-liquid interface between the raw material silicon melt 12 and the silicon single crystal 15 with a thermometer and calculating from the temperature difference in the pulling axis direction at the interface. The in-plane distribution of the temperature gradient G is indicated by a value of (Gmax−Gmin) / Gmin, where Gmax is the maximum value in the radial direction of the temperature gradient G and Gmin is the minimum value of the temperature gradient G.

  As shown in FIG. 2, the in-plane distribution (Gmax−Gmin) / Gmin of the temperature gradient G is obtained when the distance L between the lower end of the radiation shield 16 and the melt surface of the raw material silicon melt 12 is 100 mm to 60 mm. Is less than 0.18 and does not change much. On the other hand, when the separation distance L is smaller than 60 mm, the in-plane distribution of the temperature gradient G increases almost linearly as the separation distance L decreases.

  This arises from the following. That is, when the separation distance L is 60 mm or more, the solid-liquid interface between the raw material silicon melt 12 and the silicon single crystal 15 is easily maintained by the radiant heat from the heater 14, the raw material silicon melt 12, the quartz crucible 13 and the graphite crucible 13a. Become. And the in-plane distribution of the temperature gradient G in the said solid-liquid interface becomes small. On the other hand, when the separation distance L is less than 60 mm, the effect of shielding the radiant heat of the radiation shield 16 is effective, and cooling is likely to occur as the separation distance L decreases. Then, the in-plane distribution of the temperature gradient G at the solid-liquid interface increases as the separation distance L decreases.

  When the in-plane distribution (Gmax−Gmin) / Gmin of the temperature gradient G becomes less than 0.18 in the growth of the silicon single crystal 15, the radial direction of the pulled as-grown silicon single crystal or after processing The resistivity and interstitial oxygen (Oi) uniformity in the plane of the silicon wafer are stably improved. The maximum value of the resistivity in the radial direction or in the plane is ρmax, the minimum value of the resistivity is ρmin, and similarly, the maximum value of the concentration of interstitial oxygen in the radial direction or in the plane is [Oi] max, When the minimum value of the oxygen concentration is [Oi] min, the values of (ρmax−ρmin) / ρmin and ([Oi] max− [Oi] min) / [Oi] min are each less than 0.05. Thus, the uniformity is improved.

Here, the uniformity in resistivity is sufficiently ensured in a p-type and n-conductivity type silicon wafer having a specific resistance of 1 to 10 Ω · cm. Further, the uniformity in the interstitial oxygen concentration is sufficiently guaranteed at a specific concentration [Oi] of 12 to 14 × 10 ¹⁷ atoms / cm ³ .

  On the other hand, when the in-plane distribution (Gmax−Gmin) / Gmin of the temperature gradient G is 0.18 or more, the resistivity and interstitial oxygen (Oi) are increased regardless of the growth conditions of other silicon single crystals. The uniformity becomes unstable and decreases.

  Further, in the pulling growth of the silicon single crystal 15, the pulling speed V is preferably set to satisfy 0.55 mm / min ≦ V <0.75 mm / min. This will be described with reference to FIG. In FIG. 3, the vertical axis represents the in-plane distribution of the temperature gradient G, and the horizontal axis represents the pulling speed V of the silicon single crystal 15. The graph shows the correlation between the in-plane distribution of the temperature gradient G and the pulling speed V in the silicon single crystal, and the uniformity (Δ) of the R-OSF, LSTD, resistivity, and interstitial oxygen concentration.

In FIG. 3, R-OSF is generated by thermal oxidation of a silicon wafer manufactured from a pulled silicon single crystal. In a 200 mmφ silicon wafer, the case without R-OSF is indicated as OK, and the case with R-OSF is indicated as NG. The case where the surface density of the LSTD in the silicon single crystal is 150 pieces / cm ² or less is indicated by OK, and the case where it exceeds 150 pieces / cm ² is indicated by NG. Then, the case where the above-described uniformity of resistivity and interstitial oxygen concentration (Δ) is less than 0.05 is described as OK, and the case where the uniformity (Δ) is above 0.05 is described as NG.

The following can be seen from the correlation diagram shown in FIG. That is, under the condition that the in-plane distribution of the temperature gradient G is less than 0.18, (1) when the pulling speed V is less than 0.55 mm / min, R-OSF is NG, LSTD is NG, and uniformity ( Δ) is OK. Similarly, (2) when the pulling speed V is 0.55 mm / min or more and less than 0.75 mm / min, R-OSF is OK, LSTD is OK, and uniformity (Δ) is OK. Become. Similarly, (3) When the pulling speed V is 0.75 mm / min or more, R-OSF is OK, LSTD is OK, and uniformity (Δ) is unstable.
Here, in the case of (3), in the pulling of the silicon single crystal, the passing time of 1150 to 1080 ° C. is shortened, and the density of the LSTD is increased, but the size is decreased. The uniformity (Δ) becomes slightly unstable due to the solid-liquid interface protruding upward in the pulling direction.

  Under the condition that the in-plane distribution of the temperature gradient G is 0.18 or more, (4) when the pulling speed V is less than 0.55 mm / min, R-OSF is NG, LSTD is NG, and uniformity ( Δ) becomes NG. Similarly, (5) When the pulling speed V is 0.55 mm / min or more and less than 0.75 mm / min, R-OSF is OK, LSTD is OK, and uniformity (Δ) is NG. Similarly, (6) When the pulling speed V is 0.75 mm / min or more, R-OSF is OK, LSTD is OK, and uniformity (Δ) is NG.

  From the above results, in general, when the in-plane distribution (Gmax−Gmin) / Gmin of the temperature gradient G is less than 0.18, the resistivity and interstitial oxygen (Oi) of the pulled silicon single crystal are uniform. Good. Furthermore, when the pulling speed V is 0.55 mm / min or more and less than 0.75 mm / min, the above uniformity is improved and the occurrence of R-OSF and LSTD is suppressed, which is the most suitable growth condition. .

  In the pulling of the silicon single crystal, when the temperature gradient in the pulling axis direction in the temperature range from the melting point of silicon to about 1300 ° C. is Ge (° C./mm), V / Ge is 0.23 mm 2 / ° C. min or more. It is preferable to make it. The separation distance L has an upper limit, and as described above, the function of rectifying the flow of the rare gas in the main chamber 11 and the function of shielding the radiant heat must be maintained.

  In the above embodiment, as described above, in the pulling growth of the silicon single crystal, the temperature gradient G in the pulling axis direction at the solid-liquid interface between the raw material silicon melt and the silicon single crystal is controlled. This control can be easily performed by adjusting the distance between the lower end of the radiation shield and the raw material silicon melt surface. With the above control, the resistivity and the interstitial oxygen concentration uniformity of the as-grown silicon single crystal can be improved very simply. Furthermore, by setting the pulling rate V of the silicon single crystal within a specific range, it is possible to reduce LSTD, which is a vacancy-type crystal defect, and to eliminate the occurrence of R-OSF.

  Then, after the as-grown silicon single crystal grown in this way is processed into a silicon wafer, as described above, low-temperature heat treatment is performed in an atmosphere of nitrogen or oxygen at, for example, 600 ° C. or lower to perform the above-described low-temperature nucleation of BMD. . In this way, a silicon wafer that is extremely suitable for a semiconductor device and that guarantees the quality of the silicon wafer can be supplied at low cost using the silicon single crystal manufactured according to the present embodiment. The low temperature heat treatment does not cause redistribution of p-conductivity type or n-conductivity type impurities. In addition, redistribution of interstitial oxygen does not occur.

As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above does not limit this invention. Those skilled in the art can make various modifications and changes in specific embodiments without departing from the technical idea and technical scope of the present invention. For example, in the above embodiment, the case where the diameter is mainly a silicon single crystal for a 200 mmφ silicon wafer has been described, but other diameters may be used. For example, the same applies to a silicon single crystal for a 300 mmφ silicon wafer.

It is the longitudinal cross-sectional view which showed roughly the state in the single crystal manufacturing apparatus concerning the manufacturing method of the silicon single crystal of embodiment of this invention. The relationship between the in-plane distribution of the temperature gradient G of the pulling-axis direction in the solid-liquid interface of the raw material silicon melt and silicon single crystal concerning embodiment of this invention, and the separation distance L of the said melt surface and a radiation shield lower end is shown. It is a graph. In-plane distribution of the temperature gradient G in the pulling axis direction and pulling speed V at the solid-liquid interface of the silicon single crystal according to the embodiment of the present invention, R-OSF generation, LSTD generation, resistivity, and interstitial oxygen concentration are uniform. It is a correlation diagram with sex (Δ).

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Main chamber 12 Raw material silicon melt 13 Quartz crucible 13a Graphite crucible 14 Heater 15 Silicon single crystal 16 Radiation shield 17 Support shaft 18 Heat insulation member 19 Pulling shaft 20 Pull chamber

Claims (5)

A silicon single crystal by CZ method, comprising: a crucible filled with a raw material silicon melt; a heater for heating the crucible from the surroundings; and a radiation shield for shielding radiation heat from the heater to the silicon single crystal pulled up from the crucible In the production of
The distance between the lower end of the radiation shield and the raw material silicon melt surface should not be less than 60 mm,
The temperature gradient in the pulling direction at the solid-liquid interface between the raw material silicon melt and the silicon single crystal is G, the maximum value of the temperature gradient G in the radial direction of the solid-liquid interface is Gmax, and the temperature gradient G When the minimum value in the radial direction is Gmin,
A method for producing a silicon single crystal, comprising growing the silicon single crystal so that a value of (Gmax−Gmin) / Gmin is less than 0.18.   2. The silicon single crystal according to claim 1, wherein the silicon single crystal is grown so as to satisfy 0.55 ≦ V <0.75, where V (mm / min) is a pulling rate of the silicon single crystal. Crystal production method. 3. The method for producing a silicon single crystal according to claim 1, wherein the surface density of octahedral void defects in the silicon single crystal is 150 pieces / cm ² or less. In the silicon wafer processed from the silicon single crystal, the maximum value of resistivity in the silicon wafer surface is ρmax, the minimum value of resistivity in the surface is ρmin, and similarly, the concentration of interstitial oxygen in the silicon wafer surface is When the maximum value is [Oi] max and the minimum value of the interstitial oxygen concentration in the plane is [Oi] min,
The silicon single crystal is grown so that the values of (ρmax−ρmin) / ρmin and ([Oi] max− [Oi] min) / [Oi] min are less than 0.05, respectively. A method for producing a silicon single crystal according to 1, 2 or 3. The method for producing a silicon single crystal according to claim 4, wherein thermal oxidation-induced stacking faults do not occur in the thermal oxidation of the silicon wafer.

Images