JP4463950B2 - Method for manufacturing silicon wafer - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention has a defect-free layer on the surface layer of a wafer by performing a heat treatment (annealing) on a silicon wafer produced from a Czochralski method (CZ method) silicon single crystal that has been pulled up by doping nitrogen. The present invention relates to a method of manufacturing a silicon wafer suitable for manufacturing a silicon wafer (annealed wafer) in which an intrinsic gettering (IG) layer is formed in a portion.
[0002]
[Prior art]
As semiconductor devices are highly integrated and miniaturized, there is a strong demand for further enhancement of wafer surface layer integrity and gettering capability in the bulk. On the other hand, recently, a wafer satisfying the above two requirements has been developed by performing a heat treatment on a nitrogen-doped CZ method silicon wafer.
[0003]
That is, by doping nitrogen into the CZ method silicon single crystal, the size of grown-in defects (void defects formed mainly by aggregates of atomic vacancies) in the as-grown crystal is reduced. In addition, it becomes easy to eliminate defects in the wafer surface layer part by high-temperature annealing in the subsequent process, and oxygen contributes to gettering by performing precipitation heat treatment and device heat treatment process due to the oxygen precipitation promoting effect of nitrogen in the bulk part. An IG layer having a high density of defects such as precipitates (hereinafter sometimes referred to as BMD (Bulk Micro Defects)) is formed.
[0004]
[Problems to be solved by the invention]
By the way, it is known that the density of BMD that contributes to gettering and the size of the grown-in defect that affects the formation of a defect-free layer in the surface layer usually has an in-plane distribution. In particular, both the BMD density and the grown-in defect size are large near the center of the wafer, and both tend to gradually decrease around the wafer.
[0005]
This tendency is the same in the nitrogen-doped crystal, and the BMD density and the absolute value of the grown-in defect size change, but the in-plane distribution remains unchanged. Therefore, after performing high temperature annealing for forming a defect-free layer in the surface layer portion, a grown-in defect tends to remain particularly in the central portion of the annealed wafer.
[0006]
Further, regarding the BMD density after the precipitation heat treatment that determines the bulk gettering ability, the tendency of the BMD density to decrease in the peripheral portion of the wafer is particularly remarkable with respect to the nitrogen-doped wafer. It was.
[0007]
As described above, both the defect-free layer formed on the wafer surface layer portion required for the annealed wafer and the BMD density after the precipitation heat treatment or the device heat treatment have a problem that they are non-uniform in the plane at present. .
[0008]
Accordingly, the present invention has been made to solve such problems, and includes in-plane variation of the defect-free layer (that is, in-plane variation of the grow-in defect size) found in the annealed wafer after heat treatment, and precipitation heat treatment. Alternatively, a method for producing a silicon wafer suitable for producing an annealed wafer having a sufficient defect-free layer and BMD density in the surface while suppressing in-plane variation of the BMD density after heat treatment such as device heat treatment, and the like The main purpose is to provide a simple silicon wafer.
[0009]
[Means for Solving the Problems]
An invention relating to a method of manufacturing a silicon wafer according to the present invention that achieves the above object is to manufacture a silicon wafer from a silicon single crystal pulled by doping with nitrogen by the Czochralski method, and subjecting the silicon wafer to a heat treatment. In the manufacturing method, the ratio V / G of the pulling speed V (mm / min) and the temperature gradient G (K / mm) at the solid-liquid interface when pulling up the silicon single crystal is 90% in the pulling crystal diameter direction. it is characterized by growing under conditions to be 0.175~0.225mm ² / K · min in the above range.
[0010]
A silicon wafer cut out from a nitrogen-doped silicon single crystal grown under such conditions can have uniform in-plane distribution of grow-in defect size and in-plane distribution of BMD density. Therefore, if a high temperature heat treatment is applied to this, an in-plane variation of the defect-free layer in the surface layer portion of the wafer can be eliminated, and an annealed wafer having a high IG ability can be obtained in which the BMD density in the bulk portion is uniform in the surface.
[0011]
In this case, the nitrogen concentration of the silicon wafer in ^{the, 1 × 10 13 ~5 × 10} 15 atoms / cm ³ is that it is not preferable.
If the nitrogen concentration is within such a range, the effect of reducing the size of the grown-in defect is sufficient, and the growth of the single crystal is not adversely affected. In addition to facilitating defect formation, an IG layer having a high density of BMD contributing to gettering can be formed by performing precipitation heat treatment and device heat treatment due to the oxygen precipitation promoting effect of nitrogen in the bulk portion. .
[0012]
According to the present invention, the in-plane variation of the defect-free layer found in the annealed wafer after the heat treatment and the in-plane variation of the BMD density after the heat treatment such as the precipitation heat treatment or the device heat treatment are suppressed. silicon wafer can be obtained annealed wafer having BMD density in-plane uniform Ru are provided.
[0013]
Hereinafter, the present invention will be described in more detail.
In order to fabricate an annealed wafer having a sufficient defect-free layer and BMD density uniformly in the surface, the present inventor used a silicon wafer as the BMD density contributing to gettering formed in the bulk portion and the surface layer portion. It has been found that it is necessary to prepare a grain-in defect that does not have an in-plane distribution that affects the formation of a defect-free layer.
[0014]
That is, the present inventor has conducted an intensive investigation on the grown-in defect density of the wafer surface layer after high-temperature annealing is performed on a nitrogen-doped CZ method silicon wafer currently manufactured for annealing wafers and the BMD density after additional thermal processing. Went.
As a result, it was found that the number of remaining defects was large and the BMD density was high at the wafer center, but the number of remaining defects was small and the BMD density was small at the wafer periphery. Further, at the intermediate position (hereinafter referred to as R / 2 position, where R is the wafer radius), the remaining defects were moderately small and the BMD density was moderately high.
[0015]
Among these three locations, the R / 2 position provides the best balance between the integrity of the surface layer and the gettering ability in the bulk. That is, if the state of the R / 2 position can be expanded in the wafer plane, a wafer having a uniform in-plane and high quality can be obtained. Therefore, in order to expand the state at the R / 2 position, the correlation between the distribution of BMD and grown-in defects and the pulling method of the CZ method silicon single crystal was investigated.
[0016]
As a result, the reason why the in-plane distribution of the grow-in defect size and the BMD density is not uniform is that at least the pulling speed V (mm / min) during crystal growth and the pulling axis in the range from the melting point of silicon to 1400 ° C. It has been found that V / G, which is the ratio of the temperature gradient G (K / mm) at the solid-liquid interface in the direction, has a distribution in the plane, that is, V / G varies in the plane. Therefore, a specific V / G value necessary for obtaining the desired grain-in defect size and BMD density regardless of the position in the wafer plane was determined. This will be described below.
[0017]
Since it is already well known that grow-in defects are affected by V / G, the concentration of nitrogen incorporated into the pulled crystal is determined using a specific hot zone (Hot Zone, HZ, in-furnace structure) of the crystal pulling apparatus. 1 × 10 ¹³ pieces / cm ^3, and a plurality of crystals are grown at a pulling speed selected from a range of 1.0 to 1.4 mm / min. And the relationship with the BMD density after heat treatment at 800 ° C. × 4 hours + 1000 ° C. × 16 hours were investigated. The results are shown in FIG. 1 and FIG.
[0018]
FIG. 1 shows the relationship between V / G and all BMD density data measured at the center, R / 2, and peripheral part (position 10 mm from the wafer outer periphery) in the plane of the wafer. / G represents a direct correlation. V / G is decreased abruptly BMD density becomes less than around ^{0.190mm 2 / K · min, 0.175mm} 2 / K · min the below becomes insufficient gettering capability 1 × 10 ⁹ / cm It turns out that it falls to ³ or less. That is, in order to obtain high-density BMD, it has been found that V / G should be 0.175 mm ² / K · min or more regardless of the position in the wafer plane.
[0019]
On the other hand, FIG. 2 shows the result of a relative evaluation of the size of a grow-in defect using an OPP (Optical Precipitate Profiler) and the investigation of the relationship with V / G. As in FIG. 1, the relationship between all data of the OPP size measured at the center, R / 2, and periphery in the wafer surface and the V / G is shown. The OPP size is directly correlated with the V / G. It represents that. That is, when the V / G is 0.225 mm ² / K · min or less, the size of the grow-in defect is rapidly reduced, and when it exceeds 0.225 mm ² / K · min, the size of the grow-in defect is saturated at a large value. I found a new trend. Therefore, in order to obtain a small-sized grow-in defect that can be easily eliminated by heat treatment, V / G may be 0.225 mm ² / K · min or less regardless of the position in the wafer surface.
[0020]
From the results shown in FIGS. 1 and 2, when pulling the nitrogen-doped CZ method silicon single crystal, V / G is within the range of 0.175 to 0.225 mm ² / K · min in the radial direction of the crystal. If the wafer is manufactured in such a way that the wafer surface does not become non-uniform, the grown-in defect size is reasonably small, so that the grown-in defect is sufficiently eliminated over the entire surface of the wafer, and an appropriate BMD density is formed. Will be obtained.
[0021]
Here, in the outer peripheral portion of the pulled crystal, point defects that determine the size of the grown-in defect and the BMD density are diffused outward during crystal growth. Therefore, in the region from the outer peripheral edge of the pulling crystal to about 5% of the radius (for example, when the crystal having a diameter of 200 mm is pulled up to 10 mm from the outer peripheral edge), the size of the grown-in defect, BMD density and V / G Correlation weakens. That is, V / G in the present invention is applied to at least 90% of the region excluding 5% of both outer peripheral portions in the radial direction of the pulled crystal, and this region is in the range of 90 to 100% depending on the pulling condition. Fluctuates.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, a configuration example of a single crystal pulling apparatus using the CZ method used in the present invention will be described with reference to FIG. As shown in FIG. 6, the single crystal pulling apparatus 30 includes a pulling chamber 31, a crucible 32 provided in the pulling chamber 31, a heater 34 disposed around the crucible 32, and a crucible that rotates the crucible 32. Holding shaft 33 and its rotation mechanism (not shown), seed chuck 6 holding silicon seed crystal 5, wire 7 pulling up seed chuck 6, and winding mechanism (not shown) for rotating or winding wire 7 Z). The crucible 32 is provided with a quartz crucible on the inner side containing the silicon melt (hot water) 2 and on the outer side with a graphite crucible. A heat insulating material 35 is disposed around the outside of the heater 34.
[0023]
Moreover, as a manufacturing condition related to the manufacturing method of the present invention, a method for expanding an appropriate range of V / G in the radial direction and the axial direction may be performed by a well-known method. That is, for example, the solid-liquid interface temperature gradient G is flattened in the plane by reducing the difference (Ge-Gc) between the temperature gradient (Ge) around the crystal and the temperature gradient (Gc) at the crystal center. An annular solid-liquid interface heat insulating material 8 is provided on the outer periphery of the liquid interface, and an HZ in which an upper surrounding heat insulating material 9 is disposed is provided thereon. This solid-liquid interface heat insulating material 8 is installed with a gap 10 of 3 to 5 cm between its lower end and the molten metal surface of the silicon melt 2. The upper surrounding heat insulating material 9 may not be used depending on conditions. Further, a cylindrical cooling device 36 that cools the single crystal by blowing cooling gas or blocking radiant heat may be provided.
[0024]
In addition, recently, a magnet (not shown) is installed outside the pulling chamber 31 in the horizontal direction, and a magnetic field in the horizontal direction or the vertical direction is applied to the silicon melt 2 to suppress the convection of the melt. The so-called MCZ method is often used to achieve stable growth.
[0025]
Next, a single crystal growth method using the single crystal pulling apparatus 30 will be described. First, in a crucible 32, a high-purity polycrystalline raw material of silicon is heated to a melting point (about 1420 ° C.) or higher and melted. Nitrogen doping can be performed, for example, by introducing a silicon wafer with a nitride film into raw material silicon. Next, the tip of the seed crystal 5 is brought into contact with or immersed in the substantially central portion of the surface of the melt 2 by unwinding the wire 7. Thereafter, the crucible holding shaft 33 is rotated in an appropriate direction, and the winding seed crystal 5 is pulled up while rotating the wire 7, thereby starting single crystal growth. Thereafter, a substantially cylindrical single crystal rod 1 can be obtained by appropriately adjusting the pulling speed and temperature.
[0026]
The obtained single crystal rod can be cut out with a wire saw or the like by a normal method, and chamfered, lapped, etched, polished, or the like to be a nitrogen-doped silicon wafer.
[0027]
Next, in the present invention, the obtained silicon wafer is subjected to heat treatment. As a result, a defect-free layer is uniformly formed on the surface, and BMD is generated at a high density in the bulk portion. As specific heat treatment conditions, an ordinary heater-type batch furnace is used, and heat treatment is performed at 1000 to 1350 ° C. for 1 hour or longer in an inert gas such as argon, hydrogen gas, or a mixed atmosphere thereof (for example, 1200). And 1150 ° C. for 4 hours). Further, heat treatment by rapid heating / cooling can be performed using an RTA (Rapid Thermal Annealing) apparatus such as lamp heating, or a heat treatment using a batch furnace and an RTA apparatus in combination.
[0028]
【Example】
EXAMPLES Hereinafter, although an Example and comparative example of this invention are given and this invention is demonstrated concretely, this invention is not limited to these.
Example 1
As Example 1, the crystal center temperature gradient Gc = 3.543 [K / mm], the crystal periphery temperature gradient Ge = 3.933 [K / mm], and Ge-Gc = 0.390 [K / mm]. Using a single crystal pulling apparatus having an HZ with a small Ge-Gc, the pulling speed was adjusted to about 0.74 mm / min, and a nitrogen-doped silicon single crystal having a diameter of 6 inches was pulled. Nitrogen doping was performed by introducing a silicon wafer with a nitride film into the raw material silicon so that the nitrogen concentration (calculated value) at the shoulder of the pulled crystal was 2 × 10 ¹³ / cm ³ . The oxygen concentration was adjusted to be 14 to 15 ppma (JEIDA (Japan Electronics Industry Promotion Association) standard).
[0029]
FIG. 3 shows the distribution of V / G in the crystal diameter direction during crystal pulling. V / G was in the range of about 0.180 to 0.223 mm ² / K · min in the entire radial direction.
[0030]
A silicon wafer is prepared from the pulled crystal, and the size of the grown-in defect is measured by the OPP method. Then, a BMD is formed by applying precipitation heat treatment at 800 ° C., 4 hours + 1000 ° C., 16 hours, and the BMD density is increased by the OPP method. It was measured. The measurement result of the size of the grown-in defect is shown in FIG. 4, and the measurement result of the BMD density is shown in FIG.
[0031]
The grown-in defect was a size (1.5 or less) that can be sufficiently eliminated by an argon atmosphere at 1200 ° C. for 1 hour (FIG. 4), and the in-plane distribution was also small. Further, the BMD density was approximately 2 to 5 × 10 ⁹ / cm ³ at any position in the wafer plane, and a high-density and uniform in-plane distribution was obtained (FIG. 5).
[0032]
(Comparative Example 1 and Comparative Example 2)
As Comparative Examples 1 and 2, Gc = 3.778 [K / mm], Ge = 4.904 [K / mm], Ge-Gc = 1.126 [K / mm] and HZ having a relatively large Ge-Gc. Using a single crystal pulling device having a diameter of 6 inches in diameter, the pulling speed is adjusted to about 0.84 mm / min in Comparative Example 1 and about 0.87 mm / min in Comparative Example 2 to pull up a 6-inch diameter nitrogen-doped silicon single crystal. It was. Nitrogen doping was performed by introducing a silicon wafer with a nitride film into the raw material silicon so that the nitrogen concentration (calculated value) at the shoulder of the pulled crystal was 2 × 10 ¹³ / cm ³ . The oxygen concentration was adjusted to 14-15 ppma (JEIDA).
[0033]
The distribution in the crystal diameter direction of V / G at the time of crystal pulling in Comparative Example 1 and Comparative Example 2 is also shown in FIG. In Comparative Example 1, V / G was in the range of 0.175 to 0.225 mm ² / K · min, about 83% from the center of the crystal to the range of about 62 mm. Was about 48% from the position of about 30 mm to the position of about 66 mm in the outer peripheral direction from the center of the crystal.
[0034]
A silicon wafer is prepared from the pulled crystal, and the size of the grown-in defect is measured by the OPP method. Then, a BMD is formed by applying precipitation heat treatment at 800 ° C., 4 hours + 1000 ° C., 16 hours, and the BMD density is increased by the OPP method. It was measured. The measurement result of the size of the grown-in defect is shown in FIG. 4, and the measurement result of the BMD density is shown in FIG.
[0035]
In Comparative Example 1, the grain-in defect size is somewhat small on the wafer center side and extremely small on the periphery of the wafer. Although the in-plane distribution of the defect size is large, the defect has a size that is easy to disappear by annealing as a whole. However, regarding the BMD density after the precipitation heat treatment, the BMD density is as low as about 2 × 10 ⁸ / cm ^{3 at the} wafer periphery where the V / G value is low, and the gettering ability is small in the in-plane distribution at the periphery. Was found to be large.
[0036]
In Comparative Example 2, a BMD density of approximately 1 × 10 ⁹ / cm ³ or more was obtained in the plane, but the in-plane distribution of the grain-in defect size was large, and in particular, the size on the wafer center side was considerably large. It was confirmed that some grown-in defects remained in the central portion even after annealing in an argon atmosphere for 1 hour.
[0037]
From these results, in the case of HZ of the crystal pulling apparatus used in Comparative Examples 1 and 2, in order to make both the size of the grow-in defect and the BMD density uniform in the plane, even if the pulling speed is 0.84 to 0.00. It can be seen that even if it is controlled within a limited range of 87 mm / min, it is extremely difficult.
[0038]
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.
[0039]
For example, in the above embodiment, the case where a silicon single crystal having a diameter of 6 inches is grown has been described as an example. However, the present invention is not limited to this, and the silicon single crystal having a diameter of 8 to 16 inches or more is described. It can also be applied to.
Needless to say, the present invention can also be applied to a so-called MCZ method in which a horizontal magnetic field, a vertical magnetic field, a cusp magnetic field, or the like is applied to a silicon melt.
[0040]
【The invention's effect】
According to the present invention, it is possible to form a silicon wafer doped with nitrogen that has a uniform in-plane distribution of grow-in defect sizes and an in-plane distribution of BMD density. Accordingly, if this is subjected to high-temperature heat treatment, an annealed wafer having an in-plane IG layer with uniform BMD density in the bulk portion without in-plane variation of the defect-free layer in the surface layer portion of the wafer can be produced.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between V / G and BMD density in the present invention.
FIG. 2 is a diagram showing the relationship between V / G and grow-in defect size in the present invention.
FIG. 3 is a distribution diagram of V / G in the crystal diameter direction during crystal pulling for Example 1, Comparative Example 1, and Comparative Example 2.
FIG. 4 is a distribution diagram of grow-in defect size in the crystal diameter direction of a pulled crystal with respect to Example 1, Comparative Example 1, and Comparative Example 2.
FIG. 5 is a distribution diagram of BMD density in the crystal diameter direction of the pulled crystal with respect to Example 1, Comparative Example 1, and Comparative Example 2;
FIG. 6 is a schematic explanatory diagram of a single crystal pulling apparatus using a CZ method used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Growing single crystal rod, 2 ... Silicon melt, 3 ... Hot water surface, 4 ... Solid-liquid interface,
5 ... Seed crystal, 6 ... Seed chuck, 7 ... Wire,
8: Solid-liquid interface heat insulating material
10: A gap between the hot water surface and the lower end of the solid-liquid interface heat insulating material,
30 ... Single crystal pulling device, 31 ... Pulling chamber, 32 ... Crucible,
33 ... crucible holding shaft, 34 ... heater, 35 ... heat insulating material, 36 ... cooling device.

Claims (2)

In a silicon wafer manufacturing method in which a silicon wafer is produced from a silicon single crystal pulled by doping with nitrogen by the Czochralski method, and the silicon wafer is heat-treated, the pulling speed V when pulling up the silicon single crystal The ratio V / G of the temperature gradient G (K / mm) at the solid-liquid interface to 0.175 to 0.225 mm ² / K · min in the range of 90% or more in the pulled crystal diameter direction. grown under conditions, and method for producing a silicon wafer, characterized in that a nitrogen concentration of 1 × ¹⁰ 13 ~5 × ^{10 15} atoms / cm ³ of the silicon wafer in. A silicon wafer manufactured by the manufacturing method according to claim 1 .

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