JP2002057160A - Manufacturing method of silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacturing method of a silicon wafer which is favorable for forming an annealing wafer uniformly having full zero defects layers and the BMDs density within the surface of the annealing wafer suppressing an irregularity (that is, an irregularity in defect sizes within the surface of the annealing wafer in growing condition) in the zero defects layers, which are seen in the annealing wafer subsequent to a heat treatment within the surface of the annealing wafer and an irregularity in the BMDs density subsequent to a heat treatment, such as a precipitation heat treatment or a device heat treatment, within the surface of the annealing wafer, and to provide such the silicon wafer. SOLUTION: In the manufacturing method of a silicon wafer which forms the silicon wafer from a silicon single crystal pulled up after nitrogen is doped to the silicon single crystal by a CZ method and heat-treats the wafer, the wafer is grown on the condition that the ratio V/G of the pulling-up speed V (mm/min) at the time when the silicon single crystal is pulled up to a temperature gradient G (K/mm) in a solid-liquid interface is set in the ratio of 1 to 0.175 to 0.225 mm2/K.min in the extent wider than 90% in the radial direction of the pulled-up crystal and the wafer is formed by the manufacturing method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment (annealing) for a silicon wafer produced from a Czochralski method (CZ method) silicon single crystal pulled by doping with nitrogen.
Has a defect-free layer on the wafer surface layer,
Intrinsic gettering (IG, In
The present invention relates to a method for manufacturing a silicon wafer suitable for manufacturing a silicon wafer (annealed wafer) on which a thin gettering layer is formed.

[0002]

2. Description of the Related Art As semiconductor devices become more highly integrated and miniaturized, there is a strong demand for more complete wafer surface layers and enhanced gettering capability in bulk. On the other hand, recently, a wafer satisfying the above two requirements simultaneously has been developed by subjecting a CZ method silicon wafer doped with nitrogen to a heat treatment.

That is, by doping nitrogen into a CZ silicon single crystal, the size of a grown-in defect (a void defect mainly formed by an aggregate of atomic vacancies) in an as-grown crystal is reduced. Since it becomes smaller, high-temperature annealing in a later step makes it easier to eliminate defects in the surface layer of the wafer.Moreover, in the bulk part, due to the oxygen precipitation promoting effect of nitrogen, it undergoes a precipitation heat treatment and a device heat treatment step, resulting in gettering. Defects such as oxygen precipitates that contribute (hereinafter referred to as BMD (Bulk M
An IG layer having a high density (hereinafter referred to as "micro Defects") is formed.

[0004]

By the way, the density of BMD formed in the bulk portion of the CZ method silicon wafer and contributing to gettering and the size of the grown-in defect affecting the formation of the defect-free layer in the surface layer are usually different. In particular, the BMD density and the size of the grown-in defect are large near the center of the wafer, and both tend to gradually decrease around the wafer.

[0005] This tendency is the same in a nitrogen-doped crystal. Although the BMD density and the absolute value of the grown-in defect size change, they still have an in-plane distribution. Therefore, after high-temperature annealing for forming a defect-free layer on the surface layer portion, particularly, a grown-in defect tends to remain at the center of the annealed wafer.

Further, the inventors of the present invention have found that the tendency of the BMD density at the periphery of the wafer to decrease with respect to the BMD density after the precipitation heat treatment for determining the bulk gettering ability is remarkable especially for a nitrogen-doped wafer. Clarified.

As described above, the characteristics of the defect-free layer formed on the surface layer of the wafer and the BMD density after the deposition heat treatment or the device heat treatment required for the annealed wafer are as follows:
At present, there is a problem of unevenness in the plane.

The present invention has been made in order to solve such a problem, and the present invention has been made in view of the in-plane variation of the defect-free layer (ie, the in-plane variation of the size of the grown-in defect) observed in the annealed wafer after the heat treatment. Method for producing a silicon wafer suitable for producing an annealed wafer having a sufficient defect-free layer and a uniform BMD density in a plane by suppressing the in-plane variation of the BMD density after a heat treatment such as a precipitation heat treatment or a device heat treatment. And to provide such a silicon wafer.

[0009]

Means for Solving the Problems The invention according to the method for producing a silicon wafer of the present invention, which achieves the above object, comprises producing a silicon wafer from a silicon single crystal pulled by doping with nitrogen by the Czochralski method, In the method of manufacturing a silicon wafer, wherein the silicon wafer is subjected to a heat treatment, a pulling speed V when pulling the silicon single crystal is pulled.
(Mm / min) and the temperature gradient G (K / mm) at the solid-liquid interface
Is grown under a condition that the ratio V / G is 0.175 to 0.225 mm ² / K · min in a range of 90% or more in the pulled crystal radial direction (claim 1).

[0010] A silicon wafer cut from a nitrogen-doped silicon single crystal grown under such conditions can have uniform in-plane distribution of grown-in defect size and in-plane distribution of BMD density. . Therefore,
If this is subjected to a high-temperature heat treatment, it is possible to obtain an annealed wafer having a high IG capability, in which the BMD density of the bulk portion is uniform, the BMD density is uniform in the surface, and the bulk portion has no in-plane variation.

In this case, the concentration of nitrogen in the silicon wafer is preferably 1 × 10 ^{13 to} 5 × 10 ¹⁵ / cm ³ (claim 2). If the nitrogen concentration is within this 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. Defect formation is facilitated, and an IG layer having a high density of BMDs contributing to gettering can be formed by performing a precipitation heat treatment or a device heat treatment in a bulk portion due to an oxygen precipitation promoting effect of nitrogen. .

According to the present invention, the in-plane variation of the defect-free layer seen in the annealed wafer after the heat treatment and the in-plane variation of the BMD density after the heat treatment such as the deposition heat treatment or the device heat treatment are suppressed, and the sufficient non-defect is obtained. A silicon wafer capable of obtaining an annealed wafer having a defect layer and a BMD density in-plane uniformly is provided.

Hereinafter, the present invention will be described in more detail. In order to produce an annealed wafer having a sufficient defect-free layer and a BMD density in-plane uniformly, the present inventor has proposed that a silicon wafer should have a BMD density contributing to gettering formed in a bulk portion and a surface layer portion. It has been found that it is necessary to prepare one in which both the sizes of the grown-in defects affecting the formation of the defect-free layer have no in-plane distribution.

That is, the inventor of the present invention has conducted a high-temperature annealing of a nitrogen-doped CZ silicon wafer currently manufactured for an annealing wafer, and obtained a Bloom-in defect density in a surface layer portion of the wafer and a BMD density after additional thermal treatment. We conducted intensive research on. As a result, it was found that the number of residual defects was large and the BMD density was high in the central portion of the wafer, but the number of residual defects was small and the BMD density was low in the peripheral portion of the wafer. Further, at the intermediate position (hereinafter, referred to as R / 2 position, where R is a wafer radius), the number of residual defects was small, and the BMD density was also high.

Of these three locations, the R / 2 position has 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 uniform and high quality wafer in the plane can be obtained. Therefore, in order to enlarge the state of the R / 2 position, the correlation between the distribution of BMD or the grown-in defect and the pulling method of the CZ silicon single crystal was investigated.

As a result, the in-plane distributions of the grown-in defect size and the BMD density become non-uniform at least in the pulling speed V (mm / min) during crystal growth and 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 lifting axis direction, has a distribution in the plane, that is, V / G fluctuates in the plane. . Therefore, regardless of the position in the wafer surface,
Specific V / necessary to achieve the desired MD density
The G value was determined. Hereinafter, this will be described.

Since it is already well known that a grown-in defect is affected by V / G, it is taken into a pulled crystal using a specific hot zone (Hot Zone, HZ, structure inside a furnace) of a crystal pulling apparatus. Nitrogen concentration 1
× 10 ¹³ / cm ³ , 1.0 to 1.4 mm / min
A plurality of crystals are grown at a pulling speed selected from the range, and the relationship between the in-plane distribution of each V / G and the size of the grown-in defect and 800 ° C. × 4 hours + 1000
The relationship with the BMD density after heat treatment at 16C for 16 hours was investigated. The results are shown in FIGS.

FIG. 1 shows a central portion in the plane of the wafer, R / 2.
Part and peripheral part (at a position 10 mm from the outer periphery of the wafer)
Shows the relationship between V / G and all data of BMD density measured by
And BMD density is directly correlated with V / G
Is represented. V / G is 0.190mm^Two / K · min
When it becomes smaller than the vicinity, the BMD density decreases sharply,
175mm^Two / K · min, gettering ability
Is insufficient 1 × 10 ⁹ Pieces / cm^Three Drop below
I understand. That is, in order to obtain high density BMD
Sets V / G to 0.17 regardless of the position in the wafer plane.
5mm^Two / K · min or more
Was.

FIG. 2 shows an OPP (Optical P).
2 shows the results of relative evaluation of the size of a grown-in defect by using a reciprocating profiler and investigating the relationship with V / G. OPP measured at the center, R / 2, and peripheral portions in the plane of the wafer as in FIG.
It shows the relationship between all data of the size and V / G, and OP
This indicates that the P size is directly correlated with V / G. That is, V / G is 0.225 mm ² / K · min.
In the following, it has been newly discovered that the size of the grown-in defect rapidly decreases and the size of the grown-in defect tends to be saturated at a large value in a range exceeding 0.225 mm ² / K · min. Therefore, in order to obtain a small size of a grown-in defect which can be easily eliminated by the heat treatment, V / G is set to 0.1 regardless of the position in the plane of the wafer.
It may be 225 mm ² / K · min or less.

From the results shown in FIGS. 1 and 2, when pulling a nitrogen-doped CZ silicon single crystal, V / V
G is 0.175 to 0.225 mm ² / K in the radial direction of the crystal
・ If manufactured to be within the range of min, it does not become non-uniform in the wafer surface, and since the size of the grown-in defect is appropriately small, the grown-in defect is sufficiently eliminated over the entire surface of the wafer, and an appropriate BMD density is obtained. The formed annealed wafer is obtained.

Here, at the outer periphery of the pulled crystal,
Point defects that determine the size of the grown-in defect and the BMD density diffuse outward during crystal growth. Therefore, a region (for example, about 5% of the radius from the outer peripheral edge of the pulled crystal)
When a crystal with a diameter of 200 mm is pulled, 1 mm from the outer edge
(Up to 0 mm), the correlation between the size of the grown-in defect and the BMD density and V / G becomes weak. That is, V / G in the present invention is applied to at least 90% of the region except for 5% each 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. It fluctuates.

[0022]

Embodiments of the present invention will be described below 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 32 for rotating the crucible 32. Holding shaft 33
And its rotation mechanism (not shown), and a silicon seed crystal 5.
, A wire 7 for pulling up the seed chuck 6, and a winding mechanism (not shown) for rotating or winding the wire 7. Crucible 32
Is provided with a quartz crucible on the side for containing the silicon melt (hot water) 2 inside, and a graphite crucible on the outside thereof. A heat insulating material 3 is provided around the outside of the heater 34.
5 are arranged.

As a manufacturing condition relating to the manufacturing method of the present invention, a method of expanding an appropriate range of V / G in a radial direction and an axial direction may be performed by a well-known method.
That is, for example, the solid-liquid interface temperature gradient G is made flat 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 thereon is provided.
The solid-liquid interface heat insulating material 8 is provided with a gap 10 of 3 to 5 cm between its lower end and the surface of the silicon melt 2. The upper surrounding insulating material 9 may not be used depending on conditions. Further, a cylindrical cooling device 36 for spraying a cooling gas or blocking the radiant heat to cool the single crystal may be provided.

Separately, recently, a magnet (not shown) is installed outside the pulling chamber 31 in the horizontal direction, and a magnetic field in the horizontal or vertical direction is applied to the silicon melt 2 to suppress the convection of the melt. For stable growth of single crystals,
The so-called MCZ method is often used.

Next, a method for growing a single crystal using the above-described single crystal pulling apparatus 30 will be described. First, a high-purity polycrystalline silicon material is melted in a crucible 32 at a melting point (about 1420 °).
C) Heat to melt above. Nitrogen doping can be performed, for example, by charging a silicon wafer with a nitride film into raw silicon. Next, by unwinding the wire 7, the tip of the seed crystal 5 is brought into contact with or immersed substantially in the center of the surface of the melt 2. Thereafter, the crucible holding shaft 33 is rotated in an appropriate direction, and at the same time, the wound seed crystal 5 is pulled up while rotating the wire 7, thereby starting single crystal growth. Thereafter, by appropriately adjusting the pulling speed and the temperature, a substantially columnar single crystal rod 1 can be obtained.

A nitrogen-doped silicon wafer can be obtained by cutting out the obtained single crystal rod with a wire saw or the like and subjecting it to chamfering, lapping, etching, polishing and the like.

Next, in the present invention, the obtained silicon wafer is subjected to a heat treatment. As a result, a defect-free layer is formed uniformly on the surface in-plane, and BMD is generated at high density in the bulk portion. As a specific heat treatment condition, an ordinary heater type batch furnace is used, and an inert gas such as argon, hydrogen gas,
Or 1000-1350 degreeC under these mixed atmospheres
Heat treatment for 1 hour or more (for example, at 1200 ° C. for 1 hour,
Or 1150 ° C. for 4 hours). In addition, RTA (Rapid Thermal Anl) by lamp heating or the like is performed.
A heat treatment by rapid heating / rapid cooling using a nearing apparatus or a heat treatment using a batch furnace and an RTA apparatus in combination is also possible.

[0028]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these. (Example 1) As Example 1, a crystal center temperature gradient Gc =
3.543 [K / mm], crystal peripheral temperature gradient Ge = 3.
933 [K / mm], Ge-Gc = 0.390 [K / m]
m] and a single crystal pulling apparatus having a relatively small Ge-Gc HZ and a pulling speed of about 0.74 mm / min.
The nitrogen-doped silicon single crystal having a diameter of 6 inches was pulled up. In the nitrogen doping, a silicon wafer with a nitride film was put 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 is 14 to 15 ppma (JEI
It was adjusted to DA (Japan Electronics Industry Development Association) standard.

FIG. 3 shows the distribution of V / G in the crystal diameter direction during crystal pulling. V / G is about 0.180-
It was in the range of 0.223 mm ² / K · min.

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 heat treatment for precipitation is performed at 800 ° C. for 4 hours + 1000 ° C. for 16 hours to form a BMD, and the BMD is formed by the OPP method. B
The MD density was measured. FIG. 4 shows the measurement result of the size of the grown-in defect, and FIG. 5 shows the measurement result of the BMD density.

The grown-in defect had a size (1.5 or less) that could be sufficiently eliminated by an argon atmosphere at 1200 ° C. for 1 hour (FIG. 4), and the in-plane distribution was 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).

(Comparative Examples 1 and 2) As Comparative Examples 1 and 2, Gc = 3.778 [K / mm] and Ge = 4.904.
[K / mm], Ge-Gc = 1.126 [K / mm] A single crystal pulling apparatus having an HZ having a relatively large Ge-Gc was used. In Comparative Example 1, the pulling speed was about 0.84 mm / m.
In Comparative Example 2, the pressure was adjusted to about 0.87 mm / min, and a nitrogen-doped silicon single crystal having a diameter of 6 inches was pulled. In the nitrogen doping, a silicon wafer with a nitride film was put 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 .
Further, the oxygen concentration was adjusted to be 14 to 15 ppma (JEIDA).

In Comparative Examples 1 and 2, the V /
The distribution of G in the crystal diameter direction is also shown in FIG. V in Comparative Example 1
/ G was within the range of 0.175 to 0.225 mm ² / K · min in about 83% of the range from the center of the crystal to about 62 mm. In the case of Comparative Example 2, the center of the crystal was From the position of about 30 mm to the position of about 66 mm in the outer circumferential direction.

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 heat treatment for precipitation is performed at 800 ° C. for 4 hours at + 1000 ° C. for 16 hours to form a BMD, and the BMD is formed by the OPP method. B
The MD density was measured. FIG. 4 shows the measurement result of the size of the grown-in defect, and FIG. 5 also shows the measurement result of the BMD density.

In Comparative Example 1, the size of the grown-in defect was small to some extent at the center of the wafer, and extremely small at the periphery of the wafer. The in-plane distribution of the defect size was large. Was. However, regarding the BMD density after the precipitation heat treatment, the BMD density is as low as about 2 × 10 ⁸ / cm ³ in the peripheral portion of the wafer where the value of V / G is low,
It was found that the gettering ability was small in the peripheral portion and the in-plane distribution was large.

In Comparative Example 2, a BMD density of about 1 × 10 ⁹ / cm ³ or more was obtained in the plane, but the in-plane distribution of the grown-in defect size was large, and in particular, the size on the wafer center side was considerably large. It was confirmed that even after annealing in an argon atmosphere at 1200 ° C. for 1 hour, a part of the grown-in defect at the center portion remained.

From these results, in the case of the crystal pulling apparatus HZ used in Comparative Examples 1 and 2, in order to make both the size of the grown-in defect and the BMD density uniform in the plane, the pulling speed was set to 0.84. It can be seen that it is extremely difficult even if control is performed within a limited range of about 0.87 mm / min.

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

For example, in the above embodiment, the diameter 6
Although the case of growing an inch silicon single crystal has been described by way of example, the present invention is not limited to this, and a diameter of 8 to
It can be applied to a silicon single crystal of 16 inches or more. Needless to say, the present invention can 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]

According to the present invention, a silicon wafer doped with nitrogen having a uniform in-plane distribution of the grown-in defect size and a uniform in-plane distribution of the BMD density can be formed. Therefore, if this is subjected to a high-temperature heat treatment, an annealed wafer having no in-plane variation of the defect-free layer on the surface portion of the wafer and having an IG layer with a uniform in-plane BMD density in the bulk portion can be manufactured.

[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 the size of a grown-in defect in the present invention.

FIG. 3 is a distribution diagram of V / G in Example 1, Comparative Example 1, and Comparative Example 2 in the crystal diameter direction at the time of crystal pulling.

FIG. 4 is a distribution diagram of a grown-in defect size in the crystal diameter direction of a pulled crystal in Example 1, Comparative Example 1, and Comparative Example 2.

FIG. 5 is a distribution diagram of a BMD density in a crystal diameter direction of a pulled crystal in Example 1, Comparative Example 1, and Comparative Example 2.

FIG. 6 is a schematic explanatory view of a single crystal pulling apparatus by a CZ method used in the present invention.

[Explanation of symbols]

1 ... grown single crystal rod, 2 ... silicon melt, 3 ...
4: solid-liquid interface, 5: seed crystal, 6: seed chuck,
7: wire, 8: solid-liquid interface heat insulator, 9: upper surrounding heat insulator, 10: gap between the molten metal surface and solid-liquid interface heat insulator lower end, 30
... single crystal pulling device, 31 ... pulling chamber, 32 ... crucible, 33 ... crucible holding shaft, 34 ... heater, 35 ... heat insulating material, 36 ... cooling device.

Claims (3)

[Claims] 1. A method for producing 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. The ratio V / G of the pulling speed V (mm / min) and the temperature gradient G (K / mm) at the solid-liquid interface is 0.175 to 0.225 m in a range of 90% or more in the pulling crystal radial direction.
A method for producing a silicon wafer, wherein the silicon wafer is grown under a condition of m ² / K · min. 2. The method according to claim 1, wherein the silicon wafer has a nitrogen concentration of 1%.
The method for producing a silicon wafer according to claim 1, wherein the amount is from × 10 ^{13 to} 5 × 10 ¹⁵ / cm ³ . 3. A silicon wafer manufactured by the manufacturing method according to claim 1 or 2.