JPH09235174A - Production unit for single crystal and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production unit and production method for single crystal, capable of pulling a single crystal few in oxidation-induced laminate defects and excellent in oxidized film voltage endurance characteristics by controlling the thermal history of a crystal intended to be the single crystal. SOLUTION: This single crystal production unit is designed to set up a cylindrical, heat-resistant reflective member 7 enclosing the pull region for a crystal intended to be the aimed single crystal between melt level 5 and the ceiling 6a of a metallic chamber so as to screen or reflect the radiation from high- temperature section(s) such as a heater 2, the melt level 5 and/or a quartz crucible 1a and control the temperature gradient of the crystal. By using this production unit, the objective single crystal is pulled while controlling its temperature gradient so as to anneal the crystal in high-temperature zone and quench it in medium-/low-temperature zone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a single crystal such as silicon and a method for producing a single crystal using the apparatus. The present invention relates to a manufacturing apparatus and a manufacturing method suitable for manufacturing.

[0002]

2. Description of the Related Art At present, a single crystal such as silicon is often manufactured by the Czochralski method.

FIG. 7 is a schematic sectional view showing a state of implementation of the Czochralski method. The crucible 1 has a double structure, the inside being a quartz container 1a and the outside being a graphite container 1b. A heater 2 is arranged outside the crucible 1, and the crucible 1
The melt 5 of the crystal raw material melted by the heater is accommodated in the inside. By bringing the lower end of the seed crystal 3 into contact with the surface of the melt 5 and pulling it upward,
The single crystal 4 is grown by solidifying the melt 5 at its lower end. These parts and members are housed in a water-cooled metal chamber 6 and constitute a single crystal manufacturing apparatus as a whole.

[0004]

Thermal oxidation induced stacking faults (hereinafter abbreviated as OSFs) and oxide film breakdown voltage characteristics are major items for quality evaluation of single crystal silicon wafers. So far, the mechanism of generation of OSFs and the mechanism of formation of defects that deteriorate oxide film withstand voltage characteristics have not been sufficiently clarified. However, qualitatively, it is said that the temperature gradient in the single crystal after crystallization has a great influence on the OSF and oxide film withstand voltage characteristics.

Recent reports indicate that the temperature range is 1100 to 800 ° C.
Since OSF nucleation is promoted in the (medium to low temperature region), O
It is said that rapid cooling in the temperature range of 1100 to 800 ° C is effective for reducing SF (Keigo Hoshikawa, edited by Baifukan, "Bulk Crystal Growth Technology", p. 59).

On the other hand, with respect to the oxide film withstand voltage characteristic, defect nuclei that cause defective properties are generated during crystal solidification, and the defect nuclei shrink in a region of 1250 ° C. or higher (high temperature region).
It is said that gradual cooling at 1250 ° C or higher is desirable for improving the oxide film withstand voltage characteristics (The 39th Annual Meeting of the Japan Society of Applied Physics, 30P-
ZD-17).

The present invention is based on the above-mentioned findings that have been clarified so far, and an apparatus for producing a single crystal capable of adjusting an ideal temperature environment during actual pulling of the single crystal, and an apparatus for producing the same. It is an object to provide a method for producing a single crystal used.

Specifically, a temperature environment of rapid cooling in the temperature range of 1100 ° C. to 800 ° C. for the purpose of reducing the OSF generation rate and gradual cooling in the temperature range of 1250 ° C. or higher for the purpose of improving the oxide film withstand voltage characteristics is used. It is an object of the present invention to provide a manufacturing apparatus and a manufacturing method which are realized and have a low OSF generation rate and enable pull-up growth of a single crystal having excellent oxide film withstand voltage characteristics.

In Japanese Patent Laid-Open No. 7-413830, for the purpose of improving the withstand voltage characteristic of an oxide film, a single crystal is manufactured at 1200 to 850 ° C.
The invention of holding for 200 minutes or more in the range is disclosed.

However, the idea of controlling both the temperature environment in the high temperature region and the temperature environment in the middle / low temperature region and the device for realizing it have not been devised.

Further, the present applicant has proposed an invention in which a "heat-resistant and heat-insulating member" is installed by surrounding a pulled single crystal (Japanese Patent Laid-Open No. 7-277887). The main purpose of the invention is to prevent excessive cooling of the single crystal and to appropriately control the gas flow in the apparatus, for example, by a heat insulating member made of graphite.

[0012]

The gist of the present invention is the following apparatus for producing a silicon single crystal.

As shown in FIG. 1, a crucible 1 for containing a raw material melt 5 of a single crystal to be grown, a means 2 for heating the melt 5, and a seed crystal on the surface of the melt 5 in the crucible 1. Three
1. A single crystal manufacturing apparatus comprising: a pulling means 9 for bringing a single crystal 4 into contact with each other to grow a single crystal 4; and a metal chamber 6 for accommodating each of the above-mentioned members, which has a cylindrical shape surrounding a pulling region of the single crystal, or The heat-resistant reflective member 7 having a cylindrical shape whose diameter is reduced or expanded from the upper side to the lower side and the reflectance of which is 0.5 or more controls the temperature gradient of the single crystal between the melt 5 and the metal chamber 6. A single crystal pulling apparatus, which is provided at an appropriate position.

The positions at which the temperature gradient of the single crystal should be controlled are the high temperature region of the single crystal described above (a temperature region of about 1250 ° C. or higher) and the middle. It is in the low temperature range (temperature range of approximately 1100 to 800 ℃).

In order to precisely control the temperature gradient in such a temperature range, the heat-resistant reflection member 7 has its length (height, h ₁ )
50 to 250 mm, the distance (h ₂ ) between the lower end and the melt surface is
It is desirable to install it so that it is 50 mm or more.

The present invention is also characterized in that "the above-mentioned apparatus is used to perform pulling while controlling the temperature gradient of the single crystal so that the single crystal is gradually cooled in the high temperature region and rapidly cooled in the middle and low temperature regions. Method for producing single crystal ”.

As is clear from FIG. 7, the pulled crystal is radiated from the surface of the heater 2 and the melt 5 and from the high temperature part such as the quartz crucible 1a, which has a large crystal temperature. Influence. Therefore, the temperature gradient of the crystal can be controlled by controlling the radiation from the high temperature portion to the crystal. That is, by controlling the distance between the melt surface and the heat-resistant reflective member, the length of the heat-resistant reflective member, and the like, the temperature gradient in each part of the crystal can be made appropriate.

FIG. 2 is a schematic vertical sectional view schematically showing the principle of the present invention. (a) is the region to be rapidly cooled, and (b) is the region to be gradually cooled. The radiant heat from the high temperature portion such as the melt is irradiated toward the crystal, and a part thereof is supplied to the region (b) as shown in (b) to keep the region at a high temperature. On the other hand, the radiant heat to the area of (a) is
Due to the presence of the heat-resistant reflective member 7, it is reflected as shown in (a). Therefore, the heat of dissipation as shown in (c) is supplied to the region of (a), but since it is smaller than the radiant heat, the temperature decrease of the region of (a) is promoted. Furthermore, the radiant heat reflected downward as in (a) is scattered on the surface of the molten liquid, and part of it is as shown in (b).
It is supplied to the area of (b).

In order to properly control the temperature of each part of the single crystal based on the above principle, it is necessary to properly select the installation position, length and shape of the heat resistant reflection member 7. These will be described in detail below.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (a) is a longitudinal sectional view through an axis showing an example of the device of the present invention, and FIG. 1 (b) is an enlarged view showing only the essential parts of FIG. 1 (a). is there. In these figures, reference numeral 1 denotes a crucible, which has a double structure with a quartz container 1a on the inside and a graphite container 1b on the outside, and is installed on the crucible support shaft 1c. The crucible support shaft 1c can be used not only for rotating the crucible but also for raising and lowering the crucible.

The water-cooled metal chamber 6 in the figure is a cylindrical vacuum container composed of a ceiling portion 6a and a side wall 6b around the pulling axis of a single crystal, and the crucible 1 is arranged at the center thereof. The heater 2 is arranged around the outer periphery of the heater 2. On the other hand, above the crucible 1, a pulling means 9 is vertically rotatably and vertically movable from the center of the ceiling portion 6a of the metal chamber 6, and a seed crystal 3 is attached to the lower end thereof. Seed crystal 3 rises while being rotated by pulling means 9, and single crystal 4 grows at the lower end, which is the contact surface with melt 5.

As shown in FIG. 1 (b), in the apparatus of the present invention, a heat-resistant reflecting member 7 having a length (height) h ₁ coaxial with the pulling means 9 is located at a position h _{2 above} the melt surface. And is arranged so as to surround a part of the pulling region of the single crystal.

The shape of the heat-resistant reflection member 7 is, for example, as shown in FIG. 3 (a), a cylindrical shape whose diameter is reduced downward (herein, referred to as "reverse conical tube" for convenience), and (b). A cylindrical shape whose diameter expands downward (herein, referred to as "conical cylinder" for convenience), a cylinder having a constant diameter in (c), and (d)
A shape in which the cylinder and the conical cylinder are combined (here, this is also one of the "inverse conical cylinders") is conceivable.

FIG. 4 shows the heat-resistant reflective member 7 of the inverted conical cylinder.
FIG. 6 is a vertical cross-sectional view showing an example of a mode in which is attached to the ceiling portion 6a of the metal chamber by the support member 21. FIG. 7A is a vertical cross-sectional view of a holding state by the support member 21, and FIG. 7B is a horizontal cross-sectional view taken along the line AA. Further, FIG. 7C is a perspective view of the heat resistant reflection member 7. In this example, four square bar-shaped support members 21 are arranged on the ceiling 6a at intervals of 90 °, and the upper end of the heat-resistant reflection member 7 is held by the support members 21 and the fastening bolts 21a. Here, the number of the supporting members 21 is not limited to the above four, and the shape thereof does not have to be limited to the rectangular rod shape.

FIG. 5 shows the same conditions as in Example 1 described later.
6 is a graph showing the influence on the crystal temperature gradient when only the reflectance of the heat resistant reflector 7 is changed to 0.5, 0.7 and 0.9. The crystal temperature gradient is a temperature that decreases every 1 mm of the crystal length (height direction).

As shown in the figure, as the reflectance increases, the crystal temperature gradient at a position 150 to 350 mm away from the liquid surface increases. This position corresponds to the above-mentioned "region where rapid cooling is desirable". It should be noted that the influence of the reflectance is not significant in the "range where it is desirable to gradually cool" close to the liquid surface, but the temperature gradient is slightly smaller when the heat resistant reflection member is provided.
From the above test results, it can be said that the heat-resistant reflective member 7 preferably has a reflectance of 0.5 or more in order to effectively control the temperature gradient.

As the material of the heat resistant reflection member 7, for example,
Molybdenum (Mo) can be used. This is because Mo has excellent heat resistance and a large reflectance. The reflectance of 0.5 or more is obtained by sufficiently polishing the surface of Mo. However, the material of the heat resistant reflection member 7 is not limited to Mo, and may be any substance as long as it is less deteriorated in the single crystal manufacturing process and does not adversely affect the crystal quality.
It is also possible to use a composite material in which only the surface is Mo.

The heat-resistant reflection member 7 is installed between the melt surface 5 and the ceiling 6a of the chamber 6 at a position where the temperature gradient of the single crystal should be controlled. However, the distance (h ₂ ) between the lower end and the melt surface is preferably 50 mm or more. This is to reduce the influence of the flow of the inert gas (argon) 31 flowing on the melt surface 5 on the melt surface. The flow velocity of the gas flowing above the melt surface 5 has a great influence on the amount of oxygen taken into the crystal.

The height (h ₁ ) of the heat resistant reflection member 7 is set to a length that surrounds the front part or a part of the region where the temperature gradient is to be controlled. Depending on the equipment and pulling conditions, it is most effective to select h ₁ in the range of 50 to 250 mm in the normal operation of general equipment.

If it is less than 50 mm, the effect is not remarkable, and if it is more than 250 mm, the increase in the effect is small. If it is too large, it becomes difficult to secure the desired value of h _{2 in} a normal device.

The closest distance R ₁ between the straight body of the single crystal and the heat-resistant reflection member 7 shown in FIG. 1 (b) can have a larger effect on the temperature gradient as the distance R ₁ becomes smaller, but the diameter of the crystal is larger. Considering fluctuations and deflection from the central axis, it is desirable that the thickness is 20 to 40 mm.

FIG. 6 shows that the inner diameter of the lower end of the heat-resistant reflector having the shape shown in FIG. 3 (a) is changed to 200 mm and 240 mm, the closest distance R ₁ to the single crystal is changed, and the distance and the temperature of the single crystal are changed. It is a graph which shows the result of having investigated the relationship with a gradient. The other conditions were the same as in Example 1 described later. From this result R ₁
It can be seen that the smaller the value of, the greater the effect of improving the temperature gradient.

The above-mentioned heat-resistant reflective member is manufactured by the method of manufacturing equipment.
The present invention can be applied without being limited to the model or capacity. That is, it is also effective when used in combination with the heat-resistant and heat-insulating member proposed in JP-A-7-277887 mentioned above. Specifically, it was confirmed that by installing the heat-resistant reflective member of the present invention inside the heat-resistant and heat-insulating member of the prior application, the effects of gradual cooling in the high temperature region and rapid cooling in the medium / low temperature region can be further enhanced. doing.

In producing a single crystal using the apparatus of the present invention, depending on the shape of the single crystal production apparatus, the diameter of the single crystal, the required oxide film withstand voltage characteristics, the upper limit of the OSF density, and other qualities. First, the shape of the heat-resistant reflective member is determined, and the above-mentioned h ₁ and h ₂ are set to optimum values in advance, and the single crystal is pulled. Hereinafter, the effects of the device of the present invention will be specifically described based on Examples.

[0035]

Example 1 In the manufacturing apparatus of the present invention shown in FIG.
As the heat-resistant reflection member 7, a molybdenum (Mo) having an inverted conical cylindrical shape shown in FIG. 3A was used. The dimensions are as follows: height h ₁ is 130mm, upper end inner diameter is 360mm, lower end inner diameter is 200mm,
The wall thickness is 2 mm. The distance h ₂ between the lower end of the heat resistant reflection member 7 and the molten liquid surface 5 is 20 via the support member 21 of FIG.
It was arranged substantially coaxially with the pulling shaft 9 of the single crystal so as to be 0 mm. The heat-resistant reflective member 7 was a polished surface having a reflectance of 0.72.

The pulled single crystal 4 is a silicon single crystal having a diameter of 6 inches, and the quartz crucible 1a has an inner diameter (φ) of 450 mm.
(18 inches), the flow rate of argon gas flowing into the metal chamber 6 was 30 liter / min, the pulling rate was 0.8 mm / min, and the pulling length was 1200 mm.

Further, as a comparative example, pulling up was also performed in an apparatus without the heat resistant reflection member 7 under the same conditions.

The obtained single crystal was evaluated by the test items of the OSF non-defective product rate and the oxide film withstand voltage non-defective product rate.

The OSF non-defective rate was determined by cutting out a silicon wafer, subjecting it to heat treatment at 780 ° C. × 3 Hr and 1000 ° C. × 16 Hr, and then performing selective etching to find OSF defects at a standard value (10 / c).
m ² ) The following items are defined as non-defective products, and are represented by the ratio of the number of non-defective OSF wafers to the total number of wafers.

The oxide film withstand voltage non-defective rate was evaluated by the voltage ramping method. The gate electrode was composed of phosphorus (P) -doped polycrystalline silicon, and the dry oxide film had a film thickness of 250 Å and its area was 8 mm ² . Good products are standard values (average electric field 8 Mv / cm)
The wafers that did not cause dielectric breakdown were judged to be non-defective and the ratio was used.

Table 1 shows the above test results.

[0042]

[Table 1]

As shown in Table 1, the silicon single crystal produced by the method of the present invention using the apparatus of the present invention has good results for all test items as compared with the silicon single crystal produced by the method of the comparative example. ing.

[0044]

[Embodiment 2] A silicon single crystal was pulled under the same conditions as in Embodiment 1 using the four types of heat-resistant reflective members shown in FIG. 3, and the single crystal was in the 1100 ° C. to 800 ° C. region and 1250 ° C. The change in temperature gradient in the above region was measured. The results are shown in Table 2.
Shown in

The common dimension of the heat resistant reflection member is the height h.
₁ is 130 mm, wall thickness is 2 mm, distance h ₂ from the melt surface 5 is
200 mm. The other dimensions are shown in Table 2. The material is molybdenum, which is polished to a reflectance of 0.72. The inner diameter at the upper end and the inner diameter at the lower end are shown in Table 2.

[0046]

[Table 2]

As shown in Table 2, the effect on the temperature gradient in the temperature range of 1100 ° C. to 800 ° C. and the temperature range of 1250 ° C. or higher can be changed by changing the shape of the heat resistant reflection member. From the measurement results, it can be said that the desirable shape is (a) a conical cylinder and (d) a combination of a cone and a cylinder. Especially, when it is desired to perform gradual cooling in the temperature range of 1250 ° C or higher, It is effective to use a cylinder. For example, in a particular manufacturing apparatus, when the OSF quality is not a problem but the oxide film withstand voltage characteristic is inferior, (b) the heat-resistant reflective member having a conical cylinder can be used to manufacture a single crystal satisfying any quality. Have confirmed.

[0048]

According to the method for producing a single crystal using the apparatus of the present invention, the heat resistant reflection member is a heater or a quartz crucible,
Since the radiant heat from the melt surface to the crystal is blocked and the temperature gradient of the single crystal is controlled so as to be gradually cooled in the high temperature region and rapidly cooled in the medium / low temperature region, the single crystal to be pulled has a reduced OSF, and Therefore, the oxide film withstand voltage characteristic is improved.

[Brief description of drawings]

FIG. 1 (a) is a vertical cross-sectional view showing a single crystal production apparatus of the present invention, and FIG. 1 (b) is an enlarged view of a main part thereof.

FIG. 2 is a schematic sectional view around a single crystal for explaining the principle of the present invention.

3A and 3B are a longitudinal sectional view and a perspective view showing some examples of the shape of the heat resistant reflection member.

4A and 4B are views showing an example of a holding state of a heat resistant reflection member, wherein FIG. 4A is a vertical sectional view, FIG. 4B is a horizontal sectional view, and FIG. 4C is a perspective view of the heat resistant reflective member to be held.

FIG. 5 is a graph showing the results of examining the influence on the temperature gradient in the crystal growth direction by changing the reflectance of the heat resistant reflection member.

FIG. 6 is a graph showing the results of examining the influence on the temperature gradient in the crystal growth direction by changing the closest distance between the heat resistant reflection member and the crystal.

FIG. 7 is a schematic cross-sectional view showing a state of implementation of the Czochralski method.

[Explanation of symbols]

1: crucible, 1a: quartz container,
1b: Graphite container, 1c: Crucible support shaft, 2: Heater, 3: Seed crystal, 4: Pulled crystal,
5: molten liquid, 6: metal chamber, 6a: chamber ceiling, 6b: chamber side wall, 7: heat-resistant reflective member, 7a: through hole,
8: discharge port, 9: pulling means, 10: heat-resistant and heat-insulating member, 21: support member, 21a: tightening bolt,
30, 31: Gas flow

Claims (3)

[Claims] 1. A crucible for containing a raw material melt of a single crystal to be grown, a means for heating the melt, and a pulling means for growing a single crystal by bringing a seed crystal into contact with the surface of the melt in the crucible. And a metal chamber for accommodating each of the members, which is a cylindrical shape surrounding the periphery of the pulling region of the single crystal, or a cylinder whose diameter is reduced or expanded from the upper side to the lower side. And its reflectance is
A single crystal pulling apparatus, wherein a heat-resistant reflecting member of 0.5 or more is provided at a position where the temperature gradient of the single crystal between the melt and the metal chamber should be controlled. 2. The single crystal pulling apparatus according to claim 1, wherein the heat-resistant reflecting member has a height of 50 to 250 mm, and the lower end thereof is installed at a distance of 50 mm or more from the melt surface. 3. The apparatus according to claim 1 or 2, wherein pulling is performed while controlling the temperature gradient of the single crystal so that the single crystal is rapidly cooled in the high temperature region and gradually cooled in the low temperature region. And a method for producing a single crystal.