JP4525905B2 - Horizontal heat treatment furnace and annealed wafer manufacturing method - Google Patents

Description

  The present invention relates to an improved horizontal heat treatment furnace and a method for manufacturing an annealed wafer using the improved horizontal heat treatment furnace.

CZ silicon wafers are known to have crystal defects such as COP and oxygen precipitates, so-called Grown-in defects. As a method for eliminating Grown-in defects near the wafer surface, Ar gas A heat treatment performed in a 100% atmosphere or an H ₂ gas 100% atmosphere (hereinafter sometimes referred to as Ar annealing or H ₂ annealing) or a heat treatment performed in a mixed atmosphere of Ar and H ₂ has been proposed.

In the case of H ₂ annealing or heat treatment performed in a mixed atmosphere of Ar and H ₂ , since H ₂ gas having explosive properties at high temperature is used, it is inferior to Ar annealing in terms of safety and equipment cost. On the other hand, in the case of Ar annealing, for example, when oxygen or moisture is incorporated as an impurity in the process tube during the heat treatment, an oxide film is formed, and the oxide film and silicon (Si) cause a reaction of SiO ₂ + Si → 2SiO. In particular, there is a problem that Si is etched and the portion becomes pits, and the surface roughness is deteriorated. Therefore, when a horizontal heat treatment furnace, which is less confidential than a vertical heat treatment furnace, is used, there is a possibility that it becomes a problem. there were.

  Therefore, the present applicant has proposed a technique in Patent Document 1 that solves the above problem by reducing the amount of impurities mixed into the process tube from the supply side of the source gas (process gas).

  On the other hand, Patent Document 2 describes a technique for preventing intrusion of outside air by eliminating a gap existing at the lower portion of the open end in a horizontal heat treatment furnace having an open end of the process tube and a shutter for opening and closing the open end. Yes.

  In Patent Document 3, the present applicant has proposed means for improving the adhesion of the contact portion between the opening end of the process tube and the shutter that opens and closes the process tube.

  Therefore, by combining the above three techniques, even when Ar annealing is performed in a horizontal heat treatment furnace, the surface roughness of the annealed wafer caused by oxygen and moisture being incorporated as impurities into the process tube during the heat treatment It is considered that no deterioration occurs.

  However, a horizontal heat treatment furnace (see, for example, FIG. 4) is configured to take measures against intrusion of impurities from the process gas supply side and to improve the adhesion without generating a gap between the shutter and the opening end on the furnace port side. It has been clarified that even when Ar annealing is carried out using a), the surface roughness (haze) of the annealed wafer, which is estimated to be caused by the intrusion of outside air, is deteriorated.

  FIG. 4 shows a schematic structure of an example of a conventional horizontal heat treatment furnace. In FIG. 4, 10 is a horizontal heat treatment furnace having a process tube 12. One end of the process tube 12 is opened to form a furnace port portion 14 and an annular opening end portion 16 is formed. The open end 16 is closed by a shutter 18 so as to be freely opened and closed. Reference numeral 22 denotes a gas supply port provided at the other end of the process tube 12. Inside the process tube 12, a wafer support boat 20 that supports a number of wafers W in a vertical state is installed. A heater (not shown) is provided on the outer peripheral side of the process tube 12 so that a number of wafers W installed in the process tube 12 can be heat-treated.

  In FIG. 4, the shutter 18 is configured to be movable in the longitudinal direction of the process tube by a shutter moving mechanism (not shown). The shutter 18 is connected to the opening end 16 at the joint portion of the moving mechanism and the shutter 18. A mechanism having a spring that adjusts parallel to the opening end 16 so that the entire surface of the opening end portion 16 can come into contact with the shutter 18 is provided, so that a gap is formed between the shutter 18 and the opening end portion 16. There is nothing to do.

Further, in order to improve the adhesion between the shutter 18 and the opening end portion 16, at least the contact portion of the surface facing the opening end portion 16 of the shutter 18 with the opening end portion 16 and the center of the end surface of the opening end portion 16. The line average roughness (Ra) is 0.2 μm or less.
WO01 / 69666 Publication Japanese Utility Model Publication No. 5-38872 JP 2003-92302 A

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is a horizontal heat treatment that does not deteriorate the surface roughness (haze) even if Ar annealing is performed on a silicon mirror wafer at a high temperature. Another object of the present invention is to provide an annealed wafer manufacturing method capable of manufacturing an annealed wafer having an excellent quality by performing a heat treatment using the novel horizontal heat treatment furnace.

  The inventors of the present invention have taken the above-described countermeasure against intrusion of impurities from the process gas supply side, and have a configuration in which a gap is not generated between the shutter and the opening end on the furnace port side, and the adhesion is improved, as shown in FIG. As a result of earnest examination about the problem that the surface roughness (haze) of the annealed wafer, which is estimated to be caused by the intrusion of outside air, is deteriorated even if Ar annealing is performed using a heat treatment furnace, such a problem is made of quartz. It has been found that the case of using a process tube made of SiC is more prominent than the case of using a process tube.

  That is, in the case of a quartz process tube, the shutter is made of quartz, so that the connection between the opening end portion 16 and the closing surface 18a of the shutter 18 can be made of quartz, and the two are in close contact with each other. The sex was able to be raised enough. On the other hand, in the case of a process tube made of SiC, when the shutter is made of quartz due to the difference in expansion coefficient, the connection part cannot be rubbed together and the adhesion is inferior, and the heat insulating effect of the shutter is maintained. Considering it, it is difficult to change the shutter material from quartz.

  In order to solve this problem, the present applicant has proposed a method of improving the adhesion between the opening end portion 16 and the closing surface 18a of the shutter 18 in Patent Document 3. In the case of Ar gas, an exhaust port is not necessarily required, and therefore there is a case where an exhaust port is not provided in the horizontal annealing furnace for Ar annealing. In this case, Ar gas is exhausted through a very small gap between the opening end 16 and the closing surface 18a of the shutter 18. However, if the center line average roughness (Ra) of at least the contact portion of the closing surface 18a of the shutter 18 facing the opening end 16 with the opening end 16 and the end surface of the opening end 16 is too good, the poles are extremely small. Even a slight gap does not occur, and Ar gas cannot escape.

    Then, Ar gas accumulates in the process tube, and the tube internal pressure increases. When the internal pressure of the tube increases to the extent that the spring in the shutter moving mechanism and the shutter joint is pressed, the shutter opens, and a gap is created between the opening end 16 and the closing surface 18a of the shutter 18, Ar gas is exhausted at once. When the Ar gas is released, the shutter is closed again, and there is no even a slight gap between the opening end portion 16 and the closing surface 18a of the shutter 18. In order to repeat this, the shutter always vibrates, and at this time, oxygen and moisture outside the process tube are taken in as impurities, resulting in deterioration of the surface roughness of the annealed wafer.

Moreover, the nut which connects the quartz shutter and its moving mechanism gradually loosens due to this vibration.
As a result, the shutter becomes unstable, the opening end portion 16 and the closing surface 18a of the shutter 18 cannot be brought into close contact with each other, and the gap formed between them is not uniform, and Ar gas The omission is not uniform but biased. Then, oxygen and moisture outside the process tube are taken in as impurities from another gap (a gap where Ar gas cannot escape), and this causes deterioration of the surface roughness of the annealed wafer.

  Further, Patent Document 3 proposes a means for improving the adhesion between the opening end portion 16 and the closed surface 18a of the shutter 18 using an O-ring. Especially, in the case of annealing at 900 ° C. or higher, The open end portion 16 and the shutter 18 were at a high temperature, and an O-ring could not be used.

Therefore, the horizontal heat treatment furnace of the present invention is a horizontal heat treatment furnace comprising a process tube having an open end at one end and a shutter for closing the open end through a closed surface in contact with the open end. A recess having a function of exhausting the process gas supplied to the tube is formed in the closing surface of the shutter , the recess is provided so as to straddle the inner surface and the outer surface of the opening end, and The process gas is always exhausted through the recess .

  If the process gas is exhausted from the concave portion in this way, the pressure in the furnace does not increase, so that the process gas may escape from a very small gap between the opening end portion 16 and the closing surface 18a of the shutter 18. Even when the adhesion between the two is high, the shutter does not vibrate when the process gas escapes from the process tube. Oxygen and water are impurities from another gap caused by this vibration and / or loosening of the nut. As a result, the surface roughness (haze) of the annealed wafer does not deteriorate.

  The process tube used in the horizontal heat treatment furnace of the present invention is preferably made of SiC or quartz. In the case of a process tube made of quartz, there is an advantage that a semiconductor wafer to be processed is not contaminated because quartz has a high purity. However, when heat treatment is performed at a temperature exceeding 1150 ° C. and 1200 ° C. or more, the quartz process tube is disadvantageously deformed (sag), but it is preferably used for heat treatment at 1150 ° C. or less. On the other hand, as described above, in the case of a process tube made of SiC, it is impossible to make a structure with a shutter made of quartz, which is more effective for the horizontal heat treatment furnace of the present invention. In addition, when a high temperature heat treatment such as a heat treatment exceeding 1150 ° C. is performed in a horizontal heat treatment furnace, as described above, the quartz process tube is deformed and cannot be used. It is preferred to use a manufactured process tube. Further, it is desirable that the diameter of the process tube is a size that allows the introduction of a wafer of 150 mm or more in which the influence of oxygen or moisture taken in from outside the process tube becomes large.

The method for producing an annealed wafer according to the present invention uses the horizontal heat treatment furnace according to the present invention, puts the semiconductor wafer into the process tube, closes the opening end with the shutter, and heats the introduced semiconductor wafer. In the method, the semiconductor wafer is heat-treated so that the process gas is always exhausted through the recess . By doing so, it is possible to manufacture an annealed wafer that does not cause deterioration of the surface roughness of the annealed wafer due to oxygen and moisture being taken into the process tube as impurities during the heat treatment.

    The annealed wafer of the present invention is manufactured by the annealed wafer manufacturing method of the present invention, and has excellent quality without deterioration of surface roughness.

  As described above, according to the horizontal heat treatment furnace of the present invention, the effect that the surface roughness (haze) is not deteriorated even if the silicon mirror wafer is annealed with Ar at a high temperature in the horizontal furnace is achieved. According to the method for manufacturing an annealed wafer of the present invention, an annealed wafer having excellent quality can be manufactured by heat-treating the wafer using the horizontal heat treatment furnace of the present invention. The annealed wafer of the present invention has the effect of having excellent quality.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. However, the illustrated examples are illustrative and the present invention is not limited thereto. FIG. 1 is a schematic explanatory view showing a shutter portion of one embodiment of a horizontal heat treatment furnace of the present invention. FIG. 2 is a cross-sectional explanatory view in the width direction of the recessed portion formed in the shutter. FIG. 3 is an explanatory view in the longitudinal direction of the recessed portion formed in the shutter. The basic structure of the horizontal heat treatment furnace of the present invention is the same as that of the conventional horizontal heat treatment furnace shown in FIG. 4 and will not be described again. However, in FIGS. 1 to 3, the members shown in FIG. The same or similar members will be described using the same reference numerals.

  As shown in FIG. 1, the horizontal heat treatment furnace 10a of the present invention includes a process tube 12 having an open end 16 at one end, and the open end, as in the case of the conventional horizontal heat treatment furnace 10 shown in FIG. And a shutter 18 that closes the opening end 16 via a closing surface 18a that contacts the portion 16. A recess 30 having a function of exhausting the process gas G supplied to the process tube 12 is formed in the closing surface 18 a of the shutter 18. As well shown in FIG. 3, the recess 30 is formed so as to straddle the inner side surface 16a and the outer side surface 16b of the opening end portion 16. Further, most of the opening end portion 16 is in contact with the closing surface 18 a of the shutter 18, and the opening end portion 16 is not structured to be fitted into the concave portion 30. By doing so, the process gas G is always exhausted through the recess 30. The number and size of the recessed portions 30 to be provided are not limited at all, and the positions may be arbitrary places. However, if the total cross-sectional area of the recess 30 from which the process gas G is exhausted is too large, impurities such as oxygen and moisture are taken into the process tube 12, which is counterproductive. Therefore, it is preferable that the total cross-sectional area of the recess 30 is the minimum necessary.

  With respect to the drilling position of the recess 30, if it is drilled in the upper part of the closing surface 18 a of the shutter 18, the process tube 12 passes through the recess 30 through the recess 30 due to the rising airflow caused by the heated process gas G inside the process tube 12. The gas G is ejected, and the gas pressure can prevent the entry of the atmosphere from the outside. Conversely, when the gas G is drilled in the lower part of the closing surface 18a of the shutter 18, the airflow in the process tube when not provided, In other words, the process gas G flow in the lower portion near the shutter 18 is dilute due to the rising air flow caused by the heated process gas G, and thus the shutter 18 is opposed to a state in which atmospheric entrainment from the lower portion of the shutter 18 is likely to occur. An exhaust flow of process gas G is generated at the bottom, and this gas pressure can prevent the entry of air from the outside. Runode, for drilling position of the recess 30, the process gas G flow, shape (diameter, length, etc.) of the process tube 12 may be optimized by like.

  EXAMPLES The present invention will be described more specifically with reference to the following examples. However, it is needless to say that these examples are illustrative and should not be construed as limiting.

Example 1
Wafer used: Diameter 200 mm, P-type, 10 Ωcm, (100), 100 sheets charged (evaluation wafer is the fifth wafer from the furnace opening).
Annealing conditions: Ar 100%, 1200 ° C./1 h.
Haze evaluation: Particle counter SP-1 (manufactured by KLA-Tencor).

  Using a horizontal heat treatment furnace composed of a process tube made of SiC and a quartz shutter having a recess 30 as shown in FIG. 1, Ar annealing is performed on the wafer to be used under the above conditions. Haze evaluation was performed with the above apparatus. The center line average roughness (Ra) of the end face of the open end of the process tube was set to 0.10 μm by polishing, and the shutter Ra was set to 0.10 μm. Ra measurement was performed by a surf test 301 manufactured by Mitutoyo Corporation. The average value of haze on the entire surface of the wafer was 0.063 ppm, and the surface roughness was not deteriorated due to the inclusion of impurities such as oxygen and moisture, which was a good level.

(Comparative Example 1)
Ar annealing was performed in the same manner as in Example 1 except that a horizontal heat treatment furnace having no shutter 30 provided with a recess 30 was used, and the annealed wafer was evaluated. As a result, the average value of haze on the entire wafer surface is 7.489 ppm, and the haze particularly in the area of 0 to 20 mm around the wafer is deteriorated, and the deterioration of the wafer quality due to impurities such as oxygen and moisture is recognized. It was.

The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of 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 idea of the invention.
For example, in the present embodiment, the process tube having an open end portion having a flange shape is illustrated and described, but the present invention is not limited to this, and the same thickness as the thickness of the body portion of the process tube. Needless to say, it is possible to make changes such as those having a thick opening end or a thin thickness, and these are included in the scope of claims of the present application.

It is a schematic explanatory drawing which shows the shutter part of one embodiment of the horizontal type heat treatment furnace of this invention. It is a cross-sectional explanatory drawing of the width direction of the recessed part pierced by the shutter. It is a cross-sectional explanatory view in the longitudinal direction of a recessed portion formed in the shutter. It is schematic structure explanatory drawing which shows an example of the conventional horizontal heat processing furnace.

Explanation of symbols

  10: Conventional horizontal heat treatment furnace, 10a: Horizontal heat treatment furnace of the present invention, 12: Process tube, 14: Furnace port, 16: Open end, 18: Shutter, 20: Wafer support boat, 22: Gas supply port , 30: recess.

Claims (6)

In a horizontal heat treatment furnace provided with a process tube having an open end at one end and a shutter for closing the open end through a closed surface that contacts the open end, the process gas supplied to the process tube is exhausted A recess having a function to perform is formed in the closing surface of the shutter , the recess is provided so as to straddle the inner surface and the outer surface of the opening end, and the process gas always passes through the recess. A horizontal heat treatment furnace characterized by being evacuated . Said process tube, horizontal heat treatment furnace of claim 1, wherein a is made of SiC or quartz. 3. The horizontal heat treatment furnace according to claim 1, wherein the diameter of the process tube is a size capable of loading a wafer having a diameter of 150 mm or more. A horizontal heat treatment furnace according to any one of claims 1 to 3 , wherein a semiconductor wafer is put into the process tube, the opening end is closed by the shutter, and the inserted semiconductor wafer is heated. A method of manufacturing an annealed wafer, comprising: heat-treating the semiconductor wafer so that the process gas is always exhausted through the recess . The method of manufacturing an annealed wafer according to claim 4 , wherein the diameter of the semiconductor wafer is 150 mm or more. The semiconductor wafer manufacturing method of the annealed wafer according to claim 4 or claim 5, characterized in that a silicon single crystal.

Images