JP5626188B2 - Semiconductor wafer heat treatment method - Google Patents

Description

  The present invention relates to a heat treatment technique for semiconductor wafers, particularly silicon single crystal wafers.

  For silicon single crystal wafers used as semiconductor wafers, heat treatment is used for various purposes such as improving crystal quality or forming a film structure on the surface layer. Such a heat treatment technique is used in various semiconductor processes and is a basic and important technique.

JP 11-54447 A JP 2000-311866 A

When a silicon single crystal wafer is heat-treated in a heat treatment furnace, a defect called slip dislocation (hereinafter also simply referred to as slip) may occur from a contact portion with the wafer boat. This slip originates from mechanical damage that occurs when the silicon single crystal wafer comes into contact with the wafer boat, and stress due to the wafer's own weight, thermal deformation, and high-temperature thermal energy are added. It is a defect formed by shifting the silicon crystal structure from millimeter to several centimeters.
When a vertical heat treatment furnace is used, compared with a horizontal furnace, the weight of the wafer is dispersed and the uniformity of the heat distribution in the wafer surface is good, so that slip tends to be suppressed. However, even when a vertical heat treatment furnace is used, many slips occur, which sometimes causes a problem.

Patent Document 1 describes that heat treatment is performed by supporting three positions that can disperse the load of the semiconductor wafer and minimize the self-weight stress in order to reduce slip.
Patent Document 2 describes a heat treatment method that changes the maximum stress generation point of a semiconductor wafer by changing the inclination of the wafer boat during the heat treatment as a heat treatment method that does not cause slip.
However, in any method, it is difficult to stably suppress the occurrence of slip.

  The present invention has been made in view of the above problems, and an object thereof is to provide a method capable of stably suppressing the occurrence of slip in heat treatment of a semiconductor wafer using a vertical heat treatment furnace. To do.

  In order to achieve the above object, the present invention provides a method for performing a heat treatment by placing a semiconductor wafer on a wafer boat in a vertical heat treatment furnace, and a relative position between the position of the wafer boat and the placement position of the semiconductor wafer. And an initial position of a relative position between the position of the wafer boat and the mounting position of the semiconductor wafer based on the determined relationship, and a reference from the set initial position. Provided is a semiconductor wafer heat treatment method, wherein the heat treatment is performed by placing the semiconductor wafer on the wafer boat so as to be within a value.

  By performing heat treatment in this way, when semiconductor wafers are placed on a wafer boat, the semiconductor wafers can be efficiently placed at a placement position where slipping is difficult to occur, thereby generating slip during heat treatment. Can be effectively and stably suppressed.

At this time, when performing a plurality of batches of the heat treatment, it is preferable to perform the heat treatment while managing the relative position between the position of the wafer boat and the placement position of the semiconductor wafer so as to be within a reference value from the initial position.
Thus, even when performing heat treatment of a plurality of batches, heat treatment can be performed while suppressing slip more stably by managing as described above.

At this time, as the management, the displacement amount of the center position of the wafer boat is measured, and the relative position between the position of the wafer boat and the mounting position of the semiconductor wafer is determined from the initial position based on the measured displacement amount. The center position of the semiconductor wafer or the wafer boat is preferably displaced so as to be within the value.
Thus, by measuring the displacement amount of the position of the wafer boat and managing it as described above, the occurrence of slip in the heat treatment can be more effectively suppressed. Also, the relative position between the wafer boat position and the semiconductor wafer placement position can be easily and reliably displaced by displacing the wafer boat position or the semiconductor wafer placement position based on the displacement amount of the wafer boat center position. Can be managed.

At this time, it is preferable to measure the amount of displacement of the center position of the wafer boat for each batch of the heat treatment, for each predetermined number of batches, or for each maintenance of the vertical heat treatment furnace.
By measuring the amount of displacement at such an interval, it is possible to efficiently manage positional deviation.

At this time, the initial position of the relative position between the position of the wafer boat to be set and the placement position of the semiconductor wafer, the relative position between the position of the wafer boat and the placement position of the semiconductor wafer, In relation to the slip generation amount, it is preferable to set the relative position at which the slip generation amount is minimized.
By setting in this way, the occurrence of slip can be further reduced.

At this time, the reference value is preferably set to 0.5 mm.
With such a reference value, slip can be stably and reliably reduced.

  As described above, according to the present invention, heat treatment can be performed while stably suppressing slip.

It is the schematic which shows an example of the vertical heat processing furnace which can be used with the heat processing method of this invention. It is a graph which shows the relationship between the wafer mounting position calculated | required in the Example and the comparative example, and slip generation amount. It is explanatory drawing at the time of measuring the position of a wafer boat in the heat processing method of this invention. It is a graph which shows the slip generation amount measured in the Example and the comparative example.

When heat treatment is performed in a vertical heat treatment furnace, even when the same type heat treatment furnace is used, the occurrence of slipping may vary greatly.
As a result of detailed investigation of this situation, the present inventors have found that the variation is caused by individual differences in the shape of the wafer boat on which the wafer is placed. In general, quartz, SiC (silicon carbide), or the like is used as a material for the wafer boat. In particular, since SiC is excellent in heat resistance, it is often used in a high-temperature heat treatment furnace, but on the other hand, it has a very high hardness and is difficult to process. For this reason, even when processing is performed based on the same design, individual differences in shape occur in the wafer boat that is actually completed.

  Generally processed wafers are supported by parts called three or four “grooves” or “claws” formed in a wafer boat. Each “groove” has a flat surface formed on a surface serving as a support surface. Ideally, it is desirable that the support flat portions of the respective “grooves” be arranged on the same plane, but as described above, in a SiC wafer boat, processing is difficult, In some cases, they cannot be placed on the same plane. As described above, when the support plane of each groove does not coincide with the entire unified plane, the wafer is not supported by the surface but is supported by the corner portion of the groove, and a strong stress is locally generated. . In such a situation, it became clear that many slips occurred.

  Ideally, it is desirable to select and use a wafer boat with good processing accuracy. However, as described above, processing is difficult, so the processing accuracy of the wafer boat to be obtained is not always as desired. Not exclusively. In general, since a wafer boat for heat treatment is expensive, it is difficult to prepare a plurality of wafer boats for selective use because of a significant cost increase.

In order to improve this situation, as a result of further detailed investigation, even when a wafer boat with insufficient processing accuracy is used, the occurrence of slip can be prevented by finely adjusting the position of the wafer placed on the wafer boat. It was found that it can be suppressed.
In a wafer boat with insufficient processing accuracy, since the support plane of each groove does not coincide with the same plane, there is a problem that it is not supported by the surface but supported by the corner portion of the groove. However, by finely adjusting the position of the wafer in advance, the load balance changes, and it is possible to find a position that is supported by a surface instead of a corner portion.

Conventionally, as a method for setting a position for placing a wafer on a wafer boat, a transfer test using a dummy wafer is performed, and an adjustment operation is performed so that the vicinity of the center of the boat is visually observed. However, in this method, the mounting position visually determined is not necessarily the position where the slip is minimized. In addition, since the position adjustment system is poor because it is judged visually, it is difficult to stably maintain the same state.
In order to solve such problems, the present inventors have completed the present invention as described below based on the above findings.

Hereinafter, the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.
FIG. 1 is a schematic view of a vertical heat treatment furnace that can be used in the heat treatment method of the present invention.

A plurality of semiconductor wafers W can be horizontally supported on the wafer boat 13 disposed inside the reaction chamber 11 of the vertical heat treatment furnace 10. During the heat treatment, the semiconductor wafer W is heated by a heater 12 provided around the reaction chamber 11. During the heat treatment, gas is introduced into the reaction chamber 11 through the gas introduction pipe 14, flows from the upper side to the lower side, and is discharged from the gas exhaust pipe 15 to the outside. The gas to be used varies depending on the purpose of the heat treatment, but H ₂ , N ₂ , O ₂ , Ar, etc. are mainly used. In the case of impurity diffusion, these gases are also used as a carrier gas for the impurity compound gas.

  Various shapes are adopted for the wafer support surface in the wafer boat 13, a semicircular support surface formed by providing a concave groove on a columnar column, and a concave groove on a wide prismatic column. There is a rectangular support surface formed by providing.

Regarding the material of the wafer boat 13, for example, for silicon wafers, materials such as quartz (SiO ₂ ), silicon carbide (SiC), silicon (Si), etc. are usually used in order to prevent contamination of the silicon wafers. For example, in a high-temperature heat treatment process exceeding 1000 ° C., a SiC or Si boat having higher heat resistance than a quartz (SiO ₂ ) boat is used. In particular, SiC boats are often used because they can prevent metal contamination that occurs during heat treatment.

In the heat treatment method of the present invention using the vertical heat treatment furnace as described above, the relationship between the relative position between the position of the wafer boat and the placement position of the semiconductor wafer and the amount of slip generation is obtained in advance, and the obtained relationship The initial position of the relative position between the position of the wafer boat and the mounting position of the semiconductor wafer is set based on the above.
In this way, by determining the relationship between the mounting position of the semiconductor wafer and the amount of slip generation, and setting the initial position, the semiconductor wafer is securely mounted at the mounting position where the occurrence of slip during heat treatment can be effectively suppressed. can do.

  For example, the above relationship is obtained by intentionally changing the wafer boat position (position at the center of the wafer boat) and the wafer placement position (position at the center of the wafer), and based on this relationship, the relative slip is minimized. The initial position can be set by investigating various positional relationships.

As an example of the specific procedure, first, the wafer placement robot performs heat treatment by shifting the placement position setting value in the X direction on the wafer by several steps back and forth from the initial state, and slips at each placement position The generated amount is measured, and a graph as shown in FIG.
The X value is fixed at a position where the amount of occurrence of slip is the smallest among them, and then heat treatment is performed by shifting the placement position setting value in the Y direction by several stages before and after the initial state. The amount of slip generated at that time is measured, and the Y value that minimizes the amount of slip generation is determined from the obtained graph as shown in FIG.

  The X value and Y value thus determined are set as the initial position of the wafer placement position to be managed. Further, the position of the wafer boat when the above relationship is obtained is set as the initial position of the wafer boat position to be managed.

  Here, there are various methods for evaluating the amount of slip, such as an optical surface scattering method, an infrared polarized light transmission method, an X-ray diffraction method, a selective etching method, a visual confirmation method, and any method may be used. Further, as an index to be evaluated, in addition to the signal strength of slip, a method of using the number of pixels of the captured slip image as an index, a method of using the ratio of the number of slips on a wafer basis as an index, etc. can be considered, Either method may be used.

Then, the semiconductor wafer is placed on the wafer boat so as to be in the initial position set as described above, and heat treatment is performed.
Thereby, it is possible to effectively suppress the occurrence of slip due to individual differences between wafer boats and variations in the placement position of semiconductor wafers. Therefore, heat treatment with reduced occurrence of slip can be stably performed.

In addition, when performing multiple batches of heat treatment in the present invention, it is preferable to perform the heat treatment while managing the relative position between the wafer boat position and the semiconductor wafer placement position within the reference value from the initial position.
After the initial position is set and the semiconductor wafer is placed as described above, the wafer boat position or the placement of the semiconductor wafer is periodically performed so as to maintain the relative positional relationship between the wafer boat and the semiconductor wafer. Adjust the position. Since the semiconductor wafer placement position can be accurately set numerically by the wafer placement robot, it can be managed relatively easily. On the other hand, the installation position of the wafer boat in the furnace is often designed with a mechanical adjustment range in mind, and may be changed by re-installation work such as maintenance. Therefore, in the present invention, the relative position between the position of the wafer boat and the placement position of the semiconductor wafer is managed so as to be within the reference value from the initial position, so that the relative position between the two becomes the position where the slip is minimized. Can be maintained.

  In order to maintain the relative position of the wafer boat and the semiconductor wafer constant as described above, the method of managing the wafer boat to be installed at the same position every time, and the amount of positional deviation of the wafer boat is measured and adjusted accordingly. There are two methods of changing the wafer mounting position.

A simple example of the management method of installing the wafer boat at the same position every time will be described with reference to FIG.
First, a circumferential portion is found in the shape of a wafer boat when a wafer is loaded. Usually, since the vertical heat treatment furnace has a shape based on a cylindrical shape, the circumferential shape is found from the circumferential region 103 of the wafer boat shape (member shape 101 at the bottom of the wafer boat) as shown in FIG. Next, two reference points 302 and 402 are set on the extension line of the concentric circumferential portion from the approximate center point 102 of the circumferential shape. At this time, the angle at which the two reference points are viewed from the approximate center point 102 of the circumferential shape is set to a position that is 30 ° to 120 °, ideally 90 °. The reference points 302 and 402 are set to the reference objects 301 and 401 installed in the furnace.

The distance from each reference point 302, 402 to the circumferential shape of the wafer boat is measured, and the position of the wafer boat is adjusted so as to keep the two measured distances 303, 403 constant (to keep the initial position). Displace and adjust.
As a distance measuring method, an arbitrary solid scale may be referred to, or a laser length meter or the like may be installed at a reference point. In addition, when an appropriate circumferential portion cannot be found in the boat shape, a circumferential mark may be formed on the wafer boat and used.

Next, an example of a management method for changing the wafer placement position in accordance with the position displacement amount of the wafer boat will be described.
First, in advance, two distances 303 and 403 are measured for the wafer boat position to be managed by the same method as described above. Next, after a certain period of time has elapsed (preferably, for each batch of heat treatment, for each predetermined number of batches, or for maintenance of the heat treatment furnace), the wafer boat position is measured again, particularly immediately after maintenance. At this time, the two distances 303 and 403 are measured by the same method as described above, and the difference between the distances 303 and 403 is set as the displacement amount of the position of the wafer boat. In accordance with the amount of displacement, the set value of the mounting position of the semiconductor wafer is changed in the same direction by the same amount.

At this time, if the direction from the wafer boat center 102 to the reference points 302 and 402 coincides with the X and Y directions of the wafer mounting robot, the set value may be changed as it is. Even if the azimuths are different, the deviation of the azimuth angle can be easily examined, so that correction using simple geometric calculation may be performed.
In this way, it is possible to manage the wafer boat position and the relative position of the wafer placement position so as to be kept constant.

  When multiple batches of heat treatment are performed, after setting to place at the initial position, if the relative position between the wafer boat position and the semiconductor wafer placement position is constant, both positions are the first Even if it is displaced from the position, it does not affect the occurrence of slip, but if it is displaced even if the relative position is only about 0.5 mm, the occurrence of slip is affected. For this reason, it is preferable to manage the displacement amount (reference value) of the relative positions of both within 0.5 mm.

  As described above, in the present invention, the present invention can be implemented easily and efficiently by measuring and managing the distance with reference to the center of the semiconductor wafer and the wafer boat. You may implement this invention on the basis.

  With the heat treatment method of the present invention as described above, heat treatment can be performed using a vertical heat treatment furnace while efficiently and stably suppressing slip.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Examples and comparative examples)
First, the position setting value in the X direction on the wafer by the robot was set to 0 in the initial state, and heat treatment was performed by moving it several steps back and forth, and the graph of FIG. 2A was created. Next, the X value with the smallest amount of slip generation was fixed at 0.5 mm, and heat treatment was performed while changing in the Y direction, and the result of the graph shown in FIG. 2B was obtained. From the obtained results, the position X value with the smallest amount of slip generation = 0.5 mm and the Y value = 0 mm were set as the initial values of the wafer positions to be managed. Further, as an index indicating the position of the wafer boat at this time, two distances 303 and 403 in FIG. 3 were measured, and these values were set as initial values of the boat positions to be managed. FIG. 4A is a graph showing a result of measuring the amount of slip generated by placing the wafer so as to have the set initial value and performing heat treatment. The heat treatment was performed by charging 100 silicon single crystal wafers having a diameter of 300 mm and a crystal orientation <100>, and the heat treatment conditions were an Ar 100% atmosphere, 1200 ° C., and 1 hour.

  Maintenance for removing the wafer boat was performed at the timing of the vertical line 701 in the graph of FIG. When resetting the wafer boat, the position of the wafer boat was measured again, and the displacement of the boat position from the initial value was calculated. Next, the position setting values in the X and Y directions of the wafer placement position by the robot are corrected according to this displacement amount, and the displacement amounts (X, Y) of the relative position between the wafer and the boat are (0 mm, 0 mm). ). After that, when the heat treatment was continued, a small slip amount was maintained as before the maintenance.

  Further, FIG. 4B shows the result of measuring the amount of slip generated when the heat treatment is continued in the above state. At the timing of the vertical line 702 in the graph of FIG. 4B, maintenance for removing the wafer boat was performed, and the wafer boat was set again. At this time, the boat position was not particularly measured. The setting of the wafer mounting position by the robot at this time was reset while carrying out test conveyance of the dummy wafer and confirming the mounting position visually. After that (after the vertical line 702), when heat treatment was continued, the amount of slip generation increased because the accuracy of visual adjustment was insufficient. When the amount of displacement (X, Y) of the relative position between the wafer and the boat at that time was confirmed, it was found to be (−1 mm, 0.5 mm).

  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.

10 ... vertical heat treatment furnace, 11 ... reaction chamber, 12 ... heater,
13 ... Wafer boat, 14 ... Gas introduction pipe, 15 ... Gas exhaust pipe,
101: Member shape at the bottom of the wafer boat, 102: Center point,
103 ... circumferential area, 301, 401 ... reference object, 302, 402 ... reference point,
303, 403 ... distance, W ... semiconductor wafer.

Claims (6)

  In a method of performing a heat treatment by placing a semiconductor wafer on a wafer boat of a vertical heat treatment furnace, a relationship between a relative position between the position of the wafer boat and the placement position of the semiconductor wafer, and a slip generation amount is obtained. Based on the obtained relationship, an initial position of a relative position between the position of the wafer boat and the placement position of the semiconductor wafer is set, and the semiconductor wafer is placed within the reference value from the set initial position. A method for heat treating a semiconductor wafer, wherein the heat treatment is carried out by placing on a boat.   The heat treatment is performed while managing the relative position between the position of the wafer boat and the placement position of the semiconductor wafer within a reference value from the initial position when performing the batch of the heat treatment. 2. A method for heat-treating a semiconductor wafer according to 1.   As the management, the displacement amount of the center position of the wafer boat is measured, and the relative position between the position of the wafer boat and the mounting position of the semiconductor wafer is within the reference value from the initial position by the measured displacement amount. The semiconductor wafer heat treatment method according to claim 2, wherein a center position of the semiconductor wafer or the wafer boat is displaced.   4. The semiconductor wafer according to claim 3, wherein the amount of displacement of the center position of the wafer boat is measured for each batch of the heat treatment, for each predetermined number of batches, or for maintenance of the vertical heat treatment furnace. Heat treatment method.   The initial position of the relative position between the set position of the wafer boat and the placement position of the semiconductor wafer, the relative position between the obtained position of the wafer boat and the placement position of the semiconductor wafer, and the amount of slip generation 5. The method for heat-treating a semiconductor wafer according to claim 1, wherein the relative position at which a slip generation amount is minimized is set.   6. The semiconductor wafer heat treatment method according to claim 1, wherein the reference value is 0.5 mm.

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