JP6810591B2 - Heat treatment method for silicon substrate - Google Patents

Description

The present invention relates to a heat treatment method for controlling defects in a silicon substrate.

Most silicon substrates for semiconductor applications are manufactured by slicing from silicon single crystal ingots made by the Czochralski method (Cz method). It is known that oxygen dissolves into molten silicon from the surface of a quartz crucible when a silicon single crystal is grown by the Czochralski method. Then, the oxygen taken into the molten silicon becomes supersaturated in the process of cooling the silicon single crystal, and aggregates to form an oxygen precipitate (BMD: Bulk Micro Defect). The density of oxygen precipitates in the silicon substrate at the time of cutting out from the silicon single crystal ingot is also low, and the effect on the device characteristics is small.

However, as is well known, in the manufacturing process of a semiconductor device, various heat treatments are repeatedly applied to the silicon substrate, and the oxygen precipitates may become dense in the process. According to Patent Documents 1 and 2, when oxygen precipitates are generated on the surface of a silicon substrate which is a device active region, they adversely affect device characteristics such as junction leakage, but when they are present in a bulk other than the device active region, the device It is disclosed that it is effective because it functions as a gettering site for capturing metal impurities mixed in during the process.

International Publication No. 2012/008087 International Publication No. 2012/114659

Therefore, it is preferable that no oxygen precipitates are present near the surface of the silicon substrate and that oxygen precipitates are present at a high density inside the silicon substrate except for the surface. However, in a conventional heat treatment process such as Rapid Thermal Annealing (RTA), it is difficult to control the oxygen precipitates to be unevenly present in the silicon substrate as described above.

The present invention has been made in view of the above problems, and silicon in which oxygen precipitates do not exist on the surface of a silicon substrate and oxygen precipitates can be present in a high density inside the silicon substrate. An object of the present invention is to provide a method for heat-treating a substrate.

In order to solve the above problem, the invention of claim 1 is a first heating method for heating a silicon substrate to a first temperature by irradiating light from a halogen lamp in a method for heat-treating a silicon substrate produced by the Czochralski method. In the step, the halogen lamp is turned off or the output of the halogen lamp is reduced to lower the temperature of the silicon substrate to a second temperature lower than the first temperature to generate oxygen precipitates in the silicon substrate. In the step, the silicon substrate is irradiated with flash light from a flash lamp to heat the surface of the silicon substrate to a third temperature higher than the second temperature, and the oxygen precipitate disappears from the surface of the silicon substrate. In the first heating step, nitrogen gas is supplied into the chamber accommodating the silicon substrate at a first flow rate, and in the second heating step, the inside of the chamber is filled with nitrogen gas. It is characterized in that nitrogen gas is supplied at a second flow rate higher than the first flow rate .

Further, the invention of claim 2 is characterized in that, in the heat treatment method for a silicon substrate according to the invention of claim 1, the irradiation time of flash light in the second heating step is 0.1 ms or more and 10 ms or less. And.

Further, the invention of claim 3 is the method for heat-treating a silicon substrate according to the invention of claim 1 or 2, and the pressure in the chamber accommodating the silicon substrate is reduced to 13330 Pa or less before the first heating step. It is characterized by further including a depressurizing step.

According to the inventions of claims 1 to 3 , the silicon substrate heated to the first temperature by light irradiation from the halogen lamp is lowered to the second temperature to generate oxygen precipitates in the silicon substrate. Since the surface of the silicon substrate is heated to a third temperature by irradiating the silicon substrate with flash light to eliminate oxygen precipitates from the surface of the silicon substrate, no oxygen precipitates exist on the surface of the silicon substrate. Moreover, oxygen precipitates can be present at a high density inside the silicon substrate. Further, before the second heating step, in order to increase the flow rate of nitrogen gas supplied into the chamber accommodating the silicon substrate, oxygen precipitates diffused outward from the surface of the silicon substrate reattach to the surface of the silicon substrate. Can be prevented.

In particular, according to the invention of claim 3, before the first heating step, the pressure inside the chamber accommodating the silicon substrate is reduced to 13330 Pa or less, so that the oxygen precipitates diffused outward from the surface of the silicon substrate are the silicon substrate. It is possible to prevent reattachment to the surface of the silicon.

It is a vertical sectional view which shows the structure of the heat treatment apparatus used in the heat treatment method of the silicon substrate which concerns on this invention. It is a perspective view which shows the whole appearance of the holding part. It is a top view of the susceptor. It is sectional drawing of the susceptor. It is a top view of the transfer mechanism. It is a side view of the transfer mechanism. It is a top view which shows the arrangement of a plurality of halogen lamps. It is a figure which shows the drive circuit of a flash lamp. It is a figure which shows the change of the surface temperature of the silicon substrate in 1st Embodiment. It is a figure which shows typically the oxygen precipitate existing in the silicon substrate before heat treatment. It is a figure which shows typically the oxygen precipitate which exists in the silicon substrate cooled to the cooling temperature. It is a figure which shows typically the oxygen precipitate which exists in the silicon substrate after flash heating.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
First, a heat treatment apparatus for carrying out the heat treatment method for a silicon substrate according to the present invention will be described. FIG. 1 is a vertical cross-sectional view showing the configuration of a heat treatment apparatus 1 used in the heat treatment method for a silicon substrate according to the present invention. The heat treatment apparatus 1 of FIG. 1 is a flash lamp annealing apparatus that heats a disc-shaped silicon substrate W as a substrate by irradiating the silicon substrate W with flash light. The size of the silicon substrate W to be processed is not particularly limited, but is, for example, φ300 mm or φ450 mm. In addition, in FIG. 1 and each subsequent drawing, the dimensions and numbers of each part are exaggerated or simplified as necessary for easy understanding.

The heat treatment apparatus 1 includes a chamber 6 that houses a silicon substrate W, a flash heating unit 5 that incorporates a plurality of flash lamps FL, and a halogen heating unit 4 that incorporates a plurality of halogen lamps HL. A flash heating unit 5 is provided on the upper side of the chamber 6, and a halogen heating unit 4 is provided on the lower side. Further, the heat treatment apparatus 1 includes a holding portion 7 that holds the silicon substrate W in a horizontal posture inside the chamber 6, a transfer mechanism 10 that transfers the silicon substrate W between the holding portion 7 and the outside of the apparatus. To be equipped. Further, the heat treatment apparatus 1 includes a halogen heating unit 4, a flash heating unit 5, and a control unit 3 that controls each operation mechanism provided in the chamber 6 to execute heat treatment of the silicon substrate W.

The chamber 6 is configured by mounting quartz chamber windows above and below the tubular chamber side portion 61. The chamber side portion 61 has a substantially tubular shape with upper and lower openings, and the upper chamber window 63 is attached to the upper opening and closed, and the lower chamber window 64 is attached to the lower opening and closed. ing. The upper chamber window 63 constituting the ceiling portion of the chamber 6 is a disk-shaped member formed of quartz, and functions as a quartz window that transmits the flash light emitted from the flash heating portion 5 into the chamber 6. Further, the lower chamber window 64 constituting the floor portion of the chamber 6 is also a disk-shaped member formed of quartz, and functions as a quartz window that transmits light from the halogen heating portion 4 into the chamber 6.

A reflective ring 68 is attached to the upper part of the inner wall surface of the chamber side portion 61, and a reflective ring 69 is attached to the lower part. The reflective rings 68 and 69 are both formed in an annular shape. The upper reflective ring 68 is attached by fitting from the upper side of the chamber side portion 61. On the other hand, the lower reflective ring 69 is attached by fitting it from the lower side of the chamber side portion 61 and fastening it with a screw (not shown). That is, both the reflective rings 68 and 69 are detachably attached to the chamber side portion 61. The inner space of the chamber 6, that is, the space surrounded by the upper chamber window 63, the lower chamber window 64, the chamber side 61, and the reflection rings 68, 69 is defined as the heat treatment space 65.

By attaching the reflective rings 68 and 69 to the chamber side portion 61, a recess 62 is formed on the inner wall surface of the chamber 6. That is, a recess 62 is formed which is surrounded by the central portion of the inner wall surface of the chamber side portion 61 to which the reflection rings 68 and 69 are not mounted, the lower end surface of the reflection ring 68, and the upper end surface of the reflection ring 69. .. The recess 62 is formed in an annular shape along the horizontal direction on the inner wall surface of the chamber 6 and surrounds the holding portion 7 that holds the silicon substrate W. The chamber side 61 and the reflective rings 68 and 69 are made of a metal material (for example, stainless steel) having excellent strength and heat resistance.

Further, the chamber side portion 61 is provided with a transport opening (furnace port) 66 for loading and unloading the silicon substrate W into and out of the chamber 6. The transport opening 66 is openable and closable by a gate valve 185. The transport opening 66 is communicated with the outer peripheral surface of the recess 62. Therefore, when the gate valve 185 opens the transfer opening 66, the silicon substrate W is carried in from the transfer opening 66 through the recess 62 into the heat treatment space 65 and the silicon substrate W is carried out from the heat treatment space 65. It can be performed. Further, when the gate valve 185 closes the transport opening 66, the heat treatment space 65 in the chamber 6 becomes a closed space.

Further, a gas supply hole 81 for supplying the processing gas to the heat treatment space 65 is formed in the upper part of the inner wall of the chamber 6. The gas supply hole 81 is formed at a position above the recess 62, and may be provided in the reflection ring 68. The gas supply hole 81 is communicated with the gas supply pipe 83 via a buffer space 82 formed in an annular shape inside the side wall of the chamber 6. The gas supply pipe 83 is connected to the processing gas supply source 85. Further, a valve 84 is inserted in the middle of the path of the gas supply pipe 83. When the valve 84 is opened, the processing gas is supplied from the processing gas supply source 85 to the buffer space 82. The processing gas that has flowed into the buffer space 82 flows so as to expand in the buffer space 82 having a smaller fluid resistance than the gas supply hole 81, and is supplied from the gas supply hole 81 into the heat treatment space 65. As the treatment gas, for example, an inert gas such as nitrogen (N ₂ ), a reactive gas such as hydrogen (H ₂ ) or ammonia (NH ₃ ), or a mixed gas in which they are mixed can be used (this). Nitrogen gas in the embodiment).

On the other hand, a gas exhaust hole 86 for exhausting the gas in the heat treatment space 65 is formed in the lower part of the inner wall of the chamber 6. The gas exhaust hole 86 is formed at a position below the recess 62, and may be provided in the reflection ring 69. The gas exhaust hole 86 is communicated with the gas exhaust pipe 88 via a buffer space 87 formed in an annular shape inside the side wall of the chamber 6. The gas exhaust pipe 88 is connected to the exhaust unit 190. Further, a valve 89 is inserted in the middle of the path of the gas exhaust pipe 88. When the valve 89 is opened, the gas in the heat treatment space 65 is discharged from the gas exhaust hole 86 to the gas exhaust pipe 88 via the buffer space 87. A plurality of gas supply holes 81 and gas exhaust holes 86 may be provided along the circumferential direction of the chamber 6, or may be slit-shaped.

Further, a gas exhaust pipe 191 for discharging the gas in the heat treatment space 65 is also connected to the tip of the transport opening 66. The gas exhaust pipe 191 is connected to the exhaust unit 190 via a valve 192. By opening the valve 192, the gas in the chamber 6 is exhausted through the transfer opening 66.

As the exhaust unit 190, an exhaust utility of a factory in which a vacuum pump or a heat treatment device 1 is installed can be used. When a vacuum pump is adopted as the exhaust unit 190 and the atmosphere of the heat treatment space 65, which is a closed space, is exhausted without closing the valve 84 and supplying any gas from the gas supply hole 81, the inside of the chamber 6 becomes a vacuum atmosphere. The pressure can be reduced. Further, even when a vacuum pump is not used as the exhaust unit 190, the inside of the chamber 6 can be depressurized to a pressure lower than the atmospheric pressure by exhausting the gas without supplying the gas from the gas supply hole 81. ..

FIG. 2 is a perspective view showing the overall appearance of the holding portion 7. The holding portion 7 includes a base ring 71, a connecting portion 72, and a susceptor 74. The base ring 71, the connecting portion 72 and the susceptor 74 are all made of quartz. That is, the entire holding portion 7 is made of quartz.

The base ring 71 is an arc-shaped quartz member in which a part is missing from the ring shape. This missing portion is provided to prevent interference between the transfer arm 11 of the transfer mechanism 10 described later and the base ring 71. By placing the base ring 71 on the bottom surface of the recess 62, the base ring 71 is supported on the wall surface of the chamber 6 (see FIG. 1). A plurality of connecting portions 72 (four in the present embodiment) are erected on the upper surface of the base ring 71 along the circumferential direction of the ring shape. The connecting portion 72 is also a quartz member, and is fixed to the base ring 71 by welding.

The susceptor 74 is supported by four connecting portions 72 provided on the base ring 71. FIG. 3 is a plan view of the susceptor 74. Further, FIG. 4 is a cross-sectional view of the susceptor 74. The susceptor 74 includes a holding plate 75, a guide ring 76, and a plurality of substrate support pins 77. The holding plate 75 is a substantially circular flat plate-shaped member made of quartz. The diameter of the holding plate 75 is larger than the diameter of the silicon substrate W. That is, the holding plate 75 has a plane size larger than that of the silicon substrate W.

A guide ring 76 is installed on the upper peripheral edge of the holding plate 75. The guide ring 76 is a ring-shaped member having an inner diameter larger than the diameter of the silicon substrate W. For example, when the diameter of the silicon substrate W is φ300 mm, the inner diameter of the guide ring 76 is φ320 mm. The inner circumference of the guide ring 76 is a tapered surface that widens upward from the holding plate 75. The guide ring 76 is made of quartz similar to the holding plate 75. The guide ring 76 may be welded to the upper surface of the holding plate 75, or may be fixed to the holding plate 75 by a separately processed pin or the like. Alternatively, the holding plate 75 and the guide ring 76 may be processed as an integral member.

A region of the upper surface of the holding plate 75 inside the guide ring 76 is a flat holding surface 75a for holding the silicon substrate W. A plurality of substrate support pins 77 are erected on the holding surface 75a of the holding plate 75. In the present embodiment, a total of 12 substrate support pins 77 are erected at every 30 ° along the circumference of the outer circumference circle (inner circumference circle of the guide ring 76) of the holding surface 75a and the concentric circle. The diameter of the circle in which the 12 substrate support pins 77 are arranged (distance between the opposing substrate support pins 77) is smaller than the diameter of the silicon substrate W, and if the diameter of the silicon substrate W is φ300 mm, the diameter is φ270 mm to φ280 mm (this implementation). In the form, it is φ270 mm). Each substrate support pin 77 is made of quartz. The plurality of substrate support pins 77 may be provided on the upper surface of the holding plate 75 by welding, or may be processed integrally with the holding plate 75.

Returning to FIG. 2, the four connecting portions 72 erected on the base ring 71 and the peripheral edge portion of the holding plate 75 of the susceptor 74 are fixed by welding. That is, the susceptor 74 and the base ring 71 are fixedly connected by the connecting portion 72. The base ring 71 of the holding portion 7 is supported on the wall surface of the chamber 6, so that the holding portion 7 is mounted on the chamber 6. When the holding portion 7 is mounted on the chamber 6, the holding plate 75 of the susceptor 74 is in a horizontal posture (a posture in which the normal line coincides with the vertical direction). That is, the holding surface 75a of the holding plate 75 is a horizontal plane.

The silicon substrate W carried into the chamber 6 is placed and held in a horizontal posture on the susceptor 74 of the holding portion 7 mounted on the chamber 6. At this time, the silicon substrate W is supported by the 12 substrate support pins 77 erected on the holding plate 75 and held by the susceptor 74. More precisely, the upper ends of the 12 substrate support pins 77 come into contact with the lower surface of the silicon substrate W to support the silicon substrate W. Since the heights of the 12 substrate support pins 77 (distance from the upper end of the substrate support pins 77 to the holding surface 75a of the holding plate 75) are uniform, the silicon substrate W is placed in a horizontal position by the 12 substrate support pins 77. Can be supported.

Further, the silicon substrate W is supported by a plurality of substrate support pins 77 from the holding surface 75a of the holding plate 75 at a predetermined interval. The thickness of the guide ring 76 is larger than the height of the substrate support pin 77. Therefore, the horizontal misalignment of the silicon substrate W supported by the plurality of substrate support pins 77 is prevented by the guide ring 76.

Further, as shown in FIGS. 2 and 3, an opening 78 is formed in the holding plate 75 of the susceptor 74 so as to penetrate vertically. The opening 78 is provided so that the radiation thermometer 120 (see FIG. 1) receives the synchrotron radiation (infrared light) radiated from the lower surface of the silicon substrate W held by the susceptor 74. That is, the radiation thermometer 120 receives the light radiated from the lower surface of the silicon substrate W held by the susceptor 74 through the opening 78, and the temperature of the silicon substrate W is measured by a separate detector. Further, the holding plate 75 of the susceptor 74 is provided with four through holes 79 through which the lift pin 12 of the transfer mechanism 10 described later penetrates for the transfer of the silicon substrate W.

FIG. 5 is a plan view of the transfer mechanism 10. Further, FIG. 6 is a side view of the transfer mechanism 10. The transfer mechanism 10 includes two transfer arms 11. The transfer arm 11 has an arc shape that generally follows an annular recess 62. Two lift pins 12 are erected on each transfer arm 11. Each transfer arm 11 is rotatable by a horizontal movement mechanism 13. The horizontal movement mechanism 13 includes a transfer operation position (solid line position in FIG. 5) for transferring the pair of transfer arms 11 to the holding portion 7 and the silicon substrate W held by the holding portion 7. It is moved horizontally with the retracted position (two-dot chain line position in FIG. 5) that does not overlap in a plan view. The horizontal movement mechanism 13 may be one in which each transfer arm 11 is rotated by an individual motor, or a pair of transfer arms 11 are interlocked and rotated by one motor using a link mechanism. It may be something to move.

Further, the pair of transfer arms 11 are moved up and down together with the horizontal movement mechanism 13 by the elevating mechanism 14. When the elevating mechanism 14 raises the pair of transfer arms 11 at the transfer operation position, a total of four lift pins 12 pass through the through holes 79 (see FIGS. 2 and 3) formed in the susceptor 74, and the lift pins The upper end of 12 protrudes from the upper surface of the susceptor 74. On the other hand, when the elevating mechanism 14 lowers the pair of transfer arms 11 at the transfer operation position, the lift pin 12 is pulled out from the through hole 79, and the horizontal movement mechanism 13 moves the pair of transfer arms 11 so as to open each. The transfer arm 11 moves to the retracted position. The retracted position of the pair of transfer arms 11 is directly above the base ring 71 of the holding portion 7. Since the base ring 71 is placed on the bottom surface of the recess 62, the retracted position of the transfer arm 11 is inside the recess 62. An exhaust mechanism (not shown) is also provided in the vicinity of the portion where the drive unit (horizontal movement mechanism 13 and elevating mechanism 14) of the transfer mechanism 10 is provided, and the atmosphere around the drive unit of the transfer mechanism 10 is provided. Is configured to be discharged to the outside of the chamber 6.

Returning to FIG. 1, the flash heating unit 5 provided above the chamber 6 is a light source composed of a plurality of (30 in this embodiment) xenon flash lamp FL inside the housing 51, and above the light source. It is configured to include a reflector 52 provided so as to cover the above. Further, a lamp light radiation window 53 is attached to the bottom of the housing 51 of the flash heating unit 5. The lamp light emitting window 53 constituting the floor portion of the flash heating unit 5 is a plate-shaped quartz window made of quartz. By installing the flash heating unit 5 above the chamber 6, the lamp light emitting window 53 faces the upper chamber window 63. The flash lamp FL irradiates the heat treatment space 65 with flash light from above the chamber 6 through the lamp light emitting window 53 and the upper chamber window 63.

Each of the plurality of flash lamps FL is a rod-shaped lamp having a long cylindrical shape, and the longitudinal direction thereof is along the main surface of the silicon substrate W held by the holding portion 7 (that is, along the horizontal direction). They are arranged in a plane so as to be parallel to each other. Therefore, the plane formed by the arrangement of the flash lamps FL is also a horizontal plane.

FIG. 8 is a diagram showing a drive circuit of the flash lamp FL. As shown in the figure, a capacitor 93, a coil 94, a flash lamp FL, and an IGBT (insulated gate bipolar transistor) 96 are connected in series. Further, as shown in FIG. 8, the control unit 3 includes a pulse generator 31 and a waveform setting unit 32, and is connected to the input unit 33. As the input unit 33, various known input devices such as a keyboard, a mouse, and a touch panel can be adopted. The waveform setting unit 32 sets the waveform of the pulse signal based on the input content from the input unit 33, and the pulse generator 31 generates the pulse signal according to the waveform.

The flash lamp FL includes a rod-shaped glass tube (discharge tube) 92 in which xenon gas is sealed inside and anodes and cathodes are arranged at both ends thereof, and a trigger electrode attached on the outer peripheral surface of the glass tube 92. It is equipped with 91. A predetermined voltage is applied to the capacitor 93 by the power supply unit 95, and an electric charge corresponding to the applied voltage (charging voltage) is charged. Further, a high voltage can be applied to the trigger electrode 91 from the trigger circuit 97. The timing at which the trigger circuit 97 applies a voltage to the trigger electrode 91 is controlled by the control unit 3.

The IGBT 96 is a bipolar transistor in which a MOSFET (Metal Oxide Semiconductor Field effect transistor) is incorporated in a gate portion, and is a switching element suitable for handling a large amount of electric power. A pulse signal is applied to the gate of the IGBT 96 from the pulse generator 31 of the control unit 3. When a voltage equal to or higher than a predetermined value (High voltage) is applied to the gate of the IGBT 96, the IGBT 96 is turned on, and when a voltage lower than the predetermined value (Low voltage) is applied, the IGBT 96 is turned off. In this way, the drive circuit including the flash lamp FL is turned on and off by the IGBT 96. When the IGBT 96 is turned on and off, the connection between the flash lamp FL and the corresponding capacitor 93 is interrupted, and the current flowing through the flash lamp FL is controlled on and off.

Even if the IGBT 96 is turned on and a high voltage is applied to the electrodes at both ends of the glass tube 92 while the capacitor 93 is charged, the xenon gas is electrically an insulator, so that the glass is normally in a normal state. No electricity flows through the tube 92. However, when the trigger circuit 97 applies a high voltage to the trigger electrode 91 to break the insulation, a current instantly flows in the glass tube 92 due to the discharge between the electrodes at both ends, and the excitement of the xenone atom or molecule at that time. Light is emitted by.

The drive circuit as shown in FIG. 8 is individually provided for each of the plurality of flash lamps FL provided in the flash heating unit 5. In the present embodiment, since 30 flash lamps FL are arranged in a plane, 30 drive circuits as shown in FIG. 8 are provided corresponding to them. Therefore, the current flowing through each of the 30 flash lamps FL is individually on / off controlled by the corresponding IGBT 96.

Further, the reflector 52 is provided above the plurality of flash lamps FL so as to cover all of them. The basic function of the reflector 52 is to reflect the flash light emitted from the plurality of flash lamps FL toward the heat treatment space 65. The reflector 52 is made of an aluminum alloy plate, and its surface (the surface facing the flash lamp FL) is roughened by blasting.

The halogen heating unit 4 provided below the chamber 6 contains a plurality of halogen lamps HL (40 in this embodiment) inside the housing 41. The halogen heating unit 4 is a light irradiation unit that heats the silicon substrate W by irradiating the heat treatment space 65 with light from below the chamber 6 through the lower chamber window 64 by a plurality of halogen lamps HL.

FIG. 7 is a plan view showing the arrangement of a plurality of halogen lamps HL. The 40 halogen lamps HL are arranged in two upper and lower stages. Twenty halogen lamps HL are arranged in the upper stage near the holding portion 7, and 20 halogen lamps HL are also arranged in the lower stage farther from the holding portion 7 than in the upper stage. Each halogen lamp HL is a rod-shaped lamp having a long cylindrical shape. The 20 halogen lamps HL in both the upper and lower stages are arranged so that their longitudinal directions are parallel to each other along the main surface of the silicon substrate W held by the holding portion 7 (that is, along the horizontal direction). There is. Therefore, the plane formed by the arrangement of the halogen lamps HL in both the upper and lower stages is a horizontal plane.

Further, as shown in FIG. 7, the arrangement density of the halogen lamp HL in the region facing the peripheral edge portion is higher than the region facing the central portion of the silicon substrate W held by the holding portion 7 in both the upper and lower stages. There is. That is, in both the upper and lower stages, the arrangement pitch of the halogen lamp HL is shorter in the peripheral portion than in the central portion of the lamp arrangement. Therefore, it is possible to irradiate a larger amount of light on the peripheral edge of the silicon substrate W, which tends to cause a temperature drop during heating by light irradiation from the halogen heating unit 4.

Further, the lamp group composed of the halogen lamp HL in the upper stage and the lamp group composed of the halogen lamp HL in the lower stage are arranged so as to intersect in a grid pattern. That is, a total of 40 halogen lamps HL are arranged so that the longitudinal direction of the 20 halogen lamps HL arranged in the upper stage and the longitudinal direction of the 20 halogen lamps HL arranged in the lower stage are orthogonal to each other. There is.

The halogen lamp HL is a filament type light source that incandescents the filament and emits light by energizing the filament arranged inside the glass tube. Inside the glass tube, a gas in which a small amount of a halogen element (iodine, bromine, etc.) is introduced into an inert gas such as nitrogen or argon is sealed. By introducing the halogen element, it becomes possible to set the temperature of the filament to a high temperature while suppressing the breakage of the filament. Therefore, the halogen lamp HL has a characteristic that it has a longer life and can continuously irradiate strong light as compared with a normal incandescent lamp. That is, the halogen lamp HL is a continuously lit lamp that continuously emits light for at least 1 second or longer. Further, since the halogen lamp HL is a rod-shaped lamp, it has a long life, and by arranging the halogen lamp HL along the horizontal direction, the radiation efficiency to the upper silicon substrate W becomes excellent.

Further, a reflector 43 is also provided under the two-stage halogen lamp HL in the housing 41 of the halogen heating unit 4 (FIG. 1). The reflector 43 reflects the light emitted from the plurality of halogen lamps HL toward the heat treatment space 65.

The control unit 3 controls the above-mentioned various operating mechanisms provided in the heat treatment apparatus 1. The configuration of the control unit 3 as hardware is the same as that of a general computer. That is, the control unit 3 stores a CPU, which is a circuit that performs various arithmetic processes, a ROM, which is a read-only memory for storing basic programs, a RAM, which is a read / write memory for storing various information, and control software and data. It has a magnetic disk to store. When the CPU of the control unit 3 executes a predetermined processing program, the processing in the heat treatment apparatus 1 proceeds. Further, as shown in FIG. 8, the control unit 3 includes a pulse generator 31 and a waveform setting unit 32. As described above, the waveform setting unit 32 sets the waveform of the pulse signal based on the input content from the input unit 33, and the pulse generator 31 outputs the pulse signal to the gate of the IGBT 96 accordingly.

In addition to the above configuration, the heat treatment apparatus 1 prevents an excessive temperature rise of the halogen heating unit 4, the flash heating unit 5, and the chamber 6 due to the thermal energy generated from the halogen lamp HL and the flash lamp FL during the heat treatment of the silicon substrate W. Therefore, it has various cooling structures. For example, a water cooling pipe (not shown) is provided on the wall of the chamber 6. Further, the halogen heating unit 4 and the flash heating unit 5 have an air-cooled structure in which a gas flow is formed inside to exhaust heat. In addition, air is also supplied to the gap between the upper chamber window 63 and the lamp light radiation window 53 to cool the flash heating unit 5 and the upper chamber window 63.

Next, the heat treatment method for the silicon substrate according to the present invention will be described. The silicon substrate W to be processed in the present embodiment is a bare wafer cut out from a silicon single crystal ingot produced by the Czochralski method. In the silicon substrate W before the heat treatment by the heat treatment apparatus 1, the oxygen dissolved in the molten silicon from the quartz crucible when the silicon single crystal is grown by the Czochralski method becomes supersaturated in the cooling process of the silicon single crystal. There is an oxygen precipitate formed by agglomeration.

FIG. 10 is a diagram schematically showing oxygen precipitates existing in the silicon substrate W before heat treatment. Oxygen precipitates 21 generated in the cooling process of the silicon single crystal are present in the silicon substrate W before heat treatment cut out from the ingot of the silicon single crystal, but the density thereof is low. Further, the oxygen precipitate 21 is uniformly distributed over the entire silicon substrate W without being biased.

The heat treatment on the silicon substrate W is performed by the heat treatment apparatus 1 described above. Hereinafter, the heat treatment of the silicon substrate W by the heat treatment apparatus 1 will be described. The processing procedure of the heat treatment apparatus 1 described below proceeds by the control unit 3 controlling each operation mechanism of the heat treatment apparatus 1.

First, the gate valve 185 is opened to open the transfer opening 66, and the silicon substrate W is carried into the heat treatment space 65 in the chamber 6 through the transfer opening 66 by a transfer robot outside the apparatus. The silicon substrate W carried in by the transfer robot advances to a position directly above the holding portion 7 and stops. Then, the pair of transfer arms 11 of the transfer mechanism 10 move horizontally from the retracted position to the transfer operation position and rise, so that the lift pin 12 protrudes from the upper surface of the holding plate 75 of the susceptor 74 through the through hole 79. Receives the silicon substrate W. At this time, the lift pin 12 rises above the upper end of the substrate support pin 77.

After the silicon substrate W is placed on the lift pin 12, the transfer robot exits the heat treatment space 65, and the transfer opening 66 is closed by the gate valve 185. Then, as the pair of transfer arms 11 descend, the silicon substrate W is handed over from the transfer mechanism 10 to the susceptor 74 of the holding portion 7 and held in a horizontal posture from below. The silicon substrate W is supported by a plurality of substrate support pins 77 erected on the holding plate 75 and held by the susceptor 74. A predetermined distance is formed between the lower surface of the silicon substrate W supported by the plurality of substrate support pins 77 and the holding surface 75a of the holding plate 75. The pair of transfer arms 11 lowered to the lower side of the susceptor 74 are retracted to the retracted position, that is, inside the recess 62 by the horizontal movement mechanism 13.

Further, after the transfer opening 66 is closed by the gate valve 185 to make the heat treatment space 65 a closed space, the atmosphere in the chamber 6 is adjusted. Specifically, the valve 84 is opened and the processing gas is supplied to the heat treatment space 65 from the gas supply hole 81. In the present embodiment, nitrogen gas (N ₂ ) is supplied to the heat treatment space 65 in the chamber 6 as the processing gas. Further, the valve 89 is opened and the gas in the chamber 6 is exhausted from the gas exhaust hole 86. As a result, the processing gas supplied from the upper part of the heat treatment space 65 in the chamber 6 flows downward and is exhausted from the lower part of the heat treatment space 65, and the heat treatment space 65 is replaced with a nitrogen atmosphere. Further, when the valve 192 is opened, the gas in the chamber 6 is also exhausted from the transport opening 66. Further, the atmosphere around the drive unit of the transfer mechanism 10 is also exhausted by the exhaust mechanism (not shown).

FIG. 9 is a diagram showing changes in the surface temperature of the silicon substrate W in the first embodiment. After the inside of the chamber 6 is replaced with a nitrogen atmosphere and the silicon substrate W is held from below in a horizontal position by the susceptor 74 of the holding unit 7, the 40 halogen lamps HL of the halogen heating unit 4 are lit all at once at time t1. Then, rapid heating (RTA: Rapid Thermal Annealing) of the silicon substrate W is started. The halogen light emitted from the halogen lamp HL passes through the lower chamber window 64 and the susceptor 74 formed of quartz and is irradiated from the lower surface of the silicon substrate W. By receiving light irradiation from the halogen lamp HL, the silicon substrate W is rapidly heated and the temperature rises. Since the transfer arm 11 of the transfer mechanism 10 is retracted inside the recess 62, it does not interfere with heating by the halogen lamp HL.

When rapid heating is performed by the halogen lamp HL, the temperature of the silicon substrate W is measured by the radiation thermometer 120. That is, the radiation thermometer 120 receives infrared light radiated from the lower surface of the silicon substrate W held by the susceptor 74 through the opening 78, and measures the wafer temperature during temperature rise. The measured temperature of the silicon substrate W is transmitted to the control unit 3. The control unit 3 monitors whether or not the temperature of the silicon substrate W, which is raised by irradiation with light from the halogen lamp HL, has reached a predetermined first peak temperature Ts (first temperature), while monitoring the halogen lamp HL. Control the output. That is, the control unit 3 feedback-controls the output of the halogen lamp HL so that the temperature of the silicon substrate W becomes the first peak temperature Ts based on the measured value by the radiation thermometer 120. The rate of temperature rise of the silicon substrate W during rapid heating by the halogen lamp HL is 50 ° C./sec or more. The first peak temperature Ts of the halogen lamp HL is 1100 ° C. or higher and 1300 ° C. or lower.

After the temperature of the silicon substrate W reaches the first peak temperature Ts at time t2, the control unit 3 maintains the silicon substrate W at the first peak temperature Ts for about 0.5 seconds to 5 seconds. Specifically, the control unit 3 adjusts the output of the halogen lamp HL at the time t2 when the temperature of the silicon substrate W measured by the radiation thermometer 120 reaches the first peak temperature Ts, and the temperature of the silicon substrate W is substantially adjusted. The first peak temperature Ts is maintained for about 0.5 to 5 seconds.

During rapid heating by the halogen lamp HL, the entire silicon substrate W is uniformly heated to the first peak temperature Ts. At the stage of rapid heating by the halogen lamp HL, the temperature of the peripheral portion of the silicon substrate W, which is more likely to dissipate heat, tends to be lower than that of the central portion, but the arrangement density of the halogen lamp HL in the halogen heating portion 4 is high. The region facing the peripheral edge portion is higher than the region facing the central portion of the silicon substrate W. Therefore, the amount of light irradiated to the peripheral edge of the silicon substrate W, which tends to generate heat, increases, and the in-plane temperature distribution of the silicon substrate W can be made uniform.

When a predetermined time (0.5 seconds to 5 seconds) has elapsed since the temperature of the silicon substrate W reached the first peak temperature Ts at time t2, the 40 halogen lamps HL of the halogen heating unit 4 are turned off. When the halogen lamp HL is turned off, the temperature of the silicon substrate W rapidly drops from the first peak temperature Ts. The temperature of the silicon substrate W during the temperature decrease is measured by the radiation thermometer 120, and the measurement result is transmitted to the control unit 3. The control unit 3 monitors whether or not the temperature of the silicon substrate W has dropped to a predetermined cooling temperature Ta (second temperature) from the measurement result of the radiation thermometer 120. The temperature lowering rate of the silicon substrate W at the time of lowering the temperature is 50 ° C./sec or more. The cooling temperature Ta is naturally lower than the first peak temperature Ts, and is 600 ° C. or higher and 800 ° C. or lower.

Oxygen dissolved in a silicon single crystal aggregates in the process of cooling the silicon substrate W, which has been rapidly heated to the first peak temperature Ts by light irradiation from the halogen lamp HL, from the first peak temperature Ts to the cooling temperature Ta. As a result, a large amount of oxygen precipitates are formed. FIG. 11 is a diagram schematically showing oxygen precipitates existing in the silicon substrate W cooled to the cooling temperature Ta. As is clear when FIG. 11 is compared with FIG. 10, a large amount of oxygen precipitates 21 are formed in the process of cooling the silicon substrate W from the first peak temperature Ts to the cooling temperature Ta to increase the density. At this time, the oxygen precipitate 21 is uniformly densified over the entire silicon substrate W without being biased.

At time t3 when the temperature of the silicon substrate W drops to the cooling temperature Ta, the surface of the silicon substrate W is irradiated with flash light from the flash lamp FL of the flash heating unit 5. When the flash lamp FL irradiates the flash light, the power supply unit 95 stores the electric charge in the capacitor 93 in advance. Then, in a state where the electric charge is accumulated in the capacitor 93, a pulse signal is output from the pulse generator 31 of the control unit 3 to the IGBT 96 to drive the IGBT 96 on and off.

The waveform of the pulse signal can be defined by inputting a recipe in which the pulse width time (on time) and the pulse interval time (off time) are sequentially set as parameters from the input unit 33. When the operator inputs such a recipe from the input unit 33 to the control unit 3, the waveform setting unit 32 of the control unit 3 sets a pulse waveform that repeats on / off accordingly. Then, the pulse generator 31 outputs a pulse signal according to the pulse waveform set by the waveform setting unit 32. As a result, a pulse signal having a set waveform is applied to the gate of the IGBT 96, and the on / off drive of the IGBT 96 is controlled. Specifically, when the pulse signal input to the gate of the IGBT 96 is on, the IGBT 96 is turned on, and when the pulse signal is off, the IGBT 96 is turned off.

Further, the control unit 3 controls the trigger circuit 97 and applies a high voltage (trigger voltage) to the trigger electrode 91 in synchronization with the timing when the pulse signal output from the pulse generator 31 is turned on. A pulse signal is input to the gate of the IGBT 96 with an electric charge accumulated in the capacitor 93, and a high voltage is applied to the trigger electrode 91 in synchronization with the timing when the pulse signal is turned on, so that the pulse signal is signaled. When is on, a current always flows between the electrodes at both ends in the glass tube 92, and light is emitted by the excitation of xenone atoms or molecules at that time.

In this way, the 30 flash lamps FL of the flash heating unit 5 emit light, and the surface of the silicon substrate W held by the holding unit 7 is irradiated with the flash light. In the present embodiment, by connecting an IGBT 96 as a switching element in the circuit and outputting a pulse signal to the gate, the electric charge supply from the capacitor 93 to the flash lamp FL is intermittently flowed to the flash lamp FL by the IGBT 96. The current is controlled on and off. As a result, so to speak, the light emission of the flash lamp FL is controlled by the chopper, the electric charge accumulated in the capacitor 93 is divided and consumed, and the flash lamp FL repeats blinking in an extremely short time. Since the next pulse is applied to the gate of the IGBT 96 and the current value increases again before the current value flowing through the circuit becomes completely "0", the light emission output is output even while the flash lamp FL is repeatedly blinking. It is not completely "0".

By controlling the on / off of the current flowing through the flash lamp FL by the IGBT 96, the light emission pattern (time waveform of the light emission output) of the flash lamp FL can be freely defined, and the light emission time and the light emission intensity can be freely adjusted. .. The ON / OFF drive pattern of the IGBT 96 is defined by the time of the pulse width input from the input unit 33 and the time of the pulse interval. That is, by incorporating the IGBT 96 in the drive circuit of the flash lamp FL, the light emission pattern of the flash lamp FL can be freely defined only by appropriately setting the pulse width time and the pulse interval time input from the input unit 33. You can do it.

Specifically, for example, when the ratio of the pulse width time to the pulse interval time input from the input unit 33 is increased, the current flowing through the flash lamp FL increases and the light emission intensity becomes stronger. On the contrary, if the ratio of the pulse width time to the pulse interval time input from the input unit 33 is reduced, the current flowing through the flash lamp FL is reduced and the light emission intensity is weakened. Further, if the ratio of the pulse interval time and the pulse width time input from the input unit 33 is appropriately adjusted, the light emission intensity of the flash lamp FL is kept constant. Further, by lengthening the total time of the combination of the pulse width time input from the input unit 33 and the pulse interval time, the current continues to flow through the flash lamp FL for a relatively long time, and the flash lamp FL emits light. The time will be longer. In the present embodiment, the light emission time of the flash lamp FL is set between 0.1 ms and 10 ms.

In this way, the surface of the silicon substrate W is irradiated with flash light from the flash lamp FL for an irradiation time of 0.1 ms or more and 10 ms or less to perform flash heating of the silicon substrate W. By irradiating an extremely short and strong flash light with an irradiation time of 0.1 ms or more and 10 ms or less, the surface of the silicon substrate W is instantaneously raised to the second peak temperature Tp (third temperature). .. The second peak temperature Tp at the time of flash heating is higher than the cooling temperature Ta and is 1200 ° C. or higher. The surface of the silicon substrate W is the main surface of the silicon substrate W on which the device pattern is formed later, and is the upper surface of the silicon substrate W held by the susceptor 74. Further, the back surface of the silicon substrate W is the main surface of the silicon substrate W on the opposite side of the front surface.

By irradiating the silicon substrate W with flash light for an irradiation time of 0.1 ms or more and 10 ms or less to instantaneously heat the surface of the silicon substrate W to the second peak temperature Tp, the silicon substrate W The oxygen precipitate 21 can be extinguished from the surface. FIG. 12 is a diagram schematically showing oxygen precipitates existing in the silicon substrate W after flash heating. As described above, in the process of cooling the silicon substrate W rapidly heated to the first peak temperature Ts by light irradiation from the halogen lamp HL from the first peak temperature Ts to the cooling temperature Ta, the silicon substrate W including the surface The oxygen precipitate 21 is uniformly densified over the entire area (FIG. 11). When the silicon substrate W is irradiated with a strong flash light for an extremely short irradiation time of 0.1 ms or more and 10 ms or less, only the surface of the silicon substrate W is instantaneously raised to the second peak temperature Tp. On the other hand, the portion other than the surface of the silicon substrate W hardly rises from the cooling temperature Ta. As a result, as shown in FIG. 12, among the oxygen precipitates 21 which have been densified in the process of cooling the silicon substrate W from the first peak temperature Ts to the cooling temperature Ta, the oxygen precipitates 21 momentarily reach the second peak temperature Tp. Only the oxygen precipitate 21 existing on the surface of the heated silicon substrate W disappears (annealed out) by outward diffusion, and the oxygen precipitate 21 existing at a high density other than the surface of the silicon substrate W remains as it is. It will remain. In addition, crystal defects are also recovered on the surface of the silicon substrate W that instantaneously rises to the second peak temperature Tp.

In flash heating, the irradiation time of the flash light is extremely short, 0.1 ms to 10 ms. Therefore, the surface temperature of the silicon substrate W is instantaneously raised to the second peak temperature Tp, and then immediately. The temperature drops rapidly. The temperature of the silicon substrate W during the temperature decrease is measured by the radiation thermometer 120, and the measurement result is transmitted to the control unit 3. The control unit 3 monitors whether or not the temperature of the silicon substrate W has dropped to a predetermined temperature based on the measurement result of the radiation thermometer 120. Then, after the temperature of the silicon substrate W is lowered to a predetermined value or less, the pair of transfer arms 11 of the transfer mechanism 10 horizontally move from the retracted position to the transfer operation position again and rise, so that the lift pin 12 is a susceptor. The silicon substrate W that protrudes from the upper surface of the 74 and has been heat-treated is received from the susceptor 74. Subsequently, the transfer opening 66 closed by the gate valve 185 is opened, the silicon substrate W placed on the lift pin 12 is carried out by the transfer robot outside the apparatus, and the silicon substrate W in the heat treatment apparatus 1 is heat-treated. Is completed.

In the first embodiment, the silicon substrate W rapidly heated to the first peak temperature Ts by light irradiation from the halogen lamp HL is lowered from the first peak temperature Ts to the cooling temperature Ta, whereby the entire silicon substrate W is affected. Oxygen precipitate 21 is generated to uniformly increase the density. Then, the silicon substrate W is irradiated with flash light for an irradiation time of 0.1 ms or more and 10 ms or less to instantaneously heat the surface of the silicon substrate W to the second peak temperature Tp. The oxygen precipitate 21 is extinguished only from the surface of W.

As a result, the oxygen precipitate 21 does not exist on the surface of the silicon substrate W, and the oxygen precipitate 21 exists at a high density inside the silicon substrate W except for the surface. Since the oxygen precipitate 21 does not exist on the surface of the silicon substrate W, which is the device active region, it is possible to prevent adverse effects on the device characteristics due to the oxygen precipitate 21 such as junction leakage. On the other hand, since oxygen precipitates 21 are present at a high density inside the silicon substrate W except for the surface, the oxygen precipitates 21 effectively function as a gettering site for capturing metal impurities mixed in the process. It will be.

Further, in the first embodiment, the halogen lamp HL is turned off after rapid heating, and the temperature of the silicon substrate W is once lowered to the cooling temperature Ta before the flash light irradiation. By temporarily lowering the temperature of the silicon substrate W to the cooling temperature Ta, the oxygen precipitate 21 is densified and the thermal budget from rapid heating to flash heating is reduced. As a result, only the surface of the silicon substrate W can be heated to the second peak temperature Tp without raising the temperature inside the silicon substrate W from the cooling temperature Ta at the time of flash light irradiation, and the inside of the silicon substrate W can be heated. The oxygen precipitate 21 can be extinguished only from the surface while leaving the oxygen precipitate 21.

<Second Embodiment>
Next, the second embodiment of the present invention will be described. The overall configuration of the heat treatment apparatus 1 of the second embodiment is the same as that of the first embodiment. Further, the processing procedure of the silicon substrate W in the heat treatment apparatus 1 of the second embodiment is substantially the same as that of the first embodiment. The second embodiment differs from the first embodiment in that the heat treatment process is performed under reduced pressure.

In the first embodiment, the heat treatment process of the silicon substrate W was executed in a nitrogen atmosphere at normal pressure, but in the second embodiment, the silicon substrate W is rapidly heated in a reduced pressure state of 100 Torr (about 13330 Pa) or less. And running flash heating. Specifically, the heat treatment space 65 in the chamber 6 accommodating the silicon substrate W is depressurized to 13330 Pa or less before the rapid heating by the halogen lamp HL is started. Then, under the reduced pressure atmosphere, rapid heating by the halogen lamp HL, cooling by turning off the halogen lamp HL, and flash heating by the flash lamp FL are performed as in the first embodiment.

By executing flash heating in a reduced pressure state of 13330 Pa or less, it is possible to prevent the oxygen precipitate 21 diffused outward from reattaching to the surface of the silicon substrate W. Therefore, in the second embodiment, in addition to the same effect as in the first embodiment, the oxygen precipitate 21 can be more reliably eliminated from the surface of the silicon substrate W.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. The overall configuration of the heat treatment apparatus 1 of the third embodiment is the same as that of the first embodiment. Further, the processing procedure of the silicon substrate W in the heat treatment apparatus 1 of the third embodiment is substantially the same as that of the first embodiment. The third embodiment differs from the first embodiment in that the flow rate of the nitrogen gas supplied into the chamber 6 is changed.

Nitrogen gas is supplied to the chamber 6 accommodating the silicon substrate W even before the rapid heating by the halogen lamp HL, and the heat treatment space 65 has a nitrogen atmosphere. During the rapid heating by the halogen lamp HL, the flow rate of the nitrogen gas supplied into the chamber 6 is, for example, 30 liters / minute. In the third embodiment, the flow rate of the nitrogen gas supplied into the chamber 6 is increased from 30 liters / minute while the halogen lamp HL is turned off and the silicon substrate W is lowered from the first peak temperature Ts to the cooling temperature Ta. It is increased to 100 liters / minute. Then, flash heating is performed by the flash lamp FL in a state where the flow rate of the nitrogen gas supplied into the chamber 6 is 100 liters / minute.

By performing flash heating with the flow rate of the nitrogen gas supplied into the chamber 6 increased from 30 liters / minute to 100 liters / minute, the oxygen precipitate 21 diffused outward is brought into the chamber 6 together with the flow rate of the nitrogen gas. It becomes easy to be discharged to the outside, and it is possible to prevent the oxygen precipitate 21 from reattaching to the surface of the silicon substrate W. Therefore, in the third embodiment, in addition to the same effect as in the first embodiment, the oxygen precipitate 21 can be more reliably eliminated from the surface of the silicon substrate W.

<Modification example>
Although the embodiments of the present invention have been described above, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention. For example, in each of the above embodiments, the halogen lamp HL is turned off after rapid heating to lower the temperature of the silicon substrate W to the cooling temperature Ta, but instead, the output of the halogen lamp HL is lowered to make silicon. The temperature of the substrate W may be lowered from the first peak temperature Ts to the cooling temperature Ta.

Further, in the third embodiment, the flow rate of the nitrogen gas supplied into the chamber 6 was increased from 30 liters / minute to 100 liters / minute, but the flow rate is not limited to these, and the silicon substrate W is used. Any form may be used as long as the supply flow rate of nitrogen gas is increased while the temperature is being lowered.

Further, in each of the above embodiments, the flash heating unit 5 is provided with 30 flash lamp FLs, but the present invention is not limited to this, and the number of flash lamp FLs may be any number. it can. Further, the flash lamp FL is not limited to the xenon flash lamp, and may be a krypton flash lamp. Further, the number of halogen lamps HL provided in the halogen heating unit 4 is not limited to 40, and can be any number.

1 Heat treatment device 3 Control unit 4 Halogen heating unit 5 Flash heating unit 6 Chamber 7 Holding unit 21 Oxygen deposit 65 Heat treatment space 74 Suceptor 75 Holding plate 77 Board support pin 93 Capacitor 95 Power supply unit 96 IGBT
120 Radiation Thermometer FL Flash Lamp HL Halogen Lamp W Silicon Substrate

Claims (3)

It is a heat treatment method for a silicon substrate manufactured by the Czochralski method.
A first heating step of heating the silicon substrate to a first temperature by irradiating light from a halogen lamp, and
A temperature lowering step of turning off the halogen lamp or reducing the output of the halogen lamp to lower the temperature of the silicon substrate to a second temperature lower than the first temperature to generate oxygen precipitates in the silicon substrate.
A second that irradiates the silicon substrate with flash light from a flash lamp to heat the surface of the silicon substrate to a third temperature higher than the second temperature to eliminate the oxygen precipitates from the surface of the silicon substrate. The heating process and
Equipped with a,
In the first heating step, nitrogen gas is supplied at a first flow rate into the chamber accommodating the silicon substrate.
The second heating step is a method for heat-treating a silicon substrate, which comprises supplying nitrogen gas into the chamber at a second flow rate higher than the first flow rate . In the method for heat-treating a silicon substrate according to claim 1,
A method for heat-treating a silicon substrate, characterized in that the irradiation time of the flash light in the second heating step is 0.1 ms or more and 10 ms or less. In the method for heat-treating a silicon substrate according to claim 1 or 2.
A method for heat-treating a silicon substrate, further comprising a depressurizing step of reducing the pressure inside the chamber accommodating the silicon substrate to 13330 Pa or less before the first heating step.

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