JP2013161936A - Heat treatment apparatus and heat treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat treatment apparatus capable of preventing crack of a substrate in application of flash light, and a heat treatment method.SOLUTION: An upper flash lamp UFL is provided above a chamber 6 for housing a semiconductor wafer W, and a lower flash lamp LFL is provided below the chamber 6. Flash light from the upper flash lamp UFL and flash light from the lower flash lamp LFL are applied to a rear surface of the semiconductor wafer W at a time. Thereby temperature distribution generates that the surface temperature and the rear surface temperature of the semiconductor wafer W reach to the maximum temperature, and the inside temperature in a thickness direction reaches to the minimum temperature. Therefore a tensile stress generated due to a thermal expansion of the surface and the rear surface of the semiconductor wafer W acts on the inside in the thickness direction. Therefore, even if blem is formed on the rear surface, it is possible to prevent crack taking the blem as a starting point, of the semiconductor wafer W in application of flash light.

Description

  The present invention relates to a heat treatment apparatus and a heat treatment method for heating a thin plate-shaped precision electronic substrate (hereinafter simply referred to as “substrate”) such as a semiconductor wafer or a glass substrate for a liquid crystal display device by irradiating flash light. .

  In the semiconductor device manufacturing process, impurity introduction is an indispensable step for forming a pn junction in a semiconductor wafer. Currently, impurities are generally introduced by ion implantation and subsequent annealing. The ion implantation method is a technique in which impurity elements such as boron (B), arsenic (As), and phosphorus (P) are ionized and collided with a semiconductor wafer at a high acceleration voltage to physically perform impurity implantation. The implanted impurities are activated by annealing. At this time, if the annealing time is about several seconds or more, the implanted impurities are deeply diffused by heat, and as a result, the junction depth becomes deeper than required, and there is a possibility that good device formation may be hindered.

  Therefore, in recent years, flash lamp annealing (FLA) has attracted attention as an annealing technique for heating a semiconductor wafer in an extremely short time. Flash lamp annealing is a semiconductor wafer in which impurities are implanted by irradiating the surface of the semiconductor wafer with flash light using a xenon flash lamp (hereinafter, simply referred to as “flash lamp” means xenon flash lamp). Is a heat treatment technique for raising the temperature of only the surface of the material in a very short time (several milliseconds or less).

  The radiation spectral distribution of a xenon flash lamp ranges from the ultraviolet region to the near infrared region, has a shorter wavelength than the conventional halogen lamp, and almost coincides with the fundamental absorption band of a silicon semiconductor wafer. Therefore, when the semiconductor wafer is irradiated with flash light from the xenon flash lamp, the semiconductor wafer can be rapidly heated with little transmitted light. Further, it has been found that if the flash light irradiation is performed for a very short time of several milliseconds or less, only the vicinity of the surface of the semiconductor wafer can be selectively heated. For this reason, if the temperature is raised for a very short time by the xenon flash lamp, only the impurity activation can be performed without deeply diffusing the impurities.

  As a heat treatment apparatus using such a xenon flash lamp, in Patent Document 1, a semiconductor wafer is placed on a hot plate, preheated to a predetermined temperature, and then the surface temperature is desired by irradiation with flash light from the flash lamp. An apparatus for raising the temperature to the processing temperature is disclosed. In Patent Document 2, a flash lamp is disposed on the upper side of the semiconductor wafer, a halogen lamp is disposed on the lower side, the semiconductor wafer is preheated by light irradiation from the halogen lamp, and then the flash lamp is applied to the wafer surface. An apparatus for performing flash light irradiation is disclosed. In any case, the impurity is activated by preheating to a temperature at which the implanted impurities do not diffuse, and then irradiating the surface of the semiconductor wafer with flash light to rapidly heat the surface to the processing temperature. .

JP 2007-5532 A JP 2009-231676 A

  In the conventional flash lamp annealing described above, the surface temperature is rapidly increased by irradiating the surface of the semiconductor wafer with flash light after preheating. As a result, the surface having the highest temperature in the thickness direction of the semiconductor wafer is the front surface, and the surface having the lowest temperature is always the back surface. As a result, a large thermal expansion occurs on the surface of the semiconductor wafer, whereas a tensile stress acts on the back surface because the degree of thermal expansion is relatively small on the back surface.

  In addition, there may be a scratch on the back surface of the semiconductor wafer. Such scratches are often formed in a process prior to flash lamp annealing. When the surface of a semiconductor wafer having scratches on the back surface is irradiated with flash light and heated, tensile stress acts on the back surface, and as a result, there has been a problem that wafer cracking occurs starting from scratches on the back surface.

  This invention is made | formed in view of the said subject, and it aims at providing the heat processing apparatus and heat processing method which can prevent the crack of the board | substrate at the time of flash light irradiation.

  In order to solve the above-mentioned problems, a first aspect of the present invention is a heat treatment apparatus for heating a substrate by irradiating the substrate with flash light, a chamber for accommodating the substrate, and a support member for supporting the substrate in the chamber. A first flash lamp that irradiates the back surface of the substrate supported by the support member with flash light and heats the substrate from the back surface, and irradiates the surface of the substrate supported by the support member with flash light and And a second flash lamp that heats the substrate from the surface, wherein at least a part of the flash light irradiation period of the first flash lamp and the flash light irradiation period of the second flash lamp overlap each other.

  According to a second aspect of the present invention, in the heat treatment apparatus according to the first aspect of the present invention, the light emission output of the first flash lamp is different from the light emission output of the second flash lamp.

  According to a third aspect of the present invention, in the heat treatment apparatus according to the first or second aspect of the present invention, the start of the flash light irradiation period of the first flash lamp and the start of the flash light irradiation period of the second flash lamp Are different.

  According to a fourth aspect of the present invention, in the heat treatment apparatus according to any one of the first to third aspects, the end of the flash light irradiation period of the first flash lamp and the flash light irradiation period of the second flash lamp. It is characterized by being different from the end of.

  According to a fifth aspect of the present invention, in the heat treatment apparatus according to the fourth aspect of the present invention, the end of the flash light irradiation period of the first flash lamp is within a heat conduction time required for heat conduction from the back surface to the surface. The range is earlier than the end of the flash light irradiation period of the second flash lamp.

  The invention of claim 6 is the heat treatment apparatus according to any one of claims 1 to 5, wherein the first flash lamp and the second flash lamp are rod-shaped lamps; The second flash lamps are arranged to be orthogonal to each other.

  According to a seventh aspect of the present invention, in the heat treatment apparatus according to any one of the first to sixth aspects of the present invention, light shielding is provided between the first flash lamp and the second flash lamp around the support member. A light shielding member is provided.

  According to an eighth aspect of the present invention, in the heat treatment apparatus according to any one of the first to seventh aspects, the support member is made of quartz and holds the substrate in a non-contact manner by a Bernoulli effect. A chuck is included.

  According to a ninth aspect of the present invention, in the heat treatment method for heating the substrate by irradiating the substrate with flash light, the substrate is supported by irradiating the back surface of the substrate supported by the support member in the chamber with the flash light. A back flash heating step for heating from the back side, and a surface flash heating step for heating the substrate from the surface by irradiating the surface of the substrate supported by the support member with flash light. The flash light irradiation period and at least a part of the flash light irradiation period in the surface flash heating step overlap each other.

  The invention of claim 10 is the heat treatment method according to claim 9, wherein the light emission output of the flash light in the back flash heating step is different from the light emission output of the flash light in the surface flash heating step. Features.

  The invention of claim 11 is the heat treatment method according to the invention of claim 9 or claim 10, wherein the flash light irradiation period in the back surface flash heating step and the flash light irradiation period in the surface flash heating step are It is different from the beginning.

  The invention of claim 12 is the heat treatment method according to any one of claims 9 to 11, wherein the flash light irradiation period in the back flash heating step and the flash light in the surface flash heating step are used. It is characterized by being different from the end of the irradiation period.

  The invention according to claim 13 is the heat treatment method according to claim 12, wherein the end of the flash light irradiation period in the back surface flash heating step is within a heat conduction time required for heat conduction from the back surface to the surface. In the range, it is earlier than the end of the flash light irradiation period in the surface flash heating step.

  According to the first to eighth aspects of the present invention, the flash light irradiation period of the first flash lamp that irradiates the back surface of the substrate with the flash light and the flash light irradiation period of the second flash lamp that irradiates the surface of the substrate with the flash light. Since at least a part of the two overlap each other, the lowest temperature region at the time of flash light irradiation appears inside the substrate in the thickness direction, and cracking of the substrate at the time of flash light irradiation can be prevented.

  In particular, according to the invention of claim 5, the end of the flash light irradiation period of the first flash lamp is within the heat conduction time required for heat conduction from the back surface to the front surface within the flash light irradiation period of the second flash lamp. Since it is earlier than the end, heating on the front side can be assisted by heat conduction from the back side to the front side even at the end of the flash light irradiation period of the second flash lamp.

  In particular, according to the invention of claim 6, the first flash lamp and the second flash lamp are rod-shaped lamps, and the first flash lamp and the second flash lamp are arranged so as to be orthogonal to each other. The first flash lamp and the second flash lamp can mutually eliminate the uneven illuminance caused by the flash light irradiation, and the in-plane temperature distribution of the substrate can be made uniform.

  In particular, according to the seventh aspect of the present invention, since the light shielding member for shielding light between the first flash lamp and the second flash lamp is provided around the support member, the flash light from each flash lamp is transmitted to the edge portion of the substrate. Can be prevented.

  In particular, according to the invention of claim 8, since the support member is made of quartz and includes a Bernoulli chuck that holds the substrate in a non-contact manner by the Bernoulli effect, a stress that restrains deformation of the substrate during flash light irradiation acts. Without cracking the substrate.

  According to the invention of claim 9 to claim 13, in the flash light irradiation period in the back surface flash heating step of irradiating the back surface of the substrate with flash light and in the surface flash heating step of irradiating the surface of the substrate with flash light. Since at least a part of the flash light irradiation period overlaps with each other, the lowest temperature region at the time of flash light irradiation appears inside the substrate in the thickness direction, and cracking of the substrate at the time of flash light irradiation can be prevented.

  In particular, according to the invention of claim 13, the end of the flash light irradiation period in the back surface flash heating step is within the range of the heat conduction time required for heat conduction from the back surface to the surface, and the flash light irradiation in the surface flash heating step. Since it is earlier than the end of the period, heating of the front side can be assisted by heat conduction from the back side to the front side even at the end of the flash light irradiation period in the front side flash heating step.

It is a figure which shows the principal part structure of the heat processing apparatus which concerns on this invention. It is a perspective view which shows the arrangement | positioning relationship of an upper side flash lamp, a lower side flash lamp, and a halogen lamp. It is a figure which shows the drive circuit of a flash lamp. It is a flowchart which shows the process sequence of the semiconductor wafer in the heat processing apparatus of FIG. It is a figure which shows the temperature change of the surface of the semiconductor wafer in 1st Embodiment, and a back surface. It is a figure which shows the light emission output profile of the lower side flash lamp and upper side flash lamp in 1st Embodiment. It is a figure which shows the temperature distribution in the thickness direction of the semiconductor wafer in 1st Embodiment. It is a figure which shows the temperature change of the surface of a semiconductor wafer in 2nd Embodiment, and a back surface. It is a figure which shows the light emission output profile of the lower side flash lamp and upper side flash lamp in 2nd Embodiment. It is a figure which shows the temperature distribution in the thickness direction of the semiconductor wafer in 2nd Embodiment. It is a figure which shows the temperature change of the surface of a semiconductor wafer in 3rd Embodiment, and a back surface. It is a figure which shows the light emission output profile of the lower side flash lamp and upper side flash lamp in 3rd Embodiment. It is a figure which shows the temperature distribution in the thickness direction of the semiconductor wafer in 3rd Embodiment. It is a figure which shows the temperature change of the surface of a semiconductor wafer in 4th Embodiment, and a back surface. It is a figure which shows the light emission output profile of the lower side flash lamp and upper side flash lamp in 4th Embodiment. It is a figure which shows the temperature distribution in the thickness direction of the semiconductor wafer in 4th Embodiment. It is a figure which shows the temperature distribution in the thickness direction of the semiconductor wafer in 4th Embodiment. It is a figure which shows the principal part structure of the heat processing apparatus of 5th Embodiment. It is a figure which shows an example of Bernoulli chuck. It is a figure which shows the temperature change of the surface of a semiconductor wafer in 5th Embodiment, and a back surface. It is a figure which shows the light emission output profile of the lower side flash lamp and upper side flash lamp in 5th Embodiment. It is a figure which shows the temperature distribution in the thickness direction of the semiconductor wafer in 5th Embodiment. It is a timing chart which shows an example of the flash light irradiation period of an upper side flash lamp and a lower side flash lamp. It is a timing chart which shows the other example of the flash light irradiation period of an upper side flash lamp and a lower side flash lamp. It is a timing chart which shows the other example of the flash light irradiation period of an upper side flash lamp and a lower side flash lamp. It is a figure which shows the other example of Bernoulli chuck.

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

<First Embodiment>
FIG. 1 is a diagram showing a main configuration of a heat treatment apparatus 1 according to the present invention. The heat treatment apparatus 1 is a flash lamp annealing apparatus that performs heat treatment by irradiating a substantially circular semiconductor wafer W as a substrate with flash light. In FIG. 1 and the subsequent drawings, the size and number of each part are exaggerated or simplified as necessary for easy understanding.

  The heat treatment apparatus 1 mainly includes a substantially cylindrical chamber 6 that houses a semiconductor wafer W, a holding unit 7 that holds the semiconductor wafer W in the chamber 6, and the delivery of the semiconductor wafer W to the holding unit 7. A transfer part 79 for performing the above, an upper heating part 5 provided on the upper side of the chamber 6, a lower heating part 4 provided on the lower side of the chamber 6, and a gas supply part for supplying a processing gas into the chamber 6 8 and an exhaust part 2 for exhausting air from the chamber 6. In addition, the heat treatment apparatus 1 includes a control unit 3 that controls each of these units to perform the heat treatment of the semiconductor wafer W.

  The chamber 6 includes a chamber side portion 63 having a substantially cylindrical inner wall whose upper and lower ends are open. The chamber side portion 63 is formed of a metal material (for example, stainless steel) having excellent strength and heat resistance. An upper chamber window 61 and a lower chamber window 64 are respectively attached to the upper opening and the lower opening of the chamber 6 so as to be closed. A space surrounded by the chamber side portion 63, the upper chamber window 61, and the lower chamber window 64 is defined as a heat treatment space 65.

  The upper chamber window 61 constituting the ceiling portion of the chamber 6 is a disk-shaped member made of quartz, and functions as a quartz window that transmits light emitted from the upper heating unit 5 to the heat treatment space 65. Similarly, the lower chamber window 64 constituting the floor of the chamber 6 is also a disk-shaped member made of quartz, and functions as a quartz window that transmits the light emitted from the lower heating unit 4 to the heat treatment space 65. To do.

  In order to maintain the airtightness of the heat treatment space 65, the upper chamber window 61, the lower chamber window 64, and the chamber side portion 63 are sealed by an O-ring (not shown). Specifically, an O-ring is sandwiched between the lower peripheral edge of the upper chamber window 61 and the upper peripheral edge of the lower chamber window 64 and the chamber side 63 to prevent gas from flowing in and out of these gaps. It is out.

  The chamber side 63 is provided with a transfer opening 66 for carrying in and out the semiconductor wafer W. The transfer opening 66 can be opened and closed by a gate valve (not shown). When the transfer opening 66 is opened, the semiconductor wafer W can be carried into and out of the chamber 6 by a transfer robot (not shown). When the transfer opening 66 is closed, the heat treatment space 65 becomes a sealed space in which ventilation with the outside is blocked.

  The holding unit 7 provided in the chamber 6 includes a support ring 72 and a light shielding member 71. The light shielding member 71 is fixed to the inner wall surface of the chamber side portion 63. The light shielding member 71 may be formed of a material that is opaque to the light from the flash lamp FL and the halogen lamp HL, for example, a ceramic such as silicon carbide (SiC), aluminum nitride (AlN), or boron nitride (BN). The light shielding member 71 is provided in an annular shape so as to protrude from the inner wall of the substantially cylindrical chamber side portion 63. A support ring 72 is placed on the inner periphery of the upper surface of the light shielding member 71. That is, the light shielding member 71 is provided around the support ring 72.

  The support ring 72 is a ring-shaped (ring-shaped) plate-shaped member. The support ring 72 is made of, for example, silicon carbide. The outer diameter of the annular support ring 72 is larger than the diameter of the semiconductor wafer W (φ300 mm in this embodiment). Further, the inner diameter of the support ring 72 is slightly smaller than the diameter of the semiconductor wafer W. For this reason, the support ring 72 can support the peripheral portion of the semiconductor wafer W at the inner peripheral portion thereof.

  The semiconductor wafer W carried into the chamber 6 is supported in a horizontal posture (a posture in which the normal line of the main surface is directed in the vertical direction) in the chamber 6 by the support ring 72. In the present embodiment, since both the support ring 72 and the light shielding member 71 are made of a material that is opaque to the light from the flash lamp FL and the halogen lamp HL, the semiconductor wafer W supported by the support ring 72 is formed. The upper side heating part 5 and the lower side heating part 4 are optically interrupted around. That is, the light from the upper heating unit 5 does not go around the outer periphery of the semiconductor wafer W and reach the lower surface peripheral portion, but conversely, the light from the lower heating unit 4 reaches the upper surface peripheral portion. Is also prevented.

  A transfer unit 79 is provided below the holding unit 7. The transfer unit 79 is configured to be movable in the horizontal direction and in the vertical direction by a drive mechanism (not shown). When the transfer operation is not performed, the transfer unit 79 stands by at a standby position below the light shielding member 71. When the semiconductor wafer W is transferred to the holding unit 7, the transfer unit 79 moves horizontally from the standby position to the inner side of the inner periphery of the support ring 72 and then rises along the vertical direction. Thereby, the upper end of the pin of the transfer part 79 protrudes from the upper surface of the support ring 72. When the transfer operation is completed, the transfer unit 79 returns to the standby position again.

The gas supply unit 8 supplies a processing gas to the heat treatment space 65 in the chamber 6. The gas supply unit 8 includes a processing gas supply source 81 and a valve 82, and supplies the processing gas to the heat treatment space 65 by opening the valve 82. The processing gas supplied by the gas supply unit 8 is an inert gas such as nitrogen (N ₂ ), argon (Ar), helium (He), or oxygen (O ₂ ), hydrogen (H ₂ ), chlorine (Cl ₂ ), a reactive gas such as water vapor (H ₂ O), hydrogen chloride (HCl), ozone (O ₃ ), ammonia (NH ₃ ), or the like can be used. The processing gas supply source 81 may be constituted by a gas tank provided in the heat treatment apparatus 1 and a feed pump, or use the power of the factory where the heat treatment apparatus 1 is installed. May be.

  The exhaust unit 2 includes an exhaust device 21 and a valve 22, and exhausts the atmosphere in the chamber 6 by opening the valve 22. As the exhaust device 21, an exhaust utility of a factory where the vacuum pump or the heat treatment device 1 is installed can be used. When a vacuum pump is employed as the exhaust device 21 and the atmosphere of the heat treatment space 65 that is a sealed space is exhausted without supplying the processing gas from the gas supply unit 8, the inside of the chamber 6 can be decompressed to a vacuum atmosphere. Further, even when a vacuum pump is not used as the exhaust device 21, the inside of the chamber 6 is decompressed to a pressure lower than the atmospheric pressure by performing exhaust without supplying the processing gas from the gas supply unit 8. Can do.

  In the present embodiment, when the semiconductor wafer W is held by the holding unit 7, the heat treatment space 65 is vertically separated by the light shielding member 71, the support ring 72, and the semiconductor wafer W. Therefore, as shown in FIG. 1, the gas supply unit 8 supplies the processing gas to the upper side and the lower side of the holding unit 7 of the heat treatment space 65, and the exhaust unit 2 exhausts the gas from each. Is preferred.

  The upper heating unit 5 is provided above the chamber 6. The upper heating unit 5 includes a light source having a plurality of flash lamps FL, and a reflector 52 provided so as to cover the light source. The upper heating unit 5 irradiates flash light from the flash lamp FL on the upper surface of the semiconductor wafer W supported by the support ring 72 in the chamber 6 through the quartz upper chamber window 61.

  On the other hand, the lower heating unit 4 is provided below the chamber 6. The lower heating unit 4 includes a light source having a plurality of flash lamps FL and a plurality of halogen lamps HL, and a reflector 42 provided to cover the lower side of the light source. The lower heating unit 4 irradiates the lower surface of the semiconductor wafer W supported by the support ring 72 in the chamber 6 from the flash lamp FL or the halogen lamp HL through the lower chamber window 64 of quartz. When the flash lamp FL of the upper heating unit 5 and the flash lamp FL of the lower heating unit 4 are particularly distinguished, the flash lamp FL of the upper heating unit 5 is referred to as an upper flash lamp (second flash lamp) UFL. The flash lamp FL of the side heating unit 4 is referred to as a lower flash lamp (first flash lamp) LFL. Although the upper flash lamp UFL and the lower flash lamp LFL are the same bar-shaped xenon flash lamps although the arrangement positions are different, they are simply referred to as the flash lamp FL when it is not necessary to distinguish them.

  FIG. 2 is a perspective view showing an arrangement relationship of the upper flash lamp UFL, the lower flash lamp LFL, and the halogen lamp HL. Each of the plurality of upper flash lamps UFL is a rod-shaped lamp having a long cylindrical shape, and the longitudinal direction of each of the upper flash lamps UFL is along the main surface of the semiconductor wafer W supported by the support ring 72 (that is, along the horizontal direction). ) They are arranged in a plane so as to be parallel to each other. Similarly, the plurality of lower flash lamps LFL are also rod-shaped lamps each having a long cylindrical shape, and the respective longitudinal directions thereof are parallel to each other along the main surface of the semiconductor wafer W supported by the support ring 72. Are arranged in a plane.

  As shown in FIG. 2, the upper flash lamp UFL of the upper heating unit 5 and the lower flash lamp LFL of the lower heating unit 4 are arranged to be orthogonal to each other. That is, when viewed from the upper side of the upper heating unit 5, the upper flash lamp UFL and the lower flash lamp LFL are arranged so as to cross like a cross.

  FIG. 3 is a diagram showing a driving circuit for 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. As shown in FIG. 3, 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 employed. 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 and an anode and a cathode are disposed at both ends thereof, and a trigger electrode provided on the outer peripheral surface of the glass tube 92. 91. A predetermined voltage is applied to the capacitor 93 by the power supply unit 95, and a charge corresponding to the applied voltage (charging voltage) is charged. 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 high power. A pulse signal is applied from the pulse generator 31 of the control unit 3 to the gate of the IGBT 96. The IGBT 96 is turned on when a voltage higher than a predetermined value (High voltage) is applied to the gate of the IGBT 96, and the IGBT 96 is turned off when a voltage lower than the predetermined value (Low voltage) is applied. In this way, the drive circuit including the flash lamp FL is turned on / off by the IGBT 96. When the IGBT 96 is turned on / off, the connection between the flash lamp FL and the corresponding capacitor 93 is interrupted.

  Even if the IGBT 96 is turned on while the capacitor 93 is charged and a high voltage is applied to both end electrodes of the glass tube 92, the xenon gas is electrically an insulator, so that the glass is normal in the state. No electricity flows in the tube 92. However, when the trigger circuit 97 applies a high voltage to the trigger electrode 91 to break the insulation, an electric current instantaneously flows in the glass tube 92 due to the discharge between the both end electrodes, and excitation of the xenon atoms or molecules at that time Emits light.

  A drive circuit as shown in FIG. 3 is individually provided for each of the plurality of upper flash lamps UFL of the upper heating unit 5 and the plurality of lower flash lamps LFL of the lower heating unit 4. Therefore, the upper flash lamp UFL and the lower flash lamp LFL can have different control modes.

  Returning to FIG. 2, the plurality of halogen lamps HL of the lower heating unit 4 are rod-shaped lamps each having a long cylindrical shape, and the main surface of the semiconductor wafer W whose longitudinal direction is supported by the support ring 72. Are arranged in a plane so as to be parallel to each other. As shown in FIG. 2, the lower flash lamp LFL and the halogen lamp HL are arranged so as to be orthogonal to each other. Therefore, the upper flash lamp UFL and the halogen lamp HL are consequently parallel to each other.

  In the lower heating unit 4, the arrangement surface of the lower flash lamp LFL is located above the arrangement surface of the halogen lamp HL. That is, the lower flash lamp LFL is disposed closer to the support ring 72 in the chamber 6 than the halogen lamp HL. Accordingly, part of the light emitted from the halogen lamp HL passes through the flash lamp FL and enters the chamber 6.

  The halogen lamp HL is a filament-type light source that emits light by making the filament incandescent by energizing the filament disposed inside the glass tube. Inside the glass tube, a gas obtained by introducing a trace amount of a halogen element (iodine, bromine, etc.) into an inert gas such as nitrogen or argon is enclosed. By introducing a halogen element, it is possible to set the filament temperature to a high temperature while suppressing breakage of the filament. Therefore, the halogen lamp HL has a characteristic that it has a longer life than a normal incandescent bulb and can continuously radiate strong light.

  Returning to FIG. 1, the reflector 52 of the upper heating unit 5 is provided above the plurality of upper flash lamps UFL so as to cover them entirely. The basic function of the reflector 52 is to reflect the flash light emitted from the plurality of upper flash lamps UFL toward the heat treatment space 65. On the other hand, the reflector 42 of the lower heating unit 4 is provided below the plurality of lower flash lamps LFL and halogen lamps HL so as to cover them entirely. The basic function of the reflector 42 is to reflect light emitted from the plurality of lower flash lamps LFL and the plurality of halogen lamps HL toward the heat treatment space 65. The reflector 52 and the reflector 42 are formed of an aluminum alloy plate, and the surface (the surface facing the flash lamp FL) is roughened by blasting to exhibit a satin pattern.

  The control unit 3 controls the various operation 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 that performs various arithmetic processes, a ROM that is a read-only memory that stores basic programs, a RAM that is a readable and writable memory that stores various information, control software, data, and the like. It is configured with a magnetic disk. The processing in the heat treatment apparatus 1 proceeds as the CPU of the control unit 3 executes a predetermined processing program. As shown in FIG. 3, 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 in accordance therewith.

  Next, a processing procedure of the semiconductor wafer W in the heat treatment apparatus 1 having the above configuration will be described. FIG. 4 is a flowchart showing a processing procedure for the semiconductor wafer W in the heat treatment apparatus 1. 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, a gate valve (not shown) is opened to open the transfer opening 66, and a semiconductor wafer W to be processed is transferred into the chamber 6 through the transfer opening 66 by a transfer robot outside the apparatus (step S11). . In the first embodiment, a semiconductor wafer W to be processed is a silicon semiconductor substrate having a pattern formed on the surface and implanted with impurities. Note that pattern formation and impurity implantation may be performed by, for example, a photolithography apparatus and an ion implantation apparatus installed separately from the heat treatment apparatus 1.

  The hand of the transfer robot holding the semiconductor wafer W enters the chamber 6 from the transfer opening 66 and is directly above the holding unit 7 (more precisely, the center axis of the semiconductor wafer W and the center axis of the support ring 72 are Stops at the position where the two match. Subsequently, after the transfer portion 79 horizontally moves from the lower standby position of the light shielding member 71 to the inner side of the inner periphery of the support ring 72, the transfer portion 79 rises along the vertical direction, and the pin of the transfer portion 79 is supported by the support ring. A semiconductor wafer W is received from the hand of the transfer robot protruding above 72. Thereafter, the hand of the transfer robot moves out of the chamber 6 and the transfer opening 66 is closed, whereby the heat treatment space 65 in the chamber 6 is made a sealed space. Then, when the transfer unit 79 that has received the semiconductor wafer W is lowered, the semiconductor wafer W is transferred from the pins of the transfer unit 79 to the support ring 72 (step S12). The semiconductor wafer W is supported such that its central axis coincides with the central axis of the support ring 72. Therefore, the support ring 72 supports the lower surface of the peripheral edge over the entire circumference of the semiconductor wafer W. The transfer unit 79 that has transferred the semiconductor wafer W to the support ring 72 returns to the standby position.

  Here, the surface of the semiconductor wafer W is a main surface on which a device is formed. As described above, a pattern is formed on the surface and impurities are implanted. On the surface of the semiconductor wafer W, the in-plane distribution of the absorptance is not uniform because the absorptance of light varies depending on the pattern. On the other hand, the back surface of the semiconductor wafer W is a main surface opposite to the front surface. Normally, neither film formation nor pattern formation is performed on the back surface of the semiconductor wafer W. However, as a result of film formation on the front surface, a thin film such as an oxide film, a nitride film, or polysilicon may be inevitably formed on the back surface. Made. In any case, on the back surface of the semiconductor wafer W, the in-plane distribution of the light absorptance is uniform. Further, scratches may be formed on the back surface of the semiconductor wafer W by a photolithography apparatus or an ion implantation apparatus which is a previous process.

  In the first embodiment, the semiconductor wafer W is loaded into the chamber 6 and supported by the support ring 72 with the surface of the semiconductor wafer W facing upward. The upper surface of the semiconductor wafer W is a main surface facing the upper side in the vertical direction, and the lower surface is a surface facing the lower side. Therefore, the surface of the semiconductor wafer W may face the upper surface, and may face the lower surface.

  In addition, after the transfer opening 66 is closed and the heat treatment space 65 is closed, the valve 82 is opened to supply a processing gas (nitrogen gas in this embodiment) from the gas supply unit 8 to the heat treatment space 65. At the same time, the valve 22 is opened and the exhaust unit 2 exhausts from the heat treatment space 65. Thereby, an air flow of nitrogen gas is formed in the heat treatment space 65 in the chamber 6, and the periphery of the semiconductor wafer W held by the holding unit 7 is made a nitrogen atmosphere. From the viewpoint of increasing the atmosphere replacement efficiency in the chamber 6, the gas supply unit 8 is provided after the exhaust unit 2 exhausts the heat treatment space 65 without supplying the processing gas to once form a reduced-pressure atmosphere lower than the atmospheric pressure. It is preferable to supply the processing gas from.

  After the semiconductor wafer W is placed on and supported by the support ring 72 of the holding unit 7, a plurality of halogen lamps HL of the lower heating unit 4 are turned on at the same time under the control of the control unit 3 and preheating is started. (Step S13). The halogen light emitted from the halogen lamp HL is irradiated from the back surface of the semiconductor wafer W supported by the support ring 72 through the lower chamber window 64 formed of quartz. The temperature of the semiconductor wafer W rises by receiving light irradiation from the halogen lamp HL. In addition, since the transfer part 79 is retracted to the standby position below the light shielding member 71, there is no obstacle to preheating by the halogen lamp HL. In addition, a part of the light emitted from the halogen lamp HL passes through the flash lamp FL and is irradiated on the back surface of the semiconductor wafer W. However, since the flash lamp FL does not include a filament, this is also preheated. There will be no obstacles.

  The semiconductor wafer W is heated to a preset preheating temperature by light irradiation from the halogen lamp HL. The preheating temperature is 300 ° C. or higher and 800 ° C. or lower, and is 500 ° C. in the first embodiment. After the temperature of the semiconductor wafer W reaches the preheating temperature, the control unit 3 maintains the output of the halogen lamp HL so as to maintain the semiconductor wafer W at the preheating temperature for a while. Specifically, the temperature of the semiconductor wafer W is measured by a temperature sensor (contact thermometer or radiation thermometer) (not shown), and the temperature of the semiconductor wafer W measured by the temperature sensor reaches the preheating temperature. At this point, the control unit 3 controls the output of the halogen lamp HL to maintain the temperature of the semiconductor wafer W at approximately the preheating temperature. The time until the temperature of the semiconductor wafer W reaches the preheating temperature from the room temperature and the time for maintaining the preheating temperature are about several seconds.

  Next, after maintaining the temperature of the semiconductor wafer W at the preheating temperature for a predetermined time, the plurality of flash lamps FL (lower flash lamp LFL) of the lower heating unit 4 and the plurality of flash lamps FL (upper side) of the upper heating unit 5 Flash heating is executed by irradiating flash light from the flash lamp UFL to each of the back surface and the front surface of the semiconductor wafer W (step S14). FIG. 5 is a view showing temperature changes on the front surface and the back surface of the semiconductor wafer W. FIG.

  At time t11 when a predetermined time has elapsed since the temperature of the semiconductor wafer W reached the preheating temperature (500 ° C. in the present embodiment), the plurality of flash lamps FL and the upper side heating of the lower heating unit 4 are controlled by the control unit 3. Flash light is emitted from the plurality of flash lamps FL of the unit 5. When the flash lamp FL irradiates flash light, the electric power is accumulated in the capacitor 93 by the power supply unit 95 in advance. Then, in a state where charges are 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 from the input unit 33 a recipe in which the pulse width time (on time) and the pulse interval time (off time) are sequentially set as parameters. 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 that repeatedly turns on and off is applied to the gate of the IGBT 96, and the on / off driving 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 on and the circuit including the capacitor 93 and the flash lamp FL is closed. When the pulse signal is off, the IGBT 96 is off. Thus, the circuit is opened.

  Further, in synchronization with the timing when the pulse signal output from the pulse generator 31 is turned on, the control unit 3 controls the trigger circuit 97 to apply a high voltage (trigger voltage) to the trigger electrode 91. A pulse signal is input to the gate of the IGBT 96 in a state where electric charges are 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. When is turned on, a current always flows between both end electrodes in the glass tube 92, and light is emitted by the excitation of atoms or molecules of xenon at that time.

  A pulse signal that repeatedly turns on and off is output from the control unit 3 to the gate of the IGBT 96, and a high voltage is applied to the trigger electrode 91 in synchronization with the timing at which the pulse signal is turned on. Current flows intermittently. In this way, by connecting the IGBT 96 as a switching element in the circuit and outputting a pulse signal that repeatedly turns on and off to the gate, the supply of charge from the capacitor 93 to the flash lamp FL is intermittently performed by the IGBT 96 and the flash lamp FL is supplied. The flowing current is controlled. That is, a current of a sawtooth waveform that increases in the glass tube 92 of the flash lamp FL when the pulse signal input to the gate of the IGBT 96 is on and decreases when it is off is applied to the flash lamp FL. Flowing. Each current waveform corresponding to each pulse is defined by a constant of the coil 94.

  Such a sawtooth current flows, and the flash lamp FL emits light. By intermittently supplying the charge from the capacitor 93 to the flash lamp FL by the IGBT 96 and making the waveform of the current flowing through the flash lamp FL into a sawtooth waveform, the light emission of the flash lamp FL is chopper-controlled. That is, the electric charge accumulated in the capacitor 93 is divided and consumed, and the flash lamp FL repeatedly blinks in a very short time. However, since the next pulse is applied to the gate of the IGBT 96 before the current value flowing through the flash lamp FL becomes completely “0”, the current value increases again, so that the light is emitted even while the flash lamp FL is repeatedly blinking. The output is not completely “0”. Therefore, when pulse signals with relatively short intervals are output to the IGBT 96, the flash lamp FL is continuously emitting light during that time.

  The waveform of the pulse signal can be arbitrarily set by defining the time of the pulse width and the time of the pulse interval. For this reason, the on / off drive of the IGBT 96 can be arbitrarily controlled, and by setting a large number of pulses having a relatively short pulse interval, the light emission time of the flash lamp FL can be appropriately set to 10 milliseconds to 1000 milliseconds. Can do.

  FIG. 6 is a diagram showing output waveforms (profiles) of light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL. In the first embodiment, the light emission of the lower flash lamp LFL and the upper flash lamp UFL starts simultaneously at time t11 and ends simultaneously at time t12. The output waveforms of the light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL are also the same. That is, by outputting the same pulse signal to the IGBT 96 corresponding to the lower flash lamp LFL and the IGBT 96 corresponding to the upper flash lamp UFL, the lower flash lamp LFL and the upper flash lamp UFL emit light at the same time at the same time. It is letting me. The light emission time of the flash lamp FL from time t11 to time t12 is 40 milliseconds.

  By irradiating the front and back surfaces of the semiconductor wafer W supported by the support ring 72 with flash light with the same output at the same time, the semiconductor wafer W is flash-heated from the front and back. Thereby, as shown in FIG. 5, the front surface and the back surface of the semiconductor wafer W are rapidly heated from time t11 to time t12 and reach the target temperature. The target temperature is 1000 ° C. or higher at which the implanted impurity is activated, and is 1050 ° C. in the first embodiment.

  In addition, the heating rate of the front and back surfaces of the semiconductor wafer W by flash heating is set to 1000 ° C. or more and 40000 ° C. or less per second. This rate of temperature rise can be set by adjusting the pulse width of the pulse signal applied to the gate of the IGBT 96 and the time of the pulse interval. If the heating rate of the front and back surfaces exceeds 40000 ° C. per second, the semiconductor wafer W may break due to rapid thermal expansion. On the other hand, when the temperature rising rate is less than 1000 ° C. per second, there is a concern about diffusion of the implanted impurities. In addition, when annealing a high dielectric constant film (High-k film) formed on the surface of the semiconductor wafer W, a silicon base material and a high dielectric constant film have a temperature rising rate of less than 1000 ° C. per second. There is a concern that an oxide film may grow between the two.

  FIG. 7 is a view showing a temperature distribution in the thickness direction of the semiconductor wafer W. As shown in FIG. This figure shows the temperature distribution when the front and back surfaces of the semiconductor wafer W reach the target temperature (1050 ° C.) at time t12. Moreover, in the same figure, the depth from the surface of the semiconductor wafer W is shown on the horizontal axis. The semiconductor wafer W of the first embodiment is a silicon wafer having a diameter of 300 mm, and its thickness is standardized to 0.775 mm according to the standard. Therefore, the depth of 0 mm indicates the front surface of the semiconductor wafer W, and the depth of 0.775 mm indicates the back surface of the semiconductor wafer W.

  Both the front and back surfaces of the semiconductor wafer W simultaneously reach the target temperature at time t12. Further, the heat generated on the front surface of the semiconductor wafer W due to the flash light irradiation is transmitted to the back surface side, and the heat generated on the back surface is transmitted to the front surface side. As a result, as shown in FIG. 7, a temperature distribution appears such that the front surface and the back surface of the semiconductor wafer W have the same maximum temperature, and the central portion in the thickness direction has the minimum temperature. Therefore, the same degree of thermal expansion occurs on the front and back surfaces of the semiconductor wafer W, and tensile stress acts near the central portion in the thickness direction of the semiconductor wafer W having the lowest temperature.

  At the time t12, when the irradiation of flash light of the same time and the same output by the upper flash lamp UFL and the lower flash lamp LFL is completed, the temperature of the semiconductor wafer W is lowered on both the front and back sides. Thereafter, when a predetermined time (several seconds) has elapsed, the halogen lamp HL of the lower heating unit 4 is also turned off. Thereby, the temperature of the semiconductor wafer W is rapidly lowered to a temperature lower than the preheating temperature.

  After the temperature of the semiconductor wafer W has dropped to a predetermined value or less, the transfer unit 79 moves horizontally from the standby position to the inside of the inner periphery of the support ring 72 and then rises along the vertical direction. The pins lift the processed semiconductor wafer W away from the support ring 72. Then, the transfer opening 66 is opened, and the hand of the transfer robot enters the chamber 6 and stops just below the semiconductor wafer W. Subsequently, the transfer unit 79 descends and delivers the processed semiconductor wafer W to the hand of the transfer robot. Thereafter, the hand of the transfer robot that has received the semiconductor wafer W leaves the chamber 6 to carry out the semiconductor wafer W, and the flash heat treatment in the heat treatment apparatus 1 is completed (step S15). Note that the heat treatment space 65 in the chamber 6 may be replaced with an atmospheric atmosphere before the transfer opening 66 is opened.

  In the first embodiment, the front and back surfaces of the pre-heated semiconductor wafer W are irradiated with flash light at the same time with the same output. Thereby, from the time t11 to the time t12, the front surface and the back surface of the semiconductor wafer W are similarly heated to reach the target temperature that is the maximum temperature. During the flash light irradiation period, a temperature distribution is generated such that the front and back surfaces of the semiconductor wafer W are always at the highest temperature, and the central portion in the thickness direction is always at the lowest temperature. Therefore, the same degree of thermal expansion occurs on the front surface and the back surface of the semiconductor wafer W, and the tensile stress resulting from the thermal expansion of the other surface does not act on these one surfaces. On the other hand, tensile stress due to thermal expansion of the front and back surfaces acts in the vicinity of the central portion in the thickness direction of the semiconductor wafer W having the lowest temperature.

  For this reason, even if a scratch is formed on the back surface of the semiconductor wafer W in the previous step, since the tensile stress hardly acts on the back surface, the crack of the semiconductor wafer W at the time of flash light irradiation starting from the scratch Can be prevented.

  In addition, since the front and back surfaces of the semiconductor wafer W are irradiated with flash light at the same time, it is the highest in the wafer thickness direction as compared with the conventional case where the flash light is irradiated only on the front surface of the semiconductor wafer W. The temperature difference between the temperature and the minimum temperature can be reduced. Also by this, the crack of the semiconductor wafer W at the time of flash light irradiation can be suppressed.

  In the first embodiment, the upper flash lamp UFL of the upper heating unit 5 and the lower flash lamp LFL of the lower heating unit 4 are arranged so as to be orthogonal to each other. For this reason, the unevenness in illuminance caused by the arrangement of the rod-shaped lamps in the upper flash lamp UFL and the lower flash lamp LFL can be eliminated and the in-plane temperature distribution of the semiconductor wafer W can be made uniform.

  Further, since both the support ring 72 and the light shielding member 71 are formed of a material that is opaque to the light from the flash lamp FL and the halogen lamp HL, the light from the upper heating unit 5 is transmitted to the peripheral portion of the semiconductor wafer W. It is possible to prevent the peripheral edge from being heated by going around the outside and reaching the peripheral edge of the lower surface. Similarly, the light from the lower heating unit 4 is prevented from going around the outer periphery of the semiconductor wafer W to reach the upper surface periphery and heating the periphery. Therefore, the in-plane temperature distribution of the semiconductor wafer W can be made more uniform.

  Furthermore, the light emission output of the flash lamp FL can be reduced in order to reach the same target temperature on the surface of the semiconductor wafer W as compared with the case where the flash light is irradiated only on the wafer surface. For this reason, the electric current which flows into the flash lamp FL at the time of flash light irradiation can be made small, and the load of the flash lamp FL can be reduced. In particular, since the life of the flash lamp FL is shortened as the flowing current increases, the life of the flash lamp FL can be extended according to this embodiment.

Second Embodiment
Next, a second embodiment of the present invention will be described. The configuration of the heat treatment apparatus of the second embodiment is exactly the same as that of the first embodiment. Further, the processing procedure of the semiconductor wafer W in the second embodiment is substantially the same as that in the first embodiment. The second embodiment differs from the first embodiment in the light emission output of the flash lamp FL.

  Also in the second embodiment, after preheating the semiconductor wafer W, the plurality of flash lamps FL (lower flash lamp LFL) of the lower heating unit 4 and the plurality of flash lamps FL (upper flash lamp UFL) of the upper heating unit 5 are used. ) To irradiate each of the back surface and the front surface of the semiconductor wafer W with flash light to execute flash heating. FIG. 8 is a view showing temperature changes on the front surface and the back surface of the semiconductor wafer W in the second embodiment. In the figure, the surface temperature of the semiconductor wafer W is indicated by a solid line, and the back surface temperature is indicated by a dotted line.

  At time t21 when a predetermined time has elapsed since the temperature of the semiconductor wafer W reached the preheating temperature (500 ° C.), the plurality of flash lamps FL of the lower heating unit 4 and the plurality of upper heating units 5 are controlled by the control unit 3. Flash light is emitted from the flash lamp FL. The light emission control of the lower flash lamp LFL and the upper flash lamp UFL is substantially the same as in the first embodiment. That is, by supplying a pulse signal from the control unit 3 to the gate of the IGBT 96, the supply of electric charges from the capacitor 93 to the lower flash lamp LFL and the upper flash lamp UFL is intermittently performed, and the light emission is chopper-controlled.

  FIG. 9 is a diagram showing output waveforms (profiles) of light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL in the second embodiment. In the figure, the light emission output profile of the upper flash lamp UFL that irradiates the surface of the semiconductor wafer W is indicated by a solid line, and the light emission output profile of the lower flash lamp LFL that irradiates the rear surface is indicated by a dotted line. In the second embodiment, light emission from the upper flash lamp UFL and the lower flash lamp LFL starts simultaneously at time t21 and ends simultaneously at time t22. However, as shown in FIG. 9, in the second embodiment, the light emission output of the upper flash lamp UFL that irradiates the surface of the semiconductor wafer W is made larger than the light emission output of the lower flash lamp LFL that irradiates the back surface. Specifically, a plurality of pulses having a relatively long pulse width are set in the pulse signal output to the IGBT 96 corresponding to the upper flash lamp UFL, and the pulse signal output to the IGBT 96 corresponding to the lower flash lamp LFL is relatively Set multiple pulses with short pulse width. Thereby, the total ON time of the IGBT 96 corresponding to the upper flash lamp UFL becomes longer, and the light emission output of the upper flash lamp UFL can be made larger than that of the lower flash lamp LFL. The light emission time of the flash lamp FL from time t21 to time t22 is 40 milliseconds.

  By irradiating the front and back surfaces of the semiconductor wafer W supported by the support ring 72 with flash light at the same time, the semiconductor wafer W is flash-heated from the front and back. Thereby, as shown in FIG. 8, the front surface and the back surface of the semiconductor wafer W are rapidly heated from time t21 to time t22.

  In the second embodiment, the light emission timing is the same, but the light emission output of the upper flash lamp UFL is larger than the light emission output of the lower flash lamp LFL. Therefore, the intensity of the flash light applied to the front surface of the semiconductor wafer W becomes stronger than the intensity of the flash light applied to the back surface, and the temperature of the front surface is increased to a higher temperature at a faster temperature increase rate. In the second embodiment, the surface of the semiconductor wafer W reaches the target temperature of 1050 ° C. at time t22. Further, the rate of temperature rise on the surface of the semiconductor wafer W by flash heating is set to 1000 ° C. or more and 40000 ° C. or less per second. In the second embodiment, the back surface of the semiconductor wafer W does not reach the target temperature of 1050 ° C.

  FIG. 10 is a view showing a temperature distribution in the thickness direction of the semiconductor wafer W in the second embodiment. This figure shows the temperature distribution at the time when the surface of the semiconductor wafer W reaches the target temperature at time t22. Moreover, in the same figure, the depth from the surface of the semiconductor wafer W is shown on the horizontal axis similarly to 1st Embodiment.

  The surface of the semiconductor wafer W reaches the target temperature at time t22. On the other hand, in the second embodiment where the intensity of flash light on the surface is high, the back surface temperature of the semiconductor wafer W at time t22 is lower than the target temperature. However, the heat generated on the front surface of the semiconductor wafer W due to the flash light irradiation is transmitted to the back surface side, and the heat generated on the back surface is transmitted to the front surface side as in the first embodiment. As a result, as shown in FIG. 10, the lowest temperature region appears slightly closer to the back surface than the central portion in the thickness direction of the semiconductor wafer W. The tensile stress resulting from the thermal expansion generated on the front and back surfaces of the semiconductor wafer W acts on this minimum temperature region.

  As described above, in the second embodiment, similarly to the first embodiment, the front and back surfaces of the pre-heated semiconductor wafer W are irradiated with flash light at the same time. However, the intensity of the flash light applied to the front surface of the semiconductor wafer W is stronger than the intensity of the flash light applied to the back surface. For this reason, during the flash light irradiation period, although the minimum temperature region appears closer to the back surface than the central portion in the thickness direction of the semiconductor wafer W, the front or back surface does not reach the minimum temperature. Therefore, the tensile stress due to the thermal expansion of the front and back surfaces of the semiconductor wafer W acts on the lowest temperature region slightly closer to the back surface than the central portion in the thickness direction.

  For this reason, as in the first embodiment, even if a flaw is formed on the back surface of the semiconductor wafer W in the previous step, a tensile stress hardly acts on the back surface. The crack of the semiconductor wafer W at the time of irradiation can be prevented. Similarly to the first embodiment, cracking of the semiconductor wafer W during flash light irradiation can also be suppressed by reducing the temperature difference between the maximum temperature and the minimum temperature in the thickness direction of the semiconductor wafer W. . Furthermore, it is possible to reduce the load on the flash lamp FL by reducing the current flowing through the flash lamp FL during flash light irradiation.

  In the second embodiment, the intensity of the flash light irradiated on the back surface of the semiconductor wafer W is relatively small, and the maximum temperature reached on the back surface is lower than the target temperature. Therefore, the temperature of the entire semiconductor wafer W after the flash heating is determined. The temperature can be made relatively low, and the cooling rate can be increased. On the other hand, in the second embodiment, since the intensity of the flash light applied to the surface of the semiconductor wafer W is relatively large, the in-plane distribution of the light absorptance is uneven due to the pattern formed on the surface. The surface temperature distribution of the surface is likely to be non-uniform under the influence of this. For this reason, the second embodiment is suitable for flash heating of the semiconductor wafer W in which the in-plane distribution of the absorptance due to the surface pattern is relatively light.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. The configuration of the heat treatment apparatus of the third embodiment is exactly the same as that of the first embodiment. Further, the processing procedure of the semiconductor wafer W in the third embodiment is substantially the same as that in the first embodiment. The third embodiment differs from the first embodiment in the light emission output of the flash lamp FL.

  Also in the third embodiment, after preheating the semiconductor wafer W, the plurality of flash lamps FL (lower flash lamp LFL) of the lower heating unit 4 and the plurality of flash lamps FL (upper flash lamp UFL) of the upper heating unit 5 are used. ) To irradiate each of the back surface and the front surface of the semiconductor wafer W with flash light to execute flash heating. FIG. 11 is a diagram illustrating temperature changes on the front surface and the back surface of the semiconductor wafer W in the third embodiment. In the figure, the surface temperature of the semiconductor wafer W is indicated by a solid line, and the back surface temperature is indicated by a dotted line.

  At time t31 when a predetermined time has elapsed since the temperature of the semiconductor wafer W reached the preheating temperature (500 ° C.), the plurality of flash lamps FL of the lower heating unit 4 and the plurality of upper heating units 5 are controlled by the control unit 3. Flash light is emitted from the flash lamp FL. The light emission control of the lower flash lamp LFL and the upper flash lamp UFL is substantially the same as in the first embodiment. That is, by supplying a pulse signal from the control unit 3 to the gate of the IGBT 96, the supply of electric charges from the capacitor 93 to the lower flash lamp LFL and the upper flash lamp UFL is intermittently performed, and the light emission is chopper-controlled.

  FIG. 12 is a diagram showing output waveforms (profiles) of light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL in the third embodiment. In the figure, the light emission output profile of the upper flash lamp UFL that irradiates the surface of the semiconductor wafer W is indicated by a solid line, and the light emission output profile of the lower flash lamp LFL that irradiates the rear surface is indicated by a dotted line. In the third embodiment, light emission from the upper flash lamp UFL and the lower flash lamp LFL starts simultaneously at time t31 and ends simultaneously at time t32. However, as shown in FIG. 12, in the third embodiment, contrary to the second embodiment, the light emission of the lower flash lamp LFL that irradiates the back surface with the light emission output of the upper flash lamp UFL that irradiates the surface of the semiconductor wafer W. It is smaller than the output. Specifically, a plurality of pulses having a relatively short pulse width are set in the pulse signal output to the IGBT 96 corresponding to the upper flash lamp UFL, and the pulse signal output to the IGBT 96 corresponding to the lower flash lamp LFL is relatively Set multiple pulses with long pulse width. Thereby, the total on time of the IGBT 96 corresponding to the upper flash lamp UFL is shortened, and the light emission output of the upper flash lamp UFL can be made smaller than that of the lower flash lamp LFL. The light emission time of the flash lamp FL from time t31 to time t32 is 40 milliseconds.

  By irradiating the front and back surfaces of the semiconductor wafer W supported by the support ring 72 with flash light at the same time, the semiconductor wafer W is flash-heated from the front and back. As a result, as shown in FIG. 11, the front and back surfaces of the semiconductor wafer W are rapidly heated from time t31 to time t32.

  In the third embodiment, although the light emission timing is the same, the light emission output of the upper flash lamp UFL is smaller than the light emission output of the lower flash lamp LFL. Therefore, the intensity of the flash light applied to the back surface of the semiconductor wafer W becomes stronger than the intensity of the flash light applied to the front surface, and the back surface is heated to a higher temperature at a faster temperature increase rate. In the third embodiment, the surface of the semiconductor wafer W reaches the target temperature of 1050 ° C. at time t32. Therefore, in the third embodiment, the highest temperature reached on the back surface of the semiconductor wafer W exceeds the target temperature of 1050 ° C. Further, the rate of temperature rise on the surface of the semiconductor wafer W by flash heating is set to 1000 ° C. or more and 40000 ° C. or less per second.

  FIG. 13 is a view showing a temperature distribution in the thickness direction of the semiconductor wafer W in the third embodiment. This figure shows the temperature distribution at the time when the surface of the semiconductor wafer W reaches the target temperature at time t32. Moreover, in the same figure, the depth from the surface of the semiconductor wafer W is shown on the horizontal axis similarly to 1st Embodiment.

  The surface of the semiconductor wafer W reaches the target temperature at time t32. On the other hand, in the third embodiment where the intensity of flash light on the back surface is high, the back surface temperature of the semiconductor wafer W at time t32 is higher than the target temperature. However, the heat generated on the front surface of the semiconductor wafer W due to the flash light irradiation is transmitted to the back surface side, and the heat generated on the back surface is transmitted to the front surface side as in the first embodiment. As a result, as shown in FIG. 13, the lowest temperature region appears slightly closer to the surface than the central portion in the thickness direction of the semiconductor wafer W. The tensile stress resulting from the thermal expansion generated on the front and back surfaces of the semiconductor wafer W acts on this minimum temperature region.

  As described above, also in the third embodiment, similarly to the first embodiment, the front and back surfaces of the semiconductor wafer W after the preheating are irradiated with flash light at the same time. However, the intensity of the flash light applied to the back surface of the semiconductor wafer W is higher than the intensity of the flash light applied to the front surface. For this reason, during the flash light irradiation period, although the minimum temperature region appears closer to the front surface than the central portion in the thickness direction of the semiconductor wafer W, the front or back surface does not reach the minimum temperature. Therefore, the tensile stress due to the thermal expansion of the front and back surfaces of the semiconductor wafer W acts on the lowest temperature region slightly closer to the back surface than the central portion in the thickness direction.

  For this reason, as in the first embodiment, even if a flaw is formed on the back surface of the semiconductor wafer W in the previous step, a tensile stress hardly acts on the back surface. The crack of the semiconductor wafer W at the time of irradiation can be prevented. Similarly to the first embodiment, cracking of the semiconductor wafer W during flash light irradiation can also be suppressed by reducing the temperature difference between the maximum temperature and the minimum temperature in the thickness direction of the semiconductor wafer W. . Furthermore, it is possible to reduce the load on the flash lamp FL by reducing the current flowing through the flash lamp FL during flash light irradiation.

  Further, in the third embodiment, contrary to the second embodiment, the intensity of the flash light applied to the surface of the semiconductor wafer W is relatively small, so that the in-plane distribution of the light absorptance is caused by the pattern formed on the surface. Even when it is non-uniform, the influence can be suppressed. However, in the third embodiment, the intensity of the flash light applied to the back surface of the semiconductor wafer W is relatively large, and the maximum temperature reached on the back surface exceeds the target temperature, so that the temperature of the entire semiconductor wafer W after flash heating is relatively high. It becomes higher, and it takes a longer time to lower the temperature than in the second embodiment. Therefore, the third embodiment is suitable for flash heating of the semiconductor wafer W in which the in-plane distribution unevenness of the absorptance due to the surface pattern is relatively large.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described. The configuration of the heat treatment apparatus of the fourth embodiment is exactly the same as that of the first embodiment. Further, the processing procedure of the semiconductor wafer W in the fourth embodiment is substantially the same as that in the first embodiment. The fourth embodiment differs from the first embodiment in the light emission timing and light emission output of the flash lamp FL.

  Also in the fourth embodiment, after preheating the semiconductor wafer W, the plurality of flash lamps FL (lower flash lamp LFL) of the lower heating unit 4 and the plurality of flash lamps FL (upper flash lamp UFL) of the upper heating unit 5 are used. ) To irradiate each of the back surface and the front surface of the semiconductor wafer W with flash light to execute flash heating. FIG. 14 is a diagram showing temperature changes on the front surface and the back surface of the semiconductor wafer W in the fourth embodiment. In the figure, the surface temperature of the semiconductor wafer W is indicated by a solid line, and the back surface temperature is indicated by a dotted line.

  Flash light is emitted from the plurality of flash lamps FL of the lower heating unit 4 under the control of the control unit 3 at time t41 when a predetermined time has elapsed after the temperature of the semiconductor wafer W reaches the preheating temperature (500 ° C.). Subsequently, at time t <b> 42, flash light is emitted from the plurality of flash lamps FL of the upper heating unit 5 under the control of the control unit 3. The light emission control of the lower flash lamp LFL and the upper flash lamp UFL is substantially the same as in the first embodiment. That is, by supplying a pulse signal from the control unit 3 to the gate of the IGBT 96, the supply of electric charges from the capacitor 93 to the lower flash lamp LFL and the upper flash lamp UFL is intermittently performed, and the light emission is chopper-controlled.

  FIG. 15 is a diagram showing output waveforms (profiles) of light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL in the fourth embodiment. In the figure, the light emission output profile of the upper flash lamp UFL that irradiates the surface of the semiconductor wafer W is indicated by a solid line, and the light emission output profile of the lower flash lamp LFL that irradiates the rear surface is indicated by a dotted line. In the fourth embodiment, light emission of the lower flash lamp LFL starts at time t41 and ends at time t43. The upper flash lamp UFL starts emitting light at time t42 after time t41, and ends at time t44 after time t43. That is, in the fourth embodiment, the lower flash lamp LFL starts to emit light before the upper flash lamp UFL and ends light emission first. The light emission time of the lower flash lamp LFL from time t41 to time t43 and the light emission time of the upper flash lamp UFL from time t42 to time t44 are both 40 milliseconds. The elapsed time from time t41 to time t42 and the elapsed time from time t43 to time t44, that is, the delay time for delaying the light emission timing of the upper flash lamp UFL is 5 milliseconds. Accordingly, the light emission timing of the upper flash lamp UFL and the light emission timing of the lower flash lamp LFL overlap each other for 35 milliseconds from time t42 to time t43.

  Further, as shown in FIG. 15, the light emission output of the upper flash lamp UFL that irradiates the surface of the semiconductor wafer W is made smaller than the light emission output of the lower flash lamp LFL that irradiates the back surface. Specifically, a plurality of pulses having a relatively short pulse width are set in the pulse signal output to the IGBT 96 corresponding to the upper flash lamp UFL, and the pulse signal output to the IGBT 96 corresponding to the lower flash lamp LFL is relatively Set multiple pulses with long pulse width. Thereby, the total on time of the IGBT 96 corresponding to the upper flash lamp UFL is shortened, and the light emission output of the upper flash lamp UFL can be made smaller than that of the lower flash lamp LFL.

  At the time t41, flash light irradiation from the lower flash lamp LFL is started on the back surface of the semiconductor wafer W supported by the support ring 72, so that the back surface of the semiconductor wafer W is first heated. From time t41 to time t42, the surface of the semiconductor wafer W is not irradiated with flash light. Therefore, during the period from time t41 to time t42, heating is performed only from the back surface side of the semiconductor wafer W.

  16 and 17 are diagrams showing a temperature distribution in the thickness direction of the semiconductor wafer W in the fourth embodiment. In both these drawings, the horizontal axis indicates the depth from the surface of the semiconductor wafer W. FIG. 16 shows the temperature distribution immediately before time t42, that is, at the time when only the back surface of the semiconductor wafer W is irradiated with flash light.

  Between time t41 and time t42, flash light is irradiated only on the back surface of the semiconductor wafer W, so that the back surface has the highest temperature in the temperature distribution in the thickness direction. Although heat generated on the back surface of the semiconductor wafer W due to flash light irradiation is transferred to the front surface side, the temperature of the surface of the semiconductor wafer W is the lowest during this period as shown in FIG. However, during the time of about 5 milliseconds from time t41 to time t42, the back surface of the semiconductor wafer W does not increase in temperature significantly, so that a large tensile stress does not act on the surface.

  Subsequently, at time t42, the surface of the semiconductor wafer W is also irradiated with flash light. Thereby, after time t42, the semiconductor wafer W is flash-heated from the front and back. Since the front surface of the semiconductor wafer W is irradiated with the flash light later than the back surface, as shown in FIG. 14, the temperature of the front surface rises slightly later than the back surface.

  From time t42 to time t43, flash light is continuously applied to both the front surface and the back surface of the semiconductor wafer W. Then, at time t43, the flash light irradiation on the back surface of the semiconductor wafer W precedes the front surface. The back surface of the semiconductor wafer W is irradiated with flash light from time t41 to time t43, whereby the temperature of the back surface of the semiconductor wafer W rises from time t41 to time t43.

  From time t43 to time t44, only the surface of the semiconductor wafer W is irradiated with flash light. However, even during this period, heat conduction from the back surface to the front surface of the semiconductor wafer W that has been heated in advance continues. At time t44, the flash light irradiation on the surface of the semiconductor wafer W is completed. The surface of the semiconductor wafer W is irradiated with flash light from time t42 to time t44, whereby the temperature of the surface of the semiconductor wafer W rises from time t42 to time t44.

  In the fourth embodiment, the surface of the semiconductor wafer W reaches the target temperature of 1050 ° C. at time t44. Further, the rate of temperature rise on the surface of the semiconductor wafer W by flash heating is set to 1000 ° C. or more and 40000 ° C. or less per second.

  FIG. 17 shows the temperature distribution in the thickness direction when the surface of the semiconductor wafer W reaches the target temperature at time t44. By starting flash light irradiation on the surface of the semiconductor wafer W at time t42, the semiconductor wafer W is flash-heated from the front and back, and heat generated on the front surface is transferred to the back surface side, and heat generated on the back surface side. Is transmitted to the surface side. As a result, the lowest temperature region initially appearing on the surface of the semiconductor wafer W moves to the inside in the thickness direction, and moves to the vicinity of the central portion in the thickness direction at time t44 as shown in FIG. doing. The tensile stress resulting from the thermal expansion occurring on the surface of the semiconductor wafer W at the time t44 acts on the lowest temperature region near the central portion in the thickness direction. At time t44, since the flash light irradiation on the back surface of the semiconductor wafer W has already been completed, the back surface temperature is slightly lowered, and the degree of thermal expansion is smaller than that on the front surface.

  As described above, in the fourth embodiment, the flash light irradiation period of the upper flash lamp UFL and the flash light irradiation period of the lower flash lamp LFL partially overlap, and the period from time t42 to time t43. The flash light is irradiated to the front surface and back surface of the semiconductor wafer W at the same time. For this reason, from time t41 to time t42, the lowest temperature region that once appeared on the surface of the semiconductor wafer W moves to the inside in the thickness direction after time t42, and at time t44 when the surface reaches the target temperature, Move to near the center. Accordingly, there is a minimum temperature region in the thickness direction from time t43 to time t44 at which large thermal expansion occurs on the front and back surfaces of the semiconductor wafer W, and the tensile stress due to thermal expansion on the front and back surfaces Acts on the lowest temperature range.

  For this reason, as in the first embodiment, even if a flaw is formed on the back surface of the semiconductor wafer W in the previous step, a tensile stress hardly acts on the back surface. The crack of the semiconductor wafer W at the time of irradiation can be prevented. Similarly to the first embodiment, cracking of the semiconductor wafer W during flash light irradiation can also be suppressed by reducing the temperature difference between the maximum temperature and the minimum temperature in the thickness direction of the semiconductor wafer W. . In particular, in the fourth embodiment, since there is almost no temperature difference between the lowest temperature region and the back surface of the semiconductor wafer W at time t44 when the surface reaches the target temperature, the stress acting from the back surface side is extremely small. Furthermore, it is possible to reduce the load on the flash lamp FL by reducing the current flowing through the flash lamp FL during flash light irradiation.

  In the fourth embodiment, the start time (time t41) of the flash light irradiation period of the lower flash lamp LFL is earlier than the start time (time t42) of the flash light irradiation period of the upper flash lamp UFL. For this reason, the surface can be heated by irradiation with flash light while being assisted by heat conduction from the back side, and the influence of the pattern formed on the surface is reduced by reducing the intensity of the flash light irradiated from the upper flash lamp UFL. Can be small.

  In the fourth embodiment, the end of the flash light irradiation period of the lower flash lamp LFL (time t43) is earlier than the end of the flash light irradiation period of the upper flash lamp UFL (time t44). For this reason, the back surface temperature is slightly lowered at time t44 when the surface of the semiconductor wafer W reaches the target temperature. As a result, the temperature of the entire semiconductor wafer W after flash heating can be made relatively low, and the temperature drop rate can be increased.

  In particular, in the fourth embodiment, the time from the end of the flash light irradiation period of the lower flash lamp LFL to the end of the flash light irradiation period of the upper flash lamp UFL is required for heat conduction from the back surface to the surface of the semiconductor wafer W. It is shorter than the heat conduction time. Here, the “heat conduction time” is the time required for the heat generated on the back surface of the semiconductor wafer W by the flash light irradiation to be conducted to the surface. The heat conduction time is defined by the material and outer dimensions of the semiconductor wafer W, and about 15 for a φ300 mm silicon wafer (thickness is standardized to 0.775 mm by the standard) as in this embodiment. Milliseconds. As described above, the end of the flash light irradiation period of the lower flash lamp LFL is made earlier than the end of the flash light irradiation period of the upper flash lamp UFL within the range of the heat conduction time (within 15 milliseconds in the fourth embodiment). Thus, it is possible to receive assistance by heat conduction from the back side even at time t44, which is the end of the flash light irradiation period of the upper flash lamp UFL. From this point of view, the time from the end of the flash light irradiation period of the lower flash lamp LFL to the end of the flash light irradiation period of the upper flash lamp UFL is not limited to 5 milliseconds, but may be within 15 milliseconds. It ’s fine.

<Fifth Embodiment>
Next, a fifth embodiment of the present invention will be described. FIG. 18 is a diagram illustrating a main configuration of the heat treatment apparatus 1a according to the fifth embodiment. In FIG. 18, the same elements as those in FIG. 1 of the first embodiment are denoted by the same reference numerals. The fifth embodiment is different from the first embodiment in that the holding unit 7 includes a Bernoulli chuck 170 and the lower heating unit 4 includes only a flash lamp FL as a light source.

  The holding unit 7 of the fifth embodiment includes a Bernoulli chuck 170 and a light shielding member 71. As in the first embodiment, the light shielding member 71 is an annular member formed of a material opaque to the light from the flash lamp FL, and protrudes from the inner wall of the substantially cylindrical chamber side portion 63. It is provided to do. A Bernoulli chuck 170 is placed on the inner periphery of the upper surface of the light shielding member 71.

  FIG. 19 is a diagram illustrating an example of Bernoulli chuck 170. Bernoulli chuck 170 is formed of quartz that transmits the flash light from flash lamp FL. The Bernoulli chuck 170 is configured by providing a hollow portion 173 inside a quartz wall. The quartz wall surface at the ceiling of the Bernoulli chuck 170 is a circular mounting surface 171 on which the semiconductor wafer W is mounted. The diameter of the mounting surface 171 is smaller than the diameter of the semiconductor wafer W. Further, an annular recess 172 is provided so as to surround the periphery of the mounting surface 171. Further, a guide portion 175 is provided in an annular shape surrounding the concave portion 172.

  Further, a gas ejection hole 174 is formed on the mounting surface 171. As shown in FIG. 19, the ejection hole 174 is formed obliquely upward from the center side of the Bernoulli chuck 170. The ejection holes 174 may be a plurality of circular holes provided concentrically with the circular placement surface 171 or may be a plurality of slit-shaped holes. However, the ejection hole 174 is formed so that its outlet is inside the edge of the semiconductor wafer W held by the Bernoulli chuck 170. The Bernoulli chuck 170 is formed with a through hole (not shown) through which the pin of the transfer portion 79 passes, and the inside of the through hole and the hollow portion 173 are separated from each other.

  Nitrogen gas is supplied from the chuck gas supply unit 180 to the hollow portion 173 of the Bernoulli chuck 170. As shown in FIG. 18, the chuck gas supply unit 180 includes an air supply pipe 184, a gas supply source 181, a valve 182, and a flow rate adjustment valve 183. One end of the air supply pipe 184 is connected to the hollow portion 173 of the Bernoulli chuck 170 and the other end is connected to the gas supply source 181. Further, a valve 182 and a flow rate adjustment valve 183 are inserted in the middle of the route of the air supply pipe 184. By opening the valve 182, chuck gas (nitrogen in the fifth embodiment) is supplied from the gas supply source 181 to the hollow portion 173 of the Bernoulli chuck 170. The flow rate of nitrogen supplied from the chuck gas supply unit 180 to the Bernoulli chuck 170 is adjusted by a flow rate adjusting valve 183.

  When the valve 182 is opened and the chuck gas supply unit 180 supplies nitrogen to the hollow portion 173, the internal pressure of the hollow portion 173 increases and nitrogen is ejected from the ejection hole 174. When the chuck gas supply unit 180 supplies nitrogen to the hollow portion 173 when the semiconductor wafer W is mounted on the mounting surface 171 of the Bernoulli chuck 170, the nozzle hole 174 is directed toward the lower surface peripheral portion of the semiconductor wafer W. Nitrogen is blown out. Since the ejection holes 174 are formed obliquely upward, as shown in FIG. 19, the ejected nitrogen slightly floats the semiconductor wafer W from the placement surface 171 and places it on the lower peripheral edge of the semiconductor wafer W. The gap formed between the surface 171 flows toward the recess 172 (that is, from the center side of the semiconductor wafer W toward the edge).

  By the way, when a fluid such as nitrogen flows, the static pressure, which is the pressure exerted by the fluid on the outside, decreases (Bernoulli effect). The faster the nitrogen flow rate, the greater the drop in static pressure. Accordingly, the pressure in the gap between the lower surface of the semiconductor wafer W on which the nitrogen flow is formed and the mounting surface 171 becomes smaller than the atmospheric pressure. As a result, the semiconductor wafer W is moved from the ambient atmosphere to the mounting surface 171. The pressure which pushes it toward acts. That is, by ejecting nitrogen from the ejection hole 174 obliquely upward, the semiconductor wafer W is slightly floated from the mounting surface 171 by the nitrogen ejection pressure, and the semiconductor wafer W and the mounting surface 171 formed by levitation. A pressure is applied so that nitrogen flows through the gap and presses the semiconductor wafer W against the mounting surface 171. The Bernoulli chuck 170 adsorbs and holds the semiconductor wafer W in a non-contact manner by such a nitrogen jet pressure and the Bernoulli effect of the nitrogen flow.

  In a state where the semiconductor wafer W is held by the Bernoulli chuck 170 in a non-contact manner, the distance between the edge of the semiconductor wafer W and the recess 172 (the height from the recess 172 to the edge) is preferably 3 mm or more. . This is to prevent the edge portion from coming into contact with the recess 172 when the semiconductor wafer W is deformed during flash light irradiation.

  The semiconductor wafer W held in a non-contact manner by the Bernoulli effect may be slid in the horizontal direction. For this reason, a guide portion 175 is provided around the recess 172. The upper end of the guide part 175 is higher than the height position of the semiconductor wafer W held in a non-contact manner by nitrogen ejection. Further, at the height position, the inner diameter of the guide portion 175 is slightly larger than the diameter of the semiconductor wafer W. For this reason, the horizontal position of the semiconductor wafer W held in a non-contact manner is regulated by the guide portion 175. Further, in order to prevent the semiconductor wafer W from coming into contact with the guide portion 175 and cracking during flash light irradiation, the inner wall surface of the guide portion 175 is preferably a tapered surface.

  In the fifth embodiment, the lower heating unit 4 includes a plurality of flash lamps FL and reflectors 42 as light sources, but does not include a halogen lamp. That is, the heat treatment apparatus 1a of the fifth embodiment includes only the flash lamp FL as a heat source. Similar to the first embodiment, the upper flash lamp UFL of the upper heating unit 5 and the lower flash lamp LFL of the lower heating unit 4 are arranged to be orthogonal to each other.

  In the heat treatment apparatus 1a of the fifth embodiment, the remaining configuration other than the point that the holding unit 7 includes the Bernoulli chuck 170 and the lower heating unit 4 does not include the halogen lamp are the heat treatment apparatus 1 of the first embodiment. Is the same.

  The processing procedure for the semiconductor wafer W in the fifth embodiment is substantially the same as that in the first embodiment. That is, first, a semiconductor wafer W to be processed is carried into the chamber 6 by a transfer robot outside the apparatus and delivered to the Bernoulli chuck 170. At this time, the hand of the transfer robot holding the semiconductor wafer W enters the chamber 6 through the transfer opening 66 and stops immediately above the holding unit 7. Subsequently, the transfer unit 79 horizontally moves from the lower standby position of the light shielding member 71 to the lower side of the Bernoulli chuck 170 and then rises along the vertical direction, and the pin of the transfer unit 79 penetrates the Bernoulli chuck 170. The semiconductor wafer W is received from the hand of the transfer robot by protruding upward from the mounting surface 171 through the hole. Thereafter, the hand of the transfer robot moves out of the chamber 6 and the transfer opening 66 is closed, whereby the heat treatment space 65 in the chamber 6 is made a sealed space. When the transfer unit 79 that has received the semiconductor wafer W is lowered, the semiconductor wafer W is transferred from the pins of the transfer unit 79 to the Bernoulli chuck 170 and mounted on the mounting surface 171. The transfer unit 79 that has transferred the semiconductor wafer W to the Bernoulli chuck 170 returns to the standby position. Also in the fifth embodiment, the semiconductor wafer W is loaded into the chamber 6 and placed on the Bernoulli chuck 170 in a state where the surface on which the pattern is formed and the impurities are implanted faces upward.

  Next, after the transfer opening 66 is closed and the heat treatment space 65 is made a sealed space, the valve 82 is opened and the processing gas (nitrogen gas in the fifth embodiment) is supplied from the gas supply unit 8 to the heat treatment space 65. Then, the valve 22 is opened and the exhaust unit 2 exhausts from the heat treatment space 65. At the same time, the valve 182 is opened to supply nitrogen from the chuck gas supply unit 180 to the hollow portion 173 of the Bernoulli chuck 170. Nitrogen supplied to the hollow portion 173 is ejected obliquely upward from the ejection hole 174, so that the semiconductor wafer W is adsorbed and held on the Bernoulli chuck 170 in a non-contact manner by the nitrogen ejection pressure and the Bernoulli effect of the nitrogen flow. The

  After the semiconductor wafer W is held in the Bernoulli chuck 170 in a non-contact manner, the plurality of flash lamps FL (lower flash lamp LFL) of the lower heating unit 4 and the plurality of flash lamps FL (upper flash lamp UFL) of the upper heating unit 5 ) To irradiate each of the back surface and the front surface of the semiconductor wafer W with flash light to execute flash heating. That is, in the fifth embodiment, flash heating is performed by irradiating the front and back surfaces of the semiconductor wafer W at room temperature with flash light without performing preliminary heating with a halogen lamp. FIG. 20 is a diagram showing a temperature change of the front surface and the back surface of the semiconductor wafer W in the fifth embodiment.

  At a predetermined time t51, flash light is emitted from the plurality of flash lamps FL of the lower heating unit 4 and the plurality of flash lamps FL of the upper heating unit 5 under the control of the control unit 3. The light emission control of the lower flash lamp LFL and the upper flash lamp UFL is substantially the same as in the first embodiment. That is, by supplying a pulse signal from the control unit 3 to the gate of the IGBT 96, the supply of electric charges from the capacitor 93 to the lower flash lamp LFL and the upper flash lamp UFL is intermittently performed, and the light emission is chopper-controlled.

  FIG. 21 is a diagram showing output waveforms (profiles) of light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL in the fifth embodiment. In the fifth embodiment, the light emission of the lower flash lamp LFL and the upper flash lamp UFL starts simultaneously at time t51 and ends simultaneously at time t52. The output waveforms of the light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL are also the same. That is, by outputting the same pulse signal to the IGBT 96 corresponding to the lower flash lamp LFL and the IGBT 96 corresponding to the upper flash lamp UFL, the lower flash lamp LFL and the upper flash lamp UFL emit light at the same time at the same time. It is letting me. The light emission time of the flash lamp FL from time t51 to time t52 is 80 milliseconds.

  Further, the light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL are gradually decreased toward the light emission end point (time t52) after reaching the peak, and gradually approach zero. Specifically, a pulse signal in which a plurality of pulses having a pulse width gradually decreasing and a pulse interval gradually increasing from time t51 to time t52 is set to the IGBT 96 corresponding to the lower flash lamp LFL and the upper flash lamp UFL. Output. Thus, the lower flash lamp LFL and the upper flash lamp UFL emit light for 80 milliseconds from time t51 to time t52, and the light emission output gradually decreases toward time t52 after reaching the peak and gradually approaches zero.

  By irradiating the front and back surfaces of the semiconductor wafer W held in a non-contact manner with the Bernoulli chuck 170 with flash light at the same time, the semiconductor wafer W is flash-heated from the front and back surfaces. The flash light emitted from the lower flash lamp LFL passes through the quartz Bernoulli chuck 170 and is irradiated on the back surface of the semiconductor wafer W held in non-contact with the Bernoulli chuck 170. As shown in FIG. 20, the front and back surfaces of the semiconductor wafer W are rapidly heated from time t51 to time t52 to reach the target temperature (1050 ° C.) by flash heating from both the front and back surfaces. In addition, the heating rate of the front and back surfaces of the semiconductor wafer W by flash heating is set to 1000 ° C. or more and 40000 ° C. or less per second.

  FIG. 22 is a diagram showing a temperature distribution in the thickness direction of the semiconductor wafer W in the fifth embodiment. This figure shows the temperature distribution at the time when the surface of the semiconductor wafer W reaches the target temperature at time t52. Moreover, in the same figure, the depth from the surface of the semiconductor wafer W is shown on the horizontal axis similarly to 1st Embodiment.

  Both the front and back surfaces of the semiconductor wafer W simultaneously reach the target temperature at time t52. Further, the heat generated on the front surface of the semiconductor wafer W due to the flash light irradiation is transmitted to the back surface side, and the heat generated on the back surface is transmitted to the front surface side. As a result, as shown in FIG. 22, the front surface and the back surface of the semiconductor wafer W have the same maximum temperature, and the lowest temperature region appears at the center in the thickness direction. Therefore, the same degree of thermal expansion occurs on the front and back surfaces of the semiconductor wafer W, and tensile stress acts near the central portion in the thickness direction of the semiconductor wafer W having the lowest temperature.

  At the time t52, when the irradiation with the flash light of the same time and the same output by the upper flash lamp UFL and the lower flash lamp LFL is completed, the temperature of the semiconductor wafer W is lowered on both sides. After the temperature of the semiconductor wafer W is lowered to a predetermined level or lower, the transfer unit 79 moves horizontally from the standby position to the lower side of the Bernoulli chuck 170 and then rises along the vertical direction, and the pins of the transfer unit 79 are processed. The subsequent semiconductor wafer W is lifted away from the Bernoulli chuck 170. Then, the transfer opening 66 is opened, and the hand of the transfer robot enters the chamber 6 and stops just below the semiconductor wafer W. Subsequently, the transfer unit 79 descends and transfers the semiconductor wafer W to the hand of the transfer robot. Thereafter, the hand of the transfer robot that has received the semiconductor wafer W is withdrawn from the chamber 6 to carry out the semiconductor wafer W, and the flash heat treatment in the heat treatment apparatus 1a is completed.

  In the fifth embodiment, the front and back surfaces of the semiconductor wafer W at room temperature are irradiated with flash light at the same time at the same output. Thereby, from the time t51 to the time t52, the front surface and the back surface of the semiconductor wafer W are similarly heated and reach the target temperature which is the maximum temperature. During the flash light irradiation period, a temperature distribution is generated such that the front and back surfaces of the semiconductor wafer W are always at the highest temperature, and the central portion in the thickness direction is always at the lowest temperature. Therefore, the same degree of thermal expansion occurs on the front surface and the back surface of the semiconductor wafer W, and the tensile stress resulting from the thermal expansion of the other surface does not act on these one surfaces. On the other hand, tensile stress due to thermal expansion of the front and back surfaces acts in the vicinity of the central portion in the thickness direction of the semiconductor wafer W having the lowest temperature.

  For this reason, as in the first embodiment, even if a flaw is formed on the back surface of the semiconductor wafer W in the previous step, a tensile stress hardly acts on the back surface. The crack of the semiconductor wafer W at the time of irradiation can be prevented. Similarly to the first embodiment, cracking of the semiconductor wafer W during flash light irradiation can also be suppressed by reducing the temperature difference between the maximum temperature and the minimum temperature in the thickness direction of the semiconductor wafer W. .

  In the fifth embodiment, the semiconductor wafer W is brought from room temperature to a target temperature of 1000 ° C. or higher only by flash light irradiation from the lower flash lamp LFL and upper flash lamp UFL without preheating with a halogen lamp. Is reaching. Conventionally, when preheating is performed using a hot plate as disclosed in Patent Document 1, a preheating time of about 1 minute is required, and even when preheating is performed using a halogen lamp, a time of about several seconds is required. However, if the semiconductor wafer W is heated to the target temperature only by flash light irradiation, all heat treatments can be completed within 1 second (about 0.1 second in the fifth embodiment). Therefore, the processing time in the heat treatment apparatus 1a can be remarkably shortened, and the throughput can be significantly increased. In addition, if the processing time is short, an unnecessary temperature rise of members such as the chamber side portion 63 can be suppressed, and the temperature lowering rate of the semiconductor wafer W after the flash light irradiation can be increased.

  In the fifth embodiment, since the transparent Bernoulli chuck 170 holds the semiconductor wafer W in a non-contact manner by the Bernoulli effect, almost no heat conduction from the heated semiconductor wafer W to the Bernoulli chuck 170 occurs. When the semiconductor wafer W is held in contact with the chuck, heat conduction occurs only in the vicinity of the contact portion, the temperature is lowered, and the in-plane temperature distribution may be uneven. In the second embodiment, since heat conduction from the semiconductor wafer W to the Bernoulli chuck 170 hardly occurs, such a partial temperature drop does not occur, and the in-plane temperature distribution of the semiconductor wafer W can be made uniform. .

  However, since the Bernoulli chuck 170 generates the Bernoulli effect by jetting nitrogen from the ejection hole 174 to the peripheral edge of the lower surface of the semiconductor wafer W, the temperature of the peripheral edge of the semiconductor wafer W may be lowered by the air flow. . However, in the fifth embodiment, all the heat treatments are completed within 1 second only by flash light irradiation, and therefore, the influence of the temperature drop due to the jet airflow hardly occurs in that very short time.

  In addition, since the semiconductor wafer W floats from the Bernoulli chuck 170 and is held in a non-contact manner, even if the semiconductor wafer W is deformed due to a rapid temperature change at the time of flash light irradiation, stress that restricts the deformation does not act. . This can also prevent cracking of the semiconductor wafer W during flash light irradiation.

  Further, in the fifth embodiment, the light emission outputs of the lower flash lamp LFL and the upper flash lamp UFL gradually decrease toward the end of light emission after reaching the peak and gradually approach zero. Thereby, it is possible to prevent the front and back surfaces of the semiconductor wafer W from being excessively heated at the end of the flash light irradiation. Further, the temperature difference in the wafer depth direction can be gradually and gradually reduced toward the end of the flash light irradiation. As a result, the thermal stress acting on the semiconductor wafer W at the time of flash light irradiation can be relieved and wafer cracking can be prevented more reliably.

<Modification>
While 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, the start and end of the flash light irradiation period of the upper flash lamp UFL and the lower flash lamp LFL may be as shown in FIGS. 23 to 25 are timing charts showing flash light irradiation periods of the upper flash lamp UFL and the lower flash lamp LFL. The flash light irradiation period of the upper flash lamp UFL is indicated by a solid line, and the lower flash lamp LFL The flash light irradiation period is indicated by a dotted line.

  FIG. 23 shows a case where the beginning of the flash light irradiation period of the upper flash lamp UFL and the lower flash lamp LFL is the same. FIG. 23A shows an example in which the flash light irradiation of the upper flash lamp UFL and the lower flash lamp LFL starts simultaneously and ends simultaneously, and corresponds to the case of the first embodiment. FIG. 23B is an example in which the flash light irradiation of the upper flash lamp UFL and the lower flash lamp LFL is started at the same time, and the flash light irradiation to the wafer back surface by the lower flash lamp LFL is terminated in advance. . Further, FIG. 23C is an example in which the flash light irradiation of the upper flash lamp UFL and the lower flash lamp LFL is started simultaneously, and the flash light irradiation on the wafer surface by the upper flash lamp UFL is terminated in advance.

  FIG. 24 shows a case where irradiation of flash light on the surface of the semiconductor wafer W by the upper flash lamp UFL is started prior to the lower flash lamp LFL. FIG. 24A shows an example in which the flash light irradiation of the upper flash lamp UFL is started in advance, and the flash light irradiation of the upper flash lamp UFL and the lower flash lamp LFL is simultaneously ended. FIG. 24B is an example in which the flash light irradiation of the upper flash lamp UFL is started in advance and the flash light irradiation of the lower flash lamp LFL is ended in advance. Further, FIG. 24C is an example in which the flash light irradiation of the upper flash lamp UFL is started in advance and ended in advance.

  FIG. 25 shows a case where irradiation of flash light on the back surface of the semiconductor wafer W by the lower flash lamp LFL is started prior to the upper flash lamp UFL. FIG. 25A shows an example in which the flash light irradiation of the lower flash lamp LFL is started in advance, and the flash light irradiation of the upper flash lamp UFL and the lower flash lamp LFL is simultaneously ended. FIG. 25B is an example in which the flash light irradiation of the lower flash lamp LFL is started in advance and ended in advance, and corresponds to the case of the fourth embodiment. Further, FIG. 25C is an example in which the flash light irradiation of the lower flash lamp LFL is started in advance and the flash light irradiation of the upper flash lamp UFL is ended in advance.

  As shown in FIGS. 23 to 25, various combinations of flash light irradiation timings of the upper flash lamp UFL and the lower flash lamp LFL are possible. However, in any combination, at least part of the flash light irradiation period of the upper flash lamp UFL and the flash light irradiation period of the lower flash lamp LFL overlap each other. In this way, in the overlapping period, the front and back surfaces of the semiconductor wafer W are irradiated with flash light at the same time, and the lowest temperature region exists inside the thickness direction of the semiconductor wafer W. Therefore, even if a scratch is formed on the back surface of the semiconductor wafer W, since the tensile stress hardly acts on the back surface, it is possible to prevent the semiconductor wafer W from being cracked during flash light irradiation starting from the scratch. .

  In the example shown in FIGS. 23 to 25, the flash light irradiation time of the upper flash lamp UFL and the lower flash lamp LFL is not particularly limited, and may be set as appropriate according to the waveform of the pulse signal output to the IGBT 96. it can. However, the total flash irradiation period of the upper flash lamp UFL and the lower flash lamp LFL is 1 second or less. Further, the flash light irradiation period of the lower flash lamp LFL is longer than the heat conduction time required for heat conduction from the back surface to the surface of the semiconductor wafer W, so that the surface flash heating can be assisted by heat conduction to the surface. Therefore, the heating efficiency as a whole increases.

  In the example shown in FIGS. 23 to 25, the light emission outputs of the upper flash lamp UFL and the lower flash lamp LFL may be the same or different from each other.

  Further, the Bernoulli chuck of the fifth embodiment may be as shown in FIG. In FIG. 26, the same elements as those in FIG. 19 are denoted by the same reference numerals. The Bernoulli chuck 170 in FIG. 19 has the same mounting surface 171, whereas the Bernoulli chuck 170 a in FIG. 26 has an annular mounting portion 177. The diameter of the annular mounting portion 177 is smaller than the diameter of the semiconductor wafer W. An annular recess 172 is provided so as to surround the periphery of the mounting portion 177.

  The side surface of the mounting portion 177 is a tapered surface. An ejection hole 174 is formed in the quartz wall surface of the ceiling portion of the Bernoulli chuck 170a so as to follow the inclination of the inner peripheral side tapered surface of the mounting portion 177. Therefore, the nitrogen gas ejected obliquely upward from the ejection hole 174 flows along the inner peripheral side tapered surface of the mounting portion 177 as it is. The remaining configuration of the Bernoulli chuck 170a is the same as that of the Bernoulli chuck 170 of FIG.

  When the chuck gas supply unit 180 supplies nitrogen to the hollow portion 173 when the semiconductor wafer W is mounted on the mounting portion 177 of the Bernoulli chuck 170a, the nozzle hole 174 is directed toward the lower surface peripheral portion of the semiconductor wafer W. Nitrogen is blown out. As shown in FIG. 26, the ejected nitrogen flows obliquely upward along the inner peripheral side taper surface of the mounting portion 177, and the semiconductor wafer W placed on the top of the mounting portion 177 passes through the mounting portion 177. To surface slightly. Then, a nitrogen gas flow from the center side of the semiconductor wafer W toward the edge portion is formed in the gap formed between the peripheral surface of the lower surface of the semiconductor wafer W and the mounting portion 177. By forming a nitrogen gas flow in the gap formed between the semiconductor wafer W and the mounting portion 177, the Bern wafer effect causes the semiconductor wafer W to be pressed against the mounting portion 177 from the surrounding atmosphere. Works. Therefore, as in the fifth embodiment, the Bernoulli chuck 170a can adsorb and hold the semiconductor wafer W in a non-contact manner by the nitrogen ejection pressure and the Bernoulli effect of the nitrogen flow.

  The material of the light shielding member 71 is not limited to ceramic such as silicon carbide, aluminum nitride, boron nitride, and may be any material that is opaque to the light from the flash lamp FL and the halogen lamp HL. It may be opaque quartz. The opaque quartz is, for example, made by containing fine bubbles in quartz so as to have a light shielding function. The light shielding member 71 may be made of metal (for example, stainless steel). When the light shielding member 71 is made of metal, it is preferable that the light shielding member 71 is water-cooled so that it can withstand flash light irradiation and that the surface of the light shielding member 71 is a mirror surface. The light shielding member 71 may be formed by a part of the chamber side portion 63 made of stainless steel.

  Further, an area outside the semiconductor wafer W held in the Bernoulli chuck 170 may be formed of opaque quartz. In this way, it is possible to prevent the light from the upper heating unit 5 from going around the outer periphery of the semiconductor wafer W and reaching the lower surface periphery to heat the periphery. Similarly, the light from the lower heating unit 4 is prevented from going around the outer periphery of the semiconductor wafer W to reach the upper surface periphery and heating the periphery.

  Alternatively, a nickel film may be formed on the surface of the semiconductor wafer, and flash heat treatment may be performed by a heat treatment apparatus according to the present invention to form nickel silicide (silicidation). Further, a high dielectric constant film (High-k film) containing hafnium or the like is formed on the surface of the semiconductor wafer, and flash heat treatment is performed by the heat treatment apparatus according to the present invention to promote crystallization of the high dielectric constant film. (PDA: Post Deposition Anneal).

  The substrate to be processed by the heat treatment technique according to the present invention is not limited to a semiconductor wafer, and may be a glass substrate or a solar cell substrate used for a liquid crystal display device or the like.

DESCRIPTION OF SYMBOLS 1,1a Heat processing apparatus 2 Exhaust part 3 Control part 4 Lower side heating part 5 Upper side heating part 6 Chamber 7 Holding part 8 Gas supply part 65 Heat processing space 71 Light-shielding member 72 Support ring 79 Transfer part 96 IGBT
170, 170a Bernoulli chuck FL Flash lamp HL Halogen lamp LFL Lower flash lamp UFL Upper flash lamp W Semiconductor wafer

Claims (13)

A heat treatment apparatus for heating a substrate by irradiating the substrate with flash light,
A chamber for housing the substrate;
A support member for supporting the substrate in the chamber;
A first flash lamp that irradiates the back surface of the substrate supported by the support member with flash light to heat the substrate from the back surface;
A second flash lamp that irradiates the surface of the substrate supported by the support member with flash light to heat the substrate from the surface;
With
At least part of the flash light irradiation period of the first flash lamp and the flash light irradiation period of the second flash lamp overlap each other. The heat treatment apparatus according to claim 1, wherein
A heat treatment apparatus, wherein a light emission output of the first flash lamp is different from a light emission output of the second flash lamp. In the heat treatment apparatus according to claim 1 or 2,
A heat treatment apparatus, wherein a start time of a flash light irradiation period of the first flash lamp is different from a start time of a flash light irradiation period of the second flash lamp. In the heat processing apparatus in any one of Claims 1-3,
An end of a flash light irradiation period of the first flash lamp is different from an end of a flash light irradiation period of the second flash lamp. The heat treatment apparatus according to claim 4, wherein
The end of the flash light irradiation period of the first flash lamp is earlier than the end of the flash light irradiation period of the second flash lamp within a heat conduction time required for heat conduction from the back surface to the front surface. Heat treatment equipment. In the heat processing apparatus in any one of Claims 1-5,
The first flash lamp and the second flash lamp are bar lamps;
The heat treatment apparatus, wherein the first flash lamp and the second flash lamp are arranged to be orthogonal to each other. In the heat processing apparatus in any one of Claims 1-6,
A heat treatment apparatus, comprising: a light shielding member that shields light between the first flash lamp and the second flash lamp around the support member. In the heat treatment apparatus according to any one of claims 1 to 7,
The heat treatment apparatus, wherein the support member is made of quartz and includes a Bernoulli chuck that holds the substrate in a non-contact manner by a Bernoulli effect. A heat treatment method for heating a substrate by irradiating the substrate with flash light,
A back flash heating step of heating the substrate from the back surface by irradiating flash light on the back surface of the substrate supported by the support member in the chamber;
A surface flash heating step of heating the substrate from the surface by irradiating the surface of the substrate supported by the support member with flash light;
With
At least part of the flash light irradiation period in the back surface flash heating step and the flash light irradiation period in the front surface flash heating step overlap each other. The heat treatment method according to claim 9, wherein
The light-emitting output of the flash light in the said back surface flash heating process differs from the light-emitting output of the flash light in the said surface flash heating process. In the heat treatment method according to claim 9 or 10,
A heat treatment method, wherein a start time of a flash light irradiation period in the back surface flash heating step is different from a start time of a flash light irradiation period in the front surface flash heating step. In the heat treatment method according to any one of claims 9 to 11,
A heat treatment method, wherein the end of the flash light irradiation period in the back surface flash heating step is different from the end of the flash light irradiation period in the front surface flash heating step. The heat treatment method according to claim 12,
The end of the flash light irradiation period in the back surface flash heating process is earlier than the end of the flash light irradiation period in the front surface flash heating process within a heat conduction time required for heat conduction from the back surface to the surface. A heat treatment method characterized by the above.

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