JP5127532B2 - Wafer heat treatment system - Google Patents

Description

  The present invention relates to a wafer heat treatment system used when heat treating a wafer such as a semiconductor or a liquid crystal at a predetermined temperature.

  As a wafer heat treatment apparatus used when heat treating a wafer such as a semiconductor or a liquid crystal, an apparatus using induction heating is known. As a wafer heat treatment apparatus using induction heating, the present applicant has proposed means for uniformly heating a disk-shaped large wafer (see, for example, Patent Document 1). In the induction heating device disclosed in Patent Document 1, each induction heating coil is formed in a circular shape (C type) having different radii, and a plurality of the induction heating coils are arranged on a concentric circle to generate mutual induction between the induction heating coils. It is possible to arbitrarily adjust the input power while avoiding the influence. By adopting such a configuration, the radiant heat source heated by the induction heating coil can have a uniform temperature distribution with higher accuracy than in the past.

  However, when temperature control at a higher level than before is pursued, the induction heating coil arrangement form as described above inevitably has a radiant heat source due to the limitation of the input power to the center coil and the shape thereof. This caused a problem that the temperature of the central part of the glass was lowered. Such a problem also occurs in cooking utensils using induction heating coils arranged in a circle (see, for example, Patent Document 2). In this case, by arranging a metal core, a magnetic flux is applied to the core portion. Concentrate to compensate for the drop in temperature.

In the related technical field, as a method for heat-treating silicon, it has been proposed to employ two types of heating means, induction heating and laser heating, for controlling the heating temperature (see, for example, Patent Document 3). In this case, induction heating is used as a whole, and laser heating is used as spot heating.
JP 2006-278097 A Japanese Patent Laid-Open No. 11-40338 JP 2002-252173 A

  When the techniques disclosed in Patent Document 2 and Patent Document 3 are considered, both have the following problems. First, although the technique disclosed in Patent Document 2 is considered to be effective in fields that do not require temperature distribution control with extremely high accuracy, such as cooking, a portion that is induction-heated through a core, and a core It is difficult to change the ratio of the applied magnetic flux to the part that is induction-heated without going through, and it is also difficult to create an arbitrary temperature distribution.

  Since the technique disclosed in Patent Document 3 directly heats the silicon film by both induction heating and laser heating, it is possible to employ a member having high magnetic permeability or a low resistance as the wafer. Can not. That is, there is a problem that there is a great limitation on the member to be heated. Further, in the technique disclosed in Patent Document 3, the point is that the part heated by induction heating below the melting point of silicon and the part heated by induction by the laser is heated to a temperature higher than the melting point. The case where high-precision temperature control is required is not taken into consideration.

  Therefore, in the present invention, it is possible to prevent a decrease in temperature at the center of the radiant heat source heated by the C-type coil arranged in parallel with the radiant heat source to be subjected to induction heating or the wafer heated through the radiant heat source. An object of the present invention is to provide a wafer heat treatment system that can perform heat treatment while performing temperature distribution control with high accuracy.

  In order to achieve the above object, a wafer heat treatment system according to the present invention divides a process chamber in which a radiant heat source and a wafer to be heated via the radiant heat source are arranged, and a control chamber in which the heating source is arranged with a separator. A heating furnace, an induction heating device including an induction heating coil as a first heating source disposed in the control room, and a laser irradiation device including a condensing unit as a second heating source disposed in the control room; And an arithmetic means for detecting a temperature distribution of the wafer and adjusting an electric power supplied to the induction heating coil and an output of a laser irradiated from the light converging unit based on the temperature distribution of the wafer. The heating coil is formed in a substantially C shape and is arranged in parallel to the radiant heat source, and the condensing unit is surrounded by a heating region of the induction heating coil in the radiant heat source. Characterized by being arranged at a position to be irradiated to the eccentric part.

  Further, in the wafer heat treatment system having the above-described features, an opening is provided in a central portion covered with a heating region of the induction heating coil in the radiant heat source, and a laser transmitted through the separator plate opens the opening. You may arrange | position the said condensing part in the position which passes and is irradiated to the said wafer. According to such a configuration, since the wafer is directly heated by the laser, the heating efficiency can be increased as compared with indirect heating, and the laser output can be reduced.

  In the wafer heat treatment system having the above-described features, the laser irradiation surface of the radiant heat source may be roughened. With such a configuration, reflection of the laser beam on the laser irradiation surface can be suppressed, and absorption can be promoted. Therefore, heating efficiency can be improved.

  In the wafer heat treatment system having the above-described features, a semiconductor laser may be employed as the laser irradiation apparatus. A laser oscillator in a semiconductor laser can be manufactured in a small size and at a lower cost than a laser oscillator such as a solid-state laser or a gas laser. Therefore, it is possible to contribute to downsizing and cost reduction of the system and increase the degree of freedom of the laser arrangement form.

  In the wafer heat treatment system having the above-described features, the separator is made of quartz glass, the semiconductor laser cladding layer is an InP series semiconductor compound, the active layer is an InGaAsP series semiconductor compound, or the cladding layer is an AlGaAs series. The semiconductor compound and the active layer may be composed of a GaAs series semiconductor compound. This is because the wavelength of light of a semiconductor laser composed of such a semiconductor compound has good transmittance of quartz glass and good radiation rate (absorption rate) by graphite generally used as a radiation heat source.

  In the wafer heat treatment system having the above-described features, the wafer is made of silicon, a semiconductor laser is adopted as the laser irradiation apparatus, the cladding layer is made of an AlGa series semiconductor compound, and the active layer is made of a GaAs series semiconductor compound. It may be configured. This is because the wavelength of light of a semiconductor laser composed of such a semiconductor compound has good transmittance of quartz glass and good radiation rate (absorption rate) of silicon.

  Furthermore, in the wafer heat treatment system having the above-described features, it is preferable that a plurality of the induction heating coils are arranged on a concentric circle, and a power control unit that can arbitrarily control power supplied to each induction heating coil is provided. With such a configuration, it becomes possible to control the temperature distribution of the wafer to be heat-treated more finely.

  According to the wafer heat treatment system having the above-described features, the temperature of the central portion of the radiant heat source heated by the C-type coil arranged in parallel with the radiant heat source to be induction-heated, or through the radiant heat source It is possible to prevent a temperature drop at the center of the wafer to be heated and to perform the heat treatment while controlling the temperature distribution of the wafer with high accuracy.

Hereinafter, embodiments of a wafer heat treatment system of the present invention will be described in detail with reference to the drawings.
The wafer heat treatment system 10 according to the present embodiment includes at least a heating furnace 12, an induction heating device 30, a laser irradiation device 50, and a computer (calculation means) 60 for controlling both.

  The heating furnace 12 includes an induction heating coil (first heating source) 32 (32a, 32b, 32c, 32d) in an induction heating device 30 (to be described later in detail) and a collection in a laser irradiation device (second heating source) 50. There is a control chamber 14 in which a heating source such as an optical part 52 is disposed, and a process chamber 24 in which a wafer 20 to be heat-treated and a graphite 18 as a radiant heat source are disposed (the partition of the process chamber is not shown). A separator 16 is provided between the chamber 14 and the process chamber 24 to divide both chambers. The arrangement of the separator plate 16 is a measure for preventing contamination of the control chamber 14 from being mixed into the process chamber 24. As a constituent material, the member is excellent in heat resistance and translucency and transmits magnetic flux. It is desirable that One constituent material having such characteristics is quartz glass.

  In the present embodiment, when the graphite 18 and the wafer 20 are arranged in the process chamber 24, a gap is provided between the graphite 18 and the wafer 20. Such a configuration is effective when the infrared absorption rate (emissivity) of the wafer 20 is high. As a specific configuration, an edge ring 22 that supports the peripheral portion of the wafer 20 is disposed, and the edge ring 22 is arranged. The graphite 18 is placed on the top.

  The induction heating device 30 includes an induction heating coil 32 and a power control unit 34 that supplies power to the induction heating coil 32. In addition, although the induction heating coil 32 is four in FIG. 1, increase / decrease in number does not become a problem in implementing this invention.

  The induction heating coil 32 is a circular (C-type) coil. When viewed as a whole, a plurality of circular coils having different radii are arranged on a concentric circle, so that a so-called Baumkuchen-like body is formed (for example, (See FIG. 2). As shown in FIG. 1, the induction heating coil 32 formed in a substantially C shape is arranged in parallel with the graphite 18.

  The power control unit 34 is configured based on, for example, a three-phase AC power supply 44, a converter 42, a chopper 40 (40a, 40b, 40c, 40d), and an inverter 38 (38a, 38b, 38c, 38d).

The converter 42 is a pure conversion unit that converts a three-phase alternating current input from the three-phase alternating current power supply 44 into a direct current and outputs the direct current to the chopper 40 connected to the subsequent stage.
The chopper 40 is a voltage adjustment unit that changes the current conduction rate output from the converter 42 and changes the voltage of the current input to the inverter 38.

  The inverter 38 is an inverse conversion unit that converts the direct current adjusted in voltage by the chopper 40 into an alternating current and supplies the alternating current to the induction heating coil 32. In addition, the inverter 38 of the induction heating apparatus 30 exemplified in this embodiment is a series resonance type inverter in which the induction heating coil 32 and the resonance capacitors 36 (36a, 36b, 36c, 36d) are arranged in series. Further, an inverter 38 and a chopper 40 are individually connected to a plurality (four in the case of this embodiment) of induction heating coils 32. Control of output power from the inverter 38 to the induction heating coil 32 is performed based on drive control signals output from the drive control unit 46 to the inverter 38 and the chopper 40, respectively. In the drive control unit 46, the current frequency output from the inverter 38, the timing of the zero crossing, and the temperature error for each heating zone calculated by the computer 60, which will be described in detail later (error with respect to the target temperature, or each heating zone) A signal indicating a correction value for an error between them or both) is input. The drive control unit 46 outputs a gate signal for synchronizing the timing of zero crossing in the output current and adjusting the output voltage based on the various input signals.

  According to the power control unit 34 having such a configuration, the voltage of the current output from the converter 42 is controlled by the chopper 40, the direct current output from the chopper 40 is converted into an alternating current by the inverter 38, and Frequency adjustment can be performed. Therefore, the output voltage can be controlled by the chopper 40, and the phase of the current waveform input to the induction heating coil 32 in which a plurality of coils are arranged adjacent to each other can be adjusted by the inverter 38. Then, the frequencies of the output currents are matched, and the phase of the zero cross is synchronized (the phase difference is set to 0 or approximated to 0), or is kept at a predetermined interval, so that the induction heating coils 32 arranged adjacent to each other. The influence of mutual induction between the two can be avoided, and the temperature of the object to be heated can be controlled by controlling the input power to the induction heating coil 32.

Further, the induction heating coil 32 according to the present embodiment has a hollow structure as shown in FIG. 1 and is formed so that a refrigerant (for example, water) can be inserted therein. With such a configuration, it is possible to prevent the induction heating coil 32 itself from being overheated by receiving radiation or heat transfer from the graphite 18 serving as a heat source.
Further, the laser irradiation device 50 includes a condensing unit 52 for irradiating a laser and a laser oscillator 54 for exciting the laser.

  The condensing unit 52 includes a lens (not shown) for condensing the laser light transmitted from the laser oscillator 54 onto a heating part, a homogenizer or an integrator for averaging the intensity distribution of the collected laser, etc. (Not shown). The light collecting unit 52 is disposed in the control room 14. More specifically, it is arranged at the position where the irradiated laser reaches the central portion surrounded by the heating region of the graphite 18 by the induction heating coil 32, that is, the low temperature portion of the graphite 18.

  The laser oscillator 54 employed in the present embodiment is a semiconductor laser that can transmit quartz glass and can irradiate a laser (light: electromagnetic wave) having a wavelength that does not transmit the graphite 18 or the wafer 20 to be heat-treated. Good to be. This is because the semiconductor laser can simplify the configuration of the oscillator, and can be manufactured in a small size and at low cost, as compared with other laser excitation means. Further, with respect to the wavelength of the laser, it is for solving the problems caused by the configuration of the wafer heat treatment system 10 according to the embodiment. That is, in the wafer heat treatment system 10 according to the embodiment, the separator plate 16 made of quartz glass is disposed between the induction heating coil 32 and the graphite 18, and the light collecting unit 52 is located on the control chamber 14 side. This is because, in order to heat the graphite 18 by the laser, the laser needs to be absorbed by the graphite 18 while being transmitted through the separator 16.

  FIG. 3 shows the relationship between the transmittance of electromagnetic waves (light) to quartz glass and its wavelength. The solid line, broken line, and alternate long and short dash line shown in FIG. 3 indicate the difference in thickness of the quartz glass. From the data shown in FIG. 3, in the range where the wavelength of the light to be irradiated is about 200 nm to about 1.4 μm (1400 nm), if the thickness is about the thickness of the use range, regardless of the thickness of the quartz glass, It can be read that high transmittance can be obtained, and that when the thickness is 10 mm or less, good transmittance can be obtained up to about 2.0 μm (2000 nm).

  The graphite 18 has a characteristic of satisfactorily absorbing light having a relatively long wavelength. For this reason, the wavelength of the laser to be used may be in the region that transmits quartz glass. As a concrete example, an AlGaAs (Al: aluminum, Ga: gallium, As arsenic) series compound semiconductor is used for a clad layer, and a semiconductor laser (laser wavelength of about 600 nm to 800 nm) using a GaAs series compound semiconductor for an active layer. In addition, it is desirable to use a semiconductor laser (laser wavelength of about 1300 nm to 1600 nm) using an InP (In: Indium, P: Phosphorus) series compound semiconductor for the cladding layer and an indium InGaAsP series compound semiconductor for the active layer. This is because a laser having a relatively long wavelength has less loss in the transmission line, and the graphite 18 in the present embodiment is preferably subjected to roughening at least in a range irradiated with the laser. Suppresses laser reflection and promotes absorption, improving heating efficiency This is because it is Rukoto. To roughening processing in the present embodiment, it is assumed that also include those as arranging a plurality of pyramid-like irregularities.

  By the way, semiconductor lasers generally have a low output. However, as shown in FIG. 4, the light emitting elements 56 are arrayed, and lasers irradiated from the arrayed light emitting elements 56 are passed through a condenser 58. The light is condensed and output from the laser oscillator 54, so that a high output laser can be supplied. Therefore, it is possible to contribute to heating of the wafer 20 even when a semiconductor laser is used. Note that in the case where the light-emitting element 56 generates heat as the array and the output increase, it is preferable to cool the substrate 59 through which the light-emitting element 56 is fixed by inserting a coolant. This is because deterioration and damage of the light emitting element 56 can be suppressed. As the fixing layer 57 for fixing the light emitting element 56, BeO (beryllium oxide) or the like may be employed.

  In addition, when it is desired to obtain a higher output such as expanding the heating range by laser or increasing the heating temperature by laser, a well-known solid-state laser (for example, YAG laser, neodymium-added YAG laser) or gas laser (for example, carbon dioxide laser) Etc. may be used.

  The laser oscillator 54 and the condensing unit 52 are connected via a transmission path formed using a reflecting mirror, an optical fiber, or the like. By setting it as such a structure, the freedom degree of the arrangement | positioning form of the laser irradiation apparatus 50 will improve. In addition, since the laser oscillator 54 can be disposed outside the control chamber 14, it is difficult to be affected by electromagnetic waves emitted from the induction heating coil 32 when the laser is excited.

  The computer 60 is connected to the drive control unit 46, the laser oscillator 54, and temperature detection means (not shown) in the power control unit 34 having the above-described configuration. A monitor 62 is connected to the computer 60, which is detected by temperature detecting means, and the temperature of the wafer 20 or the temperature of the graphite 18 is inputted as a signal to the computer 60, and can be visually recognized by numerical values and colors. Is displayed. Here, the temperature of the wafer 20 and the temperature of the graphite 18 are detected for each heating zone by the induction heating coil 32 and the light collecting unit 52. The computer 60 calculates an error (error with a specified temperature curve) between the detected temperature for each heating zone and a set temperature profile, and a temperature difference (temperature gradient of the temperature detection target) between the heating zones. , A signal for reducing each error or temperature difference is output. The output signal to the drive control unit 46 in the power control unit 34 is a signal to the chopper 40 that controls the level of the output voltage to the induction heating coil 32. When the chopper 40 receives the signal, the timing of the gate pulse is changed, and the amount of power supplied to the induction heating coil is changed. On the other hand, the output signal to the laser oscillator 54 is a signal for adjusting the voltage applied to the semiconductor, a signal for controlling the number of light emitting elements 56 used in the array, or the like. As a result, the heating rate by the laser is changed, and the temperature distribution between the zone heated by the induction heating coil 32 and the zone heated by the light collecting unit 52 can be made uniform.

  According to the wafer heat treatment system 10 having such a configuration, the center portion of the graphite 18 that is a singular point can be heated well, and the wafer 20 that is radiantly heated by graphite can also be heated uniformly. became. In addition, according to the wafer heat treatment system 10 having the above-described configuration, the central portion of the graphite 18 can be formed without drastically improving the power supplied to the center side induction heating coil (for example, the induction heating coil 32a) having poor heating efficiency. It becomes possible to heat. Therefore, the phenomenon that the heating region such as the induction heating coil 32b is heated by the influence of the magnetic flux by the induction heating coil 32a can be suppressed, and the temperature distribution control with high accuracy can be performed.

  In the wafer heat treatment system 10 configured as described above, during operation, for example, a temperature distribution on the surface of the wafer 20 is detected by a temperature detection unit (not shown), and the detected temperature distribution information is input to the computer 60 as a temperature distribution signal. (FIG. 5: S1).

  The computer 60 to which the temperature distribution signal is input analyzes the temperature distribution for each heating zone by the light collecting unit 52 and each induction heating coil 32 (FIG. 5: S2). Based on the error of each heating zone temperature with respect to the target temperature derived as a result of the analysis, the temperature difference between each heating zone, etc., a signal indicating the increase / decrease in the heating rate is output to each of the drive controller 46 and the laser oscillator 54. (FIG. 5: S3, S5).

  The drive control unit 46 outputs a gate signal for adjusting the current flow rate to the chopper 40 connected to each inverter 38 based on the input signal. On the other hand, the laser oscillator 54 adjusts the output of the laser to be irradiated based on the input signal (FIG. 5: S4, S6).

  By repeating such control, the wafer 20 to be heat-treated is heated or lowered while maintaining a uniform temperature distribution, and it is possible to provide a high-quality wafer 20.

  In the said embodiment, about the arrangement | positioning form of the wafer 20 made into heat processing, it described that the space | interval was spaced apart from the graphite 18 via the edge ring 22. FIG. However, when the infrared transmittance of the wafer 20 is high, the efficiency of heating (radiation heating) by radiation radiated from the graphite 18 that is a radiation heat source may be remarkably deteriorated. In such a case, in addition to radiant heating, it is preferable to adopt a heating form utilizing heat conduction. Specifically, as shown in FIG. 6, by arranging the graphite 18 and the wafer 20 so as to be close to or in contact with each other, the wafer 20 can be heated not only by the radiant heat from the graphite 18 but also by the transfer heat. To do. With such a configuration, even when the infrared transmittance of the wafer 20 is high, the heating efficiency can be kept good.

  Next, a second embodiment according to the wafer heat treatment system of the present invention will be described with reference to FIG. Most of the configuration of the wafer heat treatment system according to the present embodiment is the same as the configuration of the wafer heat treatment system according to the first embodiment described above. Therefore, portions having the same function are denoted by reference numerals obtained by adding 100 to the drawings, and detailed description thereof will be omitted. The configuration of the power control unit, laser oscillator, and computer in the wafer heat treatment system 110 is the same as that of the wafer heat treatment system 10 according to the first embodiment shown in FIG.

  The differences between the wafer heat treatment system 110 according to the present embodiment and the wafer heat treatment system 10 according to the first embodiment are the configuration of the graphite 118 and the location heated by the laser.

  Specifically, in the wafer heat treatment system 110 according to the present embodiment, the opening 119 is provided at the center of the graphite 118 that is difficult to be heated by the induction heating coil 132. Further, the condensing unit 152 is brought close to the wafer side, laser irradiation is performed through an opening 119 formed in the graphite 118, and the wafer 120 is directly heated by the laser that has passed through the opening 119.

  Here, when the wafer 120 is made of silicon, the spectral emissivity characteristics as shown in FIG. 8 can be obtained. From FIG. 8, it can be seen that light having a wavelength of about 0.6 μm (600 nm) to about 1.3 μm (1300 nm) can obtain good absorption characteristics in various temperature bands and has high heating efficiency. Can be read.

  In the first embodiment, the wavelength of light with which good transmission characteristics are obtained with respect to quartz glass is shown to be about 200 nm to about 1.4 μm (1400 nm). Therefore, in this embodiment, transmission to quartz glass is performed. It is preferable to employ a semiconductor laser that can output a laser having a wavelength in a range with high performance and good absorption characteristics of silicon. Specifically, a semiconductor laser (laser wavelength of about 600 nm to 800 nm) using an AlGaAs series compound semiconductor for the cladding layer and a GaAs series compound semiconductor for the active layer can be mentioned.

  In such a configuration, since the laser directly heats the wafer 120, the laser output is lower than that of the wafer heat treatment system 10 according to the first embodiment in which the heating of the wafer 120 is indirect heating. Even so, good heating can be performed. Other functions and effects are the same as those of the wafer heat treatment apparatus according to the first embodiment.

It is a figure which shows the structure of the wafer heat processing system which concerns on 1st Embodiment. It is a top view which shows the arrangement | positioning form of an induction heating coil. It is a figure which shows the permeation | transmission characteristic of the electromagnetic wave in quartz glass. It is a figure which shows the structure of the laser oscillator which arrayed the light emitting element. It is a flowchart which shows the process of the temperature distribution control by the wafer heat processing system which concerns on embodiment. It is a figure which shows the modification of the wafer heat processing system which concerns on 1st Embodiment. It is a figure which shows the structure of the wafer heat processing system which concerns on 2nd Embodiment. It is a figure which shows the radiation characteristic of the electromagnetic wave in a silicon | silicone.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ......... Wafer heat treatment system, 12 ......... Heating furnace, 14 ......... Control room, 16 ......... Separator, 18 ...... Graphite, 20 ......... Wafer, 22 ...... Edge ring, 24 ... ... Process chamber, 30 ... Induction heating device, 32 (32a, 32b, 32c, 32d) ......... Induction heating coil, 34 ......... Power control unit, 36 (36a, 36b, 36c, 36d) ... ... Resonant capacitor, 38 (38a, 38b, 38c, 38d) ......... Inverter, 40 (40a, 40b, 40c, 40d) ... ... Chopper, 42 ... ... Converter, 44 ... ... Three-phase AC power supply, 46 ............ Drive control unit, 50... Laser irradiation device, 52... Condensing unit, 54... Laser oscillator, 60.

Claims (7)

A heating furnace in which a process chamber in which a radiant heat source and a wafer to be heated via the radiant heat source are arranged, and a control room in which the heat source is arranged are separated by a separator;
An induction heating device including an induction heating coil as a first heating source disposed in the control room;
A laser irradiation apparatus including a light collecting unit as a second heating source disposed in the control room;
Computation means for detecting the temperature distribution of the wafer and adjusting the power supplied to the induction heating coil based on the temperature distribution of the wafer and the output of the laser irradiated from the condensing unit,
The induction heating coil is formed in a substantially C shape and arranged in parallel to the radiant heat source,
The wafer heat treatment system, wherein the condensing unit is disposed at a position where a laser beam transmitted through the separator is irradiated to a central part surrounded by a heating region of the induction heating coil in the radiant heat source. An opening is provided in a central portion surrounded by a heating region of the induction heating coil in the radiant heat source,
2. The wafer heat treatment system according to claim 1, wherein the condensing unit is disposed at a position where the laser beam transmitted through the separator passes through the opening and is irradiated onto the wafer.   2. The wafer heat treatment system according to claim 1, wherein the laser irradiation surface of the radiant heat source is roughened.   4. The wafer heat treatment system according to claim 1, wherein a semiconductor laser is used as the laser irradiation device.   The separator is made of quartz glass, and the cladding layer of the semiconductor laser is made of an InP series semiconductor compound, the active layer is made of an InGaAsP series semiconductor compound, or the cladding layer is made of an AlGaAs series semiconductor compound, and the active layer is made of a GaAs series semiconductor compound. The wafer heat treatment system according to claim 1, wherein the wafer heat treatment system is performed. The wafer is silicon,
3. The wafer heat treatment system according to claim 2, wherein a semiconductor laser is employed as the laser irradiation device, the clad layer is made of an AlGa series semiconductor compound, and the active layer is made of a GaAs series semiconductor compound.   7. The power control unit according to claim 1, further comprising: a plurality of the induction heating coils arranged on a concentric circle, and a power control unit that can arbitrarily control power supplied to each induction heating coil. Wafer heat treatment system.

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