JP2013229517A - Horizontal type diffusion furnace, and dopant diffusion method for semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a horizontal type diffusion furnace capable of performing uniform diffusion in a semiconductor substrate surface and in a batch without reduction in productivity, and to provide a method of forming a uniform diffusion layer on a semiconductor substrate by using this diffusion furnace.SOLUTION: A horizontal type diffusion furnace performing thermal diffusion of a dopant for each of a plurality of semiconductor substrates arranged inside a tubular reaction chamber, comprises: a heater heating a dopant gas; a gas supply body provided at the reaction chamber, and having a plurality of gas supply ports for discharging the dopant gas into the reaction chamber toward a first lateral face of the semiconductor substrate; and a gas exhaustion part provided at the reaction chamber, and having a plurality of gas exhaustion ports for exhausting the dopant gas from a second lateral face side different from the first lateral face of the semiconductor substrate to the outside of the reaction chamber.

Description

  The present invention relates to a horizontal diffusion furnace for diffusing donor impurities or acceptor impurities (hereinafter collectively referred to as “dopants”) into a semiconductor substrate. Furthermore, the present invention relates to a dopant diffusion method for a semiconductor substrate in which a dopant diffusion region is formed in the semiconductor substrate using this horizontal diffusion furnace.

  Horizontal type in which the tube axis direction of the tubular reaction chamber is horizontal as an apparatus for introducing a dopant into the semiconductor substrate by thermal diffusion when manufacturing a semiconductor element such as a solar cell element having a crystalline silicon type semiconductor substrate A diffusion furnace is often used.

  In this horizontal diffusion furnace, after placing a semiconductor substrate in a tubular reaction chamber, the semiconductor substrate is heated in a reaction chamber while heating the semiconductor substrate using a heating means such as a resistance heater or a lamp heater arranged around the reaction chamber. A diffusion region can be formed on the surface of the semiconductor substrate by introducing a gas containing a dopant (hereinafter referred to as “dopant gas”).

  For this reason, a pn junction can be formed in the semiconductor substrate by forming a dopant diffusion region (diffusion layer) of the reverse conductivity type on the surface of the semiconductor substrate exhibiting one conductivity type. For example, a p-type silicon substrate can be used as a semiconductor substrate, and donor impurities can be diffused into the semiconductor substrate to form a pn junction. As this method, for example, a phosphorus diffusion method using phosphorus oxychloride (POCl3) as a dopant raw material is known.

  Since the dopant concentration profile in the diffusion layer of the semiconductor element is an important parameter that determines the characteristics of the semiconductor element, uniform diffusion in the surface of the semiconductor substrate and in the batch in order to improve the characteristics and yield of the semiconductor element. Various techniques for forming layers have been proposed so far.

  Patent Document 1 below discloses a horizontal diffusion furnace in which the temperature of each of the three divided heaters is independently controlled. Patent Document 2 discloses a diffusion furnace including a gas ejection body having a plurality of gas ejection ports. Patent Document 3 discloses a horizontal diffusion furnace having a ring-shaped discharge port and an exhaust passage.

  Thus, since the dopant concentration profile of the diffusion layer is limited by the concentration of the dopant gas supplied to the substrate surface and the substrate surface temperature, in order to form a uniform diffusion layer within the substrate surface and within the batch, It is necessary to improve the concentration and temperature distribution of the dopant gas supplied to the semiconductor substrate surface or to optimize the combination of the concentration distribution and the temperature distribution.

Japanese Patent Laid-Open No. 5-47685 Special table 2007-329437 JP 2006-278614 A

However, with the increase in the size of substrates for productivity improvement and the increase in the number of substrates processed per batch, the characteristics and yield of semiconductor elements due to the uniformity of the diffusion layer within the substrate surface and within the batch The impact will increase. Even in the conventional diffusion furnace described above, there is a distribution of the concentration and temperature of the dopant gas supplied to the substrate surface within the substrate surface and in the batch, and a technique for forming the diffusion layer more uniformly is desired.

  The present invention has been made in view of the above problems, and a horizontal diffusion furnace capable of performing uniform diffusion in a semiconductor substrate surface and in a batch without reducing productivity, and a semiconductor using this diffusion furnace. The main object is to provide a dopant diffusion method for a semiconductor substrate that can form a uniform diffusion layer on the substrate.

  A horizontal diffusion furnace according to an embodiment of the present invention is a horizontal diffusion furnace that thermally diffuses a dopant to a semiconductor substrate disposed in a horizontal tubular reaction chamber, and heats the dopant gas before introduction into the reaction chamber. A heater, a gas supply body having a plurality of gas supply ports for supplying the dopant gas in a predetermined first direction, and a plurality of the gases provided in the reaction chamber; A gas exhaust having a plurality of gas exhaust ports arranged corresponding to the supply ports and exhausting the dopant gas in a predetermined second direction.

  A method for diffusing a dopant into a semiconductor substrate according to an embodiment of the present invention includes: forming a dopant diffusion region in the semiconductor substrate disposed in the reaction chamber using the horizontal diffusion furnace. The dopant gas heated by the heater is supplied from the gas supply port in the first direction parallel to the first main surface of the semiconductor substrate disposed in a heated state in the reaction chamber. In addition, the dopant gas is discharged from the gas discharge port in the second direction parallel to the first main surface of the semiconductor substrate to thermally diffuse the dopant in the semiconductor substrate, and A dopant diffusion region is formed.

  According to the horizontal diffusion furnace and the semiconductor substrate dopant diffusion method described above, the dopant can be uniformly diffused in the semiconductor substrate and in the batch without reducing the productivity when the semiconductor element is manufactured.

FIG. 1 is a schematic cross-sectional view of a horizontal diffusion furnace according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing an example of a part of a gas supply body constituting a horizontal diffusion furnace according to an embodiment of the present invention. FIG. 3 is a perspective view schematically showing an example of a part of a gas discharger constituting a horizontal diffusion furnace according to an embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a horizontal diffusion furnace according to an embodiment of the present invention. FIGS. 5A and 5B are schematic views showing an example of a method for arranging a semiconductor substrate on a boat, in which FIG. 5A is a plan view and FIG. 5B is a side view. 6A and 6B are schematic views showing an example of a method for arranging a semiconductor substrate on a boat. FIG. 6A is a plan view and FIG. 6B is a side view. 7A and 7B are schematic views showing an example of a method for arranging a semiconductor substrate on a boat, in which FIG. 7A is a plan view and FIG. 7B is a side view. FIG. 8 is a graph showing a profile relating to the set temperature and gas introduction timing in the semiconductor substrate dopant diffusion method according to one embodiment of the present invention. FIG. 9 is a plan view schematically showing the measurement position of the sheet resistance (ρs) in the semiconductor substrate. FIG. 10 is a schematic cross-sectional view of a conventional horizontal diffusion furnace.

  DESCRIPTION OF EMBODIMENTS Embodiments of a horizontal diffusion furnace and a semiconductor substrate dopant diffusion method according to the present invention will be described below with reference to the drawings. In addition, drawing is shown typically and the size of each structure, positional relationship, etc. are not shown correctly.

<Basic configuration of horizontal diffusion furnace>
As shown in FIG. 1, the horizontal diffusion furnace F thermally diffuses a dopant in a semiconductor substrate 1 disposed in a horizontal tubular reaction chamber 3 and heats the dopant gas before introduction into the reaction chamber 3. A heater 6 is disposed around the reaction chamber 3.

  The reaction chamber 3 of the horizontal diffusion furnace F corresponds to the gas supply body 4 having a plurality of gas supply ports for supplying the dopant gas in a predetermined first direction, and the plurality of gas supply ports. And a gas discharger 5 having a plurality of gas discharge ports for discharging the dopant gas in a predetermined second direction.

  Here, as shown in the drawing, the semiconductor substrate 1 is preferably disposed in a boat 2 having an opening (not shown) so that the dopant gas can be efficiently discharged.

  The first direction and the second direction may be the same direction. The gas supply port may be opposed to the gas discharge port. Moreover, the gas supply body 4 may have one or more tubular parts, and the gas discharger 5 may have one or more tubular parts.

<Specific example of horizontal diffusion furnace>
Next, a more specific configuration of the horizontal diffusion furnace F will be described. As shown in FIG. 1, the horizontal diffusion furnace F includes, for example, a boat 2 that holds a plurality of semiconductor substrates 1 in a vertically standing state inside a tubular reaction chamber 3. A diffusion layer can be formed by diffusing a dopant on the surface. The materials of members mainly constituting the boat 2 and the reaction chamber 3 are appropriately determined depending on the conditions during use, the use of the semiconductor element, and the like. For example, quartz glass is preferably used.

  The semiconductor substrate 1 is made of, for example, crystalline silicon exhibiting one conductivity type. The crystal silicon substrate is industrially produced by the Czochralski method (CZ method), the floating zone method (FZ method) or the casting method (cast method).

  A semiconductor conductivity type is controlled by adding an element serving as a dopant to the semiconductor substrate 1. For example, if a Group 3 element such as boron is added to a silicon substrate, a p-type semiconductor is formed, and if a Group 5 element such as phosphorus is added, an n-type semiconductor is formed.

  The dopant raw material is supplied into the reaction chamber 3 as a gas (dopant gas). When the dopant raw material is liquid or solid, a method of supplying the vaporized gas together with the carrier gas or a method of supplying a reaction product gas with the carrier gas is used. For example, when forming a phosphorus diffusion layer on a silicon substrate using phosphorus oxychloride (POCl3), which is liquid at room temperature, as a dopant material, a mass flow controller is used for the phosphorus oxychloride of the dopant gas supply device 8 whose temperature is controlled by a thermostat or the like. Nitrogen gas and the like whose flow rate is controlled by a gas cylinder or the like is supplied from a carrier gas supply device 7, and phosphorus oxychloride vapor as a dopant gas is supplied to the reaction chamber 3 together with the carrier gas. Usually, an oxidizing gas such as oxygen gas is supplied simultaneously with a carrier gas that is an inert gas, and phosphorus oxychloride reacts with oxygen and a silicon substrate to form phosphosilicate glass (PSG). Then, a diffusion layer is formed by solid phase diffusion of phosphorus from PSG.

As a method for supplying phosphorus oxychloride, in addition to the above method, liquid phosphorus oxychloride having a controlled flow rate may be mixed with a carrier gas in a vaporizer and supplied to the reaction chamber 3. The PSG formed on the silicon substrate is removed with dilute hydrofluoric acid after the diffusion process.

  In the reaction chamber 3, a dopant gas is introduced into the reaction chamber 3 in the direction of, for example, the first side surface of the semiconductor substrate 1 disposed in the reaction chamber 3 or in one direction parallel to the first main surface of the semiconductor substrate 1. A gas supply body 4 having a plurality of gas supply ports 9 for introduction is arranged.

  Further, the reaction chamber 3 is arranged on a side different from the first side surface direction of the semiconductor substrate 1 or one direction parallel to the first main surface of the semiconductor substrate 1, and the dopant gas is discharged out of the reaction chamber 3. And a gas discharger 5 having a plurality of gas discharge ports 10.

  A heater 6 such as a resistance heating type carbon heater is disposed around the reaction chamber 3, and the semiconductor substrate 1 is heated by the heater 6.

  The gas supply port 9 and the gas discharge port 10 are disposed substantially parallel to the tube axis direction so as to face each other with the end portion of the semiconductor substrate 1 disposed therebetween. With the above structure, the concentration distribution of the dopant gas in the reaction chamber 3 can be made uniform, the dopant gas supplied to the reaction chamber 3 can be heated, and the gas temperature distribution in the reaction chamber 3 can be made uniform. can do.

  In particular, if the gas supply port 9 has a structure formed in a gas supply body 4 which is a tubular body installed in the reaction chamber 3, the dopant gas is supplied to the gas before being released into the reaction chamber 3. Since it can heat in the body 4, it is suitable.

  FIG. 2 shows an example of a tubular gas supply body 4 constituting the horizontal diffusion furnace F. As shown in the drawing, the gas supply body 4 is formed by connecting a plurality of tubular bodies 4a, 4b, 4c and 4d, for example. Specifically, for example, tubular bodies 4a and 4b having a plurality of gas supply ports 9 are connected by a tubular body 4c communicating with each other at the center thereof, and a carrier gas is connected to the tubular body 4c. The tubular body 4d connected to the supply device 7 and the dopant gas supply device 8 communicates. In addition, the gas supply body 4 may be arrange | positioned in the reaction chamber 3 on a wall surface so that replacement | exchange is possible, for example, and may be comprised with a plate-shaped body like a shower plate.

  FIG. 3 shows an example of a tubular gas discharger 5 constituting the horizontal diffusion furnace F. As shown in the figure, in the gas exhaust body 5 as well, the tubular gas exhaust body 5 having a plurality of gas exhaust ports 10 is used so that the gas supply port 9 faces the gas exhaust port 10, thereby allowing the reactor to react. Since the flow of the dopant gas in 3 can be finely controlled, the dopant gas concentration distribution can be made uniform. In addition, as above-mentioned, the gas exhaust body 5 may be arrange | positioned on a wall surface so that replacement | exchange is possible, for example, and may be comprised with a plate-shaped body. For example, as shown in FIG. 4, the gas discharge ports 10a and 10b may be provided at a plurality of locations on the wall surface.

  As described above, with respect to the gas supply body 4 having a plurality of gas supply ports for supplying the dopant gas in a predetermined first direction, the gas discharger 5 is arranged corresponding to the plurality of gas supply ports. And a plurality of gas discharge ports for discharging the dopant gas in a predetermined second direction. Here, in order that the dopant gas can be efficiently discharged and the gas pressure in the reaction chamber 3 is kept at a predetermined pressure, the first direction and the second direction are preferably the same direction. The gas supply port may be opposed to the gas discharge port.

The heater 6 for mainly heating the dopant gas can also serve as a heater for heating the semiconductor substrate 1 to simplify the structure of the horizontal diffusion furnace F. On the other hand, when the heater 6 does not sufficiently heat the dopant gas, such as when the gas supply port 9 is formed to penetrate the wall surface of the reaction chamber 3, the dopant gas passes from the gas supply port 9 into the reaction chamber 3. The temperature distribution of the dopant gas in the reaction furnace 3 can be made uniform by installing a preheating heater (not shown) in the previous stage supplied to the reactor.

  Further, for example, the overall structure of the gas supply body 4, the overall structure of the gas discharge body 5, the number of gas supply ports 9, the pitch, shape, size, etc., the number of gas discharge ports 10, the pitch, shape, size, etc. By appropriately adjusting, the concentration of the dopant gas can be suitably made uniform in the reaction chamber 3 in the region where the plurality of semiconductor substrates 1 are placed.

  For example, when the gas flow velocity and pressure continuously change in the upstream and downstream portions of the gas introduction pipe, each gas supply is performed by continuously changing the pitch of the gas supply ports 9 and the opening area thereof. The amount of dopant gas released from the port 9 can be made uniform.

  Moreover, when exhaust gas is collected from each gas exhaust port 10 through a pipe, the shape, size, pipe length, and the like of the opening may be determined so that the conductance of each pipe becomes equal.

  The shape of the gas supply body 4 and the shape of the gas supply port 9 are appropriately designed so that the dopant gas is sufficiently heated in the gas supply body 4 by the heater 6 and then released from the gas supply port 9. By doing so, the temperature variation of the dopant gas supplied in the area | region in which the some semiconductor substrate 1 in the reaction chamber 3 was mounted can be made small.

  5 to 7 show examples of placing the semiconductor substrate 1 on the boat 2. In either case, the semiconductor substrate 1 is vertically placed and placed in the reaction chamber 3. FIGS. 5A and 5B are examples in which the surface of the semiconductor substrate 1 is placed so as to be perpendicular to the tube axis direction of the tubular reaction chamber 3, and FIGS. This is an example in which the surface of the semiconductor substrate 1 is placed parallel to the tube axis direction, and FIGS. 7A and 7B show that the surface of the semiconductor substrate 1 is inclined with respect to the tube axis direction. This is an example.

  Under the gravity, the heated dopant gas causes thermal convection in the reaction chamber 3, and thus, the semiconductor substrate 1 is placed vertically in the tubular reaction chamber 3, and the gas supply body 4 and gas If the exhaust body 5 is arranged in the vertical direction so as to face the semiconductor substrate 1 and is opposed to the exhaust body 5, a dopant gas is obtained by a combination of a gas flow by thermal convection and a gas flow by the gas supply body 4 and the gas exhaust body 5 This is preferable because the concentration flow and the temperature distribution of the dopant gas on the surface of the semiconductor substrate 1 can be made more uniform.

<Dopant diffusion method of semiconductor substrate>
As described above, a suitable dopant diffusion method for the semiconductor substrate 1 is, for example, when the dopant diffusion region is formed in the semiconductor substrate 1 disposed in the reaction chamber 3 using the horizontal diffusion furnace F described above. The dopant gas heated by the heater 6 is supplied from the gas supply port 9 in a first direction parallel to the first main surface of the semiconductor substrate 1 placed in a heated state, and the first of the semiconductor substrate 1 The dopant diffusion region may be formed by thermally diffusing the dopant in the semiconductor substrate 1 so that the dopant gas is discharged from the gas discharge port 10 in the second direction parallel to the one main surface. At this time, if the heater 6 is also used for heating the semiconductor substrate 1, the configuration of the horizontal diffusion furnace F becomes simple and suitable.

<Effect of this embodiment>
As described above, according to the horizontal diffusion furnace F of this embodiment and the dopant diffusion method of the semiconductor substrate 1, the dopant gas is introduced into the reaction chamber 3 from the first side surface direction of the semiconductor substrate 1 disposed inside the reaction chamber 3. A gas supply body 4 having a plurality of gas supply ports 9 for introduction into the gas, and a gas that is disposed on a side different from the first side surface direction of the semiconductor substrate 1 and is opposed to the semiconductor substrate 1 Since the discharger 5 is provided, the dopant gas concentration distribution and temperature distribution on the surface of the semiconductor substrate 1 can be improved.

  In addition, this makes it difficult for the conventional diffusion furnace to achieve uniform diffusion within the substrate surface or in the batch. Even under diffusion conditions such as changing the set temperature or dopant gas flow rate during the diffusion process, the uniform diffusion layer Can be formed.

  Hereinafter, examples in which the above embodiment is more concretely described.

  First, p-type prepared by the Czochralski method (CZ method), doped with boron having a crystal orientation of Miller index (100), a diameter of 150 mm, a thickness of 180 μm, and a specific resistance of 2.0 Ω · cm A single crystal silicon substrate (semiconductor substrate 1) was prepared.

  As Example 1, in the horizontal diffusion furnace F shown in FIG. 1, the quartz tubular gas supply body 4 and the gas discharge body 5 shown in FIGS. 2 and 3 were prepared and installed in the reaction chamber 3. As shown in FIG. 5, 400 semiconductor substrates were placed on a quartz boat 2 to diffuse phosphorus.

  FIG. 8 shows the set temperature of the heater 6 and the phosphorus oxychloride (POCl 3) gas introduction profile during this diffusion. The diffusion method was performed in three steps (step 1 (pre-diffusion process), step 2 (diffusion process), and step 3 (post-diffusion process)) as described below.

  First, a boat 2 on which 400 semiconductor substrates 1 were placed was placed in a reaction chamber 3 maintained at a specified temperature (diffusion pretreatment temperature) while supplying a carrier nitrogen gas at a specified flow rate. Thereafter, carrier nitrogen gas, oxygen gas, and bubbling nitrogen gas for supplying phosphorus oxychloride were supplied by controlling the flow rate of each gas using a mass flow controller, and PSG was formed on the semiconductor substrate 1. . Here, phosphorus oxychloride was maintained at about 30 ° C. in a thermostat of the dopant gas supply device 8, and bubbling nitrogen gas was passed through liquid phosphorus oxychloride to supply phosphorus oxychloride vapor to the reaction chamber 3.

  Next, the supply of oxygen and phosphorus oxychloride is stopped, and the reaction chamber 3 is maintained at a specified temperature (drive-in temperature, that is, diffusion treatment temperature) higher than the pre-diffusion treatment temperature, and heat of phosphorus is obtained using PSG as a solid diffusion source. Diffusion was performed and phosphorus was diffused to an arbitrary diffusion depth.

  Furthermore, while maintaining a specified temperature (diffusion post-treatment temperature) lower than the drive-in temperature, carrier nitrogen gas, oxygen gas, and bubbling nitrogen gas are introduced to form PSG on the semiconductor substrate 1 again. Diffusion was performed so that the phosphorus concentration on the outermost surface of the substrate 1 was a predetermined concentration. Thereafter, the supply of oxygen and phosphorus oxychloride was stopped, the boat 2 was taken out after being cooled to a specified temperature (takeout temperature).

  Further, as Example 2, a tubular gas supply body 4 having the same shape as that of Example 1 was installed in a horizontal diffusion furnace F having two discharge ports 10a and 10b penetrating the reaction chamber 3 as shown in FIG. And diffused.

  Furthermore, as a comparative example, as shown in FIG. 10, a tubular gas supply body 4 having the same shape as that of Example 1 was installed in a horizontal diffusion furnace F having one discharge port 10c to perform diffusion.

  After the semiconductor substrate 1 was taken out, PSG formed on the surface of the semiconductor substrate 1 was removed with dilute hydrofluoric acid, and then the sheet resistance (ρs) of the diffusion layer was measured by a four-probe method. As shown in FIG. 9, the sheet resistance was measured at nine points M at equal intervals (45 mm) in the plane of the semiconductor substrate 1 (position of 35 mm from the end).

測定した結果を表１に示す。表１中のシート抵抗平均値は、各バッチ毎の全測定点（４００×９＝３６００点）における平均値である。また、半導体基板１の基板面内ばらつきは、上述した各測定位置（９点）毎のシート抵抗の平均値の最大値と最小値の差を全測定点の平均値で割った値である。また、半導体基板１の基板面間ばらつきは、各半導体基板（４００枚）毎のシート抵抗の平均値の最大値と最小値の差を全測定点の平均値で割った値である。

The measured results are shown in Table 1. The sheet resistance average value in Table 1 is an average value at all measurement points (400 × 9 = 3600 points) for each batch. Further, the in-plane variation of the semiconductor substrate 1 is a value obtained by dividing the difference between the maximum value and the minimum value of the sheet resistance at each measurement position (9 points) described above by the average value of all the measurement points. Further, the variation between the substrate surfaces of the semiconductor substrate 1 is a value obtained by dividing the difference between the maximum value and the minimum value of the average value of the sheet resistance for each semiconductor substrate (400 sheets) by the average value of all the measurement points.

  As shown in Table 1, in Examples 1 and 2, it was found that the sheet resistance distribution in the surface of the semiconductor substrate 1 and in the batch was improved as compared with the comparative example.

1: Semiconductor substrate 2: Boat 3: Reaction chamber 4: Gas supply body 5: Gas discharge body 6: Heating heater 7: Carrier gas supply apparatus 8: Dopant gas supply apparatus 9: Gas supply port 10: Gas discharge port F: Horizontal type Diffusion furnace

Claims (7)

A horizontal diffusion furnace for thermally diffusing a dopant into a semiconductor substrate disposed in a horizontal tubular reaction chamber,
A heater for heating the dopant gas before introduction into the reaction chamber;
A gas supply body provided in the reaction chamber and having a plurality of gas supply ports for supplying the dopant gas in a predetermined first direction;
A gas discharger provided in the reaction chamber and disposed corresponding to the plurality of gas supply ports and having a plurality of gas discharge ports for discharging the dopant gas in a predetermined second direction. Horizontal heat diffusion furnace.   The horizontal heat diffusion furnace according to claim 1, wherein the first direction and the second direction are the same direction.   The horizontal heat diffusion furnace according to claim 1, wherein the gas supply port faces the gas discharge port.   The horizontal heat diffusion furnace according to any one of claims 1 to 3, wherein the gas supply body has one or more tubular portions.   The horizontal heat diffusion furnace according to any one of claims 1 to 4, wherein the gas discharger has one or more tubular portions. A method for diffusing a dopant into a semiconductor substrate using the horizontal diffusion furnace according to any one of claims 1 to 5, wherein a dopant diffusion region is formed in the semiconductor substrate disposed in the reaction chamber,
The dopant gas heated by the heater is supplied from the gas supply port in the first direction parallel to the first main surface of the semiconductor substrate disposed in the heated state in the reaction chamber, and The dopant gas is discharged from the gas discharge port in the second direction parallel to the first main surface of the semiconductor substrate, and the dopant is thermally diffused in the semiconductor substrate to form the dopant diffusion region. A method for diffusing a dopant into a semiconductor substrate to be formed.   The method for diffusing a dopant into a semiconductor substrate according to claim 6, wherein the heater is also used for heating the semiconductor substrate.

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