Focusing ring stage

Abstract

The present invention provides a focusing ring mounting platform, which uses protective materials to protect the inner and outer sides of the adhesive material that bonds the ceramic heater for the focusing ring to the metal base, and prevents the occurrence of adverse conditions caused by the difference in thermal expansion between the adhesive material and the protective material. The focusing ring (FR) mounting platform includes: a circular ring-shaped FR ceramic heater; a FR cooling plate as a metal base; an adhesive sheet as an adhesive material for bonding the FR cooling plate and the FR ceramic heater; and inner and outer protective materials provided between the FR cooling plate and the FR ceramic heater in a manner bonded to the inner and outer portions of the adhesive sheet. The thermal expansion coefficient of the adhesive sheet is less than the thermal expansion coefficient of the inner protective material and greater than the thermal expansion coefficient of the outer protective material.

Description

Technical Field

[0001] The present invention relates to a focusing ring mounting table. Background Art

[0002] A wafer processing device is used to perform CVD, etching, etc. on a wafer using plasma. Patent document 1 discloses a wafer processing device comprising: a metal base, which is formed by connecting a disk-shaped center-side metal base and an annular outer-side metal base; a disk-shaped center-side electrostatic chuck heater, which is arranged on the upper surface of the center-side metal base; and an annular outer-side electrostatic chuck heater, which is arranged on the upper surface of the outer-side metal base. In this wafer processing device, a disk-shaped wafer is electrostatically adsorbed on the upper surface of the center-side electrostatic chuck heater, and an annular focusing ring is electrostatically adsorbed on the upper surface of the outer-side electrostatic chuck heater. In addition, the temperature of the wafer and the temperature of the focusing ring are controlled separately.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-207979 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The peripheral metal base is bonded to the peripheral electrostatic chuck heater by an adhesive sheet. The adhesive sheet may corrode in the use environment. Therefore, it is considered to prevent the corrosion of the adhesive sheet by filling the protective material in a manner surrounding the periphery (inner periphery and outer periphery) of the adhesive sheet. Within the scope known to the inventors, such a technology is not currently known. When the protective material is filled in a manner surrounding the periphery of the adhesive sheet, the adhesive sheet and the protective material are tightly bonded and integrated. In this state, when the peripheral electrostatic chuck heater becomes high temperature, the adhesive sheet and the protective material will extend outward in the radial direction. Here, when the CTE (thermal expansion coefficient) of the adhesive sheet is greater than the CTE of the protective material, the elongation of the adhesive sheet is greater than the elongation of the protective material, so at the inner periphery of the adhesive sheet, the protective material is stretched by the adhesive sheet. As a result, sometimes peeling and cracking occur in at least one of the adhesive sheet or the protective material. On the other hand, when the CTE of the adhesive sheet is smaller than the CTE of the protective material, the elongation of the protective material is greater than the elongation of the adhesive sheet, so the adhesive sheet is stretched by the protective material at the periphery of the adhesive sheet. As a result, peeling or cracking may occur in at least one of the adhesive sheet or the protective material. It should be noted that such a problem will occur regardless of whether the electrostatic adsorption function is present or not.

[0008] The present invention is completed to solve such a problem, and its main purpose is to protect the inner and outer sides of the adhesive material that bonds the ceramic heater for the focus ring to the metal base with a protective material, and to prevent the occurrence of adverse conditions caused by the thermal expansion difference between the adhesive material and the protective material.

[0009] Methods for solving problems

[0010] The focusing ring mounting platform of the present invention comprises:

[0011] The circular ceramic heater that holds the focus ring,

[0012] Metal base,

[0013] an adhesive material for bonding the metal base and the ceramic heater,

[0014] an inner peripheral side protection material provided between the metal base and the ceramic heater so as to be bonded to the inner peripheral portion of the bonding material, and

[0015] an outer peripheral side protection material, which is provided between the metal base and the ceramic heater in a manner bonded to the outer peripheral portion of the adhesive material,

[0016] The thermal expansion coefficient of the adhesive material is less than or equal to the thermal expansion coefficient of the inner circumference side protection material and greater than or equal to the thermal expansion coefficient of the outer circumference side protection material.

[0017] The focus ring mounting table is provided with inner and outer protective materials surrounding the inner and outer peripheral portions of the adhesive material. The inner and outer peripheral sides of the adhesive material are protected by the protective material. In addition, in such a focus ring mounting table, when the temperature reaches a high temperature, the adhesive material, the inner protective material and the outer protective material all extend outward in the radial direction. Here, the thermal expansion coefficient of the adhesive material is lower than the thermal expansion coefficient of the inner protective material, so the amount of the adhesive material extending outward in the radial direction is the same as or less than the amount of the inner protective material extending outward in the radial direction. Therefore, no tensile stress is generated in which the adhesive material stretches the inner protective material outward in the radial direction. Therefore, it is possible to prevent an adverse condition caused by a thermal expansion difference from occurring in at least one of the adhesive material and the inner protective material. In addition, the thermal expansion coefficient of the adhesive material is higher than the thermal expansion coefficient of the outer protective material, so the amount of the outer protective material extending outward in the radial direction is the same as or less than the amount of the adhesive material extending outward in the radial direction. Therefore, the outer peripheral side protection material does not generate tensile stress that pulls the adhesive material outward in the radial direction. Therefore, it is possible to prevent a problem caused by a difference in thermal expansion from occurring in at least one of the adhesive material and the outer peripheral side protection material.

[0018] In the focus ring mounting platform of the present invention, the thermal expansion coefficient of the adhesive material may be smaller than the thermal expansion coefficient of the inner peripheral side protection material, or may be larger than the thermal expansion coefficient of the outer peripheral side protection material. In this way, it is not necessary to make the thermal expansion coefficients of the adhesive material, the inner peripheral side protection material, and the outer peripheral side protection material the same.

[0019] In the focusing ring mounting table of the present invention, the metal base may have an insulating film on at least the portion where the inner circumference protection material and the outer circumference protection material are formed in the side surface of the metal base and the surface opposite to the ceramic heater. In this way, it is possible to prevent unexpected discharge from being caused via the metal base. The insulating film preferably has corrosion resistance in the use environment. As an insulating film, for example, a ceramic sprayed film can be cited. Such an insulating film can also be provided to cover the portion where the adhesive material is formed in the surface of the metal base opposite to the ceramic heater.

[0020] In the focusing ring mounting table of the present invention, when adjusting the thermal expansion coefficients of the adhesive material, the inner side protection material and the outer side protection material, for example, different types of materials may be used respectively. As the type of material, epoxy resin, acrylic resin, silicone resin, etc. may be cited. Alternatively, resins of different compositions may be used from the same type of resin. For example, among the types of epoxy resins, there are many epoxy resins with different compositions, and epoxy resins with different thermal expansion coefficients exist due to different compositions. This is also the same for other resins. Alternatively, resins of the same composition but with different types and amounts of additives may be used. As additives, fillers may be cited. For example, when adding a filler whose thermal expansion coefficient decreases as the amount of the filler added increases to the silicone resin of the same composition, if the amount of the filler added is the least for the inner side protection material and the most for the outer side protection material, it can be set to (CTE of the inner side protection material)>(CTE of the adhesive sheet)>(CTE of the outer side protection material). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a longitudinal sectional view of the wafer processing apparatus 10 .

[0022] Figure 2 It is a top view of the focus ring mounting table 20 .

[0023] Figure 3 yes Figure 2 AA section view.

[0024] Explanation of symbols

[0025] 10 Wafer processing device, 12 Wafer mounting table, 14 Wafer ceramic heater, 14a surface, 14b back side, 14c ceramic substrate, 14d resistive heating element, 15 adhesive sheet, 16 Wafer cooling plate, 16a Wafer cooling plate flange, 16b through hole, 20 Focusing ring (FR) mounting table, 22FR ceramic heater, 22a surface, 22b back side, 22c ceramic substrate, 22d resistive heating element, 24FR cooling plate, 24a convex portion, 25 adhesive sheet, 27i inner side protective material, 27o outer side protective material, 29i inner side insulating film, 29o outer side insulating film, 80 chamber, 82 setting plate, 84 bolt, 90 nozzle, W wafer. DETAILED DESCRIPTION

[0026] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 is a longitudinal sectional view of the wafer processing apparatus 10, Figure 2 is a top view of the focusing ring mounting platform 20, Figure 3 yes Figure 2 AA cross-sectional view (with partial enlarged view). In the following description, sometimes up and down, left and right, front and back are used for description, but up and down, left and right, front and back are just relative positional relationships.

[0027] The wafer processing apparatus 10 is used to perform CVD, etching, etc. on a wafer W using plasma, and is fixed to a setting plate 82 provided inside a chamber 80 for semiconductor processes. The wafer processing apparatus 10 includes a wafer stage 12 and a focus ring stage 20. Hereinafter, the focus ring may be abbreviated to "FR".

[0028] The wafer mounting table 12 includes a wafer ceramic heater 14 and a wafer cooling plate 16. The wafer cooling plate 16 is bonded to the back surface 14b of the wafer ceramic heater 14 opposite to the front surface 14a as the wafer mounting surface via an adhesive sheet 15. The adhesive sheet 15 is a circular double-sided adhesive tape. Examples of the material of the adhesive sheet 15 include epoxy resin, acrylic resin, silicone resin, and the like.

[0029] The ceramic heater 14 for the chip is a disc-shaped component, and a resistance heating element 14d is buried in a ceramic substrate 14c. The ceramic substrate 14c is a disc-shaped plate made of a ceramic material represented by aluminum oxide, aluminum nitride, yttrium oxide, etc. A chip W is placed on the surface 14a of the ceramic substrate 14c. The resistance heating element 14d is made of a conductive coil or printed pattern, and is wired in a single stroke from one end to the other end without crossing over the entire surface when viewed from above. One end and the other end of the resistance heating element 14d are connected to a pair of power supply rods (not shown) that pass through the setting plate 82, the chip cooling plate 16 and the adhesive sheet 15 and are inserted into the ceramic substrate 14c. Voltage is applied to the resistance heating element 14d via the power supply rods.

[0030] The wafer cooling plate 16 is a disc-shaped plate made of a metal represented by aluminum, aluminum alloy, etc., and has a refrigerant passage (not shown) inside for circulating refrigerant. The refrigerant passage is connected to a refrigerant supply passage (not shown) and a refrigerant discharge passage (not shown) that penetrate the setting plate 82, and the refrigerant discharged from the refrigerant discharge passage returns to the refrigerant supply passage again after temperature adjustment. The wafer cooling plate 16 has a wafer cooling plate flange portion 16a protruding from the outer peripheral surface of the lower end portion (the end portion on the side close to the setting plate 82) of the wafer cooling plate 16 toward the radial outside. A plurality of through holes 16b are provided in the wafer cooling plate flange portion 16a along the circumferential direction.

[0031] The FR stage 20 is separate from the wafer stage 12 and is arranged on the outer periphery of the wafer stage 12. The FR stage 20 includes a FR ceramic heater 22 and a FR cooling plate 24. The FR cooling plate 24 is bonded to the back surface 22b of the FR ceramic heater 22 opposite to the front surface 22a as the FR mounting surface via an adhesive sheet 25. The adhesive sheet 25 is a circular ring-shaped double-sided adhesive tape. Examples of the material of the adhesive sheet 25 include epoxy resin, acrylic resin, silicone resin, and the like.

[0032] The FR ceramic heater 22 has a resistive heating element 22d embedded in a ceramic base 22c. The ceramic base 22c is an annular plate made of the same material as the ceramic base 14c. A focusing ring FR is placed on the surface 22a of the ceramic base 22c. The resistive heating element 22d is made of a conductive coil or printed pattern, and is wired in a single stroke from one end to the other end without crossing over the entire surface when viewed from above. One end and the other end of the resistive heating element 22d are connected to a pair of power supply rods (not shown) that penetrate the setting plate 82, the FR cooling plate 24, and the adhesive sheet 25 and are inserted into the ceramic base 22c. Voltage is applied to the resistive heating element 22d via the power supply rods.

[0033] The FR cooling plate 24 is an annular plate made of a metal represented by aluminum, aluminum alloy, etc., and has a refrigerant passage (not shown) inside for circulating the refrigerant. The refrigerant passage is connected to the refrigerant supply passage and the refrigerant discharge passage that penetrate the setting plate 82, and the refrigerant discharged from the refrigerant discharge passage returns to the refrigerant supply passage again after temperature adjustment. The FR cooling plate 24 is provided with a plurality of convex portions 24a along the circumferential direction on the lower surface of the FR cooling plate 24. By fastening the bolt 84 to the threaded hole of the convex portion 24a from the back of the setting plate 82 while the convex portion 24a provided on the back of the FR cooling plate 24 is embedded in the through hole 16b of the wafer cooling plate flange portion 16a, the wafer mounting table 12 is fixed to the setting plate 82 via the FR mounting table 20.

[0034] On the inner peripheral side of the adhesive sheet 25 between the FR ceramic heater 22 and the FR cooling plate 24, an adhesive inner peripheral side protective material 27i is provided in a manner surrounding the inner peripheral portion (inner peripheral surface) of the adhesive sheet 25. The adhesive sheet 25 is bonded to the inner peripheral side protective material 27i. On the outer peripheral side of the adhesive sheet 25 between the FR ceramic heater 22 and the FR cooling plate 24, an adhesive outer peripheral side protective material 27o is provided in a manner surrounding the outer peripheral portion (outer peripheral surface) of the adhesive sheet 25. The adhesive sheet 25 is bonded to the outer peripheral side protective material 27o. The coefficient of thermal expansion (CTE) of the adhesive sheet 25 is less than the CTE of the inner peripheral side protective material 27i, preferably less than the inner peripheral side protective material 27i. The CTE of the adhesive sheet 25 is greater than the CTE of the outer peripheral side protective material 27o, preferably greater than the outer peripheral side protective material 27o. The inner side protection material 27i and the outer side protection material 27o are formed of a material having higher corrosion resistance than the adhesive sheet 25 in the atmosphere of the environment in which the wafer processing device 10 is used (e.g., an atmosphere of process gas, plasma, etc.). Therefore, the inner side protection material 27i and the outer side protection material 27o play a role in protecting the adhesive sheet 25 from the atmosphere of the use environment. For example, when epoxy resin is used as the material of the adhesive sheet 25, silicone resin can be used as the material of the inner side protection material 27i and the outer side protection material 27o. In this case, when the CTE of the inner side protection material 27i and the CTE of the outer side protection material 27o are set to different values, silicone resins of the same composition can be used and the type and amount of filler added to the silicone resin can be adjusted, or silicone resins of different compositions can be used. As fillers, for example, aluminum oxide, yttrium oxide, etc. can be cited.

[0035] The FR cooling plate 24 has an inner circumferential insulating film 29i and an outer circumferential insulating film 29o. The inner circumferential insulating film 29i is provided on the inner circumferential surface of the FR cooling plate 24 and the portion of the surface of the FR cooling plate 24 facing the FR ceramic heater 22 where the inner circumferential protective material 27i is formed. In the present embodiment, the inner circumferential insulating film 29i enters the adhesive sheet 25. The outer circumferential insulating film 29o is provided on the outer circumferential surface of the FR cooling plate 24 and the portion of the surface of the FR cooling plate 24 facing the FR ceramic heater 22 where the outer circumferential protective material 27o is formed. In the present embodiment, the outer circumferential insulating film 29o enters the adhesive sheet 25. The insulating films 29i and 29o preferably have corrosion resistance in the use environment. As the insulating films 29i and 29o, for example, a sprayed film can be used. As the material of the sprayed film, insulating ceramics (such as aluminum oxide, yttrium oxide, etc.) can be cited.

[0036] The FR mounting table 20 can be manufactured, for example, by the following method. First, prepare a ceramic heater 22 for FR, a cooling plate 24 for FR, and a double-sided tape. The double-sided tape eventually becomes an adhesive sheet 25, and has release paper on both sides. Next, peel off the release paper from one side of the double-sided tape to expose the adhesive surface, and paste the adhesive surface of the double-sided tape on the surface of the cooling plate 24 for FR. Next, peel off the release paper from the other side of the double-sided tape to expose the adhesive surface, and place the back side 22b of the ceramic heater 22 for FR here to bond it. As a result, the ceramic heater 22 for FR and the cooling plate 24 for FR become a state of being bonded by the adhesive sheet 25. Afterwards, an adhesive filling material is filled between the ceramic heater 22 for FR and the cooling plate 24 for FR and around the adhesive sheet 25 (inner and outer sides). The filling material eventually becomes the inner and outer protective materials 27i and 27o. At this time, the filling material is filled in a manner that the filling material and the adhesive sheet 25 are closely fitted. Then, the filling material is cured to form the inner and outer peripheral protection materials 27i and 27o. Thus, the FR mounting table 20 is obtained.

[0037] Next, use Figure 1 The following describes an example of using the wafer processing device 10. The chamber 80 includes a mounting plate 82 for mounting the wafer processing device 10 therein. The wafer processing device 10 is mounted on the mounting plate 82 as described above. A showerhead 90 is disposed on the ceiling surface of the chamber 80 to release a process gas from a plurality of gas injection holes into the chamber 80.

[0038] A disc-shaped wafer W is placed on the surface 14a of the wafer processing apparatus 10. The temperature of the wafer W can be controlled by adjusting the power supplied to the resistance heating element 14d of the wafer ceramic heater 14 and the temperature of the refrigerant supplied to the refrigerant passage (not shown) of the wafer cooling plate 16. The temperature control of the wafer W is performed by detecting the temperature of the wafer W using a temperature detection sensor (not shown) and feeding back the temperature so that the temperature becomes the target temperature.

[0039] A focus ring (FR) is placed on the surface 22a of the wafer processing device 10. The focus ring has a step along the inner circumference of the upper end portion so as not to interfere with the wafer W. The temperature of the focus ring can be controlled by adjusting the power supplied to the resistance heating element 22d of the FR ceramic heater 22 and the temperature of the refrigerant supplied to the refrigerant passage (not shown) of the FR cooling plate 24. The temperature control of the focus ring is performed by detecting the temperature of the focus ring using a temperature detection sensor (not shown) and feeding back the temperature so that the temperature becomes the target temperature.

[0040] In this state, the interior of the chamber 80 is set to a predetermined vacuum atmosphere (or reduced pressure atmosphere), and high frequency power is supplied between the wafer cooling plate 16 of the wafer stage 12 and the shower head 90 while supplying process gas to generate plasma. Then, CVD film formation or etching is performed on the wafer using this plasma. In addition, the space below the plate 82 is set to an air atmosphere.

[0041] As the wafer W is processed by plasma, the focus ring is also consumed. However, since the focus ring is relatively thick, the focus ring is replaced after a plurality of wafers W are processed.

[0042] Here, refer to Figure 3 The operation of the adhesive sheet 25, the inner and outer protective materials 27i, 27o of the FR mounting table 20 is explained in the partially enlarged view. When the FR mounting table 20 reaches a high temperature, the adhesive sheet 25 and the inner and outer protective materials 27i, 27o are all radially outward ( Figure 3 Here, since the CTE of the adhesive sheet 25 is less than the CTE of the inner peripheral side protective material 27i, the amount of outward extension of the adhesive sheet 25 in the radial direction ( Figure 3 The black arrow) and the amount of radial extension of the inner protective material 27i outward ( Figure 3 The adhesive sheet 25 has a CTE greater than or equal to the CTE of the outer protective material 27o. Therefore, the adhesive sheet 25 does not generate tensile stress that causes the inner protective material 27i to be stretched outward in the radial direction. Therefore, it is possible to prevent the occurrence of adverse conditions (such as peeling, cracking, etc.) caused by the difference in thermal expansion in at least one of the adhesive sheet 25 and the inner protective material 27i. In addition, since the CTE of the adhesive sheet 25 is greater than the CTE of the outer protective material 27o, the amount of radial outward extension of the outer protective material 27o ( Figure 3 The amount of the adhesive sheet 25 extending outward in the radial direction ( Figure 3 Therefore, the outer peripheral side protection material 27o does not generate tensile stress that pulls the adhesive sheet 25 outward in the radial direction. Therefore, it is possible to prevent the occurrence of a malfunction caused by a thermal expansion difference in at least one of the adhesive sheet 25 and the outer peripheral side protection material 27o.

[0043] Here, the correspondence between the components of the present embodiment and the components of the present invention is clarified. The FR mounting table 20 of the present embodiment is equivalent to the focus ring mounting table of the present invention, the FR ceramic heater 22 is equivalent to the ceramic heater, the FR cooling plate 24 is equivalent to the metal base, the adhesive sheet 25 is equivalent to the adhesive material, and the inner and outer protective materials 27i and 27o are equivalent to the inner and outer protective materials, respectively.

[0044] In the FR mounting table 20 described above, the adhesive sheet 25 is protected by the inner and outer protective materials 27i and 27o, so the corrosion resistance of the adhesive sheet 25 is improved in the use environment of the FR mounting table 20. In addition, since the CTE of the adhesive sheet 25 is set to be lower than the CTE of the inner protective material 27i and higher than the CTE of the outer protective material 27o, it is possible to prevent the occurrence of a malfunction caused by a difference in thermal expansion in any of the adhesive sheet 25, the inner protective material 27i, and the outer protective material 27o.

[0045] In addition, the FR cooling plate 24 has an inner insulating film 29i and an outer insulating film 29o on the side of the FR cooling plate 24 and the surface opposite to the FR ceramic heater 22, where the inner and outer protective materials 27o and 27i are formed, respectively. This can prevent unexpected discharge from occurring via the FR cooling plate 24.

[0046] It should be noted that it goes without saying that the present invention is not limited to the above-mentioned embodiments, and can be implemented in various forms as long as it belongs to the technical scope of the present invention.

[0047] For example, in the above-mentioned embodiment, when the adhesive sheet 25 and the inner circumference side protection material 27i are formed of different materials, or when the adhesive sheet 25 and the outer circumference side protection material 27o are formed of different materials, it is sometimes not easy to make their CTEs the same. Therefore, the CTE of the adhesive sheet 25 may be smaller than the CTE of the inner circumference side protection material 27i, and larger than the CTE of the outer circumference side protection material 27o.

[0048] In the above-mentioned embodiment, an electrostatic electrode may be provided between the surface 14a of the wafer ceramic heater 14 and the resistance heating element 14d, and a DC voltage may be applied to the electrostatic electrode to adsorb the wafer W to the surface 14a. Alternatively, an electrostatic electrode may be provided between the surface 22a of the FR ceramic heater 22 and the resistance heating element 22d, and a DC voltage may be applied to the electrostatic electrode to adsorb the focusing ring to the surface 22a.

[0049] In the above-described embodiment, the wafer cooling plate 16 and the FR cooling plate 24 are provided as separate components. However, the wafer cooling plate 16 and the FR cooling plate 24 may be integrated into one component.

[0050] In the above-mentioned embodiment, for example, the adhesive sheet 25, the inner circumference side protection material 27i and the outer circumference side protection material 27o may all be made of epoxy resin, and a epoxy resin having a CTE of 3×10 -5 [ / ℃] epoxy resin is used as the inner peripheral side protection material 27i, and a CTE of 1×10 -5[ / ℃] epoxy resin sheet is used as the adhesive sheet 25, and a CTE of 6×10 -6 [ / °C] epoxy resin is used as the outer peripheral side protection material 27o.

[0051] In the above-described embodiment, the adhesive sheet 25 is exemplified as the adhesive material. However, an adhesive material obtained by curing a fluid resin or the like may be used instead of the adhesive sheet 25 .

Claims

1. A focusing ring mounting platform, comprising: The circular ceramic heater that holds the focus ring, Metal base, an adhesive material for bonding the metal base and the ceramic heater, an inner peripheral side protection material provided between the metal base and the ceramic heater so as to be bonded to the inner peripheral portion of the bonding material, and an outer peripheral side protection material, which is provided between the metal base and the ceramic heater in a manner bonded to the outer peripheral portion of the adhesive material, The thermal expansion coefficient of the adhesive material is less than or equal to the thermal expansion coefficient of the inner circumference side protection material and greater than or equal to the thermal expansion coefficient of the outer circumference side protection material. 2 . The focus ring mounting table according to claim 1 , wherein a thermal expansion coefficient of the adhesive material is smaller than a thermal expansion coefficient of the inner circumference side protection material and larger than a thermal expansion coefficient of the outer circumference side protection material.

3. The focus ring mounting table according to claim 1 or 2, wherein the metal base has an insulating film at least in a portion where the inner circumference side protection material and the outer circumference side protection material are formed on a side surface of the metal base and a surface facing the ceramic heater.

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