The disclosure relates to a method of forming semiconductor devices on a semiconductor wafer. More specifically, the disclosure relates to systems for plasma or non-plasma processing semiconductor devices.
In forming semiconductor devices, stacks are subjected to processing in a plasma processing chamber. Such processes may require ultralow or cryogenic temperatures.
To achieve the foregoing and in accordance with the purpose of the present disclosure, an apparatus is provided. The apparatus comprises a processing chamber.
A substrate support is within the processing chamber, wherein the substrate support is for thermal contact with a substrate. A cooling system cools the substrate support. The cooling system comprises a first refrigeration system. The first refrigeration system comprises a first refrigerant inlet for receiving the first refrigerant from a first refrigerant source outside of the refrigeration system, wherein the first refrigerant is at a first pressure, a first throttle, wherein the first throttle allows a controlled expansion of the first refrigerant, wherein the expansion of the first refrigerant cools the first refrigerant, a first heat transfer system, for absorbing heat and transferring heat to the cooled first refrigerant, and a first refrigerant return for directing the first refrigerant from the first refrigeration system at a second pressure away from the first refrigeration system.
In another manifestation, an apparatus for processing a substrate is provided comprising a processing chamber and the supporting subsystems for the process module. A substrate support is within the processing chamber. A cooling system provides at least 20 kWatts of cooling, wherein the cooling system has a footprint with dimensions less than or equal to the footprint of the processing chamber or the process module.
In another manifestation, an apparatus for processing a substrate comprises a processing chamber and the supporting subsystems for a process module. A substrate support is within the processing chamber, wherein the substrate support comprises various components, layers, and coatings. The process module also includes other adjacent subsystems mounted to or in close proximity to the process chamber needed for the process to occur. This includes but is not limited to power boxes, RF generators, gas boxes, pumps, etc. A cooling system cools the substrate support such that no damage or degradation occurs to the substrate support due to the temperature changes that occur when switching from one temperature set point to another, especially when rapidly switching the coolant source from one channel to another.
In another manifestation, an apparatus for processing a substrate comprises a processing chamber and the supporting subsystems for a process module. A substrate support is within the processing chamber. A cooling system cools the substrate support. The cooling system comprises a first refrigeration system with a first refrigerant comprising carbon dioxide (CO2). The cooling system comprises a first compressor for compressing the first refrigerant to first pressure, a first heat transfer device for transferring heat from the compressed first refrigerant, a first throttle, wherein the first throttle allows a controlled expansion of the first refrigerant, wherein the expansion of the first refrigerant cools the first refrigerant, and an at least one channel in the substrate support, wherein the first refrigerant flows through the at least one channel.
These and other features of the present disclosure will be described in more detail below in the detailed description and in conjunction with the following figures.
The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
The present disclosure will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art, that the present disclosure may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present disclosure.
In semiconductor device fabrication, a plasma may be used for etching various layers or depositing layers, such as in plasma enhanced deposition. It has been found that during such plasma processing, a substrate may need to be cooled. Requirements for such cooling may require providing a refrigerant at a temperature of below −75° C. and a liquid coolant temperature of below −70° C. Such cooling systems also require high cooling capacities. Some systems may require providing a refrigerant at a temperature below −135° C. In plasma processing systems, refrigeration systems are typically located in a subfab on a floor above or below the plasma processing system and must fit within the space requirements provided by the plasma processing system such that the footprint of the refrigeration system must fit within the footprint of the plasma processing system also referred to as a process module. The standard SEMI E:72 provides industry standards for the size of a process module. Alternatively, refrigerant temperatures as low as of −80° C., −90° C., −100° C., −110° C., −120° C., −130° C., −150° C., −160° C. and −180° are also expected to be beneficial.
The low stage 124 comprises a low stage compressor 144, a low stage heat output heat exchanger 148, a low stage throttle 152, and a low stage heat absorption heat exchanger 156. The low stage compressor 144 compresses a second refrigerant. The second refrigerant may be the same kind of refrigerant as the first refrigerant or maybe a different refrigerant. In this example, the second refrigerant has a normal boiling point between −10° C. and −100° C. Preferably the refrigerant is comprised of a hydrofluorocarbon (HFC) (for example, R-134a, R-32, or R-23), a fluorocarbon (FC) (for example R-218, R-116, or R-14), a hydrofluoroolefin (HFO) (for examples R-1234yf or R-1234ze), or a mixture of different molecules that include these types of compounds. Alternatively, hydrocarbons (HC's) (for example n-butane, iso-butane, propane, or ethane) may be used. However, preferably the resulting mixture is nonflammable and with a low global warming potential (GWP). Use of xenon or krypton, by itself or in a mixture is also a possibility to achieve temperatures below −100° C. The low stage compressor 144 compresses the second refrigerant to a pressure above 100 psi (689 kiloPa). The low stage heat output heat exchanger 148 passes heat from the second refrigerant to the first refrigerant. The heat exchange cools the second refrigerant. The second refrigerant condenses. The low stage throttle 152 provides a controlled expansion of the second refrigerant. The controlled expansion of the second refrigerant causes the second refrigerant to cool. The low stage throttle 152 helps to control the temperature of the expanded second refrigerant. The low stage heat absorption heat exchanger 156 absorbs heat. In this example, the low stage heat absorption heat exchanger 156 absorbs heat from an electrostatic chuck
(ESC) 160. A tool cooling system 164 or other heat transfer apparatus may be placed between the low stage heat absorption heat exchanger 156 and the ESC 160. In this embodiment, a coolant heat exchanger 168 is placed adjacent to the low stage heat absorption heat exchanger 156. A coolant is circulated between the coolant heat exchanger 168 and the ESC 160. The use of conventional liquid coolants below −40°
C. can be challenging due to very high viscosities that can develop at the very low temperatures described in this disclosure. In additional embodiments, very high pressure gas, at pressures of 400 psi, 1500 psi, 15,000 psi, or 150,000 psi are recirculated to regulate the temperature of the ESC 160 in place of liquid coolants, so as to deliver effective heat transfer and avoid the high viscosity issues associated with typical liquid coolants. Gases such as helium, neon, nitrogen, argon, krypton and xenon are example gases for this embodiment. In the example of a recirculated liquid coolant, or a very high pressure gas, a prime mover is required (not shown for clarity) to force the fluid in the loop shown in tool cooling system 164. Alternatively, other means of heat transfer are possible such as, but not limited to, a conductive element, a superconducting element, a heat pipe, or a less constrained version of a heat pipe known as a thermo-siphon where liquid fluid boils from the ESC 160, is condensed in low stage heat absorption heat exchanger 156 and fed by gravity or a liquid pump back to ESC 160.
The tool cooling system 164 comprises the low stage 124, the inlet 128 and the first throttle 132, the first heat transfer system 136, and the refrigerant return 140 of the high stage 120. Since the tool cooling system 164 does not include but uses the facility compressor 112 and the cooler 116, the volume and footprint of the tool cooling system 164 may be minimized As a result, the tool cooling system 164 is able to fit within an allotted space in the tool.
In an embodiment, the tool cooling system 164 is able to fit in a footprint of 584 mm×1435 mm with a height of no more than 2000 mm This embodiment is able to provide at least 11 kilowatts of cooling at a coolant at a temperature of −70° C. or colder to the ESC 160. In this embodiment, the ESC 160 is a substrate support. The embodiment is able to have a minimum coolant flow rate of at least 7 liters per minute. The embodiment is able to provide temperature control of the coolant with an accuracy of 1° C.
This embodiment provides a three-channel system. In a three-channel system, each channel has a specified temperature control range. In the three-channel system, shown in
In an alternate embodiment, valve manifold 220 is able to selectively mix coolant from channel 1 and channel 2 and deliver all, or a portion of these streams to ESC 160 and selectively bypass some or all of the channel 1 and channel 2 flow back to the tool cooling system 164 and the tool heating system 204. Additional variations are anticipated, including using a time offset to either precondition the ESC 160 in advance of an actual need, or changing the setpoints of tool cooling system 164 or the tool heating system 204 over time to protect the ESC 160 from excessive thermal stress, or to a achieve a desired process profile. In general, each channel may need a separate refrigeration solution. However, in some cases, depending on the required temperature for a particular temperature, the refrigeration capacity of the first or second refrigeration system may be shared among multiple channels. In some cases, if active refrigeration is not needed, and the heat removal can be accomplished by normal facility-provided cooling water, then a particular channel might be cooled using facility cooling water.
During select process steps, the valve manifold is switched to change which channel's flow is delivered to the ESC 160 and which is bypassed and returned to the chiller. In yet other embodiments the valve manifold 220 mixes select amounts of the first cold channel and the warmer second channel to regulate the ESC 160 temperature and in this arrangement, a portion of one or both channels bypasses the ESC 160 and is returned to the chiller. Those skilled in the art will recognize that these various embodiments can be used to regulate the ESC 160 temperature and to do so in a way to support various wafer processing steps. In some instances, the required rate of switching the ESC 160 temperature from one temperature to another is very rapid and may be as short as 5 minutes, 3 minutes, 1 minute or less. In some embodiments, the difference between these two temperatures is at least 60° C., or 80° C. or 100° C. In some instances, the amount of difference between one required temperature at the ESC 160 and the other is so great, that when coupled with a rapid change, damage to the ESC 160 may occur. In such cases, the rate of change is regulated by either altering the supply temperature of one or both channels over time in addition to the switching process.
Other embodiments include a process that is temperature sensitive such that a single step should be run much lower than −20° C., and a second step much greater than +20° C. Other embodiments include a temperature control loop using feedback based on backside ceramic temperature of the ESC 160. Other embodiments include the use of heat transfer fluids that are cooled or heated by the chiller and delivered to the ESC 160 that provide thermal conductivity and effective heat transfer to the ESC 160.
In another embodiment, the tool cooling system 164 may be a single compression cycle, using facility compressor 112 and the cooler 116. The first refrigerant preferably has a normal boiling point between +30° C. and −60° C. Preferably the refrigerant is comprised of a hydrofluorocarbon (HFC) (for example, R-245fa, R-236fa, R-134a, R-125, or R-32), a fluorocarbon (FC) (for example R-218) , a hydrofluoroolefin (HFO) (for example i.e. R-1234yf, -1233zd(E) -1234ze(E), -1234ze(Z), or HFO-1336mzz(Z)), or a mixture of different molecules that include these types of compounds. Alternatively, hydrocarbons (HC's) (for example n-butane, iso-butane, propane, or ethane) may be used but preferably the resulting mixture is nonflammable and with a low global warming potential (GWP). In another embodiment, the first refrigerant may be one or more of low global warming potential (GWP) refrigerants such as HFO's or low GWP HFC's, natural inorganic fluids (for example carbon dioxide, ammonia, argon, nitrogen, krypton, or xenon), xenon, by itself or in a mixture is also a possibility. In other embodiments, the first or second refrigerants may be a mixture of the above refrigerants. Such a mixture provides a mixed gas vapor compression system.
In various embodiments, the first throttle 132 controls the pressure so that the second pressure is above the triple point of the first refrigerant. In other embodiments, the tool cooling system 164 is able to provide at least 20 kilowatts of cooling. In other embodiments, the tool cooling system 164 uses an auto cascade system, such as an Edwards Vacuum, Polycold PFC-552 HC product, a Polycold MaxCool 2500L, a Polycold MaxCool 4000H, a thermoelectric system, or a mixed gas refrigeration system, such as an Edward's Vacuum Polycold PCC product.
A radio frequency (RF) source 330 provides RF power to the ESC 160. In a preferred embodiment, 2 megahertz (MHz), 60 MHz, and optionally, 27 MHz power sources make up the RF source 330 and the ESC source 348. In this embodiment, one generator is provided for each frequency. In other embodiments, the generators may be in separate RF sources, or separate RF generators may be connected to different electrodes. For example, the upper electrode may have inner and outer electrodes connected to different RF sources. In this example, the gas distribution plate 306 is a grounded upper electrode or a top plate incorporated into the gas distribution plate 306. Other arrangements of RF sources and electrodes may be used in other embodiments. A controller 335 is controllably connected to the RF source 330, the ESC source 348, an exhaust pump 320, the tool temperature control system 200, and the gas source 310. An example of such an etch chamber is the Exelan Flex™ etch system manufactured by Lam Research Corporation of Fremont, Calif. A process module or plasma processing system may comprise the processing chamber 302, the gas source 310, the exhaust pump 320, the RF source 330, the ESC source 348, the controller 335, and other components of the processing tool 300. The process chamber can be a CCP (capacitively coupled plasma) reactor or an ICP (inductively coupled plasma) reactor.
In various embodiments, the tool temperature control system 200 is able to provide a coolant to the top plate in the temperature range of 10° C. to 80° C. In alternate embodiments, the coolant delivered to the top plate is in a temperature range of 10° C. to 80° C., 10° C. to 100° C., 10° C. to 120° C., 10° C. to 140° C., or 10° C. to 160° C. In various embodiments, the tool temperature control system 200 has a footprint that is less than or equal to the footprint of the processing chamber 302. In various embodiments, the tool temperature control system 200 has a footprint that is less than or equal to 25% of the footprint of the processing chamber 302.
In operation, a substrate 304 is mounted on the ESC 160. The tool temperature control system 200 would provide a refrigerant temperature of −90° C. to +100° C. at the ESC 160. Normally, a particular temperature is needed for a particular process step for the process occurring on the wafer. Different process steps may require different temperatures. Achieving these different temperatures is possible by either changing the refrigeration temperature set point to result in the desired coolant temperature. In some embodiments, the tool temperature control system 200 is as shown in
At the end of the wafer processing, there is an optional step to clean the wafer. This is called a waferless auto clean (WAC) process. For a WAC process, the valve manifold 220 is used to switch from cooling the wafer via the tool cooling system 164 to heating the wafer via the tool heating system 204. The typical construction of an ESC 160 includes multiple layers of components and elements, such as metal components, ceramic components, heaters, adhesive layers, various coatings, etc. The combination of these layers seeks to balance the needs for good heat transfer, good temperature uniformity, desired performance in the RF plasma environment, and the ability to resist erosion in the chemically aggressive process environment. The use of chillers to rapidly cool and heat the ESC can result in damage to the ESC, typically due to the failure of an interface between different internal elements and/or coatings. Therefore, a preferred embodiment is an ESC construction that can endure the change of temperatures from the low range to the high range and back again without failure or degradation of the ESC and the internal components, layers and coatings that the ESC is comprised of. In addition, when a temperature switch is made from a low-temperature coolant to a high-temperature coolant (or vice versa) it is important for the refrigeration systems to provide the required coolant temperature within 2 minutes to maximize utilization of the process module. For example, if channel 1 is normally operating at −70° C., and channel 2 is operating at +40° C. when the switch is made from cold operation at the ESC to hot operation at the ESC 160, the ESC set point of +40° C. must be achieved to +/−1° C. within 2 minutes. Likewise, when the switch is made from hot operation at the ESC 160 to cold operation at the ESC 160, the ESC set point of −70° C. must be achieved to +/−1° C. within 2 minutes. In alternate embodiments, the setpoint is reached to within +/−1° C. within 5 minutes, or within 3 minutes or within 1 minute.
In other embodiments, the wafer process applied is used to etch through multiple layers of devices on a wafer to support desired geometric attributes such as deep aspect ratios and or parallel via walls. In other embodiments, the wafer processes may be a dielectric etch including reactions that are both deposition and etch, a semiconductor process including a process that is temperature dependent, a dielectric film etch, or process for forming 3D memory devices. In other embodiments, the wafer process may deposit layers, such as in plasma-enhanced deposition.
While many of the above embodiments relate to use of a refrigeration loop to provide temperature control to a coolant that is delivered to the ESC, alternate embodiments use direct cooling or heating of the ESC using one or more of the above-mentioned refrigerants or refrigeration cycles. In these embodiments, switching from one temperature to another is accomplished by either a valve manifold 220 located close to the ESC or by having alternate control valves at the refrigeration unit to regulate the refrigerant temperature delivered to the ESC. In various embodiments, the cooling system may be at least one of a single stage vapor compression system, a cascade refrigeration system, an auto cascade system, a thermoelectric system, a mixed gas refrigerant system, or a Stirling refrigeration cycle, a Brayton refrigeration cycle, a Gifford McMahon refrigeration cycle or a pulse tube refrigeration cycle.
While this disclosure has been described in terms of several preferred embodiments, there are alterations, modifications, permutations, and various substitute equivalents, which fall within the scope of this disclosure. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present disclosure. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and various substitute equivalents as fall within the true spirit and scope of the present disclosure.
This application claims the benefit of priority of U.S. Application No. 62/799,597, filed Jan. 31, 2019, which is incorporated herein by reference for all purposes.
Filing Document | Filing Date | Country | Kind |
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PCT/US2020/015564 | 1/29/2020 | WO | 00 |
Number | Date | Country | |
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62799597 | Jan 2019 | US |