WO2007066852A1

WO2007066852A1 - Cryo pump

Info

Publication number: WO2007066852A1
Application number: PCT/KR2006/000483
Authority: WO
Inventors: Byung Jik Park
Original assignee: Byung Jik Park
Priority date: 2005-11-07
Filing date: 2006-02-10
Publication date: 2007-06-14
Also published as: KR20060013344A; KR100706818B1

Abstract

A cryopump has a dual-stage construction and includes a first stage for capturing water vapor; a cooling panel having adsorptive charcoal so that argon or nitrogen gas can condense and adsorb; a second stage on which the cooling panel is mounted; a housing containing a dual-segment cryogenic cooler; and a heat transfer member interposed between the second stage and the cooling panel. The cryopump can raise the temperature inside the chamber up to 330K or higher without heat loss during a pump regeneration process. As a result, substances and gases having large evaporation heat can be completely purified in high-temperature environments of at least 330K and discharged in a short period of time. This substantially prolongs the life of the adsorptive charcoal for removing gases from the chamber and completely restores the performance of the cooling panel after regeneration, so that the maintenance period of the pump resulting from a temperature rise inside the pump can be lengthened.

Description

CRYOPUMP

Technical Field

[1] The present invention relates to a cryopump used in an ion injection process for manufacturing semiconductor devices, and more particularly to a cryopump having a heat transfer member interposed between a second stage and a cooling panel mounted on the second stage, the heat transfer member having a large difference in thermal conductivity between low and high temperatures, so that, during regeneration of the pump, a chamber of the pump can purify substances and gases having large evaporation heat inside the second stage, while maintaining high-temperature environments, and completely discharge them to the exterior for improved regeneration efficiency and prolonged life of the devices.

Background Art

[2] In general, a cryopump refers to a cold storage type vacuum pump adapted to

perform vacuum withdrawal by condensing and adsorbing gas molecules in a cryogenic condition and is widely used as a means for creating an ultra- vacuum condition inside a processing chamber of a semiconductor manufacturing device, for example.

[3] FlG. 1 briefly shows a conventional cryopump 1.

[4] As shown in FlG. 1, the cryopump 1, which has a dual-stage construction, includes a first stage 1 for capturing water vapor, a second stage 3 for condensing and adsorbing argon or nitrogen gas, and a housing 5 containing a dual-segment cryogenic freezer 4.

[5] The first stage 1 is enclosed by the housing 5, except for a baffle 6 positioned

between the second stage 2 and a discharge chamber.

[6] The first stage 2 is cooled by the freezer 4 until its temperature ranges between

60- 130K. Gases having a high boiling point (e.g. water vapor), which flow from a working chamber, condense on the baffle 6. The remaining part of the first stage 2 protects the second stage 3 from heat radiation.

[7] The freezer 4 maintains the temperature of the second stage 3 in the range of 4-25K, in order to condense gases having a low boiling point when passing through the baffle 6.

[8] Adsorptive charcoal is attached to a cooling panel 30 of the second stage 3, in order to remove gases having a low boiling point (e.g. hydrogen). For example, a lamination plate, which includes charcoal 32, may be positioned on a surface of the base of another panel.

[9] The cryogenic freezer 4 used in the cryopump is a dual-segment freezer using Gifford-McMahon cooling cycle for cooling purpose. The cryogenic freezer 4 expands compressed helium gas to take heat away from the first and second stages 2 and 3. The freezer 4 is driven by a motor and is supplied with purified helium gas via a supply line.

[10] The cryopump, constructed as above, condenses gas molecules in the atmosphere so that the first and second stages 2 and 3 essentially create vacuum in the vacuum chamber. Particularly, when freely-floating gas molecules collide with the cryogenic stage, the stage take thermal energy away from the gas molecules. After enough thermal energy is taken away from the gas molecules, a phase change occurs on the first and second stages from vapor to condensed solid. As gases condense and/or adsorb on the first and second stages 2 and 3, a high degree of vacuum is created in the two vacuum chambers and the working chamber.

[11] After such a high degree of vacuum is created, the process product is allowed to move into/out of the working chamber via a partially- vacuumized load lock (not shown). Additional gas flows into the working chamber via its openings connected to the load lock. The gas is caused to condense on the stages, in order to vacuumize the chamber again and provide low pressure necessary for the process. As time elapses and a larger amount of condensed substance accumulates on the stages, the efficiency and performance of the pump degrade. In addition, there is a possibility that condensed gas, which includes dangerous chemicals, may sublime due to interruption of power supply or other reasons. Besides the potential danger, this may damage the process product inside the working chamber.

[12] Therefore, a regeneration process of warming the first and second stages 2 and 3 should be performed periodically (e.g. twice a mouth) according to a control scheme for discharging condensed gas from the first and second stages 2 and 3.

[13] As used herein, the regeneration process refers to a process of naturally releasing gases, which have been adsorbed on the charcoal, by raising the temperature of the cryopump so that the gases are discharged from the system.

[14] In the regeneration process, hot nitrogen gas is directed into the pump via a supply line (not shown), and an electric heater, which is positioned between the first and second stages, is used to raise the temperature inside the pump up to about 330K. As a result, the pump is purged of alien substances created in the condensation process, water, water vapor, and other type of vapor. This increases the life and efficiency of the pump.

[15] However, conventional cryopumps have technical limitations, regarding physical properties of their components, in that the temperature of the second stage, including the cooling panel, cannot exceed 330K.

[16] Particularly, the second stage 3 has a displacer (not shown) adapted to move vertically and absorb heat so that the temperature decreases. The displacer is made of very small lead balls, in order to maintain a low temperature of less than 2OK.

Considering that lead has a low melting point (i.e. it begins to have a spherical shape at 330K), the device may be defective if the temperature is above 330K.

[17] Therefore, in the conventional regeneration process of introducing inactive gas (e.g. nitrogen gas) into the pump and raising the temperature of the first and second stages 2 and 3 from low to normal temperatures so that gas molecules collected therein are discharged to the outside together with regeneration gas, any substance and gas having high evaporation temperature (373K), such as water, which have been cooled and attached to the first stage 2, fail to completely evaporate inside the pump, due to low regeneration temperature, and flow down as moisture. As a result, they contaminate the chamber and, when remain attached to the adsorptive charcoal, shorten the life and maintenance time of the device.

Disclosure of Invention

Technical Problem

[18] Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a cryopump having a heat transfer member (e.g. sapphire) interposed between a second stage and a cooling panel mounted on the second stage, the heat transfer member having a large difference in thermal conductivity between low and high temperature environments, but very stable and excellent mechanical properties without phase change even at a very low or high temperature, so that the temperature inside a chamber can be raised up to 330K or higher without heat loss during a pump regeneration process.

[19] Another object of the present invention is to provide a cryopump capable of

purifying substances and gases inside a chamber, which have large evaporation heat, in high-temperature environment of 330K or higher and completely discharging them during a regeneration process, in order to prolong the life of adsorptive charcoal for removing gases from the chamber and completely restore the performance of the cooling panel after regeneration so that life of the pump is remarkably lengthened. Technical Solution

[20] In order to accomplish these objects, there is provided a cryopump including a

housing; a freezer positioned in the housing and having first and second sections; a first stage making contact with the first section of the freezer to be cooled; a second stage making contact with the second section of the freezer to be cooled; a heat transfer member making contact with the second stage to transfer heat; a cooling panel connected to the heat transfer member to condense and adsorb gases during cooling; and an electric heater positioned between the heat transfer member and the cooling panel to supply heat during regeneration.

[21] The heat transfer member may be made of sapphire having a large difference in thermal conductivity between low and high temperatures and excellent mechanical properties, the sapphire not deforming over a large temperature range.

[22] The cryopump may further include a safety device positioned between the heat transfer member and the electric heater to interrupt power supply to the electric heater when excessive heat is transferred from the electric heater. The safety device may be a bimetal actuated by a temperature rise.

[23] The cryopump may further include a gasket made of a material having a high

thermal conductivity and positioned between the heat transfer member and the second stage to avoid heat loss resulting from a gap created by a difference in thermal expansion ratio between metal over a wide temperature range. The gasket may be made of indium or silver having a high thermal conductivity, and a coupler of a heater block may be made of stainless steel or titanium having a low thermal conductivity, the heat transfer member, the second stage, and the electric heater being mounted on the heater block.

[24] The heat transfer member may be controlled by a helium compressor or cryopump controller so that power is supplied to the electric heater positioned on the second stage only during pump operation.

Advantageous Effects

[25] The cryopump according to the present invention is advantageous in that, since it has a heat transfer member (e.g. sapphire) interposed between the second stage and the cooling panel mounted on the second stage, the heat transfer member having a large difference in thermal conductivity between low and high temperatures, the cryopump can raise the temperature inside the chamber up to 330K or higher without heat loss during a pump regeneration process. As a result, substances and gases having large evaporation heat can be completely purified in high-temperature environments of at least 330K and discharged in a short period of time. This substantially prolongs the life of adsorptive charcoal for removing gases from the chamber and completely restore the performance of the cooling panel after regeneration, so that the maintenance period of the device resulting from a temperature rise inside the pump can be lengthened.

[26] The safety device (e.g. bimetal) prevents the heater from overheating due to

excessive heat supply.

[27] The gasket, which is made of a material having a high thermal conductivity (e.g. indium or silver), avoids heat loss resulting from a gap created by a difference in thermal expansion ratio between metal over a wide temperature range between the heat transfer member and the second stage. [28] The coupler (e.g. bolt) of the heater block is made of stainless steel or titanium having a low thermal conductivity, the heat transfer member, the second stage, and the heater being mounted on the heater block. This avoids deformation resulting from temperature change and maintains the device in a stable condition.

[29] The heat transfer member is controlled by a helium compressor or cryopump

controller so that power is supplied to the electric heater positioned on the second stage only during pump operation. As such, the operation of the cryopump is controlled safely together with the safety device.

Brief Description of the Drawings

[30] The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

[31] FlG. 1 is a sectional view briefly showing the overall construction of a conventional cryopump;

[32] FlG. 2 is a sectional view briefly showing the overall construction of a cryopump according to the present invention; and

[33] FlG. 3 is a graph showing the difference in thermal conductivity between OFHC copper and sapphire at low and high temperatures.

[34] 2: a first stage 3: a second stage

[35] 4: a dual-segment cryogenic freezer

[36] 5: a housing 7: a supply line

[37] 8: a discharge line 9: a relief valve

[38] 12: a bimetal 30: a cooling panel

[39] 32: an adsorptive charcoal

[40] 34: a heater

Mode for the Invention

[41] Reference will now be made in detail to the preferred embodiments of the present invention.

[42] It is to be noted that, in the following description of a preferred embodiment of the present invention, the same reference numerals and terms are used to designate the same components as in the previous description of the prior art.

[43] FlG. 2 is a sectional view briefly showing the overall construction of a cryopump according to the present invention.

[44] As shown in FlG. 2, the cryopump 1 has a dual-stage structure including first and second stages 2 and 3 delimited by an insulation diaphragm, as well as a housing 5 containing a dual-segment cryogenic freezer 4.

[45] More particularly, the housing 5 has an opening formed on the top thereof so that gases can move through and a flange 50 formed on the outer periphery of the opening to be mounted on a port, which is formed on a container for delimiting a working chamber.

[46] The housing 5 has supply and discharge lines 7 and 8 formed on the lower end thereof so that helium gas can be supplied to or discharged from the chamber as a working gas (refrigerant). The opening/closing operation of the supply and discharge lines 7 and 8 is controlled by a relief valve 9.

[47] The housing 5 contains the freezer 4 and the first stage 2 positioned on top of the freezer 4. The first stage 2 has an insulation diaphragm 22 for cooling a condensed gas to be in a temperature range of 35- 130K. The second stage 3 is positioned on top of the first stage 2 with the insulation diaphragm 22 positioned between the first and second stages 2 and 3.

[48] The second stage 3 has a cooling panel 30 positioned thereon, which has adsorptive charcoal 32 positioned on a surface of its base for the purpose of removing gases having a low boiling point (e.g. hydrogen). The cooling panel 30 has a multi-segment structure in the vertical direction inside the chamber.

[49] The second stage 3 is connected to the dual-segment cryogenic freezer 4, which maintains the temperature of the cooling panel 30 at 4-25K.

[50] Particularly, the primary freezer of the dual-segment cryogenic freezer 4 makes contact with the insulation diaphragm 22 of the first stage 2 and freezes the insulation diaphragm 22. The secondary freezer of the cryogenic freezer 4 makes contact with the second stage 3 and freezes the cooling panel 30.

[51] The adsorptive charcoal 32 on the cooling panel 30 of the second stage 3 is

saturated with various gases, which are adsorbed in the chamber when the pump is driven. As a result, the degree of vacuum increases or the temperature of the second stage rises. In order to avoid such a temperature rise inside the chamber, a regeneration process must be performed periodically and, for efficient regeneration, the temperature inside the pump must be maintained above 330K. To this end, a heat transfer member 11, which has a large difference in thermal conductivity between low and high temperature environments, is interposed between the second stage 2 and the cooling panel 30 mounted on the second stage 2, according to the present invention.

[52] The heat transfer member 11 is made of sapphire, which has very stable and

excellent mechanical properties without phase change even at a very low or high temperature, as well as a thermal conductivity comparable to that of metal.

[53] The heat transfer member 11 is connected to a heater 34 positioned on the second stage 3 via a conventional bimetal 12, which is actuated at a predetermined

temperature to interrupt current supply to the heat transfer member 11, and constitutes a safety device. [54] Particularly, the bimetal 12 is actuated when excessive heat is generated from the heater 34 during a regeneration process and interrupts power supply to the heater 34. This prevents the second stage 3 from overheating.

[55] The operation and advantage of the cryopump according to the present invention, which is constructed as mentioned above, will now be described.

[56] As the freezer 4 is driven to condense gas molecules in the atmosphere, the first and second stages 2 and 3 essentially create vacuum inside the vacuum chamber. Particularly, when freely-floating gas molecules collide with the cryogenic stages, the stages take thermal energy away from the gas molecules.

[57] After enough thermal energy is taken away from the gas molecules, a phase change occurs on the first and second stages 2 and 3 from vapor to condensed solid. As gases condense and/or adsorb on the first and second stages 2 and 3, a high degree of vacuum is created in the two vacuum chambers and the working chamber.

[58] After this process is repeated a number of times, the adsorptive charcoal 32 on the cooling panel 30 of the second stage 3 is saturated with various gases, which are adsorbed in the chamber. As a result, the degree of vacuum increases, or the temperature of the second stage 3 rises. In order to avoid such a temperature rise inside the chamber, a regeneration process must be performed periodically.

[59] In the regeneration process, the first stage 2, as well as the heat 34 and a

temperature sensor 36, which are positioned on the second stage 3, are used to raise the temperature of the cooling panel 30 up to 373K (100 C) while flowing N gas of room or elevated temperature into the pump. This purifies the interior of the cryopump.

[60] Such a high temperature of at least 330K is made possible by the sapphire 11

interposed between the second stage 2 and the cooling panel 30. This is because the cooling panel 30 and the second stage 3 are made of OFHC copper, which has a higher thermal conductivity than the sapphire 11 in a high-temperature region, and the cooling panel 30 conducts more heat from the heater 34 than the sapphire 11.

[61] This becomes clearer from FIG. 3, which is a graph showing the difference in

thermal conductivity between OFHC copper and sapphire at low and high temperatures. The sapphire 11 has higher thermal conductivity values at low temperatures, but lower thermal conductivity values than the OFHC copper at high temperatures. This means that, in the low-temperature region, most heat from the heater is conducted by the sapphire into the chamber, but, in the high-temperature region, more heat is conducted by the cooling panel, which is made of OFHC copper.

[62] As such, interposition of sapphire makes it possible to maintain the temperature of the second stage at about 300K, while maintaining a high temperature (373K) of the cooling panel 30. As a result, the cooling panel 30 inside the pump is purified efficiently. [63] This feature will now be described in more detail with reference to FlG. 2. As shown in FlG. 2, the cooling panel 30 is connected to the upper surface of the sapphire 11. A heater block 13 is positioned between the upper surface of the sapphire 11 and the cooing panel 30 to accommodate the heater 34 and the temperature sensor 36. The lower surface of the sapphire 11 is connected to the second stage 3 of the freezer, which is made of OFHC copper.

[64] A gasket (not shown) made of indium or silver, which has a high thermal conductivity, may be positioned among the sapphire 11, the heater block 13, and the second stage 3, in order to improve the thermal conductivity and avoid heat loss resulting from a gap, which may be created by the difference in thermal expansion ratio between metal over a wide temperature range.

[65] The sapphire 11 is fixed between the heater block 13 and the second stage 3 by bolts (not shown), which are preferably made of stainless steel or titanium, which has a low thermal conductivity.

[66] During pump regeneration, increase in temperature of the heater block 13 and the cooling panel 30 raises the temperature of the upper surface of the sapphire 11, which makes contact with the heater block 13, and decreases the thermal conductivity of the sapphire 11. In accordance with a given temperature condition depending on the freezing capability of the freezer and the change in thermal conductivity of the sapphire, as shown in FIG. 3, the temperature of the second stage 3, which makes contact with the lower surface of the sapphire 11, increases and maintains a predetermined difference relative to the temperature of the cooling panel 30.

[67] As a result, interposition of the sapphire 11 makes it possible to maintain the

temperature of the second stage at about 300K, while maintaining a high temperature (373K) of the cooling panel 30. Therefore, the cooling panel 30 inside the pump is purified efficiently. By maintain such a temperature condition, the purification time can be substantially reduced while improving the purification effect, compared with conventional purification rate at 300K for one hour.

[68] Particularly, in a low-temperature condition, the thermal conductivity is very high and the cryopump can efficiently perform its main function of maintaining a cooled vacuum state.

[69] In a high-temperature condition, the thermal conductivity is lower than that of the cooling panel and the second stage, which are made of OFHC copper. This prevents components from being heated abruptly, except for a part to be heated (e.g. cooling panel).

Industrial Applicability

[70] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims.

Claims

[ 1 ] A cryopump comprising :

a housing;

a freezer positioned in the housing and having first and second sections;

a first stage making contact with the first section of the freezer to be cooled; a second stage making contact with the second section of the freezer to be cooled;

a heat transfer member making contact with the second stage to transfer heat; a cooling panel connected to the heat transfer member to condense and adsorb gases during cooling; and

an electric heater positioned between the heat transfer member and the cooling panel to supply heat during regeneration.

[2] The cryopump as claimed in claim 1, wherein the heat transfer member is made of sapphire having a large difference in thermal conductivity between low and high temperatures and excellent mechanical properties, the sapphire not deforming over a large temperature range.

[3] The cryopump as claimed in claim 1, further comprising a safety device

positioned between the heat transfer member and the electric heater to interrupt power supply to the electric heater when excessive heat is transferred from the electric heater.

[4] The cryopump as claimed in claim 3, wherein the safety device is a bimetal actuated by a temperature rise.

[5] The cryopump as claimed in claim 1, further comprising a gasket made of a material having a high thermal conductivity and positioned between the heat transfer member and the second stage to avoid heat loss resulting from a gap created by a difference in thermal expansion ratio between metal over a wide temperature range.

[6] The cryopump as claimed in claim 5, wherein the gasket is made of indium or silver having a high thermal conductivity, and a coupler of a heater block is made of stainless steel or titanium having a low thermal conductivity, the heat transfer member, the second stage, and the electric heater being mounted on the heater block.

[7] The cryopump as claimed in any one of claims 1-6, wherein the heat transfer member is controlled by a helium compressor or cryopump controller so that power is supplied to the electric heater positioned on the second stage only during pump operation.