Apparatus and method for shielding a controlled pressure environment

An apparatus for shielding a controlled pressure environment, including a shield assembly with: a gate disc arranged for location in a chamber and including a first continuous surface facing an opening in the chamber and including an outer circumference extending past the opening in a radial direction orthogonal to a longitudinal axis passing through the chamber and the opening; and an at least one actuator arranged to displace the gate disc in an axial direction parallel to the longitudinal axis. The opening is arranged for connection to an inlet of a vacuum pump. In an example embodiment, the thermal system attains and maintains thermal equilibrium in the chamber and/or to shields the chamber from unwanted thermal affects by heating or cooling the gate disc to offset cooling or heat generated by the vacuum pump. For example, the gate disc is cooled to offset heat generated by a turbo-molecular pump.

TECHNICAL FIELD

The present disclosure relates to an apparatus and method for shielding a controlled pressure environment, for example, shielding a process vacuum chamber from heat or contaminants generated by a vacuum pump. In particular, the present disclosure relates to a controllably displaceable disc for placement in a vacuum chamber. The apparatus and method can include thermal control of the disc and closed loop control of displacement of the disc based on measurement of a parameter in the chamber.

BACKGROUND

Vacuum pumps used to reduce pressure in a process chamber, for example, pumping purge or process gas out of the chamber, can introduce undesirable heat, cooling and/or contaminants into the chamber. It is known to use thermal shielding louvers in the inlet of cryogenic pumps to reduce the cooling effect of the pump on process chambers. Due to conductance loss (undesirable distortion and/or attenuation of flow patterns through the process chamber), thermal shields are not used at the inlet of turbo-molecular pumps (TMP). The effective pumping speed of a TMP is significantly reduced by the addition of baffles or louvered thermal shields at the inlet of the pump. Further, the desired symmetry for the flow of process gas being pumped out of the chamber by the TMP would be seriously compromised by the presence of such shields. Thus, for at least the preceding reasons, thermal shields have not been implemented on TMPs.

In general, adding louvers to the inlet of high vacuum pumps significantly reduces the conductance and effective pumping speed of the pump. Hence, to attain the same results as unlouvered pumps, more louvered pumps must be used. Increasing the number of pumps increases the cost of the system and the size of the vacuum process chamber considerably. For a pump with a conductance control valve at its inlet, thermal shielding causes significant and undesirable disturbance in the flow pattern of process gas. The symmetry of gas flow is extensively disturbed and altered by the thermal shield at the pump or valve inlet through which the flow must pass. However, flow symmetry is necessary to maintain uniform local gas pressure on the component which is being processed (such as a silicon wafer or a reticle in a semiconductor fabrication or inspection tool). Thus, implementing known thermal shielding at the pump inlet, sacrifices effective pumping speed and flow control, leading to much more complex and more expensive process chambers and vacuum systems.

It is known to measure temperature and/or pressure in a process chamber; however, sensors for executing the measurements are placed on the chamber walls interfering with flow through the chamber. Further, it is known to use pressure measurements in a process chamber to correlate pump operation to pump curves for the pump. Ideally the measurements would be proximate the pump inlet; however, known pressure sensors are located on the walls of the chamber, relatively far from the pump inlet.

SUMMARY

According to aspects illustrated herein, there is provided an apparatus for shielding a controlled pressure environment, including a shield assembly with: a gate disc arranged for location in a chamber and including a first continuous surface facing an opening in the chamber and including an outer circumference extending past the opening in a radial direction orthogonal to a longitudinal axis passing through the chamber and the opening; and at least one actuator arranged to displace the gate disc in an axial direction parallel to the longitudinal axis. The opening is arranged for connection to an inlet of a vacuum pump.

According to aspects illustrated herein, there is provided an apparatus for shielding a controlled pressure environment, including: a chamber with an opening and a longitudinal axis passing through the opening and centered within the opening; and a shield assembly including: a gate disc including a first continuous surface facing the opening and including an outer circumference, an entirety of the outer circumference extending past the opening in a radial direction orthogonal to the longitudinal axis; at least one actuator arranged to displace the gate disc in an axial direction parallel to the longitudinal axis; and a thermal system for controlling a temperature of at least a portion of the gate disc. The opening is arranged for connection to an inlet of a vacuum pump. The vacuum pump is arranged to create a flow through the chamber. At least a portion of the outer circumference is radially inward of the flow. In an example embodiment, the thermal system is used to attain and maintain thermal equilibrium in the chamber and/or to shield the chamber from unwanted thermal affects by heating or cooling the gate disc to offset cooling or heat generated by the vacuum pump. For example, the gate disc is cooled to offset heat generated by a turbo-molecular pump.

According to aspects illustrated herein, there is provided a method for shielding a controlled pressure environment, including: locating a gate disc within a chamber; facing a first continuous surface of the gate disc toward an opening in the chamber, to which an input of a vacuum pump is sealed; extending an outer circumference of the first continuous surface past the opening in a radial direction orthogonal to a longitudinal axis for the chamber passing through the opening; and displacing, using at least one actuator, the gate disc in an axial direction parallel to the longitudinal axis.

According to aspects illustrated herein, there is provided a method for shielding a controlled pressure environment, including: locating a gate disc within a chamber; facing a first continuous surface of the gate disc faces toward an opening in the chamber, to which a vacuum pump is sealed; extending an outer circumference of the first continuous surface past the opening in a radial direction orthogonal to a longitudinal axis for the chamber passing through the opening and centered within the opening; operating the vacuum pump to create a flow through the chamber at a first radial distance, orthogonal to the longitudinal axis, from the longitudinal axis; displacing the gate disc in an axial direction parallel to the longitudinal axis; and controlling, using a thermal system, a temperature of at least a portion of the gate disc. Extending the outer circumference of the first continuous surface past the opening in a radial direction includes locating at least a portion of the outer circumference at a second radial distance, orthogonal to the longitudinal axis, from the longitudinal axis. The second radial distance is less than the first radial distance. In an example embodiment, the method attains and maintains thermal equilibrium in the chamber and/or shields the chamber from unwanted thermal affects by heating or cooling the gate disc to offset cooling or heat generated by the vacuum pump. For example, the method cools the gate disc to offset heat generated by a turbo-molecular pump.

According to aspects illustrated herein, there is provided a method of removing impurities from a controlled pressure environment, including: locating a gate disc within a chamber so that a first continuous surface of the gate disc faces an opening, to which a vacuum pump is sealed, and extends past the opening in a radial direction orthogonal to a longitudinal axis for the chamber passing through the opening; operating the vacuum pump to create a flow through the chamber; absorbing, using a layer of getter material on the first continuous surface, an impurity; displacing, using at least one actuator, the gate disc in a first axial direction parallel to the longitudinal axis and toward the opening in the chamber; sealing at least a portion of the first continuous surface and the layer of getter material from the chamber; heating the layer of getter material; operating the vacuum pump to flow at least a portion of the impurity away from the gate disc; and displacing, using the at least one actuator, the gate disc in a second axial direction, opposite the first axial direction, to place the chamber in communication with the vacuum pump.

DETAILED DESCRIPTION

FIG. 1is a schematic side view of apparatus100for shielding a controlled pressure environment, with a gate disc in an open position.

FIG. 2is a schematic bottom view of the gate disc ofFIG. 1.

FIG. 3is a schematic top view of the gate disc ofFIG. 1. The following should be viewed in light ofFIGS. 1 through 3. Apparatus100includes shield assembly102with gate disc104and at least one actuator106. Gate disc104is arranged to be installed in chamber108. In an example embodiment, chamber108is a vacuum chamber. In an example embodiment, actuator(s)106is located outside of chamber108. In an example embodiment, apparatus100includes chamber108. Disc104includes continuous surface110facing opening112for chamber108. By “continuous” surface, we mean that the surface is free of penetrations connecting surface110with opposite surface114of disk104. Chamber108includes longitudinal axis LA passing through disc104and opening112. In an example embodiment, axis LA is centered within opening112. Chamber108is arranged for connection to vacuum pump116. For example, inlet118of the pump is arranged to be sealed to opening112so that the inlet is in communication with the opening. Pump116can be any pump known in the art, for example, a turbo-molecular pump or a cryogenic pump.

Disc104, in particular, outer circumference120of surface110, extends past opening112in radial direction RD, orthogonal to axis LA. Actuator106is arranged to displace disc104in axial directions AD1and AD2, parallel to axis LA. Disc104can be displaced in directions AD1and AD2to control a rate of flow for flow path122for a gas, such as a purge gas or process gas, in chamber108. For example, displacing the disc in direction AD2enables an increase in the rate and displacing the disc in direction AD1decreases the rate. Actuator(s)106can be any actuator known in the art.

FIG. 4is a schematic side view of apparatus100ofFIG. 1with gate disc104in a closed position. The following should be viewed in light ofFIGS. 1 through 4. In an example embodiment, gate disc104or chamber108includes seal124and the gate disc is displaceable in direction AD1to engage the seal with wall126of the chamber and with surface110to seal the chamber from the opening, for example, sealing portion110A of surface110radially inward of seal124from the chamber. Stated otherwise, engaging seal124with wall126seals the chamber from the inlet of the pump.

The vacuum pump is arranged to create flow122through the chamber, and at least a portion of outer circumference120, for example, portions120A, is located radially inward, with respect to axis LA of the flow. Stated otherwise: flow122is at radial distance128, orthogonal to axis LA, from axis LA; the at least a portion of outer circumference120is at radial distance130, orthogonal to axis LA, from axis LA; and distance130is less than distance128. The radial location of flow122is typically due to the radial location of blades132for the vacuum pump. The relative radial locations of flow122and portions120A are further discussed below.

In an example embodiment, the shield assembly includes thermal system134arranged to heat at least a portion of the gate disc, or cool at least a portion of the gate disc. In an example embodiment, system134both heats and cools respective portions of the gate disc. In an example embodiment, the thermal system is arranged to provide heat to one of: at least a portion of surface110; or at least a portion of surface114; and the thermal system is arranged to provide cooling to the other of the at least a portion of surface110or the at least a portion of the surface114. Thermal control of disc104is further described below.

In an example embodiment, the gate disc includes sensor system135with at least one sensor136for measuring a physical parameter within the chamber. Sensor(s)136can be any sensor known in the art, measuring any parameter known in the art. In an example embodiment, the at least one sensor is embedded in disc104. In an example embodiment, the at least one sensor136includes sensor136T for measuring temperature within the chamber; or sensor136includes sensor136P for measuring pressure within the chamber. In an example embodiment, the gate disc includes both sensor136T and136P. In the figures, sensors136T and136P are shown on each of surfaces110and114; however, it should be understood that assembly102is not limited to a particular number or orientation of sensors136. For example: sensors136T and136P can each be located only on side110or114; the disc can include a single sensor136T on one of sides110or114; or the disc can include a single sensor136P on one of sides110or114.

In an example embodiment, shield assembly102includes thermal system134for controlling a temperature of the gate disc, and control system138including processor140configured to receive input142from sensor, or sensors,136regarding measurement144of the physical parameter; and, according to input142: modify, using thermal system134, the temperature of at least a portion of the gate disc; or displace, using the actuator, the gate disc in direction AD1or AD2. Operation of systems134and138are further described below.

In an example embodiment, at least a portion of surface110includes layer146of getter material arranged to absorb impurities. Any getter material known in the art can be used.

In an example embodiment, thermal system134is used to cool surface110so that surface110acts as a cold plate trapping impurities in chamber108, for example, impurities generated by operation of the vacuum pump.

The following provides further detail regarding the apparatus100and the operation of apparatus100. In an example embodiment, the geometry and symmetry of the disc matches those of opening112and inlet118. For example, opening112is circular and portions120A are respective circular segments of circumference120. In an example embodiment, actuator rods148are attached to disc104, pass through wall126, and are connected to actuator106. Rods148are sealed with respect to wall126by any means known in the art. Then, the only portion of circumference120that does not mirror the symmetry of inlet118, and which may intercept flow122, is portion120B of the circumference, to which rods148are attached. Note that120B forms a relative small portion of circumference120. Two rods148are shown in the figures; however, it should be understood that a different number and/or configuration of rods can be used. In an example embodiment, a separate actuator106is used for each rod148.

As noted above, disc104is displaceable in direction AD1, toward the pump inlet, to seal the pump inlet for complete pumping isolation, and is displaceable in direction AD2, away from the pump inlet, to enable gas from the chamber to enter the vacuum pump.

In general, it is desirable, if not necessary, to attain and maintain a specified temperature in chamber108, for example, to ensure proper operation and protection of optical and other components inside the chamber. Disc104, in particular, surface110, faces the pump interior components and shields chamber108from undesirable radiated heat H generated by such components. For example, blades132are typically made of a light-weight material, such as aluminum, which is a good heat conductor. The blades absorb heat from the pump and since the blades cannot be cooled, the blades radiate heat H toward the chamber. Heat H radiates in straight lines through the pump inlet, substantially parallel to axis LA or at an acute angle with respect to axis LA. Since surface110extends radially beyond opening112, surface110intercepts the radiated heat. The radial extend of circumference120beyond opening112is configured to intercept the heat at the acute angle.

In addition, system134provides cooling to further offset undesirable heat generated by pump116. For example, system134can be used to cool surface110to prevent heat absorbed/blocked by surface110from transmitting through disc104to chamber108. Alternatively, system134can be used to cool surface114to prevent transmission of heat absorbed by surface110.

When pump116is a cryogenic pump, surface110and system134can be used to prevent undesirable cooling of chamber108. For example, system134can be used to heat surface110to counterbalance cooling of surface110by the pump operation. Alternatively, system134can be used to heat surface114to prevent transmission of cold absorbed by surface110.

Sensor(s)136and control system138enable precise closed loop control of conditions in chamber108. As noted above, it is desirable, if not necessary, to maintain a specified temperature in chamber108. For example, sensor(s)136T can be used to measure temperature in the chamber proximate surface114or proximate the pump inlet at surface110. Processor140monitors measurement144and when the measurement deviates from a predetermined threshold value150, processor140activates system134to provide heating or cooling as needed and where needed (surface110, surface114, or each of surfaces110and114) to maintain the specified temperature.

In like manner, sensor(s)136T can be used to attain a specified temperature, for example, at the beginning of a process when temperature in the chamber must be raised or lowered to the specified temperature. Advantageously, since sensor(s)136T is located on side110and/or side114, the sensor(s) does not interfere with flow122.

In general, it is desirable, if not necessary, to attain and maintain a specified pressure and gas composition in chamber108, for example, to ensure proper purging of the chamber and proper process gas pressure to ensure optimal operation and protection of optical and other components152inside the chamber. Sensor(s)136P and control system138enable precise closed loop control of pressure in chamber108. For example, sensor(s)136P can be used to measure pressure in the chamber proximate surface114or proximate the pump inlet at surface110. Processor140monitors measurement144and when the measurement deviates from a predetermined threshold value152, processor140controls actuator106to: displace disc104in direction AD1to increase pressure in the chamber; or displace disc104in direction AD2to decrease pressure in the chamber.

In like manner, sensor(s)136P can be used to attain a specified pressure, for example, at the beginning of a process when pressure in the chamber must be lowered to the specified pressure. Advantageously, since sensor(s)136P is located on side110and/or side114, the sensor(s) does not interfere with flow122.

As an example, processor140controls the actuator to displace disc104fully in direction AD2at the beginning of a process cycle, for example when a purge gas is being introduced into the chamber. It is desirable to maintain a high rate for flow122to complete the purge and remove contaminants from the chamber. Once pressure in the chamber has reached a specified level, the processor controls the actuator to displace disc104in direction AD1to an equilibrium position (note that the displacement in direction AD1can be gradual or abrupt as required). From the equilibrium position, relatively minor adjustments in directions AD1or AD2are made to maintain the desired pressure in the chamber while maintaining a fixed flow rate of process gas into the chamber and a fixed speed for the pump. This is particularly advantageous, as it is very desirable to avoid varying the gas flow rate since mechanisms for varying the flow rate typically cause undesirable vibration and noise, which is particularly problematic for optical components in the chamber. Further, changing the pump speed requires an undesirably long time for implementation.

Thus, apparatus100enables an efficient and rapid pump down of chamber108followed by precise control of pressure in the chamber. Further, the change in rate for flow122due to the displacement of disc104in direction AD1and AD2is linear, simplifying controls schemes.

It is particularly desirable to monitor temperature and pressure of the chamber proximate the pump inlet. For example, during the initial pump down of the chamber, it is important to correlate pump operation to the pump's pump curves (pressure versus flow, inlet pressure versus outlet pressure, and/or flow versus pump power) to accurately assess operation of the pump and ensure the pump operates with optimal efficiency within an acceptable range of operation for the pump. Known methods of measuring pressure in a chamber such as chamber108take pressure reading relatively far from the pump inlet, for example, on the wall of a chamber. Since pressure varies across the chamber during pump down, such reading do not accurately represent pressure at the inlet and hence do not enable accurate determination of a pump's operation with respect to pump curves. Advantageously, by locating sensor136P on side110, apparatus100enables accurate measurement of pressure proximate inlet118, which in turn enables accurate correlation of the operation of pump116with respect to pump curves for pump116.

As noted above, getter material146can be added to surface110. Advantageously, apparatus100enables a process of regenerating the getter material while maintaining constant operation of pump116and a desired vacuum or low pressure environment in the chamber. For example, disc104is displaced in direction AD1to seal the chamber with respect to opening112and inlet118. Then, surface110is heated to regenerate material146and off-gas contaminants from the material. During this process, pump116continues to operate, pumping off the contaminants. Once sufficient regeneration has occurred, disc104is displaced in direction AD2and process operations can be resumed. As a further advantage, system134can be used to cool surface114while surface110is being heated to prevent the introduction of heat into chamber108.

Typically, a turbo-molecular pump116uses a magnetically-levitated blade rotor. It is very desirable to minimize energizing and de-energizing such pumps while simultaneously avoiding exposing the pump inlet to atmospheric pressure. De-energizing the pump causes the magnetic field for the rotor to collapse, which in turn causes the rotor to drop onto a stop bearing. Dropping the rotor onto the stop bearing creates wear on the rotor, generates particles, and reduces the useful life of the rotor and pump. Advantageously, apparatus100enables pump116to continue operating during virtually all operations, such as the regeneration process described above, while maintaining a vacuum seal for the pump.

In an example embodiment, surface110has a mirror finish, which reflects a portion of heat H back toward the pump, further reducing the transmission of heat to chamber108and/or reducing the cooling needed for disc104. Typically, a flange or other parts for the pump are cooled and portions of the reflected heat are absorbed by the cooled flange or parts.

System134can use any heating or cooling means known in the art, including but not limited to fluid cooling and/or heating and electrical heating. In an example embodiment, lines156supple cooling/heating fluid and/or electrical power to disk104.

The structure and functionality of apparatus100advantageously:

A. Provide thermal shielding for vacuum pumps (such as turbo-molecular and cryogenic pumps) without disturbing the flow and conductance of gas through a chamber to the pump.

B. Enable thermal shielding and controllable conductance gas-flow to the inlet of a vacuum pump without sacrificing or impairing pumping speed of the pump.

C. Enable control of ambient temperature at the pump inlet by removal or addition of heat flux.

D. Maintain equalized temperature profile within a process chamber by compensating for heat or cooling generated by a vacuum pump(s). That is, attain and maintain thermal uniformity in a vacuum process chamber.

E. Optimize pump performance and eliminate the need to add more pumps and control systems to compensate for the loss of conductance due to addition of a thermal shield.

F. Facilitate thermal control within a variable conductance valve in a vacuum system. Heat and/or cooling can be introduced where needed and as needed.

G. Enable local thermal uniformity and temperature control at the inlet of a vacuum pump.

H. Enable temperature and pressure measurement near the inlet of a pump.

I. Enable integration into the gate of a conductance control valve.