Patent Publication Number: US-2015086387-A1

Title: Method and apparatus for warming up a vacuum pump arrangement

Description:
This application is a national stage entry under 35 U.S.C. §371 of International Application No. PCT/GB2013/051033, filed Apr. 24, 2013, which claims the benefit of G.B. Application 1207721.0, filed May 2, 2012. The entire contents of International Application No. PCT/GB2013/051033 and G.B. Application 1207721.0 are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to a method and/or apparatus for warming up a vacuum pump arrangement after it was put into an idle mode. 
     BACKGROUND 
     A system used in manufacturing semiconductor devices typically includes, among other things, a process tool, a vacuum pump arrangement having a booster pump and a backing pump, and an abatement device. The process tool typically includes a process chamber, in which a semiconductor wafer is processed into a predetermined structure. The vacuum pump arrangement is connected to the process tool for evacuating the process chamber to create a vacuum environment in the process chamber in order for various semiconductor processing techniques to take place. The gas evacuated from the process chamber by the vacuum pump arrangement might be directed to the abatement device, which destroys or decomposes the harmful or toxic components of the gas before it is released to the environment. 
     It is desired to manage and reduce the utilities, such as electric power, fuel, and water, consumed by the vacuum pumps and abatement device during the semiconductor manufacturing processes. The power consumed by the vacuum pumps and abatement device represents a significant portion of the total power consumed by the entire system in manufacturing semiconductor wafers. Many efforts have been made in the semiconductor industry to improve the efficiency of utility consumption of the vacuum pumps in order to reduce the manufacturing costs of semiconductor wafers. In addition to cost savings, new environmental regulations would often put pressure on semiconductor manufacturers to improve the energy efficiency of their manufacturing processes. 
     One conventional method for improving the efficiency is to put the vacuum pump arrangement and the abatement device in an idle mode, when the process tool does not require that the vacuum pump arrangement and the abatement device operate in their normal capacities. The term “idle mode” here is used interchangeably with other terms, such as sleep mode, green mode, hibernation, reduced/low power mode, active utility control mode, that are often customarily used in various industries. For example, when semiconductor wafers are being transferred into or out of the process chamber, the vacuum pump arrangement and abatement device might be put in the idle mode, in which they consume fewer resources than they do in a normal operation mode. When the process tool requires the vacuum pump arrangement and abatement device to operate in their normal capacities, they can be brought back to their normal operation mode from the idle mode. 
     One drawback of the conventional method is that it usually takes a long time to bring the vacuum pump arrangement and the abatement device back to the normal operation mode from the idle mode. When the vacuum pump arrangement is in the idle mode, it cools down to a low temperature. Before the vacuum pump arrangement can operate in normal conditions, it needs be warmed up to a certain temperature, which can take a long time. The longer the warming-up takes, the longer the process tool is sitting idle, waiting for the vacuum pump arrangement to be ready. This translates into lost productivity, and decreased throughput. 
     Thus, what is needed is a method for quickly warming up the vacuum pump arrangement from the idle mode, thereby shortening the time required for bringing a processing system from the idle mode to the normal operation mode. 
     SUMMARY 
     This invention relates to a method and/or apparatus for warming up a vacuum pump arrangement after it was put into an idle mode. In some embodiments of the invention, a method for warming up a vacuum pump arrangement having a booster pump and a backing pump downstream of the booster pump for evacuating a process chamber includes steps of: setting the booster pump at a first speed higher than an idle speed of the booster pump when the same is in an idle mode; and controlling a backing pressure at an outlet of the booster pump within a range from 0.1 mbar to 10 mbar, wherein suitable backing pressure will need to be selected depending on the size of the booster pump, at least for a period of time from when the vacuum pump arrangement is activated from the idle mode to when the booster pump reaches a temperature equal to or exceeding a first predetermined threshold value. 
     In some embodiments of the invention, an apparatus includes: a process chamber; a booster pump having an inlet fluidly connected to an outlet of the process chamber; a backing pump having an inlet fluidly connected to an outlet of the booster pump for, together with the booster pump, evacuating the process chamber; and a controller electrically coupled with the booster pump and the backing pump, the controller being configured to control a backing pressure at the outlet of the booster pump within a range from 0.1 mbar to 10 mbar at least for a period of time from when the booster pump and the backing pump are activated from an idle mode to when the booster pump reaches a temperature equal to or exceeding a first predetermined threshold value. 
     The construction and method of operation of the invention, however, together with additional objectives and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a schematic view of a system where a process chamber, a booster pump, and a backing pump, among other things, are connected in series in accordance with some embodiments of the invention. 
         FIGS. 2A and 2B  illustrate flow charts showing various processes for warming up a vacuum pump arrangement in accordance with some embodiments of the invention. 
         FIG. 3  illustrates a flow chart showing a process for warming up a vacuum pump arrangement in accordance with some embodiments of the invention. 
         FIG. 4  is a graph showing that the disclosed method and/or apparatus shortens the time required to warm up a vacuum pump arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is directed to a method and/or apparatus for warming up a vacuum pump arrangement after it was put in an idle mode. The vacuum pump arrangement in its simplified configuration has a booster pump and a backing pump downstream thereof. An inlet of the booster pump is connected to an outlet of a process chamber, which can be part of a semiconductor process tool, or any other equipment that requires an internal vacuum environment in order to properly function. An outlet of the booster pump is connected to an inlet of the backing pump, of which an outlet is typically in fluid connection with an abatement device, or in some cases directly with an atmospheric environment. As the vacuum pump arrangement is warming up, the speed of the booster pump is raised to and maintained at a level higher than an idle speed of the booster pump when it was in the idle mode. The backing pressure of the booster pump, that is the pressure at the outlet of the booster pump, is also raised to and maintained at a relatively high level, compared to the backing pressure, in either the normal operation mode, or in some cases the idle mode, employed by conventional methods. As a result, the power required to compress the gas through the booster pump during the warm-up period would be increased, and therefore causing the temperature of the booster pump to increase more quickly. Because the booster pump typically takes a longer time to fully warm up than the backing pump, the method and/or apparatus of the disclosure is able to shorten the time required for warming up the entire vacuum pump arrangement from the idle mode. This in turn increases the throughput of the process tool. 
       FIG. 1  illustrates a schematic view of a system  10  where a process chamber  12  and a vacuum pump arrangement  20 , among other things, are connected in series in accordance with some embodiments of the invention. The vacuum pump arrangement  20  draws gases out of the process chamber  12  and creates a vacuum environment in it to carry out certain processes, such as depositions, etching, ion implantation, epitaxy, etc. The gases can be introduced into the process chamber  12  from one or more gas sources, such as the ones designated by  14   a  and  14   b  in this figure. The gas sources  14   a  and  14   b  can be connected to the process chamber  12  via control valves  16   a  and  16   b,  respectively. The timing of introducing various gases into the process chamber  12  can be controlled by selectively turning on or off the control valves  16   a  and  16   b.  The flow rates of the gases introduced from the gas sources  14   a  and  14   b  into the process chamber  12  can be controlled by adjusting the fluid conductance of the control valves  16   a  and  16   b.    
     The vacuum pump arrangement  20  includes a booster pump  22  and a backing pump  24  connected in series. The inlet of the booster pump  22  is connected to the outlet of the process chamber  12 . The outlet of the booster pump  22  is connected to the inlet of the backing pump  24 . The outlet of the backing pump  24  might be connected to an abatement device (not shown in the figure) where the exhaust gases emitted from the backing pump  24  are treated in order to reduce the harmful impact the exhaust gases might have on the environment. Sensors (not shown in the figure) can be implemented in the vacuum pump arrangement to collect data of various measurements, such as the temperatures, power consumptions, pump speeds, etc., of the booster pump  22  and the backing pump  24 . Sensors can also be implemented to measure the gas pressures at the inlets and/or outlets of the booster pump  22  and/or the backing pump  24 . A controller  30  is configured to control various parameters of the booster pump  22  and the backing pump  24  in response to the data collected by the sensors. For example, the controller  30  might put the booster pump  22  and the backing pump  24  in a low utility consumption state, e.g., the idle mode, upon receiving a signal indicating that no immediate process is expected to be performed in the process chamber  12 . Such signal might be provided by the process chamber  12 , or the process tool incorporating the process chamber  12 , directly to the controller  30 . Alternatively, such signal might be provided by a central control unit of a semiconductor manufacturing facility to the controller  30 . 
     Upon receiving a wake-up signal, the controller  30  effects an increase of electric power supply to the vacuum pump arrangement  20 , and raises the speeds of the booster and backing pumps  22  and  24  to higher levels from their respective idle speeds. The controller  30  controls, raises, and maintains the backing pressure at the outlet of the booster pump  22  within a range from 0.1 mbar to 10 mbar at least for a period of time when the vacuum pump arrangement  20  is activated from the idle mode to when the booster pump  22  reaches a temperature equal to or exceeding a predetermined threshold value, which is required in order for the booster pump to operate in normal conditions. The pressure range disclosed herein is higher than the backing pressure of the booster pump  22  in typical, conventional warm-up processes. 
     Mathematically, the compression power (W) of the booster pump  22  equals to its swept volume (V) times the pressure differential (dP) there across. Given that the swept volume of the booster pump  22  is constant, raising the pressure differential by raising backing pressure would require higher power to compress the gas through the booster pump  22 , and therefore generating more heat as a result. This would cause the temperature of the booster pump  22  to reach the predetermined threshold value suitable for normal pump operation much quickly from the temperature when the booster pump  22  is in the idle mode. 
     In some embodiments of the invention, the backing pressure of the booster pump  22  can be controlled by adjusting the speed of the backing pump  24 . The slower the speed of the backing pump  24 , the higher the backing pressure of the booster pump  22 . An exemplary process for controlling the backing pressure of the booster pump  22  is illustrated in  FIG. 2A . The process starts at step  200 . At step  202 , it is determined whether the vacuum pump arrangement  20  has received a signal to wake up from the idle mode. If it is determined that the vacuum pump arrangement  20  has not received such signal, the vacuum pump arrangement  20  will remain in the idle mode. If it is determined that the vacuum pump arrangement  20  has received such signal, the process will proceed to step  204  where the speed of the booster pump  22  is set at a first speed higher than its idle speed. At step  206 , the speed of the backing pump  24  is set at a second speed high than its idle speed. It is noted that although steps  204  and  206  are illustrated as two separate actions in  FIG. 2A , the speeds of the booster and backing pumps  22  and  24  might be set simultaneously in some embodiments of the invention. 
     At step  208 , it is determined whether the backing pressure of the booster pump  22  is within the predetermined range from 0.1 bar to 10 mbar. If the backing pressure is not within the predetermined range, the process proceeds to step  210  where the speed of the backing pump  24  is decreased in order for the backing pressure of the booster pump  22  to fall within the predetermined range quickly. In some embodiments of the invention, the speed of the backing pump  24  is decreased once, and the process waits for the backing pressure of the booster pump  22  to move within the predetermined range. In some other embodiments of the invention, the speed of the backing pump  24  is decreased incrementally over a number of time intervals until the backing pressure of the booster pump  22  moves within the predetermined range. In yet some other embodiments of the invention, the second speed of the backing pump  24  can be set low enough at step  206  for the backing pressure of the booster pump  22  to rise up quickly, such that step  210  can be eliminated all together. All theses embodiments are within the scope of the invention. 
     If the backing pressure of the booster pump  22  is determined to be within the predetermined range, the process proceeds to step  212 . At step  212 , it is determined whether the temperatures of the booster and backing pumps  22  and  24  are equal to or exceed their respective threshold temperatures. If they do, the vacuum pump arrangement  20  will be set to be ready for evacuating the process chamber  12  in a normal operation mode. Until then, the vacuum pump arrangement  20  will remain in the warm-up process, waiting for the temperatures to rise to proper levels. It is noted that the values of the predetermined threshold temperatures of the booster and backing pumps  22  and  24  may or may not be the same. Thereafter, the process ends at step  214 . 
     In some embodiments of the invention, the backing pressure of the booster pump  22  can be controlled by adjusting the pump speed and comparing the temperature of the booster pump  22  to a threshold temperature, without directly measuring the backing pressure.  FIG. 2B  illustrates a flow chart showing an exemplary process for controlling the backing pressure of the booster pump  22 , without directly measuring it. The process in  FIG. 2B  is similar to that in  FIG. 2A , with differences in that the backing pressure of the booster pump  22  is not measured. At step  248 , the temperature of the booster pump  22  is measured and compared to the threshold temperature of the booster pump. If the measured temperature is lower than the threshold temperature, the speed of the backing pump  24  is increased at step  250 . The steps  248  and  250  are repeated periodically until the measured temperature of the booster pump  22  is equal to or exceeds the threshold temperature. Thereafter, the process proceeds to step  252  where it is determined whether the temperature of the backing pump  24  is equal to or exceeds the threshold temperature of the backing pump  24 . If it does, the vacuum pump arrangement  20  will be set as ready for evacuating the process chamber  12  in a normal operation mode. Until then, the vacuum pump arrangement  20  will remain in the warm-up process, waiting for the temperatures to rise to proper levels. Thereafter, the process ends at step  254 . 
     In some other embodiments of the invention, the backing pressure of the booster pump  22  can be raised by injecting a purge gas at the outlet of the booster pump  22  or a location in the conduit between the booster pump  22  and the backing pump  24 . As shown in  FIG. 1 , a source of purge gas  32  and a control valve  34  might be optionally provided. The control valve  34  might be placed between the source  32  and the conduit between the booster pump  22  and the backing pump  24 . The controller  30  is configured to adjust the conductance of the control valve  34 , thereby controlling the flow rate of the purge gas from the source  32  to the outlet or its downstream proximity of the booster pump  22 . This in turns alters the backing pressure at the outlet of the booster pump  22 . It is advantageous to select gases that are stable and do not react with the process gas flowing through the vacuum pump arrangement  20  as the purge gas. Examples of the purge gas include nitrogen, helium, and other inert gases. 
       FIG. 3  illustrates a process for warming up the vacuum pump arrangement  20  from the idle mode in accordance with some embodiments of the invention. The process illustrated in  FIG. 3  is similar to that in  FIG. 2 , expect that in the latter the backing pressure of the booster pump  22  is controlled and maintained by adjusting the speed of the backing pump  24 , whereas in the former the backing pressure of the booster pump  22  is controlled and maintained by injecting the purge gas at the outlet of the booster pump  22 , as described by step  300 . At step  302 , it is determined whether the backing pressure of the booster pump  22  is within the predetermined range. If it is not, the controller  30  might increase the conductance of the control valve  34  to increase the flow rate of the purge gas, until the backing pressure of the booster pump  22  moves within the predetermined range. Like the process in  FIG. 2 , at step  300 , the flow rate of the purge gas can be adjusted incrementally over a number of time intervals or abruptly to a predetermined level at once. If it is determined that the backing pressure of the booster pump  22  is within the predetermined range, the process will proceed to step  304 . 
     At step  304 , it is determined whether the temperature of the booster pump  22  is equal to or exceeds a predetermined threshold temperature. If it does not, the process will wait until it does and then proceed to step  306  where the flow of the purge gas is cut off. At step  308 , it is determined whether the temperature of the backing pump  24  is equal to or exceeds a predetermined threshold temperature. If it does not, the process will wait unit it does and then end the process at step  310 . Like the process in  FIG. 2 , here, the threshold temperatures of the booster and backing pumps may or may not be the same. 
       FIG. 4  is a graph showing that the disclosed method and/or apparatus shortens the time required to warm up a vacuum pump arrangement after it was put into an idle mode. The left side of the figure illustrates a time line for warming up a vacuum pump arrangement according to conventional methods or apparatus. The right side of the figure illustrates a time line for warming up the vacuum pump arrangement according to the method or apparatus of the disclosure. The comparison between the time lines shows that the disclosed method or apparatus is able to warm up the booster and backing pumps to their desired temperatures much more quickly than the conventional methods or apparatus, due to the increased backing pressure of the booster pump in the warm-up process. The shortened warm-up period means that the process tool can be put into operation much more quickly after the vacuum pump arrangement was instructed to wake up from the idle mode. This in turn translates into higher throughput for the process tool. 
     Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims. 
     Various embodiments of the invention have been described. These and other embodiments are within the scope of the following claims.