Vacuum pumping

In order to prevent excessive motor loading or system overheating due to the accumulation of particulate or dust, from SACVD type CVD processes, in the running clearances of the vacuum pump a vacuum pumping arrangement is provided having a plurality of vacuum pumping stages and comprising a first pump inlet through which process fluid from the vacuum chamber can enter the pump and pass through each of the pumping sections towards a pump outlet, and a second pump inlet through which process fluid can enter the pump and pass through only one or more pumping stages downstream of the most upstream pumping stage, wherein the apparatus configured to conveying process fluid from the vacuum chamber to the first pump inlet for pumping during the second processing step and conveying process fluid from the vacuum chamber to the second pump inlet for pumping during the first processing step.

The present invention relates to a method of evacuating a vacuum chamber and to a vacuum pumping arrangement for evacuating a vacuum chamber.

In, for example, chemical vapour deposition processes (such as SACVD) particles are generated as a by-product. These particles are pumped through a vacuum pump during evacuation of the vacuum processing chamber in which the process is operated. The particles, or dust, accumulate in running clearances of the vacuum pump, dead volumes (e.g. rotor balance holes/sumps) and build up on surfaces, resulting in frictional loads. The increased loading may be overcome temporarily, but ultimately leads to excessive motor loading or system overheating.

The present invention aims to mitigate the problems associated with particle generation.

The present invention provides a method of evacuating a vacuum process chamber with a vacuum pumping arrangement, wherein in the vacuum chamber a first processing step is performed at a relatively low vacuum and which generates a relatively large amount of particles and a second processing step is performed at a relatively high vacuum (low pressure) and which generates a relatively small amount of particles, the vacuum pump arrangement having a plurality of vacuum pumping stages and comprising a first pump inlet through which process fluid from the vacuum chamber can enter the pump and pass through each of the pumping sections towards a pump outlet, and a second pump inlet through which process fluid from the vacuum chamber can enter the pump and pass through only one or more pumping stages downstream of the most upstream pumping stage, wherein the method comprises conveying process fluid from the vacuum chamber to the first pump inlet for pumping during the second processing step and conveying process fluid from the vacuum chamber to the second pump inlet for pumping during the first processing step.

The present invention also provides a vacuum pumping arrangement comprising a vacuum pump having a plurality of vacuum pumping stages, a first pump inlet through which process fluid from the vacuum chamber can enter the pump and pass through each of the pumping sections towards a pump outlet, a second pump inlet through which process fluid from the vacuum chamber can enter the pump and pass through only one or more pumping stages downstream of the most upstream pumping stage, a fore-line assembly having a first duct for conveying process fluid from a vacuum chamber to the first pump inlet, a second duct for conveying process fluid from the vacuum chamber to the second pump inlet and a valve operable for selectively directing fluid along the first duct or the second duct, and a control configured to convey process fluid from the vacuum chamber to the second pump inlet during a first processing step performed in the vacuum chamber at a relatively low vacuum and which generates a relatively large amount of particles and to convey process fluid from the vacuum chamber to the first pump inlet during a second processing step performed in the vacuum chamber at a relatively high vacuum and which generates a relatively small amount of particles.

Other preferred and/or optional features of the invention are specified in the accompanying claims.

In a known chemical vapour deposition process, such as SACVD, a chemical vapour deposition step is performed in a vacuum chamber at a relatively low vacuum (e.g. 800 mbar). The deposition step generates a relatively large amount of particles. A cleaning step or other processes, such as etching or conditioning, are performed at a relatively high vacuum (e.g. 1 to 20 mbar). These other processing steps generate relative few particles in comparison to the deposition process step. Typically, when the other processes such as chamber cleaning are completed, a valve, positioned downstream of a vacuum chamber, is operated to throttle the flow of fluid and raise the vacuum chamber pressure from a relatively higher vacuum to a relatively lower vacuum. Therefore, the vacuum pump is configured to be able to evacuate the vacuum chamber to a relatively higher vacuum even though such a higher vacuum is not required for the deposition stage. The recognition that the capacity of the vacuum pump is not fully used throughout processing steps allows implementation of the embodiment of the present invention described with reference to the drawings.

Referring toFIGS. 1 and 2, a vacuum pumping arrangement10is shown which comprises a vacuum pump12having a plurality of vacuum pumping stages14,16,18,20,22. The vacuum pumping stages are driven by a motor24. In the arrangement shown, vacuum pump12can be considered a backing pump for backing a booster pump26. A first pump inlet28is provided through which fluid can enter the pump12and pass through each of the pumping sections14,16,18,20,22towards a pump outlet30. Fluid entering through pump inlet28passes first through the booster pump26. A second pump inlet32is provided through which fluid can enter the pump and pass through only one or more of the pumping stages16,18,20,22downstream of the most upstream pumping stage14. In the arrangement shown fluid entering through pump inlet32passes through only the downstream pumping stage22.

A fore-line assembly34conveys fluid from a vacuum chamber36to the pumps12and26. The assembly has a first duct38for conveying fluid from a vacuum chamber to the first pump inlet28. As shown the duct38extends from an outlet40of the vacuum chamber to the inlet of the booster pump26and from the outlet of the booster pump to the first inlet28of the backing pump12. A second duct42conveys fluid from the outlet40of the vacuum chamber to the second pump inlet32.

There are four valves44,46,48,50for controlling the flow of process fluid (i.e. process precursors and their reaction by-products) from the chamber outlet40to the vacuum pumps12,26. Valves44,46are known from the prior art. Valve44is an isolation valve for isolating the vacuum chamber from the rest of the fore-line assembly and the pumps. Valve46is a throttle valve operable for increasing the pressure in the vacuum chamber from one pressure to a relatively higher pressure for example when a cleaning step has been completed and a deposition step is to be performed.

Valves48,50are isolation valves. Valve48has a first condition for allowing the flow of fluid from the vacuum chamber along duct38and a second condition for isolating the booster pump and the first pump inlet28from the outlet40of the vacuum chamber. Valve50has a first condition for allowing the flow of fluid along duct42and a second condition for isolating the second pump inlet32from the outlet40of the vacuum chamber.

As shown inFIG. 1during a relatively low vacuum process, the throttle valve46is operated to raise chamber pressure. Valve48is in the second condition (indicated in the figure by it being blacked out) and valve50is in the first condition so that fluid flows along duct42from the chamber outlet40to the second pump inlet32(as indicated by the bold line) and the booster pump and first pump inlet28are isolated from the chamber outlet. In this deposition step, a relatively large amount of the dust or particulates are generated. However, the fluid comprising the entrained particulates and/or dust is conveyed through only one pumping stage22of the vacuum pump12.

As shown inFIG. 2, during a relatively high vacuum process, the throttle valve46is operated to provide substantially no resistance to flow such that the vacuum chamber is at a low pressure. Valve48is in the first condition and valve50is in the second condition (indicated in the figure by it being blacked out) so that fluid from the vacuum chamber flows along duct38from the chamber outlet40to the booster pump and first pump inlet28(as indicated by the bold line) and the second pump inlet32is isolated from the chamber outlet. In this process step, a relatively small amount of dust or particulates are generated and therefore the fluid can be pumped by all the vacuum stages of the vacuum pump without significant detriment.

Accordingly, the valve arrangement comprising valves48,50is operable for selectively directing fluid along the first duct38or the second duct42. Alternatively valve arrangements will be apparent to those skilled in the art and may be provided for directing the fluid as required. The valve arrangement may be operated manually dependent on the processing step to be performed. Preferably though a control is configured to convey fluid from the vacuum chamber to the second pump inlet during a first processing step performed in the vacuum chamber at a relatively low vacuum and which generates a relatively large amount of particles and to convey fluid from the vacuum chamber to the first pump inlet during a second processing step performed in the vacuum chamber at a relatively high vacuum and which generates a relatively small amount of particles. The control may receive a signal from a vacuum chamber control unit indicating the process step to be performed, and the control controls the valve arrangement in response to the signal.

The fore-line assembly34additionally comprises ducts52which convey fluid from chamber outlets54to the booster pump and the first pump inlet28. The ducts54are in the example shown partially co-extensive with the duct38. The vacuum chamber contains vacuum chucks56having platforms for receiving wafers or other objects to be processed and the vacuum generated in the chucks maintains the objects (such as silicon wafers) in position on the platforms during processing. Fluid is conveyed from the chamber outlets54to the booster pump and the first pump inlet during the first processing step whilst at the same time fluid is evacuated through the chamber outlet40to the second pump inlet32. That is, operation of the valve arrangement does not affect fluid flow from outlets54which is generally continuous regardless of the process step. The vacuum chucks need not be operable when objects are not within the vacuum chamber for example during a chamber cleaning step.

A method of evacuating the vacuum chamber36with the vacuum pumping arrangement10will now be described with reference toFIGS. 1-3. Processing in the chamber is performed in cycles. In the simplest method, objects, such as silicon wafers, to be processed are transferred to the platform(s) of the vacuum chucks possibly from a load lock chamber (62). The pumping arrangement is operated to decrease the pressure in the vacuum chucks56to a first pressure of around 1 to 20 mbar to maintain the objects in position during processing (64). The chamber is evacuated through chamber outlet40to a second pressure of around 800 mbar (66). The first pressure is at higher vacuum than the second pressure. As shown inFIG. 1, isolation valve44is opened and throttle valve46is operated to allow an unimpeded flow of fluid. The isolation valve48is operated to adopt the second condition for resisting the flow of fluid along duct38and isolation valve50is operated to adopt the first condition for allowing the flow of fluid along duct42. A deposition step is performed at the relatively low vacuum of around 800 mbar (68). This processing step generates a relatively large amount of particles which is sufficient to cause damage to a known vacuum pumping arrangement. However, the evacuated gases are conveyed along the second duct to the second pump inlet32and even though the fluid is dusty it passes through only one pumping stage22.

When the deposition step is completed, the processed objects are removed from the vacuum chamber (70). The vacuum chamber pressure is reduced by pumping fluid from chamber outlet40to the first pump inlet28through the booster pump26(72). As shown inFIG. 2, the isolation valve44and the throttle valve46are operated to allow the flow of fluid unimpeded. Valve48is placed in the second condition (i.e. opened) to allow the flow of fluid along the first duct38. Valve50is placed in the first condition (i.e. closed) to resist the flow of fluid along the second duct42. When the pressure in the vacuum chamber reaches around 1 to 20 mbar, a cleaning step is performed to clean the chamber (72). The cleaning step generates less dust compared to the deposition step and is not sufficient to cause significant damage to the vacuum pumping arrangement. Additionally, as a lower pressure is required for the cleaning step, the fluid is conveyed through the booster pump and through all of the stages of the backing pump.

When the cleaning step is complete, the throttle valve46throttles the flow of gas through the chamber outlet40thereby increasing the pressure from around 1 to 20 mbar to 800 mbar. Objects are then placed in the vacuum chamber and the processing cycle repeated.