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Positive displacement pumping chamber

Positive displacement pumping chamber description/claims

The present invention describes an apparatus for the deposition and/or removal of thin layers of materials on or from a substrate such as a silicon wafer. A number of advanced deposition and etching processes make use of discrete steps for the formation of a thin film or the etching of deep structures. These steps are preferably performed in one process chamber (either batch or single wafer).

By way of example, Atomic Layer deposition (ALD—also known as atomic layer epitaxy) is a chemical vapor deposition process in which self-limiting surface reactions produce extremely conformal coatings. There is a growing requirement to increase equipment productivity for ALD and similar processes for example to form very thin layers high dielectric constant (k) films such as HfO2 or alumina. For the ALD of a layer such as Aluminum oxide a reactant gas containing Aluminum such as trimethyl aluminum Al(CH3)3 is firstly introduced into a chamber containing the substrate(s) such that a monolayer of this gas adheres to and in many cases saturates the surface. A purge is then necessary by pumping only or with an inert (to this process) gas such as nitrogen or hydrogen to remove all but this monolayer of gas from the chamber. Then an oxidizer, such as water vapor, is flowed into the chamber and a surface reaction with the trimethyl aluminum takes place forming a monolayer of aluminum oxide. Excess oxidizer and reaction by-products are then pumped away and the chamber purged and the cycle repeated until the desired film thickness achieved.

The cycle time therefore=Exposure A+Purge A+Exposure B+Purge B

Purge is used throughout to mean the sufficient removal or dilution of the reactant. This may be achieved by pumping alone or by pumping and flowing an inert (Purge) gas or any sequence of the two as is well known in the field.

Where A and B represent the precursors from which the deposited film is derived. This is example is given simply by way of example and a review of the field will give many further examples of such step-wise deposition processes.

Whilst this binary process produces high quality films and is relatively insensitive to other process parameters it is very slow, as the layers are built up monolayer at a time.

The necessary exposure time is very short so a known attractive approach to increasing the speed of film growth is to decrease exposure times. Whilst exposure times may be reduced to very short periods e.g. sub 1 second, it is a critical requirement that the process chamber is adequately purged after the precursor exposure steps.

Presently there is no method of reducing the purge times to those as short as the exposure times and in an otherwise optimized process perhaps 75% of the total cycle time is spent (unproductively) purging the chamber.

A method of rapidly extracting the process chamber gaseous contents would therefore be advantageous as it would increase the productivity of equipment for ALD and other stepwise processes.

From one aspect the invention consists in apparatus for processing a substrate in a process cycle including a chamber for receiving a substrate in a process volume and a moveable wall displaceable to vary the process volume in accordance with the process cycle.

The apparatus may include an exhaust outlet and the moveable wall may be moveable to reduce the process volume to purge gas from the process volume through the exhaust outlet during a purge part of the process cycle. In a particularly preferred embodiment there are a plurality of exhaust valves operable in respect purge parts of the process cycle.

Similarly the apparatus may include an inlet for process gas and the moveable wall may be moveable to draw process gas through the inlet during the process part of the process cycle. There may be a plurality of inlet valves for respective process gases.

There may also be an inlet for purge gas and the purge gas inlet may be constituted by a process gas inlet.

The ratio of the largest and smallest process volumes defined by the moveable wall may be between about 5:1 and 100:1. In a particularly preferred arrangement the volume ratio is about 10:1.

The compression ratio in the process volume resulting from the movement of the wall may be about between 5:1 and about 100:1 and 10:1 is particularly preferred.

The moveable wall may act as or carry a substrate support, in which case the moveable wall may additionally be moveable between a substrate load/unload position and a process chamber defining position.

The moveable wall may be located in an extension of the process chamber, in which case the chamber and the extension may have a common housing. Additionally or alternatively the extension may be adjacent the chamber.

In an alternative embodiment the apparatus may include a substrate support and the moveable wall may be generally opposite to the substrate support. In this case the apparatus may include a fixed housing extending around the substrate support to define a process chamber together with the moveable wall and support. The moveable wall and/or housing may include a plurality of parts, at least two of which are relatively moveable to allow loading of a substrate onto the substrate support.

In any of the above cases the wall may be a piston.

In another aspect the invention may consist in a method of processing a substrate including placing the substrate in a process volume and introducing a process gas or vapour into the process volume and/or subsequently removing gas or vapour from the volume wherein the step of introducing and/or removing the gas is at least partially performed by moving a moveable wall to change the process volume in an appropriate sense.

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