Method of processing a workpiece
A method of processing a workpiece in a chamber with a reactive gas supplied to the chamber creating a chamber pressure including positioning the workpiece on a support in the chamber with a first face exposed to the reactive gas, supplying a non-reactive gas between the support and a second face of the workpiece, and controlling the differential gas pressure across the thickness of the workpiece.
1 . A method of processing a workpiece in a chamber with a reactive gas supplied to the chamber creating a chamber pressure including:
positioning the workpiece on a support in the chamber with a first face exposed to the reactive gas;
supplying a non-reactive gas between the support and a second face of the workpiece; and
controlling the differential gas pressure across the thickness of the workpiece.
2 . A method as claimed in claim 1 wherein the differential pressure is controlled such that the pressure of non-reactive gas is always greater than the pressure in the chamber but does not exceed a limit determined by the operator.
3 . A method as claimed in claim 1 wherein the step of controlling the differential pressure includes monitoring the chamber pressure; monitoring the non-reactive gas pressure and adjusting the non-reactive gas pressure in response to changes in the chamber pressure.
4 . A method of processing a workpiece as claimed in claim 1 wherein the differential pressure is prevented from exceeding the pressure of attachment of the workpiece to the workpiece support.
5 . A method as claimed in claim 3 wherein the step of controlling the differential pressure is responsive to the extent of processing of the workpiece.
6 . A method as claimed in claim 4 wherein the step of controlling the differential pressure is responsive to the extent of processing of the workpiece.
7 . A method as claimed in claim 1 wherein the differential pressure is in the range about 130 Pa to about 4 kPa.
8 . A method as claimed in claim 1 wherein the step of controlling includes monitoring a process parameter and adjusting the non-reactive gas pressure in accordance with that parameter.
9 . A method as claimed in claim 8 wherein the process parameter is at least one of: the time elapsed in the process; the chamber pressure; the flow rate of the non-reactive gas; the temperature of the workpiece or the output of a process end point monitoring device.
10 . A method as claimed in claim 1 wherein the step of controlling includes maintaining the flow rate of the non-reactive gas at a predetermined positive value or within a predetermined range of positive valves.
11 . A method as claimed in claim 10 wherein the flow rate of the non-reactive gas is controlled within the range about 0.1 sccm to about 10 sccm.
12 . A method as claimed in claim 10 wherein the step of controlling includes controlling the flow rate of the non-reactive gas in accordance with a process parameter.
13 . A method as claimed in claim 12 wherein the process parameter is at least one of: the time elapsed in the process; the chamber pressure; the flow rate of the non-reactive gas; the temperature of the workpiece or the output of a process end point monitoring device.
14 . A method as claimed in claim 1 wherein the maximum chamber pressure is in the range of about more than about 130 Pa and not more than 65 kPa.
15 . A method as claimed in claim 14 wherein the maximum chamber pressure is in the range and more than about 1.3 kPa and not more than about 13 kPa.
16 . A method as claimed in claim 1 wherein the non-reactive gas is one or more of: helium, neon, argon, krypton, xenon, radon or nitrogen or hydrogen.
17 . A method as claimed claim 1 wherein the non-reactive gas acts as a heat-exchange medium between the workpiece and the support.
18 . A method as claimed in claim 1 wherein the workpiece support temperature is controlled.
19 . Apparatus for processing a workpiece including a chamber having a processing volume, a workpiece support located in the chamber, with a support face facing the processing volume, a reactive gas inlet to the processing volume, a non-reactive gas inlet to the support face and a control system for controlling the apparatus in accordance with the method of claim 1 .
20 . An apparatus as claimed in claim 19 including means for clamping the workpiece to the support.
21 . Apparatus as claimed in claim 19 wherein the support incorporates an electrostatic chuck.
22 . Apparatus as claimed in claim 19 wherein the lateral extent of the support face is equal to or greater than the corresponding nominal dimension of a workpiece.
23 . Apparatus as claimed in claim 19 further including a seal or seals to separate the process volume from that part of the support face on which a workpiece lies in use.
24 . Apparatus as claimed in claim 23 wherein the seal includes or is constituted by lapping, polishing or dishing of the support face or a flexible seal or O-ring.
25 . Apparatus as claimed in any one of claim 19 including a gas distribution groove formed in the part of the support face on which a workpiece lies in use and being a constant radial distance inward of the periphery of that part.