Patent Application
20080000530
These features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, which illustrate examples of the invention. However, it is to be understood that each of the features can be used in the invention in general, not merely in the context of particular drawings, and the invention includes any combination of these features, where:
An embodiment of a gas flow comparator 20, as shown in
The gas control 24 provides gas at a selected gas flow rate or pressure to the apparatus. Referring to
The gas at the constant flow rate and/or pressure is applied to a principal flow splitter 40 which has an inlet port 44 connected to the outlet 32 of the gas tube 26 to receive the gas. The flow splitter 40 splits the received gas flow to first and second output ports 48a,b. The flow splitter 40 can split the gas flow into two separate and equal gas flows or split the gas flow according to a predefined ratio. In one example, the flow splitter 40 splits the received gas flow equally between the first and second output ports 48a,b. This is accomplished by positioning the output ports 48a,b symmetrically about the inlet port 44. In one version, the principal flow splitter 40 comprises a T-shaped gas coupler 41 as shown in
First and second flow restrictors 50, 52 are each connected to the first and second output ports 48a,b respectively. Each flow restrictor 50, 52 provides a pressure drop across the flow restrictor. The pressure drop provided by each of the two restrictors 50,52 is typically the same pressure drop, but they can also be different pressure drops. In one version, the first flow restrictor 50 has a restrictor outlet 54 and the second flow restrictor 52 has a restrictor outlet 56. A cross-section of an embodiment of a flow restrictor 50, as shown in
A pair of secondary flow splitters 60, 62 are connected to the restrictor outlets 54, 56 of the flow restrictors 50, 52. The first secondary flow splitter 60 comprises an inlet port 63 and a pair of first output ports 64a,b, and the second secondary flow splitter 62 also has an inlet port 66 and a pair of second output ports 68a,b. The secondary flow splitters 60,62 can also comprise the aforementioned T-shaped gas couplers 41.
A differential pressure gauge 70 is connected across the output ports 64a, 68a of the secondary flow splitters 60, 62. In one version, the differential pressure gauge 70 is suitable for measuring a pressure range of at least 1 Torr, or even at least 5 Torr, or even 50 Torr. The accuracy of the differential pressure gauge 70 depends on the pressure or flow rate of gas through the flow comparator 20. For example, a differential pressure gauge 70 having a pressure range measurement capability of 50 Torr has an accuracy of at least about ±0.15 Torr; whereas a differential pressure gauge 70 capable of measuring a pressure range of 1 Torr has an accuracy of 0.005 Torr. A suitable differential pressure gauge 70 is an MKS 223B differential pressure transducer, available from aforementioned MKS Instruments, Inc. The differential pressure gauge 70 operates by diaphragm displacement in the forward or reverse direction which generates a positive or negative voltage which corresponds to the measured pressure differential.
First and second nozzle holders 80, 82 are connected to the pair of second output ports 64b, 68b of the secondary flow splitters 60, 62. The nozzle holders 80, 82 are capable of being connected to feed gas to nozzles 100, 102, for comparative measurements of the flow rates through the nozzles. For example, the nozzle holders 80, 82 can be connected to a first reference nozzle 100, and a second test nozzle 102 which is to be tested for its flow rate relative to the reference nozzle; or the relative flow rates through two nozzles 100, 102 can be compared to one another.
To compare the flow rate of gas through the two nozzles 100, 102, the nozzles 100, 102 are attached to the nozzle holders 80, 82. An exploded view of the installation of a nozzle 102 in a nozzle holder 82 is shown in
In operation, the gas supply 34 and the gas control 24 are used to provide a constant flow rate of gas or a constant pressure of gas, to the inlet 28 of the gas tube 26 of the flow comparator 20. In one version, a pressure regulator 36 is set to provide gas at a constant pressure of, for example, from about 10 to about 150 psig, or even 40 psig. for a nozzle having a diameter of 16 mils, and a flow meter 38 is set to provide a flow rate of from about 100 to about 3000 sccm, and in one version 300 sccm. However, the set gas flow rate or gas pressure, is much larger when a large number of nozzles 102 are being measured, for example, a quadrant of nozzles 102 of a gas distributor having thousand of nozzles, for which the flow rate can be set to a level from about 80 slm to about 140 slm, or even from about 100 slm to about 120 slm.
The differential pressure gauge 70 is zeroed out at the beginning of each test session. The constant flow rate or constant pressure gas supply is provided to the principal flow splitter 40 which directs the gas through the separate first and second flow channels 120, 122 having the first and second flow restrictors 50, 52. After exiting the outlets 54, 56 of the flow restrictors 50, 52, the gas is passed through the first and second nozzles 100, 102 at least one of which is being tested. Any difference in flow rate of gas passing through, or a pressure drop across, the nozzles 100, 102 causes the pressure differential gauge 70 to register a pressure differential that is proportional to the variation in flow rate of the gas through the nozzles 100, 102. Conventional methods of measuring nozzle performance directly measure the flow through the nozzle using a mass flow meter, and such a flow measurement accuracy is limited by the measurement accuracy of the total flow through the nozzle. In contrast, the flow comparator 20 allows measurement of flow variations that are within about ±1.5% of the nominal flow rate through the nozzle 100, 102. The nozzle flow rate is measured as the percent change of the nozzle resistance through the differential pressure between the two nozzles 100, 102 and the upstream pressure. By measuring the difference in resistance, the flow comparator 20 can generate a flow measurement accuracy that is at least an order of magnitude better than conventional flow testing devices.
Operation of the flow comparator 20 can be explained with reference to a Wheatstone Bridge 94 electrical circuit as shown in
R
E={(R1+R2)·(R3+Rx)}/{R1+R2+R3+R4}
In the flow comparator 20 shown in
ΔP=Q {ΔR/[2(1+k)+ΔR/Ru]}
In one version, a kit of calibration nozzles can also be used to verify that the flow comparator 20 is in proper working order. The kit can have different types of nozzles 100, 102 or multiple nozzles of the same type, that is with the same orifice dimensions. For example, the kit of nozzles can contain nozzles having an opening that is sized from about 0.0135 to about 0.0210 inches, at increments of 0.0005 inch. The kit of calibration nozzles can also be ceramic nozzles from Kyocera, Japan, which have a controlled orifice size. The kit is useful to calibrate nozzles that are being tested to determine the actual flow rate of the test nozzles.
In another version, the flow comparator 20 is adapted to connect to nozzles 102 of a gas distributor 126 which is used to distribute process gas to substrate processing chambers. The gas distributor 126, a version of which is shown in
In one version, the sampling probe 130 comprises a first tube 129 having a first diameter, and connected to a second tube 131 having a second diameter which is smaller than the first diameter. For example, the first tube 129 can have a first diameter of about 6.4 mm (0.25 in), and receives a second tube 131 have a second smaller diameter of 3.2 mm (0.125 in). The tubes 129, 131 can be plastic tubes. An O-ring seal 134 is mounted around the opening of the second tube 131 of sampling probe 130 to form a seal, and the O-ring seal 134 can be, for example, a silicon rubber ring having an internal hole with a diameter of about 3.2 mm (0.125 in), and an external size of about of 6.4 mm (0.125 in) or larger. In one version, the silicon rubber ring has a Durometer hardness measurement of about 20. The silicon rubber ring can be for example, 20 durometer super-soft silicon rubber, available from McMaster-Carr, Atlanta Ga. In another version, the sampling probe 130 comprises a VCO fitting suitable for forming a gas tight seal against a flat surface, and having a flat end with a groove therein and an O-ring gasket in the groove. A suitable O-ring can have a diameter of about 3.2 mm (0.125 in). The gas supplied to the flow comparator 20 can be nitrogen.
In still another measurement method, the flow comparator 20 is used to measure the relative gas flow conductance of two or more arrays 128a,b of nozzles 102 of a single gas distributor 126 mounted in an enclosure 138, as shown in
Another measurement method that can be used with the flow comparator 20 comprises measuring a gas flow conductance rates of nozzles of two gas distributors 126a,b each comprising a face plate facing a blocker plate 135a,b with a large number of nozzles 100, 102, respectively, and which vent to a clean room environment, as shown in
A setup suitable for comparing total flow rates through two plates 126a,b comprises a flow comparator 20 mounted so that each nozzle holder 80, 82 is connected to an input gas manifold 144a,b of each chamber 138a,b, which feeds a separate gas distributor 126a,b. In this set up, the flow comparator 20 measures the percent difference in flow resistance or conductance by measuring the differential pressure between the two manifolds 144a,b and the upstream or input gas pressure from the gas source 30. By measuring the difference in resistance, this flow comparator 20 can be used to achieve accurate flow rate, and uniformity of flow data which can be used to improve the matching of gas distributors 126a,b in twin chambers 138a,b.
The variation in absolute flow rates that can occur between different nozzles 102 of a gas distributor 126, or different gas distributors 126a,b, as measured using conventional flow measuring apparatus is shown in
A graph of the variation in the relative difference of sampled flow rates through individual nozzles 102 of a gas distributor 126, in volts measured by the differential pressure gauge 70, is shown in
The thickness of a silicon oxide film deposited on a substrate 160 using silane gas in a process chamber was measured and shown in the contour map of
In another measurement set up, an automated flow uniformity mapping fixture can be used to measure the flow uniformity of different nozzles 102 of a gas distributor plate 126. For example, the fixture can include a flow comparator and an X-Y-Z motion stage to move the sample probe 130 across the plate 126 to different nozzles to test each nozzle 102. This test fixture allows measurement of a complete flow contour map for each new gas distributor 126.
A substrate processing apparatus 140 can also comprise a gas flow controller 141 to control a plurality of gas flow rates through nozzles 102 that introduce process gas into a plurality of substrate processing chambers 138a,b. In one version, the gas flow controller 141 comprises the flow comparator 20 and is used to automatically adjust the flow rates of the process gas to the chambers 138a,b. The process gas can be activated in a remote plasma source, such as an RPS source made by Astron, Irvine, Calif. Each chamber 138a,b comprises an input gas line 150a,b which feeds process gas to a gas manifold 154a,b which in turn feeds the gas to a gas distributor 126a,b. In operation, passage of a process gas through the first and second flow restrictors 50, 52 and nozzle holders 80, 82 of the flow comparator 20, the nozzle holders being connected to input gas lines 150a,b that feed the gas distributors 126a,b in the chambers 138a,b causes the pressure differential gauge 70 of the flow comparator 20 to register a pressure differential that is proportional to the variation in flow rate of the gas through the nozzles 102.
In operation, a pressure differential signal is sent from the pressure differential gauge 70 to a controller 148, which in response to the signal, adjusts a flow adjustment valve 158a,b connected to the input gas line 150a,b of a substrate processing chamber 138a,b, to form a closed loop control system. The flow adjustment valves 158a,b are each connected at one end to an output port 64b, 68b of a secondary flow splitter 60,62, respectively, and at another end to an input gas line 150a,b of a chamber 1.38a,b which feeds the gas distributor 126a,b in the chamber. The flow adjustment valves 158a,b control the flow of process gas passing through the input gas lines 150a,b in response to a flow control signal received from the controller 148. In the version shown, the differential pressure gauge 70 is positioned before the flow adjustment valves 158a,b. Since the gauge 70 has a high flow impedance, the gauge 70 has a minimal effect on the flow rates of the process gas passed through the valves 158a,b and gas lines 150a,b. Thus, the differential pressure gauge can also be placed in other locations along the gas supply channels.
The chambers 138a,b can also be used as enclosures 133 that serve as vacuum test fixtures to test the differential flow through the distributor plates 126a,b. The differential pressure gauge measures the differential pressure of the gas applied to input tubes that supply process gas to each chamber 138a,b.
In one version, the flow adjustment valves 158a,b are mechanized to allow automation of the flow adjustment in response to a differential pressure signal from the differential pressure gauge 70. For example, the valves 158a,b can be electrically actuated or manual actuated. In one embodiment, the two valves 158a,b are adjusted until the desired set-point is reached for a signal corresponding to a measured differential pressure of 0 Torr from the differential pressure gauge 70. Similarly, if the desired set-point is −2 Torr, for example, when un-equal flow rates are desired to each gas distributor 126a,b, the valves 158a,b can be adjusted accordingly. This allows the differential pressure to be set in the process recipe and to be automatically implemented during operation of the apparatus 140. In fact, zero differential pressure may not provide the best results, but would lead to an evenly split flow between the two gas lines 150a,b. Advantageously, differential backpressure differences of as little as 0.1 mtorr can be used to resolve flow differences down to 0.1% of total flow rates, or even 0.01% of flow rates, in contrast to conventional flow control meters which can provide resolution of flow differences only to about 1% of total flow rates, which represents a 10 times better flow resolution.
The apparatus 140 can be, for example, a Producer™ with twin chambers 138a,b from Applied Materials, Santa Clara, Calif. The pair of processing chambers 138a,b is disposed one above the other and each chamber provides the capability of processing one or more substrates 160. The chambers 138a,b can be used, as one example of many possible uses, for the deposition of silicon oxide films using silane gas on substrates 160 comprising silicon wafers, the wafers having dimensions of 300 mm. In one embodiment, the chambers 138a,b include identical components to carry out identical semiconductor processing operations, or identical sets of processing operations. Being identically configured allows the chambers 138a,b to simultaneously perform identical chemical vapor deposition operations in which an insulating or a conductive material is deposited on a wafer disposed in each respective chamber 138a,b. In other embodiments, the identical semiconductor processing chambers 138a,b are used for etching substrates 160, such as silicon wafers, typically through openings in a photoresist or other type of masking layer on the surface of the wafer. Of course, any suitable semiconductor operation can be performed simultaneously in the chambers 138a,b, such as plasma vapor deposition, epitaxial layer deposition, or even etching processes such as pas etch, etch back, or spacer etch processes. As will be described, the choice of such operation is arbitrary within the context of the system described herein.
Substrates 160a,b such as silicon wafers or other type semiconductor wafers, are transported to each chamber 138a,b to rest on a substrate support 162a,b. Each substrate support 162a,b can include a temperature control 164a,b comprising a heater, to heat the substrate 160a,b. Equalizing gas flows through the chambers 138a,b alone does not necessarily equalize film deposition rates or produce the same processing results in the chambers 138a,b. For instance, there may still be variations in the film thicknesses due to other factors such as temperature differences and the spacing between the gas distributors 126a,b and the substrates 160a,b. Wafer temperature is adjusted by varying the temperature of the substrate supports 162a,b using the temperature control 164a,b. Spacing is adjusted using a spacing control 163a,b connected to the substrate support 162a,b.
The chambers 138a,b each have exhaust ports 165a,b connected to separate exhaust lines 166a,b that join to form a common exhaust line 168 which leads to a vacuum pump 170. In operation, the chambers 138a,b are pumped down to low pressures using a pump, such as a vacuum pump for example a combination of roughing, turbomolecular, and other pumps to provide the desired pressure in the chambers 138a,b. Downstream throttle valves 174a,b are provided in the exhaust lines 166a,b to control the pressure of the gas in the chambers 138a,b.
When used for plasma enhanced processes, the chambers 138a,b, can also have gas energizers 180a,b. The gas energizers 180a,b can be electrodes within the chambers 138a,b, an induction coil outside the chambers, or a remote plasma source such as a microwave or RF source. The gas energizers 180a,b are used to set the power level applied to generate and sustain the plasma or activated gas species in the chambers 138a,b.
The foregoing description of various embodiments of the invention has been provided for the purposes of understanding of the invention. The description is not intended to be exhaustive or to limit the invention to precise forms described. For example, embodiments of the present invention may be used to match three or more chambers. Moreover, one or more of the chambers in the multiple chamber system may be configured to process simultaneously more than one wafer. Accordingly, numerous modifications and variations are possible in view of the teachings above.
The present application claims the benefit of U.S. Provisional Application No. 60/810,446, filed on Jun. 2, 2006, which is incorporated by reference herein and in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60810446 | Jun 2006 | US |
