Methods and system for mitigating CVD foreline growth

Abstract

To provide a method and a system for mitigating CVD foreline growth.SOLUTION: Various embodiments of the present technology may provide a system with a bypass line to a foreline of a reaction chamber. The system may include a pump coupled to the foreline. The system may include a pressure-flow controller upstream from the bypass line. The bypass line may be coupled to the foreline at the pump inlet. The bypass line may include a low-flow pathway where the conductance is between 1% and 10% relative to unrestricted flow. The bypass line can comprise a decomposition device configured to decompose the fluid (e.g., gas) in the bypass line.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is a nonprovisional patent application claiming priority to and the benefit of U.S. Provisional Patent Application No. 63 / 538,762, filed on September 15, 2023, and entitled "METHODS AND SYSTEM FOR MITIGATING CVD FORELINE GROWTH," which is incorporated herein by reference.

[0002] The present disclosure relates generally to methods and systems for mitigating CVD foreline growth. More specifically, the disclosure relates to metering dosage using a pressure controller, relocating a bypass termination adjacent to a pump inlet, and / or decomposing gases before they reach the foreline or within the foreline. [Background technology]

[0003] Semiconductor processing equipment performing deposition can suffer from CVD growth in undesired areas of the processing equipment. In particular, in ALD processes where precursors are pulsed with co-reactants, excessive CVD growth can be observed in the foreline due to the co-existence of the co-reactant with the precursor. This CVD growth can form a low density powder that adheres poorly to the inner walls of the foreline and can periodically flake off from the walls, be carried away by the pump, and cause pump failure. Summary of the Invention [Means for solving the problem]

[0004] Various embodiments of the present technology may provide a system with a bypass line to a foreline of a reaction chamber. The system may include a pump coupled to the foreline. The system may include a pressure flow controller upstream of the bypass line. The bypass line may be coupled to the foreline at a pump inlet. The bypass line may include a low flow path having a conductance of 1%-10%.

[0005] According to one aspect, a system includes a reaction chamber, a first container configured to contain a precursor, the first container coupled to the reaction chamber with a first gas line, a second container configured to contain a co-reactant, the second container coupled to the reaction chamber, a foreline having a first end directly coupled to the reaction chamber and an opposing second end, a pump coupled to the second end of the foreline at a first junction, a second gas line having a first section coupled to an inlet of the reaction chamber and a second section coupled to the foreline, the first section and the second section connected to each other at a second junction, and a mass flow controller coupled between the second container and the second junction.

[0006] In one embodiment, the co-reactant is one of ozone, ammonia, silane, or disilane.

[0007] In one embodiment, the first section of the second gas line has a first conductance and the second section has a second conductance, the first conductance being the same as the second conductance.

[0008] In one embodiment, the co-reactant has a high pressure gas state.

[0009] In one embodiment, the system further comprises a first valve in the first section of the second gas line and a second valve in the second section of the second gas line.

[0010] In one embodiment, the system further comprises a control unit configured to send control signals to the first and second valves.

[0011] In one embodiment, the pump is a dry vacuum pump.

[0012] In one embodiment, the system further comprises a decomposer coupled to the second section of the second gas line and configured to decompose the co-reactant. The decomposer may include a catalyst and / or a heater.

[0013] In another aspect, a system includes a reaction chamber, a foreline having a first end directly connected to the reaction chamber and an opposing second end, a pump coupled to the second end of the foreline, a first container configured to contain a precursor, the first container coupled to the reaction chamber with a first gas line, a second container configured to contain a co-reactant, the second container coupled to the reaction chamber, a second gas line having a first section coupled to an inlet of the reaction chamber, a second section coupled to the foreline, and a third section coupled to the foreline, the first section and the second section connected to each other at a junction and the second and third sections are parallel to each other, and a pressure flow controller coupled between the second container and the second junction.

[0014] In one embodiment, the system further includes a first valve in a first section of the second gas line, a second valve in a second section of the second gas line, and a third valve in a third section of the second gas line.

[0015] In one embodiment, the system further comprises a flow restrictor coupled between the junction and the third valve.

[0016] In one embodiment, the system further comprises a control unit configured to send control signals to the first, second, and third valves.

[0017] In one embodiment, the co-reactant is one of ozone, ammonia, silane, or disilane.

[0018] In one embodiment, the first section has a first conductance, the second section has a second conductance, and the third section has a third conductance, the third conductance being 95% less than the first conductance and / or the second conductance.

[0019] In one embodiment, the pump may be a dry vacuum pump.

[0020] In yet another aspect, a system comprises a reaction chamber, a foreline having a first end directly coupled to the reaction chamber and an opposing second end, a pump coupled to the second end of the foreline at a first junction, a first container configured to contain a precursor, the first container coupled to the reaction chamber with a first gas line, a second container configured to contain a co-reactant, the second container coupled to the reaction chamber, and a second gas line having a first section coupled to an inlet of the reaction chamber and a second section coupled to the first junction, the first section and the second section connected to one another at the second junction.

[0021] In one embodiment, the system further comprises a pressure flow controller coupled between the second vessel and the second junction. The second gas line further comprises a third section coupled between the second junction and the foreline. The second section and the third section may be parallel to one another.

[0022] In one embodiment, the pump may be a dry vacuum pump.

[0023] In one embodiment, the first section has a first conductance, the second section has a second conductance, and the third section has a third conductance, the third conductance being 95% less than the first conductance and / or the second conductance.

[0024] In one embodiment, the system further includes a first valve in a first section of the second gas line, a second valve in a second section of the second gas line, and a third valve in a third section of the second gas line.

[0025] In one embodiment, the system further comprises a flow restrictor coupled to the third section between the second junction and the third valve.

[0026] A more complete understanding of the present technology may be obtained by reference to the detailed description when considered in conjunction with the following illustrative figures, in which like reference numbers refer to like elements and steps throughout. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 representatively illustrates a system in accordance with one embodiment of the present technology. [Diagram 2] FIG. 2 exemplarily illustrates a system in accordance with an alternative embodiment of the present technology. [Diagram 3] FIG. 3 exemplarily illustrates a system in accordance with an alternative embodiment of the present technology. [Figure 4] FIG. 4 exemplarily illustrates a system in accordance with an alternative embodiment of the present technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The technology may be described in terms of functional block components and various process steps. Such functional blocks may be realized by any number of components configured to perform the specified functions and achieve various results. For example, the technology may employ various reaction chambers, valves, valve manifolds, gas line connectors, and vessels. Components of any of the illustrated embodiments in the figures may be combined and / or arranged in any suitable combination of components in a system (i.e., components illustrated in one embodiment in a first figure but not in a second figure may also be implemented in the second figure in accordance with the present disclosure).

[0029] With reference to FIGS. 1-4, an exemplary system 100 may include a reaction chamber 105 , a first vessel 115 , a second vessel 110 , a foreline 130 , and a pump 120 .

[0030] In various embodiments, the reaction chamber 105 may be configured to deposit a film on a substrate, such as a wafer. The reaction chamber 105 may be configured for any desired deposition process.

[0031] In various embodiments, the first container 115 may be configured to contain or otherwise hold a first chemical (e.g., a precursor). The first chemical may be in solid, liquid, or gas form. In some cases, the first container 115 may be configured to sublimate the first chemical into a gas. For example, the first container 115 may include a heating element and / or a sublimator.

[0032] In various embodiments, the second container 110 may be configured to contain or otherwise hold a second chemical (e.g., a co-reactant). The second chemical may include a chemical having a high pressure gas state, such as ozone, ammonia, silane, or disilane. The second container 110 may be configured to sublimate the second chemical into a gas. For example, the second container 110 may include a heating element and / or a sublimator.

[0033] In various embodiments, the foreline 130 may be coupled to the reaction chamber 105 and may be configured to evacuate excess chemicals from the reaction chamber 105. For example, the foreline may include a first end coupled to an opening in the bottom of the reaction chamber 105 and an opposing second end. The foreline 130 may be formed from any suitable material, such as a metallic material, e.g., stainless steel.

[0034] In various embodiments, the pump 120 may be configured to facilitate evacuation of the reaction chamber 105. For example, an inlet of the pump 120 may be coupled to a second end of the foreline 130. The connection point of the inlet of the pump 120 and the foreline 130 may be referred to as a first junction. The pump 120 may comprise a vacuum pump. An outlet of the pump 120 may exhaust gases to a waste line (not shown).

[0035] In various embodiments, the system 100 may further include a first gas line 135 configured to connect the first vessel 115 to an inlet of the reaction chamber 105. The first gas line 135 may be formed from any suitable material, such as stainless steel. The first gas line may include any number of couplings, connectors, gas line segments, and the like.

[0036] In various embodiments, the system 100 may further include a second gas line. The second gas line may be formed from any suitable material, such as stainless steel. In an exemplary embodiment, the second gas line includes a first section 140 (i.e., a main delivery line) configured to deliver gas to the reaction chamber 105. For example, a first end of the first section 140 may be coupled or otherwise connected to the second vessel 110, and a second end of the first section 140 may be coupled or otherwise connected to an inlet of the reaction chamber 105.

[0037] In an exemplary embodiment, the second gas line may further include a second section (e.g., a first bypass line), such as second section 145A or 145B. The second section may include a first end and an opposing second end. The first end of second section 145A may be connected to first section 140 at second junction 165 (or any other suitable location), and the second end of second section 145A may be connected to the first junction. The first end of second section 145B may be connected to first section 140 at second junction 165 (or any other suitable location), and the second end of second section 145B may be connected to foreline 130.

[0038] 2, the second gas line may further include a third section 200 (e.g., a second bypass line). The third section 200 may include a first end coupled to the section junction 165 (or any other suitable location) and a second end coupled to the foreline 130.

[0039] In various embodiments, system 100 may include various valves to restrict or allow the flow of gas through the gas lines. For example, system 100 may include a first valve 160 in first gas line 135, a second valve 150 in first section 140, and a third valve 155 in the second section (e.g., second section 145A or 145B).

[0040] The first valve 160 may be disposed between the inlet of the reaction chamber 105 and the outlet of the first vessel 115. The first valve 160 may comprise any suitable type of valve. In an exemplary embodiment, the first valve 160 may comprise a diaphragm valve responsive to a control signal. The control signal may open or close the valve.

[0041] The second valve 150 may be disposed between the second junction 165 and the inlet of the reaction chamber 105. The second valve 150 may comprise any suitable type of valve. In an exemplary embodiment, the second valve 150 may comprise a diaphragm valve responsive to a control signal. The control signal may open or close the valve.

[0042] The third valve 155 may be disposed between the first junction and the section junction 165 or between the second junction and the foreline 130. The second valve 150 may comprise any suitable type of valve. In an exemplary embodiment, the third valve 155 may comprise a diaphragm valve responsive to a control signal. The control signal may open or close the valve.

[0043] Further, in the exemplary embodiment, the third section 200 may include a fourth valve 205 and / or a restrictor 210. The fourth valve 205 and the restrictor 210 may be disposed between the second junction 165 and the foreline 130. The restrictor 210 may be disposed upstream of the fourth valve 205. The fourth valve 205 may comprise any suitable type of valve. In the exemplary embodiment, the fourth valve 205 may comprise a diaphragm valve responsive to a control signal. The control signal may open or close the valve.

[0044] In various embodiments including a third section 200, the second section 145B may not be present. In various embodiments, the third section 200 may not be present, but a flow restrictor may be coupled to the second section 145B.

[0045] 1, 3, and 4, the system 100 may further include a mass flow controller 125. The mass flow controller 125 may be coupled to the second gas line between the outlet of the second vessel 110 and the second junction 165. In particular, the mass flow controller 125 may be located upstream of the second junction 165. In various embodiments, in addition to or in place of the mass flow controller 125, there may be a pressure flow controller (e.g., similar to pressure flow controller 215).

[0046] In another embodiment, and referring to FIG. 2, the system 100 may further include a pressure flow controller (PFC) 215 configured to regulate the flow rate and conductance of the second gas line. The PFC 215 may be coupled to the second gas line between the outlet of the second vessel 110 and the second junction 165. In particular, the PFC 215 may be disposed upstream of the second junction 165. The PFC 215 may be configurable, for example, to be set to a desired pressure setpoint (e.g., a relatively high setpoint pressure may lead to a larger flow rate, and a relatively low setpoint pressure may lead to a smaller flow rate). The PFC 215 may be any suitable type of PFC that regulates the gas flow according to pressure. In various embodiments, in addition to or instead of the PFC 215, there may be a mass flow controller (e.g., similar to the mass flow controller 125).

[0047] In various embodiments, system 100 may further include a control unit 170. The control unit 170 may be in electronic communication with any other suitable components of system 100 (e.g., to generate and send valve control signals and / or control the mass flow controllers and / or PFCs). The control unit may also be used to set a set point for PFC 215.

[0048] During operation, the system 100 may perform an atomic layer deposition (ALD) process. For example, the system 100 may perform a sequence of pulses with precursors and co-reactants, and purge steps between pulses with an inert gas, such as argon.

[0049] In conventional systems, the full flow of co-reactant into the foreline (e.g., during purging of the second gas line and / or during a precursor pulse or purge) can cause CVD reactions with the precursor in the foreline (e.g., on the sidewalls of the foreline), which is undesirable because this buildup can flake off the sidewalls and enter the pump, causing it to fail.

[0050] Embodiments of the present technology may mitigate CVD foreline buildup. For example, in operation and with reference to FIG. 1, during a co-reactant pulse, the second valve 150 is open and the third valve 155 is closed. During a co-reactant purge and / or a precursor pulse and purge, the second valve 150 is closed and the third valve 155 is open. During a purge, gas flows directly through the second section 145A to the inlet of the pump 120 (e.g., to the first junction), thus avoiding most or all of the foreline 130, thus mitigating or preventing CVD buildup along most of the entire length of the foreline 130. The second section 145A may be coupled to the foreline 130 at or near the inlet of the pump 120, and / or the second section 145A may be coupled to the pump 120 at an inlet separate from the pump inlet coupled to the foreline 130.

[0051] As another example, with reference to FIGS. 3 and 4, at least a portion of the second gas line and / or the second section of the foreline 130 can include a decomposition device configured to decompose the co-reactant. For example, the second section 145B of the second gas line can include a decomposition device 183 disposed along at least a portion of the second section 145B (e.g., between the second junction 165 and the foreline 130). The decomposition device can be configured to decompose the co-reactant before reaching the foreline 130. As another example, the foreline 130 can include a decomposition device 186 disposed along at least a portion of the foreline 130 (e.g., to decompose the co-reactant and / or any other gases therein, such as precursors). The decomposition device may also be disposed along at least a portion of the second section of the second gas line and the foreline 130. Thus, by decomposing the co-reactant in the decomposition device, reactions between the co-reactant and precursors are reduced or prevented, reducing or preventing film formation and / or buildup in the foreline 130.

[0052] In various embodiments, the decomposition device can be any suitable structure or device for decomposing the gases flowing through the respective gas lines (e.g., co-reactants and / or precursors). For example, the decomposition device can include a heater device (e.g., a heater coupled to and / or disposed around the second gas line and / or the second section of the foreline 130). The heater device can be configured to heat the gases (e.g., co-reactants) in the respective gas paths (e.g., the second gas line and / or the second section of the foreline 130) to decompose the gases flowing therethrough via pyrolysis. The heater device can be configured to heat the gases to a temperature that can at least partially, substantially, or completely decompose the gases (e.g., co-reactants). For example, to decompose the gases, a heating temperature can be selected such that the half-life of the respective gases is less than 10 seconds, less than 5 seconds, less than 2 seconds, less than 1 second, and / or less than 0.5 seconds. For gases containing ozone, for example, the temperature to which the gas is heated can be about or at least 200°C, greater than 200°C, 200-400°C, 200-300°C, etc. For gases containing silane and / or disilane, for example, the temperature to which the gas is heated can be about or at least 200°C or 300°C, 200-400°C, 200-300°C, 300-400°C, etc. For gases containing ammonia, for example, the temperature to which the gas is heated can be about or at least 400°C, 400-700°C, 400-600°C, 400-500°C, etc. (In this context, "about" means plus or minus 50°C.)

[0053] As another example, the decomposition device can include a catalytic device (e.g., a catalyst bed) configured to receive and decompose gases in the respective gas paths (e.g., the second gas line and / or the second section of the foreline 130) via catalytic decomposition. The catalytic device can include a body that houses a catalyst. The catalyst can be any suitable material or compound configured to at least partially decompose the gases and can be selected based on the co-reactants or other gases to be decomposed. For example, to decompose the gases, the catalyst can be selected such that the half-life of the respective gases is less than 10 seconds, less than 5 seconds, less than 2 seconds, less than 1 second, and / or less than 0.5 seconds.

[0054] For example, for co-reactants including ozone, the catalyst can include a metal and / or a metal oxide. The metal can be any suitable metal (e.g., a transition metal), such as platinum, palladium, ruthenium, copper, tungsten, copper, silver, tin, nickel, iron, gold, iridium, rhodium, cerium, manganese, cobalt, titanium, zinc, vanadium, chromium, molybdenum, and / or any combination thereof. The metal oxide can include any of the aforementioned oxides (e.g., manganese oxide). The catalyst can include other oxide materials (e.g., ceramic materials), such as silicon oxide, aluminum oxide, zirconium oxide, and / or the like. The catalyst can include a metal or metal oxide supported by another material (e.g., ceramic materials), such as manganese oxide supported by silicon oxide, aluminum oxide, zirconium oxide, and / or titanium oxide. The catalyst can include carbon or a carbon material (e.g., activated carbon, carbon black, graphite, carbon fiber, and / or the like). A co-reactant catalyst including ozone can decompose ozone (e.g., into oxygen (O2)), which may not react with the precursors in the foreline 130, thereby reducing or preventing buildup in the foreline 130.

[0055] In various embodiments, the cracker can include multiple components for cracking each gas (eg, a catalyst and a heater).

[0056] As another example, and referring to FIG. 2, the PFC 215 may be set to a desired pressure set point to achieve a desired flow rate of the co-reactant into the reaction chamber 105. In an exemplary embodiment, the third section 200 may be set to have a conductance that is 1%-10%, or about 5%, relative to the conductance through the first section 140 (e.g., the lower conductance of the third section 200 may be relative to an unrestricted flow rate through the flow path) (in this context, "about" means plus or minus 3%). The conductance through the third section 200 can be set (e.g., restricted) by the restrictor 210 and / or the fourth valve 205. Thus, the third section may have a conductance that is 95% less than the conductance of the first section and / or the second section of the second gas line. In this case, in response to the second valve 150 and / or the third valve 155 being closed and the fourth valve 205 being opened (e.g., during a time when co-reactant is not being provided to the reaction chamber 105), this relatively restricted and / or low co-reactant flow rate through the third section 200 reduces the amount of co-reactant to the foreline 130. Thus, reaction between the co-reactant and precursor is reduced or prevented, mitigating or preventing film formation and / or build-up in the foreline 130.

[0057] In various embodiments, the third section 200 can include a breaker (similar to the breaker described in connection with FIGS. 3 and 4) disposed along at least a portion of the third section 200.

[0058] In the preceding description, the technology has been described with reference to certain exemplary embodiments. The specific implementations shown and described are illustrative of the technology and its best modes, and are not intended to otherwise limit the scope of the technology in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the methods and systems may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and / or steps between the various elements. Many alternative or additional functional relationships or physical connections may exist in an actual system.

[0059] The present technology has been described with reference to certain exemplary embodiments. However, various modifications and changes may be made without departing from the scope of the present technology. The description and figures are to be regarded in an illustrative manner, not restrictive, and all such modifications are intended to be included within the scope of the present technology. Thus, the scope of the technology should be judged by the general embodiments described, and their legal equivalents, and not merely by the specific examples described above. For example, the steps recited in any method or process embodiment may be performed in any order, unless expressly specified otherwise, and are not limited to the explicit order presented in the specific examples. Furthermore, the components and / or elements recited in any apparatus embodiment may be assembled in various permutations or configured to operate in other ways to produce substantially the same results as the present technology, and therefore are not limited to the specific configurations recited in the specific examples.

[0060] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. Any benefit, advantage, solution to a problem, or any element that may cause or make more pronounced any particular benefit, advantage, or solution, is not, however, construed as a critical, required, or essential feature or component.

[0061] The terms "comprise", "comprising", or any variation thereof, are intended to refer to an open-ended inclusion such that a process, method, article, composition, or apparatus comprising a list of elements may include not only those elements listed, but also other elements not expressly listed or inherent to such process, method, article, composition, or apparatus. In addition to those not specifically listed, other combinations and / or modifications of the above-described structure, arrangement, application, proportions, elements, materials, or components used in the practice of the technology may be changed or otherwise specifically adapted to particular environments, manufacturing specifications, design parameters, or other operating requirements without departing from the general principles thereof.

[0062] The present technology has been described above with reference to exemplary embodiments. However, changes and modifications may be made to the exemplary embodiments without departing from the scope of the technology. These and other changes or modifications are intended to be included within the scope of the technology, as expressed in the following claims. [Explanation of symbols]

[0063] 100 Systems 105 Reaction Chamber 110 Second Container 115 First Container 120 Pump 125 Mass Flow Controller 130 Foreline 135 First Gas Line 140 First Section 145A, 145B Second Section 165 Second joint, section joint 183, 186 Decomposition equipment 200 Third Section 210 Limiter 215 Pressure Flow Controller

Claims

1. 1. A system comprising: A reaction chamber; a first vessel configured to contain a precursor, the first vessel being connected to the reaction chamber by a first gas line; a second vessel configured to contain a co-reactant, said second vessel being coupled to said reaction chamber; a foreline having a first end directly connected to the reaction chamber and an opposing second end; a pump coupled to the second end of the foreline at a first junction; a second gas line comprising a first section coupled to the inlet of the reaction chamber and a second section coupled to the foreline, the first section and the second section being connected to one another at a second junction; a mass flow controller coupled between the second vessel and the second junction.

2. The system of claim 1 , wherein the co-reactant is one of ozone, ammonia, silane, or disilane.

3. 2. The system of claim 1, wherein the first section of the second gas line has a first conductance and the second section has a second conductance, the first conductance being the same as the second conductance.

4. The system of claim 1 , further comprising: a first valve in the first section of the second gas line; and a second valve in the second section of the second gas line.

5. The system of claim 4 , further comprising a control unit configured to send control signals to the first and second valves.

6. 10. The system of claim 1, further comprising a destroyer coupled to the second section of the second gas line and configured to destroy the co-reactant.

7. The system of claim 6 , wherein the decomposition device comprises at least one of a catalyst or a heater.

8. 1. A system comprising: A reaction chamber; a foreline having a first end directly connected to the reaction chamber and an opposing second end; a pump coupled to the second end of the foreline; a first vessel configured to contain a precursor, the first vessel being connected to the reaction chamber by a first gas line; a second vessel configured to contain a co-reactant, said second vessel being coupled to said reaction chamber; a second gas line comprising a first section coupled to an inlet of the reaction chamber, a second section coupled to the foreline, and a third section coupled to the foreline, the first section and the second section being connected to each other at a junction, and the second and third sections being parallel to each other; a pressure flow controller coupled between the second vessel and the junction.

9. 9. The system of claim 8, further comprising: a first valve in the first section of the second gas line, a second valve in the second section of the second gas line, and a third valve in the third section of the second gas line.

10. The system of claim 9 , further comprising a flow restrictor coupled to the third section between the junction and the third valve.

11. 10. The system of claim 9, further comprising a control unit configured to send control signals to the first, second, and third valves.

12. The system of claim 8 , wherein the co-reactant is one of ozone, ammonia, silane, or disilane.

13. 9. The system of claim 8, wherein the first section has a first conductance, the second section has a second conductance, and the third section has a third conductance, the third conductance being 95% less than the first conductance.

14. The system of claim 8 , wherein the pump is a dry vacuum pump.

15. 1. A system comprising: A reaction chamber; a foreline having a first end directly connected to the reaction chamber and an opposing second end; a pump coupled to the second end of the foreline at a first junction; a first vessel configured to contain a precursor, the first vessel being connected to the reaction chamber by a first gas line; a second vessel configured to contain a co-reactant, said second vessel being coupled to said reaction chamber; a second gas line comprising a first section coupled to the inlet of the reaction chamber and a second section coupled to the first junction, the first section and the second section being connected to each other at a second junction.

16. a pressure flow controller coupled between the second vessel and the second junction; 16. The system of claim 15, wherein the second gas line further comprises a third section coupled between the second junction and the foreline, the second and third sections being parallel to one another.

17. The system of claim 15 , wherein the pump is a dry vacuum pump.

18. 17. The system of claim 16, wherein the first section has a first conductance, the second section has a second conductance, and the third section has a third conductance, the third conductance being 95% less than the first conductance.

19. 17. The system of claim 16, further comprising: a first valve in the first section of the second gas line, a second valve in the second section of the second gas line, and a third valve in the third section of the second gas line.

20. 20. The system of claim 19, further comprising a flow restrictor coupled to the third section between the second junction and the third valve.

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