Patent Application
20120168662
1. Field of the Invention
Embodiments of the present disclosure relate to the field of valves used in vacuum environments. More particularly, the present invention relates to a valve assembly having sealing surfaces protected from deposits and contaminants which may compromise vacuum seals and lead to premature valve failure.
2. Discussion of Related Art
Vacuum environments are used in various types of processing systems especially in semiconductor fabrication where the vacuum prevents airborne contaminants from jeopardizing device manufacture. One type of process that is used to fabricate semiconductor devices is ion implantation. Ion implantation is used to dope impurity ions into a semiconductor substrate to obtain desired device characteristics. An ion implanter tool generally includes an ion source chamber which generates ions of a particular species, a series of beam line components to control the ion beam and a platen to secure a wafer or substrate that receives the ion beam.
These valves may be used to connect various vacuum chambers within the same processing tool. For example, in an ion implanter one or more valves may be disposed along the beam line component path and may be used to isolate chambers of the ion implanter. In an open state, the beam is free to propagate down the beam line path. In a closed state, sections of the beam line path may be isolated for maintenance procedures or for isolating particular regions or portions of the implanter to maintain pressures differentials.
When various dopant types are implanted into a substrate, different feed gases are supplied to the ion source chamber to obtain ion beams having particular dopant characteristics. For example, the introduction of phosphine (PH3) fed into the source chamber is used to obtain phosphorous ion species corresponding to N-type dopants. The introduction of BF3 into the ion source chamber is used to obtain Boron (B) ion species corresponding to P-type dopants. However, when an ion beam formed by these ion species is extracted from the ion source chamber, various surfaces of the beam line components are exposed to process contamination. In particular, particulates may deposit on the various components of valve assemblies disposed along the ion beam path. These particulates may contaminate the seals and seats of the valve assemblies causing premature valve failures which may compromise the vacuum processing environment. When valves used in vacuum environments fail, they require expensive replacement and more importantly, equipment downtime which negatively impacts device manufacturing through-put. Accordingly, there is a need for improved methods and apparatus for protecting the seals and seats of valve assemblies used in vacuum environments.
Exemplary embodiments of the present invention are directed to a valve assembly having sealing surfaces protected from deposits and contaminants which may compromise vacuum seals and lead to premature valve failure. In an exemplary embodiment, a valve assembly includes a piston housing, a sealing piston, a valve seal, a flange portion, a transverse gate chamber and a gate. The sealing piston has a coaxial through-passage capable of displacement within the piston housing. The valve seal is disposed around the coaxial through-passage of the sealing piston. The flange portion has a coaxial through passage aligned with the coaxial through passage of the sealing piston. The transverse gate chamber is formed between the sealing piston and the flange portion. The gate is capable of displacement within the transverse gate chamber to define a closed position. The sealing piston may be displaced away from the flange portion to allow the gate to be displaced within the transverse gate chamber. The gate is capable of removal from the transverse gate chamber to define an open position where the sealing piston is displaced toward the flange portion to engage the valve seal with a surface of the flange.
In another exemplary embodiment, a method for protecting sealing surfaces of a valve assembly in a vacuum environment includes mounting a valve assembly within a vacuum environment along a propagation path of a process media. The valve assembly includes a sealing piston and a flange portion that define a passage through the valve assembly for the process media. A valve seal is disposed around the passage of the sealing piston and configured to engage a surface of the flange portion when the valve assembly is in an open position. The sealing piston is displaced toward the flange portion to engage a surface of the valve seal with the surface of the flange portion to define an open position of the valve assembly such that the surface of the valve seal is not exposed to the process media. The sealing piston is displaced away from the surface of the flange portion to define a chamber therebetween when the valve assembly is to be closed. A gate is disposed within the chamber wherein a first surface of the gate provides a seat for the valve seal. A gate seal, attached to a second surface of the gate, engages the surface of the flange portion when the valve assembly is in the closed position. In this manner, the sealing surfaces of both the valve seal and the gate seal are protected from exposure to the process media which avoids deterioration of these surfaces and prolongs usable life of the valve assembly.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention, however, may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout.
Different feed gases are supplied to the source chamber to generate ions having particular dopant characteristics. The ions are extracted from source chamber 102 via a standard extraction electrode assembly 104 to form ion beam 95. Beam 95 passes through a mass analyzer chamber 106 having a magnet which functions to pass only ions having the desired charge-to-mass ratio to a resolving aperture. In particular, analyzer magnet includes a curved path where beam 95 is exposed to the applied magnetic field which causes ions having the undesired charge-to-mass ratio to be deflected away from the beam path. Deceleration stage 108 includes a plurality of electrodes which outputs a diverging ion beam. A corrector or collimator magnet chamber 110 is positioned downstream of deceleration stage 108 and is configured to deflect the ion beam 95 into a ribbon beam having parallel trajectories. The beam is targeted toward a work piece which is attached to a support or platen 114. An additional deceleration stage 112 may also be utilized which is disposed between collimator magnet chamber 110 and support 114. Typically, the ion source chamber 102 is at a relatively low vacuum and the remaining components of implant tool 100 are at a relatively higher vacuum level.
As noted above, ion source 102 is used to generate ions which are extracted therefrom and implanted into a substrate or workpiece. In this example, the extracted ions are the process media that form a beam 95 which travels through a pathway defined by gate valve assembly 200 along a “Z” axis. When the valve assembly is in an open position, beam 95 propagates toward mass analyzer chamber 106. Consequently, these components are exposed to byproducts of the various ions that form beam 95 such as, for example, Boron, As, P205, C, etc. Over time, these byproducts leave deposits or particulates along the interior surfaces of valve assembly 200 as well as the seals that provide a vacuum seal for the valve. In particular, this build up of particulates may deposit on the sealing surface of the valve causing premature valve failures either by compromising the seal of the valve seat or the gate seal. Moreover, this contamination on the sealing surfaces that prevents the ability to seal the valve may preclude the ability to isolate the respective chambers during maintenance procedures. By protecting the sealing surfaces of both the gate and valve seals of valve assembly 200 from the path of ion beam 95 (or plasma in a PLAD tool), this valve assembly of the present disclosure isolates components within the implanter 100, but avoids potential valve failures as well as downtime associated with valve or seal replacements which may negatively impact process throughput.
In addition, flange 201a and piston 201b define a transverse narrow chamber or space 210 of sufficient width to allow a movable gate 203 to pass therethrough. Gate 203 is disposed within gate housing 207 to maintain the vacuum environment. Gate 203 includes a gate seal 206 which extends around the circumference of a surface 203b (see
In order to close the valve 200, sealing piston 201b is displaced by depressurizing piston housing 202 which allows piston 201b to be displaced away from flange 201a in the negative Z direction or in a direction opposite the propagation direction of beam 95. This breaks the seat of seal 205 with flange portion 201a and allows sufficient clearance for gate 203 to be disposed within transverse gate chamber 210. This closed position causes surface 206a of gate seal 206 to engage a surface of flange 201a and surface 205a of seat 205 to engage a surface 203a of gate 203 to seat the gate within transverse gate chamber 210.
Piston rod 211 which is attached to gate 203 is used to displace the gate to an open position to allow beam 95 to pass there-through and to displace the gate into transverse gate chamber 210 when in a closed position to isolate various components upstream and downstream of valve assembly 200. Piston 211 may be activated pneumatically, mechanically or other known method in order to exert a sufficient force to displace gate 203 from housing 207 into transverse gate chamber 210 to close the valve assembly 200. In this manner, the vacuum environment is maintained during the displacement of gate 203 in and out of transverse gate chamber 210.
Although the exemplary embodiments included herein refer to gate valves in which the gates are opened and closed via linear motion, it should be understood that the scope of this disclosure also includes pendulum and/or rotary gate valve configurations as well as alternatives. In these alternative configurations, known forms of actuation may be used to open and close the respective gates of the valves.
Similarly, when the gate valve assembly 200 moves to an open position, sealing piston 201b is depressurized and the seal between seal 205 and surface 203a of gate 203 is broken. The gate 203 is displaced out of space 210 and piston housing 202 is pressurized forcing sealing piston 201b toward surface 204 of flange 201a. Consequently, this forces seal 205 against surface 204 of flange 201a. Since seal 206 is disposed on surface 203b of gate 203, it is not exposed or is downstream of ion beam 95 when it moves into transverse gate chamber 210. This allows the surface of seal 205 that engages surface 204 of flange 201a to be isolated from the particulate deposits that form as a consequence of ion beam 95 propagating through valve assembly 200.
Sealing flange 201a and sealing piston 201b define transverse gate chamber 210 therebetween. In addition, sealing flange 201a and sealing piston 201b form interior pathway 220 along the Z axis through which an extracted ion beam 95 propagates. Seal 205 is attached around the circumference of sealing piston 201b. Sealing piston 201b is disposed within piston housing 202 and is displaced in the directions illustrated by arrows 225 by pressure within piston housing 202. For example, when piston housing 202 is pressurized, sealing piston 201b is forced toward flange portion 201a forcing surface 205a of seal 205 to engage surface 204 of flange 201a. When piston housing 202 is depressurized, sealing piston 201b is forced away from flange portion 201a releasing the seat formed by seal 205 and surface 204. In this configuration, only surface 205b of seal 205 is exposed to ion beam 95 propagating through pathway 220 of assembly 200. However, surface 205b is not the sealing surface between seal 205 and flange 201a. Rather, seating surface 205a engages surface 204 of flange 201a when the valve assembly is in an open position and surface 205a is not exposed to the ion beam. Consequently, surface 205a will not be subject to particulate deposits thereby avoiding contamination of the seat during operation of the processing tool. Gate 203 includes gate seal 206 which is disposed within gate housing 207 when the valve assembly is in an open position.
Similarly, when the valve assembly moves to an open position, the process is reversed. In particular, piston housing 202 is depressurized which displaces sealing piston 201b in a direction opposite to arrow 225. This releases the seats formed between seal 205 and surface 203a of gate 203 as well as allowing the seat formed between gate seal 206 and surface 204 of flange 201a to disengage when gate 203 is moved out of transverse gate chamber 210. Gate 203 then recedes into gate housing 207. Piston housing 202 is re-pressurized and sealing piston 201a is displaced again in the direction indicated by arrow 225 toward flange 201a. This allows surface 205a of seal 205 to engage surface 204 of flange 201a. The valve assembly 200 is now in an open position similar to the position shown with reference to
In this manner, when the valve assembly 200 is in an open position, surface 205b of seal 205 is not exposed to ion beam 95 and associated process byproduct contamination. Similarly, when the valve assembly is in a closed position, gate seal 206 is downstream from 102 and is not susceptible to process byproduct contamination and surface 205a of seal 205 engages surface 203a of gate 203. In this manner, process byproducts that may deposit on surface of seal 205 (e.g. surface 205b) do not compromise the seal formed between flange 201a and sealing piston 201b. This allows seal 205 to be protected from process byproducts, thereby providing a more reliable vacuum seal which has a longer operational life.
While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.
