The present invention relates to plasma enhanced chemical vapor deposition (PECVD) apparatus and processes.
Plasma enhanced chemical vapor deposition (PECVD) is a process used to deposit thin films from a gas state (vapor) precursor to a solid state coating on a substrate. Chemical reactions are involved in the process of reacting the precursor in a deposition chamber with a plasma. In conventional CVD, heating is usually applied to promote precursor decomposition reactions. PECVD deposition on a substrate can be accomplished at ambient or relatively low temperatures compared with traditional thermal chemical vapor deposition (CVD). PECVD differs from sputtering in that the material forming the plasma electrode does not form a significant amount of the deposited film in a PECVD process.
PECVD has not been more widely used owing to the coating not just on the substrate where it is wanted, but also on other surfaces including critical electrode surfaces of the plasma source. If the coating is non-conducting, the operating characteristics of the plasma source become an operational dynamic that inhibits coating uniformity in commercial production. For instance, with an insulating film such as SiO2, electrode coating can cause arcing or the complete cessation of source operation after typically about 4 to 8 hours of continuous operation thereby requiring production to be interrupted for disassembly and cleaning.
In PECVD, the breakdown of precursor gases occurs in the presence of plasma. If the electrodes driving plasma generation are exposed to the precursor gas, a significant percentage of deposition occurs on the electrode. This is especially true when sputter magnetron type plasma sources are used and the precursor is exposed to the intense racetrack negative glow. Coating buildup on the magnetron electrode(s) causes severe process difficulties: The electrical circuit impedance varies with the buildup affecting process stability and the efficiency of the process, including the deposition rate and materials usage, is reduced to the degree of electrode coating.
In prior art PECVD apparatus, while useful coatings may be deposited on the substrate, the source is quickly coated causing process drift and arcing. In semiconductor batch applications, an etch process is run after set intervals to clean the exposed electrode(s). In continuous processes, such as roll-to-roll web or in-line coating systems, a PECVD process must run for many tens of hours without stopping. In these applications an etch cleaning cycle is not practical. There exists a need to maintain a continuous performance PECVD process over a timescale amenable to mass production.
There also exists a need for a plasma source capable of such operation and deposition onto a wide substrate of greater than 1 meter linear uniformity.
In the embodiments of the invention, coating buildup on the magnetron is minimized and long PECVD coating runs are made possible. The configurations of the embodiments of the invention PECVD deposition on large area substrates are particularly benefited and long, continuous PECVD processes are enabled.
In accordance with the principles of the invention, a plasma enhanced chemical vapor deposition apparatus for depositing material onto a substrate surface has a process chamber; and at least one plasma source disposed within the process chamber. The plasma source produces a negative glow region and a positive column. The at least one plasma source is disposed in proximity to the substrate surface such that the positive column is directed to the substrate surface. The PECVD apparatus further comprises at least one inlet to inject a precursor gas into the process chamber to interact with the positive column to deposit material onto the substrate; and at least one outlet for providing a pumped exit for gas in the chamber. The at least one inlet, at least one outlet, and the at least one plasma source are positioned in relationship to the substrate surface and to each other such that substantially all the precursor gas injected into the process chamber from the at least one inlet flows into the positive column adjacent the substrate surface.
In embodiments of the invention, apparatus is provided within the process chamber to channel or direct the precursor gas to flow into the positive column. In certain embodiments of the invention the apparatus has a shield to channel precursor gas into the positive column.
In some embodiments of the invention an inlet manifold provides the at least one or more inlets.
In some embodiments of the invention the apparatus is disposed adjacent to the inlet manifold to channel the precursor gas into the positive column adjacent the substrate surface.
In various embodiments of the invention, the substrate is a moving substrate. In certain embodiments, the substrate is a flexible substrate.
In specific embodiments the at least one plasma source includes a rotary plasma; at least one dual rotary magnetron plasma source; a planar magnetron; or at least one dual planar magnetron plasma source.
Embodiments include at least a second inlet to provide reactive gas to the at least one plasma source.
A process for plasma enhanced chemical vapor deposition coating of material onto a surface of a substrate is provided that includes provision of a process chamber in which at least one plasma is disposed. Each of said at least one plasma producing a negative glow region adjacent to a plasma and encompassed within a positive column projecting toward the substrate surface. A chemical vapor deposition precursor gas is injected into the process chamber to interact substantially only with said positive column and to deposit the material by plasma enhanced chemical vapor deposition coating onto the surface of the substrate. Interaction of the gas with said negative glow region is inhibited thereby keeping the plasma source free of fouling material deposits.
In accordance with embodiments, the method includes providing apparatus within the chamber to channel the precursor gas into the positive column. Certain embodiments include utilizing dual magnetron plasma sources. The process is applicable to flexible and self supporting substrates. Deposition can proceed in excess of 100 continuous hours owing the lack of magnetron fouling by the material, especially with the material is an electrically insulating material such as a metal oxide.
The invention will be better understood from a reading of the following detailed description of embodiments of the invention in which like reference designators are utilized to identify like elements, and in which the relative sizes and positions of various elements are exemplary only and are not intended to be limiting in any way, and in which:
The present invention has utility in the plasma enhanced chemical vapor deposition (PECVD) of volatile precursors onto a substrate. The present invention largely overcomes the prior art problem of electrically insulating coatings building up on deposition electrodes by preferentially injecting precursor gas into the positive column and adjacent to a deposition substrate, such that the negative glow region is exposed to a limited amount of precursor so as to limit coating growth onto the magnetron target proximal to the negative glow region.
In each of the embodiments shown and described hereinafter, the process chamber, magnetron plasma source, precursor gas inlet, and pump outlet are configured to provide a flow path or flow paths that preferentially channel injected CVD precursor gas into the plasma source positive column adjacent the substrate such that precursor gas interaction with the lobular areas defining the negative glow regions is disfavored and substantially eliminated. The various embodiments described herein are representative of configurations and it will be appreciated by those skilled in the art that the invention is not limited in scope to the particular configurations shown and described.
For purposes of clarity, various structural features of the process chambers, plasma sources and substrate transport apparatus are not shown. In addition, various shield and channel structural apparatus and configurations are not shown. The specific structures and configurations likewise are not to be considered as limiting the scope of the invention.
A magnetron plasma discharge may be described by three regions: a cathode dark space (CDS), a negative glow region (NG), and a positive column (PC). Planar magnetron 1 has an exposed electrode surface termed the target 2 and can be surrounded by a grounded shield 3. Between the high voltage magnetron 1 and shield 3 is dark space 4. Dark space 4 exists to prevent a plasma from lighting on the sides or back of magnetron 1 and also to prevent unwanted arcing. Magnetic field lines 50 contain negative glow NG adjacent to target 2. These designations are used throughout the following drawings. These regional designations are intended to have the common meaning and physical attributes, as understood by one of skill in the art to which the invention pertains.
In a conventional PECVD arrangement, CVD precursor gas introduced into a process chamber disperses at a high rate of speed, i.e., the speed of sound, throughout the chamber. The precursor gas interacts with the plasma to produce condensable constituents that deposit material onto nearby surfaces. In prior art PECVD systems and processes, the precursor gas was not directed into the positive column. Because the magnetron negative glow NG is the densest plasma, the precursor gas interacted strongly with the NG and material deposited onto the magnetron target.
Magnetrons 221, 223 are connected on opposite sides of AC power supply 319. Power supply 319 is an alternating current power supply with an exemplary frequency range of between 20 kHz and 6000 kHz. Power supplies with higher or lower frequencies can also be used.
PECVD apparatus 200 is configured with positive columns PC disposed proximate substrate surface 201 such that precursor gas flow paths 290 from the precursor inlets 249 and 249A pass preferentially into positive columns PC adjacent to the substrate surface 201 to deposit material onto substrate surface 201. Magnetrons 221, 223 and inlets 249 and 249A disposed relative to each other and to substrate surface 201 to ensure that precursor gas 251 is injected into positive columns PC adjacent to the substrate surface 201. Upon contact with the plasma positive columns PC, the precursor gas 251 is broken apart and condensing molecular components form. These components land on nearby surfaces and form the PECVD coating. By positioning the precursor inlet 19 to be proximal to substrate s and distant from rotary magnetrons 30,31 negative glows NG, the condensable molecules preferentially deposit onto the substrate rather than the rotary magnetron electrode surface. By providing apparatus or shields 245, 247 and selectively positioning precursor gas inlets 249 and 249A and pumped outlet 261 with respect to apparatus or shields 245, 247 and magnetrons 221, 223, precursor flow paths 290 are defined such that precursor gas interaction with negative glow regions NG is significantly reduced if not substantially eliminated, thereby allowing PECVD apparatus 200 to operate for long periods of continuous operation in excess of 100 hours for oxide deposition without significant degradation. It is appreciated that alternate positions are provided for inlets 249, 249A, 269, 269A and outlet 261 to avoid coating deposition onto magnetrons 221 and 223. Illustrative of these positions include slotted or periodically apertured manifolds within PC perpendicular to the plane of the page in
Dual rotary magnetrons 30, 31 are utilized in this embodiment as the plasma source. Each rotary magnetron 30, 31 extends perpendicular to the plane of the drawing sheet with a length and in a manner analogous to 221 and 223 per
Precursor gas distribution manifolds 11 are installed inside sheet metal conduits 34. The manifolds 10 and 11 each have a length that approximately corresponds to that of the magnetrons 30 and 31. Precursor gas 251, flowing from manifolds 11, is conducted into the PC adjacent to the substrate S by conduit 34 shield 13. Conduit shield 13 stops adjacent to the PC at opening 19. Shield 33 is close to substrate S and limits the flow of precursor gas 17 away from the PC. A reactive or inert gas manifold 10 is installed adjacent to rotary magnetrons 30 and 31. Reactive or inert gas flow 15 is directed to flow between the precursor gas and the magnetron 30, 31. Shield 13 helps to direct the flow of reactive or inert gas 15. Manifolds 11 and 10 are designed to provide theoretically uniform flow across the width of the manifold to promote uniform PECVD deposition on the substrate S.
The flow of precursor gas 251 and reactive or inert gas 15 flow into the PC is enhanced by the configuration of the vacuum pumping. By configuring the vacuum pumping opposite the gas manifolds as shown, the gases 15 and 251 are drawn into and through the PC before reaching the vacuum pumps. This increases the efficiency of precursor gas 251 and reactive or inert gas 15 utilization. The vacuum pumping 361 is configured to draw the gas out at a theoretically uniform rate over the entire length of the process area. It is appreciated that each of the rotary magnetrons 30 and 31 is independently replaced with a stationary planar magnetron 231 or 232 as detailed with respect to
PECVD apparatus 300 is configured such that precursor gas 251 is injected into positive columns PC adjacent substrate surface 301 to interact with positive columns PC to deposit material onto substrate surface 301. Flow paths 390 are selected such that any unreacted CVD precursor gas, after the initial contact with the positive columns PC, 251 is inhibited from reacting the lobular negative glow regions NG. By providing shield 13 and selectively positioning precursor gas inlets 19 and pumped outlet 361 with respect to rotary magnetrons 30, 31, precursor gas interaction with negative glow regions NG is substantially eliminated, thereby allowing PECVD apparatus 300 to operate for long periods of continuous operation of at least 24 hours and in excess of 40 hours, 60 hours, 80 hours, and even 200 hours without significant degradation associated with CVD electrically insulating deposition of magnetron targets.
A roll coater or web coater is a special batch-type system that allows coating of a flexible material sheet (“web”) in the form of a roll. This type of system is typically used to coat polymer, paper and steel sheet materials. In these types of systems the material to be coated is unrolled, passed through a deposition zone, and re-rolled. Due to the long lengths of sheet material efficiently contained in rolled form, a deposition process to coat the entire roll can require long periods of time.
In the “web coating” process, a flexible substrate sheet is supplied from one roll, taken up by a second roll. The rolls may be located either in the vacuum, or outside with the web being passed through multiple, differentially pumped seals.
Turning now to
In this embodiment, magnetrons 208 and 210 are positioned facing each other across substrate S. Magnetrons 208 and 210 are shown in a perspective view in
Magnetrons 208 and 210 are each independently planar magnetrons with an unbalanced magnetic field configuration with the larger magnet on the outside of the racetrack. This is classically termed a Type II unbalanced magnetron (Window and Saavides, J. Vac. Sci. Technol., A 4 (1986)). Magnetrons 208 and 210 are connected on opposite sides of AC power supply 319. Power supply 319 is an alternating current power supply with an exemplary frequency range of between 20 kHz and 6000 kHz. Power supplies with higher or lower frequencies can also be used. Each magnetron 208 and 210 produces negative glow regions NG and form a merged positive column PC.
To enhance the operating time of the process, shielding 213 is provided for PECVD apparatus 500 to direct the flow of precursor gas 251 and to thereby protect each magnetron 208 and 210 from unwanted deposition. The shielding arrangement preferably has a shield 213 that encloses or isolates magnetrons 208 and 210 such that precursor gas 251 preferentially does not interact with negative glow regions NG and deposit material onto magnetrons 208 and 210. Shield 213 includes elongate apertures 219 positioned such that the positive column PC emanating from magnetrons 208 and 210 passes through the elongate or slit-like apertures 219 toward substrate S. Shield 213 is disposed such that it is spaced apart from substrate S.
Distribution manifold 211 for precursor gas 251 is positioned such that the precursor gas 240 is injected into the PC along the length of the PC over substrate S. A vacuum pump (not shown) is provided to remove the PECVD process remnants from the deposition areas as shown at 961. The shield 213 and vacuum pump configuration are preferably designed to promote flow of the process gases through the PC before reaching the exhaust 961 so as to increase the usage efficiency of the PECVD process.
It will be apparent to those skilled in the art that different configurations of shield 213 may be provided. It will also be apparent to those skilled in the art that while a single shield box 213 is shown, each plasma source 208 and 210 are alternatively enclosed within a separate shield portion. In all of the embodiments shown and described, the various shields may comprise aluminum or similar plasma chamber construction materials.
The present invention is further detailed with respect to the following nonlimiting example. The example is only exemplary of the operation of the present invention and is not intended to limit the scope of the appended claims in any way.
Patent documents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These documents and publications are incorporated herein by reference to the same extent as if each individual document or publication was specifically and individually incorporated herein by reference.
The invention has been described in terms of several embodiments. It will be apparent to those skilled in the art that various changes and modifications can be made to the embodiments without departing from the spirit or scope of the invention. It is not intended that the invention be limited by the embodiments shown and described. It is intended that the scope of the invention be limited in scope only by the claims appended hereto.
This application claims priority of U.S. Provisional Patent Application Ser. No. 61/275,930, filed Sep. 5, 2009, which is incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2010/047994 | 9/7/2010 | WO | 00 | 3/5/2012 |
Number | Date | Country | |
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61275930 | Sep 2009 | US |