Patent Application
20140360429
This application is related to a construction element enabling gas confinement and suppression of unwanted parasitic plasma behind a radio frequency (RF) electrode in a PECVD system working at pressures higher than 300 Pa.
Ceramic elements work for low pressure regimes (<300 Pa), but do not achieve sufficient leak tightness in the sub-chamber behind the electrode when processing at higher pressures. Using ceramic elements may cause ignition of parasitic plasma at the edges of the electrode that may not be avoided at pressures >300 Pa and at typical gap distances between 1-8 mm between electrode and grounded parts.
High process pressure (e.g., >300 Pa) for depositing silicon layers on large (e.g., >1 m2) substrates, may result in unwanted process conditions. Silicon layer deposition may be done using plasma-enhanced chemical vapor deposition (PECVD) by energizing gas (e.g., plasma) that is opposite the substrate. The gas may be energized by an electrode that may also be opposite the substrate and may distribute the gas into the plasma processing region. In one instance, the gas may be distributed from a gas distribution plenum through the electrode. However, when the gas is confined behind the electrode it may produce unwanted parasitic plasma gas distribution plenum and in some eases arcing may occur at the edges of the electrode.
This application relates to a wall element manufactured from Teflon or other non-conductive material to form a fluid seal between the hot electrodes and grounded surfaces to suppress plasma ignition at working pressure higher than 300 Pa and to provide a pressure step of at least 2 Pa between the gas distribution plenum and the plasma processing region. In one specific embodiment, the gap distances are less than or equal to 8 mm. The pressure step may be 1 to 10 times the lateral pressure drop in a 1100×1300 mm2 reactor, which can exceed 2 Pa at reactor pressures >300 Pa. Preferred values for the pressure step are 1-100 Pa, more preferred 5-50 Pa and even more preferred 25-35 Pa.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. Additionally, the left most digit(s) of a reference number identifies the drawing in which the reference number first appears.
Generally, the plasma processing region may include a substrate holder for a substrate (e.g., glass or silicon) that receives a chemical vapor deposition treatment. It is well known that solar cells may be generated by depositing successive silicon (e.g., microcrystalline or amorphous, doped or undoped) layers. The substrates (not shown) may have a surface area of greater than 1 m2. To achieve consistent silicon layer uniformity, gas and RF energy may be evenly distributed across the plasma processing region. In one embodiment, a gas distribution system may include a gas distribution plenum 106 disposed between the electrode 102 and a ground barrier 104 for the plasma chamber. The gas may be energized to generate plasma that may enable plasma-enhanced chemical vapor deposition on the substrate. However, in some instances, the gas may become energized in regions outside of the plasma processing regions (e.g., parasitic plasma), such as the gas distribution plenum 106, ground barrier 104, or other portions of the plasma chamber that are not desirable. At least two approaches may be used to prevent parasitic plasma, the first being to prevent gas distribution into small spaces where parasitic plasma is more likely to occur and the second being to prevent RF energy from being exposed to those small spaces and generating parasitic plasma.
In one embodiment, a gas barrier 108 comprising a flexible non-conductive material that can form a fluid seal between the electrode 102 and the ground barrier 104. The fluid seal may be formed between contacting surfaces of the gas barrier 108 and the electrode 102 and may prevent gas from being disposed in small areas between the electrode 102 and the ground barrier 104. The small areas may have gaps no more than 1 mm, The non-conductive material should be able to maintain the fluid seal under pressures of more than 300 Pa and temperatures of greater than 150 C. In one specific embodiment, the non-conductive material may include, but is not limited to, Polytetrafluoroethylene (e.g., Teflon®) or any other similarly situated plastic.
In another embodiment, the gas distribution plenum 106 may also include one or more isolation grids 110 that may prevent arcing between the electrode 102 and the ground barrier 104. The isolation grids may also prevent plasma generation within the gas distribution plenum 106. The isolation grids may be supported by the gas barrier 108 that may be arranged around the perimeter of the electrode 102. The isolation grid(s) 110 may form a mesh that may be permeable to the gas mixture within the gas distribution plenum 106. The gas distribution plenum 106 may also include two isolation grids 110 that are substantially parallel to each other and are coupled to the gas barrier 108. The isolation grids may be comprised of a conductive material that may include, but is not limited to, a metal that may be substantially unreactive to the gas at pressures greater than 300 Pa and temperatures greater than 150 C. In one specific embodiment, the gas distribution plenum 106 may be a gap of less than or equal to 16 mm between the electrode 102 and the ground barrier 104. The gap distance may be adjusted or controlled by mechanical means described in the description of
The gap of the gas distribution plenum 106 may be disposed between the ground barrier 104 and the electrode 102 and may be less than 16 mm, The gap may controlled by several indexing mechanisms that may be coupled to the ground barrier 104 and the electrode 102. One of the indexing mechanisms is illustrated in
In one embodiment, the gas barrier 108 may have a thickness that is optimized to fill the gap between the isolation grids 110 and the grounded surfaces and/or form the fluid seal under a certain range of process conditions. For example, the gas barrier 108 may expand to fill up the or close the gap to less than or equal to 0.5 mm under process conditions. The process conditions may include, but are not limited to, a temperature greater than 160 C and a pressure greater than 15 mbar, The gas barrier 108 may also be designed to minimize the horizontal level uniformity of the isolation grids 110 to be less than 0.5 mm across the chamber. Under these conditions, the horizontal and vertical movement of the isolation grids may be limited to less than 0.5 mm under the aforementioned processing conditions.
Pursuant to 37 C.F.R. §1.78(a)(4), this application claims the benefit of and priority to prior filed co-pending Provisional Application Ser. No. 61/831,661 filed Jun. 6, 2013, which is expressly incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61831661 | Jun 2013 | US |
