Patent Application
20250212311
The present invention relates to a design for a plasma or glow discharge generation chamber (“plasma generation chamber”), in which reactive gases are ionized into reactive species in a plasma state and supplied to a downstream reaction chamber where the reactive species participate in a chemical reaction, such as a cleaning application.
To facilitate the following description of system operations,
As known to those of ordinary skill in the art, the electrical current in solenoid 101 is typically driven from matching network 104, which matches the impedances of plasma system 100 to RF power source 107, thereby ensuring that energy received from RF power source 107 is inductively coupled into an axial magnetic field (“RF field”) in plasma generation chamber 105 in an efficient manner. This RF field—which determines the plasma density in plasma generation chamber 105—is roughly uniform along the length of plasma chamber 105 because of the substantially uniform turns ratio in solenoid 101.
U.S. Pat. No. 7,015,415 to G. Gorin (the “'415 patent”), entitled “Higher Power Density Downstream Plasma,” issued Mar. 21, 2006, discloses constricting conduit 106 to increase power density in the vicinity of conduit 106. To that extent, the '415 patent discloses an “inside diameter [for conduit 106] ranging from one millimeter (mm) to less than 19 millimeters, and a [longitudinal length of conduit 106 to be] substantially equal to or greater than one millimeter” (the '415 patent, at col. 5, lines 5-9). The '415 patent, however, provides not teaching as how the configuration of plasma generation chamber 105 may help to optimize its power density and, hence, affect the reaction rates in the reaction chamber 103.
According to one embodiment of the present invention, a plasma generation assembly in a plasma source powered by an external radio-frequency (RF) power source includes: (a) a plasma generation chamber having an inlet end and an outlet end, the inlet end being configured to receive a reactive gas and an outlet end being configured to provide one or more plasma-state reactive species through a conduit to an external reaction chamber; and (b) a coil or solenoid provided coaxially enclosing the plasma generation chamber, wherein the coil or solenoid is configured to receive an electric current from the RF power source, wherein the coil or solenoid has a turns ratio that varies along the axial length of the coil or solenoid. The electric current generates a magnetic field in the plasma generation chamber to ionize the reactive gas, thereby creating the plasma-state reactive species at the outlet end. The plasma generation chamber may be formed in a quartz tube or a ceramic tube.
The plasma generation assembly may include an aperture disc at the outlet end of the plasma generation chamber, wherein the conduit is provided as an aperture in the aperture disc. According to one embodiment of the present invention, the aperture of the aperture disc may be a selected one of a plurality of desirable diameters.
According to one embodiment of the present invention, the turns ratio of the coil or solenoid is greater at the outlet end of the plasma generation chamber than at the inlet end of the plasma generation chamber.
According to one embodiment of the present invention the plasma generation chamber may include various metalized parts that are attached and sealed using a brazing technique, so as to ensure vacuum-sealing of the plasma generation chamber during operation. The plasma generation assembly may include a mounting flange that connects the external reaction chamber to the plasma generation chamber. The mounting flange may be formed out of stainless steel. Metalized bellows may be provided to attach the mounting flange to the plasma generation chamber.
These and other advantages, aspects, and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood upon consideration of the following description and drawings.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings. Although the drawings depict various examples of the invention, the invention is not limited by the depicted examples. It is to be understood that, in the drawings, like reference numerals designate like structural elements. Also, it is understood that the depictions in the FIGS. are not necessarily to scale.
In one embodiment, plasma system 200 may operate with a power input rated at up to 300 W. A desirable operating pressure in the inductively coupled tube of plasma generation chamber 205 for a cleaning application may be, for example, 7.0 mTorr. In one cleaning application, an oxygen-containing gas may be used to generate reactive species in the plasma state to remove carbonaceous contamination. For example, in some instances, atmospheric air is used as a “plasma driving gas.” Some components of the plasma driving gas (e.g., oxygen and nitrogen in air) may be ionized in plasma generation chamber 205 to become reactive species. Alternatively, pure molecular oxygen (O2) gas may be used. The reactive species in the plasma state include, for example, atomic oxygen (O), O2+, O+ and O−. Each of these reactive species is more reactive than the molecular oxygen gas from which it is formed. In another cleaning application, molecular hydrogen (H2) may be used. The reactive gas may be provided in a mixture that includes non-reactive gas or gases, such as argon (Ar).
The inventor expects that the different aperture discs would provide different gas volumes that accumulate upstream of conduit 206. It is believed that the accumulated gas volume upstream of conduit 206 is inversely proportional to the ratio of the radius of conduit 206 to the radius of the inductively coupled tube. A greater gas volume accumulated upstream of conduit 206 would result in a greater pressure differential across conduit 206 (i.e., the greater pressure difference between plasma generation chamber 205 and reaction chamber 203) and a longer resident time of the reactive gases upstream of conduit 206, depending on the diameter of conduit 206 and the gas flow rates. An increased resident time of the reactive gases increases their exposure to the RF energy delivered by coil or solenoid 201, thereby increasing the density of resulting reactive species in the plasma state.
In addition, unlike conventional plasma systems, the turns-per-unit length (“turns ratio” or N/L) of solenoid 201 need not be uniform along its length. Specifically, the turns ratio may be made significantly higher in the vicinity of aperture disc 202, relative to further upstream in the inductively coupled tube. This configuration increases the intensity of the RF field around the volume of gas accumulated upstream of conduit 206, thereby increases the RF field's interaction with the gas volume, thus providing a greater density of plasma-state reactive species that may be introduced into reaction chamber 203. To summarize, the higher turns ratio increases the probability of ionization in the vicinity of aperture disc 202, relative to the probability of ionization further upstream in the inductively coupled tube. Consequently, the density of reactive species in the plasma state immediately upstream from aperture 206 is significantly higher than that of the prior art, for the same total gas volumes in the inductively coupled tube.
The brazing technique ensures that inductively coupled tube 511 to be considerably more robust by eliminating the polymer seals (e.g., o-rings) that are customarily used in the prior art to provide air-tight seals. The robustness reduces the risk of vacuum leakage during high-power or prolonged operations. Moreover, the metalized sealing points characteristic of the brazing technique allows plasma generation assembly 500 to be attached onto ultra-high vacuum reaction chambers without using isolation valves and pre-pumps.
In this detailed description, various embodiments or examples of the present invention may be implemented in numerous ways. A detailed description of one or more embodiments of the invention is provided above along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. Numerous modifications and variations within the scope of the present invention are possible. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications, and equivalents. Numerous specific details are set forth in the description to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured. The present invention is defined by the appended claims.
