Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With radio frequency antenna or inductive coil gas...
Reexamination Certificate
2001-06-06
2003-11-25
Alejandro-Mulero, Luz (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With radio frequency antenna or inductive coil gas...
C118S7230AN
Reexamination Certificate
active
06652711
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to plasma processing systems and, more particularly, relates to inductively-coupled plasma processing systems for cleaning a substrate surface before depositing a coating material.
BACKGROUND OF THE INVENTION
Plasmas are widely used in materials processing for treating the surfaces of substrates, such as semiconductor wafers and flat panel displays, prior to a processing step. In particular, plasmas are used to remove native oxide layers and other contaminants from the substrate surface in preparation for a subsequent deposition of a film of coating material, such as a metallization layer, onto the surface. If the contaminants were not removed by a pre-deposition cleaning process, the physical characteristics, such as the electrical and mechanical properties, of the interface between the layer of coating material and the substrate would be adversely affected.
A conventional approach for removing contaminants is to expose the substrate surface to a plasma in a plasma cleaning step before depositing the film of coating material. The plasma cleaning step may rely on a plasma as a source of reactive species that chemically react with the contamination to form volatile or quasi-volatile products. For example, oxidation can be cleaned from copper metallization on a substrate surface using a hydrogen-containing plasma that chemically reduces the oxide to form volatile etch products. Alternatively, the plasma cleaning step may rely on sputtering due to ion bombardment for cleaning contamination from the substrate surface. For example, oxidation can be removed from aluminum metallization by bombarding the substrate surface with energetic ions from a plasma generated from a noble process gas. Other plasma cleaning steps combine chemical and physical mechanisms for removing contamination from the substrate surface by bombarding the substrate surface with energetic chemically-active plasma species. Preferably, the plasma cleaning removes contaminants from the surface without causing damage or altering the properties of any existing film residing on the surface.
Conventional plasma processing systems designed for plasma cleaning or plasma etching have a vacuum chamber that incorporates a window formed of a dielectric material, such as quartz, and an antenna adjacent the non-vacuum side of the window. Radiofrequency (RF) energy is coupled from the antenna through the dielectric material of the window to the plasma. In certain conventional plasma processing systems, the dielectric window is a bell jar of dielectric material which is sealed to a metal chamber base to define a vacuum chamber. In other conventional plasma processing systems, the dielectric window is a cylindrical or planar structural wall section of dielectric material incorporated into the chamber wall of the vacuum chamber.
Conventional plasma processing systems that utilize a plasma for cleaning substrate surfaces have certain significant disadvantages. In particular, contaminant material sputtered from the substrate surface tends to travel in line-of-sight paths from the substrate toward the interior surfaces of the vacuum chamber. The sputtered contaminant material accumulates, possibly along with chemically-active species originating from the plasma and volatile or quasi-volatile species removed from the substrate surface, as a residue or buildup on interior surfaces, such as the vacuum-side surface of the dielectric window. The residues generated by processing can flake and break off as small particles that are a source of particulate matter detrimental to the fabrication of semiconductor devices. In particular, the residue has a particularly poor adhesion to the surface of the dielectric window. When the plasma is extinguished, the particulate matter can be electrostatically attracted to the substrate. Alternatively, small particles of particulate matter can grow in size while suspended within the plasma and, when the plasma is extinguished, fall under the influence of gravity to the substrate. Such particulate matter may locally compromise the quality of the coating material subsequently deposited on the substrate surface and, thereby, act as defects that reduce device yield.
The accumulation of metal on the dielectric window is a particularly acute problem if the substrates to be sputter cleaned have a significant surface coverage of metal. In particular, the sputter cleaning of metal-covered surfaces produces relatively large accumulations of contaminant residue which serves as a potential source of particulate matter. Moreover, sputtered metal that accumulates on the vacuum-side surface of the dielectric window can affect the operation of the plasma processing system. If the residue is conductive, currents circulating in the buildup tend to reduce the effectiveness of the coupling of RF energy from the antenna to the plasma. Even if the accumulated metal is highly resistive and not limiting of the coupling of the RF energy, the metal residue on the dielectric window can still inhibit plasma ignition and decrease the efficiency of radiofrequency power transmission through the window.
To reduce the occurrence of particulate matter and to maintain efficient coupling of RF energy, the vacuum-side of the dielectric window must be periodically cleaned by chemical and/or abrasive techniques to remove the accumulated residue. Cumulative damage from successive cleanings gradually degrades the mechanical properties of the dielectric material forming the window. As a result, the service life of the dielectric window is reduced and the likelihood of a premature catastrophic failure is enhanced. Typically, the dielectric window is removed from service when the mechanical properties are degraded such that the window can no longer safely support the load applied by atmospheric pressure to the non-vacuum side of the window.
Electron temperature and plasma uniformity are important factors that are balanced such that the plasma distribution is relatively uniform at an operating pressure where the electron temperature is not excessive. Non-uniform plasma densities and excessive electron temperatures can damage the substrates. Asymmetries in the plasma density distribution can result in non-uniform etching or cleaning of the substrates. Although the electron temperature can be reduced by raising the operating pressure of the process gas in the vacuum chamber, the increased operating pressure frequently reduces the uniformity of the plasma density distribution.
The geometry of the vacuum chamber system is another important factor in determining plasma density and plasma uniformity. Ultimately, the processing uniformity over the surface area of the substrate is directly related to the uniformity of the plasma adjacent to the exposed surface of the substrate. Furthermore, in conventional plasma processing systems that utilize chemical activity during treatment, the concentration of chemically-active species from the plasma is depleted near the substrate center and increased near the substrate's peripheral edge due to gas flow inhomogeneities. This nonuniformity enhances treatment rates at the substrate periphery than at the substrate center, resulting in high center-to-edge nonuniformity. The asymmetrical treatment due to non-uniform plasmas and inhomogeneous concentrations of chemically-active species from the plasma is compounded for large-diameter substrates, such as 300 mm silicon wafers.
Conventional plasma processing systems must be optimized to accommodate large-diameter wafers. For example, to provide a uniformly-distributed plasma near the substrate, the footprint of the antenna and the associated dielectric window must be increased and the plasma source-to-substrate separation distance must be increased. To achieve an acceptable plasma uniformity with a reasonable electron temperature in a large-diameter substrate plasma processing system, the cost of manufacturing the dielectric window increases significantly.
Dielectric windows for large-diameter substrate plasma pr
Brcka Jozef
Drewery John
Grapperhaus Michael
Leusink Gerrit
Reynolds Glyn
Alejandro-Mulero Luz
Tokyo Electron Limited
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