Etching a substrate: processes – Gas phase etching of substrate – Application of energy to the gaseous etchant or to the...
Reexamination Certificate
2000-10-11
2004-12-07
Goudreau, George A. (Department: 1763)
Etching a substrate: processes
Gas phase etching of substrate
Application of energy to the gaseous etchant or to the...
C156S345380, C156S345450, C118S7230MP, C118S7230ER
Reexamination Certificate
active
06827870
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to the fields of plasma processing and semiconductor manufacturing, and to plasma etching and deposition techniques.
BACKGROUND OF THE INVENTION
Plasmas are routinely used in the manufacturing of integrated circuits and inicroelectromechanical systems (MEMS). Such plasmas are used for etching of the semiconductor substrates and for the etching or depositing of thin films of materials on the substrates, e.g., films of polycrystalline silicon, silicon dioxide, silicon nitride and metals. The reactive plasmas may be excited in a gas in various ways, commonly by applying a voltage across two electrodes to establish an electric field between the electrodes in a gas at a low pressure. The spacing between the electrodes is typically a few centimeters. The gas is maintained at a pressure low enough such that a plasma is established at a voltage between the electrodes which is below that at which arcing between the electrodes will take place. One of the electrodes may comprise the workpiece on which etching or deposition will take place, while the other electrode may be the wall of the reactor. Typical operating pressures in the plasma chamber are in the range of 1-1000 millitorr, relatively low pressure levels that are necessary to avoid arcing during ignition of the plasma. The requirement for relatively low pressures necessitates the use of fairly expensive vacuum pumps, can require the use of load locks, and can limit the production speed because of the time required to pump down the plasma confinement chamber to the required pressure level.
Silicon etching in commercial plasma processing systems is commonly performed in parallel plate reactors by applying RF power (typically at 13.56 MHz) between two electrodes placed several centimeters apart. The silicon wafer is located on the powered electrode for reactive ion etching. The operating pressure and power are in the range of 10-500 mtorr and 10-500 mW/cm
2
, respectively. Since the plasma exists globally across the wafer, the etch is selectively masked by a thin film of, e.g., photoresist, SiO
2
or metal, which is patterned on the wafer surface. More recently, fast anisotropic etches have been demonstrated by alternative plasma etchers utilizing electron cyclotron resonance (ECR) and inductively coupled plasmas (ICP). All of these options, however, employ a single plasma that acts over the entire surface area of a wafer. Creating several different etch depths or profiles in a single die mandates the use of a like number of masking steps.
A particular challenge in the use of reactive plasmas in semiconductor processing is the need to maintain spatial uniformity in etching or deposition over the entire surface of the semiconductor wafer. Commercial semiconductor wafers have diameters presently as large as 12 inches, with a trend toward increasingly larger wafers. To process such wafers, progressively larger and more expensive reactive plasma systems will be required with the use of conventional plasma processing technology.
SUMMARY OF THE INVENTION
In accordance with the present invention, plasma treating to remove material from a surface (e.g., etching) or to add material (e.g., deposition or implantation) or both can be performed over large areas of substrates, such as semiconductor wafers, utilizing spatially localized micro-plasmas operating in parallel with one another. A plasma can be developed in each spatially localized region which is tailored to the plasma treatment requirements of that region, avoiding the non-uniformity of plasma treatment encountered with conventional large area plasma deposition and etching systems, while permitting specific regions of the substrate to receive selected levels of plasma treatment independently of other regions of the substrate. The invention may thus be utilized, for example, to plasma etch some regions of the substrate for longer times than other regions with resulting deeper etches in certain regions than in others, or to provide etches of particular dimensions or patterns. In plasma etching, the power density can be approximately 100 times higher than in conventional plasmas. In addition, DC power can be used to etch the substrates, eliminating the need for matching impedance networks associated with RF driven plasmas. Plasma confinement can be varied from a few tens of microns to more than a centimeter by changing operating conditions. The electrodes for the micro-plasmas may also serve to mask the etch in regions where the micro-plasma is ignited. The etch dimensions are consequently confined to the openings in the mask, allowing as precise masking of the etched areas as in conventional etching. For deposition processes, the invention may be utilized to allow plasma mediated deposit of different materials in various regions of the substrate in a pattern. For example, a plasma may be established at certain of the spatially separated regions of the substrate while a first precursor gas is supplied to the region, and then a plasma may be established in other regions of the substrate while a second precursor gas is supplied, allowing multiple plasma deposition processes to take place without requiring separate lithography masks or removal or replacement of masks.
In the present invention, a plasma generating electrode is positioned closely adjacent to an exposed surface of the substrate, such as above the surface or laterally spaced from the surface. A selected pressure of the gas in the region of the electrode and the substrate is established, and a voltage is applied between the electrode and the substrate to ignite a plasma in the region between the electrode and substrate for a selected period of time. The plasma is limited to the region of the electrode adjacent to the exposed surface so that the substrate is plasma treated in a pattern defined by the electrode. The electrode may be formed as separated electrode segments which are held over and spaced from the surface of the substrate so that a plasma may be established between the electrode and the substrate in the ambient gas surrounding the electrode and substrate. An electrode patterned in this manner may be selectively moved around the substrate, either continuously or stepwise, to provide patterned etching or deposition treatment of the substrate surface. A single electrode may also be used as a probe to plasma treat the substrate as the probe is moved over the surface of the substrate. The various segments of the electrode may be independently supplied with voltage so that different voltage levels may be applied between the electrodes for different lengths of time to tailor the amount of plasma etching or deposition at particular locations on the substrate. The electrode may also be formed by utilizing a dielectric layer in contact with the surface of the substrate with openings therein, with the electrode formed on the dielectric layer such that a plasma is established in the pattern of
1
openings in the dielectric layer as a voltage is applied between the electrode and the substrate. Separate electrodes which may be separately supplied with voltage may be formed at or adjacent to the various openings in the substrate to allow tailoring of the plasmas at specific regions of the substrate. The dielectric layer and electrode may be formed separately from the substrate and mounted onto the substrate at a particular position at which the plasma treatments are to be performed, removed from a position on that substrate, and then applied to a new substrate, or may be moved in a stepwise fashion from position to position about a single substrate to provide a repeated selected pattern of plasma treatment over the surface of the substrate. The dielectric layer may also be formed as a layer in situ on the substrate, with the electrode formed over it either permanently or subject to subsequent removal. The dielectric layer may be formed directly on the surface of the substrates, or a second base electrode may be formed on the substrate surface and the dielectric layer formed
Gianchandani Yogesh B.
Wilson Chester G.
Foley & Lardner
Wisconsin Alumni Research Foundation
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