Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-05-04
2002-08-13
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230AN, C361S234000
Reexamination Certificate
active
06431112
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the processing of a substrate utilizing a plasma in the production of integrated circuits, and specifically relates to the improvement of a plasma processing system such as one utilizing an electrostatic chuck to secure a substrate to a susceptor during processing.
BACKGROUND OF THE INVENTION
Gas plasmas are widely used in a variety of integrated circuit fabrication processes, including plasma etching and plasma deposition applications, such as PECVD. Generally, plasmas are produced within a processing chamber by introducing a low-pressure process gas into the chamber and then directing electrical energy into the chamber for creating an electric field therein. The electric field creates an electron flow within the chamber which ionizes individual gas molecules by transferring kinetic energy to the molecules through individual electron-gas molecule collisions. The electrons are accelerated within the electric field, producing efficient ionization of the gas molecules. The ionized particles of the gas and the free electrons collectively form what is referred to as a gas plasma.
Gas plasmas are useful in a variety of different processes. One commonly used plasma process is a plasma etch process wherein a layer of material is removed or “etched” from a surface of a substrate. In an etch process, the ionized gas particles of the plasma are generally positively charged, and the substrate is negatively biased such that the positive ionized plasma particles are attracted to the substrate surface to bombard the surface and thereby etch the substrate surface. For example, a substrate might be etched to remove an undesirable material layer or coating on the substrate before another layer is deposited. Such a pre-deposition etch process is often referred to a s etch cleaning of the substrate.
Other common plasma processes involve deposition, wherein a material layer is deposited upon the substrate. Chemical vapor deposition, or CVD, for example, generally involves the introduction of material gases into a processing chamber wherein the gases chemically interact and form a material layer or coating on the exposed substrate surface. A gas plasma can be utilized to enhance the chemical interaction. Consequently, such a CVD deposition process utilizing a plasma is referred to as plasma-enhanced CVD or PECVD. The plasma is utilized to provide energy to the process and enhance the deposition quality and/or deposition rate. Other plasma deposition processes also exist as are commonly understood by a person of ordinary skill in the art.
During plasma processing of a semiconductor substrate, it is often useful to apply an accelerating voltage to the surface of the substrate. The accelerating voltage or substrate bias is utilized to accelerate ions or other charged particles within the plasma to the substrate surface. In an etch process, the charged plasma particles are attracted to the substrate surface to actually bombard the surface and provide the etch as discussed above. In a deposition process, such as PECVD, the energy provided by such charged particle bombardment may be utilized to further enhance the deposition rate or to enhance the deposition quality, as mentioned above. Generally, biasing of the substrate in plasma enhanced etch and deposition processes is accomplished by capacitatively coupling an RF field from a susceptor or other substrate support, through the substrate, and to the exposed substrate surface which is to be etched, or which is to receive a deposited material layer. The susceptor is biased with an RF power supply and the capacitatively coupled RF field from the susceptor creates a relatively uniform DC bias potential across the substrate surface. The DC bias, in turn, affects the plasma to enhance the etch or deposition process.
Within a plasma processing system, the plasma will usually have particular non-uniformities associated therewith. For example, the plasma density is often greatest in the center of the plasma and the center of the processing chamber due to edge effects proximate the sides of the processing chamber. The non-uniformities in the plasma translate to non-uniformities and discrepancies within the etch and deposition processes in which the plasma is utilized. For example, an undesirable variation in etch rate may occur wherein the etch rate proximate the center of the substrate is greater than the etch rate proximate the outer edges of the substrate. Furthermore, within a plasma-enhanced deposition process, the deposition may be affected proximate the center of the substrate differently than at the edges of the substrate thus creating a non-uniform deposition layer and a non-uniform deposition rate radially across the wafer. It is thus an objective of the present invention to address plasma non-uniformities within plasma processing systems. It is further an objective to do so with a biased substrate.
During integrated circuit fabrication, the substrate being processed is supported within the processing chamber by a substrate support, commonly referred to as a susceptor. Oftentimes, the substrate is physically secured on the susceptor during processing, such as to improve heat transfer between the substrate and susceptor. One way of securing a substrate involves the use of an electrostatic chuck (ESC), which electrostatically attracts and secures the substrate to the susceptor. Electrostatic chucks are known in the art with one suitable design being shown in U.S. Pat. No. 5,117,121, which is incorporated herein by reference.
Generally, electrostatic chucks utilize one or more electrodes which are embedded in the susceptor. Also, the substrate might be used as an electrode. The susceptor is usually formed of a dielectric material, and an applied voltage on the electrodes causes a voltage gradient to develop within the dielectric material. The voltage gradient, in turn, affects the electrical charges on the surface of the substrate abutting the dielectric material of the susceptor such that charge differences are created between the substrate and susceptor electrodes. Thereby, the substrate is clamped to the electrostatic chuck due to attractive electrical forces between the differently charged surfaces of the susceptor electrodes and the substrate.
More specifically, with a unipolar electrostatic chuck, the voltage bias is applied to a single electrode in the susceptor and the substrate itself acts as a second electrode. In that way, the combination of the dielectric susceptor materials separating the electrode and substrate forms a parallel plate capacitor, and the attractive electrical force between the two electrodes effectively clamps the substrate to the susceptor.
Alternatively, in a bipolar electrostatic chuck, which is commonly utilized in existing processing systems, a voltage difference is applied across two or more electrodes embedded within the susceptor and spaced apart from each other. The multiple electrodes are separated by the dielectric material of the susceptor and therefore an electric field develops across the susceptor between the electrodes. When a substrate is placed on the susceptor, the electric field causes charges to accumulate on the back side of the substrate. The charges on the back side of the substrate and those on the electrodes attract one another to clamp the substrate to the susceptor. Electrostatic chucks are often utilized within plasma processing systems. Therefore, it is a further objective to address plasma non-uniformities within a processing system utilizing an electrostatic chuck.
Still further, as noted above, a substrate may be electrically biased in addition to being electrostatically clamped to a susceptor. It is therefore another objective of this invention to address the above-discussed objectives without adversely affecting the biasing of the substrate which is desirable for plasma processing.
SUMMARY OF THE INVENTION
The processing system, in accordance with the principles of the present invention, comprises a processing chamber for containing
Baldwin Craig T.
Jones William D.
Sill Edward L.
Mills Gregory
Tokyo Electron Limited
Wood Herron & Evans L.L.P.
Zervigon Rudy
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