Electricity: measuring and testing – Testing potential in specific environment – Voltage probe
Reexamination Certificate
2001-06-06
2003-06-10
Le, N. (Department: 2858)
Electricity: measuring and testing
Testing potential in specific environment
Voltage probe
Reexamination Certificate
active
06577113
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 determination of substrate RF bias parameters in 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 or discharge.
Gas plasmas are useful in a variety of different processes for forming integrated circuits. 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 positively 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 as 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 and the process. 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 of the material layer which is being deposited.
Generally, biasing of the substrate in plasma-enhanced etch and deposition processes is accomplished by capacitively coupling an RF field from RF biased electrodes in the processing chamber, through the substrate, and to the exposed substrate surface which is to be etched, or which is to receive a deposited material layer. Specifically, the electrodes, which are positioned within a susceptor or substrate support, are biased with an RF power supply to create an RF field. The RF field is then capacitively coupled through the susceptor and substrate to create a relatively uniform DC bias potential across the upper exposed substrate surface. The substrate surface DC bias, in turn, affects the plasma, as discussed above, 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, due to edge effects proximate the sides of the processing chamber. The non-uniformities in the plasma may translate to 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 edge of the substrate thus creating a non-uniform deposition layer and a non-uniform deposition rate radially across the substrate.
Attempts have been made in the art to address such plasma non-uniformities in a plasma processing system. For example, U.S. Patent Application entitled “Improved Apparatus and Method for Plasma Processing of a Substrate Utilizing an Electrostatic Chuck, ” U.S. Ser. No. 09/565,606, filed May 4, 2000, discloses a plasma processing system which selectively adjusts the bias on the substrate to offset plasma non-uniformities in the system; that application is incorporated herein by reference in its entirety. While that system improves the overall plasma process, it has been difficult to achieve precise selectivity in varying the substrate bias. Therefore, it is an objective of the present invention to provide more precise adjustments to the substrate bias in a plasma processing system for addressing non-uniformities and other vagaries in the plasma.
In accordance with another aspect of the invention, it is desirable to provide precise bias control even in a system utilizing an electrostatic chuck. Particularly during integrated circuit fabrication, the substrate being processed is supported within the processing chamber by a substrate support or 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 uses an applied DC bias to the substrate to electrostatically attract and secure the substrate to the susceptor. Electrostatic chucks are known in the art with suitable designs being shown in U.S. Patent Application entitled “Improved Apparatus and Method for Plasma Processing of a Substrate Utilizing an Electrostatic Chuck,” U.S. Ser. No. 09/565,606, filed May 4, 2000, noted above, and in U.S. Pat. No. 5,117,121, which patent is also incorporated herein by reference. Electrostatic chucks will usually use the same electrodes as are used to bias the substrate. This practice has made precise measurement of the substrate surface bias levels even more difficult due to the effect of the electrostatic clamping voltage on such measurement. Therefore, it is a further objective of the invention to provide more precise biasing of a substrate to address plasma non-uniformities within a processing system utilizing an electrostatic chuck.
Systems have been proposed for measuring substrate bias surface levels for an RF induced DC bias on a substrate. One such system is the subject of a U.S. Patent Application entitled, “Improved Apparatus and Method for Monitoring Substrate Biasing During Plasma Processing of a Substrate, U.S. Ser. No. 09/580,824 and filed on May 26, 2000, which application is incorporated herein by reference. While that application discloses an apparatus and methodology for measuring the substrate bias, it is affected by the level of DC current that is available to the measuring circuit. Particularly, suitable DC current levels may not be available for proper measurements.
The dielectric material utilized between the RF electrodes of a s
Baldwin Craig T.
Jones William D.
Sill Edward L.
Teresinski John
Tokyo Electron Limited
Wood Herron & Evans LLP
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