Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
1999-03-25
2001-03-27
Mills, Gregory (Department: 1765)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C324S076190
Reexamination Certificate
active
06207007
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing system using a plasma of a process gas for processing a substrate such as a semiconductor wafer or the like by a plasma process, such as plasma etching process.
Minimum device dimensions specified by pattern rules have progressively been decreased with the ongoing miniaturization of semiconductor devices and the growth of the number of components per IC chip. Accordingly, fine etching techniques have become particularly indispensable to the fabrication of semiconductor devices. Integrated circuit fabrication processes that use plasma etching processes are most prevalent at present.
Generally, a RF capacitive coupled reactor is used to carry out a plasma etching process. A reactive ion etching system (RIE system), which applies a RF voltage to an electrode supporting a wafer and uses the physical actions of radicals and ions, is capable of highly anisotropic etching and is suitable for fine processing.
Incidentally, the reaction vessel of the RIE system needs to be maintained at a relatively high pressure of several hundreds mTorrs in view of achieving highly reactive etching. In such a reaction vessel, a relatively large amount of dust of reaction byproducts is produced, which tends to reduce the yield rate of semiconductor devices requiring fine processing.
High-energy ions impinge on a semiconductor wafer during the operation of a RIE process and thereby charge-up damage, i.e., the destruction of devices by charge-up, is liable to be caused.
Efforts have been made to determine appropriate process conditions through the simulation using various parameters to simulate the condition of a plasma. However, any plasma etching process using properly controlled plasma has not successfully been developed so far through the adjustment of the generally known parameters.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide a plasma processing system capable of properly controlling the condition of a plasma for a plasma process.
The inventors of the present invention have found through the examination of the foregoing problems that it is effective in more properly controlling the condition of a plasma for carrying out a plasma process to use the electronegativity of the plasma as a parameter.
Generally, when a process gas is ionized to produce a plasma, the plasma contains ions, electrons and radicals. It has been usual to simulate the condition of a plasma on an assumption that ions contained in the plasma are positive ions. Most plasma etching processes use an electronegative CF gas, such as CF
4
. When such an electronegative CF gas is used, the plasma will contain negative ions in a considerably large number density. Therefore, it is impossible to know the condition of the plasma accurately on an assumption that all the ions are positive.
The present invention uses electronegativity indicating the rate of the number density of negative ions contained in a plasma as a new parameter to take into consideration the existence of negative ions in carrying out a plasma process, and a plasma processing system in accordance with the present invention controls the electronegativity of a plasma.
The ratio between the positive ion number density and the negative ion number density can properly be adjusted by controlling the electronegativity of a plasma, which may possibly eliminate charge-up damage to the wafer. There is some possibility that the pressure for a plasma process can be reduced by enhancing reactivity by controlling electronegativity so as to adjust the negative ion rate of the plasma to a predetermined value. If this technique is applied to a plasma etching process, finer processing can be expected.
Basically, a plasma process in accordance with the present invention can be carried out by a general RF capacitive coupled processing system provided with a RF power generator for generating RF power necessary for ionizing a process gas to produce a plasma, and a vessel in which a plasma process using the plasma of the process gas is carried out. The frequency of the RF power generator and the pressure in the vessel are adjusted to control the electronegativity of the plasma.
According to one aspect of the present invention, a plasma processing system for carrying out a plasma process for processing a wafer by using a plasma produced by ionizing a process gas comprises a processing vessel in which the plasma process is carried out; a process gas supply system for supplying a process gas into the processing vessel; an evacuating system for evacuating the processing vessel, an electrode disposed in the processing vessel; a RF power generating means for supplying RF power to the electrode to produce a plasma by ionizing the process gas in the vessel; and a control means previously storing data on the relation of the pressure in the processing vessel and the frequency of the RF power generating means with the electronegativity of a plasma produced by the agency of the RF power, and capable of controlling the pressure in the processing vessel and/or the frequency of the RF power generating means in a feedback control mode so that the electronegativity of the plasma may be adjusted to a predetermined proper value previously determined in accordance with conditions for the plasma process.
Any means for measuring the electronegativity of a plasma is not available at present, the electronegativity of a plasma has never been determined by simulation. The present invention achieves the determination of the electronegativity of a plasma by simulating the state of a plasma by a one-dimensional RCT model.
According to another aspect of the present invention, a plasma processing method of processing a substrate by using a plasma produced by ionizing a process gas comprises the steps of determining a predetermined, appropriate electronegativity of a plasma according to conditions for a plasma process; and regulating the electronegativity of the plasma so as to coincide with the predetermined, appropriate electronegativity during the plasma process.
According to the present invention, the electronegativity of the plasma is regulated while a wafer is being processed by the plasma process to maintain the plasma in an optimum state throughout the plasma process.
The plasma processing method of the present invention which regulates the electronegativity of a plasma is particularly effective in application to a general etching process using an electronegative CF gas.
REFERENCES:
patent: 4172020 (1979-10-01), Tisone et al.
patent: 5467013 (1995-11-01), Williams et al.
Stevenson, et al, “A Plasma Process Monitor/Control System”, Surface and Interface Analysis, vol. 26, 124-133, Jan. 1998.*
Wolf, et al, “Silicon Processing for the VLSI Era, vol. 1: Process Technology”, Lattice Press,Sunset Beach, California, Jan. 1998.
Makabe Toshiaki
Segawa Sumie
Mills Gregory
Powell Alva C
Smith , Gambrell & Russell, LLP
Tokyo Electron Limited
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