Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-12-17
2002-07-02
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S230100, C204S230700, C204S272000
Reexamination Certificate
active
06413389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for recovering metal from by-products deposited on the inside of a reactor chamber during processing (e.g., etching, chemical or physical vapor deposition, etc.) of a substrate in the reactor chamber containing a plasma. More specifically, this invention provides an electrochemical method for recovering metal (e.g., platinum, iridium, etc.) from deposits and/or byproducts formed and collected on an internal structure of a reactor chamber wherein substrates are being etched in a plasma of a processing gas.
2. Description of the Prior Art
It is well known that various magnetically enhanced radio frequency (RF) diodes and triodes have been developed to improve performance of plasma reactors. As mentioned in an article entitled “Design of High-Density Plasma Sources” by Lieberman et al from Volume 18 of “Physics of Thin Films”, copyright 1994 by Academic Press Inc. of San Diego, Calif., these include by way of example only, the Applied Materials AMT-5000 magnetically enhanced reactive ion etcher and the Microelectronics Center of North Carolina's split cathode RF magnetron. Magnetically enhanced reaction ion etchers (MERIE) apply a dc magnetic field of 50-100 Gauss (G) parallel to the powered electrode which supports a semiconductor wafer. The dc magnetic field enhances plasma confinement, resulting in a reduced sheath voltage and an increased plasma density when the magnetic field is applied. However, the plasma generated in MERIE systems is strongly nonuniform both radially and azimuthally. It is well known that in order to increase process uniformity, at least azimuthally, the magnetic field is rotated in the plane of the semiconductor wafer at a certain frequency, e.g. 0.5 Hz. While this is an improvement, MERIE systems still do not have the desired uniformity and high density in the generated plasma, which may limit the applicability of MERIE systems to next-generation, sub-micron device fabrication.
The limitations of RF diodes and triodes and their magnetically enhanced variants have led to the development of reactors operating at low pressures with high-efficiency plasma sources. These reactors can generate a higher density plasma and have a common feature in that processing power (e.g. RF power and/or microwave power) is coupled to the plasma across a dielectric window, rather than by direct connection to an electrode in the plasma, such as for an RF diode. Another common feature of these reactors is that the electrode upon which the wafer is placed can be independently driven by a capacitively coupled RF source. Therefore, independent control of the ion/radical fluxes through the source power and the ion bombarding energy through the wafer electrode power is possible.
While the limitations of RF diodes and triodes and their magnetically enhanced variants have motivated the development of high-density plasma reactors with low pressures, high fluxes, and controllable ion energies, these developed high-density plasma reactors have a number of challenges. One challenge is the inability of high-density plasma reactors to achieve the required process uniformity over 200-300 mm wafer diameters. High density sources are typically cylindrical systems with length-to-diameter usually exceeding unity. In such cylindrical systems plasma formation and transport is inherently radially nonuniform.
Another challenge is that the deposition of materials on the dielectric window during etching of semiconductor wafers in a process chamber has necessitated frequent and costly reactor cleaning cycles. This is especially true when metals, such as platinum, copper, aluminum, titanium etc., are etched or deposited in the production of integrated circuit (IC) devices. After a metal layer on a substrate has been etched or deposited for a period of time, the etch or deposit rate on the metal may decrease. The dropping in metal etch or deposit rate is due to the build up of conductive by-products deposited on the dielectric window. Such deposited conductive by-products behave as a Faraday shield to reduce the efficiency of rf energy transmission into the plasma by blocking the rf energy transmission through the dielectric window. Thus, there is no stable power transmission into the plasma processing chamber; and there is no efficient power transfer across dielectric windows over a wide operating range of plasma parameters.
A further challenge is that the materials deposited on the inside of a process chamber from etching a conductive metal layer on a semiconductor wafer include metal emanating from the metal layer being etched. This results in a metal loss which is costly especially when the metal layer being etched includes one of the noble metals, such as platinum, palladium, iridium, rhodium, ruthenium, etc. Thus, not only does the deposition of materials on the inside of a process chamber resulting from etching of a metal layer produce conductive byproducts which reduce the efficiency of rf energy transmission and effect the etch rate of the metal layer being etched, but there is also the concomitant loss of metal that was etched from the metal layer.
Therefore, what is needed and what has been invented is a method for recovering metal from metal by-products deposited on the inside of a reactor chamber during processing of a substrate in a plasma reactor chamber. What is further needed and what has been invented is an electrochemical method for recovering metal from etch byproducts produced, by etching of the metal in a reactor chamber containing a plasma of the processing gas.
SUMMARY OF THE INVENTION
The present invention provides a method for recovering a metal, preferably a noble metal, from by-products produced in a plasma processing chamber comprising:
a) recovering from a plasma processing chamber a deposit or residue (e.g., by-products) containing a metal, preferably a noble metal such as platinum or iridium;
b) disposing (e.g., preferably by dissolving) the deposit including the metal in a liquid, such as an acid (e.g., hydrochloric acid and/or nitric acid) and water mixture; and
c) recovering the metal from the liquid.
In a preferred embodiment of the present invention for the immediate foregoing method, the liquid preferably comprises an acid such as hydrochloric acid. In a preferred embodiment of the invention, the liquid comprises an acid (e.g. hydrochloric acid) plus another acid (nitric acid) and/or deionized water. In another preferred embodiment of the invention, the liquid comprises a HNO
3
:HCl:H
2
O mixture to dissolve a metal rich deposition, such as a platinum rich deposition in which Pt
2+
, Pt
4+
and metal Pt exist. A HCl:HNO
3
mixture having 3:1 mixing ratio by volume has been found acceptable, or a HCl:HNO
3
:H
2
O mixture having a 2:1:1 mixing ratio by volume, or a 1:1:1 mixing ratio by volume, has also been found acceptable. In yet another preferred embodiment of the invention, the liquid comprises from about 0% vol. to about 40% vol. deionized water, from about 20% vol. to about 100% vol. hydrochloric acid (e.g. 37% by wt in deionized H
2
O concentrated hydrochloric acid with 12N concentration) and from about 0% vol. to about 60% vol. nitric acid (e.g. 67% by wt in deionized H
2
O concentrated nitric acid with 15N concentration). The recovering step (c) may preferably comprise inserting a working electrode into the liquid until the liquid reaches a first level on the working electrode, and passing a current through the working electrode. Subsequently, the working electrode may be further immersed into the liquid until the liquid reaches a second level on the working electrode, and the amount of current flowing through the working electrode may be increased. The second level on the working electrode is preferably higher than the first level on the working electrode such that the working electrode is deeper in the liquid. The immediate foregoing method preferably additionally comprises etching, prior to the recovering step (a), a layer of the metal in the plasma pr
Han Nianci
Lu Danny
Ma Diana
Shih Hong
Xu Li
Applied Materials Inc.
Bach Joseph
Bean Kathi
Church Shirley L.
Phasge Arun S,.
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