Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
1999-10-29
2001-05-29
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298090, C204S298050, C118S7230IR, C118S7230ER, C118S724000
Reexamination Certificate
active
06238532
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improvements in radio-frequency (RF) coils used in ionized physical vapor deposition (IPVD) apparatus, which are widely used in the fabrication of semiconductor devices.
BACKGROUND OF THE INVENTION
Physical vapor deposition (PVD or sputtering) is a well-known process for depositing thin solid films on substrates, and is widely practiced in the semiconductor industry. Ionized physical vapor deposition (IPVD), also referred to as ionized metal plasma (IMP) deposition, has been used more recently to deposit metal films (notably copper) in etched structures such as vias and contact holes. IMP deposition apparatus differs from earlier versions of PVD apparatus in that it requires a metal RF coil in the process chamber in order to generate a plasma which can ionize the metal atoms during the sputter deposition process. The RF coil is, in general, constructed of the same material (with respect to composition and purity) as the sputter target; this is necessary to avoid contamination of the substrate, because sputtering will take place at the coil surface just as at the target surface.
The RF coil is subject to considerable heating due to ion bombardment and high coupled power into the process plasma. The coil temperature may reach 700° C. This in turn causes the temperature of the substrate (typically a semiconductor wafer) to increase; this is not desirable because the substrate temperature cannot be easily controlled. Furthermore, the RF coil is prone to mechanical deformation and premature failure due to the high thermal load. This problem is particularly acute when the coil is constructed of a relatively soft, malleable material such as copper. As shown schematically in
FIG. 1
, the coil
100
is generally circular in shape with a break in its circumference; the RF voltage is applied across the break through leads
101
,
102
. Thermal expansion of the coil can cause the ends
111
,
112
of the coil to touch, resulting in an electrical short.
There is a need for an RF coil for use in IPVD process apparatus in which excessive heating and deformation are avoided, thereby extending the lifetime of the coil, improving the efficiency and reliability of the IPVD apparatus, and reducing the cost of operating the apparatus in the manufacture of semiconductor devices.
SUMMARY OF THE INVENTION
The present invention addresses the above-described need by providing a cooling structure and/or a reinforcing structure for an RF coil in which deformation of the RF coil due to thermal expansion is reduced or avoided.
In accordance with a first aspect of the present invention, a cooling structure including a portion for carrying coolant is provided for the RF coil; the cooling structure is proximate to the RF coil along the outer circumference thereof. The cooling structure is at a lower temperature than the RF coil, and may have thermal expansion properties different from those of the RF coil. Furthermore, the cooling structure is shaped relative to the RF coil so that thermal expansion of the RF coil causes the RF coil to be in close contact with the cooling structure, thereby facilitating heat transfer from the RF coil to the coolant.
The RF coil also may be demountable from the cooling structure. The cooling structure is shielded by the RF coil from sputtering during the IPVD process.
In accordance with a second aspect of the invention, a reinforcing structure is provided which gives mechanical reinforcement for the RF coil. The reinforcing structure is proximate to the RF coil along the outer circumference thereof. The reinforcing structure and the RF coil are of materials having different thermal expansion properties and are shaped so that thermal expansion of the RF coil causes the RF coil to be in close contact with the reinforcing structure.
Furthermore, the cooling structure may be shaped to provide mechanical reinforcement for the RF coil, so that the cooling structure and the reinforcing structure are integrated.
In accordance with another aspect of the invention, the RF coil (or cooling or reinforcing structure) is mounted on a fixed portion of the IPVD device by a mounting post having a first portion and a second portion slidably connected thereto. This arrangement permits the mounting post to telescope in accordance with thermal expansion of the RF coil. In addition, the mounting post provides electrical insulation between the RF coil and the fixed portion of the PVD device. Specifically, the first portion of the mounting post may be attached to the fixed portion of the PVD device and include an electrical insulator, while the second portion of the mounting post is attached to the RF coil; the electrical insulator mates with the second portion and slides along an interior surface thereof in accordance with the thermal expansion of the RF coil.
In accordance with an additional aspect of the invention, the electrical leads to the RF coil may be fed through the wall of the IPVD device arranged in a coaxial fashion instead of in parallel, thereby reducing the electrical inductance of the leads.
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“RF Work Coil for Evaporative Deposition System,” IBM Technical Disclosure Bulletin, vol. 30, No. 2, pp. 698-699, Jul. 1987.*
J. L. Vossen and W. Kern, eds. “Thin Film Processes” (Academic Press, 1978), p. 31-32 (Month Unknown).
E. Uberbacher, “Multistage Through-hole,” IBM Technical Disclosure Bulletin 10,882, Dec. 1967.
Restaino Darryl D.
Rossnagel Stephen Mark
Simon Andrew Herbert
Smetana Pavel
Anderson Jay H.
Diamond Alan
International Business Machines - Corporation
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