Electric heating – Metal heating – By arc
Reexamination Certificate
2003-01-17
2004-06-22
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121430, C219S121520, C156S345420
Reexamination Certificate
active
06753498
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of plasma processing of silicon wafers and more particularly to plasma processing equipment having automated electrode handling capabilities.
As is known in the art, a fundamental step in the manufacturing of semiconductor devices, such as integrated circuits (ICs), is the process of forming electrical interconnections. The formation of electrical circuits containing components such as semiconductor transistors, involves a series of steps starting with the formation of a blank silicon wafer. The blank silicon wafer or substrate is then processed using successive steps of depositing to and etching away various materials to form the proper interconnections and therefore the electrical circuits.
Such depositing and etching operations may be performed in a plasma reactor system. In semiconductor manufacturing, plasma reactor systems are used to remove or deposit material to or from a workpiece (e.g., semiconductor substrate) in the process of making integrated circuit (IC) devices. A key factor in obtaining the highest yield and overall quality of ICs is the uniformity of the etching and deposition processes.
When it is desired to deposit materials onto the wafer, a plasma reactor system may be used to sputter a variety of materials, one of which could be silicon, onto semiconductor wafers. In these sputtering applications, a silicon disk, or silicon dioxide disk or doped-silicon disk is used as a facing on the metal drive electrode to provide a source of material to be deposited on the semiconductor wafers to form variety of circuit patterns. This silicon disk is herein referred to as the source electrode or target.
There are several different kinds of plasma processes used during wafer processing. These processes include (1) plasma etching, (2) plasma deposition, (3) plasma assisted photo resist stripping and (4) in situ plasma chamber cleaning. One artifact of these plasma processes is the erosion of the source electrode as it is consumed during the formation of plasma, hence, a purpose for the source electrode is to serve as a protective barrier between the driven RF electrode and the plasma. Furthermore, each of these plasma processes has associated plasma density non-uniformities, for example, due to the generation of harmonics of the plasma excitation frequency. These non-uniform plasmas erode the plasma system silicon source electrode non-uniformly. The non-uniformly etched silicon electrode in turn exacerbates the non-uniformity of the plasma. To ensure uniform plasmas, these silicon electrodes are changed frequently. Otherwise, if a system with a non-uniform plasma is used for semiconductor wafer processing, the non-uniform plasma discharge can produce non-uniform etching or deposition on the surface of the semiconductor wafers. Thus, the control of the uniform etching or erosion of the silicon electrode directly affects the quality of integrated semiconductor chips manufactured by the semiconductor industry.
As illustrated in
FIG. 1
, a typical prior art plasma reactor system
10
includes, a plasma chamber
11
in which a wafer
18
is processed. Wafer
18
is placed on a chuck
16
and exposed to various plasmas depending on whether the wafer is undergoing an etch or deposition step. The plasma formed in plasma chamber
11
also varies depending on the material being deposited or etched on wafer
18
. The plasma within chamber
11
is formed by electro-mechanically coupling a source electrode
14
to the metal drive electrode
12
and driving a RF signal through the metal electrode
12
and consequently through source electrode
14
. Source electrode
14
, in effect, becomes the electrode in direct physical and electrical contact with plasma. The plasma formed within chamber
11
depends on a variety of factors including the RF power magnitude, the RF drive frequency, the chamber gas pressure and the composition of gases residing in the chamber. As described above, during processing of silicon wafers, a silicon electrode may be used as the source electrode.
As also described above, during silicon wafer processing, the silicon electrode is consumed and thus must be changed periodically in order to maintain consistent processing conditions within the plasma chamber. In prior art systems such as that shown in
FIG. 1
, the silicon source electrode
14
is attached to the metal electrode
12
by means of metal screws
23
which pass through clearance holes in the silicon electrode and mate with threaded holes in the metal electrode or metal nuts
25
on the back side of metal drive electrode
12
. The clearance holes in the silicon electrode are countersunk to assure that the heads of the attachment screws do not protrude beyond the surface of the silicon electrode.
Due to the electrical, thermal and physical contact requirements between the silicon disk and the drive electrode, there is a need to insure proper electrical and mechanical connection between the silicon electrode
14
and the metal electrode
12
. Even when an initial proper contact is established between metal drive electrode
12
and silicon source electrode
14
, as plasma processing proceeds and the silicon drive electrode is consumed, the plasma changes. However, systems currently available, such as plasma system
10
shown in
FIG. 1
, provide no means of adjusting the source electrode/metal drive electrode contact during processing. There is therefore a need to provide a way to adjust the contact of the silicon disk to the electrode in real time during a wafer processing step and/or between wafer processing steps in order to fine-tune plasma uniformity.
Furthermore, since the silicon source electrode described above is consumed during use, it must be changed on a relatively frequent basis. Even when the silicon source electrode is not consumed, it may be desirable to change a source electrode to one made of a different material or one having a different shape to produce a different plasma in plasma chamber
11
. Unfortunately, in prior art plasma processing systems, changing the source electrode
14
requires shutting down the plasma process, venting the chamber, opening the chamber, removing the attachment screws, replacing the consumed silicon electrode manually with a new one and putting everything back together again. This process is time consuming, reduces wafer throughput, and may create added defects through contamination.
It would be advantageous therefore to provide a plasma processing system where the source electrode could be replaced automatically without opening the plasma chamber. It would be further advantageous to provide an apparatus for plasma processing of semiconductor wafers which allows for secure, repeatable attachment of a source electrode to the metal drive electrode where the contact between the source electrode and metal drive electrode is dynamically adjustable during operation of the plasma processing system.
BRIEF SUMMARY OF THE INVENTION
According to one aspect of the present invention, a plasma processing system is provided that includes an automated electrode retention mechanism as well as an automated electrode handling system. The retention mechanism includes an elevator system that raises and lowers a source electrode in order to dynamically couple and decouple the source electrode from the drive electrode. In one embodiment the automated retention mechanism includes a plurality of lift arms coupled to associated drive units. Activating the drive units causes the lift arms to move in a vertical direction within the plasma processing system vacuum chamber. Coupled to the lower end of the lift arms is an electrode shelf that supports the source electrode while it is being raised and lowered as well as retaining the source electrode to the drive electrode. The shelf is generally ring-shaped and supports the source electrode about the perimeter of its lower face. That is, the interior diameter of the shelf is slightly less than the diameter of the source electrode. In the preferred embodiment, the
Bibby Yu Wang
Cronin John E.
Sirkis Murray D.
Strang Eric
Paschall Mark
Pillsbury & Winthrop LLP
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