Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
1998-05-07
2001-04-10
Dang, Thi (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C315S111210, C118S7230ER, C118S728000
Reexamination Certificate
active
06214160
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to plasma processing in the fabrication of semiconductor devices and, more particularly, to techniques for removing particulate matter from semiconductor substrates in plasma processing chambers, such as plasma enhanced chemical vapor deposition (PECVD), reactive ion etch (RIE) or sputter etch processing chambers. As is well known, semiconductor device geometries have been steadily shrinking in scale, and key features of devices have become more densely packed in each integrated circuit. When dealing with structural features at a microscopic level, engineers throughout the integrated circuit industry have had to deal with a critical problem of particulate control. Simply stated, the presence of particulates on integrated circuit substrates causes defects in some of the circuits. In most integrated circuit fabrication, many identical integrated circuits are formed on a single wafer, using a step-and-repeat lithographical process. The percentage of properly functioning integrated circuits formed on a wafer is referred to as the yield. Higher concentrations of particulates result in lower production yields. The problem is further compounded in the fabrication of extremely large, “wafer scale” integrated circuits, where significant particulate contamination can render an entire wafer useless.
It is generally agreed that the major source of particulates is the processing equipment itself, but there are no commercially available methods for removing particulates from wafers after their entry into a processing chamber. Because the present invention uses electrostatic forces to remove particulates from a processing chamber, it should be noted that the use of electrostatic energy to exert forces on particles has been known for many years, and was first demonstrated by Miliken in historic work discovering and quantifying the charge of the electron. Miliken's particles were small oil droplets, which he demonstrated could be moved up or down by the application of electrostatic fields.
A well known phenomenon in plasma etch reactors is the generation of a direct current (dc) bias between the plasma and a lower electrode to which rf power is applied. The dc bias accelerates positive ions in the reactor chamber toward the lower electrode, to which a semiconductor wafer is secured for etching. The energy of the ions accelerated from the plasma is one of the most important factors that determine the rate at which etching of the wafer takes place. As a result of the dc bias phenomenon, plasma etch processors already have a built-in technique for launching particulates electrostatically from the wafer surface. However, when there is no dc bias, as in PECVD processes, any particulates on the wafer surface are not automatically removed. Simply applying a permanent dc bias to the wafer does not work because the plasma tends to react in a way that compensates for the bias. Mobile charges in the plasma move to a position that shields out the effect of the biased surface.
It will be appreciated that there is an increasing need for particulate removal in semiconductor plasma processing chambers, such as PECVD chambers. The present invention fulfills this need.
SUMMARY OF THE INVENTION
The present invention resides in apparatus, and a method for its operation, for removing particulates electrostatically from a semiconductor wafer in a plasma processing chamber. In terms of a method, the invention comprises the steps of applying high-frequency plasma power across a two electrodes, one of which is normally grounded and supports a semiconductor wafer to be processed, whereby the plasma power initiates and maintains a plasma between the electrodes; then, at selected times, electrically isolating the wafer-supporting electrode and simultaneously applying to it a bias voltage selected to launch particulates from the surface of the wafer by electrostatic action; and maintaining the plasma during the selected times for launching the particulates. Launched particulates are suspended in the plasma until they can be later removed by purging with inert gas.
Preferably, the step of applying a bias voltage includes applying an alternating voltage, whereby both positively charged and negatively charged particulates will be launched from semiconductor wafer. The alternating bias voltage is selected to be in the same range as plasma potentials, such as approximately 100 v to 2,000 v. More specifically, in the preferred form of the method the steps of electrically isolating the wafer-supporting electrode and applying a bias voltage to it are performed prior to normal plasma processing within the chamber, to remove any particulates before an operation such as deposition is started.
The apparatus of the invention comprises a pair of generally parallel, first and second electrodes, the second one of which supports a semiconductor wafer for plasma processing; an isolation switch connected between the second electrode and ground; a high-frequency generator coupled between the upper electrode and ground, to provide power to initiate and sustain a plasma region between the first and second electrodes; a bias voltage generator providing sufficient voltage to launch any particulates on the wafer by electrostatic force; and a bias control switch connected between the bias voltage generator and the second electrode. Closing the bias control switch and opening the isolation switch results in application of the bias voltage to the lower electrode and launches particulates electrostatically from the wafer surface and into the plasma region, from which they may be later purged. The high-frequency generator maintains the plasma while the isolation switch is open, because of capacitive coupling from the second electrode to ground.
In the preferred form of the apparatus, the bias voltage generator generates an alternating voltage to ensure that both positively charged and negatively charged particulates will be launched from the wafer, and operates at a selected frequency between 60 Hz and approximately 13.56 MHz, and at a voltage in the range of 100 volts to 2,000 volts. The apparatus may also include a filter connected in series with the bias voltage generator, to protect it from damage from energy generated by the high-frequency generator used to initiate and maintain the plasma.
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Dornfest Charles
Girard Gerald
Gupta Anand
Applied Materials Inc.
Church Shirley
Dang Thi
Goudreau George
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