Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With heating or cooling means for apparatus part other than...
Reexamination Certificate
2000-03-07
2003-02-04
McDonald, Rodney G. (Department: 1753)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With heating or cooling means for apparatus part other than...
C156S345420, C156S048000, C156S345530, C204S298090, C204S298310, C118S7230IR, C118S7230IR, C118S7230AN, C118S724000, C118S728000
Reexamination Certificate
active
06514376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention is related to heating and cooling apparatus in an inductively coupled RF plasma reactors of the type having a reactor chamber ceiling overlying a workpiece being processed and an inductive coil antenna adjacent the ceiling.
2. Background Art
In a plasma processing chamber, and especially in a high density plasma processing chamber, RF (radio frequency) power is used to generate and maintain a plasma within the processing chamber. As disclosed in detail in the above-referenced applications, it is often necessary to control temperatures of surfaces within the process chamber, independent of time varying heat loads imposed by processing conditions, or of other time varying boundary conditions. In some cases where the window/electrode is a semiconducting material, it may be necessary to control the temperature of the window/electrode within a temperature range to obtain the proper electrical properties of the window. Namely, for the window/electrode to function simultaneously as a window and as an electrode, the electrical resistivity is a function of temperature for semiconductors, and the temperature of the window/electrode is best operated within a range of temperatures. The application of RF power to generate and maintain the plasma leads to heating of surfaces within the chamber, including windows (such as used for inductive or electromagnetic coupling of RF or microwave power) or electrodes (such as used for capacitive or electrostatic coupling of RF power, or for terminating or providing a ground or return path for such capacitive or electrostatic coupling of RF power) or for combination window/electrodes. Heating of those surfaces can occur due to 1) ion or electron bombardment, 2) absorption of light emitted from excited species, 3) absorption of power directly from the electromagnetic or electrostatic field, 4) radiation from other surfaces within the chamber, 5) conduction (typically small effect at low neutral gas pressure), 6) convection (typically small effect at low mass flow rates), 7) chemical reaction (i.e. at the surface of the window or electrode due to reaction with active species in plasma).
Depending on the process being performed with the plasma process chamber, it may be necessary to heat the window or electrode to a temperature above that temperature which the window or electrode would reach due to internal sources of heat as described above, or it may be necessary to cool the window or electrode to a temperature below that temperature which the window or electrode would reach due to internal sources of heat during some other portion of the operating process or sequence of processes. In such cases, a method for coupling heat into the window or electrode and a method for coupling heat out of the window or electrode is required.
Approaches for heating window/electrodes from outside the process chamber include the following:
1. heating the window/electrode by an external source of radiation (i.e., a lamp or radiant heater, or an inductive heat source),
2. heating the window/electrode by an external source of convection (i.e. forced fluid, heated by radiation, conduction, or convection),
3. heating the window/electrode by an external source of conduction (i.e., a resistive heater).
The foregoing heating methods, without any means for cooling, limit the temperature range available for window or electrode operation to temperatures greater than the temperature which the window or electrode would reach due to internal sources of heat alone.
Approaches for cooling window/electrodes from outside the process chamber include the following:
1. cooling the window/electrode by radiation to a colder external surface,
2. cooling the window/electrode by an external source of convection (i.e., natural or forced),
3. cooling the window/electrode by conduction to an external heat sink.
The foregoing cooling methods, without any means for heating other than internal heat sources, limit the temperature range available for window or electrode operation to temperatures less than that temperature which the window or electrode would reach due to internal sources of heat alone.
Additionally the foregoing cooling methods have the following problems:
1. cooling the window/electrode by radiation is limited to low heat transfer rates (which in many cases are insufficient for the window or electrode temperature range required and the rate of internal heating of window or electrodes) at low temperatures due to the T
4
dependence of radiation power, where T is the absolute (Kelvin) temperature of the surface radiating or absorbing heat;
2. cooling the window/electrode by an external source of convection can provide large heat transfer rates by using a liquid with high thermal conductivity, and high product of density & specific heat when high flow rates are used, but liquid convection cooling has the following problems:
A) it is limited to maximum temperature of operation by vapor pressure dependence of liquid on temperature (i.e. boiling point) (unless a phase change is allowed, which has its own problems—i.e. fixed temperature of phase change—no control range, as well safety issues),
B) incompatibility of liquid cooling with the electrical environment, depending upon liquid electrical properties,
C) general integration issues with liquid in contact with reactor structural elements. Cooling the window or electrode by an external source of convection (e.g., a cooling gas) is limited to low heat transfer rates which in many cases are insufficient for the window or electrode temperature range required and the rate of internal heating of window or electrodes;
3. cooling the window/electrode by conduction to an external heat sink can provide high rates of heat transfer if the contact resistance between the window or electrode and the heat sink is sufficiently low, but low contact resistance is difficult to attain in practice.
Approaches for both heating and cooling window/electrodes from outside the process chamber include heating the window/electrode by an external source of conduction (i.e., a resistive heater) in combination with cooling the window/electrode by conduction to an external heat sink. In one implementation, the structure is as follows: a window or electrode has a heater plate (a plate with an embedded resistive heater) adjacent an outer surface of the window electrode. Additionally, a heat sink (typically liquid cooled) is placed proximate the opposite side of the heater plate from the window or electrode. Contact resistances are present between window or electrode and heater plate, and between the heater plate and the heat sink. In such a system integrated with automatic control of window or electrode temperature, a temperature measurement is made (continuously or periodically) of the window or electrode to be controlled, the temperature measurement is compared with a set point temperature, and based on the difference between the measured and set point temperatures a controller determines through a control algorithm how much power to apply to the resistive heater, or alternatively, how much cooling to apply to the heat sink, and the controller commands output transducers to output the determined heating or cooling levels. The process is repeated (continuously or periodically) until some desired degree of convergence of the window or electrode temperature to the set point temperature has occurs, and the control system remains active ready to respond to changes in requirements of heating or cooling levels due to changes in internal heat or cooling levels or to changes in the set point temperature. Besides contact resistance problems that limit the cooling capability of the system to control the temperature of the window or electrode, the system exhibits a time lag in transferring heat from the window or electrode to the head sink as required when the internal heating or cooling load changes during plasma reactor operation. This is due in part to the contact resistance between the window or electrode and the heater, a
Askarinam Eric
Buchberger Douglas
Collins Kenneth
Rice Michael
Roderick Craig
Applied Materials Inc.
Bach Joseph
McDonald Rodney G.
Wallace Robert M.
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