Cooled window

Details Cooled window Cooled window

1999-05-27

2001-09-04

Mills, Gregory (Department: 1763)

Coating apparatus

Gas or vapor deposition

With treating means

C156S345420, C118S050100

Reexamination Certificate

active

06284051

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to semiconductor processing apparatus, and specifically to apparatus for radiant heating of semiconductor wafers.
BACKGROUND OF THE INVENTION
In rapid thermal processing of semiconductor wafers, a radiant source, such as a tungsten-halogen lamp or array of lamps, is commonly used to heat the wafer. A transparent window, typically made of quartz or sapphire, is used to separate the processing chamber from the heater. The window must be strong enough to withstand the pressure difference between the vacuum of the chamber and atmospheric pressure outside it, and therefore must be fairly thick. Quartz, however, is opaque to wavelengths above 4 &mgr;m, and also absorbs a small amount of radiation in the region between 0.2 to 4 &mgr;m. The total absorption grows with window thickness.
Under these conditions, in the absence of effective cooling, the window can reach high temperatures, typically up to 500° C., after a few process cycles in the chamber. A thick, hot window can affect the process in a number of undesirable ways:
“First wafer effect”—The first few wafers in a batch are processed before the window reaches its equilibrium temperature, and the repeatability of the process may therefore be affected.
Because of the low thermal conductivity of quartz, the temperature across the window may be non-uniform, thus affecting the uniformity of temperature across the wafer.
Some rapid thermal chemical vapor deposition (RTCVD) processes, such as polysilicon deposition, can also cause deposition of material on hot parts of the vacuum chamber, including the window. The deposition reduces window transmittance, so that more lamp power must be used to reach the desired wafer temperature. Deposition on the window can also affect process uniformity and repeatability.
Deposition on the window also increases the number of particles in the chamber, which can cause to contamination of the wafer, and leads to a requirement for more frequent cleaning.
Methods and apparatus for window cooling are known in the semiconductor processing art. For example, U.S. Pat. No. 4,550,684, to Mahawili, which is incorporated herein by reference, describes a vapor deposition system that uses a lamp to heat a wafer with radiation in the wavelength range between 0.3 and 0.9 &mgr;m. A window separates the lamp from a vacuum chamber containing the wafer. The window is constructed of two spaced-apart plates, between which water is pumped to control the window temperature. Although the water passing through the window absorbs infrared radiation emitted by the lamp, Mahawili considers this effect to be beneficial. He indicates that the desirable wavelength range for heating the wafer is between 0.3 and 0.9 &mgr;m, and wavelengths outside this range should be excluded from the chamber.
U.S. Pat. No. 5,487,127, to Gronet et al., which is incorporated herein by reference, describes rapid thermal heating apparatus in which lamps are disposed in a plurality of light pipes in order to illuminate and supply heat to a semiconductor substrate. The light pipes are integrated with a liquid-cooled window, which separates the lamps from an evacuated processing chamber. The window is constructed so that cooling water can be injected into spaces between the light pipes without entering or passing in front of the light pipes themselves. The light pipes themselves are evacuated. The radiation from the lamps thus reaches the chamber without being attenuated by the water, but the integrated structure of lamps, evacuated light pipes and cooled window is complex and difficult to construct and maintain.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved cooled window for use in radiative heating of a semiconductor wafer in a vacuum chamber.
In preferred embodiments of the present invention, a cooled window for a thermal process chamber comprises upper and lower layers of a suitable transparent material, preferably quartz, with passages between the layers through which a cooling fluid passes. The cooling fluid is chosen, unlike water, to have high transmittance in an infrared range of wavelengths above 1.1 &mgr;m, and preferably extending to above 1.4 &mgr;m. A radiant heater, preferably comprising an array of lamps, is configured and positioned to heat a semiconductor wafer in the chamber, such that the radiation from the heater, including both visible and infrared radiation, passes through the upper and lower layers of the window and through the cooling fluid and impinges on the wafer without substantial attenuation. Thus, the cooled window, of simple and robust structure, enables efficient delivery to the wafer of substantially the entire spectrum of useful radiation emitted by the lamp.
In preferred embodiments of the present invention, the thermal process chamber is evacuated during use, and the upper layer of the transparent material is made thick enough so that the window can withstand force exerted thereon due to the difference between ambient, atmospheric pressure outside the chamber and vacuum inside it. The lower layer is made substantially thinner than the upper layer, so that a lower surface of the lower layer, adjacent to the wafer, is thoroughly and uniformly cooled by heat conduction through the lower layer to the fluid. The lower layer would be too thin by itself to withstand the pressure difference across the window when the chamber is evacuated. But the lower layer is supported mechanically by a structure fixed between the upper and lower layers, which defines the passages through which the fluid flows and is configured so as to minimize blockage of radiation passing through the window.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a cooled window assembly for a thermal processing chamber, wherein an object in the chamber is heated by a radiation source outside the chamber emitting radiation that includes infrared radiation, the assembly including:
upper and lower transparent plates defining passages therebetween; and
a cooling fluid flowing through the passages, which fluid is substantially transparent to the infrared radiation, such that the infrared radiation from the source passes through the plates and through the fluid in the passages to heat the object.
Preferably, the cooling fluid is substantially transparent to radiation having a wavelength greater than 1.1 &mgr;m, and most preferably to radiation having a wavelength greater than 1.4 &mgr;m. Further preferably, the cooling fluid is substantially transparent to visible radiation. In a preferred embodiment, the cooling fluid includes a liquid fluorocarbon.
Preferably, the window assembly includes segments of a transparent material fixed between the upper and lower plates so as to define the passages, wherein the passages are generally aligned with a geometrical pattern of the radiation emitted by the radiation source.
Further preferably, the upper plate is substantially thicker than the lower plate, wherein the upper plate has a thickness sufficient so that the window assembly is able to withstand atmospheric pressure when the chamber is evacuated.
There is also provided, in accordance with a preferred embodiment of the present invention, a cooled window assembly for an evacuable thermal processing chamber, wherein an object in the chamber is heated by a radiation source outside the chamber, the assembly including:
an upper transparent plate, positioned adjacent to the radiation source and having a thickness sufficient so that the window assembly is able to withstand atmospheric pressure when the chamber is evacuated;
a lower transparent plate, positioned adjacent to the object in the chamber and having a thickness substantially less than the thickness of the upper transparent plate; and
supporting pieces fixed between the upper and lower plates so as to provide mechanical support to the lower plate and arranged so as to define passages between the plates through which a cooling fluid passes to cool the plates.
Prefera

Affiliated with

Also associated with

Rating

Cooled window does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Cooled window, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cooled window will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2437369