MXPA97008509A - Thermal processor for semiconductor plates - Google Patents

Abstract

The present invention relates to a thermal processor for at least one semiconductor wafer including a reactor chamber having a material substantially transparent to light that includes a wavelength within the range of about 200 nanometers to about 800 nanometers to hold at least one semiconductor insert. A coating that includes a substantially infrared reflective material may be present on at least a portion of the reactor chamber. A light source provides radiant energy to at least one semiconductor wafer through the jacket and reactor chamber. The light source may include an ultraviolet discharge lamp, an incandescent infrared halogen lamp, or a metal halide visible discharge lamp. The coating can be located on an internal or external surface of the reactor chamber. If the reactor chamber has internal and external walls, the coating can be placed on the internal wall or the external wall.

Description

THERMAL PROCESSOR FOR SEMICONDUCTOR PLATES BACKGROUND OF THE INVENTION The silicon wafers have traditionally been processed in stages such as deposition, oxidation and etching, for example in batches of twenty to forty plates at a time. The batches are processed inside quartz tubes where the plaqutas are kept separately on quartz "insert holders". The tubes and plates are heated in ovens at a temperature ranging from 800 ° C to approximately 1200 ° C. Typically, these furnaces are oven structures heated by resistance, such as furnaces heated with electric metal coils and have processing times of several hours. The individual insert processors have recently been developed. Instead of large tubes with insert carriers, smaller cameras are used and the processing time of one insert can be in the order of one minute. One of the most common individual insert processes employs a quartz chamber and is referred to as a fast thermal process (RTP). The RTP and other similar individual insert processes heat the inserts from about 1000 ° C to 1200 ° C; however, tungsten lamps are used instead of resistive heating. Some batch processes similarly use halogen lamps instead of resistive heating.

Such processes are generally referred to as "fast batch processes" because they require more time than the individual insert processes although less time than traditional batch processes. Conventional RTP systems for semiconductor fabrication use tungsten halogen lamps to rapidly heat the individual silicon wafers that lie horizontally within the parallel-plate quartz reactors. In such systems, the efficiency is compromised since the spectral emittance of the tungsten lamps is tilted towards the infrared region (where the absorption of silicon is low) and because the heat radiated by the hot silicon surfaces is transmitted through of the reactor wall and is lost outside the reactor. In addition to requiring a large amount of electrical energy for the above reasons, the variations of heating through the plates are caused by the relative position of the plates with respect to the lamps.

BRIEF DESCRIPTION OF THE INVENTION It would be desirable to have a thermal processor for semiconductor inserts with higher energy efficiency (and longer lamp life and corresponding lower power consumption) than conventional processors.

It would also be desirable to have a thermal processor for semiconductor wafers with improved heating uniformity over conventional processors and thereby achieving a uniform surface temperature. In one embodiment of the present invention, the efficiency is increased by coating walls of a transparent reactor with a selective wavelength layer to allow the ultraviolet (UV) and visible radiation from the lamps to enter the reactor while blocking the output of the infrared radiation emitted from the hot semiconductor plates. Trapping the radiation inside the reactor will increase the efficiency of the process by requiring less radiation incident on the chamber and improving the uniformity of heating by increasing the fraction of indirect radiation that is insensitive to the position of the lamp. In another embodiment, a halogen infrared incandescent lamp or a shorter wavelength mercury lamp or a metal halide discharge lamp is used which requires less energy than a tungsten lamp since it emits a wavelength of greater absorption of silicon. This lamp is also more reliable since the tungsten filament is not present. These two modalities can be used individually or in combination in thermal processes such as individual insert processes, rapid thermal processes and rapid batch processes, for example.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention considered novel are set forth with particularity in the appended claims. However, the invention itself, both for the organization and for the method of operation, together with additional objects and advantages thereof, can be better understood by reference to the following description taken together with the accompanying drawings, in which similar references represent similar components, in which: FIG. 1 is a sectional side view of a thermal processor embodiment of the present invention. FIG. 2 is a view similar to that of Fig. 1 where a selective wavelength coating is placed on an internal chamber and covered by a passivation layer. FIGs. 3-5 are views similar to that of FIG. 1 with a double wall camera. FIG. 6 is a sectional side view of a vertical thermal processor embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED MODE OF THE INVENTION Fig. 1 is a sectional side view of a thermal processor embodiment of the present invention. A semiconductor wafer 10 is placed in a reactor chamber 12 and supported by small pins 14. The camera has a selective coating of wavelength 16 and receives radiant energy from the heating elements of the lamp 18 and a lamp reflector 20. The insert 10 may comprise any of a number of semiconductor materials such as silicon, silicon carbide, gallium arsenic, gallium nitride, for example. If desired, these semiconducting materials can be in combination with thin insulators and / or metal layers. The chamber 12 may comprise a material that is optically transparent enough to allow high transmission of ultraviolet light and / or visible light (light that includes a wavelength within the range of about 200 nanometers to about 800 nanometers). Examples of material for chamber 12 include quartz, quartz doped with alumina, alumina and synthetic silica. In the embodiment of Fig. 1, the insert 10 is located horizontally within the chamber and is supported by pins 14 comprising quartz with the device surface confronting the opposite side of the chamber (the side without pin) and the elements of heating the lamp. Placing the insert in the camera is not critical. For example, the insert can be held in an inclined or vertical position or be supported by a quartz pedestal over the middle part of the reactor chamber. The coating 16 can be selected from any of a number of wavelength selective materials that reflect infrared light such as, for example, indium tin oxide (ITO), antimony tin oxide (FTO), tin oxide not impurified, dichroic filters or, thin metal films such as silver, aluminum or gold. The dichroic filters can be manufactured from a pile of titanium oxide and layers of silicon dioxide or tantalum oxide and layers of silica dioxide, for example, and are advantageous since they can survive for a long time at high temperatures. Like the camera material, the coating material is capable of transmitting light including a wavelength within the scale of about 200 nanometers to about 800 nanometers. Selective infrared mirror coatings comprising doped semiconductor oxides, called Drude mirror coatings, have been characterized with respect to electrical, optical and material properties as described in T. Gerfin and M. Gratzel, "Optical properties of tin-doped indium oxide determined by spectroscopic ellipsometry ", J. Appl. Phys., Vol. 79, pp. 1722-1729, February 1, 1996. Drude mirror coatings have been used on greenhouse glass sheets to reduce energy losses caused by the emission of infrared radiation while allowing sunlight to enter freely as described in SD Silverstein, "Efect of Infrared Transparency on the Heat Transfer Through Windows: A Clarification of the Greenhouse Effect" Science, Vol. 193, pp. 229-31, July 16, 1976. Antimony-tin oxide (ATO) films have been deposited by deposition of chemical vapor onto layers of silicon oxide as described in T.P. Chow, M. Ghezzo, and B.J. Baliga "Antimony-doped tin oxide films deposited by the oxidation of tetramethylin and trimethylantiminy", J. Electrochem. Soc, pp. 1040-45, May 1982 and therefore it is expected that the ATO films can be deposited on quartz. Dichroic filters have been used in halogen-IR parabolic aluminum (PAR) reflector lamps available from General Electric Company, Cleveland, Ohio, to reflect infrared radiant heat from the lamp housing while allowing visible radiation to be transmitted outwardly. . The present invention differs from such halogen-IR PAR lamps wherein the light source is within the coated chamber since, in the present invention, the light source is located outside the coated chamber. The heating elements of the lamp 18 can comprise ultraviolet (UV) discharge lamps 18 such as mercury discharge lamps, metal halide visible discharge lamps, or infrared halogen incandescent lamps, for example. The wavelength scale for the visible spectrum is from about 200 nanometers to about 400 nanometers and the wavelength scale for the UV spectrum is from about 400 nanometers to about 800 nanometers. Therefore, the camera 12 and the coating 16 are capable of preferably passing light at a wavelength included in a scale from about 200 nanometers to about 800 nanometers. If the heating elements of the lamp are cylindrical, they can be aligned in parallel at a periodic distance from each other and at an equal distance from the semiconductor plate. The lamp reflector 20 may comprise a group of concave mirrors 22 positioned above the lamps to efficiently reflect the back lighting of the lamps. Using a UV discharge lamp to process the silicon wafers, for example, it is expected to increase the utilization of light efficiently by thirty percent or more over designs of tungsten lamps even without a coating on the camera. The expected increase in efficiency is due to the fact that the absorption spectrum of silicon has a greater overlap with the emission spectrum of the discharge lamp. Using the coating to provide heat recovery is expected to improve the energy efficiency by an additional 65%. A general improvement of approximately 95% is expected.

Fig. 2 is a view similar to that of Fig. 1 where the wavelength selective coating 16a is located on the inner side of the chamber wall 12a and covered by a passivation layer 24. Placing the coating on an internal wall side helps to reduce the absorption of IR radiation by the wall of the chamber 12a. The coating in this mode must be a refractory material that does not spill particles on the insert and is free of contaminants. The passivation layer 24 may comprise a material such as, for example, silicon oxide (SiO2) having a thickness in the scale from about 0.1 microns to about 0.2 microns and may be added to the coating 16a of Fig. 2 or the coating 16 of FIG. 1 to protect the coating. Figs.3-5 are views similar to that of Fig. 1 with a double wall chamber for gas cooling that is useful if a single wall would result in the chamber wall temperature that exceeds the thermal capacity of the coating. This is useful because the silicon wafers, for example, can reach temperatures that exceed 1000 ° C. In Figs. 3 and 4, the coverings 16b and 16c respectively, are placed between the chamber walls 12 b and 26 and, 12c and 26c respectively. The forced air 28 and 28c can be pumped between the walls of the chamber. In Fig. 3 the cover 16b is located on an external surface of the chamber wall 12b, and in Fig. 4, coating gel 16c is placed on an inner surface of chamber wall 28c. In Fig. 5, chamber walls 12d and 26d have forced air 28d pumped therebetween and cover 16d is present on an inner surface of chamber wall 12d. In addition, FIG. 5 illustrates a plurality of inserts 10a and 10b in a single chamber 12d. FIG. 6 is a side sectional view of a vertical thermal processor embodiment 2 of the present invention wherein the camera 612 is coated with wavelength selective coating 616 and encloses a plurality of inserts 610 that can be stacked using pins of quartz (not shown), for example. The chamber is sealed by a cover 630 which may comprise a material such as quartz for example. Gases such as N2, 02, or pyrogenic generated current can be supplied through the air inlet port 634. Radiant energy is supplied by the lamp heating elements 618 of the lamp assemblies 619. While only Certain preferred features of the invention have been illustrated and described herein, those skilled in the art can devise many changes and modifications. It is therefore understood that the appended claims are intended to cover all such modifications and changes as they fall within the true spirit of the invention.

Claims (9)

1. A thermal processor for at least one semiconductor wafer comprising: a reactor chamber for holding at least one semiconductor wafer, the reactor chamber comprising a material substantially transparent to light that includes a wavelength within a scale of approximately 200 nanometers to approximately 800 nanometers; a coating on at least a portion of the reactor chamber, the coating comprising the material substantially transparent to light that includes a wavelength within a range of about 200 nanometers to about 800 nanometers and substantially reflective of infrared radiation; and a light source for providing radiant energy to at least one semiconductor wafer through the jacket and reactor chamber.

2. The processor of claim 1, wherein the light source is an ultraviolet discharge lamp, an incandescent infrared halogen lamp, or a metal halide visible discharge lamp.

3. The processor of claim 1, wherein the reactor chamber is quartz, quartz doped with alumina, alumina or synthetic silica.

4. The processor of claim 1, wherein the coating is indium-tin oxide, antimony-tin oxide, fluor-tin oxide, unpurified tin oxide, a dichroic filter or a thin metal film.

5. A thermal processor for at least one semiconductor wafer comprising: a reactor chamber for holding at least one semiconductor wafer, the reactor chamber comprising a material substantially transparent to light that includes a wavelength within one scale of approximately 200 nanometers to approximately 800 nanometers; and a lamp comprising an ultraviolet discharge lamp, an incandescent infrared halogen lamp, or a metal halide visible discharge lamp, the lamp capable of providing radiant energy to at least one semiconductor wafer through the reactor chamber. The processor of claim 5, wherein the reactor chamber is quartz, quartz doped with alumina, alumina or synthetic silica. 7. A thermal processor for at least one semiconductor wafer comprising: a substantially transparent reactor chamber for holding at least one semiconductor wafer; a coating comprising a selective infrared reflective material that covers at least a portion of the reactor chamber; and an ultraviolet discharge lamp for providing radiant energy for at least one semiconductor wafer through the coating and the reactor chamber. The processor of claim 7, wherein the reactor chamber is quartz, quartz doped with alumina, alumina or synthetic silica and the coating is indium-tin oxide, anti-monio-tin oxide, fluor-tin oxide, unpurified tin oxide, a dichroic filter or a thin metallic film. 9. An apparatus for use in a thermal processor, the apparatus comprising: a reactor chamber for holding at least one semiconductor wafer, the reactor chamber comprising a material substantially transparent to light that includes a wavelength within from a scale of approximately 200 nanometers to approximately 800 nanometers; and a coating on at least a portion of the reactor chamber, the coating comprising material substantially transparent to light that includes a wavelength within the range of about 200 nanometers to about 800 nanometers and substantially reflective of radiation infrared The apparatus of claim 9, wherein the reactor chamber is quartz, quartz doped with alumina, alumina or synthetic silica.