WO2002003418A1

WO2002003418A1 - Lamp for a rapid thermal processing chamber

Info

Publication number: WO2002003418A1
Application number: PCT/US2001/019293
Authority: WO
Inventors: Joseph M. Ranish
Original assignee: Applied Materials, Inc.
Priority date: 2000-06-30
Filing date: 2001-06-15
Publication date: 2002-01-10

Abstract

A halogen lamp for use in semiconductor processing comprises a bulb enclosing at least one coil having a pair of inner leads, a lamp base configured to receive the inner leads, and a heat shield disposed between the coil and the lamp base. The lamp can include a bulb enclosing at least one col having a pair of inner leads; a lamp base enclosing a bulb enclosing the inner leads and a plurality of foils, each inner lead electrically coupled to one of the foils, wherein the inner leads have a helical shape within the lamp base; and an elongated member disposed within the each inner lead, such that gaps between the lamp bulb and the foils are helcal in shape.

Description

LAMP FOR A RAPID THERMAL PROCESSING CHAMBER

BACKGROUND OF THE INVENTION This invention relates generally to a semiconductor processing system and, more specifically, to improved lamps for use in a semiconductor processing system. Rapid thermal processing (RTP) systems are employed in semiconductor chip fabrication to create, chemically alter or etch surface structures on semiconductor wafers. One such RTP system, as described in U.S. Patent No. 5,155,336, which is assigned to the assignee of the subject application and which is incorporated herein by reference, includes a semiconductor processing chamber and a heat source assembly or lamphead located on the semiconductor processing chamber. A number of infrared lamps are located in the lamphead. During processing, infrared radiation from the lamps radiates through an upper window, light passageways and a lower window onto a rotating semiconductor substrate in the processing chamber. In this manner, the wafer is heated to a required processing temperature. As shown in Figure 1, a conventional halogen lamp 100 (also referred to as a tungsten-halogen lamp) for use in semiconductor processing includes a bulb 102 that has a coil 104 electrically coupled between a short inner lead 106 and a long inner lead 108. Inner leads 106 and 108 are coupled to outer leads 116 by foils 112. The foils are commonly made from molybdenum. The inner leads, outer leads, and foils are held in place at a lamp base 110. The lamp base is pressed together during manufacturing over the foil area to form a press seal that hermetically seals the lamp bulb. The bulb is commonly made of quartz.

During semiconductor processing operations, such lamps operate at extremely high temperatures. Elaborate structures have been designed to conduct heat away from the lamp base. According to such conventional methods, the lamp base is encapsulated within a precision outer diameter stainless steel tube using a high thermal conductivity potting compound. This high precision stainless steel tube is inserted into another high precision stainless steel tube which has its outer surface (for most of its length) water cooled. This elaborate cooling mechanism causes the lamp to operate at a temperature low enough to permit long lamp life. SUMMARY OF THE INVENTION In general, the invention is directed to a semiconductor processing system. In one aspect, the invention features a halogen lamp comprising a bulb enclosing at least one coil having a pair of inner leads; a lamp base configured to receive the inner leads; and a heat shield disposed between the coil and the lamp base.

Particular implementations include one or more of the following. The heat shield can include a reflective surface configured to reflect radiation generated by the coil away from the lamp base. The heat shield can be planar or curved, as with a conic section. The heat shield can be configured to direct the radiation in a predetermined direction. The heat shield can be electrically non-conductive.

The heat shield can include a multilayer dielectric film supported by at least one of silica, alumina, and alkali-free alumino-silicate glass. The film can have maximum reflectance near the peak wavelength emitted by the coil. The heat shield can include metal encased in at least one of silica, alumina, and alkali-free alumino-silicate glass. The lamp bulb can be dimpled to hold the heat shield in place. , At least one of the inner leads can be bent to hold the heat shield in place. The lamp can include alkali-free solder glass coupling the heat shield to at least one of an inner lead and the lamp bulb.

In another aspect, the invention features a halogen lamp comprising a bulb enclosing at least one coil having a pair of inner leads; a lamp base enclosing the inner leads and a plurality of foils, each inner lead electrically coupled to one of the foils, wherein the inner leads have a helical shape within the lamp base; and an elongated member disposed within the each inner lead, such that gaps between the lamp bulb and the foils are helical in shape. The elongated member can include at least one of tungsten, platinum, or molybdenum. The foils can include molybdenum. The elongated member can be disposed within the inner leads within the lamp base. The elongated member can extends along substantially the entire length of the inner leads.

Among the advantages of the invention are the following. Radiation of the lamp seal is reduced, thereby lengthening bulb life. Additional coil radiation is focused upon the substrate being processed, resulting in increased lamp efficiency. The heat shield holds the inner leads, and thus the coil, in place. By reducing the rate of mass transport, lamp life is increased.

Other features and advantages of the invention will be apparent from the following detailed description, the accompanying drawings and the claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described by way of examples with reference to the accompanying drawings.

Figure 1 shows a conventional halogen lamp for use in semiconductor processing. Figure 2 shows a lamp that includes a planar heat shield disposed between the coil and the lamp base according to an embodiment of the present invention.

Figure 3 shows a lamp that includes a heat shield having a curved reflective surface disposed between the coil and the lamp base according to an embodiment of the present invention. Figure 4 depicts a section of a conventional halogen lamp for use in rapid thermal processing of semiconductors.

Figure 5 depicts a section of another conventional halogen lamp for use in rapid thermal processing of semiconductors.

Figure 6 is a section of a halogen lamp according to the present invention for use in rapid thermal processing of semiconductors.

Like reference numbers and designations in the various figures indicate like elements.

DETAILED DESCRIPTION OF THE INVENTION

A lamp for use in semiconductor processing is described. In the following description, specific details are set forth in order to provide a thorough understanding of the invention. It will be appreciated, however, by one skilled in the art, that the invention may be practiced without these specific details. In other instances, well-known elements have not been shown in order to avoid unnecessarily obscuring the invention.

According to one embodiment of the invention, a reflective heat shield is used within the lamp bulb between the coil and the lamp base to reflect radiation generated by the coil away from the lamp base. In conventional incandescent lamps, aluminum heat shields have been used. However, these heat shields are not chemically compatible with halogen lamps. In conventional H4 automobile lamps, molybdenum reflectors have been used within the bulb to perform beam sculpting. However, these reflectors do not act as heat shields.

As shown in Figure 2, a halogen lamp 200 for use in semiconductor processing includes a bulb 202 that has a coil 204 electrically coupled between a short inner lead 206 and a long inner lead 208. Inner leads 206 and 208 are coupled to outer leads 216 by molybdenum foils 212. The inner leads, outer leads, and foils are held in place at a lamp base 210. The lamp base can be pressed together during manufacturing over the foil area to form a press seal that hermetically seals the lamp bulb. The bulb is made of quartz. Lamp 200 includes a planar heat shield 218 disposed between the coil and the lamp base. The heat shield includes a reflective surface 220 configured to reflect radiation generated by the coil away from the lamp base.

As shown in Figure 3, a halogen lamp 300 for use in semiconductor processing includes a bulb 302 that has a coil 304 electrically coupled between a short inner lead 306 and a long inner lead 308. Inner leads 306 and 308 are coupled to outer leads 316 by molybdenum foils 312. The inner leads, outer leads, and foils are held in place at a lamp base 310. The lamp base can be pressed together during manufacturing over the foil area to form a press seal that hermetically seals the lamp bulb. The bulb is made of quartz.

Lamp 300 includes a heat shield 318 having a curved reflective surface 320. The curve can be a conic section. The curved reflective surface directs the radiation of the coil in a predetermined direction. One advantage of this arrangement is that additional coil radiation can be focused upon the substrate being processed, resulting in increased lamp efficiency. Another advantage is that radiation from the coil is directed away from the lamp base, maintaining the base and press seal at a lower operating temperature. Thus, the high thermal conductivity potting compound may be eliminated while maintaining long lamp life.

In one embodiment, the heat shield is electrically non-conductive. In this embodiment, contact between the heat shield and the inner leads is permitted. The use of non-conducting heat shields overcomes the problem of arcing across the heat shield, which would otherwise require an elaborate design for use in higher voltage lamps. In one embodiment, the heat shield is made from multi-layered dielectric films supported on silica, alumina, or alkali-free alumino-silicate glass. The films are selected for maximum reflectance near the peak wavelength emitted by the coil. In another embodiment, the heat shield is fashioned from metals encased in a protective coating of alumina or silica or enclosed within a transparent envelope of silica or alkali-free alumino-silicate glass.

In various embodiments, the heat shields are held in place by bends in one or more of the inner leads, dimples formed in the lamp bulb, or using an alkali-free solder glass to attach the shield to the inner leads or the lamp bulb. During fabrication, the heat shield cam be used to center the coil within the bulb. One failure mode of such halogen lamps is corrosion of the foil in the lamp base. The rate of corrosion determines the life of the bulb according to this failure mode. The rate of corrosion is linked to the rate of mass transport within the bulb. Mass transport is the movement of material from one location to another. Chemically assisted mass transport moves material by virtue of chemical reactions, such as the conversion of a non-volatile metal to a volatile metal oxyhalide compound within a halogen lamp bulb. In the case of molybdenum foil corrosion, the mass transport involves the movement of corrosive chemicals from the area of the coil to the area of the foil and the movement of products of the corrosive reaction away from the area of the foil. When the foil corrodes sufficiently, current continuity is lost between the inner and outer leads and the lamp will not light. Also, depending upon the temperature in the lamp seal area, some solid corrosion products can build up on the foil, increase the stress in that region, and split open the hermetic seal. This causes immediate failure by oxidation of the coil and can even cause the lamp to non-passively fail (explode). Figure 4 depicts a section of a conventional halogen lamp 400 for use in rapid thermal processing of semiconductors. The lamp includes a bulb 402, and a lamp base 410 where an inner lead 406 is in electrical contact with a molybdenum foil 412. A lamp seal 411, such as a press seal or pinch seal, hermetically seals the bulb 402. An annular ; gap 414 exists between the lamp bulb walls and inner lead 406. It is through this annular gap that the mass transport to and from foil 412 occurs.

Figure 5 depicts a section of another conventional halogen lamp 500 for use in rapid thermal processing of semiconductors. The lamp includes a bulb 502, and a lamp base 510 where an inner lead 506 is in electrical contact with a foil 512. A lamp seal 511 is also provided. Inner lead 506 is helical in design, providing a central gap 514 through the coils of the inner lead. It is through the central gap that mass transport to and from foil 512 occurs in this design. In some conventional buds, a short spud is placed within the helical portion of the inner lead to prevent crushing the helical portion of the inner lead during manufacture. However, this spud is only located over the foil, and so does not significantly reduce mass transport to and from the foil. Figure 6 is a section of a halogen lamp 600 according to the present invention for use in rapid thermal processing of semiconductors. The lamp includes a bulb 602, and a lamp base 610 where an inner lead 606 is in electrical contact with a foil 612. A lamp seal 611 is also provided. Each inner lead 606, there being two, has a helical shape within the lamp base 610. An elongated member 620, such as a rod, is disposed within each inner lead, such that the gaps between the lamp bulb and the foils 612 are helical in shape. The rod can be made of tungsten, platinum, or molybdenum. The rod 620 can extend the length of the inner leads or extend only within the base region of the leads.

Mass transport from the coil region to the lamp base region occurs mainly by natural convection with some help from diffusion. The convection arises from thermal gradients set up by the coil. However, mass transport between the lamp base region and the foil itself occurs primarily by diffusion due to the much lower thermal gradients in that region and the comparatively narrow cross-sectional areas in the gaps surrounding the inner leads in the lamp base region. In addition, pressure changes within the bulb caused by lamp thermal cycling induce a force convection component that increases mass transport to and from the foil.

By providing a helical gap, the path length in the diffusion region increases the time required for materials to diffuse to and from the foil, thereby decreasing the mass transport rate. By decreasing the mass transport rate in the lamp base, the corrosive chemicals become less corrosive for two reasons. First, the chemicals have more time to react with each other to form less corrosive species. For example, the halogen in a halogen lamp is typically supplemented with an inert gas, such as argon, that is doped with bromine. Two bromine atoms will combine to form a bromine molecule. Second, the corrosive chemicals react with exposed metal along the path to form less corrosive chemicals. For example, bromine and metal combine to form metal bromide. Both of these mechanisms result in a less corrosive agent being delivered to the molybdenum foil, and consequently a slower corrosion rate of the foil and longer lamp life.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described, since modifications may occur to those ordinarily skilled in the art.

Claims

What is claimed is:

1. A halogen lamp comprising: a bulb enclosing at least one coil having a pair of inner leads; a lamp base configured to receive the inner leads; and a heat shield disposed between the coil and the lamp base.

2. The lamp of claim 1, wherein the heat shield comprises a reflective surface configured to reflect radiation generated by the coil away from the lamp base.

3. The lamp of claim 1 , wherein the heat shield is planar.

4. The lamp of claim 1, wherein the heat shield is configured to direct the radiation in a predetermined direction.

5. The lamp of claim 4, wherein the reflective surface is curved.

6. The lamp of claim 5, wherein the reflective surface is a conic section.

7. The lamp of claim 1, wherein the heat shield is electrically non-conductive.

8. The lamp of claim 1 , wherein the heat shield comprises a multilayer dielectric film supported by at least one of silica, alumina, and alkali-free alumino-silicate glass.

9. The lamp of claim 8, wherein the film has maximum reflectance near the peak wavelength emitted by the coil.

10. The lamp of claim 1 , wherein the heat shield comprises metal encased in at least one of silica, alumina, and alkali-free alumino-silicate glass.

11. The lamp of claim 1 , wherein the lamp bulb is dimpled to hold the heat shield in place.

12. The lamp of claim 1 , wherein at least one of the inner leads is bent to hold the heat shield in place.

13. The lamp of claim 1, further comprising alkali-free solder glass coupling the heat shield to at least one of an inner lead and the lamp bulb.

14. A halogen lamp comprising: a bulb enclosing at least one coil having a pair of inner leads; a lamp base enclosing the inner leads and a plurality of foils, each inner lead electrically coupled to one of the foils, wherein the inner leads have a helical shape within the lamp base; and an elongated member disposed within each inner lead, such that gaps between the lamp bulb and the foils are helical in shape.

15. The lamp of claim 14, wherein the elongated member comprises at least one of tungsten, platinum, or molybdenum.

16. The lamp of claim 15, wherein the foils comprise molybdenum.

17. The lamp of claim 16, wherein the elongated member is disposed within the inner leads within the lamp base.

18. The lamp of claim 16, wherein the elongated member extends along substantially the entire length of the inner leads.