Halogen lamp assembly with integrated heat sink

A halogen lamp assembly 20 for a substrate processing chamber 100 has a halogen lamp 22 and a ceramic heat sink monolith 24. The halogen lamp 22 includes a filament 28 and a pair of electrical connectors 30 encapsulated in an envelope 26 having a pinch seal end 34. The ceramic heat sink monolith 24 includes a block 38 and an array of spaced apart posts 40 projecting outwardly from the block 38. The block 38 includes a cavity 42 that has a recessed inner surface 44 shaped to mate with the pinch seal end 34 of the lamp 22 and an opening that allows the electrical connectors 30 of the halogen lamp 22 to pass through.

BACKGROUND

The present invention relates to a halogen lamp assembly for a substrate processing chamber.

Substrate processing chambers, in which a substrate such as a semiconductor wafer or display is processed, often use halogen lamps for heating the substrate or chamber walls. Halogen lamps are incandescent lamps that typically have tungsten filaments in a halogen gas environment encapsulated in a quartz glass envelope. The envelope is constricted at the base of the lamp to form a pinch seal end about metal connectors that pass current to the filament. These lamps give off heat that is used to anneal a layer of material on the substrate, as for example, in a rapid thermal processing (RTP) chamber; or to decompose a gas to form a layer on a substrate as in an epitaxial chamber. The halogen lamps can generate the infrared heat energy quickly, controllably, and with uniform coverage, and thus they are useful for rapidly heating the substrate.

However, the heat emitted by the halogen lamp can cause failure of critical regions of the lamp and thereby reduce the lifetime of the lamp. One region of the lamp that is particularly susceptible to failure is the pinch seal end. The pinch seal end is exposed to even higher temperatures by the additional resistive heat generated from the passage of the electrical current through the connectors passing through this region. The high operating temperatures can cause the glass to metal seal to fail due to stresses arising from a mismatch in thermal coefficients of expansion of the glass, metal, and glass to metal sealing material. The heat can also cause partial oxidation or other deterioration of the metal connectors. Thus, a halogen lamp with an expected lamp life of about 2000 hours or greater for a maximum operating temperature of 300° C. at the pinch seal end, has a much shorter lifetime of about 1000 hours when the operating temperature in the pinch seal end is 350° C., and a lifetime of only about 250 hours when the operating temperature is 400° C.

Thus it is desirable to have a halogen lamp assembly with a heat sink that is capable of reducing the operating temperature of the lamp. It is also desirable to keep the pinched seal region temperatures below critical levels to reduce premature failure of the lamp. It is also desirable to remove the heat generated by the lamp during its operation without complex cooling equipment.

SUMMARY

A halogen lamp assembly for a substrate processing chamber comprises a halogen lamp and a ceramic heat sink monolith. The halogen lamp has a substantially transparent envelope with a pinch seal end, a filament in the envelope, and a pair of electrical connectors that connect to the filament and pass through the pinch seal end. The ceramic heat sink monolith comprises a block having a recessed inner surface shaped to mate with the pinch seal end of the halogen lamp, the block having an opening that allows the electrical connectors of the halogen lamp to pass through. The ceramic heat sink monolith also comprises an array of spaced apart posts projecting outwardly from the block.

In one version, the ceramic heat sink monolith also mates with a receptacle in the substrate processing chamber. In another version, the heat sink block is rectangular and a circular plate extends from the block with a hole aligned to the opening in the block. In this version, a pair of arrays of posts project outwardly from the opposing external surfaces of the block.

A substrate processing chamber uses a plurality of the halogen lamp assemblies. The substrate processing chamber also includes enclosing walls, a substrate support, a gas distributor and a gas exhaust.

DESCRIPTION

An embodiment of a halogen lamp assembly20that may be used to supply heat energy to process substrates in a substrate processing chamber is illustrated inFIGS. 1 and 2. The halogen lamp assembly20comprises a halogen lamp22and a ceramic heat sink monolith24. The halogen lamp22and ceramic heat sink monolith24described herein are illustrative exemplary embodiments and they should not be used to limit the scope of the invention.

Generally, the lamp22comprises a light transmissive envelope26that contains an internal atmosphere about a filament28and that allows electrical connectors30to pass therethrough. In the version shown, the envelope26comprises a tubular shape, a pinch seal end34and an evacuation tube36. The shape of the envelope26can also be non-tubular, including conical, spherical or multi-arcuate shapes. The envelope26comprises quartz, silica glass, aluminosilicate glass or other suitably light-transmissive materials. The internal atmosphere contained in the envelope26comprises a halogen containing gas. The evacuation tube36is used to remove or add gases to the envelope26during manufacture and is subsequently sealed.

The filament28inside the envelope26comprises two ends which are electrically coupled to the electrical connectors30. The filament28comprises a resistive metal wire, and in one version is a tungsten wire. The filament28can be a single or multiple coils or planar strips. The filament28is coupled to electrical connectors30at midpoints or endpoints of the filament28. The electrical properties of the filament28can be tuned by its weight per length, diameter, or coil pitch (period of the coil divided by the diameter of the wire). In operation, the filament28can produce radiation at a wattage range up to about 2 kilowatts with operating voltages of about 120 VAC. Typically, the radiation is in the deep ultraviolet, ultraviolet, visible, or infrared ranges.

The connectors30typically comprise metal wires or foils with good electrical conductivity, such as molybdenum wires. The connectors30may also comprise other metals, such as tungsten, nickel plated steel, or any other metal with a low electrical resistance and the ability to reliably carry high currents. In one version, the connectors30comprise first metal wires leading from the filament into the pinch seal end34, foil sheets encapsulated inside the pinch seal34connected to the first metal wires, and second metal wires connected to the foil sheets and extending away from the pinch seal34. The first and second metal wires may be directly connected to the foil sheets or connected to the foil sheets by additional wire leads welded onto the foil sheets and the first and second wires. In another version, the connectors30may comprise a single strand or multiple strands of wires connected to the filament28and passing through the pinch seal end34.

The pinch seal end34comprises the region of the envelope26which is physically constricted about the electrical connectors30as they enter into the envelope26to electrically couple an external power source to the filament28. The connectors30pass through and are held in place by the pinch seal end34. The pinch seal end34forms a hermetic seal to maintain the pressure and composition of the internal atmosphere of the envelope26. In another version, the lamp22can have two pinch seal ends34, at substantially opposite ends of the envelope26, with a single connector30passing through each pinch seal end34. In yet another version, there could be three connectors30passing through a single pinch seal end34.

The halogen lamp assembly20further comprises a ceramic heat sink monolith24, as illustrated inFIG. 1. The ceramic heat sink monolith24comprises a block38coupled directly to the pinch seal end34of the lamp22. The block38draws heat energy out of the pinch seal end34and dissipates this energy directly to the environment, through convection and radiation. The block38comprises a unitary monolith that is absent interfaces or junctions within its volume that would generate additional thermal impedances in addition to the impedance of the bulk block material. Conventional lamp assembly heat sinks often contain multiple parts that contact at interfaces which have warps, roughness, or gaps. The poor contact between the part interfaces create thermal impedances that are much higher than the impedance of the solid conduction path of the bulk material. Thus, the unitary monolith block38provides a higher thermal conductivity compared to conventional heat sink assemblies due to the absence of such interfaces within its volume.

The block38also has a cavity42that receives the pinch seal end34of the lamp22. The cavity42forms a recessed surface44that is shaped to mate with an external surface35of the pinch seal end34of the lamp22. The mating between the external surface35of the pinch seal end34and the recessed inner surface44provides a substantially conformal interface between the lamp22and the heat sink24that maximizes heat transfer rates therebetween. Conventional lamp assembly heat sinks provide inefficient heat transfer due to non-conformal mating between the heat sink and the heat-generating lamp, or due to gaps or roughness between the contacting surfaces that have high thermal impedances. Any gap present between the external surface35and the recessed inner surface44is filled with a filler material comprising a ceramic to provide a continuous thermal interface between the external surface35of the pinch seal end34and the recessed inner surface44of the ceramic heat sink monolith24.

The ceramic heat sink monolith24further comprises an array39of spaced apart posts40that project outwardly from the block38. The array39comprises a two-dimensional grid of posts40that are periodically spaced apart in both array dimensions. For example, in one version, a single array39may comprises sixty posts40arranged in 5 rows of 12 posts each. However, the array39may comprise a different total number of posts40. The exact number of rows and the exact number of posts40within each row may vary. The posts40project outwardly substantially perpendicularly from the plane from which they originate. The posts40receive heat that is generated at the pinch seal end34of the lamp22and passes conductively through the recessed inner surface of the block38. The extended posts40dissipate the heat through radiation and convention to the surrounding environment. Preferably, the posts40form a unitary monolithic extension of the block38and do not have interfaces or junctions of different materials or parts therebetween. The posts40are part of the ceramic heat sink monolith24.

In one version, a pair of arrays39of spaced apart posts40project outwardly from opposing external surfaces56a,bof the block38. The arrays39are on opposing surfaces56a,bthat are joined by side surfaces57a,b.Having arrays39of posts40projecting only from two opposing surfaces56a,ballows the halogen lamp assemblies20to be arranged close together with the side surfaces57a,babutting to one another in a ring concentric about a substrate in a chamber. This arrangement provides a high density of lamps to generate more uniform heat or greater amounts of heat without sacrificing heat dissipation.

In one version, each post40has an approximately rectangular cross-section over a post length that projects outward from the surface56of the block38. The dimensions of the rectangular cross-section may vary over the length of the post40. In one version, the posts40taper as they project outward from the block38, with the cross-sectional area of the posts40decreasing with distance from the surface56of the block38. The tapered post40increases heat conduction close to the block38from the larger cross-sectional area in contact and integral with the block38while providing more gas for efficient convection and radiation from the posts40along the projection further away from the block38. In one version, the posts40have an average cross-sectional area of about 8 mm2to about 15 mm2, an average length of about 8 mm to about 12 mm, and taper at an angle of up to about 3 degrees. In another version, the posts40comprise a ratio of average cross-sectional area to length of about 0.5 mm to about 2.0 mm.

The heat transfer from the pinch seal end34can be tuned by adjusting the size of the block38, the cross-sectional dimensions and length of the posts40, and the thermal conductivity of the ceramic material of the block38. For example, the size of the block38and the cross-sectional dimensions and length of the posts40can be selected by constructing a mathematical model based on the geometry of the heat sink monolith24and boundary value information such as expected ambient and pinch seal end temperatures. Mathematical symbol manipulation software can aid in the development of formulas that express the heat transfer from the pinch seal end34in terms of the size of the block38and the cross-sectional dimensions and length of the posts40. Another method of selecting the size of the block38and the cross-sectional dimensions and length of the posts40is to use a finite element analysis (FEA) model. An FEA model of the heat sink monolith24comprises a multitude of infinitesimally small elements that each model heat conduction, convection, and radiation within a finite area. Computing power is then used to model the behavior of the heat sink monolith24as a whole based upon the known interaction of the multitude of small elements. FEA modeling software is commercially available from sources such as the DesignSpace software package from Ansys, Inc., based in Canonsburg, Pa.

The heat sink monolith24also provides a surface51that mates with a receptacle that receives the lamp assembly20in a substrate processing chamber. In one version, the ceramic heat sink monolith24comprises a circular plate50extending from the block38and having a holes53aligned to openings in the block that allow the connectors30from the lamp to pass through the block38. Preferably, the circular plate50forms a unitary monolithic extension of the block38and there are not interfaces or junctions of different materials or parts therebetween. The circular plate50is part of the ceramic heat sink monolith24. The circular plate50allows ease of alignment of the lamp assembly20to a receptacle in a substrate processing chamber. For example, the circular plate50can be sized to fit a matching depression in a receptacle in a chamber. The circular plate50also provides a regular, flat surface that may abut in a stable manner to a surface of a receptacle. This second conformal mating surface can further enhance heat transfer by conduction through the conformal interface and into the chamber receptacle.

In one version the block38and posts40are composed of a ceramic such as aluminum oxide. The ceramic heat sink monolith24is resistant to thermal degradation and is selected to provide good thermal conductivity. For example, aluminum oxide has a relatively good thermal conductivity among ceramics, on the order of about 25 W/m·K to about 35 W/m·K. The aluminum oxide ceramic is resistant to oxidation and capable of withstanding temperatures up to about 1800° C. Alternative ceramics include aluminum nitride, silicon carbide, or silicon nitride. Aluminum nitride exhibits particularly good thermal conductivity and may also be desirable.

The halogen lamp assembly20provides excellent heat conduction and better lifetimes. The better lifetime is provided by reducing the temperature of the pinch seal end34of the lamp22. This reduces oxidation of the metal connectors30during operation. Stresses arising from thermal expansion mismatches between the thermal expansion of the envelope26and the conductive connector30which can lead to cracks and fissures in the pinch seal end34of the lamp22are also reduced. In addition, the halogen lamp assembly20can accept greater electrical loads to generate additional heat if desirable for a particular process application.

The halogen lamp22with its envelope26and related encapsulation of the filament28and connectors30within the pinch seal end34can be manufactured by conventional quartz or glass fabrication methods, which can include molding, blowing, and machining. The ceramic heat sink is attached to the lamp22to form a conformal union of the block38to the pinch seal end34. The ceramic heat sink monolith24can be fabricated by making a ceramic slurry and pouring the ceramic slurry into a mold shaped to form the block38and posts40. Alternatively, a rectangular piece of a ceramic can be machined to form the posts and block surfaces. The pinch seal end34of the halogen lamp22can be mated to the cavity42of the block38of the ceramic heat sink monolith24with a filler material comprising a ceramic therebetween to form a solid union of the halogen lamp22to the ceramic heat sink monolith24. For example, a suitable filler material can be a ceramic powder such as alumina, silica, mulite or flyash combined with a bonding material such as sodium silicate or aluminum phosphate.

The halogen lamp assemblies20can be used in a substrate processing chamber to heat substrates either during a process being performed or as a separate process.FIG. 3contains a schematic illustration of an exemplary embodiment of a substrate processing chamber100comprising a plurality of the halogen lamp assemblies20, however, the halogen lamp assemblies20can be used in other chambers and the illustrative chamber embodiment should not be used to limit this invention.

The chamber100contains enclosing walls102, a gas distributor104, and a gas exhaust106, as illustrated inFIG. 3. Upper and lower covers124,126contain the process environment. The gas distributor104comprises a gas supply108, a gas valve110, and a gas inlet112. The gas distributor can distribute both process gases to a process zone122above the substrate128or purge gases to the area below the substrate128. The gas exhaust106comprises a gas outlet114, an exhaust valve116, and a pump118. The chamber100also comprises a substrate support120to hold a substrate128in the process zone122. The substrate support120comprises support arms121to hold a support platform123onto which the substrate128is placed. The chamber100can also comprise a shaft132and a shaft motor134to rotate the substrate support120during a process cycle to promote processing uniformity.

The chamber100further comprises upper optical temperature detectors130a,bto measure the temperature on the substrate128from above and a lower optical temperature detector130cto measure the temperature on the substrate support120from below. For example, the detectors130can be infrared pyrometers. The upper and lower covers124,126are transparent to optical and infrared radiation to allow the operation of the optical temperature detectors130a,b,cand the introduction of heat energy to the substrate128and process zone122in the form of infrared radiation. The covers124,126may be fabricated from a material such as quartz.

The substrate processing chamber100has a plurality of receptacles146for receiving the halogen lamp assemblies20, which can be positioned both above and below the substrate128. For example, as illustrated inFIG. 3, a plurality of upper lamp assemblies20aare positioned above the substrate128to generate infrared radiation. The upper lamp assemblies20amay be arranged in a ring concentric to the substrate128. A plurality of lower lamp assemblies20b,care also positioned below the substrate128. In the version shown inFIG. 3, there are two sets of lower lamp assemblies: outer lower lamp assemblies20band inner lower lamp assemblies20c. The lower lamp assemblies20b,calso may be arranged in rings concentric to the substrate128. Additionally, the chamber may also have reflectors136,138,140to reflect the infrared radiation generated by the lamp assemblies20towards the substrate and substrate support. Upper lamp reflector136reflects the infrared radiation generated by the upper lamp assemblies20adownward to the substrate128. Outer lower reflector138and inner lower reflector140reflect the infrared radiation generate by the lower lamp assemblies20b,cupward to the substrate support120and substrate128.

The upper, outer lower, and inner lower lamp assemblies,20a,b,care separately controllable to provide a large degree of flexibility in controlling the uniformity and accuracy of the temperature on the substrate128and the substrate support120. For example, the outer and inner lower lamp assemblies20b,cmay be operated at differently varying power levels in order to customize the heat energy delivered to various portions of the substrate128and substrate support120.

A controller142controls a power supply144, detectors130, shaft motor134, and the plurality of lamp assemblies20a-c. The controller142typically comprises a suitable configuration of hardware and software to operate the components of the substrate processing chamber100. For example, the controller142may comprise a central processing unit (CPU) that is connected to a memory and other components. The CPU comprises a microprocessor capable of executing a computer-readable program. The memory may comprise a computer-readable medium such as hard disks, optical compact disc, floppy disk, random access memory, and/or other types of memory. An interface between a human operator and the controller can be, for example, via a display, such as a monitor, and an input device, such as a keyboard. The controller142may also include drive electronics such as analog and digital input/output boards, linear motor driver boards, or stepper motor controller boards.

Although the present invention has been described in considerable detail with regard to the preferred versions thereof, other versions are possible. Therefore, the appended claims should not be limited to the description of the preferred versions contained herein.