1. Field
Embodiments of the present invention generally relate to a tubular lamp. More particularly, embodiments described herein relate to a tubular lamp for a rapid thermal processing (RTP) apparatus.
2. Description of the Related Art
RTP systems are employed in semiconductor chip fabrication to create, chemically alter, or etch surface structures on semiconductor substrates or wafers. RTP typically depends upon an array of high-intensity incandescent lamps fit into a lamphead and directed at the substrate. The lamps are electrically powered and can be very quickly turned off and on and a substantial fraction of their radiation can be directed to the substrate. As a result, the substrate can be very quickly heated without substantially heating the chamber and can be nearly as quickly cooled once the power is removed from the lamps.
Typically the lamps for RTP apparatus are single-ended lamps each having a socket for electrical contact disposed at one end of the lamp. The single-ended lamps generally are oriented vertically with respect to the substrate. In this configuration, only the end opposite the socket is directed at the substrate, while the elongated body of the lamp radiates heat in a direction that is parallel to the substrate. Typically, about half of the radiant energy from the lamp goes out towards the substrate. About half of the radiant energy from the lamp is absorbed in the lamp and in the lamphead structure. This can cause the lamp to reach much higher temperatures as compared to a lamp radiating in open space. If the lamp gets too hot, the average lamp lifetime can be substantially reduced. Heat absorbed in the lamphead can also cause the lamphead to deform. One approach to maintain the same radiation energy output while reducing the filament temperature is to increase the surface area of the filament inside the single-ended lamp, such as providing an overwind to the filament. However, it is desired to have a higher heating efficiency and lower filament temperature.
Therefore, there is a need for an improved lamp for a RTP apparatus.
Embodiments of the present invention generally relate to a tubular lamp with a coil filament having an overwind wrapped around the coil. In one embodiment, the tubular lamp has a coiled coil filament, and the coiled coil has an overwind wrapped around the coiled coil.
In one embodiment, a tubular lamp is disclosed. The tubular lamp includes a tubular envelope having a first end and a second end, and a coiled filament having a first diameter. The coiled filament extends from the first end to the second end of the tubular envelope and has an overwind having a second diameter. The tubular lamp further includes a ratio of the first diameter to the second diameter ranging from about 3:1 to about 15:1.
In another embodiment, a tubular halogen lamp for a RTP apparatus is disclosed. The tubular halogen lamp includes an envelope having a first end and a second end, and a coiled filament extending from the first end to the second end. The coiled filament has an overwind.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
Embodiments of the present invention generally relate to a tubular lamp with a coil filament having an overwind wrapped around the coil. In one embodiment, the tubular lamp has a coiled coil filament, and the coiled coil has an overwind wrapped around the coiled coil.
The lamp base 106 contains a foil 108 that is used to couple a lead-in conductor 110 to a second lead-in conductor 112. The lead-in conductors 110, 112 may be made of a material having good electrical conductivity, such as molybdenum, tungsten, nickel plated steel, or any other metal with a low electrical resistance and the ability to reliably carry high currents. Typically, for halogen lamps the lead-in conductor 112 is made of molybdenum or tungsten. For silica envelopes, the foil seal is made of molybdenum.
During the manufacturing of the tubular lamp, the lamp base 106 is pressed together over the foil area to form a press seal that hermetically seals the tubular envelope 102. In one embodiment, the sealed envelope 102 is filled with a halogen containing gas. A radiation generating filament 104, which is shown in the form of a coil, is disposed in the envelope 102 and extends an axial length of the envelope 102. The ends of the filament 104 are coupled to the second lead-in conductor 112. The filament 104 may be a resistive metal wire, such as a tungsten wire or a potassium doped tungsten wire. The electrical properties of the filament 104 can be tuned by adjusting parameters such as weight per unit length, diameter, and coiling parameters. In operation, the filament 104 can produce radiation at a wattage range of up to about 1 kW with operating voltages of about 120 V. Typically, the radiation is in the deep ultraviolet, ultraviolet, visible, or near infrared ranges.
In one embodiment, the filament 104 is a coil having an overwind wrapped around the coil. In another embodiment, the filament 104 is a coiled coil having an overwind wrapped around the coiled coil. The overwind on the coil or the coiled coil increases the surface area of the filament and as a result, the intensity of the radiation increases. Another result of the increased surface area of the filament 104 is to operate the tubular lamp 100 at a lower filament temperature while having the same radiation output.
A plurality of filament support 114 is disposed spaced apart along the filament 104 inside the envelope 102. The filament support 114 may be a thin wire connected to the filament 104 and may extend outwardly to the wall of the envelope 102 to reduce the opportunity for the filament 104 to sag. The filament support 114 is placed along the filament 104 periodically. In one embodiment, the filament support 114 is placed every 2 cm along the filament 104. The filament support 114 may be made of a resistive metal, such as tungsten. Any suitable filament support may be used as the filament support 114.
A plurality of tubular lamps such as the tubular lamp 100 with the filament 104 having the overwind 204 may be placed in a RTP apparatus. The tubular lamps 100 may be substantially parallel to the substrate. With the elongated body of the tubular lamp 100 emitting radiation towards the substrate, the substrate may be heated more efficiently compared to heating by single-ended lamps. In addition, with the horizontal orientation, the tubular lamps may radiate more directly to the substrate with little reabsorption, in contrast to a single-ended lamp which typically exhibits substantial reabsorption. The tubular lamps may be disposed in reflectors to capture radiation emitted away from the substrate, if desired.
The overwind 204 may have a smaller diameter than the primary coil 202. The ratio of the diameter of the primary coil 202 to the diameter of the overwind 204 may range from about 3:1 to about 15:1, such as between about 6:1 and about 12:1. In one embodiment, the ratio is about 10:1. The overwind 204 may have a pitch ratio between about 1.1 and about 2.0. The pitch ratio is the distance between two complete turns divide by the diameter of the overwind. In one embodiment, the pitch ratio is about 1.4.
Prolonged exposure to high temperature may “melt” the overwind 204 into the primary coil 202. However, for a process performed in a RTP chamber, such as annealing, the spike in temperature has a typical high temperature exposure of less than 1 second. Thus, a tubular lamp with an overwind such as the overwind 204 may be useful in a RTP chamber.
In summary, a tubular lamp having a coil or coiled coil filament is disclosed. An overwind is wrapped around the coil or coiled coil filament. As a result, the surface area of the filament is increased and the filament temperature is reduced while maintaining the same radiant energy output.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/788,137, filed on Mar. 15, 2013, which herein is incorporated by reference.
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