Patent Application
20120062097
The invention relates to a high-pressure discharge lamp according to the preamble to claim 1.
Such lamps have a discharge vessel filled with a discharge medium, for example, a noble gas—with or without the addition of mercury and any other additional fillings. Two electrodes are arranged facing each other inside the discharge vessel. Two piston shafts are arranged on the discharge vessel, via which current feed elements are fed in a gastight manner to the outside for electric contact. For lamp types operated with direct current, the anode is usually designed with an electrode head with high thermal resistance, in which the radiated heat power is optimized by adequate dimensioning. In contrast, the electrode on the cathode side is designed with a comparatively small, conical electrode head.
High-pressure discharge lamps which emit UV radiation are used for the patterning (lithography) of semiconductors. Suitable mercury vapor short-arc discharge lamps from OSRAM are sold under the product name HBO®. To increase productivity, the semiconductor industry requires powerful discharge lamps which emit UV radiation in the region of the mercury i-line at 365 nm. In operation such discharge lamps may not as a rule exceed a line width (FWHM) of approx. 2.5 nm, so that to increase the radiation intensity the mercury density of the filling cannot simply be increased. This in turn means that the lamp voltage applied to the electrodes cannot be significantly increased either.
One possibility for significantly increasing the radiated power is therefore to increase the lamp current and thereby the electric power for connection purposes. In particular, in the case of HBO IC lamps and an effective supply current of more than 220 A, the sealing elements (e.g. sealing films) become very warm (Joule heat loss). An effort is made to reduce the thermal load of the large anode by diverting part of the heat via the current feed and the supply line on the anode side.
The electrodes are each connected to the respective supply lines via an electrode rod, several molybdenum sealing films and an outer current feed which penetrates the piston shaft on the front side, as a rule the supply on the anode side being via a flexible supply line which extends from the lamp axis in an approximately radial direction. The contact on the cathode side is as a rule via a base pin which projects from the base on the cathode side.
In particular, the base on the anode side requires efficient cooling in the case of high-wattage, high-pressure discharge lamps with currents of more than 220 A because as a result of the Joule heat of the sealing films and as a result of the heat conducted by the electrode and also as a result of the heat radiation in a lamp housing (e.g. with lithography use) possibly reflected back, it is heated very intensely. The outer current feed components, which are in direct contact with the ambient atmosphere, can in this case oxidize at temperatures of more than 300° C. during operation of the lamp and then lead to the failure of the discharge lamp.
To improve cooling a solution is shown in WO 2007/000141 A1 in which the base is designed with cooling fins on the anode side in order to expand the heat exchange surface. With such a solution, there is also the problem that the thermal contact between the base and the outer current feed is only made indirectly by welding the supply line to the outer current feed on the one hand and to the base on the other hand. I.e. the section of the supply line between the outer current feed and base wall represents a kind of heat bridge, the size of which on account of the length of the supply line between power supply and base peripheral wall and the small supply cross-section is too small, however, to ensure adequate heat dissipation from the outer current feed to the base. I.e. even in the case of a base with heat fins, on account of the poor thermal contact between outer current feed and base, overheating is not ruled out.
In contrast, the object of the invention is to create a high-pressure discharge lamp in which thermal problems are reduced. An additional aspect of the invention is to be able to ensure operating currents of more than 220 A.
This object is achieved by a high-pressure discharge lamp with the features of claim 1. Particularly advantageous embodiments of the invention are described in the dependent claims.
According to the invention the high-pressure discharge lamp has two electrodes which are arranged facing each other in a discharge vessel and are each in electric contact via a current feed system (internal current feed, gastight current feed and outer current feed). The current feed systems each penetrate a piston shaft attached in a gastight manner to the discharge vessel, on which a base can be arranged, there being a cooling element in the area of the outer current feed of at least one piston shaft. According to the invention this cooling element and the outer current feed are in direct thermal and electric contact. I.e. contact does not take place—as in the prior art—via a bridge formed by a supply section but extensively by means of the corresponding design of the outer current feed and of the cooling element.
In this way it is possible to dissipate a sufficient heat flow via the outer current feed and the cooling element to the surroundings so that overheating and thus oxidation of the components of the current feed system can be prevented.
In a preferred exemplary embodiment the cooling element is designed as a base so that the high-pressure discharge lamp has a very simple construction and furthermore optimum heat dissipation is ensured by direct thermal and electrical contact between outer current feed and base/cooling element.
Heat dissipation can be improved if the cooling element is designed with geometry which expands the heat exchange surface. This can, for example, be by means of cooling fins which preferably extend in a radial direction.
It is preferred if the diameter of the cooling fins tapers away from the piston shaft in order to avoid shadowing effects in an imaging device as far as possible.
In such a variant the diameter can be reduced in such a way that a conical cooling fin structure is produced in the lateral view.
In a particularly simple exemplary embodiment the outer current feed and the cooling element are designed as one piece made from a single component.
In this variant the best possible heat transfer and thus efficient cooling is guaranteed. In order to remedy manufacturing disadvantages of such an embodiment, direct contact between heat sinks and outer current feed can take place in an appropriate way by means of clamping, pressing, bolting, welding or the like. The advantages of a welded version correspond to those of a one-piece embodiment, wherein various materials can be used for current feed and cooling element when welding.
In an additional embodiment the cooling element is made of multiple parts, wherein the cooling element parts together form a receptacle which an end section of the outer current feed penetrates.
To improve the contact a thermal compound or the like can be arranged in the transition area between the cooling element and the outer current feed.
In a compact exemplary embodiment the base on the anode side surrounds the assigned piston shaft.
The invention is explained in more detail below with reference to preferred exemplary embodiments as follows:
The invention is described below on the basis of an HBO® mercury vapor high-pressure discharge lamp which is used, for example, in microlithography to produce semiconductors. As mentioned at the beginning, the invention is not restricted to such types of lamp however. Rather, the advantages according to the invention also appear in other discharge lamps, for example, in xenon short-arc lamps (OSRAM XBO®). In a xenon short-arc lamp, a discharge arc burns in an atmosphere of pure xenon gas (or xenon gas mixture) under high pressure. XBO lamps are used, for example, in traditional and digital film projection.
The highly schematic representation according to
The electrode 18 forming one cathode is designed with an approximately conical electrode head, while the electrode 16 forming an anode 16 is approximately barrel-shaped or cylindrical with much larger dimensions. Both electrodes 16, 18 are each held by electrode rods 20, 22 which penetrate the respectively assigned piston shaft 9, 10 and have a molybdenum plate 24 on their end section which is connected to the piston shafts 9, 10 with gastight, melted molybdenum films 26. Their end sections are in turn connected to a contact plate 28 which is connected to a rod-shaped current feed 30 projecting from the piston shaft, which is in electric and thermal contact on the anode side with a supply line 32. The contact plate 28 and rod-shaped current feed 30 are designed in one piece here and together form the outer current feed. On the cathode side contact is via a base pin which is not visible in the diagram according to
The reflector 4 (only indicated here) consists, for example, of quartz glass with a reflective coating.
As mentioned at the beginning, in conventional solutions the supply line 32 is welded to the rod-shaped current feed 30 and is also in contact with a base sleeve so that heat transfer from the outer current feed to the base is determined by the cross-section of the supply line 32. According to the invention the cooling base 12 on the other hand is in direct contact with the rod-shaped current feed 30.
Details of this construction are explained on the basis of
In the exemplary embodiment shown the cooling base 12 is designed in two parts, wherein the junction plane lies in the drawing plane so that the entire cooling base 12 is composed of two cooling base halves which are bolted together. The bolt holes 36 provided for bolting are visible in the diagram according to
To improve the heat exchange surface with the surroundings, on the outer circumference of the cooling base 12 there are a large number of cooling fins 40 extending in a radial direction, the external diameter of which tapers upwards away from the piston shaft 9, i.e. in the diagram according to
For exact positioning on the front side 34 of the piston shaft 9, in the transition region with the centering flange 42 there is a surrounding annular groove 44 on the cooling base 12 so that this is only positioned on the front face 34 of the piston shaft 9 with a hub-shaped boss 46.
In
In the aforementioned exemplary embodiment the cooling base 12 is designed in several parts. The advantage of such a variant, which for example, is assembled by means of bolts 15, lies in the simpler processing of the discharge lamp when melting down the electrodes, as the base can then be put on after this procedure and therefore does not impede melting down.
A further advantage of the embodiment shown in
The material of the cooling base 12 is selected with regard to the thermal and electric contact, wherein outer current feed 28, 30 and cooling base 12 may consist of different materials. Of course, the shape of the cooling fins 40 may also be appropriately adjusted to the respective application.
The invention discloses a high-pressure discharge lamp having two electrodes arranged in a discharge vessel. Two piston shafts are arranged on the discharge vessel, wherein a current feed system for the electrodes penetrates said shafts. According to the invention, the outer current feed on the anode side is in direct thermal contact with a cooling element.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 021 524.7 | May 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/55328 | 4/22/2010 | WO | 00 | 11/15/2011 |
