EP2198668A1

EP2198668A1 - Apparatus for an irradiation unit

Info

Publication number: EP2198668A1
Application number: EP08802533A
Authority: EP
Inventors: Sven Linow
Original assignee: Heraeus Noblelight GmbH
Current assignee: Heraeus Noblelight GmbH
Priority date: 2007-10-09
Filing date: 2008-09-23
Publication date: 2010-06-23
Also published as: CN101822122A; WO2009049752A1; DE102007048564A1; US20100219355A1

Abstract

The invention relates to an apparatus with a chamber (1) for irradiating at least one substrate (2), comprising a lock for introducing and removing the substrate (2), a substrate holder within the chamber, a vacuum pump (4) and at least one irradiation unit (5) for irradiating the substrate (2), wherein the irradiation unit (5) comprises at least one infrared radiator with an integrated reflector.

Description

Device for an irradiation unit

The invention relates to a device for the irradiation of at least one substrate, wherein the device has an irradiation device with at least one infrared radiator.

A variety of processes requires vacuum for optimal conditions. For this purpose, a substrate must first be introduced into the vacuum. Often a preparatory step is then inserted before the substrate is subsequently vacuum treated. Typical processes are the application of coatings to various materials by means of a wide variety of processes. The substrates used here are metal parts or even endless metal strips, glass panes, semiconductor substrates, etc. Typical coating processes are chemical vapor deposition (CVD) plasma etching, sputtering via plasma coating methods, etc.

Very often, for this purpose, the substrate must be specially conditioned during or after the introduction into the vacuum apparatus. This conditioning includes, among other things, a heating up. The heating takes place, for example, to avoid the harmful for the process or the vacuum occupancy of the surface with water molecules. For this purpose, the substrate is typically heated to temperatures between 140 ⁰ C and 300 ⁰ C, so that the water molecules can pass into the gas phase. For a number of coating processes, the achievement of a specific substrate temperature is also a prerequisite for the optimal course of the process and must be set via the conditioning.

Heating processes can also be used after a vacuum process.

Equal to all these applications is that in an at least temporally or spatially partial vacuum environment effective heating of a substrate should take place, that the efficiency of the heating by the infrared radiators used should be as high as possible, and that the Reflections of the materials involved and surfaces of the chamber and the infrared radiators contribute significantly to the efficiency and the cost of the plant itself.

In most cases, these processes are batch processes, since material has to be introduced into the process space via locks in order to keep the ambient conditions constant. An additional difficulty of such batch processes is that all substrates must leave the heating phase at the same temperature and conditioning. In most cases, the process windows of such plants are tight, so that even small deviations lead to a substrate being rejected. Nevertheless, in normal systems it still has to go through the process area in order to be discharged, resulting in considerable costs. A heating area in a vacuum process must therefore have very high heating rates in order to achieve fast cycle times, but at the same time it must be able to react very quickly in order to react flexibly to changing heating times. In particular, overheating should be avoided, as e.g. due to high thermal mass, or inertia arises.

Various prior art approaches are known for subjecting substrates to irradiation and thermal treatment. Only heating by means of radiation can be used successfully in vacuum and on sensitive surfaces.

For example, there are heating elements, which have a stainless steel tube, which is electrically heated from the inside and can reach temperatures of about 600 ⁰ C. Such metal heating elements have sufficient chemical resistance in vacuum, are inexpensive, have excellent properties for vacuum processes, but are extremely thermally inert and can not deliver high power due to the low maximum surface temperature. If oxygen is present in the vicinity of these bar heating elements at any time in the process, they start up and change their radiation behavior.

Furthermore, known from the prior art infrared radiator, consisting of a vacuum sealed quartz tube and heating conductors therein. The heating conductors are usually made of tungsten or carbon. Such infrared radiators are usually very fast in their thermal reaction, that is, the power is available quickly and can be controlled quickly, and achieve considerable radiation performance. To achieve these high radiant powers of each individual radiator, quite high voltages are required for vacuum applications. Both rod heaters, as well as infrared heaters radiate once Their performance evenly in all directions and thus achieve only an unsatisfactory process efficiency.

Furthermore, such infrared radiators in combination with external reflectors are known from the prior art. The external reflectors are usually polished sheets made of stainless steel, molybdenum or aluminum. With such external reflectors, some of the power of the radiators can be directed back to the substrate, thus increasing the efficiency. These sheets absorb some of the incident radiation and thus store large amounts of heat. Further, they often start due to residual amounts of oxygen or process gases (e.g., selenium), resulting in a great reduction of reflectivity and a strong further heating of the sheets. The consequence is also an increasing thermal inertia of the radiation source and thus of the plant, as well as a reduced efficiency.

Reflectors made of aluminum oxide (Al ₂ O ₃ ) or zirconium oxide (ZrO ₂ ) powder sintered onto the emitter tube are described in the prior art. These reflectors are applied directly to the radiator tube and can not oxidize. Such reflectors made of aluminum or zirconium oxide tend to break off and are thus a source of impurities. Because they are open-pore, they can bind large amounts of gases during cyclic operation and release them again during heating. Process gases, such as selenium, readily settle in the open pores and then destroy the reflection effect of the material. Their reflection effect is limited to typical values of 30%. They are therefore not necessarily used for the described applications.

IR emitters with reflectors made of gold are known, but can not be used because the gold reflector decomposes in a vacuum due to the low ambient pressure and the high temperature of the quartz tube of the radiator that can not be cooled by an air flow here, in no time.

In particular, in the pressure range around 1 mbar, a transition region which is reached in any vacuum lock at a time or place, it comes to voltage flashovers and destructive gas discharges when voltages of about 100 V are exceeded in conventional geometries. This limits the power or the maximum length of the heating filament of IR lamps. EP 1 228 668 A1 describes IR radiators which are introduced into additional cladding tubes of quartz glass, these cladding tubes being sealed in a vacuum-tight manner with respect to the recipient. This makes it possible for each of the individual radiators to be operated at high voltages. In principle, with sufficient cooling, a highly efficient gold reflector can also be applied to the individual radiator. Disadvantage of this device, however, is that a cooling of the individual radiator or the tube proves to be difficult, as always sets a temperature gradient in the radiator or in the cladding tube in the direction of the flowing cooling fluid (air). As a result, temperature gradients are formed in the substrate, which are undesirable and have a negative effect, or even lead to rejects.

The use of IR transparent cooling fluids for such a geometry and radiator arrangement is described in DE 10 2004 002 357. A disadvantage is the high technical complexity for the realization of an additional gas-tight, to be operated at low pressure cooling circuit.

EP 1 071 310 A1 describes a device for the homogeneous heating of silicon wafers in a vacuum. In this case, a plurality of round infrared radiators is arranged in front of an external reflector and cooled by directed air flow. The radiator and the air cooling are separated by a window relative to the actual process chamber with its substrate.

In EP 1 089 949 B1, a chamber is described in which the substrate is arranged together with the infrared radiator between two reflectors. The reflectors consist of thin sheet metal, preferably of aluminum. The cooling of the reflector is achieved in that this is blackened backwards, so that radiation can be done by a heat transfer from the reflector to the cooled wall. Additional control of the temperature of the substrate is achieved by adding a heat-conducting gas, so that in addition to the heat transfer by radiation, heat transfer via heat conduction and free convection, the heat from the substrate reflector and radiator can be dissipated to the cooled chamber wall.

The above devices all have the disadvantage that they have a large thermal inertia and thus are not necessarily suitable for the rapid heating and holding a sample at a defined temperature. The object of the invention is therefore to provide a device which avoids the disadvantages mentioned above and allows rapid heating and a subsequent long holding of the substrate at a defined temperature.

This object is already achieved with the features of the independent claim.

Advantageous developments are shown in the respective subclaims.

The device according to the invention with a chamber for the irradiation of at least one substrate comprises at least one lock for introducing and removing the substrate, a substrate holder within the chamber, a vacuum pump and at least one irradiation unit for irradiating the substrate, wherein the irradiation unit has at least one infrared radiator with an integrated reflector ,

Such a device enables the chamber to be made substantially smaller than the hitherto known chambers, since the infrared radiator is already provided with an integrated reflector, and thus can be dispensed with an external reflector and counter reflector, which usually take up a lot of space.

It has also been shown that the use of such a radiator in such a chamber results in that the chamber can be better formed with respect to their thermal reaction rate and thus better results when irradiating the substrate can be achieved. Also, with such a radiator heating and cooling with the device according to the invention allows and at the same time the thermal inertia is minimized.

In this case, each chamber which is suitable for receiving and thermally treating a substrate, as described, for example, in EP 1089 949 B1, can serve as a chamber.

It has been shown that it is advantageous if the reflector consists of a material which, at least in the dense state, is broadband-band transparent, in particular for radiation in the near and middle infrared, but is formed as an opaque material. This reflector has particularly high reflectivity and has very good properties in terms of mechanical stability and vacuum compatibility.

It is also advantageous if the reflector has a closed-pored structure. It is advantageous if a coating is applied to the back of the infrared radiator and the coating has a high absorption in the far infrared range. It has been shown that a coating comprising quartz glass is particularly suitable for this purpose.

This material has a very high temperature resistance.

A device according to the invention results in that, for example, the cooled vacuum chamber is designed as the only additional reflector of the device.

This in turn contributes to material savings and thus to a cost reduction.

The reflector described above is thus optimally suited for use in a vacuum chamber, since it is highly efficient and suitable for vacuum. It also has a minimal tendency to emit gases, as it can absorb almost none.

In the device according to the invention has also been shown that startup and / or oxidation tion of such a chamber can be avoided because there are no components that are present at a temperature at which they can start or oxidize.

It is advantageous if the radiator is removable from the chamber.

The invention will be explained in more detail below with reference to a preferred embodiment and with reference to the accompanying figures.

It shows in a schematic representation:

Figure 1 shows the axial radiation behavior of a typical IR radiator with AI2O3 coating.

Figure 2 shows the axial radiation behavior of typical short-wave IR emitters for different types of reflectors.

FIG. 3 shows the axial radiation behavior of typical carbon IR radiators for different reflector types. FIG. 4 shows a device according to the invention.

FIG. 5 shows a further development of the device according to the invention

In order to be able to evaluate the radiation behavior of reflector types, a device was used which detected by means of a thermopile sensor broadband the entire incoming radiation power. This sensor is guided in a circle around the radiator axis and thus a measured value is recorded every 5 °. The measurements are carried out in air. From these measurements, a reflectivity R of the reflector can also be calculated during operation, which is defined as

D _ ₁ _ * _ reflector is total groove _Σ _l e ⁿ total total total Re flektnr Nulzseite

where / _TOTAL, the total emitted intensity and / _{«EFLE / ct} o _r emitted from the reflector side intensity summed over the respective measurements; n _total , the number of total measurements and n _Ref , _{eMor is} the number of measurements on the reflector side. iN _υ t _zΣ eite is the summed intensity and n _Nutzseιte the number of measuring points on the useful side.

FIG. 1 shows the measurement result for a commercial halogen round tube emitter with 180 ° coating of the tube with sprayed-on Al ₂ O ₃ powder as IR reflector. The reflectivity for this data is 32% and is even lower in vacuum, where the AI ₂ O ₃ is hotter due to lack of convective cooling. The coating is arranged in the picture above.

In FIG. 2, a number of reflector types are compared for mechanically more stable twin-tube radiators, with tungsten always being used as the heating filament.

The lines reflect the measurement result for different reflector types: Line 21: -> a twin tube without reflector Line 22: -> a stainless steel reflector Line 23: -> an aluminum reflector

Line 24: -> a reflector according to the invention on a twin pipe line 23: -> a reflector according to the invention on a twin pipe and in front of an aluminum reflector. Twin pipe refers to an IR lamp without reflector. Such a spotlight was then measured before a new high-gloss stainless steel reflector and new high-gloss aluminum reflector, in which case only over 180 ° in front of the reflector could be measured. Furthermore, an irradiation unit with a spotlight and a reflector over 360 °, as well as an irradiation unit with a spotlight and a reflector in front of a new high-gloss aluminum reflector were measured. All reflector layers are mounted in the picture above between 3 o'clock and 9 o'clock.

The reflectivities are 50% for the pure stainless steel 22, 61% for aluminum 23, 74% for the reflector of the irradiation unit according to the invention 24 and 87% for the reflector and aluminum irradiation unit according to the invention 25. It was in the 180 ° measurements respectively l used _together from the measurement without reflector. The reflectivities of the metallic reflectors are smaller than the theoretical values, since a considerable portion of the radiation is reflected back onto the radiator.

In FIG. 3, a number of reflector types are compared for mechanically more stable twin tube radiators, carbon being used as heating filament.

The lines reflect the measurement result for different reflector types:

Line 31: -> a twin tube without reflector

Line 32: -> a stainless steel reflector

Line 33: -> an aluminum reflector

Line 34: -> a reflector according to the invention on a twin pipe

Line 33: -> a reflector and aluminum reflector according to the invention.

Twin pipe refers to an IR lamp without reflector. Such a spotlight was then measured before a new high-gloss (stainless steel) reflector and new high-gloss (aluminum) reflector, in which case only over 180 ° in front of the reflector could be measured. Furthermore, an irradiation unit with a spotlight and with a reflector over 360 °, as well as an irradiation unit with a spotlight and with a reflector in front of a new high-gloss (aluminum) reflector was measured. All reflector layers are mounted in the picture above between 3 o'clock and 9 o'clock.

The reflectivities are 61% for pure stainless steel 32, 63% for aluminum 33, 64% for the reflector of the irradiation unit 34 according to the invention and 91% for the reflector and aluminum of the irradiation unit 35 _{according to} the invention. In the case of the 180 ° measurements, the _{total length} of the measurement without reflector was used. The reflectivities of the metallic reflectors are smaller than the theoretical values, since a considerable portion of the radiation is reflected back onto the radiator.

Since most of the substrates have an angle dependence of the reflectivity and this increases for flat angles, only the contributions arriving at an angle of approximately 45 ° to the normal to the substrate are available for effective heating. For this reason, the irradiation unit with a radiator and with a reflector as described in the invention are even more effective, since they not only have a much higher efficiency, such as new external reflectors, but even limit the radiation primarily on the process-relevant angle range.

Application example 1

FIG. 4 shows a device according to the invention in cross section. In a vacuum chamber 1, a substrate 2 is conveyed forward by means of suitable devices 3 on rollers perpendicular to the image plane. The loading sluice, as well as other process chambers are not shown. The gas pressure within the chamber 1 is controlled by means of suitable pumps 4 with closed lock to the atmosphere. The irradiation unit with a radiator 5 with a reflector layer 6 are arranged above the substrate 2. In the entire wall of the chamber cooling channels 7 are introduced, which allow to keep the chamber wall at a constant temperature. The interior walls of the chamber are made of bare, preferably polished metal (aluminum or stainless steel). For this purpose, the finished chamber 1 is finally processed from the inside. The thus equipped chamber 1 is extremely easy to manufacture and very accessible, since only vinous components are arranged in their interior. At the same time it has a very high efficiency in the heating, since almost no radiation primarily reaches and heats the chamber wall or other built-in components. The chamber wall retains its relatively high reflectivity (> 65%, depending on the material and the radiator), as it is cooled and can not start. As well as the radiator 5 itself almost no masses are present in the chamber 1, which must be heated or cooled, the entire apparatus is thermally very nimble. The emitters consist almost exclusively of quartz glass, that has a mass of 2.2 g / cm ³ , or the reflector according to the invention, which has a density of approximately 1.75 g / cm ³ . Typically, from a material thickness of 3 mm, the substrate 2 itself thermally the laziest part of the apparatus, this is so desired. FIG. 5 shows a device according to the invention in which the radiation cooling between the radiator 5 and the chamber 1 as well as the substrate 2 has been optimized. For this purpose, the two large surfaces 9 have been additionally coated with a transparent or translucent layer 8, which shows similar absorption properties, such as quartz glass. Thus, the useful radiation is reflected in the range between 400 nm and 4000 nm substantially back into the chamber 1, since the layer 8 transmits the radiation to the metallically reflecting chamber wall, at the same time, however, the radiation occurring at higher wavelengths effectively from the chamber through the layer 8 absorbed.

Claims

Device for an irradiation unit Claims

1. A device with a chamber for irradiation of at least one substrate comprising at least one lock for introducing and removing the substrate, a substrate holder within the chamber 'a vacuum pump and at least one irradiation unit for irradiating the substrate, characterized in that the irradiation unit with at least one infrared radiator includes integrated reflector.

2. Apparatus according to claim 1, characterized in that the reflector is formed of a broadband in the visible and infrared transparent, but opaque executed material.

3. Device according to one or more of the preceding claims, characterized in that the material of the reflector in the non-opaque state in the wavelength range of 780 nm to 2200 nm, preferably from 400 nm to 2700 nm and more preferably from 400 nm to 5000 nm is transparent ,

4. Device according to one or more of the preceding claims, characterized in that on the back of the infrared radiator, a coating is applied.

5. Device according to one or more of the preceding claims, characterized in that the coating has a high emissivity in the far infrared range.

6. Device according to one or more of the preceding claims, characterized in that the coating comprises quartz glass.

7. Device according to one or more of the preceding claims, characterized in that the reflector is designed as a vacuum suitable reflector.

8. Device according to one or more of the preceding claims, characterized in that the infrared radiator is removable from the chamber.

9. Device according to one or more of the preceding claims, characterized in that the chamber has a wall which is formed as a reflector.

10. Device according to one or more of the preceding claims, characterized in that the radiator is removable from the chamber.

1 1. A device according to one or more of the preceding claims, characterized in that at least parts of the inner chamber wall are provided with a transparent or translucent layer in the far infrared above

2200 nm, preferably 2700 nm and more preferably above 5000 nm has a high absorption.

12. The device according to one or more of the preceding claims, characterized in that the coating of the chamber wall consists essentially of glass, quartz glass or Al ₂ O ₃ .

13. Device according to one or more of the preceding claims, characterized in that the substrate can be moved automatically in the chamber before or during the irradiation.

14. The device according to one or more of the preceding claims, characterized in that the infrared radiators are arranged so that a homogeneous distribution of the penetrating into the substrate and the substrate-heating radiation over the surface of the substrate is achieved.