Device and method for heat treating an object

Abstract

The present invention relates to a device for heat treating an object, in particular a coated substrate, with an in particular gas-tightly sealable housing that encloses a hollow space, wherein the hollow space has a separating wall, by which the hollow space is divided into a process space for accommodating the object and an intermediate space, wherein the separating wall has one or a plurality of openings, which are implemented such that the separating wall acts as a barrier for the diffusion out of the process space into the intermediate space of a gaseous substance generated in the process space by the heat treatment of the object. The housing has at least one housing section coupled to a cooling device for its active cooling, wherein the separating wall is arranged between the object and the coolable housing section. The invention further relates to the use of a separating wall as a diffusion barrier in a device for heat treating an object as well as a corresponding method for heat treating an object.

Claims

1. Device for heat treating an object, such as a coated substrate, comprising one housing that encloses a hollow space, wherein the hollow space has a separating wall, by means of which the hollow space is divided into a process space for accommodating the object and an intermediate space, wherein the separating wall has one or a plurality of openings, which are implemented such that the separating wall acts as a diffusion barrier for a gas exchange between the process space and the intermediate space during the heat treating of the object and enables a gas exchange between the process space and the intermediate space through the separating wall before and after the heat treating of the object, wherein the housing has at least one coolable first housing section coupled with a cooling device for its active cooling, wherein the separating wall is arranged between the object and the coolable first housing section, and wherein the housing further comprises at least one second housing section which is implemented such that the object is heat treatable by means of electromagnetic thermal radiation impinging on the housing, or at least one second housing section coupled to a heating device for heating the process space, with the second housing section being different from the first housing section, wherein the first housing section has a sealable gas passage opening into the intermediate space for removing or feeding or both of at least one gaseous substance.

2. Device according to claim 1, wherein the separating wall is implemented such that a mass loss of the gaseous substance during the heat treatment is less than 50%, wherein an area ratio, formed from a total opening area of the one or a plurality of openings divided by an inner surface of the process space, is in the range from 510.sup.5 to 510.sup.4.

3. Device according to claim 1, wherein the separating wall contains a material, which has such a coefficient of thermal expansion that a total opening area of the one or a plurality of openings is reduced by heating the separating wall during the heat treatment to a maximum of 50% of a total opening area before the heat treatment.

4. Device according to claim 3, wherein the separating wall contains a material, whose coefficient of thermal expansion is greater than 510.sup.6K.sup.1.

5. Device according to claim 1, wherein the housing is made of a material, whose coefficient of thermal expansion is less than 510.sup.K.sup.1.

6. Device according to claim 1, wherein the separating wall is arranged between a warmer zone and at least one colder zone of the hollow space.

7. Device according to claim 1, wherein the housing section coupled to a cooling device is a side wall section of the housing, which includes a seal for sealing a housing opening.

8. Device according to claim 1, wherein the separating wall does not reach a housing wall, wherein an opening remains between the separating wall and the housing wall.

9. Device according to claim 1, wherein the housing is made of quartz glass.

10. Device according to claim 2, wherein a mass loss of the gaseous substance duringthe heat treatment is less than 20%.

11. Device according to claim 2, wherein a mass loss of the gaseous substance during the heat treatment is less than 10%.

12. Device according to claim 3, wherein a total opening area of the one or a plurality of openings is reduced by heating the separating wall during the heat treatment to a maximum of 30% of a total opening area before the heat treatment.

13. Device according to claim 3, wherein a total opening area of the one or a plurality of openings is reduced by heating the separating wall during the heat treatment to a maximum of 10% of a total opening area before the heat treatment.

14. Method for heat treating an object, such as a coated substrate, the method comprising: introducing an object into a hollow space of one housing, wherein the hollow space is divided by a separating wall, which has one or a plurality of openings, into a process space accommodating the object and an intermediate space, heat treating the object, wherein the separating wall acts as a barrier for the diffusion out of the process space into the intermediate space of a gaseous substance generated in the process space by the heat treatment of the object, cooling at least one housing section delimiting the intermediate space during the heat treatment of the object.

15. The method of claim 14, wherein the separating wall has such a coefficient of thermal expansion, that a total opening area of the one or a plurality of openings is reduced by heating the separating wall during the heat treatment of the object to a maximum of 50% of a total opening area before the heat treatment, wherein the separating wall contains in particular a material with a coefficient of thermal expansion of more than 510.sup.6K.sup.1.

16. Method according to claim 14, wherein the process space is pumped out by removal of at least one gaseous substance from the intermediate space and/or at least one gaseous substance is fed to the process space by introduction into the intermediate space.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now explained in detail with reference to the accompanying figures. They depict, in simplified representation not true to scale:

(2) FIG. 1 a generalized cross-sectional representation of a device for processing a coated substrate;

(3) FIG. 2 a perspective view of the device of FIG. 1 with a front seal;

(4) FIG. 3 a variant of the device of FIG. 2;

(5) FIG. 4 a generalized cross-sectional representation of a device for processing any object;

(6) FIG. 5A-5F different variants of a temperature-controlled separating wall of the device of FIGS. 1 to 4.

(7) Reference is made first to FIGS. 1 and 2, in which a generalized sectional view of a device 1 for processing an object 2 (FIG. 1), as well as a perspective view of such a device 1 with a front seal 9 (FIG. 2) is depicted. The device 1 serves, for example, for processing a substrate coated on one side for heat treating precursor layers for conversion into a compound semiconductor, in particular, a chalcopyrite compound. Although only a single substrate is depicted, the device 1 could likewise be used for processing two or more substrates. The substrate is made, for example, of glass with a thickness in the range from 1 mm to 4 mm, in particular 2 mm to 3 mm. The substrate is provided with a layer structure (not shown in detail), which consists, for example, of precursor layers of an absorber (e.g., chalcopyrite compound or kesterite compound), which must be subjected to RTP thermal processing. For example, the layer structure is a sequence of the layers silicon nitride/molybdenum/copper-indium-gallium/selenium. For example, the silicon nitride layer has a thickness in the range from 50 nm to 300 nm; the molybdenum layer, a thickness in the range from 200 nm to 700 nm; the copper-indium-gallium layer, a thickness in the range from 300 nm to 1000 nm; and the selenium layer, a thickness in the range from 500 nm to 2000 nm.

(8) The device 1 comprises here, for example, a rectangular-solid-shaped housing 3 with a housing wall 4, composed of a bottom wall 5, a top wall 6, and a peripheral side wall 7. The housing wall 4 encloses a gas-tight or evacuable hollow space 11, which is gas-tightly sealable by a removable seal 9. As depicted in FIG. 2, the housing 3 can have, for example, a front housing opening 8, which is sealable by a seal 9 mountable like a door, which forms a part of the side wall 7. Generally speaking, the housing opening 8 and the associated seal 9 can be selectively placed on any wall section of the housing wall 4. The bottom wall 5 serves in a central zone as a supporting surface for the substrate 2, with it being likewise possible also to provide corresponding spacers or support elements.

(9) The housing wall 4 of the process box 1 can be made of the same material or from materials different from each other, for example, metal, glass, ceramic, glass ceramic, carbon fiber reinforced carbon materials, or graphite.

(10) In the example illustrated in FIG. 2, the device 1 serves as a not independently heatable process box for heat treating the object 2 realized as a substrate. It is essential that at least one housing section, here, for example, the top wall 6 and the bottom wall 5 are in each case implemented such that heat treatment of the coated substrate by thermal energy fed in from the outside in the form of electromagnetic thermal radiation is possible. The thermal energy can be fed in by radiant heaters 12 arranged, for example, in rows above the top wall 6 as well as below the bottom wall 5. For example, the top wall 6 and the bottom wall 5 are made, for this purpose, from a material that is transparent or at least partially transparent to the electromagnetic radiation radiated in, for example, glass ceramic. The top wall 6 and the bottom wall 5 can also be made of such a material only in sections. It is also equally possible that the top wall 6 and the bottom wall 5 are made of a material that is suitable to at least partially, in particular completely, absorb the electromagnetic radiation in order to be heated themselves, for example, graphite. In this case, the top wall 6 and the bottom wall 5 serve as passively heated, secondary heat sources.

(11) As is discernible in FIG. 2, the housing wall 4, here, for example, the seal 9, is provided with two coolant connections 13, 13, which serve as an inlet or an outlet for coolant in a coolant line system (not shown in detail) running through the peripheral side wall 7 at least in sections, in particular completely. By means of the coolant introduced, the side wall 7 can be temperature controlled at least in sections, in particular completely, to a pre-definable temperature (actively cooled relative to the substrate temperatures during the heat treatment). The two coolant connections 13, 13 can be fluidically connected for this purpose to a temperature controlling device or cooling device 14 for preparation and cooling of the coolant. In general, in the device 1, only those housing sections that do not serve for heat treating the coated substrate are temperature controlled, by thermal energy fed in from outside in the form of electromagnetic thermal radiation, here, for example, the peripheral side wall 7 or at least a section thereof. In the present example, only the seal 9 is temperature controlled (cooled). Oil or water, for example, can be used as coolant. The temperature control or active cooling can alternatively also be obtained through contact cooling (heat conduction) through contact with heat sinks (for example, cooling plates), a blower (convection cooling) or without contact by spaced heat sinks (radiative cooling).

(12) The housing 3 further comprises a gas passage 16 provided with a valve 15 that opens into the hollow space 11. Here, the gas passage 16 is arranged, for example, in the front seal 9. The hollow space 11 can be evacuated via a gas connection 17 by connection to a pumping out device 18 (e.g., vacuum pump). Also, the gas connection 17 can be connected to a gas supply device 19 in order to purge the hollow space 11 by introduction of an inert purge gas and/or to fill it with a reactive process gas. Filling with the process gas can be done at negative or positive pressure. By means of the valve 15 (for example, a multipath valve), the gas passage 16 can be selectively opened or gas-tightly sealed. The hollow space 11 has a relatively low clear height, for example, in the range from 7 to 12 mm, in order to enable rapid evacuation and efficient filling with process gas.

(13) The hollow space 11 is divided quasi-gas-tight by a strip-shaped separating wall 20 into a process space 21 and an intermediate space 22, with object 2 implemented as a coated substrate accommodated only in the process space 21. The gas passage 16 opens into the intermediate space 22. The separating wall 20 is provided with one or a plurality of openings or breaks, by means of which the process space 21 is fluidically connected to the intermediate space 22.

(14) As is discernible in the vertical sectional view of FIG. 1, the separating wall 20, which extends vertically from the bottom wall 5 in the direction of the top wall 6, does not reach all the way to the top wall 6, such that a gap 23 remains as an opening of the separating wall 20. FIG. 2 depicts a variant of the separating wall 20 in which the separating wall 20 extends all the way to the top wall 6 and is provided with a plurality of horizontal slots 24 arranged roughly centrally in a row. Through the gap 23 or the slots 24, the process space 21 is fluidically connected to the intermediate space 22 such that a mutual gas exchange is possible but is inhibited because of the small vertical dimension or height of the gap 23 or slots 24. The separating wall 20 thus acts as a diffusion barrier or a vapor barrier between the process space 21 and the intermediate space 22.

(15) The property of the separating wall 20 to act as a diffusion barrier or a vapor barrier is based on the pressure dependency of free path length: at almost normal pressure (700-1000 mbar), the diffusion is inhibited by the relatively small opening(s) of the separating wall 20. In contrast, when the intermediate space 22 is evacuated to pressures in the pre-vacuum range (10-1000 bar), the free path length is greatly increased and the separating wall 20 then represents only a weak diffusion barrier for the gas exchange. The process space 21 can thus be pumped out through the separating wall 20 and, after the pumping out, process gas can also flow into the process space 21 via an inlet into the intermediate space 22. On the other hand, by means of the separating wall 20, the partial pressure of readily volatile chalcogen components, such as selenium or sulfur, which diffuse/evaporate out of the coated substrate during the heat treatment, can be kept at least largely constant in the process space 21 during the heat treatment of the substrate. The separating wall 20 thus acts, for example, as a selenium barrier during the heat treatment of the coated substrate.

(16) Generally speaking, a (common) opening area 25 of the gap 23 or slots 24 is dimensioned such that, during the heat treatment of the substrate, a mass loss of a gaseous substance generated by the heat treatment of the coated substrate out of the process space 21 is less than 50%, preferably less than 20%, more preferably less than 10%, of the mass of the gaseous substance generated in the process space 21 during the heat treatment. For this purpose, the separating wall 20 is implemented such that an area ratio, formed from the opening area 25 divided by an internal surface or inner surface 26 of the process space 21, is in the range from 510.sup.5 to 510.sup.4.

(17) For example, the inner surface 26 of the process space 21 has a size of ca. 1.2 m.sup.2. A mean gap height of the gap 23 is, for example, in the range from 50 to 100 m, corresponding to an opening area 25 in the range from 2 to 5 cm.sup.2. The separating wall 20 has, for example, a height of of 9 mm. These values yield an area ratio of 1.510.sup.4.

(18) By means of the separating wall 20 serving as a vapor barrier or diffusion barrier, a diffusion of volatile components developing in the process space 21 during the thermal processing into the intermediate space 22 can at least be largely suppressed such that a condensation of the volatile components on the temperature-controlled (actively cooled) side wall 7, here, specifically the seal 9, is prevented. The process atmosphere in the process space 21 can thus be kept at least approximately constant.

(19) As illustrated in FIG. 1, the intermediate space 22 is situated at least partially, in particular completely, outside a (common) radiation field of the radiant heaters 12 such that during the heat treatment a temperature gradient is formed in the intermediate space 22 from the separating wall 20 to the temperature-controlled (actively cooled) side wall 7, here, specifically the seal 9. This temperature gradient serves as a temperature barrier for protection of vacuum-compatible components of the process box 1 against high thermal stress. For this purpose, the radiant heaters 12 are arranged exclusively above or below the process space 21 in front of or up to the separating wall 20. The radiant heaters 12 end in each case at least a few centimeters in front of the intermediate space 22 or separating wall 20. On the other hand, the radiant heaters 12 are arranged such that a rising temperature gradient is formed such that a desired process temperature for heat treating the coated substrate 2 is obtained starting from the side wall 7, specifically seal 9, to the separating wall 20 in front of or at least at the level of the separating wall 20 in order to ensure an adequate conversion of the precursor layers of the substrate into compound semiconductors.

(20) In the general embodiment illustrated in FIG. 1, the separating wall 20, the intermediate space 22, and the temperature-controllable or coolable section(s) of the side wall 7 can be designed laterally in one direction, in two directions, or peripherally (frame). In the embodiment of FIG. 2, the separating wall 20, the intermediate space 22, and the temperature-controllable or coolable section of the side wall 7 (seal 9) are realized only in one spatial direction.

(21) FIG. 3 illustrates a variant of the device 1, in which only the differences relative to the device of FIGS. 1 and 2 are explained and, otherwise, reference is made to the statements concerning this.

(22) Accordingly, the device 1 is at the tempering furnace independently heatable and includes, for this purpose, a heating device 10, which, for example, is (only) accommodated in the process space 21. The heating device 10 is, for example, implemented as an electric (resistance) heater. Heating of the object 2 by radiant heater 12 is not provided. Accordingly, the housing 3 can also be made of a homogeneous material, for example, ceramic, quartz, or metal. Moreover, temperature control of the seal 9 is not provided. For example, a sensor (not shown), which should be protected from the corrosive gases of the process space by the separating wall 12, is situated in the intermediate space 22.

(23) FIG. 4 illustrates a generalized sectional representation of a device 1 according to the invention for processing any object 2, in which only the differences relative to the device of FIGS. 1 and 2 are explained and, otherwise, reference is made to the statements concerning this.

(24) Accordingly, the device 1 is used for the processing, in particular coating of any object 2. The cross-section could, for example, represent a conventional zoned furnace with a plurality of heating zones, here, for example, an inner hot core zone 28 for processing the object 2, which is surrounded by two colder edge zones 29. The warmer core zone 28 also has, accordingly, a warmer housing wall 4 than the colder edge zones 29. The device 1 comprises, here, for example, a cylindrical housing 3 as part of a tempering furnace with a heating device 10, which comprises a resistance heater (not shown) and radiant heaters 12. The separating wall 20 separates, for example, the hottest core zone 28 of the zoned furnace, in which the object 2 rests, and the edge zones 29 from each other. A temperature control of the seal 9 is not provided in the device 1 of FIG. 4.

(25) By means of the separating wall 20 serving as a vapor barrier or a diffusion barrier, diffusion of volatile components developing during the heat treatment in the core zone 28 into the edge zones 29 can be at least largely suppressed such that condensation of the volatile components on the colder housing wall 4 of the edge zones 29 is prevented.

(26) Reference is now made to FIG. 5A-5F, in which different variants of the separating wall 20 of the device 1 according to the invention are illustrated. This is in each case a temperature-controlled separating wall 20, which is, for this purpose, made of a material that has a coefficient of thermal expansion such that a total opening area 25 of the respective openings or breaks is reduced by heating the separating wall 20 during the heat treatment to a maximum of 50%, preferably a maximum of 30%, more preferably a maximum of 10%, of the starting value (total opening area 25 before the heat treatment). The separating wall 20 is made, for this purpose, of a material with a coefficient of thermal expansion of more than 510.sup.6 K.sup.1. Examples for this are certain glass ceramics with a coefficient of thermal expansion of 910.sup.6 K.sup.1, aluminum oxide (Al.sub.2O.sub.3) with a coefficient of thermal expansion in the range from 6.510.sup.6 K.sup.1 to 910.sup.6 K.sup.1, zirconium oxide and magnesium oxide with a coefficient of thermal expansion in the range from 1010.sup.6 K.sup.1 to 1310.sup.6 K.sup.1. The material of the separating wall 20 must also be temperature resistant and corrosion resistant.

(27) FIGS. 5A and 5B depict the separating wall 20 of the process box 1 implemented as a vertical strip, in each case in a vertical sectional representation. Accordingly, the separating wall 20 does not extend all the way to the top wall 6 such that the gap 23 remains as an opening for the fluidic connection of the process space 21 and the intermediate space 22. FIG. 5A depicts a situation in which the side wall 7 is temperature controlled to a temperature of T=150 C., whereas the separating wall 20 has a temperature of T=50 C. The material of the separating wall 20 is relatively cold; the gap 23 is wide open. The vertical dimension or mean gap height (clear width) of the gap 23 is in the range from 50 to 100 m with a height of the separating wall 20 of ca. 10 mm. During heating, the material of the separating wall 20 expands relatively dramatically, with the mean gap height decreasing (FIG. 5B). For example, with heating of the separating wall 20 to a temperature of T=450 C. (temperature difference 400 C.), a change in the vertical dimension of the separating wall 20 of ca. 40 m is attained such that the mean gap height of the gap 23 decreases to a value in the range from 10 to 50 m, i.e., a maximum of 50% of the starting value.

(28) In this case, it is essential that the height of the process space 21 is enlarged less by thermal expansion than the gap 23. This can, for example, be achieved in that the material of the process space 21 in FIG. 2 consists of quartz glass (coefficient of thermal expansion 5*10.sup.7/K) or another material with a coefficient of thermal expansion less than 1*10.sup.6/K. Alternatively, as depicted in the configuration of in accordance with FIG. 1, the height of the housing 3 can be kept constant by the temperature control of the sidewall 7.

(29) FIGS. 5C and 5D depict a variant with reference to a view of the separating wall 20. To avoid unnecessary repetitions, only the differences relative to FIGS. 5A and 5B are explained, and, otherwise, reference is made to the statements there. Accordingly, the strip-shaped separating wall 20 extends from the bottom wall 5 to the top wall 6, with one or a plurality of vertical gaps 23 implemented in the form of breaks of the separating wall 20. The gap width measured in the horizontal direction is in the range from 50 to 100 m (FIG. 5C). By means of a dimensioning of the separating wall region between two gaps 23 greater compared to the height of 10 m, relatively greater travel, which can, for example, amount to several 100 m, can be obtained with heating of the separating wall 20 to a temperature of, for example, T=450 C. In particular, the total opening area of the gaps 23 can be reduced to, for example, a maximum of 50% of the starting value.

(30) FIGS. 5E and 5F depict another variant with reference to a view of the separating wall 20. To avoid unnecessary repetitions, again only the differences relative to FIGS. 5A and 5B are explained, and, otherwise, reference is made to the statements there. Accordingly, a plurality of round holes 27 are provided instead of a gap 23, which are in each case implemented in the form of perforations of the separating wall 20. Starting from a situation in which the temperature of the separating wall 20 is, for example, T=150 C. (FIG. 5E), a reduction of the diameter of the opening of the round holes 37 can be obtained by means of heating the separating wall 20 to a temperature of, for example, T=450 C. (FIG. 5F). In particular, the entire opening area of the round holes 27 can be reduced to, for example, a maximum of 50% of the starting value.

LIST OF REFERENCE CHARACTERS

(31) 1 device 2 object 3 housing 4 housing wall 5 bottom wall 6 top wall 7 sidewall 8 housing opening 9 seal 10 heating device 11 hollow space 12 radiant heater 13, 13 coolant connection 14 cooling device 15 valve 16 gas passage 17 gas connection 18 pumping-out device 19 gas supply device 20 separating wall 21 process space 22 intermediate space 23 gap 24 slot 25 opening area 26 inner surface 27 round hole 28 core zone 29 edge zone