METHOD FOR CONTROLLING A FLUX DISTRIBUTION OF EVAPORATED SOURCE MATERIAL, DETECTOR FOR MEASURING ELECTROMAGNETIC RADIATION REFLECTED ON A SOURCE SURFACE AND SYSTEM FOR THERMAL EVAPORATION WITH ELECTROMAGNETIC RADIATION

Abstract

The present invention relates to a method for controlling a flux distribution (30) of evaporated source material (20) in a system (10) for thermal evaporation with electromagnetic radiation (120), wherein the system (10) comprises an electromagnetic radiation source (110) for providing an electromagnetic radiation (120), a vacuum chamber (12) containing a reaction atmosphere (16) and a detector (40) for measuring electromagnetic radiation (120), wherein a source material (20) and a target material (18) to be coated are arranged in the vacuum chamber (12) and the radiation source is arranged such that its electromagnetic radiation (120) impinges at an angle, preferably at an angle of 45°, on a source surface (22) of the source material (20) for a thermal evaporation and/or sublimation of the source material (20) below the plasma threshold, and wherein the detector (40) for measuring electromagnetic radiation (120) is arranged such that electromagnetic radiation (120) reflected on the source surface (22) reaches the detector (40). Further, the present invention relates to a detector (40) for measuring electromagnetic radiation (120), the detector (40) preferably suitable for a method according to the present invention, and additionally to a system (10) for thermal evaporation with electromagnetic radiation (120) suitable for the method according to the present invention.

Claims

1-30. (canceled)

31. Method for controlling a flux distribution of evaporated source material in a system for thermal evaporation with electromagnetic radiation, wherein the system comprises an electromagnetic radiation source for providing an electromagnetic radiation, a vacuum chamber containing a reaction atmosphere and a detector for measuring electromagnetic radiation, wherein a source material and a target material to be coated are arranged in the vacuum chamber and the radiation source is arranged such that its electromagnetic radiation impinges at an angle, on a source surface of the source material for a thermal evaporation and/or sublimation of the source material below the plasma threshold, and wherein the detector for measuring electromagnetic radiation is arranged such that electromagnetic radiation reflected on the source surface reaches the detector, the method comprising the following steps: a) defining a desired distribution of a flux of source material evaporated from the source surface and an impinging distribution of electromagnetic radiation required for the desired distribution, b) determining an expected distribution of electromagnetic radiation reflected on the source surface based on the desired distribution and the impinging distribution of step a), c) providing electromagnetic radiation with the required impinging distribution defined in step a) by the electromagnetic radiation source, d) measuring electromagnetic radiation reflected on the source surface by the detector, e) determining a measured distribution of electromagnetic radiation reflected on the source surface based on the measurement data of step d), f) determining differences between the expected distribution determined in step b) and the measured distribution determined in step e), g) redetermining the required impinging distribution of electromagnetic radiation provided by the electromagnetic radiation source to minimize the differences determined in step f), and h) providing electromagnetic radiation with the required impinging distribution redetermined in step g) by the electromagnetic radiation source.

32. Method according to claim 31, wherein the desired distribution defined in step a) comprises a time dependency.

33. Method according to claim 31, wherein the expected distribution in step b) is determined by calculating the expected distribution and/or experimentally measuring the expected distribution and/or empirically estimating the expected distribution.

34. Method according to claim 31, wherein steps d) to h) are repeatedly carried out.

35. Method according to claim 31, wherein as the electromagnetic radiation light with a wavelength between 100 nm and 1400 nm is used.

36. Method according to claim 31, wherein in step e) and/or f) a response function of the detector is considered.

37. Method according to claim 31, wherein in step f) a size and/or shape of the expected distribution and the measured distribution are used for determining the differences.

38. Method according to claim 31, wherein the electromagnetic radiation source comprises two or more emitter sections, whereby in step c) and h) each emitter section provides electromagnetic radiation impinging on the source surface, and wherein the system respectively comprises two or more detectors, each detector being accordingly arranged to measure electromagnetic radiation provided by one of the emitter sections and reflected on the source surface.

39. Detector for measuring electromagnetic radiation reflected on a source surface, comprising a sensor element with an absorption body, the absorption body comprising an absorption surface for at least partly absorbing the electromagnetic radiation, wherein the sensor element further comprises a heat sensing element for measuring a temperature of the absorption body for detecting an absolute temperature and/or a temperature change caused in the absorption body by the absorbed electromagnetic radiation, wherein the heat sensing element comprises a temperature sensor arranged in a bore in the absorption body, wherein the bore ends within the absorption body.

40. Detector according to claim 39, wherein the detector is usable in a method for controlling a flux distribution of evaporated source material in a system for thermal evaporation with electromagnetic radiation, wherein the system comprises an electromagnetic radiation source for providing an electromagnetic radiation, a vacuum chamber containing a reaction atmosphere and a detector for measuring electromagnetic radiation, wherein a source material and a target material to be coated are arranged in the vacuum chamber and the radiation source is arranged such that its electromagnetic radiation impinges at an angle, on a source surface of the source material for a thermal evaporation and/or sublimation of the source material below the plasma threshold, and wherein the detector for measuring electromagnetic radiation is arranged such that electromagnetic radiation reflected on the source surface reaches the detector, the method comprising the following steps: a) defining a desired distribution of a flux of source material evaporated from the source surface and an impinging distribution of electromagnetic radiation required for the desired distribution, b) determining an expected distribution of electromagnetic radiation reflected on the source surface based on the desired distribution and the impinging distribution of step a), c) providing electromagnetic radiation with the required impinging distribution defined in step a) by the electromagnetic radiation source, d) measuring electromagnetic radiation reflected on the source surface by the detector, e) determining a measured distribution of electromagnetic radiation reflected on the source surface based on the measurement data of step d), f) determining differences between the expected distribution determined in step b) and the measured distribution determined in step e), g) redetermining the required impinging distribution of electromagnetic radiation provided by the electromagnetic radiation source to minimize the differences determined in step f), and h) providing electromagnetic radiation with the required impinging distribution redetermined in step g) by the electromagnetic radiation source.

41. Detector according to claim 39, wherein the absorption surface absorbs light with a wavelength between 100 nm and 1400 nm.

42. Detector according to claim 39, wherein the absorption body comprises a cooling system for an active cooling of the absorption body, whereby the cooling system comprises at least one cooling duct within the absorption body for a flow of coolant through the absorption body.

43. Detector according to claim 39, wherein the absorption body comprises metal.

44. Detector according to claim 39, wherein the absorption body encloses at one end a hollow absorption volume, whereby the inner sidewalls of the absorption volume form the absorption surface and wherein the absorption volume comprises an absorption orifice, whereby the absorption orifice can be aligned to an assumed and/or determined impinging direction of the electromagnetic radiation to be measured.

45. Detector according to claim 39, wherein the detector comprises an aperture with an aperture opening, wherein the aperture is arranged upstream with respect to the sensor element along the assumed and/or determined impinging direction of the electromagnetic radiation to be measured.

46. Detector according to claim 39, wherein the detector comprises two or more sensor elements, whereby the two or more sensor elements are adjacent to each other and thermally decoupled.

47. Detector according to claim 46, wherein the two or more sensor elements are arranged in a rotationally symmetric pattern or in rows or in a matrix in a plane perpendicular or at least essentially perpendicular to the assumed and/or determined impinging direction of the electromagnetic radiation to be measured.

48. Detector according to claim 46, wherein, in a plane perpendicular or at least essentially perpendicular to the assumed and/or determined impinging direction of the electromagnetic radiation to be measured, the two or more sensor elements comprise one of the following shapes: rectangle square circle circular ring circular ring segment.

49. Detector according to claim 39, wherein the detector comprises arrangement elements for arranging the absorption body at a vacuum feedthrough.

50. System for thermal evaporation with electromagnetic radiation, comprising an electromagnetic radiation source for providing an electromagnetic radiation, a vacuum chamber containing a reaction atmosphere and a detector for measuring electromagnetic radiation, wherein a source material and a target material to be coated are arranged in the vacuum chamber and the radiation source is arranged such that its electromagnetic radiation impinges at an angle on the source surface of the source material for a thermal evaporation and/or sublimation of the source material below the plasma threshold, wherein the detector for measuring electromagnetic radiation is arranged such that electromagnetic radiation reflected on the source surface reaches the detector, wherein the system is adapted to carry out a method according to claim 31.

Description

[0080] The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings. There is shown:

[0081] FIG. 1 A system according to the present invention,

[0082] FIG. 2 A first possible embodiment of the detector according to the present invention,

[0083] FIG. 3 An absorption body with an absorption volume,

[0084] FIG. 4 An embodiment of the detector according to the present invention with two sensor elements,

[0085] FIG. 5 Arrangement patterns of sensor elements,

[0086] FIG. 6 A flux of evaporated source material from a flat source surface,

[0087] FIG. 7 A flux of evaporated source material from a concave source surface,

[0088] FIG. 8 A flux of evaporated source material from a convex source surface,

[0089] FIG. 9 Tilting of a melted drop of source material,

[0090] FIG. 10 Behavior of the melted drop with two impinging electromagnetic radiations,

[0091] FIG. 11 Possible arrangement of three radiation emitters, and

[0092] FIG. 12 Sweeping of the target by adjusting two beams of impinging electromagnetic radiation.

[0093] In FIG. 1, the main components of a system 10 for thermal evaporation of source material 20 with electromagnetic radiation 120 according to the present invention are shown. The source material 20 is arranged within a vacuum chamber 12, whereby the vacuum chamber 12 confines a reaction atmosphere 16. The vacuum chamber 12 itself is only indicated next to a vacuum feedthrough 14. At one of the vacuum feedthroughs 14 an electromagnetic radiation source 110 is arranged, at the other a detector 40 according to the present invention.

[0094] During operation of the system 10, the electromagnetic radiation source 110 provides electromagnetic radiation 120 directed and impinging on the source surface 22 of the source material 20. The source material 20 absorbs a fraction of the electromagnetic radiation 120 and therefore some of the source material 20 evaporates or sublimates, indicated in FIG. 1 by the dashed circular line. Opposite to the source material 20, a target material 18 is arranged. The evaporated source material 20 reaches the target material 18 and forms a coating on the surface of the target material 18.

[0095] The remaining fraction of the electromagnetic radiation 120 is reflected on the source surface 20. As the emitting direction of the electromagnetic radiation source 110 and the position and general orientation of the source surface 22 are known, it is possible to arrange a detector 40 in the assumed and/or determined impinging direction 122 of the reflected electromagnetic radiation 120. As already described for the electromagnetic radiation source 110, also the detector, in particular its absorption body 52, can be arranged at a vacuum feedthrough 14 of the vacuum chamber 12.

[0096] The detector 40 according to the present invention acts as a bolometer. The electromagnetic radiation 120 impinges onto the absorption surface 60 of the absorption body 52 and gets absorbed at least partly. As depicted, the absorption surface 60 faces the source surface 22 and hence also gets coated by evaporated source material 20, indicated in FIG. 1. Hence, after a short build up time, the absorption surface 60 comprises the same or at least similar absorption and reflection properties as the source surface 22.

[0097] The aforementioned energy deposit into the absorption body 52 causes a change in temperature of the absorption body 52 or at least a rise of a demand for cooling. By measuring the temperature or its changing behavior, an evaporation rate and/or a flux distribution of the source material 20 evaporated or sublimated by the impinging electromagnetic radiation 120 can be determined.

[0098] FIG. 2 depicts a cross-section of a possible embodiment of detector 40 according to the present invention. The detector 40 comprises a single sensor element 50 with an absorption body 52, preferably consisting of a metal with high thermal conduction like copper or aluminum. An arrangement element 40 allows arranging the absorption body 52 at a vacuum feedthrough 14 of the vacuum chamber 12 of the system 10 according to the present invention. In particular, the arrangement element 42 comprises positioning elements 44 to alter the actual position of the absorption body 52 within reaction atmosphere 16 of the vacuum chamber 12. A movement of other elements of the system 10 arranged in the vacuum chamber 12 as for instance the source material 20, see FIG. 1, can therefore be provided without any hindrance caused by the detector 40.

[0099] The detector 40 according to the present invention is based on the principle of a bolometer. Electromagnetic radiation 120 impinges onto an absorption surface 60 of the absorption body 52 and gets absorbed at least partially. This energy deposit can be measured by measuring the absolute temperature or a change of the temperature of the absorption body 52.

[0100] For this, in the depicted detector 40 according to the present invention two different measurement methods and respective sensing elements 70 are implemented. The respective methods can be used separately to measure the temperature or its change. However, higher accuracy can be provided by combining the two methods described in the following.

[0101] For the first method, a temperature sensor 74, preferably a thermocouple element 76, is arranged in a bore 54 of the absorption body 52, in particular in the vicinity of the absorption surface 60. As mentioned above, the energy deposited by the electromagnetic radiation 120 impinging on the absorption surface 60 causes a rise in temperature of the absorption body 52. The thermocouple 76 located within the absorption body 52 near to the absorption surface 60 can measure this as absolute temperature or as a change in temperature. Hence, also this measurement method allows to precisely determine the amount of energy deposited into the absorption body 52.

[0102] For the second method, the absorption body 52 comprises a cooling system 80 for an active cooling. Coolant 84 flows through a cooling duct 82 through the absorption body 52 and thereby assimilates the energy deposited into the absorption body 80 by the impinging electromagnetic radiation 120. Flow sensors 72 measure the flow rate of the coolant 84, temperature sensors 74 measure the temperature of the coolant 84, as depicted in FIG. 2 both at the inlet port and at the outlet port of the cooling duct 82, respectively. In summary, these measurements combined allow to precisely determine the amount of energy deposited into the absorption body 52.

[0103] FIG. 3 shows a cross-section of a rotationally symmetrical preferred embodiment of the detector 40 according to the present invention, in particular of its absorption surface 60. According to this embodiment, the absorption body 52 of the depicted sensor element 50 comprises at its end, which faces the impinging direction 122 of the electromagnetic radiation 120 to be measured, a hollow absorption volume 56. This absorption volume 56 comprises a single opening, namely an absorption orifice 62, which allows the impinging electromagnetic radiation 120 to enter the absorption volume 56. Inner sidewalls 58 of the absorption volume 56 form the absorption surface 60. In other words, the electromagnetic radiation 120 enters the absorption volume 120 and is reflected many times within the absorption volume 56, indicated in FIG. 3 by arrows, whereby at each reflection a fraction of the energy of the impinging electromagnetic radiation 120 is absorbed. Ideally, the electromagnetic radiation 120 is trapped in the absorption volume 56 and consequently completely absorbed by the absorption surface 60. To enhance a probability for this ideal case, the part of the sidewall which forms a rim 64 surrounding the absorption orifice 62 is tilted inward with respect to the absorption volume 56. This inwardly tilted surface provides the additional advantage that a reflection of electromagnetic radiation impinging on these surfaces back into the impinging direction can be avoided. In addition, the part of the absorption surface 60 arranged opposite of the absorption orifice 62 is conically shaped with the cone tip pointing towards the absorption orifice 62.

[0104] In FIG. 4 a detector 40 with two sensor elements 50 is shown. The sensor elements 50 are arranged adjacent to each other and thermally decoupled. Each sensor element 50 comprises its own absorption body 52 and absorption surface 60. The remaining parts of the sensor elements 50 are not shown. In summary, providing two or more sensor elements 50 can provide a more detailed information about the absorbed electromagnetic radiation 120, for instance for a determination of an evaporation rate and/or of a distribution of a flux of the evaporated source material 20 (not shown).

[0105] In addition, upstream of the each of the respective sensor elements 50, two stacked and aligned apertures 90 are arranged. The aperture openings 92 confine the solid angle of acceptance of the respective sensor element 50. Cross talk between the sensor elements 50, indicated by the dashed arrow, can be avoided. Further, between the apertures 90 and the absorption body 52, and even further along the respective aperture body 52, shielding elements 94 are arranged. These shielding elements 94 on one hand further diminish the aforementioned crosstalk. On the other hand, also electromagnetic radiation 120 impinging on a side surface of the absorption body 52 is stopped and cannot distort the measurement results.

[0106] As mentioned with respect to FIG. 4, the detector 40 according to the present invention can comprise two or more sensor elements 50. A few examples for shapes and arrangement patterns of sensor elements 50 and their absorption surfaces 60 are shown in FIG. 5. Obviously, other arrangements, in one limit a high-resolution pixel array similar to an electronic camera, are possible. In summary, out of the different arrangement patterns the most suitable can be chosen with respect to the purpose of the measurement of the detector 40, for instance a determination of an evaporation rate and/or of a distribution of a flux of the evaporated source material 20.

[0107] The standard geometry with a simple circular active area is shown in the top left panel of FIG. 5.

[0108] A movement of the impinging direction 122 of the electromagnetic radiation 120 can be detected with four quadrants as shown in the top right panel. Here, the sensor elements 50 are shaped as squares and are arranged such that primarily movements in the horizontal and vertical directions along their diagonals can be detected, while keeping the number of sensor elements 50 small.

[0109] The third arrangement with sensor elements 50 forming a rotationally symmetric pattern of circular rings is shown in the lower left panel of FIG. 5. This pattern is most sensitive to focusing or defocusing of the electromagnetic radiation 120 provided by the electromagnetic radiation source 110.

[0110] Both position and defocusing, although in this case only in the vertical direction, may be detected by a stripe arrangement of rectangular shaped sensor elements 50, such as shown in the lower right panel of FIG. 5. This can be favorable, as the electromagnetic radiation 120, being reflected in the impinging direction 122 around 45° on the source surface 22, is more strongly affected in the plane containing the incident and reflected beam, than perpendicular to it.

[0111] The following three figures FIGS. 6, 7 and 8 show the influence of the shape and form or the source surface 22 of the source material on both the flux distribution 30 of the evaporated source material 20 and the distribution of the electromagnetic radiation 120 reflected on the source surface 22 into measured distribution 134 on the detector 40. In the following, the figures FIGS. 6, 7 and 8 are described together, whereby the differences of the figures are highlighted. Additionally, the method according to the present invention will be described.

[0112] The electromagnetic radiation source 110 provides electromagnetic radiation 120 with an impinging distribution 130. This provision of the electromagnetic radiation 120 is done in step c) of the method according to the present invention. According to step a), the impinging distribution 130 is defined such that the flux distribution 30 of the source material 20 evaporated from the source surface 22 correspond to the also in step a) defined desired distribution 32 of the evaporated and/or sublimated source material 20. Especially in the situation shown in FIG. 6 with a flat source surface 22, this condition can be met easily. The target material 18, arranged in the reaction atmosphere 16 opposite to the source material 20, can be coated with the evaporated source material 20 as expected.

[0113] For allowing a control of this coating process, a detector 40 is arranged such that electromagnetic radiation 120 reflected on the source surface 22 in the impinging direction 122 can be measured, in particular in step d) of the method according to the present invention. As result, the detector 40, preferably with considering a response function of the detector 40, provides a measured distribution 134 of the measured electromagnetic radiation 120. As any changes in form and/or shape of the source surface 22 will imprint themselves onto the reflected electromagnetic radiation 120, this measured distribution 134 can be used to detect any deviations from the assumed ideal case.

[0114] For this, in the second step b) of the method according to the present invention an expected distribution 132 of the reflected electromagnetic radiation 120 is determined, for instance calculated, empirically estimated or experimentally determined. By comparing the measured distribution 134 of the electromagnetic radiation 120 reflected on the source surface 22 with the expected distribution 132 in step f) of the method according to the present invention, differences of these two distributions 132, 134 can be determined.

[0115] Based on the differences found in step f) of the method according to the present invention, step g) includes a redetermination of the impinging distribution 130 for eliminating these differences. Finally, in the last step h) the electromagnetic radiation source 110 provides electromagnetic radiation 120, for instance laser light with a wavelength between 100 nm and 1400 nm, with newly redetermined impinging distribution 130. An actual control of the flux distribution 30 of the evaporated source material 20 can thereby be provided.

[0116] In particular, at least the steps d) to h) of the method according to the present invention can be repeatedly carried out to provide an active closed loop control of the evaporation. Alternatively or additionally, in step a) the desired distribution 32 already can be defined with a time dependency.

[0117] As already mentioned above, in FIG. 6 a source material 20 with a flat source surface 22 is shown. This is an ideal case and easily to calculate. The actual flux distribution 30 equals the desired distribution 32.

[0118] After some irradiation by the electromagnetic radiation 120, the source surface 22 may develop a concave section, for instance due to the actual evaporation of source material 20. By this, both the flux distribution 30 and the distribution of the reflected electromagnetic radiation, respectively, change. The flux distribution 30 no longer equals the desired distribution 32 (not shown). By comparing the newly measured distribution 134 with the expected distribution 132, this situation can be identified and solved by accordingly redetermining the impinging distribution 130.

[0119] FIG. 8 shows an analogue situation to FIG. 7. The only difference is the shape of the source surface 22, which is not concave but convex. All descriptions with respect to the distributions 30, 130, 132, 143 and the above presented solution approach are the same as described with respect to FIG. 7 and hereby referred to.

[0120] In FIG. 9 a special behavior of some source materials 20 is shown. The depicted source material 20 is provided as self-supporting rod, whereby the source surface 22 is arranged at the upper end of the rod. By illuminating the source surface 22 with impinging electromagnetic radiation 120, a drop of melted source material 20 establishes at this upper end of the rod consisting of source material 20. As the electromagnetic radiation 120 impinges at an angle, for instance at 45°, the side of the rod nearer to the electromagnetic radiation 120 absorbs more energy. Hence as a result, the drop of melted source material 20 leans and/or tilts into the direction of the electromagnetic radiation 120. In particular, also the flux distribution 30 follows this spatial orientation.

[0121] FIG. 10 shows a possible solution for this problem. According to the method according to the present invention, a second beam of electromagnetic radiation 120 can be used to balance the energy deposit into the source material 20. The flux distribution 30 is no longer distorted and again equals the desired distribution 32.

[0122] The number of beams of electromagnetic radiation 120 is not limited to two. FIG. 11 shows an embodiment of a system 10 according to the present invention with an electromagnetic radiation source 110 comprising three emitter sections 112. The emitter sections 112 are arranged rotationally symmetric around the source surface 22 on the source material 20. For each beam of electromagnetic radiation 120, a dedicated detector 40 is provided. Hence the method according to the present invention described above can be carried out with each pair of emitter section 112 and detector 40 both individually and combined, respectively. In particular, the emitter sections 112 can provide electromagnetic radiation 120 with adjustable power densities and/or shapes and/or sizes. Hence, the actual impinging distribution 130, and therefore also the flux distribution 30 and the desired distribution 32, can provide even a spatial variation at the source surface 22.

[0123] This situation is depicted in FIG. 12. Two impinging beams of electromagnetic radiation 120 are shown, whereby their impinging distributions 130 differ, as hinted by the different thickness of the depicted arrows. This difference, for instance provided by different power densities of the provided beams of electromagnetic radiation 120, results in a slightly distorted flux 30 of the source material 20 evaporated from the source surface 22. In this case, this is intentional and the flux distribution 30 equals the desired distribution 32. It is clearly visible, that the target material 18 will not be coated equally by this flux distribution 30, as the flux distribution 30 is directed to one side of the target material 18. By varying the individual impinging distributions 130 of the beams of electromagnetic radiations 120, the direction of the flux distribution 30 can be altered. As result, a desired deposition thickness or thickness variation, or a time dependent sweep of the desired distribution 32 over the target material 18 can be realized and tracked by the actual flux distribution 30.

TABLE-US-00001 List of references 10 System 12 Vacuum chamber 14 Vacuum feedthrough 16 Reaction atmosphere 18 Target Material 20 Source material 22 Source surface 30 Flux distribution 32 Desired distribution 40 Detector 42 Arrangement element 44 Positioning element 50 Sensor element 52 Absorption body 54 Bore 56 Absorption volume 58 Sidewall 60 Absorption surface 62 Absorption orifice 64 Rim 70 Heat sensing element 72 Flow sensor 74 Temperature sensor 76 Thermocouple element 80 Cooling system 82 Cooling duct 84 Coolant 90 Aperture 92 Aperture opening 94 Shielding element 110 Electromagnetic radiation source 112 Emitter section 120 Electromagnetic radiation 122 Impinging direction 130 Impinging distribution 132 Expected distribution 134 Measured distribution