Method for determining material removal and device for the beam machining of a workpiece

Abstract

A method for determining material removal by an ion beam (3) on a test workpiece (7) which is disposed in a machining chamber (5) of a housing (6) of a device (1) for beam machining, wherein the test workpiece (7) has a substrate (8) and a layer (9) applied to the substrate. The method includes a) optically determining a layer thickness (d1) of the layer applied to the substrate, b) removing material of the layer from the test workpiece with the ion beam, c) optically determining the layer thickness (d2) of the layer applied to the substrate, and d) determining the material removal by comparing the layer thickness determined in step a) with the layer thickness determined in step c). Also disclosed is a device (1) for beam machining a workpiece (2) with which the method can be carried out.

Claims

1. A method for determining a material removal (Δd) by an ion beam on a test workpiece which is disposed in a machining chamber of a housing of a device for beam machining, wherein the test workpiece has a substrate and a layer applied to the substrate and wherein the machining chamber has an imaging optical unit having an entry-side part, and has a shielding annularly surrounding the entry-side part of the imaging optical unit and the test workpiece, the method comprising: a) optically determining, initially, a layer thickness (d1) of the layer applied to the substrate, b) removing material of the layer of the test workpiece with the ion beam, c) optically determining the layer thickness (d2) of the layer applied to the substrate subsequent to said removing, and d) determining the material removal (Δd) by comparing the layer thickness (d1) determined in said initial determining with the layer thickness (d2) determined in said subsequent determining, wherein a workpiece, to be machined, is disposed in the machining chamber; and wherein the shielding protects the test workpiece and the entry-side part of the imaging optical unit during machining of the workpiece with the ion beam.

2. The method as claimed in claim 1, wherein said initial determining and said subsequent determining comprises irradiating the test workpiece with illumination radiation.

3. The method as claimed in claim 2, wherein the layer and the substrate of the test workpiece are transparent to the illumination radiation.

4. The method as claimed in claim 2, wherein said initial determining and said subsequent determining comprise recording an interference spectrum of the illumination radiation reflected on the test workpiece.

5. The method as claimed in claim 4, further comprising guiding the illumination radiation reflected on the test workpiece for recording the interference spectrum by way of a light conductor to a spectrometer disposed outside the housing.

6. The method as claimed in claim 5, wherein the reflected illumination radiation is coupled into the light conductor by way of the imaging optical unit.

7. The method as claimed in claim 1, wherein the layer thickness (d1) is between 0.1 μm and 20 μm.

8. A device for beam machining a workpiece with an ion beam, comprising: an ion beam source generating the ion beam, a housing in which a machining chamber for beam machining the workpiece is formed, at least one test workpiece disposed in the housing and comprising a substrate and a layer applied to the substrate, an illumination source illuminating the test workpiece with illumination radiation, a spectrometer recording an interference spectrum of illumination radiation reflected on the test workpiece a workpiece, to be machined, disposed in the machining chamber, an imaging optical unit having an entry-side part and arranged relative to the test workpiece, and a shielding annularly surrounding and protecting the test workpiece and the entry-side part of the imaging optical unit when the workpiece is machined with the ion beam.

9. The device as claimed in claim 8, wherein the spectrometer is disposed outside the housing.

10. The device as claimed in claim 8, further comprising: an evaluation unit configured to evaluate the interference spectrum for determining in each case a layer thickness (d1, d2) of the layer applied to the substrate before and after machining the layer with the ion beam.

11. The device as claimed in claim 8, further comprising: a light conductor for guiding illumination radiation reflected back on the test workpiece to the spectrometer disposed outside the housing.

12. The device as claimed in claim 11, further comprising: an imaging optical unit for coupling the reflected illumination radiation into the light conductor.

13. The device as claimed in claim 8, wherein the substrate and the layer are transparent to the illumination radiation.

14. The device as claimed in claim 8, wherein the substrate is polished on both sides thereof.

15. The device as claimed in claim 8, wherein the workpiece to be machined comprises a material which is identical to the material of the layer of the test workpiece.

16. The device as claimed in claim 8, wherein the shielding has a shutter which is movable between a first, closed position and a second, opened position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments are illustrated in the schematic drawing and will be explained in the description hereunder. In the figures:

(2) FIG. 1 shows a schematic illustration of a device for beam machining a workpiece with an ion beam; and

(3) FIGS. 2A and 2B show schematic illustrations of a test workpiece prior to (FIG. 1A) and after (FIG. 2B) beam machining with the ion beam.

DETAILED DESCRIPTION

(4) In the following description of the drawings, identical reference signs are used for identical or functionally identical components, respectively.

(5) FIG. 1 shows a device 1 for beam machining a workpiece 2 with a machining beam in the form of an ion beam 3 which is generated by a radiation source 4 in the form of an ion source. The workpiece 2 is disposed in a machining chamber 5 which is formed within a housing 6. The housing 6, more specifically the machining chamber 5, is evacuated with the aid of vacuum pumps (not shown), that is to say that a vacuum environment prevails in the housing 6.

(6) In order for machining of the workpiece 2 in a manner as precise as possible to be enabled, said workpiece 2 in the case of the example shown being a quartz glass blank, it is favorable for the material removal of the ion beam 3 in the workpiece 2 (per unit of time) to be determined as accurately as possible. For this purpose, a test workpiece 7 which is formed from a substrate 8, in the example shown from Zerodur, and from a layer 9 from quartz glass that is applied to the substrate 8, is incorporated in the machining chamber 5. The material of the layer 9 is thus identical to the material of the workpiece 2.

(7) In order for the material removal of the ion beam 3 on the layer 9 of the test workpiece 7 at a predefined irradiation duration to be determined, interferometric layer thickness measuring is performed on the layer 9 of the test workpiece 7. For this purpose, the test workpiece 7 on the rear side thereof, that is to say on that side that faces away from the layer 9, is irradiated with illumination radiation 10 which is generated by an illumination source 11 which is disposed outside the housing 6. The illumination source 11 in the example shown comprises two lamps which generate illumination radiation 10 at wavelengths between 190 nm and 1050 nm. The use of an illumination source 11 having two or more lamps has proven favorable when the illumination source 11 is to generate illumination radiation 10 in a wide spectral range, for example between 190 nm and 1050 nm, since the emission spectrum of a single lamp in this case does not cover the entire desired spectral range. The use of a wide spectral range of the illumination radiation 10 is particularly advantageous for layer thickness measuring on a very thin layer 9.

(8) The illumination radiation 10 by way of a fiber portion 12 is coupled into a light conductor 13 in the form of a glass fiber, said light conductor by way of a vacuum conduit 14 in the housing 6 being guided into the machining chamber 5. The light conductor 13 at the end side is connected to the housing of an imaging optical unit 15 (lens) which serves for focusing the illumination radiation 10 onto the test workpiece 7. In the case of the example shown in FIG. 1, the illumination radiation 10 is beamed in so as to be substantially parallel to the thickness direction of the substrate 8, or of the layer 9, respectively.

(9) The substrate 8 of the test workpiece 7 as well as the layer 9 are formed from a material that is transparent to the illumination radiation 10, that is to say that the illumination radiation 10 is substantially transmitted by the test workpiece 7. A minor proportion of the illumination radiation 10 is reflected by virtue of the respective difference in the refraction index on the boundary surface between the substrate 8 and the layer 9, as well as on the boundary surface between the layer 9 and the vacuum environment in the machining chamber 5. The illumination radiation 10a reflected back on the test workpiece 7 thus has two radiation proportions which have travelled different optical path lengths, as is in each case indicated by a double arrow in FIG. 1, on account of which a phase difference results.

(10) The illumination radiation 10a reflected back on the test workpiece 7 is guided out of the housing 6 by way of the light conductor 13 and the vacuum conduit 14 and enters a spectrometer 16 which records an interference spectrum S of the reflected illumination radiation 10a. The reflected illumination radiation 10a in the spectrometer 16, in the example shown the Model MCS 601-c (UV-NIR) of the Carl Zeiss Spectroscopy company, impinges upon a diffraction grating and is divided into the spectral proportions thereof. The illumination radiation 10a diffracted at the diffraction grating is directed to a spatially-resolving detector. The layer thickness of the layer 9 can be determined from the interference spectrum S obtained with the spectrometer 16, for example by a Fourier analysis, as is described in the article “Koaxiale interferometrische Schichtdickenmessung” (“Coaxial interferometric layer thickness measuring”), Dr. Gerd Jakob, Photonik March 2000, cited at the outset. The spectrometer 16 for determining the layer thickness of the layer 9 is connected to an evaluation unit 17.

(11) The procedure for determining the material removal Δd of the ion beam 3 on the layer 9 is as described hereunder: The test workpiece 7 is first incorporated in the machining chamber 5 and adjusted relative to the imaging optical unit 15, that is to say that the spacing and the alignment of the test workpiece 7 in relation to the imaging optical unit 15 are set in a suitable manner. The layer thickness d1 of the test workpiece 7 is subsequently measured with the aid of the spectrometer 16 and of the evaluation unit 17 (cf. FIG. 2A), wherein d1=3 μm results in the example shown. Having determined the (original) layer thickness d1, the test workpiece 7 is machined with the ion beam 3 and material of the layer 9 is removed, as can be seen in FIG. 2B, on account of which a smaller layer thickness d2 results. The material removal on the layer 9 can be performed locally, as is illustrated in FIG. 2B; however, it is also possible for the material of the layer 9 to be removed in a homogeneous manner across the entire layer 9. A homogeneous removal of the material of the layer 9 has proven favorable since the result of the determination of the layer thickness d2 in the case of a homogeneous material removal is more stable in relation to positioning errors of the ion beam 3 as well as of the imaging optical unit 15.

(12) After the machining of the layer 9 with the ion beam 3, a determination of the layer thickness d2 is again carried out in the spectrometer 16, or with the evaluation unit 17, respectively, wherein the layer thickness d2 of 1 μm shown in FIG. 2B is measured. The material removal Δd results from comparing the layer thickness d1 of the layer 9 prior to the machining with the ion beam 3 and the layer thickness d2 after the machining with the ion beam 3, said material removal Δd corresponding to the difference Δd=d1−d2 between the two layer thicknesses d1, d2.

(13) The determination of the material removed Δd on the layer 9 can optionally be carried out multiple times in the manner described earlier, wherein the parameters of the ion beam 3, for example the ion energy, are in each case varied in order for the workpiece 2 to be able to be machined as precisely as possible. It is favorable in particular in this case for the initial thickness of the layer 9 of the test workpiece 7 to be as large as possible, and to be d1=approx. 20 μm, for example.

(14) As soon as the determination of the material removal Δd has been completed, the machining of the workpiece 2 with the ion beam 3 can be performed. For this purpose, the ion source 4 is moved from the measuring position to a machining position which in FIG. 1 is illustrated by dashed lines, where the machining of the workpiece 2 with the ion beam 3 is performed.

(15) Since the machining of the workpiece 2 can lead to sputtering (atomizing) of material of the workpiece 2, said material potentially being deposited on the test workpiece 7 as well as on the imaging optical unit 15, the entry-side part of the imaging optical unit 15 and also the test workpiece 7 are surrounded by an annular shielding 18. In the example shown in FIG. 1, the test workpiece 7 received in the shielding 18 serves as a “window” and thus as protection for the imaging optical unit 15. The test workpiece 7 per se is optionally not protected against deposits which are formed in the sputtering. In order for deposits which arise in the machining of the workpiece 2 to be removed from the test workpiece 7, a brief in-situ cleaning step of the test workpiece 7 can be carried out with the aid of the ion beam 3.

(16) Alternatively or additionally, the shielding 18 can have a shutter 18a which is movable between a first, closed, position, illustrated by dashed lines in FIG. 1, and a second, opened, position, illustrated by a solid line in FIG. 1. The shutter 18a during the machining of the workpiece 2 with the ion beam 3 is typically in the closed position and is moved to the opened position when material is removed from the test workpiece 7 with the ion beam 3. The shutter 18a can be moved from the closed to the opened position and vice-versa in that the ion source 4 is suitably displaced in the machining chamber 5 such that said ion source 4 pushes against the shutter 18a. A drive, or an actuator, respectively for moving the shutter 18a in the machining chamber 5 can also be provided in the machining chamber 5. It is understood that the shutter 18a does not have to be mandatorily displaced between the first and the second position, but can carry out another type of movement, for example a rotating movement.

(17) It is understood that the determination of the material removal Δd can also be carried out by another type of machining beam which enables a contactless removal of material, for example an electron beam or a laser beam. As opposed to the illustration in FIG. 1, the illumination source 11 can be integrated in the evacuated machining chamber 5 of the housing 6 so as to achieve a more homogeneous illumination of the test workpiece 7 with the illumination radiation 10.

(18) In order for the test workpiece 7 not to have to be replaced too frequently, to which end said test workpiece 7 has to be retrieved by venting and opening the housing 6 and substituted by a further test workpiece 7, a plurality of test workpieces 7 can optionally be disposed in a magazine in the machining chamber 5, only one of said plurality of test workpieces 7 being in each case measured and disposed on the measuring position, illustrated in FIG. 1, in the machining chamber 5. The magazine can be configured in the manner of a rotary plate, for example, as is described in DE 10 2015 215 851 A1 which is cited at the outset and is incorporated in its entirety into this application by way of reference. A vacuum lock can be used for introducing and extracting the test workpiece 7 into the housing 6 or from the housing 6, respectively, said vacuum lock being different from a vacuum lock for introducing and extracting the workpiece 2, so as to avoid any stoppage in the machining of the workpiece 2 when the test workpiece 7 is being replaced.