This application is a national stage of International Application No. PCT/EP/2007/004781, filed Jan. 10, 2008, which claims priority under 35 U.S.C. ยง119 to German Patent Application No. 10 2006 030 874.3, filed Aug. 3, 2007, the entire disclosure of which is herein expressly incorporated by reference.
The invention relates to a method and apparatus for treating a workpiece using electron radiation. Within the scope of the present invention, treating a workpiece includes material-altering treatment (particularly the removal of material), as well as material-neutral treatment (particularly the measurement of workpieces).
Various basic problems must be overcome when treating workpieces. A first problem is precisely positioning the workpiece before it is to be treated, for example, in a material-altering manner. Such positioning may, for example, depend on the position of hard surface structures. Particularly in the case of workpieces consisting of non-transparent materials, exact positioning is difficult when it depends on the position of surface structures situated on the back of the workpiece. The workpiece therefore has to be measured and/or the treatment system has to be correspondingly adjusted at high expenditures.
A second problem is determining the remaining thickness of the material layer when material is removed. This problem occurs, for example, during material-removing workpiece treatment by means of an electron beam, but also, for example, during the wet-chemical etching of silicon wafers.
A further problem consists of terminating the material removal precisely when a layer boundary has been reached during the material-removing treatment of a multi-layer workpiece.
One object of the present invention is to provide a common operating principle, by which all above-mentioned problems can be solved in a simple and elegant manner.
This and other objects and advantages are achieved by the method and apparatus according to the invention, in which the workpiece is irradiated on a first workpiece side, by electron radiation which is selected such that it generates x-ray radiation in the material of the workpiece. The x-ray radiation emerging from the workpiece on a second workpiece side situated opposite the first workpiece side will then be detected.
A system according to the invention for treating workpieces therefore includes, in addition to a workpiece receiving device, a corresponding electron radiation source on a first side of the workpiece receiving device and a corresponding x-ray radiation detector on a second side of the workpiece receiving device opposite the first side, which x-ray radiation detector is situated opposite the electron radiation source.
The invention utilizes the fact that electron beams generate x-rays in the material, which can be detected by a simple detector. Although the material itself absorbs the x-rays again, starting at a certain material thickness, the x-rays are no longer completely absorbed by the material. By detecting the x-ray radiation emerging on the back of the workpiece, a conclusion can be drawn concerning the thickness of the material layer on the concerned side.
On the one hand, the same principle can also be used for measuring the workpiece surface and determining concrete surface structures. In this case, the electron radiation is expediently selected to be so low that it does not alter the material. Preferably, a bundled electron beam is used to scan the first workpiece, for example, along one or more lines. By means of changing x-ray radiation intensity values, at points of the workpiece which are sufficiently thin for the x-ray radiation generated in the workpiece by the electron beam to emerge at the back of the workpiece, a conclusion concerning surface structures can be drawn. However, without additional information, no reliable conclusion can be drawn as to whether those surface structures are situated on the front of the workpiece, the back of the workpiece or both sides. At any rate, by means of the amount of the detected x-ray radiation intensity, a measurement can be derived for the layer thickness and a layer thickness profile which can be exactly quantified by a comparison with material-dependent reference values.
However, if surface structures on the workpiece front and on the workpiece back are known but not their vertical distance from one another and/or their lateral position with respect to one another, a conclusion can be drawn with respect to their relative vertical and lateral position, based on the determined thickness profile. In particular, this makes it possible to position a workpiece laterally in a precise manner before it is further processed in any fashion.
During a (subsequent) material-removing workpiece treatment, the measuring principle according to the invention can be used, for example, to determine a residual layer thickness. As soon as the removal of material has progressed so far that the x-ray radiation generated in the material by the electron radiation is not completely absorbed on its path through the remaining material layer thickness, but emerges at the back of the workpiece, the x-ray radiation intensity detected on the back of the workpiece can be used as a measurement for the remaining layer thickness, and can be analyzed. As soon as the detected x-ray radiation reaches or exceeds a given threshold value, which defines a certain material layer thickness for the concerned material, the material removal operation can be terminated. This principle is particularly suitable for methods by which the material is removed by the electron beam itself. However, it is equally suitable for other methods by which the removal of material takes place in a different fashion.
It is also possible to let the respective actually detected x-ray radiation, (hence, the actual thickness value) influence a control loop, to control the removal of material as a control variable. For example, the power of an electron beam causing the removal of material may be appropriately reduced, the closer one comes to the desired residual thickness of the layer of material. In this case, the detected x-ray radiation is always a function of the beamed-in electron beam intensity per surface, of the material layer thickness and of the material itself.
A further interesting possibility of controlling a material-removing treatment process using the principle according to the invention consists of terminating the material removal in the vertical direction precisely when a layer boundary has been reached in a multi-layer material. In this case, the physical characteristic is utilized that the x-ray spectrum of the x-ray radiation generated by the electron radiation differs for different materials. When a layer boundary is reached, the characteristic of the detected x-ray radiation therefore changes abruptly.
The invention can therefore be used in multiple respects for the treatment of workpieces, particularly during the workpiece adjusting for the lateral position determination or during the removal of material for the vertical position determination or for both. The invention is, for example, suitable for use in the manufacture of micro components for high-temperature pressure sensor systems, particularly for the control of the membrane thickness when etching silicon and determining the residual membrane thickness.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
The electron beaming device 1 and the x-ray radiation detector 5 are connected to an analyzing device 6 which takes into account the actual position of the electron beaming device 1 and the x-ray radiation detected by the x-ray radiation detector 5, and determines the thickness of the workpiece 3 at the point of the workpiece irradiated by the electron beam 4 at the particular point in time. Because the electron radiation impinges on a defined point of the workpiece 3 as a bundled electron beam 4, the x-ray radiation detector 5 itself does not have to operate in a locally resolved manner. For the local resolution, the electron beaming direction of the electron beam 4 or the actual position of the electron beaming device 1 can be used.
The system according to
On the other hand, the system according to
When scanning the surface 3a by means of the electron beam 4 for determining the relative lateral position of the lower local layer 13 with respect to the upper recess 7, the electron beam 4 sweeps from the left to the right first over a relatively thick area of the workpiece 3 in which the x-ray radiation 8 generated in the workpiece 3 by the electron radiation 4 is completely absorbed on its path to the workpiece back 3b. As soon as the electron beam 4 reaches the recess 7, the layer thickness of the workpiece 3 becomes sufficiently narrow for the generated x-ray radiation 8 to emerge on the back of the workpiece 3b, so that it can be detected by the x-ray radiation detector 5 (not shown in
In the further course, the electron beam 4 sweeps over the local coating 13. In this section, no x-ray radiation exits on the back 3b of the workpiece 3 since it is completely absorbed as a result of the increased layer thickness of the material. Even if it were not absorbed completely, the x-ray radiation intensity emerging in this section would at least decrease, so that the relative position of the local layer 13 with respect to the opposite indentation 7 would nevertheless be clearly detectable. On the basis of the data thus determined measuring, the workpiece and/or the workpiece treating system can be precisely adjusted for the further treating of the workpiece 3.
In this case, the x-ray radiation detector 5 (not shown in
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
Number | Date | Country | Kind |
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102006030874.3 | Jul 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2007/004781 | 5/30/2007 | WO | 00 | 7/2/2009 |