DETECTION CIRCUIT, ELECTROSTATIC HOLDING DEVICE AND METHOD FOR DETECTING A COMPONENT ON AN ELECTROSTATIC HOLDING DEVICE

Abstract

Detection circuit for detecting electrical capacitance of electrode device in electrostatic holding device with clamp carrier, particularly for detecting component held by holding device, includes phase control circuit couplable to electrode device and has reference oscillator device, phase comparator and VCO circuit (VCOC). Phase comparator is arranged to generate a control voltage of VCOC as a function of reference signal from reference oscillator device and of VCO feedback signal from VCOC, at least one phase control circuit is configured for controlling VCOC as a function of capacitance to be detected, and for outputting an output signal characteristic of capacitance based on control voltage of VCOC, phase control circuit is configured for connection to electrode device such that VCOC contains capacitance to be detected as frequency-determining component, and reference oscillator device is configured for generating reference signal with adjustable reference frequency. Electrostatic holding device includes at least one such detection circuit.

Claims

1. A detection circuit which is configured for detecting an electrical capacitance of an electrode device in an electrostatic holding device with a clamp carrier, comprising at least one phase control circuit which can be coupled to the electrode device and which has a reference oscillator device, a phase comparator and a voltage-controlled oscillator circuit (VCO circuit), wherein the phase comparator is arranged for generating a control voltage of the VCO circuit in dependency on a reference signal from the reference oscillator device and on a VCO feedback signal from the VCO circuit, and the at least one phase control circuit is configured for controlling the VCO circuit in dependency on the capacitance to be detected, and for outputting an output signal characteristic of the capacitance based on the control voltage of the VCO circuit, wherein the at least one phase control circuit is configured for a connection to the electrode device such that the VCO circuit contains the capacitance to be detected as a frequency-determining component, and the reference oscillator device is configured for generating the reference signal with an adjustable reference frequency.

2. The detection circuit according to claim 1, wherein the reference oscillator device comprises a reference oscillator and an oscillator processor, wherein the oscillator processor is configured for outputting the reference signal and for setting the reference frequency based on an output signal from the reference oscillator.

3. The detection circuit according to claim 2, wherein the oscillator processor is coupled to the phase comparator and is configured for calculating the reference frequency in dependency on a comparator output signal from the phase comparator.

4. The detection circuit according to claim 1, wherein the electrode device comprises measurement electrodes which can be coupled to the VCO circuit and indicate the capacitance contained in the VCO circuit when the detection circuit is coupled to the electrode device.

5. The detection circuit according to claim 1, wherein the electrode device comprises clamp electrodes for generating electrostatic holding forces, which can be coupled to the VCO circuit and determine the capacitance contained in the VCO circuit when the detection circuit is coupled to the electrode device.

6. The detection circuit according to claim 1, wherein the VCO circuit can be coupled to the electrode device via blocking condensers, wherein the at least one phase control circuit is configured for operation at a lower voltage potential than the electrode device.

7. The detection circuit according to claim 6, wherein a protection circuit is provided which is configured for protecting the at least one phase control circuit against voltage peaks.

8. The detection circuit according to claim 1, wherein the electrode device and a voltage source can be coupled to the VCO circuit for loading the electrode device with a clamp voltage, such that the VCO circuit can be operated at the same voltage potential as the electrode device.

9. The detection circuit according to claim 8, wherein the VCO circuit is galvanically separated from other components of the at least one phase control circuit.

10. The detection circuit according to claim 8, wherein an entirety of the at least one phase control circuit is configured for operation on the same voltage potential as the electrode device.

11. The detection circuit according to claim 1, which is configured for detecting a component held by the electrostatic holding device.

12. An electrostatic holding device which is configured for holding a component by electrostatic holding forces, comprising a clamp carrier which is configured to receive the component, an electrode device with at least one pair of clamp electrodes configured for generating electrostatic holding forces, and at least one detection circuit according to claim 1 which is coupled to the electrode device.

13. The electrostatic holding device according to claim 12, wherein the electrode device comprises several pairs of clamp electrodes and several detection circuits are provided, wherein each pair of clamp electrodes is coupled to one of the detection circuits, respectively.

14. The electrostatic holding device according to claim 12, wherein a voltage source is connected to the electrode device via inductances or gyrator circuits.

15. A method for detecting a component which is held by an electrostatic holding device according to claim 12, comprising the steps (A) output of the output signal of the at least one phase control circuit which is characteristic of the capacitance, and (B) analysis of the output signal with detection of at least one of a placing and a clamped state of the component on the electrostatic holding device.

16. The method according to claim 15, wherein the reference frequency of the reference oscillator device is set in dependency on an output signal from the phase comparator such that the VCO circuit is operated in a capture range of the at least one phase control circuit.

17. The method according to claim 16, wherein the reference frequency of the reference oscillator device in a first operating phase is set to detect the placing of the component on the electrostatic holding device, and in a second operating phase, if the placing of the component on the electrostatic holding device has been detected, to detect the clamped state of the component on the electrostatic holding device.

18. The method according to claim 16, wherein the electrode device comprises several pairs of clamp electrodes and several detection circuits are provided, wherein each pair of clamp electrodes is coupled to one of the detection circuits, and the analysis of the output signal from the detection circuits comprises detection of the position of the component on the clamp carrier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Further details and advantages of the invention are described below with reference to the enclosed drawings. These show in:

[0034] FIG. 1: a block diagram of features of a first embodiment of the detection device and the electrostatic holding device according to the invention;

[0035] FIG. 2: a further illustration of the embodiment according to FIG. 1 showing a wafer;

[0036] FIG. 3: a block diagram of features of a second embodiment of the detection device and the electrostatic holding device according to the invention;

[0037] FIG. 4: a further illustration of the embodiment according to FIG. 3 showing a wafer; and

[0038] FIGS. 5 to 7: top views of different variants of electrode devices of the electrostatic holding device according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Features of preferred embodiments of the invention are described below with reference to the electrical configuration of the detection circuit in conjunction with an electrostatic holding device. Details of the electrostatic holding device, in particular the mechanical and geometric structure of the clamp carrier and the embedding of the electrode device in the clamp carrier, and its operation, in particular the reception, movement and deposit of components, in particular semiconductor wafers, are not described since these are known from the prior art. The clamp carrier may in particular have receiving surfaces which are flat on one or both sides and each of which is provided to receive a component. Although the invention is described with reference to the holding of semiconductor wafers as an example, the use of the invention is not restricted to the holding of wafers but it may also be used with other components.

[0040] FIGS. 1 and 2 show schematically features of a first embodiment of the invention with the electrostatic holding device 200, comprising an electrode device 210, a clamp carrier 220 and a voltage source 230, and the detection circuit 100. The first embodiment of the invention is distinguished in that the phase control circuit 110 of the detection circuit 100 is capacitatively separated from the electrode device 210 by means of blocking condensers 120, and is operated at low voltage potential. Real condensers have an extremely high resistance to direct voltage and are therefore able to separate direct voltage.

[0041] The electrode device 210 embedded in the clamp carrier 220 comprises at least two clamp electrodes 212 (shown as condenser plates) which provide the capacitance 211 to be detected and are connected to the voltage source 230 via inductances 213. The inductances 213 serve to supply the charge current to the electrode device 210. They are selected such that no resonance arises in cooperation with the capacitance 211, and their value amounts for example to 10 mH to 100 mH. The inductances 213 constitute chokes which decouple the clamp electrodes for alternating current voltage from the voltage source 230 and block undesirable voltage peaks from the voltage source 230. The voltage source 230 is configured to generate a high voltage. The voltage applied at the clamp electrodes of the electrode device 210 is for example +/−3000 V.

[0042] The detection circuit 100 is configured to detect the capacitance change in both operating phases of placing of the wafer 1 on the clamp carrier 220 and of transition into the clamped state, and hence to detect the state of the wafer 1. The capacitance 211 when the clamp carrier 220 is empty amounts for example to 600 pF, and when the clamp carrier 220 is occupied by a wafer 1 (see FIG. 2) it amounts for example to 3 nF. If, when the electrode device 210 is loaded with a high voltage, the wafer 1 is drawn against the surface of the clamp carrier 220, the capacitance 211 increases for example by 100 pF.

[0043] The detection circuit 100 comprises the phase control circuit 110, the blocking condensers 120 and the protection circuit 130. The blocking condensers 120 form a series circuit with the capacitance 211 to be detected of the electrode device 210, wherein the blocking condensers 120 are arranged for potential separation of the phase control circuit 110 from the electrode device 210. The blocking condensers 120 for example have a capacitance of 680 pF. The protection circuit 130 comprises two varistors which are switched conductively when voltage peaks occur at the blocking condensers 120 against ground potential. For example, 6V varistors are used which form a short-circuit to ground potential on voltage peaks above a voltage of 6 V.

[0044] The phase control circuit 110 comprises a reference oscillator device with a reference oscillator 111 and an oscillator processor 112, a phase comparator 113, a VCO circuit 114, a low-pass filter 115 and an analogue-digital converter 116.

[0045] The reference oscillator 111 comprises for example a quartz oscillation circuit, the output signal of which has a base frequency of for example 8 MHz. The output signal is processed by the oscillator processor 112 for output of the reference signal with the reference frequency F.sub.ref. For this, the oscillator processor 112 contains for example a frequency splitter which is controlled as a function of a locked state signal derived from the comparator output signal. Further information on the situation of the detection range of the phase control circuit is given for example by the analogue-digital converter 116.

[0046] The VCO circuit 114 is a voltage-controlled oscillator, wherein the frequency-determining component of which is provided by the capacitance 211 of the electrode device 210. For this, the blocking condensers 120 are connected to the VCO circuit 114. The VCO circuit 114 gives a VCO feedback signal with a VCO frequency F.sub.VCO. The VCO feedback signal with the VCO frequency F.sub.VCO and the reference signal with the reference frequency F.sub.ref are applied at the inputs to the phase comparator 113, the comparator output signal Ph from which is characteristic for the phase error between the two frequencies F.sub.VCO and F.sub.ref. The low-pass filter 115 delivers a direct voltage U.sub.LP based on the phase error Ph, which voltage is characteristic of the phase error and is given as an input parameter firstly to the VCO circuit 114 and secondly to the analogue-digital converter 116. For the VCO circuit 114, the direct voltage U.sub.LP serves as a control voltage for tracking the VCO frequency. In locked state, the direct voltage U.sub.LP also gives the desired information on the capacitance 211 to be detected, or on the state of the wafer 1 to be detected. The analogue-digital converter 116 provides information on the locked state of the phase control circuit 110 which is used to control the oscillator processor 112.

[0047] The locked state of the phase control circuit 110 is detected so as to check whether the direct voltage U.sub.LP lies in the middle of a predefined detection range, and corresponds for example to half the operating voltage of the VCO circuit 114. This test may be carried out software-based with the oscillator processor 112. If said condition is not fulfilled, the reference frequency F.sub.ref is changed using the oscillator processor 112 until the locked state is detected (e.g. detection of a locked signal with oscillator processor 112).

[0048] The series connection of the capacitance 211 to be detected and the blocking condensers 120 forms a total capacitance C.sub.RF which determines the frequency of the VCO circuit 114. The capacitance C.sub.RF is calculated as follows:

C.sub.RF=[C.sub.A.sup.−1+C.sub.B.sup.−1+(C.sub.211+ΔC.sub.211).sup.−1].sup.−1,

[0049] wherein C.sub.A and C.sub.B are the capacitances of the blocking condensers 120, and C.sub.211 is the capacitance value of the capacitance 211 to be detected.

[0050] Detection of the capacitance gives a linear dependency of the direct voltage U.sub.LP on the capacitance C.sub.RF in the VCO circuit 114 when the phase control circuit 110 is in the locked state. The linear dependency may be used both to detect the locked state and to determine the amount of the capacitance 211 to be detected.

[0051] One advantage of the first embodiment of the invention according to FIGS. 1 and 2 is that, irrespective of the interposition of the blocking condensers 120 and the resulting slight changes in C.sub.RF in the pF range on placing or clamping of the wafer 1, the change in the capacitance 211 to be detected can be detected reliably and reproducibly. The direct voltage U.sub.LP may be used as a direct measure of the change in the capacitance 211 to be detected.

[0052] The value of the voltage U.sub.LP is provided as information to an external device for signal analysis, in particular an external control device, in order to detect whether the wafer 1 is placed on the clamp carrier 220 and the high voltage can be switched on, and whether, after switching on the high voltage, the wafer 1 is in the clamped state. If the clamped state has been detected, the electrostatic holding device 200 may be operated, e.g. the wafer 1 may be moved to a station in a processing line for semiconductor processing. Alternatively, these steps may be performed by the oscillator processor 112.

[0053] The diagrammatic depiction of the first embodiment of the invention in FIG. 2 illustrates the separation into a high-voltage region and a low-voltage region by the blocking condensers 120 (see dotted line). The high voltage is applied by the voltage source 230 (see FIG. 1) to the electrode device 210 via the inductances 213. For example, the electrode device 210 comprises two clamp electrodes 212 which each extend over half the surface of the clamp carrier 220 and are each illustrated by a condenser plate. When the wafer 1 is placed on the clamp carrier 220, the capacitance of the electrode device 210 is influenced by the material of the wafer 1, in particular its electrical conductivity, as illustrated in FIG. 2. On the low-voltage side, the detection circuit 100 is arranged in particular with the VCO circuit 114 which is not influenced by the high voltage at the electrode device 210.

[0054] The first embodiment of the invention according to FIGS. 1 and 2 can be modified so that several pairs of clamp electrodes are provided on the clamp carrier 220, each of which is connected to a detection circuit (see FIG. 4).

[0055] FIGS. 3 and 4 illustrate schematically a second embodiment of the invention in which at least the VCO circuit 114 is operated at the high voltage potential of the electrode device 210. According to FIG. 3, it is possible here to operate the entire phase control circuit 110 at high voltage potential and separate this galvanically from the further signal analysis (see double arrows). Alternatively it is possible, according to FIG. 4, to operate only the VCO circuit 114 at high voltage potential and separate this galvanically from the other components of the phase control circuit (see double arrows). The galvanic separation of the detection circuit 100 from a device for further signal analysis, e.g. a further control device for signal analysis and control of the electrostatic holding device 200 (not shown), or the VCO circuit 114 from the other components, is achieved for example using an opto-coupler with a signal transmission based on infrared radiation, or with a wireless radio interface.

[0056] According to FIG. 3, the electrostatic holding device 200 comprises the clamp carrier 220 with the electrode device 210 and the voltage source 230, and the detection circuit 100 with the phase control circuit 110. The clamp carrier 220 is configured for receiving a component to be detected, in particular a wafer 1.

[0057] By deviation from the first embodiment according to FIG. 1, the VCO circuit 114 is connected directly to the clamp electrodes 212 of the electrode device 210 without capacitative separation. The high voltage source 230 is connected to the clamp electrodes 212 and the VCO circuit 114 via two gyrator circuits 240. The use of gyrator circuits 240 compared with the inductances 213 according to FIG. 1 has the advantage that for each pair of clamp electrodes, only one integratable, miniaturizable circuit is provided, which allows integration together with the voltage source 230 on the electrostatic holding device 200, in particular on the clamp carrier 220.

[0058] Furthermore, if the entire detection circuit 100 is laid to high voltage potential, this can also be provided as an integral component of the clamp carrier 220. Here the phase control circuit 110 is operated as described above with reference to FIG. 1.

[0059] FIG. 4 illustrates an alternative variant of the second embodiment of the invention in which only the VCO circuit 114 is operated at high voltage potential and galvanically separated from the other components of the phase control circuit (see double arrow). FIG. 4 furthermore shows a variant in which two pairs of clamp electrodes 212, 212A are provided on the clamp carrier 220, each of which is coupled to a detection circuit 100, 100A according to the invention. The part electrodes of each pair of clamp electrodes 212, 212A are direct components of the capacitive measurement circuit, without blocking condensers being provided as in FIG. 1. This advantageously increases the sensitivity of detection with the detection circuit.

[0060] The part electrodes of each pair of clamp electrodes 212, 212A are each loaded with the same bipolar high voltage. For this, both clamp electrodes are connected via inductances 213 to the same high-voltage source 230. The inductances 213 prevent a short-circuit for alternating current voltage in the detection circuit 100 since they have a choke effect for voltage peaks.

[0061] FIG. 5 shows a further variant of the invention in which several clamp electrodes 212, 212A are provided on the clamp carrier 220. The area of the clamp carrier 220 is divided into four quadrants, each of which carries a pair of clamp electrodes 212, 212A, 212B, 212C. Each pair of clamp electrodes 212, 212A, 212B, 212C is connected to a detection circuit according to the invention (not shown) in order to detect the capacitance of the respective clamp electrodes 212, 212A, 212B, 212C. Advantageously, this allows a location-resolving detection of the wafer on the clamp carrier 220. By formation of a ratio of capacitance values, the position of the wafer on the clamp carrier 220 can be determined directly.

[0062] FIG. 6 shows a further example with several clamp electrodes, wherein two pairs of clamp electrodes 212, 212A are provided in each quadrant, and each connected to a detection circuit. This arrangement of electrodes advantageously has an increased sensitivity of detection for detecting the clamped state. One of the pairs of electrodes may constitute measurement electrodes 214 which are not connected to a voltage source for clamping the wafer.

[0063] According to a further variant of an electrostatic holding device with several clamp electrodes 212, 212A, these are connected together in nested fashion as illustrated schematically in FIG. 7. Each pair of clamp electrodes 212, 212A is provided with its own detection circuit. This arrangement of electrodes is advantageously suitable in particular for clamping poorly conductive materials such as for example sapphire.

[0064] The features of the invention disclosed in the description above, the drawings and the claims may be important, both individually and in combination or sub-combination, for implementing the invention in its various embodiments.