JPS62267093A - Focusing method - Google Patents

Abstract

PURPOSE:To realize high-accuracy focusing of laser beam processing by comparing the displacements of piezo-actuators detected by strain gages, etc., with a command value and focusing an optical system in accordance with the result of the comparison thereof. CONSTITUTION:The laser light which is oscillated from a laser oscillator 7 for measurement and is reflected by a reference mirror 9 and the reflected light from the working surface of a wafer 6 via half mirrors 4, 8 are measured by an interference method using a receiver 10 and the deviation Al from the distance l between a focusing lens 5 and the working surface of the wafer 6 is inputted to an AF controller 14. A focusing device 15 is constituted by supporting a wafer chuck plate 16 by means of the plural piezo-actuators 17, detects the individual actual displacements of the piezo-actuators 17 by the strain gages stuck to the piezo-actuators and feeds the same back to the AF controller 14. The high-accuracy focusing is thus executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to focusing in laser precision processing of thin film modular or LSI.

In particular, it relates to a focusing method that can be applied to continuous processing.

[Conventional technology]

In focusing methods related to laser processing.

Conventionally, as described in JP-A-59-159291,
A method of detecting relatively large processes such as welding or cutting rings using a TV camera is used.

However, in terms of accuracy, it could not support the laser precision processing of film modules and LSIs.

[Problem that the invention seeks to solve]

Laser processing of thin film modules or LSI is ±1
Accuracy on the order of μm is required, and the accuracy of the positioning device related to this must be on the order of submicrons. Furthermore, when processing the above object, the laser spot diameter is φ
Since the diameter is 1 μm to φ5 μm, the focusing accuracy is ±2 due to the relationship between the energy distribution on the machined surface and the depth of focus.
Must be within μ door. In the conventional technology, the object to be laser processed is large, and the technical field is different in terms of accuracy.

An object of the present invention is to realize focusing in high-precision laser processing that satisfies the above accuracy.

[Means for solving problems]

The above purpose is to equip the positioning table with a chuck mechanism that allows fine movement of the workpiece in the direction of laser incidence, and use a piezo element (piezoelectric element) as the actuator for fine adjustment. Highly accurate focusing is achieved by inputting the focal position correction amount calculated based on this into the piezo actuator, detecting the displacement amount of the piezo actuator with a strain gauge, and feeding it back.

[Effect]

One problem with fine adjustment using a piezo actuator is that: ■ Piezo elements have individual differences in electric field and displacement characteristics, and have hysteresis characteristics; ■ How to input the applied voltage 1. For example, using a square wave In this case, shocking vibrations occur when the piezo actuator expands and contracts.

Regarding (2) above, this can be solved by attaching strain gauges to each of the plurality of piezo actuators used to detect the nine individual displacement amounts and feeding them back to the controller. Moreover, the above-mentioned problem (2) can be solved by controlling the applied voltage input method to have a smooth analog curve. However, in this case, the operation time of the piezo actuator will be extended, but this can be dealt with by a control method appropriate to the application.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

Figure 1 shows a part of the configuration of the precision processing equipment for LSI trimming, Figure 2 shows the focusing device driven by a piezo actuator, and Figure 3 shows the electric field and displacement cover of the piezo actuator. Characteristic diagram, Figure 4 is a diagram of a piezo actuator with a strain gauge attached, Figure 5 is a displacement/resistance characteristic diagram of the actuator shown in Figure 4,
FIG. 6 is a procedure explanatory diagram of the focusing method.

In Fig. 1, the laser processing of six sides of the wafer is shown.

Nd: YAG After the laser beam oscillated from the laser oscillator 1 is focused into parallel light by the expander 2, it is
The beam is focused by a focusing lens 5 through the wafer 6 and irradiated onto the processed surface of the wafer 6. At this time, the distance between the focusing lens 5 and the wafer 6 is
This distance is determined in advance in relation to the energy distribution at the processing position of the laser beam, and this distance is defined as l. but,
this! The distance Δl is determined by factors such as the flatness and thickness of the wafer, as well as the horizontality of the XY table 12 controlled by the table controller 13, and this Δl is generally considered to be about 10 μm. . Of this, the part caused by wafer 6 is usually ±5 μm, and the remaining part is due to problems with the processing equipment.
It can be processed by software as fixed data, but what if the laser spot diameter (do)' on the machined surface? If rφ is 1 μm.

The depth of focus is ±1.4 μm when JT do is applied, and it can be seen that a focusing function is required. Therefore,
The position of the machined surface is measured using a laser 11-length instrument.
This +7- laser length measuring device is a well-known device, and its usage will be briefly described in FIG. The reflected light from the processed surface via the half mirrors 4 and 8 is measured by interferometry using a receiver 10-. In other words, the distance l between the focusing lens 5 and the processing surface of the wafer 6 is fixed data processed by software, and the output of the laser length measuring device is converted into a voltage n' distance by the V/l converter 11. After that, calculate the deviation amount ±Δno with respect to l, and calculate A F (Auto Focus
s) Input to the controller.

The focusing device 15, whose sectional view is shown in FIG. 2, has a structure in which four piezo actuators 17 support a phenol chuck plate 16 and slightly move it up and down, and are fixed to an XY table 12. and use it. here,
A piezo actuator has electric field/displacement z (V#) characteristics as shown in FIG.

There are individual differences inherent to the elements. Furthermore, since it has hysteresis characteristics, high precision positioning cannot be achieved with open loop control. Therefore, as shown in Fig. 4, a strain gauge 18 is attached to the piezo actuator 17 in a manner that covers its length in the expansion and contraction direction, and the actual displacement of each piezo actuator is detected to form a servo circuit (not shown). This enables high-precision focusing. As shown in FIG. 5, the strain gauge 18 used has good linearity and corresponds to the amount of displacement necessary for focus adjustment. The focusing method is a control method using servo, as shown in FIG.

Here, one embodiment of the present invention will be described with respect to continuous processing, which is considered to be the most difficult focusing method, that is, focusing for laser processing while the XY table is traveling.

The above-mentioned slope of ±5 μm (i!1 constant) caused by the sea urchin... changes smoothly and can be predicted in advance. Therefore, after mounting the wafer 6 on the wafer chuck 16 and before processing, the XY table 12 is driven to scan the wafer in a cross shape, and the wafer 6 is
Measure ノ. By predicting the adjustment amount of the focal length of the processing surface of the wafer 6 based on this measurement data and driving the piezo actuator 17, smooth adjustment without vibration or delay can be achieved.

〔Effect of the invention〕

As stated above (1) According to the focusing method and device of the present invention, precision adjustment on the submicron order is possible;
Thin film modineal, which is in high demand.

It is suitable for laser precision processing in the semiconductor manufacturing field, and has a wide range of applications. Also, is there an adjustment method with high precision and low vibration?

Product quality improvement 1 Yield improvement can be expected.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an LSI/IJ camera to which the focusing method and device according to the present invention are applied. Figure 2 is a cross-sectional view of the focusing device, Figure 3 is a V/l characteristic diagram of the piezo actuator, Figure 4 is a diagram of the piezo actuator with a strain gauge attached, and Figure 5 is the
l/Ω characteristic diagram of the piezo actuator shown in Fig. 6.
The figure is a procedure explanatory diagram of a focusing method. 1.7... Laser oscillator, 2... Expander. 3...Mirra, 4,8...Half mirror-15...Focal lens, 6...Wafer. 9...Reference mirror, 10...Receiver. 11...V/l converter, 12...XY table. 13...Table controller. 14...AF controller. 15... Focusing device, 16... Wafer chuck. Fig. 1 Fig. 2 Hands to the sea urchin 17 times! Figure 3 Uv

Claims (1)

[Claims] 1. Attach a detector such as a strain gauge to the piezo actuator, detect the displacement amount of the piezo actuator with the strain gauge, compare the detected displacement amount of the piezo actuator with the command value, and based on the comparison result. and adjusting the position of the component so that the position of the component coincides with the focal position of an optical system.