JPS6180212A - Automatic focus detecting mechanism - Google Patents

Abstract

PURPOSE:To detect the focus of a rough surface of a mirror surface without using the reflected light of probe light by projecting two kinds of slit images upon the surface of a base plate and finding out the shift value from a focal position on the basis of the structure of the synthesized slit image. CONSTITUTION:Parallel luminous flux 10, 12 for probing which are radiated a laser or the like are irradiated to slit plates 11, 13 provided with slits having different shapes respectively and the slit images of the slit plates 11, 13 are projected upon a working surface 15. On the other hand, a working laser beam 19 forms its image on the working surface 15 through a total reflection mirror 16 and a condenser lens 14. A certain position B of the working surface 15 is the correct focal position of the laser condenser lens 14 and the synthesized image of the slits of the slit plates 11, 13 is symmetrical about the optical axis center of the condenser lens 14. A detector part 18 using a one-dimensional CCD arranged on the upper part of the condenser lens 14 and the mirror 16 detects the change of the shape of the synthesized slit image, so that focusing can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus detection mechanism, and more particularly to an automatic focus detection device used in a laser trimming device or the like and useful for focusing on a rough surface such as a ceramic substrate.

In recent years, with the automation of manufacturing equipment and devices such as electronic components,
Various automatic focus detection mechanisms have been put into practical use. The mainstream method is to shine a probe light such as a laser onto the surface of the object and use the reflected light, as is used in LSI-related mask manufacturing and inspection equipment. This method is effective when the target object is close to a mirror surface, but cannot be used if the surface is rough because the probe light will be scattered.

On the other hand, a laser trimming device often trims a thin film resistor on a large ceramic substrate by laser irradiation while moving the resistor in steps.

In this case, there is an inevitable error in the parallelism between the moving plane of the handling mechanism (XY table) and the surface of the large substrate set on the stage, so as the step feed is repeated, the focus may shift depending on the position of the substrate. occurs. At this time, if the ceramic substrate surface is a mirror surface, a focus detection method using reflected laser light is also effective, but since the ceramic substrate surface is often rough, such a focus detection method cannot be adopted.

The present invention projects two types of slit images onto a substrate surface, forms a composite slit image on a detector section through a monitor optical system with a deep focal depth, and calculates the amount of deviation from the focal position from the structure of the composite slit image. The object of the present invention is to provide an automatic focus detection mechanism that can perform focus detection on a rough surface or a mirror surface without using the reflected light of the probe light.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic side view of an automatic focus detection mechanism according to an embodiment of the present invention. In the figure, reference numerals 10° and 12 are parallel beams of light for probes, such as laser beams, which irradiate the slit plates 11 and 13, respectively. The slit plates 11 and 13 each have slits of different shapes. The slit images of the slit plates 11 and 13 are both projected onto the processing surface 15Vc.

In the example shown in FIG. 1, the slit plate 11 has two strip-shaped slits If, and the other slit plate 13 has one strip-shaped slit. In FIG. 1, a processing laser beam 19 is connected to a processing laser total reflection mirror 16. Condensing lens 1
4, the image is formed on the processing surface 15. Note that the processing laser total reflection mirror 16 is configured to allow probe light to pass therethrough, as will be described later. The position B where the processing surface is located is the correct focal position of the laser condenser lens 14, and at this time the composite image of the slits of the slit plate 11.13 is as shown in Fig. 2 (b>
As shown in K, a composite image becomes symmetrical with respect to the optical axis center 23 of the condenser lens 14. In FIGS. 2(a) to 2(C), 21 is an image of the slit plate 11 having two slits, and 22 is an image of the slit plate 13 having one slit. Condenser lens 14 and slit plate 11.13
The machining surface 15 changes from position B to A and C in Fig.
When the position changes, the composite slit image changes from the state shown in FIG. 2(b) to the states shown in FIG. 2(a) and FIG. 2(C), respectively.

Referring again to FIG. 1, the detector unit 18 disposed above the condensing lens 14 and mirror 16 uses one-dimensional COD in this embodiment, and the detector unit 18 is arranged above the condensing lens 14 and the mirror 16. Detects changes in the shape of the slit image. Then, the amount of defocus is estimated from the asymmetry of the slit images 21 and 22 with respect to the optical axis center 23 in FIG. The monitor optical section 17 in this embodiment is designed to have a deeper depth of focus when combined with the condenser lens 14 than when the condenser lens is used alone. This is because it is necessary to correctly detect changes in the shape of the composite slit image even at defocus positions (positions A and C in FIG. 1). In addition, in the above embodiment, a one-dimensional COD was used for the detector section, but
In addition to this, the present invention can also adopt a pattern recognition method using a photodetector such as a two-split or four-split photodetector or an ITV camera.

As described above, by employing the present invention, it is possible to focus not only on a mirror surface but also on a rough surface.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of an automatic focus detection mechanism according to an embodiment of the present invention, and FIG. 2(a) shows a composite slit image when the processed surface is shifted from the focused position to the condensing lens side. Figure 2(b) is a diagram showing the composite slit image when the processed surface is at the focal point position, and Fig. 2(C) is a diagram showing the composite slit image when the processed surface is shifted from the focused position in the direction away from the focusing lens. FIG. 3 is a diagram showing a composite slit image of FIG. 10.12...Parallel light beam for probe. 11.13...Slit plate, □14...Condensing lens, 15...Processing surface, 16...Laser total reflection mirror for processing. 17... Monitor optical section, 18... Detector section, 19... Laser beam for processing, 21.22... Slit image, 23... Optical axis center.

Claims (1)

[Claims] It has a projector that projects two types of slit images at different angles of incidence onto a surface to be focused, and a detector unit that determines the degree of matching of the focus from the form of the composite image of these two types of slits. An automatic focus detection mechanism characterized by: