JPH0645931Y2 - Laser scanning optical system - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention is mainly directed to high-speed and high-precision positioning of laser light,
The present invention relates to a laser scanning optical system used in a laser trimming device that needs to perform scanning and an object thickness detection device that uses laser light.

[Conventional technology]

Conventionally, in this type of optical system, generally, when it is desired to obtain an arbitrary scanning amount, a galvanometer type optical scanner is used to drive the deflection mirror, and the converging light is rotated by the rotation angle of the deflection mirror and the movement on the image plane. An fθ lens designed to have a proportional amount is used.

[Problems to be solved by the device]

However, in the above-described conventional method, no matter how accurately the galvanometer type optical scanner is controlled, the scanning distortion in the image plane caused by the engineering distortion of the fθ lens itself does not improve the characteristics of the fθ lens unless the characteristics of the fθ lens are improved. In many cases, it is difficult to solve the problem. In particular, as shown in FIG. 2, in the case of using an fθ lens having a characteristic (the deviation of the telecentricity is large) with respect to the principal axis as the principal ray on the output side is further away from the lens center in order to obtain a large scanning width. In addition, there is a drawback that not only the image is blurred when the distance between the lens and the sample surface is changed, but also the size (scanning width) of the image is changed. In order to solve this, an fθ lens having a sufficiently large aperture including the scanning width and the incident beam diameter is used, and the characteristic that the chief ray on the output side is completely parallel to the principal axis of the lens (completely telecentric). (2) an optical system, or a control system and mechanism for keeping the distance between the sample surface and the fθ lens precisely constant even if the sample changes.

[Differences from the Prior Art of Invention]

The above-mentioned conventional optical system requires a large-diameter lens that takes the scanning surface and the beam diameter into consideration, a unit that measures the distance between the fθ lens and the sample, and a mechanism that moves the sample surface in the axial direction with respect to the optical axis. On the other hand, in the optical system of the present invention, the thickness of the sample object is simply measured without using these means,
The difference is that the change of the scanning width is obtained by calculation according to the difference and is fed back to the control unit of the galvanometer type optical scanner.

[Means for Solving the Problems]

In the optical system according to the present invention, a galvanometer type optical scanner, a scan mirror attached to the axis of the scanner, an fθ lens, a means for measuring the thickness of the sample, and a change in the thickness converted into a change in the scanning width. And a control unit for correcting the rotation angle of the galvanometer type optical scanner.

〔Example〕

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

FIG. 1 is a schematic view of the configuration of an embodiment of the present invention. In the figure, a laser beam 2 passes through a galvanometer type optical scanner (hereinafter, scanner) 3 and is focused on a sample 4 through an fθ lens 1. Here, when the laser light 2 is condensed using the portion closest to the periphery of the fθ lens 1, the light beam is inclined by Δθ from the main axis of the lens as shown in FIG. Therefore, if the thickness of the sample 4 changes by Δt, the amplitude Δ changes by Δt · tan Δθ and becomes 1 ′. If the characteristics of the fθ lens 1 are known in advance, the change in the amplitude (Δt · tan Δθ) with respect to the change in the thickness of the sample 4 at an arbitrary position can be calculated.

FIG. 3 is a block diagram of the control unit 5 that performs the calculation.

Here, the thickness measuring unit 6 is a unit for measuring the thickness Δt of the sample 4 using a well-known means, although the details are not described. The arithmetic processing unit 7 is a control unit including software. Further, the scanner driver 8 drives the scanner 3 with a signal from the arithmetic processing unit 7. The unit of each of these control units makes it possible to correct the rotation angle of the scanner according to the thickness of the sample and keep the amplitude Δ on the sample surface constant. Of course, the change in the thickness of the sample is not limited, but is allowed within the range of the depth of focus of the laser light.

[Effect of device]

As described above, the present invention measures the thickness of a sample in a laser beam scanning device that scans a laser beam on a sample surface by combining a galvanometer type optical scanner and an fθ lens, and converts the change into an amplitude change by calculation. Then, by feeding back the rotation angle of the galvanometer type optical scanner as a signal for controlling, a fθ lens having a large aperture, a mechanism for moving the position of the sample in the axial direction, or the like is used, and the scanning amplitude of the change of the sample thickness Since correction is possible, it is very effective when particularly precise amplitude accuracy is required.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG. 2 is fθ.
FIG. 3 is a block diagram of a control unit, and FIG. 3 is a diagram for explaining the inclination of a light beam around the lens. 1 ... f.theta. Lens, 2 ... laser light, 3 ... galvanometer type optical scanner, 4 ... sample surface, 5 ... control unit, 6 ... thickness measuring unit, 7 ... arithmetic processing unit, 8 ... scanner driver.

Claims (2)

[Scope of utility model registration request] 1. A laser beam scanning device for scanning a laser beam on a sample surface in combination with a galvanometer type optical scanner and an fθ lens, and a measuring means for measuring the thickness of the sample, and the thickness according to the output of the measuring means. Laser scanning optical system including a control unit for converting a change in the scanning width into a change in the scanning width by the galvanometer type optical scanner and feeding back the control to the scanner. 2. The controller controls the amount of change in the amplitude of the scanning beam Δt · tan, where Δt is the thickness measured by the measuring means.
The rotation angle of the scanner is controlled so that Δθ (Δθ is the inclination of the beam farthest from the main axis of the fθ lens with respect to the main axis) is zero, and the rotation angle of the scanner is controlled. Laser scanning optical system.