JP2002107120A - Position detector for surface and rear, and apparatus and method for marking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detector for the surface and the rear, which can be applied to a marking apparatus which hardly damages the rear of an object to be marked. SOLUTION: A bolding base holds the object having a surface and a rear. Using a light source, a light-beam flux is made incident on the object held by the holding base from the side of the surface obliquely with respect to the surface. The light-beam flux emitted from the light source is reflected by the surface of the object, held by the holding base, and it turns into a first reflected light. It is refracted by the surface of the object, reflected by the rear of the object, refracted again by the surface of the object, and turns into a second reflected light. The first reflected light and the second reflected light are incident on the light-receiving face of a photodetector. The photodetector detects the position of a beam spot by the first reflected light and that of a beam spot by the second reflected light on the light-receiving face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an apparatus for detecting the positions of the front and back surfaces of an object, and an apparatus for marking the inside of the object using the apparatus.

[0002]

2. Description of the Related Art Japanese Patent Laying-Open No. 11-156568 discloses a method for marking inside a laser beam by condensing a laser beam inside the object to be marked to generate cracks. In this method, the laser beam is focused inside the marking target object by the fθ lens. Since the fθ lens is used, the depth from the surface of the marking object to the focal point can be kept constant even if the optical axis of the laser beam is changed. Thus, a mark can be formed at a desired depth inside the marking object. Further, Japanese Patent Application Laid-Open No. H11-156568 discloses a method for improving the accuracy of the depth of a converging point in consideration of the refractive index of an object to be marked.

[0003]

Even if the depth from the surface of the marking object to the focal point is strictly adjusted, the back surface of the marking object (the surface opposite to the laser beam incident surface) ) May be damaged. Despite the fact that the focal point of the laser beam is located inside the object to be marked, cracks occur on the back because the energy density (threshold) per pulse required to generate cracks is high. It is considered that the height is low on the back surface of the marking target. Possible reasons for the lower threshold value on the rear surface include the effect of fine particles adsorbed on the rear surface, the effect of heat due to contact with the holding table heated by the laser beam, and the reflection of the laser beam on the rear surface.

[0004] It is an object of the present invention to provide a marking device and a marking method in which the rear surface of a marking object is hardly damaged.

It is another object of the present invention to provide a front and back position detecting device applicable to the above-described marking device.

[0006]

According to one aspect of the present invention, a holding table for holding an object having a front surface and a back surface;
A light source that causes a light beam to be obliquely incident on the surface of the object held on the holding table from its surface side, and a light beam emitted from the light source is an object held on the holding table. A light-receiving surface on which a first reflected light reflected on the surface of the object and a second reflected light refracted on the surface of the object, reflected on the back surface of the object, and re-reflected on the surface of the object again And a light receiving device for detecting the positions of the beam spots of the first and second reflected lights on the light receiving surface.

[0007] One ray bundle is split into two beams on the surface of the object, and these two beams are observed. For this reason, the position of the front surface and the back surface can be detected only by installing one light source.

According to another aspect of the present invention, a holder for holding a marking object having a front surface and a back surface, a laser light source for emitting a laser beam, and a laser beam emitted from the laser light source, A light-collecting optical system that allows the light to enter from the surface side of the marking object held by the laser beam and condense the light inside the marking object, and change the depth of the light-converging position in the marking object; On the marking object held on the table, the measurement light beam from the surface side thereof, a measurement light source for obliquely entering the surface, and the measurement light beam of the object held on the holding table. The first reflected light reflected on the surface, and the light receiving surface on which the second reflected light refracted on the surface of the object, reflected on the back surface of the object, and further refracted on the surface of the object is further incident. Having the light receiving surface A light receiving device for detecting the positions of the first and second reflected light beam spots, and the condensing optics based on the first and second reflected light beam spot positions detected by the light receiving device. A control device for controlling the depth of the focusing position of the laser beam focused by the system.

From the positions of the beam spots of the first and second reflected lights, the positions of the front surface and the back surface of the marking object can be determined. Since the depth of the focused position of the laser beam is controlled based on the determined positions of the front surface and the back surface, more precise depth control is possible.

According to another aspect of the present invention, a step of obliquely inputting a measuring light beam from a front surface side to a marking object having a front surface and a back surface, and holding the measuring light beam on the holding table. The first reflected light reflected on the surface of the subject, and the second reflected light refracted on the surface of the subject, reflected on the back of the subject, and further refracted on the surface of the subject. Receiving the light on a light receiving surface, and determining the positions of the front and back surfaces of the marking object from the positions of the beam spots of the first and second reflected lights on the light receiving surface; A step of converging a laser beam at a position at a certain depth from the surface of the marking target to perform the marking based on the above method.

Since the depth of the focused position of the laser beam is controlled based on the determined positions of the front surface and the back surface, more precise depth control becomes possible.

[0012]

FIG. 1 is a schematic diagram of a marking device according to an embodiment of the present invention. The laser light source 11 emits a pulse laser beam. As the laser light source 11, for example, a mode-locked Ti: sapphire laser oscillator can be used. The Ti: sapphire laser oscillator emits a pulse laser beam having, for example, a pulse width of 130 fs, a wavelength of 800 nm, an average output of 1 W, and a pulse repetition frequency of 1 kHz. Alternatively, a YAG laser oscillator or a YLF laser oscillator can be used as the laser light source 11. Alternatively, various laser light sources that generate a harmonic laser can be used by combining these laser oscillators and a nonlinear optical medium.

On the holding table 15, the objects to be marked 1,
For example, a glass substrate is held. The marking target 1 is held so that its front surface is directed upward and its back surface is in contact with the holding base 15. Consider an XYZ orthogonal coordinate system in which a plane parallel to the surface of the marking target 1 held by the holding base 15 is an XY plane, and a normal direction of the surface is a Z axis.

A laser beam emitted from a laser light source 11 enters a beam shaper 12. Beam shaper 12
Makes the power density distribution in the beam cross section of the laser beam close to a desired distribution and shapes the cross section.

The shaped laser beam enters the galvano scanner 13. The galvano scanner 13 includes a pair of galvanometer mirrors 13x and 13y.
The galvanometer control system 19 includes the galvanometer mirrors 13x and 13x.
Controls the oscillating movement of y. Galvanometer mirrors 13x and 1
The laser beam reflected at 3y enters the fθ lens 14. lens 14 focuses the laser beam inside the marking target 1. The galvano scanner 13
By shaking the optical axis of the laser beam, the focal point inside the marking target 1 can be moved in a direction parallel to the XY plane. The lens driving device 18 adjusts the height of the fθ lens 14 from the holding table 15.

The control unit 30 synchronizes the repetition of the pulse of the pulse laser beam emitted from the laser light source 11 with the scanning of the optical axis of the laser beam by the galvano scanner 13.

An observation laser light source 16 makes an observation laser beam obliquely incident on the surface of the marking object 1. The observation laser light source 16 is composed of, for example, a HeNe laser oscillator or the like. The light receiving device 17 receives the reflected light of the laser beam emitted from the observation laser light source 16 on the light receiving surface. The light receiving device 17 is composed of, for example, a CCD camera or the like, and can detect the position of a beam spot on the light receiving surface.

Referring to FIG. 2, a description will be given of a method for determining the positions of the front surface and the back surface of the marking target 1 from the position of the beam spot on the light receiving surface of the light receiving device 17.

FIG. 2 shows the state of propagation of the laser beam within the plane of incidence of the observation laser beam on the surface of the marking target 1. A reference plane 20 parallel to the front surface 1F and the back surface 1R of the marking target 1 is defined. The position of the beam spot on the light receiving surface when the observation laser beam is assumed to be reflected by the reference plane 20 is defined as a reference point O. When the positions of the observation laser light source 16, the reference plane 20, and the light receiving device 17 are fixed, the reference point O can be determined on the light receiving surface.

The distance between the reference plane 20 and the surface 1F is g ₁ ,
The distance between the reference plane 20 and the rear 1R and g _2. Surface 1
The incident angle of the observation laser beam to F is θ ₁ and the refraction angle is θ ₂ . Let A be the position of the beam spot on the light receiving surface of the observation laser beam reflected by the surface 1F. Surface 1
The position of the beam spot on the light receiving surface of the observation laser beam refracted at F, reflected at the back surface 1R, and further refracted at the surface 1F is denoted by B. The distance between the reference point and the point A and d _1, the distance between the points A and B and d _2.

The interval g ₁ is

[0022]

G ₁ = d ₁ / (2 tan θ ₁ ) (1) Also, assuming that the refractive index of the marking object 1 is n,

[0023]

## EQU2 ## The following holds: sin θ ₁ / sin θ ₂ = n (2) The interval g ₂ is

[0024]

G ₂ = g ₁ + d ₂ / ( ₂ tan θ ₂ ) (3) From equations (1) to (3), θ ₁ , d ₁ and d ₂
Is determined, the intervals g ₁ and g ₂ can be obtained. That is, the relative positions of the front surface 1F and the back surface 1R with respect to the reference plane 20 can be determined.

In the method described with reference to FIG.
The laser beam is divided into two beams by partially reflecting the laser beam, and the two beams are observed. For this reason, it is possible to detect the positions of the front surface 1F and the back surface 1R only by preparing one observation laser light source 16.

When the points A and B are too far apart, for example, when the incident angle θ ₁ is large or when the marking target 1 is thick, the light is condensed between the light receiving device 17 and the marking target 1. A lens or the like may be arranged so that the optical axes of the two laser beams gradually approach each other. In this case, it is necessary to consider the magnification of the condenser lens when calculating the intervals g ₁ and g ₂ .

Returning to FIG. 1, the description will be continued. Light receiving device 17
, Beam spot position information, for example, the distances d ₁ and d ₂ shown in FIG. Control device 3
0 calculates the relative positions of the front surface 1F and the back surface 1R of the marking target 1 with respect to the reference plane 20 shown in FIG. Thus, the position (Z coordinate) in the thickness direction where the laser beam is to be focused is determined. Here, the position to be focused means a position where the beam diameter becomes minimum.

The lens driving device 18 adjusts the height of the fθ lens 14 so that the laser beam is focused on the determined position. When the refractive index of the marking target 1 is n, the depth from the surface 1F of the marking target 1 to the light condensing position is n times the depth when the refractive index is set to 1. Therefore, when adjusting the height of the fθ lens 14, it is preferable to consider the refractive index of the marking object 1.

In the above embodiment, the relative positions of the front surface 1F and the rear surface 1R of the marking object 1 with respect to the reference plane 20 are detected, and the focusing position of the laser beam is controlled based on the relative positions. For this reason, it is possible to prevent a shift in the depth of the light condensing position due to a variation in the thickness of the marking target 1.

Next, a preferred depth of the light condensing position will be described. As the laser beam for marking, assume laser beam of TEM ₀₀ mode is superior in quality. The spot diameter d when condensing a laser beam having a Gaussian intensity distribution is

[0031]

D = λf / (πD) (4) Where λ is the wavelength, f is the focal length of the lens, D
Is the beam diameter of the beam incident on the lens. Assuming that the refractive index of the marking target 1 is n and the depth from the surface 1F to the focusing position is s _F , the beam spot diameter d _F on the surface 1F is

[0032]

[Number 5] becomes a _{d F = ns F / (fD} ) ··· (5). Here, it is assumed that the beam spot at the focusing position is infinitesimal. Similarly, assuming that the depth from the back surface 1R to the condensing position is s _R , the beam spot diameter d _R on the back surface 1R is

[0033]

D _R = ns _R / (fD) (6)

Surface 1F and back 1 of marking object 1
In order to prevent the occurrence of cracks in R,
And the energy density of the laser beam on the back 1R,
It must be smaller than the threshold at which cracks occur. According to various experiments performed by the inventor of the present application, the rear 1R
Is about 2 of the threshold value on the surface 1F.
/ 3. That is, cracks are more likely to occur on the back surface 1R than on the front surface 1F.

The energy density in the cross section of the laser beam is
It is inversely proportional to the square of the beam spot diameter. Therefore, surface 1
In order not to exceed the threshold value of crack generation at both the F and the rear surface 1R and to exceed the threshold value at which the crack occurs at the condensing position,

[0036]

It is preferable that d _F / d _R = (2/3) ^1/2 (7). From equations (5) to (7),

[0037]

S _F / s _R = (2/3) ^1/2 (7)

As shown in FIG. 2, since the relative positions of the front surface 1F and the back surface 1R with respect to the reference plane 20 are measured,
The height of the fθ lens 14 can be adjusted so that the depths s _F and s _R satisfy Expression (7).

In the above embodiment, the case where the marking is performed by generating a crack inside the object to be marked has been described. However, the marking is performed by changing the refractive index of the condensing position without generating the crack. It is also possible. Also in this case, the marking target 1
By measuring the positions of the front surface 1F and the back surface 1R, and controlling the depth of the condensing position based on the positions, the surface 1F
Marking can be performed without damaging the rear surface 1R.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0041]

As described above, according to the present invention,
By irradiating one measurement light beam, it is possible to detect the positions of both the front surface and the back surface of the object. By adjusting the depth of the condensing position of the laser beam based on the detected positions of the front surface and the back surface, it is possible to prevent a displacement due to a variation in the thickness of the target object or the like.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a laser marking device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a method of detecting the positions of a front surface and a back surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Marking target 11 Laser light source 12 Beam shaper 13 Galvano scanner 14 fθ lens 15 Holder 16 Observation laser light source 17 Light receiving device 18 Lens driving device 19 Galvano control device 20 Reference plane 30 Control device

Claims (3)

[Claims] 1. A holding table for holding an object having a front surface and a back surface, and a light source for causing a light beam to be obliquely incident on the object held by the holding table from the front surface side, A light beam emitted from the light source is first reflected light reflected on the surface of the object held by the holding table, and refracted on the surface of the object, reflected on the back surface of the object, A light-receiving surface on which the second reflected light refracted on the surface of the object is incident, and a light-receiving device for detecting a position of a beam spot of the first and second reflected lights on the light-receiving surface; Front and back position detection device. 2. A holder for holding a marking object having a front surface and a back surface, a laser light source for emitting a laser beam, and a marking object for holding the laser beam emitted from the laser light source on the holding table. A focusing optical system capable of changing the depth of a focusing position in the marking object by allowing light to enter from the surface side of the marking object and condensing the inside of the marking object; and a marking object held by the holding table. An object, a measurement light source that obliquely enters a measurement light beam from the surface side of the object, and a first light source in which the measurement light beam is reflected by the surface of the object held by the holding table. Reflected light, and a light receiving surface on which the second reflected light refracted on the surface of the object, reflected on the back surface of the object, and further refracted on the surface of the object is incident, on the light receiving surface The first and second A light receiving device for detecting the position of the beam spot of the reflected light, and a laser focused by the light collecting optical system based on the positions of the beam spots of the first and second reflected lights detected by the light receiving device. A control device for controlling the depth of the beam focusing position. 3. A step of obliquely inputting a measurement light beam from a front surface side to a marking object having a front surface and a back surface, and the measurement light beam is held on a surface of the object held by the holding table. The first reflected light reflected, and the second reflected light refracted on the surface of the object, reflected on the back surface of the object, and further refracted on the surface of the object, is received on the light receiving surface, A step of obtaining the positions of the front and back surfaces of the marking object from the positions of the beam spots of the first and second reflected lights on the light receiving surface; and Focusing the laser beam at a position at a certain depth from the surface of the object to perform marking.