JPH03209151A - Focusing method for glass substrate defect detecting optical system - Google Patents

Abstract

PURPOSE:To focus a spot and to align a slit by receiving the regularly reflected light from front and rear faces of a bending substrate by a CCD sensor to calculate the vertical extent of movement and the angle of inclination of the substrate. CONSTITUTION:The spot to which a laser beam L is focused is made incident at an angle phi on a glass substrate S, and the regularly reflected light from front and rear faces of the substrate S is received by the CCD sensor to measure the variation of the light reception position. A vertical extent DELTAZ of movement and an angle DELTAtheta of inclination of the substrate are calculated based on a prescribed formula in accordance with the angle phi of incidence and regular reflection, the refractive index and the thickness of the substrate S, the variation of the light reception position, and the distance between the spot and the CCD sensor. The substrate or a defect detecting optical system is vertically moved by DELTAZ to focus the spot, and the slit of a light reception system is moved by the angle 2DELTAtheta and is aligned.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of Industry-L] This invention relates to a method of focusing a defect detection optical system on a glass substrate.

[Conventional technology] Large and sophisticated liquid crystal panels have been developed that are used for image display, with thin film transistors built into each microscopic crystal element. A glass plate is used as the substrate, and if there is a defect on the surface, the quality deteriorates, so it is inspected by a defect inspection device.

FIG. 3(a) shows the basic configuration of a defect detection optical system for a glass substrate (hereinafter simply referred to as a substrate). A laser beam L from a light source (not shown) is angularly deflected, and a spot focused by a focusing lens 2 is projected onto the substrate 1 to be inspected at an incident angle φ, and scans the surface of the substrate 1 in a perpendicular direction. . When there is a defect on the surface, the spot will be scattered, and the scattered light will pass through the Toko lens 3 installed in the direction of the reflection angle ε (ε<φ).
The light is focused by , passes through the slit St of the slit plate 4 provided at the focal position with respect to the spot, and is converted into a photoelectric conversion case 5.
The light is received and the detection voltage is output. In addition, Thrift S
t is used to improve the S/N ratio by removing stray light from places other than the spot.

Now, when it comes to liquid crystal panels, defects that occur in the front panel on which the original device is formed will determine the quality. But the back side! Since it only irradiates the backlight to I1,)
1 (Defects and attached foreign matter on the plate 1l body are not considered as a problem unless they are particularly large. On the other hand, the diameter of the laser beam grooves is made small in order to increase the intensity, so Its depth of focus is not very deep.Therefore, it is necessary to precisely align the focus of the spot on the surface of the plate 1.For this purpose, focusing is performed. There is.

The conventional focusing method will be explained using the 31st sentence I(a) and (b). For a laser beam L with an incident angle φ, the reflection angle φ is 1:11 and 11:. The reflected light LC is focused by the light receiving lens 6 and received by the CCI) sensor 7. Board 1
In the normal case, Lc is received at point a in the figure, and as the substrate 1 moves in the direction of 7 degrees as shown in figure (b), the spot moves from point P to point Q, so Lc becomes ~F. The light receiving position changes to point a' by the row movement. This change in the received light {-j'Z position fa(a'-a) is measured to calculate the L downward movement amount ΔZ of the substrate 1, and the spots are aligned by moving the substrate 1 or the detection optical system.

[Problems to be Solved] As mentioned above, there is no need to detect foreign objects on the back side of the liquid crystal panel since they are not defects. A method is used in which a detection optical system is provided symmetrically also on the back side.

Figure 4(a) shows the method of supporting the board.
is supported by supports 8 at the edges of the periphery.

For this reason, if the size of the λ plate is large, it will curve.

The above method is effective for movement in the -tod direction, but cannot be applied to curved JA plates.

Figure 4(b) explains the problem when applying the above focusing force method to curved double plates.
Take a part of the surface of the board and draw a straight line (plane) with an oblique angle Δθ
shall be carried out. Due to the curvature, subbo 7} moves from point P to point Q.
The spot moves down by ΔZ, and the light receiving position 1a changes from a to a#. Furthermore, due to the inclination angle Δθ, the specularly reflected light Lc
Since the direction of changes by an angle of 2Δ0, the receiving position changes by that amount and becomes a', and as a changing star, (a
'-a) is measured. Note that if the distance between the spot and the CCD sensor 7 is R, then (a - a'') is 2RΔO, but this is included in (a' - a) and cannot be measured alone. As the direction of the reflected light Lc changes, the direction of the optical axis Ls of the light receiving system with respect to the scattered light changes at an angle of 2.
There is a problem in that the focus of the spot deviates from the slit (St) due to a change in Δ0, and it becomes impossible to determine everything.

In the above, Δ2' is different from ΔZ in FIG. 3(b), and Δθ is unknown. Therefore, it is impossible to focus the grooves and position the slits st.

This decision was made in view of the above, and Mtlf]
It is an object of the present invention to provide a method for reliably focusing the subonoto and positioning the slit with respect to the slit.

[A Thousand Steps to Solve the Problem] The present invention provides a projection system that projects a focused laser beam onto a glass substrate and scans it, and a projection system that focuses scattered light due to defects on the surface of the glass substrate. A focusing method for a defect detection optical system consisting of a condenser lens, a slit provided at a focal position 1H of the condenser lens with respect to the spot, and a light receiving system comprising a light receiver that receives the condensed scattered light. be.

A CCD sensor is provided that receives the specularly reflected light of the laser beam from the front and back surfaces of the glass substrate, and measures changes in the light receiving position due to vertical movement and inclination caused by the curvature of the glass substrate.

The amount of upward movement and inclination angle of the glass substrate is calculated from the measured amount of change in the light receiving position, and the glass substrate or defect detection optical system is moved by the calculated amount of vertical movement to align with the surface. In addition, the slit of the light receiving system is moved by the calculated angle of inclination to align the slit with the focal position of the condenser lens.

In the above, the incident angle and the reflection angle of the Luresa beam with respect to the surface of a normal glass substrate are φ, and the refraction angle and thickness of the glass substrate are n. d, the receiving position of the specularly reflected light on the front and back surfaces are a, b, the light receiving position changed due to the bending of the glass μ plate is a', b, and Suboto and -1- C C
I) When the distance between the sensors is R, the inclination angle Δ0 of the J-Yo plate is
and -human movement amount Δ2 are expressed by the following formula: Δ0=sln-' [Δt÷( 2 d tanφ'
cosφ}co

...... (1) However, Δj= (b
'-b)-(a'-a)...(2) Δz=(1-tanφ tanΔ0) X[(a'-a)-2R Δ θ cosφ
÷ sin2 φ・・・・・・(3) sinφ' = (sinφ)÷n
− − Calculate according to (4).

[Sakukawa: From the above calculation formulas (1) to (4), the tilt angle ΔO of the substrate
] Since the needle movement amount ΔZ can be changed, the spot is focused by moving the substrate or detection optical system up and down ΔZ using an appropriate moving mechanism, and the slit plate is also moved angularly by 2ΔO with respect to the spot. the slits are aligned.

Here, the above calculation formulas (1) to (4) can be obtained by taking the - part of the curved plank, imitating it as it is, and graphically analyzing the change in the direction of specularly reflected light with respect to it. The analysis method and results will be explained in the next example.

[Example] Using Figures 1 (a) and (b), first, the direction of specularly reflected light with respect to the surface of the C plate which is inclined due to curvature is analyzed.

i[The plane of the part of the substrate whose surface is S1 bay■ is S'', and the inclination angle is Δθ.On the other hand, the spot of the laser beam L is projected at the incident angle φ. As in FIG. 4(b), the spot moves from point P to point Q due to the bay l11], and the difference in height between them is ΔZ'.

The specularly reflected light Lc in the direction of the IE reflection angle φ is reflected by the surface S
The light is received at point a of CD and at point a' by plane S'. Now, when Δθ=0, the receiving position of the specularly reflected light at point Q is represented by a#, and if a perpendicular line is drawn from point Q to line segment Pa and the intersection is T, the length of line segment TQ is (a”-a). Also, as can be seen in the detailed view of figure (b), point P
The angle between PQ and the modulus apv of surface S at is φ, and PQ
Since the angle between and TQ is (2φ-π/2), (a”-
The following relational expression holds between a) and Δz' (=PV).

(a”-a)=TQ=PQ sin2φ=Δ2′÷co
sφXsjn 2φ (5) In this case, the change in the specularly reflected light Lc is also caused by
=2RΔθ is added, (a'-a)=Δzsin2φ÷COSφ+2RΔθ
・・・・・・(6)
becomes. Here, R is the known distance between the spot and the CCD sensor, and (a a) is the waste to be measured.

Note that the direction of the optical axis LS of the light receiving system with respect to the scattered light is at an angle of 2
As mentioned above, Δ0 changes.

In order to focus the spot, it is necessary to return from point Q to P, and either the substrate or the detection optical system is moved up and down, but the displacement may be Δ2 as shown in the figure instead of Δ2'.

This difference is shown in the figure as ΔZ - Δz=VQtanΔθ :PQsinφtanΔθ =Δz' tanφtanΔθ Transforming this, Δz=(1−tanφtanΔ0)Δ2' is changed, and then Δ2' is calculated from equation (5) and equation (3) I can be hatched.

Δz=(1−tanφ tanΔ0) X[(a' −a) −2R Δθ cosφ
÷ sln2 φ...(3) Here, it is assumed that Δθ is a tree or has been found, and if the substrate or detection optical system is moved up and down by Δ2 calculated by equation (3), the point can be reached. Q returns to P. However, since the λ plate remains tilted, is it light? It is still necessary to align Ls with slit St. For this purpose, the distance between the spot and the slit plate 4 is set to D, and the slit plate is moved by 2DΔ0 in a direction perpendicular to the optical axis.

In this invention, in order to find Δ0, a method is used to detect specularly reflected light from the back surface as well as the front surface, and this is detected by the second
Figure (a). This will be explained using (b) and (C). Figure (a
), in the case of a normal substrate, the projected laser beam L is refracted at point Q on the surface S by the refraction 'I n of the substrate, and then FI
The specularly reflected light beams 1. and c2 have the same direction as the specularly reflected light beams Lcl from the point P.ノ■
(Due to the curvature of the plate, the refracted and reflected light Lc2 from the front surface S' and back surface B', which have moved to L and tilted, is Δ from the original point Q''.
Light is emitted from point Q', which is lowered by Z#, is received at point b', and (b'-b) is measured. Assuming that specularly reflected light Lc2 is emitted from point K at the same height as point Q, the light receiving position will be point b#. Point Q' and point K in this case
The difference in quality is (Δ2'-Δ2"), which is (b'
−b”) (=Δt). However, (b
'-b'') cannot be measured.

To find this, Δt is the inclination angle Δθ, so surface S'
Note that corresponds to the distance descended from point Q to Q'. In figure (C), from point K to line segment Q' b
Draw a perpendicular line to ' and let the intersection point be J, then triangle KJQ'
The relationship between Δt and Δ0 can be determined by:

sinΔO=Δt÷(QQ' cask) --(
7) However, if k=π/2-φ-Δ0=π/2-φ and the thickness of the substrate is d, then QQ': 2d tan
Since φ', equation (7) becomes the following equation.

sinΔO=Δt÷(2dtanφ' sinφ)−
(8) Here, the incident angle φ and the refraction angle φ' are sinφ' = (sinφ〉÷n = (
4) There is a relationship.

Next, Δt is the change m (b' b) and (a' - a) Z in the reception f1γ position of the reflected lights Lc1 and Lc2, respectively.
It can be found from i. The reason for this is that, as described above, Δt is caused by the difference in height between points Q and Q' due to the slope of surface S'. Therefore, Δt= (b'-b)
- (a' -a) ·-={2).

Rearranging the above, the formula for Δ0 is: Δ0=sln-' [Δt÷( 2 d tanφ'
cosφ) ko...0) Changed.

Calculation formulas (1) to (1) in this invention obtained from the above
When applying 4) to focusing on a glass substrate, it is necessary to quickly perform calculations for each point on the substrate in response to the movement of the lens. For this purpose, data of Δθ with respect to Δt according to formula (1) and data of ΔZ with respect to ΔO and (a'-a) according to formula (3) are set to R.
Δt stored in the OM table and totaled by i1tl1
Δ0 was calculated for Δ0, and then ΔO was measured (a'-
The method of determining ΔZ using a) is effective. Further, it is preferable to use the ROM for the moving distance #t2DΔ0 of the slit plate. Note that the mechanism for -L movement of the J& plate or the tilted optical system and the mechanism for moving the slit will be omitted.

[Kanmei's effect] As is clear from the explanation below, in the focusing method of the glass substrate defect detection optical system according to the present invention, the specularly reflected light from the front and back surfaces is affected by the movement of the spot due to the curved substrate. The change in direction is graphically analyzed, and the vertical movement distance and inclination angle of the substrate are calculated from the change in the light receiving position of the CCD sensor of the specularly reflected light using the obtained calculation formula.
It is possible to focus the spot on the substrate and align the slit with respect to the spot, which has a great effect on improving the reliability of the detection data of the defect detection optical system for the glass substrate of the liquid crystal panel. be.

[Brief explanation of drawings]

1(a) and 1(b) are analytical diagrams for the direction change of specularly reflected light due to the surface of a curved glass κ plate in the focusing method of the glass substrate defect detection optical system according to the present invention, and FIG. a), (b) and (c) are shown in Fig. 1(a).
, (b) An analysis diagram of the direction change of the IE reflected light due to the back surface of the glass substrate, Fig. 3 (a) and (b)
is a basic configuration diagram of the defect detection optical system for glass substrates,
FIGS. 4(a) and 4(b) are explanatory views of the conventional method of focusing the laser spot on the substrate
FIG. 3 is an explanatory diagram of problems with tth and spot focusing. 1... Glass substrate, 2... Focusing lens, 3
...Condenser lens, 4.Slit plate, 5.
...Photoelectric converter, 6...Focusing lens, 7...
C C I) Sensor, 8... Support shell, L...
Laser beam, LCl, LC2... specular reflection light,
Ls...Optical axis, φ...Incidence angle, 11.
, reflection angle, ε...reflection angle, φ'...kj
{Reflection angle, Δ0...Solid angle of the substrate, d...Thickness of the substrate, n...Refractive index of the substrate, R, D...Distance. Patent source

Claims (1)

[Claims] (1) A projection system that focuses a laser beam onto a spot and projects it onto a glass substrate to scan it, a condensing lens that condenses light scattered by defects on the surface of the glass substrate, and a condensing lens that condenses light scattered by defects on the surface of the glass substrate; In a defect detection optical system constituted by a slit provided at the focal point of a lens and a light receiving system including a light receiver that receives the focused scattered light, the laser beam is detected by the front and back surfaces of the glass substrate. A CCD sensor is provided that receives each specularly reflected light and measures the amount of change in the light receiving position due to the vertical movement and tilt caused by the curvature of the glass substrate, and from the measured amount of change, the amount of vertical movement and the amount of vertical movement of the glass substrate is determined. Calculating the tilt angle, moving the glass substrate or the defect detection optical system by the vertical movement amount to focus the spot on the surface, and moving the slit of the light receiving system by the tilt angle. A method for focusing a glass substrate defect detection optical system, the method comprising: aligning the focal point of the condensing lens.