JP2000258116A - Height measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the load on an operator while faster operation is realized. SOLUTION: Related to a galvano-mirror 104 which scans, with a measurement light, a specimen 101 which is examined and provided on a pupil plane of an objective lens 102 which, arranged in opposition to the specimen 101, converges the measurement light, a projection position of an axisymmetric image by an imaging optical system which, elongated along the line towards the rotational center, images the axisymmetric image at a position which is axisymmetric about the optical axis of the optical flux which has transmitted the objective lens 102 after reflected on the specimen 101 I comprised along the longitudinal direction of the form.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a lead frame,
The present invention relates to a ball grid array (BGA), and more particularly, to a height measuring apparatus used for shape inspection of a minute object represented by an electric component such as a bump, particularly, height measurement.

[0002]

2. Description of the Related Art For example, in a semiconductor manufacturing process, there is a process of measuring the height of a minute and continuous structure such as a lead grid of a lead frame or a ball grid array for mounting a bare chip. Semiconductor components are becoming more and more highly integrated, and accordingly, there is a demand for a height measuring device capable of measuring many measuring points on these measuring objects at higher speed.

Conventionally, as a height measuring apparatus applied to such a semiconductor manufacturing process, an apparatus which measures the height of a measuring point using a defocus signal has been considered. In other words, in such an apparatus, the measurement point of the measurement object is
A light beam is irradiated through an objective lens, the reflected light is split by a beam splitter, and one of the split beams is detected by a first light receiving element via a first stop disposed in front of a focal plane, and the other is detected. Is detected by the second light receiving element via the second stop disposed behind the focal plane.
In this case, the output signals of the first and second light receiving elements are in-focus, and the difference is zero. In the vicinity thereof, a positive sign corresponding to the defocus and a focus having a magnitude corresponding to the defocus amount are provided. A shift signal is obtained, and the objective lens is moved in the height direction so that the focus shift signal becomes zero, and by measuring the height of the objective lens at this time,
The height of the measurement point of the measurement object is determined.

[0004]

However, in such a height measuring device, the height of one measuring point on the object to be measured is measured, and the height of the one point is measured. Each time, the stage scans and moves to the next measurement point, so as seen in recent electronic components, height measurement of multiple points has been performed in the trend of high density and large size of mounted components. It takes an enormous amount of time to measure what needs to be done at each location where it is necessary, which not only imposes a heavy burden on the workers, but also significantly lowers the work efficiency. There was a problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a height measuring device capable of reducing the burden on an operator and realizing a high-speed operation.

[0006]

According to the first aspect of the present invention,
A light source that emits measurement light, an objective lens that is disposed to face the subject, and converges the measurement light on the subject, and that is rotatably provided near a pupil plane of the objective lens or a conjugate plane thereof. An optical scanning mirror that scans the measurement light, an imaging optical system that forms an axially symmetric image at a position that is axially symmetric with respect to the optical axis of the light beam transmitted through the objective lens from the reflected light of the subject, and Light position detecting means disposed on an image forming plane of the image forming optical system and detecting a light spot whose position changes according to the height of the subject; and the light scanning mirror extends along a rotation center direction. And a size that includes a projection position of an axially symmetric image by the imaging optical system along a longitudinal direction of the shape.

According to a second aspect of the present invention, in the first aspect of the present invention, a collimating optical system is provided, and the measurement light emitted from the light source satisfies an axially symmetric region where the optical axis of the objective lens is symmetrical. The method is characterized in that a light beam having a light beam diameter is generated, and the light beam is projected on the subject along the axially symmetric region.

According to a third aspect of the present invention, in the second aspect, the collimating optical system comprises a light source and first to third lens systems, and the first to third lens systems are If the respective NAs are NA1, NA2, and NA3 and the focal lengths are f1, f2, and f3, NA1f1 ≧ NA2
f2, NA2 ≦ NA3, and f3≪f2.

As a result, according to the first aspect of the present invention,
Since the continuous height measurement can be performed for each measurement point based on the reflected light from the subject, it is possible to realize a high-speed measurement of the height of a high-density measurement object requiring measurement of many points, In addition, by using an optical scanning mirror having a small inertia, a higher-speed height measurement can be realized.

According to the second or third aspect of the present invention, the beam diameter of the projection beam can be minimized, and an unmeasurable area due to insufficient light quantity can be reduced.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a schematic configuration of a height measuring apparatus to which the present invention is applied.

Referring to FIG. 1, reference numeral 101 denotes an object, which is mounted on a stage (not shown) and is movable in at least one direction (a direction orthogonal to the scanning direction of the measuring light in the object plane). ing.

The objective lens 10 is opposed to the subject 101.
2 are arranged. As the objective lens 102, an object-side telecentric lens designed at infinity is used.

At the center of the pupil plane 103 of the objective lens 102, a galvanomirror 104 having its center of rotation is arranged. The galvanomirror 104 is rotatable by a control circuit (not shown).

A laser diode 105 is arranged corresponding to the galvanometer mirror 104. The measurement light emitted from the laser diode 105 is converted into parallel light by a collimator lens 106, transmitted through a polarizing beam splitter 107 and a 波長 wavelength plate 108, reflected by a galvano mirror 104, and reflected by an objective lens 102. By
The light is converged telecentrically at an arbitrary position on the surface of the subject 101 as convergent light having an NA determined by the pupil diameter and the focal length of the objective lens 102. The measurement light reflected by the subject 101 is transmitted through the objective lens 102,
After being reflected by the galvanometer mirror 104, the １ ／ wavelength plate 1
08, is reflected by the polarization beam splitter 107, and is focused on the primary image plane 110 by the first imaging lens 109.

The luminous flux passing through the primary image plane 110 passes through a pupil relay lens 111, which is a second objective lens designed to be an infinite system, and is divided into a substantially semicircular shape by a right-angle mirror 112. , 113b, and apertures 114a, 114b, and are condensed on optical position detecting elements (PSDs) 116a, 116b by separator lenses 115a, 115b as second imaging lenses.

Here, the front focal point of the first imaging lens 109 is on the pupil plane 103 of the objective lens 102, and the separator lenses 115a and 115b are the rear focal plane of the pupil relay lens 111 which is the second objective lens. , The separator lenses 115 a and 115 b are located at positions conjugate with the pupil plane 103 of the objective lens 102. Further, the separator lenses 115a and 115b form measurement spots on the light position detection elements (PSDs) 116a and 116b with the luminous flux of the measurement light reflected from all the measurement points and passing through the same portion of the pupil plane 103. Will do.

As is clear from the figure, the subject 1 irradiated by the change in the angle of the galvanomirror 104 is illuminated.
The reflected light from all the points 01
By being reflected at 04, the light travels exactly the same path as the light projection optical path, and always forms an image on the axis of the primary image plane 110. Thereby, the light position detecting elements (PSD) 116a, 116
The spot b moves only when the height of the subject 101 changes.

On the other hand, assuming that stop images 114 'formed by the stops 114a and 114b are arranged at both ends of the pupil image 103' formed by the pupil plane 103 of the objective lens 102 as shown in FIG. The fact that the positions of the spots incident on the light position detection elements (PSDs) 116a and 116b change in opposite directions is based on the well-known principle of triangulation.

Accordingly, a control circuit (not shown) measures the coordinates X and Y of the measurement position of the subject 101 known from the angle of the galvanometer mirror 104 and the position of the stage, and the light position detection elements (PSDs) 116a and 116b. The subject 101 is calculated based on the deviation amounts δ1 and δ2 from the center of the spot position.
Height can be determined.

Next, the calculation method will be described in detail with reference to FIG.

FIG. 2 shows only the portion behind the primary image plane 110 shown in FIG. 1, and the subject image on the primary image plane 110 is considered as a new subject image 101 '.

As a system parameter, the focal length of the pupil relay lens (second objective lens) 111 is expressed by f
p, the focal length of the separator lenses 115a and 115b is fs, the imaging magnification of the primary image is M, the height from the optical axis to the center of the separator lenses 115a and 115b is h, and the pupil relay lens 111 and the separator lenses 115a and 115b. Is D, and the NA of the objective lens 102 is NA _OB .

The defocus amount (height) Z 'of the primary image is
When the height of the subject and Z, a ZM ^2, the PSDs (PSD) 116a, the 116 b, a light spot is formed at a position of δ from the center. At this time, from the figure, δ becomes δ = fs · tanα (1) tanα = h / (b−D) (2)

Therefore, δ = fs · h / (b−D) (3) h = fp · NA _OB / MP (4) Here, P is the ratio P = Φ / φ between the distance φ to the center of the stop image 114 ′ calculated on the pupil image 103 ′ of the objective lens 102 shown in FIG. 3 and the radius Φ of the pupil image 103 ′.

Next, when b is calculated,

[0028]

(Equation 1)

Therefore,

[0030]

(Equation 2)

## EQU1 ## To summarize these equations,

[0032]

(Equation 3)

## EQU1 ## Further, as described above, since the distance D between the separator lenses 115a and 115b and the pupil relay lens 111 is fp,

[0034]

(Equation 4)

Thus, δ and Z have a completely linear relationship.

The actual measured quantity is δ. Therefore, the equation for calculating the height Z of the subject from the measured amount δ is given by the equation (8).
By transforming

[0037]

(Equation 5)

## EQU4 ##

Therefore, according to this configuration, the subject 1 irradiated by the change in the deflection angle of the galvanomirror 104 is
01 can be continuously measured at each measurement point based on the reflected light from all the points 01. Compared with the method in which the stage is moved for each measurement point, it is possible to realize much higher speed. In addition, since the expression indicating the relationship between the height Z of the subject and the position δ of the spot at this time can be made completely linear, an operation for correcting a nonlinear term can be omitted, and the height can be accurately and quickly increased. Measurement can also be realized.

By the way, in the device configured as described above,
Although a much higher speed can be realized than the conventional method, the speed at this time is limited by the frequency and deflection angle of the galvanomirror 104. That is, in the general case, the galvanometer mirror 104 is, as shown in FIG.
The mirror body 104c is provided at the tip of a shaft 104b rotatably instructed by the mirror body 104c.
Is set to vibrate at high speed with a predetermined deflection angle,
In this case, the pupil image 103 'is used as the mirror body 104c.
At the same time, in the direction orthogonal to the center of rotation of the shaft 104b, the stop images 114 ', which are axially symmetric images with the optical axis of the objective lens 102 symmetrical, are included, and the projection positions of these stop images 114' are sufficiently adjusted. Those that can be covered are selected. Here, the pupil image when the galvanomirror 104 is arranged at 45 ° with respect to the optical axis is 103 ″,
The stop image is indicated by 114 ″.

However, in this case, if the diameter of the pupil image 103 'of the objective lens 102 exceeds 10 mm, it may be vibrated at a speed of 100 Hz or more due to the inertia of the mirror body 104c. It becomes difficult. This means that the galvanomirror 104 has a maximum of 100
Even if beam scanning is performed at a speed of 1 Hz, when one sample is measured by 1024 scanning lines, the scanning time is as long as 10.24 seconds. A tact time as long as 15 seconds is required, which limits the improvement of productivity in online inspection of mass-produced products.

In the present invention, as shown in FIG. 5, the galvanometer mirror 104 is used as the galvanometer mirror 104.
The mirror body 104c provided at the tip of the shaft 104b, which is instructed to be rotatable, is formed in a vertically long shape narrower than the diameter of the pupil image 103 'and elongated in the direction along the rotation center of the shaft 104b. Mirror body 104 like
An aperture image 114 ′ which is an axially symmetric image in which the optical axis of the objective lens 102 is symmetrical along the longitudinal direction of c is included. That is, the mirror main body 104c is
4b has a vertically elongated shape in which the width dimension in the direction orthogonal to the rotation center is reduced, and such a vertically elongated shape can sufficiently cover the projection position of the aperture image 114 'in which the optical axis of the objective lens 102 is symmetrical. Like that.

When the galvanomirror 104 constructed as described above is used, the optical system after the right-angle mirror 12 is rotated by 90 ° about the optical axis, and the separator lenses 115a, 115b, etc. are perpendicular to the paper surface. Will be placed.

Accordingly, in this case, the galvanometer mirror 104 is configured such that the size of the mirror body 104c in the vertical direction is
It is almost the same as before, but the width can be reduced to about 1/3, and the thickness can be reduced to about half as the overall shape becomes smaller. As a result, the inertia of the mirror main body 104c is reduced to 1/10 or less of that of the related art, and high-speed scanning can be performed several times even by using the same scanner.

(Second Embodiment) In the second embodiment, the measurement speed is improved and the measurement light quantity is also improved.

FIG. 6 shows a schematic configuration of the second embodiment of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals.

For example, when the height of a row of bumps arranged on a plastic substrate is to be measured as the height from the substrate surface, the amount of reflected light from the bumps can be sufficiently ensured, but the reflection from the substrate surface is extremely small. Due to the weakness, accurate measurement may not be possible. In the above-described first embodiment (FIG. 1), the advantage of measurement using two optical paths is as follows.
There is an advantage that the measurement sensitivity is improved and it is easy to determine whether or not the measurement is possible. However, the function of the light receiving element is reduced due to a shortage of the measurement light amount, which affects the measurement accuracy.

Therefore, in the second embodiment, FIG.
The measurement using the two optical paths of the optical axis described in the above is limited to only one optical path.

In the second embodiment, a collimating optical system is constituted by first, second, and third lenses 118, 119, and 120 instead of the collimator lens 106 described with reference to FIG. Here, the first, second, and third lenses 1
The focal lengths of 18, 119 and 120 are f1, f2 and f3
And NA is NA1, NA2, NA3.

The measurement light emitted from the laser diode 105 is divided into first, second, and third lenses 118, 1
19 and 120, the light becomes a light beam composed of parallel light and becomes vertically symmetric with respect to the optical axis of the objective lens 102.
After being transmitted through the polarizing beam splitter 107 and the quarter-wave plate 108 along one of the axially symmetric regions of the optical path, it is reflected by the galvanomirror 104, and passes through the objective lens 102 to the surface of the subject 101. Is collected. The measurement light reflected by the subject 101 passes through the objective lens 102 along the other axially symmetric region, is reflected by the galvanomirror 104, passes through the quarter-wave plate 108, and passes through the polarization beam splitter. The light is reflected by 107 and condensed on the primary image plane 110 by the first imaging lens 109, further passes through the pupil relay lens 111, passes through the stop 114, and is separated by the separator lens 115 by the light position detecting element (PSD) 116. Is collected.

In such a configuration, for example, if f1 = 45 mm and NA1 = 0.15 for the lens 118 and the beam spread of the laser diode 105 is 0.15 or more with respect to NA, the lens 118 The diameter of the first collimated light C1 is 13.5 mm. Next, for the lens 119, f2 = 90 mm,
Assuming that NA2 = 0.08, the beam diameter that the lens 119 can receive is 14.4 mm, and the parallel light that has exited the lens 118 can be sufficiently received.
Assuming that f3 = 35 mm and NA3 = 0.15, the diameter of the parallel light emitted from the lens 120 is 0.0
8 × 35 × 2 = 5.6 mm.

Since there is no light amount loss up to this point, the lens
The luminous flux density of the collimated light C2 exiting 0 is (13.5 /
5.6) ² = 5.8 times.

The lenses 118, 119, 1
Projection beam 12 on galvanomirror 104 due to 20
The position 1 is arranged so as to be vertically symmetrical with respect to the projection position of the stop image 114 'and the optical axis of the objective lens 102, as shown in FIG. The axially symmetric region 122 in which the optical axis of the optical axis 102 is symmetrical is sufficiently satisfied.

When the above relationship is generally formulated, NA1f1 ≧ NA2f2: a condition under which all the light beams exiting the lens 118 are propagated by the lens 119.

NA2 ≦ NA3: A condition under which the lens 120 can sufficiently pick up the light beam emitted from the lens 119.

F3≪f2: The condition is such that the collimated light C2 is sufficiently thinner than the collimated light C1, and the magnification of the light flux density is (NA1f1 / NA2f3) ² .

In the second embodiment, the reason why NA1 and f1 are not constituted only by a sufficiently small lens system from the beginning is that the spread of the measuring light on the surface of the object due to the astigmatic difference of the semiconductor laser. This is because f1 must be made sufficiently large with respect to f of the objective lens 102 in order to reduce the value of NA, and NA1 cannot be made too small in order to secure a sufficient amount of light.

Accordingly, since the beam diameter of the projection beam can be set to a necessary minimum, this makes it possible to reduce an unmeasurable area due to insufficient light quantity, thereby reducing the number of bump rows arranged on the plastic substrate. In the case where the height is measured as the height from the substrate surface, good measurement can be realized.

[0059]

As described above, according to the present invention, continuous height measurement can be performed for each measurement point based on the reflected light from the subject, so that measurement at many points is required. Even when measuring the height of an object to be measured with high density, a remarkable measurement speed can be realized as compared with the conventional method in which the measurement is performed while scanning the stage point by point, and the burden on the operator is reduced. Reduction can be realized. In addition, by using an optical scanning mirror having a small inertia, a higher-speed height measurement can be realized.

Further, the beam diameter of the projection beam can be minimized, an unmeasurable region due to insufficient light quantity can be reduced, and the measurement accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a main part of the first embodiment.

FIG. 3 is a diagram for explaining the first embodiment.

FIG. 4 is a diagram showing a schematic configuration of a general galvanometer mirror.

FIG. 5 is a diagram showing a schematic configuration of a galvanomirror used in the first embodiment.

FIG. 6 is a diagram showing a schematic configuration of the first embodiment of the present invention.

FIG. 7 is a view for explaining a positional relationship between a projection beam and a stop image in a galvanomirror according to the first embodiment.

[Description of Reference Numerals] 101: subject 101 ': subject image 102: objective lens 103: pupil plane 103': pupil image 104: galvanometer mirror 104a: galvanometer scanner 104b: shaft 104c: mirror body 105: laser diode 106: collimator Lens 107: polarizing beam splitter 108: quarter-wave plate 109: first imaging lens 110: primary image plane 111: pupil relay lens 112: right angle mirror 113a. 113b ... Mirror 114 ... Aperture 114a. 114b ... stop 114 '... stop image 115 ... separator lens 115a. 115b ... Separator lens 116 ... Optical position detecting element (PSD) 116a. 116b ... Position detection element (PSD) 118.119.120 ... Lens 121 ... Light beam 122 ... Axisymmetric region

Claims (3)

[Claims] A light source that emits measurement light, an objective lens that is arranged to face the subject and converges the measurement light on the subject, and that is rotatably provided near a pupil plane or a conjugate plane of the objective lens. An optical scanning mirror that scans the subject with measurement light, and an image forming an axisymmetric image at a position that is axisymmetric with respect to the optical axis of a light beam transmitted through the objective lens from the reflected light of the subject. An optical system, and an optical position detecting unit that is disposed on an image forming surface of the image forming optical system and detects a light spot whose position changes according to the height of the subject. A height measuring device having an elongated shape along a moving center direction and having a size along a longitudinal direction of the shape to include a projection position of an axially symmetric image by the imaging optical system. 2. A collimating optical system for generating a projection beam having a light beam diameter satisfying an axially symmetric region in which an optical axis of the objective lens is symmetric from measurement light emitted from the light source, and The height measuring device according to claim 1, wherein a light beam is projected on the subject along the axially symmetric region. 3. The collimating optical system comprises a light source and first to third lens systems, wherein the first to third lens systems have respective NAs of NA1, NA2, NA3 and a focal length of f1. , F2, f3, NA1f1 ≧ NA
3. The height measuring device according to claim 2, wherein a condition of 2f2, NA2 ≦ NA3, f3≪f2 is satisfied.