JPH08327327A - Method and apparatus for measuring height of bump - Google Patents

Abstract

PURPOSE: To measure the height of a bump having relatively smooth upper end face at a high speed highly accurately and judge whether the bump is good or not, by moving a surface to be measured or a reference surface in the direction of optical axis so that an area where an optical interferometer can interfere comes to the vicinity of an estimated position of the bump. CONSTITUTION: A silicon wafer 50 having a solder bump 54 formed thereon is set under an optical interferometer using a light source 12 projecting a light of a large spectral width. Based on a measuring reference position in heightwise direction, a surface to be measured of a work W or the reference surface of a reference mirror 8 is moved in the direction of optical axis by a PzT driver 32 so that an area where the interferometer can interfere comes to the vicinity of a position where the upper end face of the bump 54 is estimated to be present. In this state, while optical path difference is minutely changed, interference fringe patterns of different phases are obtained for at least three screens with a camera 26 and stored in a frame memory 28. A CPU 30 calculates an intensity of the interference fringes for every pixel based on image data and obtains an average value of the intensities for a fixed pixel area corresponding to the bump 54.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump height measuring method and apparatus, and more particularly to a bump height which is relatively smooth on the upper end surface such as a solder bump formed on a silicon wafer, a circuit board or a lead frame at high speed. The present invention relates to a bump height measuring method and apparatus for measuring bump height.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring the height of a bump, linear light is projected obliquely onto an object to be measured, and the reflected light is received by an area sensor or the like to read the deviation of the light from the straight line. By this method, the shape of the measured object can be obtained (light cutting method), or the optical system can be moved up and down so as to always focus on the measured surface, and the height of the measured object can be determined based on the driving amount. A method called a focus tracking method for measuring is known.

In Japanese Patent Publication No. 6-1167, an optical interferometer using a light source with low coherence is used, and the interferometer is scanned in the optical axis (Z) direction to improve coherence. A method and apparatus for detecting the maximum point and measuring the three-dimensional shape of the object to be measured are disclosed. On the other hand, as the material of the bump, two kinds of gold and solder are mainly used. Among them, as a method effective for measuring the height of a bump having a relatively rough upper end surface such as a gold bump, the present applicant Have already proposed a method for detecting the speckle of light by the upper end surface of the bump (see Japanese Patent Application No. 7-29130).

[0004]

However, in the conventional optical cutting method, since the measuring range is a cross section, the work is placed on a movable stage or the like to obtain three-dimensional data of the work (work). There is a problem that it is difficult to perform high-precision measurement because the work needs to be moved and the measurement performed by moving the work. Further, since the inclination of the work directly causes a measurement error, there is a problem that the same measurement value cannot be obtained even for bumps of the same height in the same wafer due to warping or waviness of the wafer.

On the other hand, in the focus tracking method, since the measurement is performed at one focal spot, it is necessary to scan the work in the x and y directions in order to obtain three-dimensional data of the work, and it takes a long time for the measurement. There is a problem in accuracy as well as it takes. Further, in the method of detecting the coherence, it is necessary to scan the entire measurement range with a step width of about 0.1 μm in the height direction (z direction), which causes a problem that the measurement time becomes long.

On the other hand, the method described in the above-mentioned Japanese Patent Application No. 7-29130 is suitable for measurement of a bump whose upper end surface is relatively rough such as a gold bump, but on the bump such as a solder bump. For bumps with smooth end faces, it has been newly confirmed that speckles are difficult to detect and measurement repeatability is poor. The present invention has been made in view of such circumstances, and it is possible to measure the height of a bump having a relatively smooth upper end surface, such as a solder bump, at high speed and with high accuracy. In particular, the bump has a design value (including a tolerance). It is an object of the present invention to provide a bump height measuring method and device capable of rapidly determining whether or not the inside of the bump is inside.

[0007]

In order to achieve the above object, the present invention provides a light source for irradiating a surface to be measured and a reference surface with light having a wide spectrum width, an optical path passing through the surface to be measured, and An interference optical system that generates interference fringes in which the intensity of the interference fringes appears strongly in the vicinity of the optical path length difference of the optical path passing through the reference surface becomes 0, and the intensity of the interference fringes decreases as the optical path length difference increases. A variable mechanism for changing at least one of the surface to be measured or the reference surface in the optical axis direction to change the optical path length difference, and an image pickup means for picking up an interference fringe pattern generated according to the optical path length difference. In the bump measuring method for measuring the height of the bump formed on the surface to be measured by using an optical interferometer, the reference is used when measuring the height of the bump formed on the surface to be measured. Position in the height direction The position of the optical path length difference when the intensity of the interference fringes strongly appears in the vicinity of the optical path length difference of 0 in the optical interferometer is defined as the coherence range, and the measured reference position is used as a reference for the measurement target position. The variable mechanism is set so that the coherent range of the optical interferometer is near the bump estimated position where the upper end surface of the bump formed on the target surface is estimated to exist, and the optical path is set by the variable mechanism in the setting state. While slightly changing the length difference, the interference fringe patterns having different phases are imaged by at least three screens by the imaging unit, and the interference fringe intensity is pixel by pixel based on the image data of at least three screens obtained by the imaging unit. Is calculated, and an average value of the interference fringe intensity is calculated for a certain pixel area corresponding to an area where bumps are present in the screen, and the average value and the upper end surface of the bump are within the coherence range. Compared with a predetermined threshold value indicating that it is within a predetermined allowable range, if the average value is larger than the predetermined threshold value, the height of the bump to be measured is the bump estimated position. If it is determined that the average value is equal to or less than the predetermined threshold value, the height of the bump to be measured is near the estimated bump position. It is characterized in that it is judged to be outside the above-mentioned predetermined range.

[0008]

According to the present invention, the object to be measured on which the bumps are formed is placed under an optical interferometer using a light source for irradiating light with a wide spectral width, and the measurement reference position in the height direction is used as a reference. , A variable mechanism is used to light the measured surface or the reference surface so that the coherent range of the optical interferometer is near the bump estimated position where the upper end surface of the bump formed on the measured surface is estimated to exist. Move in the axial direction. Then, while slightly changing the optical path length difference in that state, at least three screens of interference fringe patterns having different phases are acquired, the interference fringe intensity is calculated for each pixel based on the image data, and a constant corresponding to the bump is obtained. The average value of the intensity of the interference fringes is calculated for the pixel area. Since the spectrum width of the light source light is wide, the coherence is poor, and the coherence range is narrow. Therefore, when the upper end surface of the bump is in the coherence range of the interferometer, the interference fringe strength becomes large and the average value becomes large. Become. On the other hand, when the upper end surface of the bump is not within the coherence range of the interferometer, the intensity of the interference fringe is extremely small, and the average value is also small.
With respect to the average value, a predetermined threshold value is determined, and the height of the bump is measured by comparing with the threshold value. That is, if the average value is larger than the predetermined threshold value, it is determined that the upper end surface of the bump is within a certain range in the vicinity of the previously set estimated bump position, while the average value is the predetermined threshold value. If the value is less than or equal to the value, it is determined that the value is outside the predetermined range near the previously set estimated bump position. As a result, the bump height can be measured at high speed with the accuracy of the coherence range of the interferometer.

When the average value is less than or equal to the predetermined threshold value, the previously set estimated bump position is changed to another position (plus side or minus side) and the above measurement process is repeated. Thus, the upper end surface of the unknown bump can be detected and its height can be measured. By changing the spectral width of the light source using the interference filter, the coherence range of the interferometer can be adjusted and changed, and the accuracy of bump height measurement can also be changed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a bump height measuring method and apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram for explaining the configuration of an embodiment of a bump height measuring apparatus to which the bump height measuring method according to the present invention is applied. As shown in the figure, this measuring apparatus mainly comprises a light source lamp 12, a collimator lens 14, a beam splitter 16, a reference mirror 18, and a piezo element (PzT) 2.
0, displacement sensor 22, objective lens 23, imaging lens 2
4, a monochrome solid-state imaging camera 26, a frame memory 28, a central processing unit (CPU) 30, and the like.
In the figure, a Twyman-Green type interferometer is described as an example, but the present invention is not limited to this, and a Linic type, a Mirau type interferometer or the like may be used.

The light source lamp 12 uses, for example, a white light source,
The light emitted from the light source lamp 12 is collimated by the collimator lens 14 and split into two directions by the beam splitter 16. That is, the light reflected by the beam splitter 16 is applied to the object to be measured (workpiece) W via the objective lens 23, while the light transmitted through the beam splitter 16 is applied to the reference mirror 18.

The work W is placed on a fixed stage table (not shown), and the light reflected by the surface of the work W reaches the camera 26 via the beam splitter 16 and the imaging lens 24, while the reference mirror is used. The light reflected by 18 passes through the beam splitter 16 and the imaging lens 24, and then the camera 26
Reach The PzT 20 is driven by the PzT driver 32 to displace the reference mirror 18 in the optical axis direction, and the displacement sensor 22 is driven via the displacement sensor driver 34 to detect the displacement amount of the reference mirror 18.

The camera 26 images the interference fringes observed corresponding to the difference in optical distance (optical path length difference) of the two light beams, converts the interference fringe image into a predetermined electric signal, and then the frame memory 28. Output to. The frame memory 28 records the interference fringe image with the optical path length difference, that is, the position (or displacement amount) of the reference mirror 18 as a variable. CPU30 is bus 3
6 through the frame memory 28, PzT driver 3
2 and the displacement sensor driver 34,
The bump pattern of the work W is detected by processing the interference fringe data input via the frame memory 28. The data processing will be described later.

A keyboard 40 and a monitor TV 42 are connected to the CPU 30 so that the operator can monitor the monitor T.
While observing the display of V42, various inputs can be performed through the keyboard 40, and the monitor TV 42 can display the bump shape measurement result of the work W and the like. Further, it is possible to connect the recording medium 46 to the bus 36 via the interface 44. The recording medium 46 includes a hard disk drive 47 and a floppy disk drive 48, and can store the measured bump measurement data of the work W and the like. Incidentally, the recording medium 4
6 (portion indicated by dotted line in the figure) is not essential for the configuration of the present invention.

Next, the measuring principle of this measuring apparatus will be described. FIG. 2 is an enlarged schematic view of an essential part of the interferometer portion of FIG. Assuming that the distance between the beam splitter 16 and the reference mirror 18 is LR and the distance between the beam splitter 16 and the work W is LW, the optical path length difference (OPD: Optical) in this case.
The path difference) is expressed by the following equation (1) OPD = 2 × (LR-LW) (1).

The OPD is defined as a variable Z, which is a variable that can be changed by driving the PzT 20 to displace the reference mirror 18 on the optical axis. Here, when OPD (= Z) is continuously changed in the vicinity of zero, the intensity I of the interference fringe observed at one point on the camera 26.
(Z) becomes a function like I (Z) shown in FIG. Since the measuring device uses a white light source, the coherence range is about ± 0.6 μm. Since the coherence range depends on the spectrum width of the light source used for the interferometer, if the interference filter (not shown) is placed in front of the light source or in front of the camera to narrow the spectrum width of the light source, the coherence range is expanded. .

FIG. 4A is a plan view showing an example of a work to be measured, and FIG. 4B is a sectional view thereof.
The workpiece shown in the figure has a substantially spherical solder bump 54 formed on a silicon wafer 50. The solder bump 54 is formed with a height design value d based on the silicon wafer surface 50a. In addition, the solder bump 54
The upper end surface 54a has a relatively smooth surface roughness (see FIG. 4B).

When the solder bump 54 is irradiated with white light from the light source lamp 12 of the optical interferometer, the following phenomenon is observed. That is, when the position of the bump upper surface 54a is not within the coherence range of the interferometer, the light source light is reflected by the smooth silicon substrate surface and the upper surface 54 of the solder bump 54 is also reflected.
It is reflected at a. At this time, since the two materials are different from each other, the reflectance is also different, and the bump portion 52 becomes darker than the surrounding silicon portion 50. In this case, since the upper surface of the bump is not within the coherence range, the contrast of interference fringes is not observed.

On the other hand, when the position of the upper surface 54a of the bump is within the coherence range of this interferometer, the light from the light source is the solder bump 5
Since the light is reflected by the smooth upper surface 54a of No. 4 and interferes, interference fringes having a remarkable contrast are observed in the bump portion.
The measuring device detects the interference fringe intensity for each pixel for this interference fringe, calculates the average value of the interference fringe intensity in a predetermined XY region in the screen corresponding to the region of the bump portion, and calculates the average value. If the value is equal to or greater than a certain value, it is determined that the bump exists, and if the value is less than the certain value, it is determined that the bump does not exist. Then, by determining whether or not the height of the solder bump 54 is within the coherence range, it is determined at high speed and with high accuracy whether or not the solder bump 54 is within the allowable range (including the tolerance) of the design value d. It is a thing.

Although FIG. 4 shows a magnified version of one bump, normally, a large number of hundreds or thousands of bumps are formed on a single wafer, and one bump is displayed on one screen. It is possible to measure multiple bumps at the same time. The measurement principle of the bump height measuring apparatus configured as described above will be described according to the measurement procedure with reference to FIGS.

First, using the upper surface 50a of the wafer substrate as a reference surface, the position of the bump design value d from this reference surface is set as the Z = 0 position of the interferometer. An example of the method of detecting the reference plane will be described. Using the configuration shown in FIG. 1, OPD
When (= Z) is continuously changed in the vicinity of zero, the brightness intensity I of the interference fringe observed at one point (one pixel) on the camera
(Z) becomes a function like I (Z) shown in FIG. Also, the differentiation of I (Z) with respect to Z is shown in FIG.
It becomes a function like (Z). In this measurement device, Z is changed within the entire measurement range, and a Z value giving the maximum value (or minimum value) of J (Z) at each measurement point on the camera, that is, Z value.
By obtaining a (or Zb), the wafer surface height of the work W is calculated.

Below, Z giving the maximum value of J (Z)
A method of simply detecting the value, that is, Za will be described. Z can be discretely changed at predetermined constant intervals, an interference fringe image is acquired according to each Z value, and the intensity of the interference fringe is observed from the data of the image. And two consecutive points Z
Using the brightness intensity data I (Zk) and I (Zk-1) at k and Zk-1, the differential value J (Zk) is calculated by the following equations (2), (3) .I (Zk)> I (Zk -1) J (Zk) = I (Zk) -I (Zk-1) (2) ・ I (Zk) ≤I (Zk-1) J (Zk) = 0 (3) However, Zk-Zk-1 = constant C: C is a constant distance for moving the reference mirror 18, 0 <Zk-Zk-1 ≤ λ / 6: λ is the central wavelength of the light source.

By changing Z within the entire measuring range, the above J
(Z) is calculated, and a Z value giving the maximum value of J (Z), that is, a set of Zk and Zk-1, is discriminated, and the following equation (4) Za = (Zk + Zk-1) / 2 .. (4) detects Za that gives the maximum value of J (Z). This makes it possible to easily detect Za.

Further, instead of the equation (4), FIG.
, Zk and Z that give the maximum value of J (Z)
Two points of k-1 A (Zk, I (Zk)) and B (Zk-1, I)
The intersection of the straight line L1 connecting (Zk−1)) and the bias value (DC value) of the light-dark intensity may be detected as Za that gives the maximum value of J (Z). The Za obtained thereby has higher accuracy than the Za obtained from the equation (4).

The DC value can be obtained not only as the brightness value of each pixel outside the coherence range, but also as the average value of a plurality of measurement points or by frequency analysis. Good. Based on the Za thus obtained, the height position of the wafer substrate surface 50a, which is the measurement reference value, is measured. It is not necessary to measure this reference plane every time the bump height is measured. Also, when using the above method,
It is conceivable that the same measuring apparatus shown in FIG. 1 can be switched between the reference plane measurement mode and the bump height determination and mode.

The reference surface is not limited to the wafer surface, but may be any height as long as it serves as a reference for designating the solder bump 54. Further, the measurement of the reference plane is not limited to the above-mentioned method, and may be performed by another method, or a predetermined reference plane may be set and input in advance. FIG. 6 is a flow chart when detecting the position of the wafer substrate surface which is the reference surface for the bump measurement described in FIG. First, the measuring apparatus shown in FIG. 1 is set to the reference plane measurement mode, and the height of the wafer surface 50a serving as the reference plane is measured. This includes each measurement point on the wafer substrate surface 50a of the work W.
The differential maximum value J '(x, y) for each (x, y) and the memory of φ' (x, y) giving the maximum value are cleared, the measuring device is initialized, and PzT20 is driven. The measurement position in the Z direction is moved to the initial position (step 102).

Then, by the above-mentioned method, each measurement point (x,
The differential value J (x, y) in y) is calculated (step 10
4). Next, J (x, y) obtained in step 104 for each measurement point (x, y) is compared with the maximum differential value J '(x, y) up to the last time stored in the memory. (Step 106), if J (x, y)> J ′ (x, y), replace J ′ (x, y) with J (x, y) to obtain the maximum differential value J ′ (x, y). While updating, Z position φ'at that time
Update (x, y) (step 108). At the initial position, the memory is cleared and J '(x, y) and φ' (x,
y) is not recorded, so J '(x, y),
φ '(x, y) is recorded.

Subsequently, the PzT 20 is driven to drive the reference mirror 18.
Is moved in the Z direction by a constant distance C to move the measurement position (step 110). Step 10 at the measurement position
When steps J4 and 106 are performed and J (x, y)> J '(x, y), J' (x, y) is replaced with J (x, y) and the maximum differential value J '(x , y) and the Z position φ ′ at that time
Update (x, y) (step 108).

On the other hand, in step 106, J (x, y) ≤J '
In the case of (x, y), J '(x, y) is not updated. Similarly, the above steps are repeated until the measurement within the entire measurement range is completed, and when the displacement sensor 22 detects the final measurement position (step 112), the measurement is completed and φ '(x, The position of the silicon substrate surface is obtained based on y) (step 114).

In this embodiment, the case where the replacement of the differential value J '(x, y) is sequentially performed for each measurement position has been described, but the present invention is not limited to this, and a partial range of the measurement range (Z) or The maximum value of the differential value J (x, y) may be calculated after capturing a plurality of image data for the entire range and storing the image data in the memory.
The position of the silicon substrate surface may be detected by any other method than the above method. Also, once detected, it is not necessary to detect each time the bump height is measured.

Next, a method of measuring the height of the solder bumps 54 formed on the wafer surface which is the reference surface will be described. FIG. 7 is a flowchart showing the procedure of bump height determination. After the reference plane is detected by the procedure described in FIG. 6 (step 201), the reference mirror 18 is attached to the solder bump 5
It moves to the design value height d of 4 (step 206) and captures the measurement image I1 (step 208).

Subsequently, the reference mirror 18 is moved by a predetermined amount (hereinafter referred to as a measurement image capturing interval, for example, λ / 8) (step 221) to capture the measurement image I2 (step 222). Step 221 and Step 22
The step 2 is repeated a plurality of times (at least three times or more) to acquire measurement images I1, I2, I3, .... Then, based on the obtained image data, the interference fringe intensity is calculated for each pixel i. It is not always necessary to calculate the interference fringe intensity for all pixels of the image data, but it is sufficient to calculate for the pixels in a certain pixel area corresponding to the bump portion described later.

The calculation formula of the interference fringe intensity may be defined in various ways. For example, when the measurement image is calculated based on three screens captured at λ / 8 intervals, the interference fringe intensity m (i ) Is calculated by the following equation (5) m (i) = {I ₁ (i) -I ₂ (i)} ² + {I ₃ (i) -I ₂ (i)} ² (5).

If the height of the bump is within the coherence range, the interference fringe intensity m (i) becomes large. On the other hand, if the bump height is not within the coherence range, the interference fringe strength m (i) is small. Next, a certain area of the bump portion, that is, a pixel (i = 1,2, ... n) in a certain area on the screen corresponding to the bump portion.
Then, the average value M of the interference fringe intensity m (i) is calculated. The formula for calculating the average value M is the interference fringe intensity for each pixel expressed by the formula (5).
The average value M calculated by the following equation (6) However, I _k (i) is the pixel of the measurement image captured in the kth position.
The brightness intensity n of i is calculated by the total number of pixels i in the certain area (step 211).

Incidentally, the steps 208 to 22
When 4 screens of the measurement image are captured at λ / 8 intervals in 2 and the average value is calculated from the image data of the 4 screens, the average value M is expressed by the following formula (7). However, I _k (i) is the pixel of the measurement image captured in the kth position.
The brightness intensity n for i can be calculated by the total number of pixels i in the fixed region.

The calculation intervals of the measurement image capturing interval, the interference fringe intensity, and the average value thereof are not limited to those described above, and the capturing intervals do not necessarily have to be equal intervals. In this embodiment, the measurement image acquisition interval is set to λ / 8, and image data is acquired at continuous equal intervals. However, when the reference mirror 18 is moved by λ / 8, the phase of the interference fringes is shifted by 90 degrees. This is because it is suitable that the average value of the interference fringe intensity is calculated based on the image data where the phase is shifted by about 90 degrees, because the calculation load is relatively small.

On the other hand, it is considered that the certain area is, for example, a part of the area including the center of the bump portion, but the shape and size of the area are not particularly limited, and the average value is not limited. It is desirable to set an area that is convenient for calculation. It is also possible to divide the bump region into a plurality of blocks, obtain an average value for each block, and exclude blocks showing an inappropriate value from the calculation.

The center position of the bump on one screen is
Since it is not always located at a fixed place on the screen, a known image processing technique is used to detect the center position of the bump existing in the screen, and the average value is calculated in a certain area including the center. It is possible to calculate. Formula (6)
The average value of the intensity of the interference fringes obtained from the above is compared with a fixed reference comparison value (step 226), and when it is equal to or larger than the reference comparison value, it is determined that there is a bump at the design position d (step 22).
8) On the other hand, if it is less than the reference comparison value, it is determined that there is no bump at the design position (step 230). The accuracy of the discrimination is about the coherence range (about ± 0.6 μm).

Therefore, for example, when the tolerance of the solder bump is ± 5 μm, it is particularly effective in determining whether or not the bump is within the design value ± 5 μm.
If the bump height determination method is further expanded and it is determined that the bump height is not within the design value, the reference mirror is moved to the plus side or the minus side with respect to the design value, and the step ( It is also possible to specify the height of the bump and measure the height by repeating steps 206 to 230). Therefore, it can be used not only as a device for determining OK / NG of whether the bump is within the allowable range of the design value, but also as a measuring device for measuring an unknown bump height. Moreover, when a plurality of bumps are present in one screen, it is possible to measure them at the same time, and the measurement efficiency is good.

The order in which the image data is taken in and the order in which the average value of the interference fringe intensity is calculated are not limited to the above, and the images may be sequentially taken in while the reference mirror 18 is moved in one direction at predetermined intervals. Further, the calculation of the average value may be performed after capturing all the images, or may be sequentially performed each time the images are captured. In the above-described embodiment, the measurement of the solder bump formed on the silicon wafer 50 has been described, but the present invention is not limited to this. The bump portion and the base portion on which it is formed can be distinguished on the screen, and the position of the bump can be determined. It is only necessary to be able to specify, and in principle it is possible to measure the same material, but it is usually a work in which the material of the base surface and the material of the bump are different, and it is possible to apply them widely. It is particularly effective for different metals having a smooth bump top surface.

In the above embodiment, the light source lamp 12 is described as a white light source. However, the light source lamp 12 is not limited to this, and the spectrum width may be adjusted by using an interference filter (not shown) for the white light source, or Alternatively, a wide area light source having a certain spectral width may be used. It is also conceivable to arrange an interference filter (not shown) in front of the camera. Since the coherence range can be changed by adjusting the spectrum width of light in this way, it is also possible to appropriately change the accuracy of bump height determination. For example, it can be used for rough determination of bump height.

[0042]

As described above, according to the bump height measuring method and apparatus according to the present invention, the surface to be measured is measured by using the optical interferometer using the light source for irradiating the light having the wide spectrum width. The variable mechanism is set so that the coherent range of the optical interferometer is near the bump estimated position where the upper end surface of the bump formed in is present, and at least interference fringe patterns having different phases obtained in that state are set. Three or more screens are imaged, the interference fringe intensity is calculated for each pixel based on the image data, the average value of the interference fringe intensity is calculated for a certain pixel area corresponding to the bump, and the average value is predetermined. Since the bump height is measured by comparing it with the threshold value, the calculation load is relatively small, the calculation speed can be increased, and the bump height can be as high as the coherence range of the interferometer. It is possible to perform the measurement.

Thus, the height of a bump such as a solder bump whose upper end surface is relatively smooth can be measured at high speed and with high accuracy, and in particular, whether or not the bump is within the design value (including the tolerance) can be determined at high speed. can do. When the average value is less than or equal to the predetermined threshold value, the previously set estimated bump position is changed to another position (plus side or minus side), and the measurement process is repeated to obtain an unknown value. The upper end face of the bump can be detected and its height can be measured.

Furthermore, since the coherent range of the interferometer can be adjusted and changed by changing the spectral width of the light source using an interference filter in the optical interferometer, the accuracy of bump height measurement can be changed appropriately. It is also possible to do so.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram for explaining a configuration of a bump height measuring device according to the present invention.

FIG. 2 is an enlarged view of a main part of the interferometer portion of FIG.

FIG. 3 is a graph showing the intensity of interference fringes observed at one point on the camera when the optical path difference of the interferometer is continuously changed near zero.

FIG. 4 (A) is a plan view showing an example of bumps formed on a wafer surface, and FIG. 4 (B) is a sectional view thereof.

5 (A) is a graph showing the intensity of interference fringes observed at one point on the camera of FIG. 1 and its differential value, FIG.
(B) is a graph for explaining a method of accurately calculating Za, which gives the maximum value of the differential value J (Z) of the interference fringe intensity, using the DC value

6 is a flow chart for explaining a procedure for detecting a position of a wafer substrate surface which is a reference surface for bump measurement of the bump height measuring apparatus of FIG.

FIG. 7 is a flow chart showing a procedure for determining a bump height of the bump height measuring apparatus of FIG.

[Explanation of symbols]

 12 ... Light source lamp 16 ... Beam splitter 14, 23, 24 ... Lens 18 ... Reference mirror 20 ... Piezo element (PzT) 22 ... Displacement sensor 26 ... Monochrome solid-state imaging camera 28 ... Frame memory 30 ... CPU 50 ... Silicon wafer 54 ... Solder bump

Claims (4)

[Claims] 1. A light source for irradiating a measured surface and a reference surface with light having a wide spectrum width, and an area in which an optical path length difference between an optical path passing through the measured surface and an optical path passing through the reference surface becomes zero. Intensity of interference fringes appears strongly, and an interference optical system that generates interference fringes such that the intensity of interference fringes decreases as the optical path length difference increases, and at least one of the measured surface or the reference surface An optical interferometer including a variable mechanism that moves in the axial direction to change the optical path length difference and an imaging unit that images an interference fringe pattern generated according to the optical path length difference is used to measure the object to be measured. In the bump measuring method for measuring the height of the bumps formed on the surface, the position in the height direction that is the reference when measuring the height of the bumps formed on the surface to be measured is used as the measurement reference position, and About the interferometer Assuming that the range of the optical path length difference when the intensity of the interference fringes strongly appears in the vicinity of becomes the coherence range, it is estimated that the upper end surface of the bump formed on the surface to be measured exists with the measurement reference position as a reference. The variable mechanism is set so that the coherence range of the optical interferometer is close to the estimated bump position, and the variable mechanism slightly changes the optical path length difference in the setting state, and the interference fringes having different phases are set. The pattern is imaged by at least three screens by the imaging unit, the interference fringe intensity is calculated for each pixel based on the image data of at least three screens obtained by the imaging unit, and a region where bumps are present in the screen The average value of the interference fringe intensity is calculated for a certain pixel area corresponding to, and the average value and a predetermined threshold indicating that the upper end surface of the bump are within a predetermined allowable range within the coherence range. If the average value is larger than the predetermined threshold value,
The height of the bump to be measured is determined to be within a certain range corresponding to the predetermined allowable range near the estimated bump position, and if the average value is less than or equal to the predetermined threshold value, the measurement is performed. A bump height measuring method comprising: determining that the height of a target bump is outside the predetermined range near the estimated bump position. 2. When it is determined that the average value is equal to or less than the predetermined threshold value and the height of the bump is outside the predetermined range near the estimated bump position, another estimated bump position is set. 3. The bump height measuring method according to claim 1, wherein the bump height is measured by changing the position to, and repeating the bump measuring method of claim 1 to detect the upper end surface of the bump. 3. The interference filter for limiting the spectral width is used to adjust the coherence range to make variable the resolution of the optical path length difference and change the accuracy of the discrimination. Bump height measurement method. 4. A light source for irradiating a measured surface and a reference surface with light having a wide spectrum width, and an area in which an optical path length difference between an optical path passing through the measured surface and an optical path passing through the reference surface becomes zero. Intensity of interference fringes appears strongly, and an interference optical system that generates interference fringes such that the intensity of interference fringes decreases as the optical path length difference increases, and at least one of the measured surface or the reference surface An object to be measured is utilized by using an optical interferometer including a variable mechanism that moves in the axial direction to change the optical path length difference, and an imaging unit that images an interference fringe pattern generated according to the optical path length difference. In the bump measuring device that measures the height of the bumps formed on the surface, the position in the height direction that is the reference when measuring the height of the bumps formed on the surface to be measured is the measurement reference position, and About the interferometer When the range of the optical path length difference when the intensity of the interference fringes strongly appears in the vicinity of becomes the coherence range of the optical interferometer, the measurement reference position is used as a reference, and the bumps formed on the measured surface are measured. In the state where the coherence range of the optical interferometer is set near the bump estimated position where the upper end surface is estimated to exist, the variable mechanism slightly changes the optical path length difference, and interference of different phases is obtained. The interference fringe intensity is calculated for each pixel on the basis of image data obtained by capturing at least three screens of the fringe pattern by the image capturing means, and a constant pixel area corresponding to an area where bumps are present in the screen. With respect to the calculation means for calculating the average value of the interference fringe intensity, the average value is compared with a predetermined threshold value indicating that the upper end surface of the bump is within a predetermined allowable range within the coherence range. ,Before If the average value is larger than the predetermined threshold value, the height of the bump to be measured is determined to be within a certain range corresponding to the predetermined allowable range near the estimated bump position, and When the average value is less than or equal to the predetermined threshold value, the comparison determination unit determines that the height of the bump to be measured is outside the certain range in the vicinity of the estimated bump position, and Bump height measuring device.