JP2011191285A - Method for measurement of stepped structure in light transmissive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for correctly and speedily measuring any stepped structural shape such as depth in a hole of high aspect ratio made on a material through which visible light, far-red light or infrared light transmits. <P>SOLUTION: The method includes: applying light L for measuring visible light, far-red light or infrared light from a backside 103 of a silicon wafer 101 with a non-penetrated via 104 formed; measuring an apparent shape of the non-penetrated via 104 by measuring the position where the measuring light L connects focal point to both surface 102 on the silicon wafer 101 and bottom surface 105 on the non-penetrated via 104 through confocal measuring method; and calculating an actual shape of the non-penetrated via 104 by converting a measured shape, using either previously-obtained refractive index of the silicon wafer 101 or the refractive index of the silicon wafer 101 measured by using refractometry device for measuring any refractive index. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for measuring the shape of a stepped structure such as a bottomed hole provided in a material capable of transmitting visible light, near-infrared light, or infrared light. For example, a stacked LSI (Large Scale Integrated circuit) In order to grasp in advance the shape of steps such as the depth of the through silicon vias (Through Silicon Via (TSV)) used for stacking when creating a chip, it is not through vias before completing the through vias. The present invention relates to a step structure measuring method for measuring the shape and the like.

Semiconductor microfabrication technology is currently around 65 nm, but mass production is progressing toward 25 nm. However, it is predicted that the limit of miniaturization will come in a few years.
In addition, the price of manufacturing equipment is high, and it is said that one semiconductor manufacturer exceeds the limit of capital investment.
Thus, the limit is approaching in 2D, and the approach to 3D has begun.

In order to make an LSI three-dimensional, through holes are provided in silicon, electrodes are passed through, and bumps are connected and laminated.
For example, as a method of forming a stacked DRAM (Dynamic Random Access Memory), there is a Via First method in which a through electrode is formed before forming a DRAM device. When a DRAM device is formed by the Via First method, the following is roughly performed. This is done through various processes.

1. A silicon wafer is etched by dry etching to form a bottomed hole for a through via (non-through via).
2. An insulating film is formed on the sidewall of the non-through via by CVD (Chemical Vapor Deposition)
3. Fill the non-penetrating via with polysilicon with high P (phosphorus) concentration by CVD,
4). The polysilicon on the silicon wafer surface is removed by CMP (Chemical Meshanical Polishing)
5. After the DRAM element is formed, micro bumps are formed on the silicon wafer surface side by electroplating.
6). A silicon wafer is thinned to a predetermined thickness of about 50 μm by BG (Back Grinding) and CMP to form a through via,
7). A nitride film is formed by CVD,
8). Form wiring by opening the through electrode part by dry etching,
9. After micro bumps are formed on the back side by electrolytic plating, dicing is performed.

Since a laminated LSI chip such as a laminated DRAM is formed as described above, there is a sufficient possibility that it will become defective in the market for the measurement of the shape such as the depth of the through hole constituting the through via and the quality assurance. You must have a predictable test.
This cannot be detected only by electrical inspection, and it is necessary to capture the possibility of an abnormality in the internal analysis with an image.

First, it is necessary to inspect that the shape of the through hole, such as the depth and diameter, is made stable before lamination.
However, the required specification of the through hole is, for example, a hole with an aspect ratio of 1:25 having a diameter of 2 μm and a depth of 50 μm, which is difficult due to a diffraction phenomenon in ordinary optical measurement. This is a laminated structure. If heat cannot be released, the degree of freedom in design will be narrowed. Therefore, heat countermeasures should be taken by filling a small gap and a material with good thermal conductivity (for example, silicon compound). Is related to becoming essential.

For example, as shown in FIG. 1, the depth of a high aspect ratio through via formed in a predetermined diameter and depth (for example, a diameter of 2 μm and a depth of 50 μm) from the front surface 102 of the silicon wafer 101 toward the back side 103. A method is conceivable in which the shape is measured by causing the visible light L for measurement to enter the non-through via 104 at the stage of the non-through via 104 before completion of the through via.
However, even if the visible light L is incident on the non-penetrating via 104, the diffraction L phenomenon does not return more than a predetermined amount of light L necessary for measurement from the bottom surface 105 of the non-penetrating via 104. It is difficult to measure the shape.
In FIG. 1, when the non-through via 104 is changed to the through via, the silicon wafer 101 is deleted from the back surface 103 to the broken line C position.

On the other hand, near-infrared light or infrared light can penetrate silicon to some extent, so that the inside of the silicon wafer 101 can be observed using this.
However, the refractive index of the non-penetrating via 104 (the refractive index of air contained in the non-penetrating via) is approximately 1, and the refractive index of the silicon wafer 101 is approximately 3.4 to 3.8. Therefore, as shown in FIG. 2, the light is reflected by the side wall of the non-penetrating via 104, and it is difficult for near infrared light or infrared light L to enter the bottom surface 105 of the non-penetrating via 104.

Therefore, as long as light is used for measurement, it is difficult to measure the shape such as the depth of a hole with a high aspect ratio as described above even from other methods such as interferometry and confocal method. It is.
On the other hand, Patent Document 1 discloses an invention in which the depth of a trench, which is a kind of high-aspect-ratio minute hole, is measured with infrared light from the back surface.

  However, in claim 1 of Patent Document 1, a light source having a wavelength that can transmit through the wafer is used to receive reflected light from the front surface and the back surface of the wafer, and the front surface supports the inside of the trench. In addition, the operation of measuring the height of the protrusion of the trench and the operation of calibrating the height of the protrusion by conversion of the difference in the measured height between the front surface and the back surface How to measure depth. >.

In order to easily understand this, the flow chart of FIG. Looking at the points in this flow chart, it is as follows.
1. First, responses from the front and back surfaces of the wafer are received.
2. Next, the height values of the front and back surfaces from each sensor are recorded.
3. The thickness value is converted based on each height value.
4). Calculate and display wafer shape changes.
It is described.

In short, the bottom position of the trench is proportionally calculated from the thickness of the silicon wafer.
However, in this case, if there is a variation in the thickness of the silicon wafer that serves as a reference, this will be a variation in the measured value of the trench depth. Actually, for example, a 12-inch wafer has a variation of 0.775 mm ± 0.025 mm in thickness of a silicon wafer. That is, there is a variation of ± 3.2%, which becomes a measurement error of the trench depth as it is, and there is a problem that the measurement accuracy is poor.
In order to solve this problem, it is necessary to measure the thickness of the silicon wafer in advance and correct the measured value based on the thickness. However, since it takes a long time to measure the thickness of the silicon wafer in advance, there is a problem that high-speed measurement is difficult.

  In addition, a measuring apparatus presumed to be capable of measuring a hole with a high aspect ratio as described above by infrared light interferometry is sold under the product name DeeProbe from the French company FOGALE. However, in the measuring apparatus, it takes nearly 2 seconds to measure one hole, and it is difficult to greatly increase the speed by this method, and there is a problem that the production tact is lowered when used in an in-line inspection of production.

JP 2008-83059 A

  An object of the present invention is to accurately and rapidly measure a step structure such as a depth of a high aspect ratio hole provided in a material that transmits visible light, near infrared light, or infrared light.

  According to the present invention, a step structure such as a non-through via, a trench, or a MEMS (Micro Electro Mechanical Systems) provided in a material that transmits visible light, near infrared light, or infrared light is measured. In the step structure measurement method, visible light, near infrared light, or infrared measurement light is irradiated from the back side of the surface on which the step structure is formed, and the position where the measurement light is focused on the material is measured. Measuring the shape of the step structure by measuring reflected light from the material, or using the refractive index of the material acquired in advance or measured by a refractive index measuring means An actual shape of the step structure is calculated by converting the measured shape by using the refractive index of the step structure measurement method.

  According to the present invention, it is possible to accurately and rapidly measure a step structure such as the depth of a high aspect ratio hole provided in a material that transmits visible light, near infrared light, or infrared light.

It is explanatory drawing which shows the general measuring method using visible light. It is explanatory drawing which shows the general measuring method using near-infrared light. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is the schematic of the confocal microscope used for embodiment of this invention. It is the schematic of the XY scanning part used for embodiment of this invention. It is explanatory drawing explaining operation | movement of embodiment of this invention, and is a high NA ray figure. It is explanatory drawing explaining operation | movement of embodiment of this invention, and is a low NA ray figure. It is the schematic of XY scan in embodiment of this invention. It is explanatory drawing of the Brewster angle used in embodiment of this invention. It is explanatory drawing which shows the relationship between the dense non-penetrating via | veer and light ray in embodiment of this invention. It is explanatory drawing of the method of calculating | requiring the refractive index of a silicon wafer from Brewster angle measurement in embodiment of this invention.

As described above, the shape measurement of a rigid structure such as a bottomed hole having a high aspect ratio such as a diameter of 2 μm and a depth of 50 μm is measured from the bottom surface 105 of the non-penetrating via 104 by a diffraction phenomenon in the case of visible light. In the case of near-infrared light or infrared light, it is difficult to allow light to enter the hole from the surface side, or light rays are scattered, which can be a major obstacle to measurement. Therefore, measurement is difficult.
In an embodiment of the present invention, a material having a step structure (e.g., a silicon wafer) is conversely used without resolving the idea to make the measurement light incident on a step structure such as a non-penetrating via. ) (The back side of the surface (surface) where the step structure is formed) is irradiated with near-infrared light or infrared light, and observed and inspected from the outside of the step structure, thereby the aspect ratio of the step structure such as a hole It realizes a measurable method no matter how high.

Here, the step structure is a non-through via formed from the surface side to the back side of a material that can transmit visible light, near infrared light, or infrared light such as a transparent body such as glass or a silicon wafer. Or a bottomed hole such as a trench, a bottomed groove, a MEMS, or the like, which means a structure having a step between the surface of the silicon wafer. The shape means a shape that can be measured by visible light, near-infrared light, or infrared light, such as the depth, diameter, length, and area of a stepped structure such as a bottomed hole.
Hereinafter, with reference to the drawings regarding embodiments of the present invention, an example of measuring a shape such as the depth of a non-through via deeply drilled in a silicon wafer with a high aspect ratio by dry etching or the like with high accuracy at high speed will be described. To do.

In the embodiment of the present invention, visible light, near-infrared light, or infrared light can be used as light used for measurement. Visible light having a wavelength of 350 nm or more is applied to a transparent material such as glass. It is valid. For silicon wafers, near infrared light or infrared light in the range of 900 nm to 3000 nm is preferable. The reason why near-infrared light or infrared light having such a wavelength is preferable is that light of less than 900 nm does not pass through silicon. In the following description, a silicon wafer material is described. However, in the present invention, when light is transmitted through the material, light of that wavelength can be used, so the material is limited to a silicon wafer. It is not a thing.
Further, the Airy disk radius (= 0.61λ / NA (where λ is the wavelength of the measurement light to be used and NA is the aperture ratio)), which is a measure of the resolution, is increased by increasing the wavelength of the measurement light. As a result, the measurement accuracy is greatly deteriorated. Therefore, the upper limit wavelength at which the required measurement accuracy is obtained is set to an upper limit value of 3000 nm.

FIG. 3 is a schematic explanatory diagram of the step structure measuring method according to the embodiment of the present invention.
The example of FIG. 3 is an example of a step structure in which a step (corresponding to the depth of the non-penetrating via 104 in this example) is formed by the surface 102 of the silicon wafer 101 and the bottom surface 105 of the non-penetrating via 104. The non-penetrating via 104 is a stage prior to the formation of the penetrating via, and is a bottomed hole formed with a predetermined diameter and a predetermined depth from the front surface 102 side to the rear surface 103 side of the silicon wafer 101. 101 is exposed on the surface 102 side.

First, when measuring the shape of the step structure (for example, the depth of the non-penetrating via 104), visible light from the back surface 103 side of the silicon wafer 101 to the surface 102 of the silicon wafer and the bottom surface 105 of the non-penetrating via 104, The measurement light L which is light of a predetermined wavelength in near infrared light or infrared light is irradiated.
Next, the measurement light L reflected by the surface 102 of the silicon wafer 102 and the bottom surface 105 of the non-penetrating via 104 is detected using a measurement method such as a confocal measurement method, and the measurement light L from a predetermined position serving as a reference to the surface 102 is detected. The distance and the distance from the predetermined position to the bottom surface 105 are measured. The apparent depth of the non-penetrating via 104 is measured by calculating the difference between the distance from the predetermined position to the surface 102 and the distance from the predetermined position to the bottom surface 105.

Next, using the refractive index of the silicon wafer 101 that has been acquired as information in advance, or using the refractive index of the silicon wafer 101 measured by using a refractive index measuring unit that measures the refractive index of the silicon wafer 101, The actual shape is calculated by subjecting the apparent shape to a conversion process using the refractive index.
A significant difference from Patent Document 1 is that an actual value is directly measured using information on the refractive index.
In FIG. 3, when the through via is formed from the non-through via 104, the silicon wafer 101 is deleted from the back surface 103 to the broken line C position.

  By the measurement method according to the present embodiment, visible light, near infrared light, or infrared light (a wavelength of 1127 nm or more is more preferable from the viewpoint of easy transmission of silicon and 3000 nm or less from the viewpoint of obtaining a certain resolution or more. Is irradiated from the back surface 103 side of the silicon wafer 101, the non-penetrating via 104 can be measured with no problem even if the aspect ratio of the non-penetrating via 104 is 1:25, 1: 200, or more. In addition, more accurate shape measurement can be performed by the conversion process using the refractive index.

Although details will be described later, in order to measure the refractive index, the Brewster angle is measured in a short time, and in order to obtain it accurately, the refractive index at one refractive index measurement point is measured several times and the average of them is measured. Further, the measurement is performed at a plurality of refractive index measurement points in the XY directions in the measurement target region of the silicon wafer.
For example, when measuring by the confocal method described later, an area of 2000 × 2000 pixels as a 1 μm square area per pixel is used as a unit area to be measured at a time, and the measurement target area of the silicon wafer is a plurality of units. The region is divided into regions, the shape of the step structure (step shape) is measured for each unit region, and this is performed for all measurement target regions of the silicon wafer.

In this case, at the start of the step structure measurement (immediately before measuring the apparent step shape for each unit region), each unit of the silicon wafer is measured using the measurement light having the same wavelength as the measurement light for measuring the step shape. Measure the refractive index of the region, and measure the shape of each unit region measured by the measurement light. The refractive index of the unit region (the refractive index measured multiple times in the unit region to increase the accuracy of the refractive index) The average shape of the refractive index may be converted to the actual shape to obtain an error so that no error occurs even if the refractive index distribution changes in the silicon wafer. Thereby, sufficient measurement accuracy can be ensured.
The refractive index may be measured not at the start of the step structure measurement but at the end of the step structure measurement (immediately after the measurement of the apparent step shape in each unit region).

  In the case of a TSV hole, since it may be formed with a diameter of 2 μm and a pitch of 6 μm, when the TSV is densely packed to a predetermined density or more, an aperture 601 disposed in front of the objective lens 407 as shown in FIG. If the numerical aperture NA is reduced so that the measurement light is not reflected by the side walls of the non-penetrating vias, an image with high contrast may be obtained.

  Further, in the measurement where the TSVs are not denser than the predetermined density, as shown in FIG. 6, by increasing the aperture arranged in front of the objective lens 407, the numerical aperture NA is increased and the focused spot is formed. The smaller the resolution, the better the resolution. This condensing spot is generally called an Airy disk and has an Airy disk radius ε = 0.61λ / NA. This is because a diffraction phenomenon occurs due to the property as a wave of light.

In the embodiment of the present invention, as shown in FIG. 6 or FIG. 7, the numerical aperture NA of the optical system used for measuring the shape of the step structure is changed in accordance with the shape of the step structure.
In order to prevent the Airy disk from becoming large, the wavelength of near-infrared light is preferably 1127 nm or more, but is preferably suppressed to 3000 nm or less, more preferably 1500 nm or less at the upper limit.
As a result, when a plurality of non-defective LSI chips are bonded together, there is no abnormality in the bonded portion and its periphery, or there is no bonding abnormality after product shipment, or there is a microcrack, etc., which grows. It becomes possible to inspect with a three-dimensional image, for example, whether there is a possibility of a defect that becomes defective in the market and leads to defect recovery.

Next, a schematic configuration and measurement operation of the measurement apparatus used in the method for measuring a step structure according to the embodiment of the present invention will be described in detail.
FIG. 4 is a configuration diagram showing an optical system of a confocal laser microscope used in the present embodiment.
In FIG. 4, a laser light source 401 outputs measurement light L having a predetermined wavelength in visible light, near infrared light, or infrared light, and expands the measurement light L into parallel light by an expander 402 and a collimator 403. The S-polarized component of the measurement light L is reflected by the beam splitter 404 and led to the XY scanner unit 405.

As shown in FIG. 5, the XY scanner unit 405 includes a resonant resonant scanner 501 for scanning the measurement light L in the X direction and a galvano scanner 502 for scanning the measurement light L in the Y direction perpendicular to the X direction. Yes.
A resonant scanner 501 is a resonance type scanner capable of mirror driving at high speed. The resonant scanner 501 used in this embodiment reciprocates at about 8 KHz. That is, one line can be scanned at 0.0625 msec.

The galvano scanner 502 scans the measurement light L in the Y direction in a predetermined row (for example, 2000 rows).
By scanning the measurement light L from the resonant scanner 501 in the column direction with the 2000-row galvano scanner 502, an image of one screen (for example, 2000 pixels in the X direction × 2000 pixels in the Y direction) is obtained in 125 msec. This means that an image of 2000 × 2000 pixels, which is one unit of shape measurement, can be acquired at 8 frames / second.

From this, when the acquisition time per pixel is calculated, it becomes 31.25 nsec and a readout speed of a photodetector of 32 MHz is required, but the product G8376-03 manufactured by Hamamatsu Photonics Co., Ltd. has 2.5 nsec. The A / D (analog / digital) converter needs only to be 10 bits at 32 MHz or more. For example, the AD12V170 made by National Semiconductor has 12 bits, 170 MSPS (megasample second), and the speed is still enough. There is.
If the speed of the resonant scanner 501 increases, the image acquisition speed further increases. In addition, if a MEMS scanner that satisfies the required specifications can be obtained, it can be used.

  The measurement light L output via the XY scanner unit 405 is converted into circularly-polarized measurement light L by the λ / 4 wavelength plate 406, and then the silicon wafer 101 that is the measurement object via the objective lens 407. Is irradiated. The λ / 4 wavelength plate 406 is used together with the polarization beam splitter 404 to prevent the reflected light from the silicon wafer 101 from returning to the laser light source 401.

As a result, the silicon wafer 101 is scanned by the measurement light L from the back surface 103 side. As shown in FIG. 8, one unit region of the silicon wafer 101 (2000 pixels in the X direction in this embodiment) is arranged in the XY direction. Scanning is performed with the measurement light L every 801 pixels in the × Y direction).
By the scanning, the measurement light L is reflected by the surface 102 of the silicon wafer 101 and the bottom surface 105 of the non-penetrating via 104 in each pixel in each unit region.

The reflected measurement light L passes through the objective lens 407, the λ / 4 wavelength plate 406, the XY scanner unit 405, and the polarization beam splitter 404 in this order, and is detected by the photodetector 410 via the imaging lens 408 and the pinhole 409. Detected.
The measurement operation is performed while scanning in the Z-axis direction in predetermined length units. The position in the Z direction when a clear image is detected by the photodetector 410 becomes the position of the surface 102 of the silicon wafer 101 and the bottom surface 105 of the non-penetrating via 104 with the predetermined position as a reference. The apparent depth of the non-penetrating via 104 is obtained by taking the difference in position between the front surface 102 and the bottom surface 105.

  By performing the above operation over the entire measurement target region of the silicon wafer 101, the apparent positions of the surface 102 and the bottom surface 105 of the non-penetrating via 104 in the total measurement target region of the silicon wafer 101 are measured. The apparent depth of the non-penetrating via 104 provided in the target region is measured.

  Thereafter, using the refractive index of the silicon wafer 101 obtained in advance as information, or using the refractive index of the silicon wafer 101 measured at the start of the measurement operation or at the end of the measurement operation, the apparent measurement value is obtained. Converting to an actual value, the actual depth of the non-penetrating via 104 is calculated. For example, when the apparent depth of the non-penetrating via 104 is DM, the refractive index of air is n1, and the refractive index of the silicon wafer 101 is n2, the actual depth DS is DM · n2 / n1.

  In the present embodiment, the refractive index is measured a plurality of times for each unit region for measuring the step shape, the average value thereof is calculated, and the average value is used as the refractive index of the unit region. The measured value is converted into an actual value. A plurality of points are selected from the entire silicon wafer 101 to measure the refractive index, and the average value of these points is set to 1 of the silicon wafer 101 common to each unit region. Various changes can be made, for example, the measured value for each unit region is converted by the one refractive index and the actual value is obtained by using it as one refractive index.

The method for measuring the depth of the non-penetrating via 104 having a depth of 50 μm from the surface 102 formed on the silicon wafer 101 with the above specifications will be described in detail as follows.
1. In order to start the measurement of the silicon wafer 101, automatic positioning is first performed. This is done by positioning marks (not shown) of the silicon wafer 101 provided on the surface of the silicon wafer 101 or a plurality of non-through vias 104 having a certain distance or more, and at least two XY (horizontal) positions and Z (vertical). ) Determine the position and import.
This is possible if, for example, the time is about 5 seconds. ------- (1)

2. Move to the first measurement chip in the silicon wafer 101 and determine the XYZ position. This is possible if, for example, the time is about 1 second. ------- (2)
3. Next, for example, measurement is started with a 1 mm square per pixel and a 2 mm square of 2000 × 2000 pixels as one unit area.

4). The first step of measuring the shape of the step structure is performed by measuring the refractive index of the silicon wafer 101. Since the refractive index is measured not from the front surface 102 but from the back surface 103 side (for example, reflection measurement by Brewster angle), in order to prevent useless movement of the wafer 101 in the thickness direction Z, first, a certain unit (for example, 2 mm interval). ), The refractive index distribution (refractive index of a plurality of points) of the entire silicon wafer 101 is measured for all measurement target regions for measuring the non-penetrating vias 104, and the measurement error of each measurement value is reduced by averaging as necessary. . For example, when one refractive index is used for the entire silicon wafer 101 when calculating the actual shape of the non-penetrating via 104, the refractive index is averaged for all measurement target regions to calculate one refractive index. When calculating the shape using the refractive index of each unit region, the refractive index measured a plurality of times for each unit region is averaged to calculate the refractive index of each unit region.
Here, it is necessary to measure if it is assumed that the circuit area of the 300 mm wafer is 85% of the area of 300 mm in diameter considering the orientation flat and the outer periphery, and 10% of the area is the TSV area. Area (area of all measurement target areas) is
3.1415 × 150 × 150 × 0.85 × 0.1 = 6008 mm ²
It becomes. When the refractive index is measured several times in a unit of 2 mm square and averaged to increase the measurement accuracy and the refractive index measurement and the data acquisition of the refractive index are performed at 10 msec per location, the moving time of 2 mm is 0.2 seconds. Refractive index distribution data is fetched per silicon wafer 101 at the following time.
0.21 seconds × (6008/4) = 315.42 seconds ------ (3)
Here, (6008/4) is the number of capture areas in all measurement target areas.

5. Next, the position of the first surface 102 for measuring the depth of the non-through via 104 in the silicon wafer 101 is detected.
This is possible, for example, if the time is about 1 second. ------ (4)
6). From here, the measurement of the depth of the non-penetrating via 104 is started. In order to ensure accuracy, it is preferable to measure from the surface 102 of the silicon wafer 101 in the depth direction of the non-penetrating via 104.
For example, it takes about 0.1 second to return and set the surface 102 position. The time required for this is
0.1 seconds × ((6008/4) -1) = 150.1 seconds ------ (5)

7). The time required for the depth measurement can be efficiently and accurately measured by scanning in the depth direction (Z direction) in the steps shown in Table 1 below, for example.

When measuring in Table 1, 11 screen images are captured in the vertical (Z) direction. The measurement time is multiplied by the number of capture areas from Table 1,
1.445 seconds × (6008/4) = 2170 seconds ------ (6)
The measurement time per wafer is 2642 seconds (44.04 minutes), which is the sum of the above times (1) to (6).
The number of sheets that can be measured per day is 60 minutes × 24 ÷ 39.04 minutes / sheets = 32.7 sheets, and 981 sheets / 30 days can be measured in one month.
When the number of LSIs taken per wafer is 600, the measurement speed is 588,000 chips / month.
The refractive index measurement for the silicon wafer 101 may be performed when the apparent shape measurement of all the measurement target regions is completed.

Next, a method for measuring the refractive index of the material will be specifically described.
In order to measure the refractive index, there are two types: a case where a spectroscopic ellipsometer is used and a case where the refractive index is obtained by measuring the Brewster angle.
In general, it is said that measuring with a spectroscopic ellipsometer is more accurate, but it takes more measurement time for modeling, matching, etc., so in order to shorten the time, it is better to measure the Brewster angle accurately. It is suitable for high-speed equipment.
Therefore, this embodiment describes a method for obtaining the refractive index from Brewster angle measurement.
However, the refractive index may be measured using a spectroscopic ellipsometer.

When light is incident at an angle at the interface between two materials having different refractive indexes, the reflectance is the polarization component parallel to the incident surface (P-polarized component) and the polarization component perpendicular to the incident surface (S-polarized component). Unlike the P-polarized light component, the reflectance decreases to 0 at a certain angle (Brewster angle θp) and then increases. The reflectance of the S-polarized component increases monotonously.
The Brewster angle θp is obtained from the refractive indexes n1 and n2 of the two materials by the following equation.
Brewster angle θp = Arctan (n2 / n1)
n1 is the refractive index of the incident side material (air in the present embodiment), and n2 is the refractive index of the transmission side material (silicon in the present embodiment). Therefore, when the refractive index n1 of the incident side material is known, the refractive index n2 of the transmission side material can be obtained by measuring the Brewster angle θp.

For example, in the case of glass (n = 1.52), the relationship between the P-polarized component, the S-polarized component and the Brewster angle θp is expressed as shown in FIG.
From the above formula, in the case of glass (n = 1.52), when the refractive index n of air is n = 1.000292, the Brewster angle θ is θp = 56.65 degrees, and the refractive index of silicon is the same, for example. When n = 3.412 in near infrared light, θp = 73.66 degrees. Conversely, when the Brewster angle θp is accurately determined, the refractive index n can be accurately determined.

FIG. 11 is an explanatory diagram of a method for obtaining the refractive index of the measurement object from the Brewster angle θp measurement using the above principle.
In FIG. 11, a laser light source 1101 is a light source that irradiates measurement light L for refractive index measurement at a variable angle with respect to a measurement object, and a polarizing plate 1102 is polarized light that passes a P-polarized component of the measurement light L. The plate / light receiver 1103 is a light detection means for detecting the measurement light L reflected from the measurement object, and these constitute a refractive index measurement device for measuring the refractive index by Brewster angle measurement. In addition, the laser light source 1101, the polarizing plate 1102, and the light receiver 1103 constitute a refractive index measuring unit.

The measurement light L for refractive index measurement emitted from the laser light source 1101 passes through a polarizing plate 1102 disposed in air (refractive index is n1) 1104, and is a silicon wafer (refractive index) that is an object of refractive index measurement. Is reflected by n2) 1105, and then the light L for measuring the P-polarized component is detected by the light receiver 1103.
While changing the angle at which the measurement light L is incident on the silicon wafer 1105 from the laser light source 1101 via the polarizing plate 1102, the P light detected by the light receiver 1103 is detected by the light receiver 1103. The incident angle when the polarization component becomes 0 is measured. The incident angle when the P-polarized light component becomes 0 is the Brewster angle θp.
By making the measurement light L output from the laser light source 1101 for refractive index measurement into light having the same wavelength as the visible light, near infrared light, or infrared light output from the laser light source 401 for measuring the step shape. The refractive index can be accurately measured, and as a result, the actual step shape can be accurately measured.

  In this way, the refractive index is measured at a plurality of points on the silicon wafer 1105, the refractive indexes at all the measurement points are used as one refractive index of the entire silicon wafer, and the measured shape is converted by the refractive index. Calculate the actual shape. Alternatively, the measured refractive index of each unit region is used as the refractive index of each unit region of the silicon wafer 1105, and the refractive index of the unit region is measured for each unit region whose shape is measured. The actual shape may be calculated by conversion using a rate.

Next, as described with reference to FIGS. 6 and 7, the numerical aperture NA of the optical system is changed in accordance with the measurement target so that effective measurement can be performed. A case will be described.
Reducing the numerical aperture NA is disadvantageous in reducing the focal point, in other words, in reducing the air disk, but a high aspect ratio non-through via 104 is formed in the silicon wafer 101 as shown in FIG. It may be advantageous if the density is higher than the density.

This is because the measurement light L totally reflected or reflected by the dense walls of the non-penetrating vias 104 becomes noise, which may reduce the contrast of the image. In such a case, accurate measurement can be performed by reducing the numerical aperture NA.
Therefore, it is effective to change the numerical aperture NA in accordance with the shape of the measurement object. For example, when the non-through vias 104 are densely packed in the silicon wafer 101 with a density of a predetermined value or more as shown in FIG. The measurement is performed while changing the NA to be small.

In this embodiment, the apparent position (in other words, the apparent shape) of the step structure is measured by measuring the position where the focal point is formed using the confocal measurement method. An apparent shape is measured by measuring reflected light using a measurement method, and the actual shape is calculated by converting the measured shape into a known refractive index or a measured refractive index. May be.
In the present embodiment, as the refractive index measuring means, means for obtaining the refractive index by Brewster angle measurement is used. However, a spectroscopic ellipsometer may be used.

In the present embodiment, the refractive index of the silicon wafer is obtained by measuring the refractive index using a refractive index measuring unit. However, if one refractive index as a whole is known in advance, the known refractive index is used. Alternatively, the actual shape may be calculated by converting the measured shape. In addition, when the refractive indexes of a plurality of points on the silicon wafer are known, the actual shape may be obtained by converting the measured shape by the refractive index for each region where the shape is measured.
In this embodiment, the example of the silicon wafer is described as the material provided with the step shape, but any material that can transmit visible light, near infrared light, or infrared light is applicable. It can also be applied to glass, ceramics, and compound semiconductors.

  As described above, according to the embodiment of the present invention, measurement for measuring a step structure such as a non-through via, a trench, or a MEMS provided in a material through which visible light, near infrared light, or infrared light is transmitted. In the method, by irradiating measurement light of visible light, near infrared light, or infrared light from the back side of the surface on which the step structure is formed, and measuring the position where the measurement light is focused on the material Alternatively, the apparent shape of the step structure is measured by measuring reflected light from the material, and the measured shape is obtained using the refractive index of the material obtained in advance or the refractive index of the material obtained by measurement. It is characterized by calculating an actual shape by conversion.

Further, for example, the measurement light L of visible light, near infrared light, or infrared light is irradiated from the back surface 103 side of the silicon wafer 101 on which the non-penetrating via 104 is formed, and the measurement light L is emitted by the confocal measurement method. The apparent shape of the non-penetrating via 104 is measured by measuring the position that focuses on the surface 102 of the silicon wafer 101 and the bottom surface 105 of the non-penetrating via 104, and the refractive index or refractive index of the silicon wafer 101 acquired in advance is measured. The actual shape of the non-penetrating via 104 is calculated by converting the measured apparent shape using the refractive index of the silicon wafer 101 measured by the refractive index measuring means to measure.
Therefore, the shape of the step structure such as the depth of a high aspect ratio hole provided in a material that transmits visible light, near infrared light, or infrared light can be measured accurately and at high speed.

Here, as a method for measuring the shape of the step structure, a confocal measurement method that measures the shape of the step structure by measuring a position where the measurement light is focused on the material is used. Measurement is possible.
In addition, as a method for measuring the shape of the step structure, it is possible to perform measurement with higher accuracy by using an optical interferometry method that measures the shape of the step structure by measuring reflected light from the material.
In addition, as a method for measuring the shape of the step structure, a laser triangulation measurement method that measures the shape of the step structure by measuring reflected light from the material can be used.
Further, by using a refractive index measuring device that measures the refractive index by Brewster angle measurement as the refractive index measuring means, it is possible to perform a higher-speed refractive index measurement.
Further, by using a spectroscopic ellipsometer as the refractive index measuring means, it is possible to measure the refractive index with higher accuracy.
Further, by setting the wavelength of the light for measuring the refractive index of the material and the wavelength of the measuring light for measuring the step structure to the same wavelength, more accurate refractive index measurement can be performed.

In addition, it is possible to shorten the total measurement time by measuring the refractive index or refractive index distribution of the material from the back surface of the measurement target region at the start of shape measurement or at the end of shape measurement of the step structure. Become.
In addition, by making the numerical aperture NA of the optical system used for measuring the shape of the step structure variable in accordance with the shape of the step structure, high-accuracy measurement according to the shape of the measurement object or the like is possible.

In addition, it is not affected by variations in the thickness of the silicon wafer. Also, the focus is measured from the back surface to the front surface of the silicon wafer, and the focus is moved in the depth direction of the hole, and the depth of all holes is measured. It is not necessary to measure the thickness because the measurement should be finished when it is completed. In other words, for example, even if a wafer having a thickness of 0.775 mm has a hole depth of 50 μm, and the hole having the deepest variation is, for example, 55 μm, the measurement can be terminated at that time, so the measurement time Get faster. Further, in measuring the depth of the hole, it is not necessary to measure the back surface of the wafer at all.
Therefore, it is possible to directly and accurately measure the shape of the step structure such as a high aspect ratio hole.

Further, the shape of a hole having a diameter of 2 μm and a depth of 50 μm with an aspect ratio of 1:25 can be measured at high speed, and measurement can be performed at high speed and accurately without dropping production tact in production.
In addition, even if a small hole (2 μm to 100 μm) formed in silicon and the aspect ratio of diameter and depth is large such as 1:25 or more, the depth and shape of the hole are measured regardless of the aspect ratio. Is possible.

In addition, when multiple non-defective LSI chips are bonded together, there is a possibility that an abnormality will occur in the bonded portion and its surroundings, a possibility that a bonding abnormality may occur after product shipment, micro cracks, etc. As a result, it becomes possible to inspect with a three-dimensional image whether or not there is a possibility of occurrence of defects leading to market failure and failure recovery.
In addition, the observation and connection of laminated silicon wafers and their surroundings can be realized with the same method and equipment, and inspection and quality that support laminated wafer technology can be guaranteed not only at the time of shipment but also after shipment. In this way, it is possible to prevent problems such as quality abnormalities and defective recovery in the market.

  In addition to the measurement of stepped structures such as fine, high aspect ratio bottomed holes and staircase shapes provided on silicon wafers, materials other than silicon that transmit visible light, near infrared light, or infrared light, such as glass It can be applied to the measurement and inspection of step structures provided in ceramics and compound semiconductors.

101 ... silicon wafer 102 ... front surface 103 ... back surface 104 ... non-penetrating via 105 ... bottom surface 401, 1101 ... laser light source 402 ... expander 403 ... collimator 404 ... Polarizing beam splitter 405 XY scanner section 406 λ / 4 wavelength plate 407 objective lens 408 imaging lens 409 confocal pinhole 410 photodetector 501 ..Resonant resonance scanner 502... Galvano scanner 601... Aperture 801... 1 unit area 1102.

Claims (10)

In a step structure measurement method for measuring a step structure such as a non-through via, a trench or a MEMS provided in a material that transmits visible light, near infrared light, or infrared light,
Irradiate measurement light of visible light, near infrared light or infrared light from the back side of the surface where the step structure is formed,
Measure the shape of the step structure by measuring the position where the measuring light focuses on the material or by measuring the reflected light from the material,
The actual shape of the step structure is converted by converting the measured shape using the refractive index of the material measured in advance by using the refractive index of the material obtained in advance or by the refractive index measuring means for measuring the refractive index. A method for measuring a step structure, characterized by calculating.   2. The step structure measuring method according to claim 1, wherein a confocal measurement method is used for measuring the shape of the step structure.   2. The step structure measuring method according to claim 1, wherein an optical interference measurement method is used for measuring the shape of the step structure.   2. The step structure measuring method according to claim 1, wherein a laser triangulation method is used for measuring the shape of the step structure.   5. The step structure measuring method according to claim 1, wherein a refractive index measuring device that measures a refractive index by Brewster angle measurement is used as the refractive index measuring means.   5. The step structure measuring method according to claim 1, wherein a spectroscopic ellipsometer is used for the refractive index measuring means.   The step structure measuring method according to any one of claims 1 to 6, wherein the wavelength of the light for measuring the refractive index of the material and the wavelength of the measuring light for measuring the step structure are the same wavelength. .   The step according to any one of claims 1 to 6, wherein a refractive index or a refractive index distribution of the material is measured from the back surface of the measurement target region at the start of shape measurement or at the end of shape measurement of the step structure. Structure measurement method.   9. The step structure measuring method according to claim 1, wherein a numerical aperture NA of an optical system used for measuring the shape of the step structure is variable according to the shape of the step structure. The step structure is a non-through via provided in a material that transmits near infrared light or infrared light,
The step structure measuring method according to claim 1, wherein the measurement light is near infrared light or infrared light.

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