JPH0444210A - Glass wafer and method for detecting surface position thereof - Google Patents

Abstract

PURPOSE:To automatically detect and correct an error caused in the thickness of a glass wafer by forming a film having a prescribed reflectivity against the detecting light of an automatic focus detector on the rear of the wafer and, at the same time, another film which does not transmit the detecting light in a part of the surface of the wafer. CONSTITUTION:In order to correct a detecting error component caused by reflected light 5b from the rear of a glass wafer substrate 1, surface position detection is performed on the area 2 of a glass wafer in addition to the other area 3 of the wafer by using the glass wafer partially formed with a light shielding film 7 which does not transmit detecting light. In the area 2, a film 7 of, for example, Cr, two-layer Cr, which does transmit the detecting light is formed on the substrate 1. When the area 2 is constituted in such way, no detection error occurs and it is confirmed that a surface position detecting quantity catches the surface of a photoresist 8, because the reflected light from the rear surface of the substrate 1 does not exist and, accordingly, no detection error occurs. The detection error caused by the reflection of the detecting light at the rear surface of the substrate 1 in the area 1 can be confirmed from the difference between the detecting quantities in the areas 3 and 2. Therefore, an erroneous value in surface position detecting values caused by the reflected light from the rear surface of the glass wafer substrate can be detected automatically.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a glass wafer and a method for detecting the surface position of the glass wafer, and in particular detects the surface position of the glass wafer in a projection exposure apparatus for semiconductor manufacturing. This is suitable when using an automatic focus detection device that optically detects the surface position of a wafer for manufacturing actual devices.

(Prior art) With the recent demand for miniaturization of semiconductor devices and LSI devices,
In the production process of highly integrated LSIs, a reduction projection exposure device (stepper) is used for pattern transfer. In this method, a circuit pattern on an original plate called a reticle is reduced and projected onto the wafer surface using a projection lens system, and a circuit pattern image is transferred onto the wafer surface in reverse for each reticle using a step-and-repeat method. It is.

If exposure (transfer) is performed with foreign matter still attached to the reticle of the stepper, all chips will be defective as a result, resulting in severe damage.

For this reason, in the stepper, it is necessary to perform a strict foreign matter inspection on the reticle itself before setting it in the exposure device.

Furthermore, it is desirable to perform a reconfirmation inspection even after setting it in the exposure apparatus. As this method, a method is known in which a reticle pattern is once printed on a wafer with a resist, and after development, the transferred pattern is inspected for defects.

This method has the advantage of being able to inspect not only foreign matter on the reticle, but also dust in the optical system of the exposure device and whether the exposure conditions are good or bad.

As a reticle defect inspection method, there is also a method that takes advantage of the fact that the reticle is composed of multiple chips. That is, since the circuit patterns of the actual chips are the same, defects can be inspected by comparing different chip patterns on the reticles constituting the multi-chip.

In the actual inspection, two or more chips in the wafer produced by the method described above are compared. For example, it is possible to compare images taken by multiple dedicated imaging systems for each of the chips to be compared with each other, or to take an image of a certain chip using a single imaging system and store this image in a delay memory. Image processing is performed to compare the stored image with the image taken of the next chip. The result of image comparison should be the same 2
Any location that is not common to the two chips is determined to be a defect due to foreign matter on the reticle, and the reticle is cleaned or replaced based on the result.

This is a conventional method of detecting foreign matter on a reticle and preventing defects due to pattern defects caused by foreign matter.

Generally, as a wafer on which RTE detection of reticle defects is to be performed, in addition to using a normal silicon wafer, a method is known in which a glass wafer whose surface is coated with metal is used. A glass wafer whose surface is coated with metal is exposed to light through a reticle pattern and then etched to produce a pattern of metal film on its surface. Patterns made of metal films clearly transmit and do not transmit light, so they can be observed using high-contrast transmission images, making it easy to compare patterns.

In recent years, as LSIs have become more highly integrated, the reliability of image comparison inspection has increased.
While such methods are used to improve detection ability, there is a need for simpler testing methods.

For this reason, recently, a dye-containing resist is coated on a glass wafer, this resist is exposed to light through a pattern on a reticle, and the pattern transferred to the resist is processed in the same way as the method described above without developing it. A method has been developed in which images are compared by observing the transmitted images. When using dye-containing resists, it is clearer whether the light is transmitted or not than when using regular resists, and it is possible to observe transmission images with high contrast, making it easy to compare patterns, and making it easy to obtain accurate and accurate images. It is known that good measurements can be made.

(Problem to be solved by the invention) In order to detect foreign matter on a reticle using the method of directly observing a transmission image of the wafer without developing the pattern transferred to the resist on the glass wafer, First of all, it is necessary to transfer the image of the reticle pattern onto the glass wafer in the correct focus state. Many of today's steppers are equipped with an optical automatic focus detection device. However, since the glass wafer is transparent to the detection light used to detect the surface position of the wafer surface by an automatic focus detection device, the reflected light from the back surface of the glass wafer and the reflected light from the chuck surface are reflected as disturbance light on the resist. Enters the reflected light from the surface,
There is a problem in that an error occurs in the measurement result of the surface position. For this reason, we are currently applying a reflective film on the back side of the glass wafer that has a high reflectance only for this detected light, making the intensity of the reflected light from the back side of the glass wafer constant, making the amount of error constant, and correcting it as an offset amount. A method has been devised to do this.

However, this method requires management of variations in the thickness of individual glass wafers.
This method has the disadvantage that the amount of error in the measurement results varies due to the reflected light from the back surface of the wafer. Therefore, in order to use this method effectively, it is necessary to align the thickness of each glass wafer with high precision, resulting in a very high cost. In addition, the only way to determine the amount of error in the surface position of the wafer, that is, the amount of offset, is to print a reticle pattern on a glass wafer, which takes a lot of time and effort to make samples for image comparison inspection. There was a problem that it took a long time.

The present invention was made in view of these problems, and it is possible to improve the quality of the glass wafer by coating a part of the surface of the glass wafer with a non-transparent film and measuring the surface of the resist on the non-transparent film. The object of the present invention is to provide a glass wafer suitable for a projection exposure apparatus for semiconductor manufacturing, which allows errors caused by the thickness of the glass wafer to be automatically detected and corrected, and a method for detecting the surface position of the glass wafer.

(Means for Solving the Problems) The glass wafer of the present invention is a glass wafer used in a projection exposure apparatus equipped with an automatic focus detection device, and the glass wafer is a glass wafer used in a projection exposure apparatus equipped with an automatic focus detection device. Applying a film having reflectance to the back surface RA of the wafer,
It is characterized in that a film that is opaque to the detection light is applied to a part of the region B of the surface RB of the wafer.

Furthermore, in the present invention, a film having a predetermined reflectance for the detection light from the automatic focus detection device is applied to the back surface RA, and a film that is opaque to the detection light is applied to a part of the region B of the front surface RB. Detection light is incident on the treated glass wafer from the surface RB side, and information on the incident position on a predetermined surface of the reflected light from both the region B and the region A other than the region B of the detection light is used. By doing so, the glass wafer area A
The feature is that the surface position information of each shot in the image is detected.

(Embodiment) FIG. 1(A) shows a close-up view of a glass wafer 23 according to a first embodiment of the present invention, and FIG. 1(13) shows a cross-sectional view of FIG. 1(A). In FIG. 1(B), reference numeral 1 denotes a glass wafer substrate, and a film 6 having a high reflectance for detection light consisting of infrared rays from an automatic focus detection device is applied on the back surface. On the other hand, on a portion (periphery) of the surface of the glass wafer substrate 1, a film 7 is formed by vapor-depositing a substance that is non-transmissive to the detection light and has a low reflectance. This portion is shown as a shaded region 2 in FIG. 1(A). Region 3 on the surface of glass wafer substrate 1 is a region where non-transparent film 7 is not formed. Further, on the surface of the glass wafer substrate 1, a photoresist 8 is applied to the entire surface including areas 2 and 3 in order to transfer a reticle pattern thereto.

The method of optically detecting the surface position of the wafer surface (the position of the wafer with respect to the optical axis direction of the projection lens system) used in a reduction projection exposure apparatus (stepper) is as shown in FIG. 1(C). Optical automatic focus detection device (21,
22, 25), the light projecting means 2 is placed on the wafer 23.
1, the detection light 24 made of infrared light is obliquely incident, and the reflected light generated by the detection light 24 being reflected on the wafer 23 is incident on the position sensor 22 via the detection optical system 25. The incident position 22a is detected by the sensor 22.
Detection based on the output signal from. The position of the reflection point on the wafer 23 changes as the wafer moves up and down,
This change is captured by the position sensor 22, and the vertical height of the surface of the wafer 23 (the surface position of the wafer 23) is detected. has been done.

Next, a surface position detection method when using the glass wafer shown in FIGS. 1(A) and 1(B) will be described.

In FIG. 1(B), 4 is the light projecting means 2 shown in FIG.
1 indicates the detection light projected onto the glass wafer substrate 1 and reflected at the area 2, and 5 indicates the detection light projected onto the glass wafer substrate 1 from the light projecting means shown in FIG. 1 and reflected at the area 3. It shows. Of the luminous flux 5 reflected in the region 3,
The light flux indicated by the solid line 5a indicates the reflected light from the front surface of the glass wafer substrate 1, and the light flux indicated by the broken line 5b reaches the back surface of the glass wafer substrate 1 via the resist 8, and is reflected from the surface of the glass wafer substrate 1.
The figure shows the reflected light that is reflected by the substrate 1, returns to the surface of the substrate 1, and is emitted.

A method for detecting the surface position of the glass wafer surface using detection light in region 3 will be explained. In general, since a glass wafer is as thin as 500 to 600 μm, the reflected lights 5a and 5b are separated from each other on the light receiving surface of the position sensor 22, and the incident position cannot be detected. That is, the reflected light flux 5
is formed by each component of these reflected lights 5a and 5b overlapping each other, and the presence of this reflected light 5b from the back surface of the glass wafer substrate 1 indicates the surface position of the front surface of the glass wafer substrate 1 of the reduction projection exposure apparatus. This will cause an error in the detection results.

That is, here, the surface position detection amount of the reduction projection exposure device is F, the component based on the reflected light 5a from the front surface of the photoresist 8 is F(top), and the reflected light 5b from the back surface of the glass wafer substrate 1 is F(top). The component based on ΔF (bott
om), the detected amount F can be approximately expressed as FF (top) + ΔF (bottom). This detection error component ΔF (bottom)
After considering and conducting experiments, we found that the component ΔF (bo
It was found that ttom) is determined by the reflectance of the coach ink film 6 on the back surface of the glass wafer substrate 1 and the thickness of the glass wafer substrate 1, and has a unique value for each glass wafer.

In the present invention, the detection error component ΔF (bottom
), as shown in FIGS. 1A and 1B, a glass wafer is used that has a light-shielding film 7 formed on a portion of its surface that does not allow the detection light to pass through. That is, the present invention is characterized in that, in addition to region 3, surface position detection is performed for region 2 of the glass wafer. In region 2, a film 7 made of, for example, Cr or double-layer Cr, which does not have transparency to detection light, is formed on the glass wafer substrate 1. When region 2 is configured in this way, there is no light reflected from the back surface of glass wafer substrate 1, so there is no detection error of component ΔF (bottom), and in actual experiments, the detection error of component ΔF (bottom) does not exist. It was confirmed that the surface of the photoresist 8 was detected by the position detection amount F. That is, in region 2, the following equation holds true.

F'=F(top) Here, detection in area 3! From F and the detection amount F' in area 2, F-F'-F (top) +ΔF (bottom
) -F (tOP) = ΔF (bottom) is established, and by detecting and calculating the detection amounts F and F', it is possible to detect the reflection of the detection light on the back surface of the glass wafer substrate l that occurs in area 3. It is possible to know the detection error ΔF (bottom). Therefore, when transferring the reticle pattern for reticle pattern defect inspection to each shot of the glass wafer in area 3, the detection error ΔF
(bottom), the detection amount F of the surface position for each shot based on the output signal from the position sensor 22 of the apparatus shown in FIG. 1(C) is compensated, that is, F (e
The surface position of the shot resist 8 in the area 3 of the glass wafer is determined as xpo)-F-ΔF (bottom), and based on this result, the glass wafer is
Move the resist 8 downward to align the surface of the resist 8 with the image plane of the projection lens system (
After the reticle pattern for each shot in the inclined wall 8 has been transferred to a plurality of predetermined shots,
The glass wafer is carried out from the stepper, and the pattern image recorded on the resist of the glass wafer is observed using a microscope (TV camera) without being developed. All transcription can be done with hest focus.

This observation is carried out using visible light, and a film 6 is formed on the back surface of the glass wafer so that the transmitted image of the pattern recorded on the resist can be visualized clearly. The reticle defect inspection method is performed by conventional shot-to-shot image comparison.

FIG. 2 shows a flowchart of reticle pattern transfer in this embodiment. Figure 1 (
By moving the wafer stage to sequentially feed regions 2 and 3 of the glass wafer substrate l to the projection position of the detection light by the detection device shown in C), and measuring the surface positions of regions 2 and 3, By determining the detection error based on the light reflected from the back surface of the glass wafer and then correcting the measured values for each shot of the glass wafer, it is possible to easily determine the accurate surface position of the glass wafer. .

FIG. 3 is a schematic diagram of the main parts of a glass wafer according to a second embodiment of the present invention. FIG. 3(A) shows a bird's-eye view of the glass wafer, and FIG. 3(B) shows a cross-sectional view of the glass wafer. The biggest difference between the second embodiment shown in FIG. 3 and the first embodiment shown in FIG. 1 is that in the second embodiment, the glass wafer substrate 1 is entirely tilted. this is,
Plane 1 shown by the broken line created by the movement of the wafer stage on which the glass wafer 23 is placed in the reduction projection exposure apparatus
3 and the plane 14 formed by the imaging plane of the projection lens system indicated by the two-dot button line are not parallel due to the inclination of the imaging plane due to the inclination of the optical axis of the projection lens system, the glass This is because the wafer chuck that attracts and holds the wafer is tilted and the wafer itself is tilted, so the plane 13 and the surface of the wafer are also tilted relative to each other by an angle θ.

With the inclination θ, the above-mentioned detection error ΔF(b o
Consider the case where t t o m ) is measured.

At this time, if the interval between the measurement points in region 2 and region 3 is d, it can be seen that a systematic measurement error dtan θ is added to the measurement value.

Eliminate errors caused by such slope θ, and further improve F# density.
Obtaining the correction amount ΔF (bottom) for autofocus is achieved by performing the following in this embodiment.

In this embodiment shown in FIG. 3(A), all measurement points are aligned on the same straight line for regions 2 and 3 on the surface of the glass wafer substrate 1, and two points each, for a total of four measurement points. That's it. Here, as shown in FIG. 3(B), measurements similar to those of the previous example are performed at two locations indicated by R in the figure, which are located on both sides of the boundary of region 2.3. First, regarding the area on the left side, detection light 9 incident on area 2 and detection light 10 incident on area 3 are detected.
The surface position detection value of each point detected by FL
' FL. Similarly, regarding point R on the right side, detection light 12 enters area 2 and detection light 1 enters area 3.
The surface position detection value of each point detected by 1 is F
Let R′FR. Detection light incident on area 3 10.11
are the reflected light 10a and ll on the photoresist surface, respectively.
As described above, the light beam is composed of the light beam a and the reflected light beams 10b and 11b from M6 on the back surface of the glass wafer substrate 1.

Further, here, the distance d between the reflection points of the light beams 9 and 10 on the photoresist surface is set to be the same as the distance between the reflection points of the light beams 11 and 12 on the photoresist surface.

Surface position detection value FL' by detection light 9.10 in such an arrangement, FL is FL' = FL (top) FL - PL (top) + dtanθ◆ ΔF
(bottogg), and similarly, the luminous flux is 11.12
The surface position detection values FR' and FR are respectively FR-FR(top)+ΔF(bottom)FR'
−FR(top)+dtanθ. Next, when the same calculation as in the above embodiment is performed on the L side and the R side, FL-PL -FL(top)+dtanθ t ΔF (b
ottoII+>-FL(top)=dtanθ+ΔF
(bottom) FR - FR' = FR (top) + ΔF (bottom) - FR (t
op)-dtanθ-ΔF (bottom)-dta
It becomes nθ.

As can be seen from this equation, if the entire glass wafer 23 is tilted, an error of dtan θ will occur in the measured value. However, if the surface position of area 12.13 is measured at two locations in this way, the detection error Δ
F (bott.

m) is ΔF(bottom)・((PL−FL′)+(F
It can be determined correctly by calculating R-FR') ) /2.

In addition, in this example, the equation may be simplified because the deviation amount d at the left and right measurement points is made equal, or if the deviation amount d cannot be made equal due to system constraints, the number of measurement points may be further increased to calculate the equation. Interpolation calculation or detection error ΔF (bot
In order to improve the accuracy of the correction (tom), it is possible to measure at three or more locations and average them, or to set multiple locations two-dimensionally instead of just setting measurement points in a straight line as in this example. Various modifications are possible, such as taking measurements.

Therefore, in the case of this embodiment, when transferring a reticle pattern for inspection of reticle pattern defects, the detection error ΔF (bottom) is determined in advance based on the above calculation.
The true value F (ex
po) to F (expo)-F-ΔF (bottom
) and determine the position of the glass wafer 23 for printing. As a result, the printing of each shot is all performed with the hemost focus, and the reticle pattern can be transferred well. Further, in order to enable such correction, it is effective to configure the non-transparent portion of the surface of the glass wafer substrate 1 so that a plurality of measurement points can be taken, for example, to arrange it symmetrically.

FIG. 4 shows a flowchart of reticle pattern transfer in this embodiment.

(Effects of the Invention) As explained above, according to the present invention, by using a glass wafer in which a part of the glass wafer substrate is coated with a film that is non-transparent to detection light, the surface position in the area can be determined. From the detected amount and the surface position detected amount in the area where no non-transparent film is applied, calculate the surface position detection error due to the reflected light generated on the back side of the wafer, and prepare that value in advance as an offset value. By using this method, it is easy to autofocus the projection lens system of a stepper on a glass wafer, which is inspected for pattern defects by image comparison to detect foreign objects on the reticle or in the optical system of the exposure device without developing the image. It has the advantage of being able to be set accurately and automatically transferring patterns to each shot of a glass wafer in a short period of time without the need for trial printing.

That is, in the surface position detection method of the present invention, it is possible to automatically detect the amount of error in the surface position detection value due to the influence of reflected light from the back surface of the glass wafer substrate.

Therefore, even if the amount of error in the surface position detection value differs from glass wafer to glass wafer due to variations in the thickness of the glass wafer as in the past, if this measurement is performed for each glass wafer, the amount of error can be easily and automatically calculated. You can know. As a result, there is no need to control the thickness of the glass wafer, and the cost of glass wafers can be reduced.

According to the present invention, it is possible to successfully transfer a reticle pattern onto the glass wafer surface of a sample used for pattern defect inspection in a short time. For this reason, the time required for pattern defect inspection is shortened, and the reliability and detection rate of defect inspection are improved due to automatic inspection, which has the effect of improving the yield rate during the production of highly integrated LSIs. What can you accomplish with the device?

[Brief explanation of drawings]

FIG. 1(A) is a bird's-eye view showing a glass wafer and its detected light flux showing the first embodiment of the present invention, and FIG. 1(B) is a bird's-eye view showing the glass wafer and its detected light flux showing the first embodiment of the present invention. 1(C) is a schematic diagram of an automatic focus detection device used in a conventional reduction projection exposure apparatus, and FIG.
The figure is a flowchart showing the correction method of the first embodiment of the present invention, and FIG.
FIG. 3(B) is a cross-sectional view showing a glass wafer and its detection light flux in the case of a tilted glass wafer according to the second embodiment of the present invention, and FIG. It is a flowchart for performing correction. In the figure, 1 is a glass wafer, 2 is a region with a non-transparent coating on the surface of the glass wafer, 3 is a region with no non-transparent coating on the surface of the glass wafer, and 4, 9.12 corresponds to region 2. 5°10.11 is the focus detection light beam applied to area 3, 6 is a coating that has high reflection characteristics for the focus detection light beam, and 7 is a coating that is opaque to the focus detection light beam. , 8 is photoresist, 13
is a plane created by moving the stage carrying the object to be exposed, 1
4 is a plane formed by the imaging plane of the projection lens.

Claims (3)

[Claims] (1) A glass wafer used in a projection exposure apparatus equipped with an automatic focus detection device, in which a film having a predetermined reflectance for the detection light of the automatic focus detection device is applied to the back surface RA of the wafer. Also, the surface RB of the wafer
A glass wafer characterized in that a part of region B of the glass wafer is coated with a film that is opaque to the detection light. (2) A film having a predetermined reflectance for the detection light from the automatic focus detection device is applied to the back surface RA, and a film that is opaque to the detection light is applied to a part of the region B of the front surface RB. Detection light is made incident on the glass wafer from the surface RB side, and information on the incident position on a predetermined surface of reflected light from both the region B and the region A other than the region B of the detection light is used. 1. A method for detecting a surface position of a glass wafer, characterized in that surface position information of each shot in the glass wafer area A is detected. (3) Detection light is made incident on a plurality of different locations in area A and area B located in a straight line on the glass wafer, and information on the incident position on the predetermined surface of the reflected light from the plurality of locations is used. 3. The method for detecting the surface position of a glass wafer according to claim 2, wherein surface position information of each shot in the area A of the glass wafer is detected.