JPH07134013A - Surface shape measuring method and projection exposure apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the accuracy and measurement speed of a method and apparatus for measuring the surface shape and height of a semiconductor wafer using an interference optical system and its apparatus. [Structure] An interference fringe signal waveform obtained by interference between laser reflected light from a wafer and reference light is pattern-matched with a template sine wave, and the phase in the entire detection region is detected from the phase difference change. Further, the phase jump of the phase is corrected to connect the phases correctly, the height and the inclination of the wafer surface are obtained by the regression calculation of the phase information, and the position and orientation of the wafer stage are controlled. . [Effect] The surface shape of an LSI having a structure with a pattern line width of 0.5 μm or less and a step of about 1 μm can be exposed with high resolution including the peripheral portion even when the exposure depth of focus is 1 μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface shape measuring apparatus utilizing optical interference, and more particularly to a wafer surface shape measuring method and a projection exposure apparatus having a circuit pattern having a line width of 0.5 .mu.m or less.

[0002]

2. Description of the Related Art In an exposure apparatus for semiconductor integrated circuits,
For example, it is required to faithfully expose a line width pattern of 0.5 μm or less over the entire exposure area of about 20 mm square having a step structure of about 1 μm with little variation. However, as the pattern becomes finer, the NA (numerical aperture) of the exposure projection lens must be increased, which narrows the image formation range (depth of focus) to ± 1 μm or less, and the pattern image can be accurately formed on the photoresist surface of the wafer. It is important to form an image at. Therefore, the uneven shape of the wafer surface is accurately measured to adjust the tilt and height of the wafer.

In Japanese Patent Laid-Open No. 3-40417, coherent light is obliquely incident on a wafer, and interference fringes obtained from reflected light from the wafer and reference light generated from the coherent light source are detected by a one-dimensional array sensor. It is disclosed that the pitch and the phase of the interference fringe signal are detected and detected by Fast Fourier Transform (FFT) to obtain the tilt and height of the wafer surface.

Further, Japanese Patent Laid-Open No. 2-280313 discloses that the above coherent light is obliquely incident on the wafer at an incident angle of 85 degrees or more to enhance the accuracy of detecting the inclination and height of the wafer surface. There is. Further, in Japanese Unexamined Patent Publication No. 2-99804, laser light is made incident on a sample at an inclination angle of 1 to 20 degrees, and the reflected light and the laser light intensity distribution of the above laser light indicate the laser light of the reflected light. It is disclosed that the slit pattern portion on the wafer surface is detected by correcting the intensity fluctuation.

[0005]

In measuring the surface shape of a wafer having a step as described above, it is necessary to subdivide the detection region and perform the fast Fourier transform. Therefore, if the number of data points in each region is small, the calculation error increases. Further, there is a problem that the calculation time is long because the calculation is performed for each divided area. In addition, since the height / tilt detection is more heavily weighted in a portion having a higher interference intensity, it is difficult to measure the step structure. An object of the present invention is to provide a surface shape measuring method which can solve the above-mentioned problems and can measure a step structure on a wafer accurately and at high speed.

[0006]

In order to solve the above-mentioned problems, coherent light is divided into detection light and reference light, and the detection light is applied to a test object at a predetermined angle to reflect light and reference light. In the surface shape measuring method for detecting the surface shape of the object to be inspected from the interference fringe signal obtained by interfering with the interference fringe signal, the surface pattern of the object to be inspected is detected from the phase information by detecting the waveform pattern of the interference fringe signal intensity by the pattern matching method. Measure the shape. Therefore, the waveform pattern is compared with the template sine wave signal, and goal seeking seeks to minimize the sum of squares of the matching errors of the both waveforms.

Further, the pattern matching is performed using linear regression analysis of trigonometric functions. Further, the phase information of the interference fringe signal is roughly detected using an inverse trigonometric function. Further, the difference between adjacent phase data in the phase information of the waveform pattern is compared with a predetermined threshold value to detect a phase discontinuity, and the phase discontinuity is corrected and connected.

In the projection exposure apparatus, the means for detecting the phase information of the detected interference fringe signal by the surface shape measuring method, the means for designating the range of the phase information, and the height of the wafer surface in the phase information range. And a means for calculating the inclination, and means for adjusting the height and the inclination of the wafer surface based on the calculation result, and further, the wafer surface using the linear regression analysis of the phase information of the detected interference fringe signal. To calculate the height and slope of the.

[0009]

The waveform pattern of the interference fringe signal intensity is pattern-matched with the template sine wave signal or the like, and the matching error is minimized by goal seeking. The surface shape of the test object is calculated from the phase information of the matching waveform.

The pattern matching is also performed by linear regression analysis of trigonometric functions. Further, the rough detection of the phase information of the interference fringe signal is performed by using an inverse trigonometric function. Further, the phase discontinuity is detected by comparing the difference between mutually adjacent phase data in the phase information of the waveform pattern with a predetermined threshold value, and is used for correcting the phase discontinuity.

In the projection exposure apparatus, the means for detecting the phase information of the detected interference fringe signal, the means for designating the range of the phase information, and the means for calculating the height and inclination of the wafer surface within the phase information range. And a means for adjusting the height and inclination of the wafer surface based on the calculation result, and further, calculating the height and inclination of the wafer surface using linear regression analysis of the phase information of the detected interference fringe signal. , Correct these.

[0012]

1 is a block diagram of a projection exposure apparatus used in a surface shape measuring method according to the present invention. The laser beam from the coherent laser light source 1 is made into a desired beam diameter by the collimator 11 and is divided into two by the beam splitter 10 and one of the beams (detection light 16) is irradiated onto the wafer 4 at an incident angle θ ₁ .
The other is the reference light 17 for generating interference fringes. The detection light 16 and the reference light 17 are returned by the folding plane mirror 14 after passing through the optical paths that are close to each other, return to the original optical path again, and are guided to the detection optical path by the beam splitter 12. That is, the reflected beam 26 ″ from the wafer 4 and the reference beam 27 ″ are reflected by the lenses 21, 2
2. After passing through the pinhole 23, the light is superimposed on the one-dimensional array sensor 3 such as a CCD, and the light intensity of the interference fringes formed here is detected by the one-dimensional array sensor 3.

The processing circuit 5'detects the phase change of the interference fringe signal by a pattern matching method to calculate the surface shape of the wafer 4, and from this, obtains the height and inclination of the wafer surface to determine the height of the stage 7. The tilt is adjusted so that the image plane of the reticle 9 exactly matches the wafer surface. As a result, the fine pattern can be exposed with high resolution over the entire exposure area. In addition, the above optical detection system is the X
, And the Y direction, but FIG. 1 shows only the optical detection system 100X in the X direction.

The solid line in FIG. 2 is an example of the waveform of the interference fringe signal obtained according to the wafer surface shape. The vertical axis represents the signal intensity of the interference fringes detected by the interference optical detection system, and the horizontal axis represents the pixel coordinates of the one-dimensional array sensor, which corresponds to the pixel address i of the CCD detector. In the present invention, the solid line interference fringe signal is compared with the sine wave signal [Asin (2πi / p) + Ao] of the pattern matching template shown by the dotted line, and the phase difference φ between the two signals is obtained by the Gol seeking method. Minimize the sum of squares of (j). Since the interference fringe signal is originally a sine wave, the pattern matching can minimize the error component due to the noise of the phase difference.

Further, the height of the wafer surface is the above phase difference φ.
It can be obtained from [j]. That is, the detection light 16
Is λ and the incident angle on the wafer 4 is θ ₁ , the wafer surface height ΔZ [j] can be obtained from ΔZ [j] = (λ / 8πcos θ ₁ ) φ [j] (1). The inclination of the wafer surface is ΔZ [j] above.
It can be calculated from the rate of change.

For example, when λ = 633 nm and θ ₁ = 88 °, ΔZ [j] = 0.72 (μm / rad) × φ
Therefore, in order to obtain the height detection accuracy of 0.01 μm, the phase φ [j] should be obtained with the accuracy of about 0.014 rad (0.8 °). Further, the inclination detection accuracy at this time is 0.01 for a detection area length of 20 mm.
μm / 20 mm = 0.5 μrad.

FIG. 3 is a flowchart of the surface shape measurement and calculation process. The reflected light from the wafer 4 incident on the one-dimensional array sensor 3 interferes with the reference light to generate an interference fringe signal whose phase change corresponds to the surface shape of the wafer 4. Therefore, first, the A / D converter 51 converts the interference fringe signal obtained from each pixel of the one-dimensional array sensor 3 into a digital signal, and the phase detection circuit 52 obtains the phase change of each cycle of the interference fringe signal. A method of obtaining the phase of this interference fringe signal will be described later with reference to FIGS.

Further, when the phase is obtained from the interference fringe signal, a phase jump phenomenon in which the phase changes discontinuously every 2nπ appears. Therefore, the phase jump connection circuit 53 corrects this phase jump and a continuous phase change occurs. To get
Note that this phase jump connection method will be described later with reference to FIG. 7. The phase change of the interference fringe signal obtained as described above is displayed on the display circuit such as a CRT or the printer 54 as the measurement data of the surface shape of the test object.

FIG. 4 is a flow chart of a process for adjusting the height and inclination of the surface of the wafer 4 on the stage 7. After performing A / D conversion, phase detection, phase jump connection, etc. of the interference fringe signal in the same manner as in FIG. 3, the regression line of the height of the wafer surface and the unevenness is calculated from this phase information and the wafer from the image plane is calculated. The deviation and inclination of the surface height are calculated, and this is converted into the drive signal of the stage 7 on which the wafer is mounted to control the drive mechanism of the stage 7 to determine the deviation and inclination of the wafer surface. Minimize.
The method of obtaining the height and inclination of the wafer surface from the regression line will be described later with reference to FIG.

FIG. 5 is a flow chart of a method for detecting the phase of the interference fringe by goal seeking by pattern matching. First, one-dimensional array sensor (CCD)
The following calculation is performed on (2w + 1) pieces of interference fringe signal data within the range of address i = (j ± w) of 3. In addition,
If the range of (2w + 1) is too large, the pattern matching error increases. Therefore, the pitch (cycle) of the interference fringe signal is set to p, and it is selected to be about (2w + 1) = (p + 2).

Next, the maximum value Smax and the minimum value Smin of the interference fringe signal within the above i = (j ± w) range are obtained, and the amplitude A and the offset Ao of the template sine wave are obtained from these. Further, the interference fringe signal data S [j] at i = j,
The phase angle rough detection value φc [j] is obtained from S [j + 1] and A, Ao as shown in FIG.

Next, within the above (j ± w) range,
The deviation Δφ [j] from the phase angle coarse detection value φc [j] is used as a variable in goal seeking as a template sine wave St.
The value of [i] is calculated, and the sum E [j] of the squared error of the interference fringe signal and the template sine wave is calculated and used as the evaluation function. In addition, St
For the interference fringe pitch p of [i], the pitch of the interference fringe signal at the time of detecting the reference plane such as the image plane in the projection exposure apparatus is set, and the final phase detection result is obtained as the inclination with respect to this reference plane. To be able to

In the above goal seeking method, Δφ [j] in which the template sine wave optimally matches the interference fringe signal.
Is calculated with a predetermined phase angle accuracy. At this time, the value of the evaluation function E [j] becomes the minimum. In FIG. 5, p, φc
From [j] and Δφ [j], finally φf [j] and phase angle precision detection value φ
Seeking [j]. The last equation is 2nπ from φf [j]
This is an operation for setting −π ≦ φ [j] <π except for the indeterminacy of.

Next, after calculating the phase angle of the interference fringe signal with respect to the phase angle detection center i = j, the phase angle detection center is moved by k addresses, and the phase angle of the interference fringe at i = j '= j + k is precisely adjusted. The detected value φ [j '] = φ [j + k] is obtained in the same manner as φ [j]. That is, in FIG. 2, after the phase angle precise detection value φ [j] of the solid line interference fringe signal with respect to the dotted template sine wave is obtained in the address range of (2w + 1) = 11 with the phase angle detection center j as the center, j + 9 The phase angle precision detection value φ [j '] of the interference signal with respect to the template sine wave is obtained for the range centered around = j'.

The distance k between the detection center positions may be determined in consideration of the resolution required for the surface shape measurement and the calculation processing time. For example, the interval k is set to a value similar to the pitch of the interference fringes. After that, the phase angle precision detection value corresponding to each detection center position is sequentially obtained while changing the phase angle detection center position by k addresses over a desired range on the CCD address.

FIG. 6 is a flow chart for explaining another method of detecting the interference fringe phase performed by the phase detection circuit 52 shown in FIGS. Here, pattern matching using linear regression analysis of trigonometric functions is used. First, as in the case of FIG. 5, the phase angle detection center position j is increased by an interval k over a desired range on the CCD address, the phase angle fine detection value is obtained for each j, and then the sine wave is detected without performing rough detection. Pattern matching is performed by linear regression analysis of trigonometric functions to detect the phase angle.

In FIG. 6, x ₁ [i] = sin (2πi /
p), x ₂ [i] = cos (2πi / p), the interference fringe signal is S [i] = b ₁ x ₁ [i] + b ₂ x ₂ [i] + Ao, so x
Linear regression analysis can be performed using ₁ [i] and x ₂ [i] as independent variables, and the phase angle precision detection value φ [j] can be obtained from the regression coefficients b ₁ and b ₂ obtained at that time. . In this phase detection method, since the calculation algorithm is simple and the calculation time is short, it is possible to obtain the effect that the surface shape of the test object can be measured at high speed.

FIG. 7 is a flow chart showing a method for connecting the discontinuous phase jump of the phase angle fine detection value, which is performed by the phase jump connection circuit 53 shown in FIGS. 3 and 4. After the phase angle detection calculation in FIG. 5 or FIG. 6, the phase change amount is compared with the phase jump determination threshold value for each of the same phase angle detection center position j, and the phase jump connection processing operation is performed according to the result and the detection is performed. The height detection value ΔZ [j] of the surface of the test object with respect to the center position j is obtained.

FIG. 8 shows the height / tilt calculation circuit 5 shown in FIG.
5 is a flowchart of a method for obtaining the height / inclination of the object to be inspected by the method 5. Now, assume that the surface shape of the wafer 4 is ΔZ in FIG.
If [j] is set, first, the calculation range is appropriately set. Figure 9
Then, the whole detection area is set to this calculation range. A linear regression analysis by the least squares method relating to ΔZ [j] shown in FIG. 8 is performed on this calculation range, and a regression coefficient b ₁ and an intercept bo are obtained. As a result, the regression line shown by the dotted line in FIG. 9 is obtained.

Using the results of this regression analysis, the height detection value ΔZc and tilt detection value δ of the object to be measured are obtained from the equations in FIG. 8, and the height / tilt drive mechanism of the wafer stage is adjusted according to these detection values. To do. In addition, for the portion where the surface shape ΔZ [j] is the same as that in FIG. 9, the regression analysis is performed by setting the two left and right flat portions excluding the central groove portion as the calculation range as shown in FIG. I do. As a result, since the regression line coincides with the left and right flat portions, for example, in a wafer process that requires particularly high resolution for the left and right flat portions, the focal plane is aligned with the left and right flat portions rather than the central groove portion. Therefore, a large resolution margin can be obtained.

According to the method shown in FIG. 8, the surface shape of the steps in various processes is measured in advance and the height / tilt calculation region according to the pattern structure and the resolution request for each process is set, so that the resolution is particularly high. The height and tilt can be adjusted by obtaining the best focus latitude for the required exposed portion.

[0032]

According to the present invention, the surface shape of an object to be inspected such as a semiconductor wafer can be scanned with a precision of about 0.01 μm and in a single scan without being affected by the intensity distribution of the interference fringe signal of laser light. It is possible to provide a surface shape measuring method capable of measuring in 0.5 to several ms. In addition, since the pattern line width of 0.5 μm or less and the deep step structure of about 1 μm can be accurately measured at high speed by this measuring method, even if the depth of focus of exposure is as shallow as 1 μm or less, the entire surface of the wafer including the peripheral portion can be made high. It is possible to provide a projection exposure apparatus that reliably exposes at a resolution, and it is possible to improve the performance and reliability of the LSI and at the same time improve the yield.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a projection exposure apparatus according to the present invention.

FIG. 2 is a waveform diagram of interference fringes and a template in the surface shape measuring method of the present invention.

FIG. 3 is a diagram showing a procedure of detecting an interference fringe phase according to the present invention.

FIG. 4 is a diagram showing a wafer height / tilt measurement and adjustment procedure thereof according to the present invention.

5 is a flowchart showing a method of calculating an interference fringe phase in FIGS. 3 and 4. FIG.

6 is a flowchart of a method for obtaining the interference fringe phase in FIGS. 3 and 4 by linear regression analysis of trigonometric functions.

FIG. 7 is a flow chart showing a connection processing method for phase jump of interference fringes in FIGS. 3 and 4.

8 is a flowchart of a method for calculating the height and inclination of the wafer in FIG. 4 by linear regression analysis by the least square method.

9 and 10 are waveform charts showing the height detection value of the wafer surface and its regression line.

[Explanation of symbols]

1 ... Laser light source, 3 ... One-dimensional array sensor, 4 ... Wafer, 5 '... Processing circuit, 7 ... Stage, 8 ... Reduction projection lens, 9 ... Reticle, 10, 12 ... Beam splitter,
81 ... Exposure illumination system, 100X ... Optical detection system, 51 ... A /
D converter, 52 ... Phase detection circuit, 53 ... Phase jump connection circuit, 55 ... Height / inclination calculation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Nakayama 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Incorporated company, Hitachi, Ltd.

Claims (7)

[Claims] 1. Coherent light is divided into detection light and reference light, the detection light is applied to a test object at a predetermined angle, and the test is performed from an interference fringe signal obtained by interfering the reflected light and the reference light. In the surface shape measuring method for detecting the surface shape of the object, the phase information of the waveform pattern of the interference fringe signal strength is detected by a pattern matching method, and the surface shape of the object is measured from the phase information of the waveform pattern. A surface shape measuring method characterized by the above. 2. The method according to claim 1, wherein the waveform pattern of the interference fringe signal intensity is compared with a template sine wave signal, and two of the matching errors of the two waveforms due to goal seeking are detected.
A surface shape measuring method characterized by minimizing the sum of multiplications. 3. The surface shape measuring method according to claim 1, wherein the pattern matching is performed using linear regression analysis of trigonometric functions. 4. The surface shape measuring method according to claim 2, wherein the phase information of the interference fringe signal is roughly detected using an inverse trigonometric function. 5. The phase discontinuity is detected by comparing the difference between adjacent phase data in the phase information of the waveform pattern with a predetermined threshold value and detecting the phase discontinuity. A surface shape measuring method characterized in that parts are corrected and connected. 6. In a projection exposure apparatus, means for detecting phase information of the detected interference fringe signal by the surface shape measuring method according to claim 1, means for designating a range of the phase information, and the phase information range. And a means for calculating the height and inclination of the wafer surface, and a means for adjusting the height and inclination of the wafer surface based on the calculation result. 7. The projection exposure apparatus according to claim 6, wherein the height and inclination of the wafer surface are calculated by using linear regression analysis of phase information of the detected interference fringe signal. .