JPH07110215A - Interference measuring instrument - Google Patents

Abstract

PURPOSE:To prevent measurement errors due to the complicated change of a diffraction efficiency caused by the differences of the material, film thickness, etc., among wafers by providing a variable gain amplifier and gain control section which controls the gain of the amplifier. CONSTITUTION:Two laser beams having difference frequencies and planes of polarization intersecting each other at right angles are emitted from a two- frequency laser 1. The laser beam made incident on a young-leaf type prism is divided into two luminous fluxes through a polarization beam splitter section 4a and reflecting sections 4b and 4c and the luminous fluxes irradiate a mark 6 for measuring superimposing accuracy on a wafer 5 at prescribed angles. The primary diffracted light rays of the luminous fluxes reflected from the mark 6 interfere with each other in a Glan-Thompson prism 9 after passing through a mirror 7 and lens 8. Variable gain amplifiers 17 and 18 set gains in accordance with gain adjusting commands from a gain control section 20 and amplify beat signals from the amplifiers 15 and 16. The phase difference between two beat signals outputted from a phase detector 19 corresponds to the relative deviation between diffraction gratings 6a and 6b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an interferometric measuring apparatus for irradiating a lattice-shaped measuring mark on a wafer with a laser beam and utilizing diffracted light from the lattice-shaped measuring mark. .

[0002]

2. Description of the Related Art A conventional interferometric measuring device of this type is a fine exposure device for manufacturing a semiconductor element, which is formed on a plurality of objects such as a plurality of masks and reticles, or which is stored as drawing data. The electronic circuit pattern of
It is used to measure whether or not the patterns at the time of baking are accurately overlapped on the photoconductor when they are sequentially aligned and printed on the same wafer or the like having the photoconductor.

The output of the laser beam in the above-mentioned interferometer is measured immediately after output from the laser head, in an optical system before irradiation of the semiconductor wafer, or by placing a measuring part on a part of the wafer. .

Further, the prior art disclosed in Japanese Patent Laid-Open No. 1-109718 uses a 0th-order diffracted light which is a diffracted light of a lower order than the diffracted light originally used for the measurement (referred to as measurement light), and uses the measurement light. The gain is switched automatically.

[0005]

However, in the conventional interferometric measuring apparatus, the diffraction efficiency greatly changes due to the difference in film quality and shape on the wafer. As a result, the intensity of the diffracted light from the lattice-shaped measurement mark changes greatly, and there is a problem that a correction operation by a person or a measurement error occurs.

Further, since the tendency of the change in the diffraction efficiency may differ between the diffracted lights of the respective orders, the gain control may be unsuccessful in the technique disclosed in JP-A-1-09718. That is, when the diffraction efficiency of the 1st-order diffracted light decreases even though the diffraction rate of the 0th-order diffracted light increases, the gain for the 1st-order diffracted light becomes insufficient if the gain adjustment is performed with the 0th-order diffracted light as a reference. There was a problem.

Further, in addition to the measurement light receiving system, the 0th-order diffracted light receiving system is required, so that there are problems that the structure becomes complicated and the cost becomes high from the viewpoint of product development.

It is an object of the present invention to provide an interference measuring device that solves the above problems.

[0009]

According to the invention of claim 1, an interferometric measuring apparatus for irradiating a laser beam on a lattice-shaped measuring mark on a semiconductor substrate and measuring the diffracted light from the lattice-shaped measuring mark. A first signal detecting means for detecting a first signal having displacement information from the Nth diffracted light;
Second signal detecting means for detecting a second signal having displacement information from the first signal, and first gain adjusting means for adjusting the gain of the second signal detecting means on the basis of the first signal are provided. As a result, it is possible to prevent a gain from being insufficient and prevent a measurement error from occurring.

Further, according to the invention of claim 2, since the gain adjusting means for adjusting the gain of the first signal detecting means and the gain of the second signal detecting means is provided, the N-th order diffracted light is excessively incident, or It is possible to measure accurately even with weak incidence.

[0011]

【Example】

Example 1. FIG. 1 is a configuration diagram in which the first embodiment of the present invention is applied to an overlay accuracy measuring apparatus of a semiconductor manufacturing apparatus.

In FIG. 1, 1 is a dual frequency laser light source,
2 is a folding mirror, 3 is a collimator lens, 4 is a young leaf prism, 4a is a modified beam splitter unit, 4b and 4
Reference numeral c is a reflecting portion, 5 is a wafer, 6 is an overlay accuracy measurement mark formed on the wafer 5, and is composed of a diffraction grating 6a and a diffraction grating 6b.

Reference numeral 7 is a folding mirror, 8 is a magnifying lens, and 9
Is a Gram Thomson lens, 10 is an edge mirror, 11 is a reduction lens for receiving the reflected light from the edge mirror 10,
12 is a reduction lens that receives the transmitted light of the edge mirror 10, 13 is a photodetector that receives the transmitted light of the reduction lens 12, 14 is a photodetector that receives the transmitted light of the reduction lens 11, and 15 is a photodetector 13 Of the photodetector 14, 17 is a variable gain amplifier, 18 is a variable gain amplifier, and 19 is an output signal 17 of the variable gain amplifiers 17 and 18.
a, a phase difference detector for inputting 18a, 20 is a gain control unit for controlling the gain of the variable gain amplifiers 17, 18, and 21 is a look-up table storing the relation between the semiconductor process parameter and the gain. Two
Reference numeral 2 is a communication line with a host computer (not shown), and reference numeral 23 is information when the gain control unit refers to the lookup table.

The preamplifiers 15 and 16 are the Nth
The first signal detecting means for detecting the first signal having displacement information from the second-order diffracted light is formed, and the variable gain amplifiers 17 and 1 are provided.
Reference numeral 8 forms second signal detecting means for detecting a second signal having displacement information from the first signal.

The operation of the first embodiment will be described below. The two-frequency laser 1 has two frequencies (fa1 and fb, respectively) whose frequencies are different from each other and whose planes of polarization are orthogonal to each other.
1) is emitted. The laser light emitted from the dual frequency laser 1 is adjusted by the bending mirror 2 so as to be incident on the collimator lens 3. The beam diameter of the laser light is sufficiently narrowed by the collimator lens 3 and is incident on one side of the young leaf-shaped plybum 4.

The laser light incident on the young leaf prism 4 is split into two light beams by the deflecting beam splitter section 4a and the reflecting sections 4b and 4c inside the prism, and for measuring overlay accuracy on the surface of the wafer 5 at a predetermined angle. The mark 6 is illuminated. The 1st-order diffracted light reflected from the overlay accuracy measurement mark 6 is bent by the bending mirror 7, passes through the magnifying lens 8, and is polarized by the Gram-Thomson prism 9 so that the polarization planes of the light beams interfere with each other.

The diffraction gratings 6a and 6b constituting the accuracy measuring mark 6 are equidistant diffraction gratings which are formed on the wafer 5 by different printing processes and are adjacent to each other. The edge mirror 10 spatially separates the diffraction interference light from the diffraction grating 6 a and the diffraction interference light from the diffraction grating 6 b, and the interference light from the diffraction grating 6 a that has passed through the edge mirror 10 passes through the reduction lens 12. The interference light from the diffraction grating 6b reflected by the edge mirror 10 is guided to the photodetector 14 via the reduction lens 11.

The beat signals detected by the photodetectors 13 and 14 are input to the preamplifiers 16 and 15, respectively, and amplified with a predetermined gain. The output signals 15a and 16a of the preamplifiers 15 and 16 are input to the variable gain amplifiers 17 and 18, and are also sent to the gain control unit 20. In the gain control unit 20, the preamplifier 15,
A gain adjustment command corresponding to the beat signal amplitude sent from 16 is sent to the variable gain amplifiers 17 and 18.

The variable gain amplifiers 17 and 18 set the gain based on the gain adjustment command from the gain control section 20, and amplify the beat signals sent from the preamplifiers 15 and 16. The beat signals 17a and 18a amplified by the variable gain amplifiers 17 and 18 are input to the phase detection detector 19.

The phase detector 19 detects and outputs the phase difference φ between the two beat signals. This phase difference φ corresponds to the amount of relative displacement between the diffraction grating 6a and the diffraction grating 6b which are marks for overlay accuracy measurement.

FIG. 2 is an enlarged view of the diffraction gratings 6a and 6b (measurement marks) on the wafer, which are the overlay accuracy measurement marks 6 in FIG.

The diffraction grating 6a and the diffraction grating 6b are two adjacent linear gratings formed at different intervals and having the same pitch. Then, a positional deviation at the time of printing occurs in the x direction between the diffraction grating 6a and the diffraction grating 6b, and the value is xb-xa.

FIG. 3 is a flow chart showing the operation of the gain control section 20 shown in FIG. 1 in detail.

First, when a series of processing is started in the processing block 201, the amplitude value Vs of the output signal 15a sent from the preamplifier 15 is read in the next processing block 202, and similarly, in the processing block 203, the preamplifier 1 is read.
The amplitude value Vr of the output signal 16a sent from 6 is read.

Next, in processing block 204, the amplitude value V obtained in processing block 202 and processing block 203 is obtained.
Using s and Vr, the maximum gain value Ks that can be set in the variable gain amplifier 17 and the maximum gain value Kr that can be set in the variable gain amplifier 18 are calculated by the following equations (1) and (2). .

Ks = Rs / Vs (1) Kr = Rr / Vf (2) where Rs is the maximum allowable amplitude of the input signal 17 a of the phase difference detector 19, and Rr is the input signal of the phase difference detector 19. 18a
Is the maximum allowable amplitude of.

Next, in processing block 205, maximum gain value Ks and maximum gain value K obtained in processing block 204 are obtained.
The gain command value Gs (n + n) sent from the gain control unit 20 to the variable gain amplifier 17 by using r.
1), the gain command value Gr (n + 1) sent from the gain controller 20 to the variable gain amplifier 18 is calculated by the following equations (3) and (4).

Gs (n + 1) = 0.8Ks (3) Gr (n + 1) = 0.8Kr (4) Here, the subscript (n + 1) is a gain command set next to the current gain command value. It is a value.

The coefficient 0.8 on the right-hand side of equations (3) and (4) means that an excessive signal exceeding the maximum amplitude is not added to the signal input of the phase difference detector 19. It is a safety factor. Therefore, the coefficients on the right side of the equations (3) and (4) are not limited to 0.8, and can take various values of 1.0 or less depending on the performance of the phase detector 19 and the noise level.

Next, in processing block 211, an appropriate gain for the process parameter of the semiconductor substrate to be measured is obtained from the look-up table 21. The process parameters are film material, film thickness, shape, surface condition, and the like. Then, in process 212, the gain command value obtained in process 205 is compared with the proper gain obtained in process 211, and if there is a significant difference, the host computer is notified of the abnormality.

Next, in processing block 206, the gain command values Gs (n + 1) and Gr obtained from equations (3) and (4) are used.
It is determined whether or not (n + 1) is equal to Gs (n) and Gr (n), respectively, and if they are equal, the process proceeds to branch 209, while if they are not equal, the process proceeds to branch 210. Branch 2
If the processing proceeds to 09, it is not necessary to update the current gain command value, and therefore the processing returns to the bottom of the processing block 201 and the above-described series of processing is performed again. If the process proceeds to branch 210, the current gain command value needs to be updated, so the process proceeds to processing block 207.

At processing block 207, the gain control unit 20 sends the new gain command value Gs (n + 1) to the variable gain amplifier 17, and at processing block 208, the gain control unit 20 receives the new gain command value Gr (n +).
1) is sent to the variable gain amplifier 18. After the processing block 208, the process returns to the bottom of the processing block 201 and the above-described series of processing is performed again.

Although the processing 211 is arranged downstream of the processing 205 in FIG. 3, the processing 211 may be arranged upstream of the processing 202.

Example 2. FIG. 4 shows an electric circuit diagram in which the second embodiment of the present invention is applied to an overlay accuracy measuring apparatus of a semiconductor manufacturing apparatus, and an optical system part is omitted because it is the same as that in FIG.

In FIG. 4, 301 and 302 are avalanche photodiodes, 303 and 304 are variable bias power sources, and 305 and 306 are preamplifiers, which form the first signal detecting means. 307 and 308 are variable gain amplifiers, which form second signal detecting means. 309 is a gain control unit, 310 is a phase difference detector, 311 is lookup table reference information, 3
Reference numeral 12 is a communication line with the host computer, and 313 is a look-up table that stores the relationship between semiconductor process parameters and the appropriate gain of the variable gain amplifier.

Next, the operation of the second embodiment will be described. The beat signals detected by the avalanche photodiodes 301 and 302 are input to the preamplifiers 305 and 306, respectively, and amplified with a predetermined gain. This preamplifier 305,
Output signals 305a and 306a of 306 are input to the variable gain amplifiers 307 and 308 and also sent to the gain control unit 309. The gain control unit 309 sends a gain adjustment command corresponding to the beat signal amplitude sent from the preamplifiers 305 and 306 to the variable gain amplifiers 307 and 308.

The variable gain amplifiers 307 and 308 set the gain based on the gain adjustment command from the gain control unit 309, and amplify the beat signals sent from the preamplifiers 305 and 306. This variable gain amplifier 30
Beat signals 307a and 308a amplified by 7,308
Is input to the phase detector 310. The phase detector 310 detects and outputs the phase difference φ between the two beat signals.
This phase difference φ corresponds to the amount of relative displacement between the diffraction grating 6a and the diffraction grating 6b which are marks for overlay accuracy measurement.

However, when the amount of light incident on the avalanche photodiodes 301 and 302 is too weak and the phase difference φ cannot be detected by the above operation, or the amount of light incident on the avalanche photodiodes 301 and 302 becomes excessive. In some cases, the phase difference φ cannot be detected.
In such a case, the gain control unit 309 sends a command to adjust the bias to the variable bias power sources 303 and 304.

That is, the avalanche photodiode 3
When the amount of light incident on 01, 302 is too weak, the bias is increased to increase the avalanche photodiode 301,
Increase the multiplication factor of 302. When the amount of light incident on the avalanche photodiodes 301 and 302 is excessive, the bias is reduced to reduce the avalanche photodiode 30.
Decrease the multiplication factor of 1,302. By this operation, the phase difference φ of the diffracted light pairs from various wafers can be detected.

Further, the gain controller 309 refers to the look-up table 313 for the proper gain.
The variable bias power supply 30 is operated in the same sequence as in the first embodiment.
Proper values of 3,304 and variable gain amplifiers 307, 308
The appropriate gain is obtained from the look-up table 313 and compared with the actual command value to determine.

FIG. 5 is a table showing the experimental results of the diffraction efficiency of the diffraction grating on the semiconductor wafer sample subjected to the typical semiconductor manufacturing process, for the 0th-order diffracted light and the 1st-order diffracted light. In FIG. 5, samples of wafer types 501-1 to 503-4 differ in material, film thickness, and structure. It can be seen that there is no simple correlation between the diffraction efficiency of the 0th-order diffracted light and the diffraction efficiency of the 1st-order diffracted light.

[0042]

As described above, according to the invention of claim 1,
First signal detecting means for detecting a first signal having displacement information from the Nth diffracted light, second signal detecting means for detecting a second signal having displacement information from the first signal, and the first signal as a reference And a gain adjusting means for adjusting the gain of the second signal detecting means, and the gain of the Nth-order diffracted light (measurement light) reflected from the wafer is determined with reference to the Nth-order diffracted light itself. It is possible to obtain an effect that a measurement error does not occur under the influence of a complicated change in diffraction efficiency due to a difference in wafer material, film thickness, and structure.

According to the invention of claim 2, the first signal detecting means for detecting the first signal having the displacement information from the Nth diffracted light and the second signal having the displacement information from the first signal are detected. Since the second signal detecting means and the gain adjusting means for adjusting the gain of the first signal detecting means and the gain of the second signal detecting means on the basis of the first signal are provided,
Even if the Nth-order diffracted light reflected from the wafer is excessively incident or weakly incident, there is an effect that it can be accurately measured.

Furthermore, in the first and second aspects of the present invention, since the proper gain and the actual command value are compared and judged by using the look-up table, it is possible to detect the abnormality of the process parameter of the semiconductor substrate. .

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of overlay accuracy measurement marks.

FIG. 3 is a flowchart illustrating the operation of the gain control unit according to the first embodiment.

FIG. 4 is a configuration diagram of a second embodiment of the present invention.

FIG. 5 is a table showing experimental data of diffraction efficiency.

[Explanation of symbols]

15 preamplifier (first signal detecting means) 16 preamplifier (first signal detecting means) 17 variable gain amplifier (second signal detecting means) 18 variable gain amplifier (second signal detecting means) 19 phase difference detector 20 gain control section ( Gain adjusting means) 301 Avalanche photodiode (first signal detecting means) 302 Avalanche photodiode (first signal detecting means) 303 Variable bias power source (first signal detecting means) 304 Variable bias power source (first signal detecting means) 305 Preamplifier (First signal detecting means) 306 Preamplifier (first signal detecting means) 306 Variable gain amplifier (second signal detecting means) 306 Variable gain amplifier (second signal detecting means) 309 Gain control section (gain adjusting means)

Claims (2)

[Claims] 1. An interferometer that irradiates a laser beam onto a lattice-shaped measuring mark on a semiconductor substrate and measures the diffracted light from the lattice-shaped measuring mark, wherein the interferometer has displacement information from the Nth-order diffracted light. A first signal detecting means for detecting a signal, a second signal detecting means for detecting a second signal having displacement information from the first signal, and a gain of the second signal detecting means based on the first signal An interferometer according to claim 1, further comprising: a gain adjusting means, and a look-up table in which a relationship between the proper value of the gain and a process parameter of the semiconductor substrate is stored in advance. 2. An interferometer for irradiating a laser beam onto a lattice-shaped measuring mark on a semiconductor substrate and measuring the diffracted light from the lattice-shaped measuring mark, the first interferometer having displacement information from the Nth-order diffracted light. A first signal detecting means for detecting a signal; a second signal detecting means for detecting a second signal having displacement information from the first signal; a gain of the first signal detecting means based on the first signal; A gain adjusting means for adjusting the gain of the second signal detecting means, and a relationship between a proper value of the gain of the first signal detecting means, a proper value of the gain of the second signal detecting means, and a process parameter of the semiconductor substrate. An interference measuring apparatus, comprising: a lookup table stored in advance.