JPH05196567A - Complex reflectivity measurement method and device - Google Patents

Abstract

PURPOSE:To enable easily measuring the complex reflectivity of basic layer in a multilayer structure. CONSTITUTION:At point B between defraction grids 2 and 3 on a defraction mask 1, parallel light C2 with interference and high directional characteristics is reflected to be reference light A0. Simlar defraction light of parallel light C1 is generated at the defraction grid 2, which is irradiated horizontally on wafer 6 to be totally reflected and be reflection light A1 of (s) polarized light. On the defraction grid 3, similar defraction light of the parallel light is generated, which is irradiated vertically on the wafer 6 to be reflected and is synthesized as reflection light A1 with the reference light A0 as parallel light C2. The reference light A0 is separated to (p) and (s) polarized light with a beam spliter 9. This (p) polarized light and the reflected light A1 are synthesized with a beam spliter 15 and heterodyne-interfered in a sensor 18. Also, these (p) and (s) polarized lights are sythesized with a beam spliter 4 and heterodyne- interfered in a sensor 19. The synthesized light of the reflected light A1 and the reference light A0 are heterodyne-interfered in sensors 20 and 21. From these interference results, phase items of complex reflectivity are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a complex reflectance measuring method and apparatus used for producing a circuit pattern on a wafer surface, and more particularly to a complex reflectance suitable for producing a semiconductor or measuring a processed thin film. The present invention relates to a rate measuring method and device.

[0002]

2. Description of the Related Art Currently, in the manufacture of semiconductor integrated circuits,
A photolithography technique using a reduced projection method is widely used for generating a circuit pattern. In this technique, a resist is applied on the surface of a wafer to form a coating film, and an image of a mask pattern is projected and exposed onto the resist by using ultraviolet rays to partially expose the resist, and then a development process is performed. As a result, a portion to be processed such as etching is exposed, and a fine pattern is formed by performing processing in a limited region.

By the way, in recent years, the degree of integration of semiconductors has been remarkably increased, the pattern dimensions have become smaller and finer, and the device structure has become three-dimensional, and the manufacturing process has become more and more complicated.
Therefore, in photolithography, it is indispensable to increase the pattern resolution, and in order to realize this, the NA (numerical aperture) of the lens is increased and the exposure light has a shorter wavelength.

On the other hand, as the exposure light, one having a single wavelength with a relatively narrow wavelength band is used. Therefore, as shown in FIG. 9, the resist film 50 and the underlying layer forming film having light transmittance are used. When 51 is present, the exposure light 52 is reflected multiple times in these films, mutual interference of these reflected lights occurs, and the light intensity changes in the depth direction in the resist film 50 as shown in FIG. .. Therefore, a difference occurs in the exposure energy in the depth direction, and when a phenomenon occurs, the cross section of the resist film 50 becomes uneven in the depth direction.

Further, if there are process variations in various manufacturing apparatuses such as a film forming apparatus, the resist film thickness t and the state of formation of a light-transmitting underlayer differ between wafers and from wafer to wafer. Therefore, when the resist is exposed with the same exposure energy, the resist film thickness t and the complex reflectance A (= aexp (iθ); a: amplitude, a ² = reflectance intensity, which is represented by the equation (1) in FIG. , Θ: phase), the formation state of the underlying layer is different,
Since the shape of the unevenness in the depth direction changes, the width W of the resist in contact with the uppermost layer of the underlayer changes as shown in FIG.
The pattern size to be formed differs from the desired pattern size. Therefore, in order to stabilize the pattern size, it is indispensable to set the optimum exposure energy corresponding to these process fluctuations, and the complex reflectance A corresponding to the resist film thickness t and the fluctuation of the formation state of the underlying layer is measured. There is a need.

In the measurement of the complex reflectance of the underlayer, the amplitude a can be easily obtained from the reflectance intensity of the wafer, but the phase θ cannot be easily obtained.

One method for this purpose is, for example, ellipsometry. As shown in FIG. 12, the ellipsometry method irradiates a sample 63 with light 62 whose azimuth angle 61 is set to a specific angle by a polarizer 60 and reflects the light on a surface of the sample 63 to form elliptically polarized light. The change in the polarization state of the reflected light (azimuth angle 64 and elliptic angle 65 of elliptically polarized light)
Is used to determine the complex reflectance A (FIG. 13) which is the optical constant of the layer on the surface of the sample 63.

[0008]

However, in the above-mentioned prior art, due to the performance of ellipsometry, a thin film formed on a thin film having a light-transmitting property of a limited number of layers, that is, one or two layers, is used. Only, it was possible to measure the film thickness and optical properties. That is, when the underlying layer has a multi-layer structure, in the method using the conventional ellipsometry, the thin film and optical characteristics of each layer are sequentially measured, and the complex reflectance must be calculated based on the result. However, the complex reflectance cannot be measured because the film thickness and optical characteristics of the thin film on the multilayer structure cannot be measured by this method.

An object of the present invention is to solve the above problems and provide a complex reflectance measuring method and apparatus capable of simply measuring the complex reflectance of an underlayer having a multi-layer structure. ..

[0010]

In order to achieve the above object, the present invention provides coherent and highly directional collimated light perpendicular to the surface of an object to be measured set at a reference height position. Irradiation is performed from an angle that is substantially horizontal, and the phase difference between the two interference lights due to the interference between the reflected light of the vertical irradiation light from the surface of the object to be measured and the reference light and the surface of the object to be measured are substantially horizontal. Detecting the phase term of the complex reflectance of the DUT from the phase difference between the interference light due to the interference of the reflected light and the reference light from the oblique direction and the interference light due to the interference of the reference light itself, The complex reflectance is obtained by detecting the amplitude of the complex reflectance of the DUT from the intensity of the reflected light of the vertically irradiated light.

[0011]

As shown in FIG. 13, the complex reflectance of the object to be measured has the term of the amplitude a and the term of the phase θ, and the term of the amplitude a is the vertical irradiation light to the object to be measured. It is obtained from the intensity of the reflected light.

Although the reference light does not include the phase term of the complex reflectance of the DUT, the reflected light of the vertically irradiated light includes the phase term of the complex reflectance of the DUT. , The phase difference between the two interference lights due to these interferences includes this phase term. On the other hand, the reflected light of the obliquely nearly horizontal surface of the DUT does not include the phase term of the complex reflectivity in the reference light, and the interference of these causes The phase difference between the interference light and the interference light due to the interference of the reference light itself does not include this phase term. Therefore, the phase term of the complex reflectance can be calculated from these phase differences.

[0013]

First, the principle of the present invention will be described. Figure 2
At, the upper surface (reference surface) 68 of the parallel flat glass plate 1
These are arranged at a predetermined interval (reference height) H so that the upper surface of the wafer 6 having only the underlayer or the thin film formed on the underlayer is parallel. In this case, a displacement ΔZ occurs in the reference height H according to the state of the upper surface of the wafer 6, and therefore the distance between the glass plate 1 and the wafer 6 is H + ΔZ.

This principle is based on the case where heterodyne interference is used to measure the phase θ of the complex reflectance A shown in FIG.

That is, when the glass plate 1 is irradiated with parallel light such as laser light having high coherence and directivity from above,
Part of the light is reflected by the reference surface 68 of the glass plate 1 to be reflected light (hereinafter referred to as reference light) (A ₀ ), and the other part is the glass 1
Is transmitted and reflected by the wafer 6 to become reflected light (A ₁ ).
If the underlying layer of the wafer 6 has a light-transmitting multilayer structure, the reflected light (A ₁ ) includes not only the reflected light from the upper surface of the wafer 6 but also the reflected light from each layer. Further, the incident angle θ ₀ is increased to irradiate the wear 6 with parallel light having high coherence and directivity, such as a laser light, from a direction close to the horizontal direction, and defines the reflected light (A ₂ ).

The interference beat signal between the reference light (A ₀ ) and the reflected light (A ₁ ) includes a reference height H, a displacement ΔZ component, and a phase θ component of the complex reflectance A. Light (A ₀ )
The interference beat signal between the reflected light (A ₁ ) and the reflected light (A ₁ ) includes only the component of the reference height H and the displacement ΔZ. Therefore, the phase θ can be obtained from these interference beat signals.

That is, now, the reference light (A ₀ ) and the reflected light (A ₁ ) consist of two parallel lights F ₁ and F _{2 having} slightly different frequencies f ₁ and f ₂ (f ₁ > f ₂ ), If the reflected light (A ₂ ) is composed of either the parallel light F ₁ or F ₂ having the frequencies f ₁ and f ₂ , the reference light (A ₀ ) and the reflected light (A ₂ ) are Interference fringe strength I when interference is caused
₁ (t) is represented by the following equation (1.1).

I ₁ (t) = a + b cos (2π (f ₁ −f ₂ ) t + 4π f ₂ cos θ ₀ ΔZ / c + φ ₀₁ ) ... (1.1) where t is time, c is the speed of light, and φ is ₀₁ is the initial phase.

When the lights F ₁ and F _{2 of} the reference light (A ₀ ) are caused to interfere with each other, the intensity I ₂ (t) of the interference fringe is expressed by the following equation (1.2).

I ₂ (t) = a + bcos (2π (f ₁ −f ₂ ) t + φ ₀₂ ) (1.2) where φ ₀₂ is the initial phase.

Therefore, the phase difference φ between the interference beat signal of intensity I ₁ (t) and the interference beat signal of intensity I ₂ (t) is φ = 4πf ₂ cos θ ₀ ΔZ / c + φ ₀₁ −φ ₀₂ (1 .3) and is given as a function of the displacement ΔZ. From this equation (1.3), the displacement ΔZ is represented by the following equation (1.4).

ΔZ = c (φ−φ ₀₁ + φ ₀₂ ) / 4πf ₂ cos θ ₀ (1.4) On the other hand, when the reflected light (A ₁ ) from the wafer 6 and the reference light (A ₀ ) are interfered with each other, The intensity I ₃ (t) of the interference fringes of the interference beat signal between the one light F ₁ and the other light F _2, and the intensity I ₄ of the interference fringes of the interference bit signal of the _one light F ₂ and the other light F _1. (t) are, respectively, and φ _03, the φ ₀₄ as the initial phase, the following equation (1.
5) and (1.6).

I ₃ (t) = a + bcos (2π (f ₁ −f ₂ ) t + 4πf ₁ ΔZ / c + θ + φ ₀₃ ) (1.5) I ₄ (t) = a + bcos (2π (f ₁ −f ₂ ) t + 4πf ₂ ΔZ / c−θ + φ ₀₄ ) (1.6) And the interference beat signal of intensity I ₃ (t) and intensity I ₃ (t)
The phase difference ψ of the interference beat signal of ₄ (t) is calculated by the following equation (1.
As shown in 7), it can be expressed by a function of the phase θ of the wafer 6 complex reflectance A and the displacement ΔZ.

Ψ = 4π (f ₁ + f ₂ ) ΔZc + 2θ + φ ₀₃ −φ ₀₄ (1.7) Therefore, from the equation (1.4) and the equation (1.7), the wafer 6 is obtained.
The phase θ of the complex reflectance A of is θ = (ψ− (f ₁ + f ₂ ) (φ−φ ₀₁ + φ ₀₂ ) / f ₂ cos θ ₀ −φ ₀₃ + φ ₀₄ ) / 2 (1.8) ..

FIG. 3A shows the above equations (1.1), (1.
2 (b) shows temporal changes in the intensity I ₁ (t) and I ₂ (t) of the interference fringes represented by 2) and the phase difference φ between them represented by the above equation (1.3). ) Is the above formula (1.
5) and intensity of interference fringes represented by (1.6) I
Changes in ₃ (t) and I ₄ (t) with time and the above equation (1.7)
The phase difference ψ represented by The intensity of these interference fringes I ₁ (t), I ₂ (t), I ₃ (t), I
₄ (t) is detected by the respective sensors, and the detected intensity I
Phase difference φ from ₁ (t) and I ₂ (t) is detected intensity I
_The phase difference ψ can be obtained from ₃ (t) and I ₄ (t), respectively. Therefore, the phase θ of the complex reflectance A of the wafer 6 shown in FIG. 13 can be obtained.

An embodiment of the present invention based on the principle described above will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a method and apparatus for measuring complex reflectance according to the present invention, in which 1 is a diffractive light mask made of a glass plate, 2 and 3 are diffraction gratings, and 4 is a λ / 4 wavelength. A plate, 5 is an auto-focus system, 6 is a wafer, 7 is a prism, 8, 9 and 10 are polarized beam splitters, 11 is a mirror, 12 is a λ / 2 wavelength plate, 13, 14 and 15 are beam splitters, and 16 and 17 Is a lens, 18, 19, 20, 2
1 is a sensor.

In the figure, a diffractive light mask 1 is provided at a predetermined interval above a wafer 6 on which only a base layer or a thin film is formed. By the autofocus system 5, the diffractive light mask 1 and the wear 6 are arranged so that the phase is within a range not deviated by 2π with respect to the detection signal when the distance between the diffractive light mask 1 and the wear 6 is at the reference height H. Interval is set.

The diffractive light mask 1 has a chrome layer formed on the front surface of the glass plate except the positions A and C where the diffraction gratings 2 and 3 are provided to form a reflecting surface. And
Coherent and highly directional parallel light C ₁ irradiates the diffraction grating 2, parallel light C ₃ irradiates the diffraction grating 2, and parallel light C ₂ irradiates the B position between positions A and C from oblique directions. To be done. These parallel lights C ₁ , C ₂ , and C ₃ are composed of parallel lights F ₁ p (p-polarized light) having a frequency f ₁ p whose polarization directions are orthogonal to each other and parallel light F ₂ s (s-polarized light) having a frequency F ₂ s. And these frequencies f
₁ p and f ₂ s are slightly different (f ₁ p> f ₂ s).

The parallel light C ₁ is diffracted by the diffraction grating 2 to be -1.
Next-order diffracted light is generated, and the minus first-order diffracted light is incident on the wafer 6 at an incident angle θ ₀ . The incident angle θ ₀ is set to be sufficiently large depending on the wavelength of the parallel light C ₁ and the pitch of the diffracted light 2, so that the −1st order diffracted light is almost totally reflected on the surface of the wafer 6. , Is transmitted to the polarization beam splitter 8 through the prism 7. The polarization beam splitter 8 is an s-polarized light F ₂ s having a high reflectance of the incident light.
Only pass through. This s-polarized light F ₂ s is the reflected light A ₂ in FIG.

The incident parallel light C ₂ is on the diffracted light mask 1 A, C.
The light is reflected at the position B between the positions and becomes the reference light (A ₀ ) in FIG.

The incident parallel light C ₃ is applied to the diffraction grating 3 at the position C on the diffracted light mask 1, and first-order diffracted light in the direction perpendicular to the surface of the wafer 6 is generated. This first-order diffracted light is λ / 4
The wafer 6 is vertically irradiated through the wave plate 4 and reflected,
It again passes through the λ / 4 wave plate 4 and the diffraction grating 3. The light that has passed through the diffraction grating 3 is the reflected light (A ₁ ) in FIG. 2 and is combined with the light reflected by the diffraction grating 3 (corresponding to the reference light (A ₀ ) in FIG. 2). This reflected light (A ₁ ) is transmitted through the λ / 4 wave plate 4 by 2
The angle of polarization is π / with respect to the original incident parallel light C ₃
It is off by 2. That is, in the reflected light (A ₁ ),
The p-polarized light F ₁ p of the incident parallel light C ₃ is s-polarized light F ₁ s, and the s-polarized light F ₂ s is p-polarized light F ₂ p.

As described above, the reference light (A ₀ ) and the reflected lights (A ₁ ) and (A ₂ ) shown in FIG. ₂ are obtained. The reference light (A ₀ ) is sent to the polarization beam splitter 9, the p-polarized light F ₁ p of the reference light (A ₀ ) is transmitted, and the s-polarized light F ₂ s is reflected, so that the reference light (A ₀ ) is separated into these polarization components. .. The p-polarized light F ₁ p is reflected by the mirror 11 and s / 2 by the λ / 2 wave plate 12.
The polarized light changes to F ₁ s and is split into two by the beam splitter 13. One s-polarized light F ₁ s from the beam splitter 13 is sent to the beam splitter 15, and is combined with the s-polarized light F ₂ s that is the reflected light (A ₂ ) from the polarized beam splitter 8.
This combined light undergoes heterodyne interference on the sensor 18 at a position conjugate with the position of the wafer 6 by the lens 17, and an interference beat signal of interference fringe intensity I ₁ (t) represented by the above formula (1.1) is obtained. ..

The other s-polarized light F ₁ s from the beam splitter 13 is sent to the beam splitter 14 and is combined with the s-polarized light F ₂ s from the polarizing beam splitter 9. This combined light undergoes heterodyne interference on the sensor 19, and an interference beat signal having the interference fringe intensity I ₂ (t) represented by the above equation (1.2) is obtained.

The reference light (A ₀ ) from the position C on the diffracted light mask 1 is p-polarized light F ₁ p and s-polarized light F ₂ s, and the reflected light (A ₁ ) is p-polarized light F ₂ p and s-polarized light F. _It consists of ₁ s.
The combined light of the reference light (A ₀ ) and the reflected light (A ₁ ) passes through the lens 16 and is combined by the polarization beam splitter 10 with the combined light of the p-polarized light F ₁ p and F ₂ p and the s-polarized light F ₁ s, F. _The former is subjected to heterodyne interference on the sensor 21 which is conjugate with the wafer 6 by the lens 16, and the latter is separated on the sensor 20 which is also conjugate with the wafer 6 by the lens 16. .. As a result, the sensor 20
And the interference fringe intensity I ₃ (t) expressed by the above equation (1.5)
The interference beat signal of (1.
An interference beat signal having the interference fringe intensity I ₄ (t) represented by 6) is obtained.

Therefore, the phase θ of the complex reflectance A can be obtained from the interference beat signals as described above, and the wear 6 for the vertical irradiation light can be obtained as in the conventional case.
Since the amplitude a (a ² = reflectance intensity) of the complex reflectance A can be easily obtained from the reflectance intensity of A, the complex reflectance A of the wafer 6 can be obtained by the equation shown in FIG.

FIG. 4 is a diagram showing another embodiment of the method and apparatus for measuring the complex reflectance according to the present invention.
4, 25 are beam splitters, 26, 27, 28, 29
Is a mirror, and 30 is an input / 2 wavelength plate, and the portions corresponding to those in FIG.

In the embodiment shown in FIG. 1, the wafer 6 is obliquely or vertically irradiated using the diffraction grating or the prism, but in the embodiment shown in FIG. 4, a different means is used. The same irradiation is performed.

In FIG. 4, the incident parallel light F is divided into two by the beam splitter 22, and one parallel light F ₁ output from this is almost horizontally obliquely irradiated to the surface of the wafer 6 by the mirror 26, and is substantially radiated. The light is totally reflected, and only the s-polarized light F ₂ s of this reflected light is extracted by the polarization beam splitter 8 to be reflected light (A ₂ ).

The other parallel light F ₂ output from the beam splitter 22 is partly reflected by the beam splitter 23 to become reference light (A ₀ ), the rest of which passes through, and part of it further passes through the beam splitter. After passing through 24, it becomes reference light (A ₀ ). The processing of the reference light (A ₀ ) and the reflected light A ₂ is similar to that of the embodiment shown in FIG. 1, and the sensor 18 produces the interference fringe intensity I ₁ (t) represented by the above equation (1.1). As the interference beat signal, the sensor 19 detects the interference beat signal having the interference fringe intensity I ₂ (t) expressed by the above equation (1.2). The mirror 28 is. The s-polarized light F ₂ s separated by the polarization beam splitter 9 is converted into a beam splitter 25.
To be reflected and supplied to the beam splitter 14 in order to be combined with the s-polarized light F ₁ s from.

The parallel light reflected by the beam splitter 24 passes through the beam splitter 25 and irradiates the wafer 6 vertically, and the reflected light passes through the beam splitters 25 and 24 to become reflected light (A ₁ ). This reflected light (A ₁ ) passes through the λ / 2 wave plate 30 (corresponding to passing twice through the λ / 4 wave plate 4 in FIG. 1) and is supplied to the polarization beam splitter 10 via the lens 6. Beam splitter 23 to mirror 2
It is combined with the reference light (A ₀ ) sent via 9.
In the embodiment of FIG. 1, the reference light (A ₀ ) and the reflected light (A ₁ ) are combined at the position C of the diffractive light mask 1, but in FIG. 4, they are combined by the polarization beam splitter 10. Therefore, the interference beat signal of the interference fringe intensity I ₃ (t) expressed by the above formula (1.5) in the sensor 20 is changed to the interference fringe intensity I ₄ (t) expressed by the above formula (1.6) in the sensor 21. The interference beat signals of are detected respectively. The beam splitter 25 is for superimposing the optical path of the beam used in the autofocus system 5 on the optical path of parallel light for vertical irradiation.

Thus, also in this embodiment,
The phase θ of the multiple reflectances A shown in FIG. 13 can be obtained.

FIG. 5 is a view showing still another embodiment of the complex reflectance measuring method and apparatus according to the present invention. 1'is a diffractive light mask, 3'is a diffraction grating, 7a and 7b are prisms,
9'is a polarization beam splitter, 11a and 11b are mirrors, 12a and 12b are λ / 2 wave plates, 16a and 16b are lenses, 31 is a beam splitter, 32 is a prism, and 3
3 is a polarization beam splitter, 34 is a laser output unit, 35 is an AOM unit, 36 is a light guide unit, 37
Is a measuring unit, 38 is a laser light source, 39 is a laser power controller, 40 is a half mirror, 41 is a λ / 2 wave plate, 42 and 43 are mirrors, 44 and 45 are acousto-optic elements, 46 and 47 are pinholes, and 48. Is a polarization beam splitter, 49 to 52 are lenses, 53 and 54 are pinholes,
Reference numeral 55 is a mirror, and the same reference numerals are given to the portions corresponding to the above drawings.

In FIG. 5, in this embodiment, a laser output unit 34 for stabilizing the laser output, and a p-polarized light and an s-polarized light having different polarization directions by branching the output laser light into two are provided by an acoustooptic device. An AOM unit 35 that synthesizes the optical axes by making the frequencies slightly different and matching the optical axes again, and guides the combined light to the measurement unit 37 by limiting the field of view of the irradiation light at the measurement point and removing stray light of the laser beam. The unit 36 includes a unit 36, a measurement unit 37 including a plurality of interferometers that measure the complex reflectance by the combined light guided from the light guide unit 36, and an autofocus unit 5 that focuses a measurement point.

In the laser output unit 34, if the g-line (436 nm) is used as the exposure light and the complex reflectance at that time is measured, the laser light source 38 may be, for example, a linearly polarized He--Cd laser having a near wavelength. (441.6n
Adopt m). The laser power controller 39 stabilizes the output of the laser.

In the AOM unit 35, the laser light from the laser output unit 34 is split into two by the half mirror 40. One of the split lasers is λ /
The polarization direction is reversed by the two-wave plate 41, reflected by the mirror 42, and then supplied to the acousto-optic element 45. The other branched laser beam is supplied to the acousto-optic element 44. As a result, these laser lights become lights λ ₁ p and λ ₂ s whose frequencies of the first-order diffracted lights are slightly different from each other. These two two lights λ ₁
The p, λ ₂ s passes through the pinholes 47, 46, and the light λ ₂ s is reflected by the mirror and is combined by the polarization beam splitter 48 to be one laser light with the matched optical axis. These pinholes 47 and 46 are 0 from the acousto-optic elements 45 and 46.
This is for blocking the next-order diffracted light.

In the light guide unit 36, the laser light from the AOM unit 35 is removed of stray light by the pinhole 53 at the focal position of the objective lens 49, and the lens 5
When 0, parallel light is obtained. The optical path of this parallel light is changed by the mirror 55, and the measurement area is limited by the pinhole 54 at the conjugate position with the wafer 6 between the lenses 51 and 52.

In the measuring unit 37, the prism 3
2 splits the parallel light from the light guide unit 36 into three parallel lights C ₁ , C ₂ and C ₃ . The parallel light C ₂ from the prism 32 is specularly reflected by the chrome surface of the diffraction grating mask 1 ′,
The reflected light (A ₀ ) is sent to the polarization beam splitter 9 ′ and separated into s-polarized light and p-polarized light. The s-polarized light reflected by the polarization beam splitter 9'is reflected by the prism 11a, and the polarization direction is reversed by the λ / 2 wavelength plate 12b to become p-polarized light. The p-polarized light transmitted through the polarization beam splitter 9 ′ is
After being split into two by the beam splitter 31, one of them is reflected by the prism 11b, is combined with the s-polarized light from the λ / 2 wave plate 12b by the beam splitter 14, and is guided to the sensor 19 to emit light λ ₁ p, λ ₂ An interference beat signal due to s heterodyne interference is obtained. This becomes the reference beat signal of the interference fringe strength shown in the above equation (1.2).

The parallel light C ₃ from the prism 32 is
The light enters the diffraction grating 3 ′ provided on the diffraction grating mask 1 ′ at an incident angle Θ. As a result, the first-order diffracted light is generated. The pitch p and the incident angle Θ of the diffraction grating 3 ′, the wavelength of the incident parallel light C ₃ of the diffraction grating 3 ′ are set to λ so that the diffracted light irradiates the wafer 6 vertically. Then, set so as to satisfy the following relationship. sin Θ = λ / p λ on the surface opposite to the diffraction grating 3 ′ of the diffraction grating mask 1 ′.
A quarter-wave plate 4 is provided, and the linearly-polarized first-order diffracted light generated by the diffraction grating 3 ′ is converted into circularly-polarized light by the λ / 4 wavelength plate 4 and irradiates the wafer 6 from the vertical direction.
The reflected light from the wafer 6 passes through the λ / 4 wavelength plate 4 again, and the light λ ₁ s, λ whose polarization direction is inverted with respect to the parallel light C ₃ .
It becomes ₂ p, is diffracted again by the diffraction grating 3 ', and is incident parallel light C ₃
And the reference light (A ₀ ) and the reflected light (A ₁ ) are combined to travel in the same direction. This combined light is split into p-polarized light and s-polarized light by the polarization beam splitter 10, and the former is a sensor 21 at a conjugate position with the wafer 6 by a lens 16b, and the latter is a sensor 20 at a conjugate position with the wafer 6 by a lens 16a. And the heterodyne interference is performed to obtain an interference beat signal having the interference fringe intensity of the above expressions (1.5) and (1.6).

Further, the parallel light C ₁ from the prism 32 is
The polarized beam splitter 33 selects only λ ₂ s of polarized light having a high surface reflectance on the wafer 6, and the prism 7 a irradiates the surface of the wafer 6 at an incident angle that is substantially horizontal and causes almost total reflection. This reflected light is guided to the beam splitter 15 as reflected light A ₂ via the prism 7b. The p-polarized light separated by the beam splitter 31 has its polarization direction reversed by the λ / 2 wave plate 12a and is guided to the beam splitter 15 as s-polarized light λ ₁ s, which is reflected light (A ₁ ). The light is synthesized and guided by the lens 17 to the sensor 18 at a conjugate position with the wafer 6. In this sensor 18, the synthetic light causes heterodyne interference, and the above formula (1.
An interference beat signal having the interference fringe intensity of 1) is obtained.

By performing the Fourier transform of the interference beat signals measured by the above four sensors 18 to 21 as described above, the phase θ of the complex reflectance A can be obtained, and therefore the complex reflectance A is obtained. be able to.

If the complex reflectance and the refractive index of the underlying layer before forming the thin film are known, the complex reflectance A is measured based on the formula shown in FIG. The thickness of the formed thin film can be obtained.

FIG. 6 is a block diagram showing a specific example of the film thickness measuring apparatus using the present invention. In the figure, when the wafer on which the thin film is formed and processed is carried into the complex reflectance measuring unit 56 described as the above embodiment, the above interference beat signal measured at an arbitrary position is obtained. These interference beat signals are transferred to the phase detector 57 and their complex reflectance A
Is required. Based on the measurement result of the complex reflectance A obtained by the phase detection unit 57, the refractive index stored in the data unit 59, and the measurement result of the complex reflectance measured in advance with respect to the underlying layer before the thin film is generated and processed. The film thickness measuring section 58 calculates the film thickness of the thin film.

FIG. 7 is a block diagram showing a specific example of a control system for a thin film forming / processing apparatus using the present invention.
In the figure, the complex reflectance of the wafer on which the thin film is formed and processed is measured by the complex reflectance measuring device 56 having the configuration shown in FIG. The process control system 62 uses this result, the measurement result of the complex reflectance of the wafer before the thin film of the data section 63 is generated and processed, and the information such as the refractive index of the thin film to be generated and processed, Obtain the film thickness of the processed thin film, calculate the process variation from this film thickness data, and create the thin film.
By feeding back to the processing device 60 and controlling the process conditions, thin film formation and stabilization of the processing device 60 can be achieved.

FIG. 8 is a block diagram showing a specific example of a system for controlling the exposure amount of the stepper using the present invention.

In the above embodiments, the film thickness of a thin film formed on a multi-layered thin film as a base layer of a semiconductor was measured, but the invention is not limited to semiconductors, but may be applied to substances such as lenses and glass. It can also be applied to the measurement of the thickness of the produced thin film.

[0057]

As described above, according to the present invention,
It is possible to easily measure the complex reflectance of an underlying layer having a multi-layer structure, and it is possible to accurately measure the film thickness of a thin film formed and processed on the underlying layer.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a complex reflectance measuring method and apparatus according to the present invention.

FIG. 2 is a principle diagram of the present invention.

FIG. 3 is a diagram showing the intensity of interference fringes of the interference beat signal in FIG.

FIG. 4 is a diagram showing another embodiment of the complex reflectance measuring method and apparatus according to the present invention.

FIG. 5 is a diagram showing still another embodiment of the complex reflectance measuring method and apparatus according to the present invention.

FIG. 6 is a block diagram showing a specific example of a film thickness measuring apparatus using the complex reflectance measuring method according to the present invention according to the present invention.

FIG. 7 is a block diagram showing a specific example of a control system of a thin film forming / processing apparatus using the complex reflectance measuring method according to the present invention.

FIG. 8 is a block diagram showing a specific example of a stepper exposure amount control system using the complex reflectance measuring method according to the present invention.

FIG. 9 is a diagram showing an influence of multiple reflection in a resist and a light-transmitting underlayer forming film.

FIG. 10 is a diagram showing a change in light intensity in the resist film in FIG.

FIG. 11 is a diagram showing a standing wave effect of the width of the resist film due to the unevenness of the formed resist film.

FIG. 12 is a principle diagram of ellipsometry.

FIG. 13 is a diagram showing an equation of complex reflectance.

[Explanation of symbols]

 1, 1 ′ Diffraction light mask 2, 3, 3 ′ Diffraction grating 4 λ / 4 wavelength plate 5 Autofocus system 6 Wafer 7 Prism 8, 9, 9 ′, 10 Polarization beam splitter 12, 12a, 12b λ / 2 wavelength plate 13, 14, 15 Beam splitter 18, 19, 20, 21 Sensor 22, 23, 24 Beam splitter 30 λ / 2 wavelength plate 31 Beam splitter 32 Prism 33 λ / 2 wavelength plate 34 Laser output unit 35 AOM unit 36 Light guide unit 37 Measuring Unit 56 Wafer Complex Reflectance Measuring Section 57 Phase Detection Section 58 Film Thickness Measuring Section 59 Data Section 60 Thin Film Generation / Processing Equipment 61 Complex Reflectance Measuring Equipment 62 Process Control System 63 Data Section 64 Resist Coating Equipment 65 Stepper 66 Process Control system

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Komoritani 5-22-1, Kamisumihonmachi, Kodaira-shi, Tokyo Hitachi, Ltd. Musashi factory

Claims (6)

[Claims] 1. A surface of an object to be measured, which is coherent and highly directional, is irradiated onto a surface of the object to be measured, which is set at a reference height position, obliquely from a vertical direction and a nearly horizontal direction. From the interference light of the reflected light of the vertical irradiation light from the reference light and the reference light, and from the phase difference between the reflected light of the irradiation light from a diagonal direction nearly horizontal to the surface of the object to be measured and the interference light of the reference light. A complex reflectance measuring method comprising detecting a phase term of the complex reflectance of the DUT and detecting the amplitude of the complex reflectance of the DUT from the intensity of the reflected light of the vertically irradiated light. 2. The complex reflectance measuring method according to claim 1, wherein the object to be measured is formed of a multi-layered object. 3. A refractive index of an object to be measured, a first complex reflectance of the object to be measured before thin film formation and processing, and a second complex reflection of the object to be measured thin film formation and processing. In the film thickness measurement method that detects the film thickness of the thin film from the ratio, the coherent and highly directional parallel light is applied to the surface of the object to be measured, which is set at the reference height position, vertically and almost Irradiation is performed from an angle near horizontal, and the interference light between the reflected light of the vertical irradiation light from the surface of the object to be measured and the reference light and the irradiation light from the angle almost horizontal to the surface of the object to be measured The phase term of the complex reflectance of the DUT is detected from the phase difference between the reflected light and the interference light of the reference light, and the amplitude of the complex reflectance of the DUT is detected from the intensity of the reflected light of the vertically irradiated light. Then, the complex reflectance measuring method is characterized in that the first and second complex reflectances are obtained. 4. The process conditions of a thin film forming and processing apparatus on the object to be measured are controlled by information on optical characteristics such as the refractive index of the object to be measured and the complex reflectance of the object to be measured. In a thin film generation and processing system, coherent and highly directional parallel light is irradiated onto the surface of the object to be measured set at the reference height position from a vertical and nearly horizontal oblique direction, and the object is measured. Of the reflected light of the vertically radiated light from the surface of the reference light and the reference light, and the phase difference between the reflected light of the light radiated from an oblique direction nearly horizontal to the surface of the object to be measured and the interference light of the reference light The complex reflectance of the object to be measured is detected from the phase term, the amplitude of the complex reflectance of the object to be measured is detected from the intensity of the reflected light of the vertical irradiation light, and the complex reflectance is obtained. Complex reflectance measurement method. 5. A means for setting an object to be measured at a reference height position, and coherent and highly directional parallel light is applied to the surface of the object to be measured from a diagonal direction which is almost vertical and nearly horizontal. Means, interference light between the reflected light of the vertically irradiated light from the surface of the object to be measured and the reference light, and the reflected light of the parallel light irradiated to the surface of the object to be measured obliquely from nearly horizontal Means for detecting the phase term of the complex reflectance of the object to be measured from the phase difference between the light and the interference light; and the object to be measured from the intensity of the reflected light of the vertically irradiated light from the surface of the object to be measured. A complex reflectance measuring apparatus comprising: a unit for detecting the amplitude of the complex reflectance, wherein the complex reflectance of the object to be measured is obtained from the detected phase term and the amplitude. 6. The complex reflectance measuring device according to claim 5, wherein the object to be measured is formed of a multi-layered object.