JP3195018B2 - Complex reflectance measurement method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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 a wafer surface to form a coating film, and the resist is partially exposed to light by projecting and exposing an image of a mask pattern thereto using ultraviolet rays, and further undergoes a development process. In this way, a fine pattern is formed by exposing a portion to be processed such as etching and performing the processing in a limited region.

In recent years, the degree of integration of semiconductors has been remarkably increased, the pattern dimensions have been further miniaturized, and the element structure has been made three-dimensional, so that the manufacturing process has become more and more complicated.
For this reason, in photolithography, it is essential to increase the pattern resolution, and to achieve this, the NA (numerical aperture) of the lens has been increased and the wavelength of the exposure light has been shortened.

On the other hand, a single wavelength light having a relatively narrow wavelength band is used as the exposure light. Therefore, as shown in FIG. 9, a resist film 50 and a light-transmitting underlayer forming film are formed as shown in FIG. When 51 is present, the exposure light 52 is multiple-reflected in these films, and 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. . For this reason, when a difference occurs in the exposure energy in the depth direction and the phenomenon occurs, the cross section of the resist film 50 becomes uneven in the depth direction.

[0005] Further, when there is a process variation in various manufacturing apparatuses such as a film forming apparatus, the resist film thickness t and the formation state of the light-transmitting underlayer are different within the wafer and from wafer to wafer. Therefore, when the resist is exposed with the same exposure energy, the resist thickness t and the complex reflectance A (= aexp (iθ); a: amplitude, a ² = reflectance intensity represented by the equation (1) in FIG. 13) , Θ: phase) are 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 formed pattern size is different 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 measure the complex reflectance A according to the resist film thickness t and the formation state fluctuation of the underlayer. There is a need.

Here, 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, an ellipsometry. In the ellipsometry, as shown in FIG. 12, a sample 63 is irradiated with light 62 having an azimuth 61 set to a specific angle by a polarizer 60, and reflected on the surface of the sample 63 to form elliptically polarized light. The change in the polarization state of the reflected light (the azimuthal angle 64 and the elliptical angle 65 of the elliptically polarized light) is determined by the analyzer 66.
This is a method of determining the complex reflectance A (FIG. 13), which is the optical constant of the layer on the surface of the sample 63, by performing measurement using.

[0008]

However, in the above prior art, due to the performance of the ellipsometry, a thin film formed on a light transmitting thin film having a limited number of one or two layers is required. Only the film thickness and the optical characteristics could be measured. In other words, when the underlying layer has a multilayer structure, in the method using the above-mentioned conventional ellipsometry, the thin film and optical characteristics of each layer must be measured successively, and the complex reflectance must be calculated based on the results. However, since this method cannot measure the thickness and optical characteristics of a thin film on a multilayer structure, it cannot measure the complex reflectance.

An object of the present invention is to provide a method and an apparatus for measuring a complex reflectance which can solve such a problem and can easily measure a complex reflectance with respect to an underlayer having a multilayer structure. .

[0010]

In order to achieve the above-mentioned object, the present invention provides a coherent and highly directional parallel light beam which is vertically and coherently set on a surface of an object to be measured set at a reference height position. Irradiation is performed from a nearly horizontal oblique direction, and the phase difference between two interference lights due to interference between the reflected light of the vertical irradiation light from the surface of the object and the reference light, and substantially horizontally on the surface of the object to be measured. The phase term of the complex reflectance of the device under test is detected from the phase difference between the interference light due to the interference between the reflected light of the irradiation light from the near oblique direction and the reference light and the interference light due to the interference of the reference light itself, The complex reflectance is determined by detecting the amplitude of the complex reflectance of the device under test from the intensity of the reflected light of the vertical irradiation light.

[0011]

The complex reflectance of the device under test has a term of amplitude a and a term of phase θ as shown in FIG. From the intensity of the reflected light.

Although the reference light does not include the phase term of the complex reflectance of the object to be measured, the reflected light of the vertical irradiation light includes the phase term of the complex reflectance of the object to be measured. This phase term is included in the phase difference between two interference lights due to these interferences. On the other hand, the reflected light of the irradiation light from the oblique direction which is almost horizontal to the surface of the object to be measured, and the reference light also does not include the phase term of the complex reflectance. 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]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described. FIG.
, The upper surface (reference surface) 68 of the parallel flat glass plate 1
These are arranged at a predetermined interval (reference height) H such 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 an example in which heterodyne interference is used to measure the phase θ of the complex reflectance A shown in FIG.

That is, when a coherent and highly directional parallel light such as a laser beam is irradiated onto the glass plate 1 from above,
A part of the light is reflected by the reference surface 68 of the glass plate 1 and becomes reflected light (hereinafter referred to as reference light) (A ₀ ).
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. Also, the incident angle θ ₀ is increased to irradiate the coherent and highly directional parallel light, such as laser light, from the near-horizontal direction to the wear 6 to obtain the reflected light (A ₂ ).

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

That is, the reference light (A ₀ ) and the reflected light (A ₁ ) are composed 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 one of the parallel lights F ₁ and F ₂ having the frequencies f ₁ and f ₂ , the reference light (A ₀ ) and the reflected light (A ₂ ) Interference fringe intensity I when caused to interfere
₁ (t) is represented by the following equation (1.1).

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

Accordingly, the phase difference φ between the interference beat signal having the intensity I ₁ (t) and the interference beat signal having the intensity I ₂ (t) is as follows: 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 expressed by the following equation (1.4).

ΔZ = c (φ−φ ₀₁ + φ ₀₂ ) / 4πf ₂ cos θ ₀ (1.4) On the other hand, if the reflected light (A ₁ ) from the wafer 6 and the reference light (A ₀ ) interfere with each other, The intensity I ₃ (t) of the interference fringe 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 fringe of the interference bit signal between the one light F ₂ and the other light F ₁ (T), assuming that φ ₀₃ and φ ₀₄ are initial phases, respectively, the following equation (1.
5), (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) The interference beat signal having the intensity I ₃ (t) and the intensity I
₄ The phase difference 干 渉 of the interference beat signal in (t) is expressed by the following equation (1.
As shown in 7), the complex reflectance A of the wafer 6 can be represented by a function of the phase θ and the displacement ΔZ.

Ψ = 4π (f ₁ + f ₂ ) ΔZc + 2θ + φ ₀₃ −φ ₀₄ (1.7) Therefore, the wafer 6 is obtained from the equations (1.4) and (1.7).
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 equations (1.1) and (1.
FIG. 3B shows a temporal change in the intensity I ₁ (t) and I ₂ (t) of the interference fringes expressed by 2) and their phase difference φ expressed by the above equation (1.3). ) Is the above equation (1.
5), the intensity I of the interference fringes represented by (1.6)
₃ (t), I ₄ (t) with time and the above equation (1.7)
These phase differences さ れ る are represented by The intensity of these interference fringes I ₁ (t), I ₂ (t), I ₃ (t), I
₄ (t) are detected by the respective sensors, and the detected intensity I
₁ (t) and I ₂ (t), the phase difference φ is detected and the detected intensity I
_The phase difference ψ can be obtained from ₃ (t) and I ₄ (t), and 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 above-described principle 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, wherein 1 is a diffractive light mask made of a glass plate, 2 and 3 are diffraction gratings, and 4 is a λ / 4 wavelength. Plate, 5 is an autofocus system, 6 is a wafer, 7 is a prism, 8, 9, and 10 are polarization 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 FIG. 1, 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. The diffracted light mask 1 and the wear 6 are moved by the autofocus system 5 so that the phase is not shifted by 2π with respect to the detection signal when the distance between the diffracted light mask 1 and the wear 6 is at the reference height H. Is set.

The diffractive light mask 1 has a chromium layer formed on the front surface of the upper surface of the glass plate except for the positions A and C where the diffraction gratings 2 and 3 are provided to form a reflection surface. And
The parallel light C ₁ having coherence and high directivity is applied to the diffraction grating 2, the parallel light C ₃ is applied to the diffraction grating 2, and the parallel light C ₂ is applied to the position B between the positions A and C from an oblique direction. Is done. These parallel lights C ₁ , C ₂ , and C ₃ are composed of a parallel light F ₁ p (p-polarized light) having a frequency f ₁ p and a parallel light F ₂ s (s-polarized light) having a frequency F ₂ s whose polarization directions are orthogonal to each other. And these frequencies f
₁ p, f ₂ s are slightly different _{(f 1 p> f 2 s} ).

The parallel light C ₁ is diffracted by the diffraction grating 2 and −1
A first-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. , Through the prism 7 to the polarization beam splitter 8. The polarization beam splitter 8 has a high reflectance s-polarized light F ₂ s of the incident light.
Only let through. This s-polarized light F ₂ s is the reflected light A ₂ in FIG.

The incident parallel light C ₂ is reflected on the diffracted light mask 1 by 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 irradiates the diffraction grating 3 at the position C on the diffractive light mask 1 to generate first-order diffracted light in a direction perpendicular to the surface of the wafer 6. This first-order diffracted light is λ / 4
Irradiated perpendicularly to the wafer 6 through the wave plate 4 and reflected,
The light again passes through the λ / 4 wavelength plate 4 and the diffraction grating 3. The light passing 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). The reflected light (A ₁ ) passes through the λ / 4 wavelength plate 4
Degree, the polarization angle of the original incident parallel light C ₃ is π /
It is off by two. 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, where 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, thereby being separated into these polarized light components. . The p-polarized light F ₁ p is reflected by the mirror 11 and is reflected by the λ / 2 wave plate 12 as s
The polarization 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, which 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 having the interference fringe intensity I ₁ (t) represented by the above equation (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 combined with the s-polarized light F ₂ s from the polarization 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 C position on the diffractive light mask 1 is composed of 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 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 and F ₁ . _The light is separated into a combined light of ₂ s, and the former undergoes heterodyne interference by the lens 16 on the sensor 21 conjugated with the wafer 6, and the latter also by the lens 16 on the sensor 20 conjugated to the wafer 6. . Thereby, the sensor 20
The interference fringe intensity I ₃ (t) represented by the above equation (1.5)
Is obtained, and the sensor 21 obtains the above-mentioned equation (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 these 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 reflectivity A can be easily obtained from the reflectivity intensity, the complex reflectivity 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 / two-wavelength plate, and the portions corresponding to those in FIG.

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

In FIG. 4, the incident parallel light F is split into two by a beam splitter 22, and one of the parallel lights F ₁ output from the beam is substantially horizontally obliquely applied to the surface of the wafer 6 by a mirror 26, and is substantially oblique. The light is totally reflected, and only the s-polarized light F ₂ s of the reflected light is extracted by the polarization beam splitter 8 to become reflected light (A ₂ ).

The other parallel light F ₂ output from the beam splitter 22 is partially reflected by the beam splitter 23 to become reference light (A ₀ ), the rest passes, and part of the parallel light F ₂ is further transmitted to the beam splitter. The light passes through the reference light 24 and becomes reference light (A ₀ ). The processing of the reference light (A ₀ ) and the reflected light A ₂ is the same as in the embodiment shown in FIG. 1, and the sensor 18 calculates the interference fringe intensity I ₁ (t) represented by the above equation (1.1). The interference beat signal is detected by the sensor 19 as the interference beat signal having the interference fringe intensity I ₂ (t) represented by the above equation (1.2). In addition, the mirror 28. 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 combine with the s-polarized light F ₁ s.

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 wavelength plate 30 (corresponding to twice passing through the λ / 4 wavelength plate 4 in FIG. 1), and is supplied to the polarization beam splitter 10 through the lens 6. Beam splitter 23 to mirror 2
9 is combined with the reference light (A ₀ ) transmitted through the reference light 9.
In the embodiment shown in 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 equation (1.5) is obtained by the sensor 20, and the interference fringe intensity I ₄ (t) expressed by the above equation (1.6) is obtained by the sensor 21. Are detected respectively. Note that the beam splitter 25 is for overlapping the optical path of the beam used in the autofocus system 5 with the optical path of the parallel light for vertical irradiation.

As described above, also in this embodiment,
The phase θ of the plurality of reflectances A shown in FIG. 13 can be obtained.

FIG. 5 is a view showing still another embodiment of the method and apparatus for measuring complex reflectance according to the present invention, wherein 1 'is a diffracted light mask, 3' is a diffraction grating, 7a and 7b are prisms,
9 'is a polarizing beam splitter, 11a and 11b are mirrors, 12a and 12b are λ / 2 wavelength plates, 16a and 16b are lenses, 31 is a beam splitter, 32 is a prism, 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 measurement unit, 38 is a laser light source, 39 is a laser power controller, 40 is a half mirror, 41 is a λ / 2 wavelength plate, 42 and 43 are mirrors, 44 and 45 are acousto-optical elements, 46 and 47 are pinholes, 48 Is a polarizing beam splitter, 49 to 52 are lenses, 53 and 54 are pinholes,
Reference numeral 55 denotes a mirror, and portions corresponding to the above-mentioned drawings are denoted by the same reference numerals.

Referring to FIG. 5, in this embodiment, a laser output unit 34 for stabilizing a laser output, and this output laser light is branched into two to form p-polarized light and s-polarized light having different polarization directions. An AOM unit 35 for making the frequencies slightly different and aligning the optical axes again for synthesis, and a light guide for guiding the synthesized light to the measurement unit 37 by limiting the visual field of the irradiation light at the measurement point and removing the stray light of the laser beam. It comprises a unit 36, a measuring unit 37 composed of a plurality of interferometers for measuring complex reflectivity with the combined light guided from the light guiding unit 36, and an autofocus unit 5 for focusing measurement points.

In the laser output unit 34, if 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
m). The laser power controller 39 stabilizes the output of the laser.

In the AOM unit 35, the laser beam 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-wavelength plate 41, and after being reflected by the mirror 42, it is supplied to the acousto-optic element 45. The other split laser light is supplied to the acousto-optic element 44. As a result, these laser beams become light beams λ ₁ p and λ ₂ s having slightly different frequencies of the first-order diffracted light beams. These two lights λ ₁
p and λ ₂ s pass through the pinholes 47 and 46, and the light λ ₂ s is reflected by a mirror and combined by the polarization beam splitter 48 to form one laser beam having the same optical axis. These pinholes 47 and 46 are provided with 0
This is for blocking the next-order diffracted light.

In the light guide unit 36, stray light is removed from the laser light from the AOM unit 35 by the pinhole 53 at the focal position of the objective lens 49, and
0 makes parallel light. The optical path of the parallel light is changed by the mirror 55, and the measurement area is limited by the pinhole 54 at the position conjugate 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 on the chrome surface of the diffraction grating mask 1 ′,
The reflected light (A ₀ ) is sent to the polarizing beam splitter 9 ′ to be 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 polarizing beam splitter 9 ′ is
After being split into two by the beam splitter 31, one of them is reflected by the prism 11 b, combined with the s-polarized light from the λ / 2 wave plate 12 b by the beam splitter 14, guided to the sensor 19, and the 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 intensity shown in the above equation (1.2).

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

Further, the parallel light C ₁ from the prism 32
In the polarization beam splitter 33, only λ ₂ s of the polarized light having a high surface reflectance on the wafer 6 is selected by the polarization beam splitter 33, and the prism 7a irradiates the surface of the wafer 6 at an almost horizontal incident angle and is almost totally reflected. This reflected light through the prism 7b, is guided to the beam splitter 15 as reflected light A _2. This beam splitter 15, also guided a p-polarized light that has been separated polarization direction at lambda / 2 wave plate 12a are reversed s-polarized light lambda ₁ s by the beam splitter 31, the reflected light (A ₁₎ The light is synthesized and guided by a lens 17 to a sensor 18 at a position conjugate with the wafer 6. In the sensor 18, the combined light causes heterodyne interference, and the above equation (1.
An interference beat signal having the interference fringe intensity of 1) is obtained.

By subjecting the interference beat signals measured by the four sensors 18 to 21 to Fourier transform 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 reflectivity and the refractive index of the underlayer before forming the thin film are known, the complex reflectivity A is measured based on the equation shown in FIG. The thickness of the thin film thus obtained can be obtained.

FIG. 6 is a block diagram showing a specific example of a film thickness measuring apparatus using the present invention. In the figure, when the wafer on which the thin film is generated and processed is carried into the complex reflectance measuring section 56 described as the above embodiment, the above-mentioned interference beat signal measured at an arbitrary position is obtained. These interference beat signals are transferred to the phase detection unit 57 and the complex reflectance A
Is required. The measurement result of the complex reflectance A obtained by the phase detection unit 57 and the measurement result of the complex reflectance previously measured for the underlayer before the generation and processing of the refractive index and the thin film stored in the data unit 59 are performed. The thickness of the thin film is calculated by the thickness measuring unit 58.

FIG. 7 is a block diagram showing a specific example of a control system for a thin film forming and 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 the result, the measurement result of the complex reflectance of the wafer before generating and processing the thin film of the data unit 63, and information such as the refractive index of the thin film to be generated and processed. The thickness of the processed thin film is determined, and the process variation is calculated from the thickness data to generate a 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 are achieved.

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

In the above embodiment, the thickness of a thin film formed on a multilayer thin film as an underlayer of a semiconductor is measured. However, the present invention is not limited to a semiconductor but may be applied to a material such as a lens or glass. It can also be applied to the measurement of the thickness of the formed thin film.

[0057]

As described above, according to the present invention,
The complex reflectance of the underlying layer having a multilayer structure can be easily measured, and the thickness of the thin film formed and processed on the underlying layer can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a method and an apparatus for measuring complex reflectance 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. 2;

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

FIG. 5 is a view showing still another embodiment of the method and apparatus for measuring complex reflectance 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 view showing the influence of multiple reflection in a resist and a light-transmitting underlayer forming film.

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

FIG. 11 is a view 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 an ellipsometry.

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

[Explanation of symbols]

 1, 1 'Diffractive 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 Measurement Unit 56 Wafer Complex Reflectance Measurement Unit 57 Phase Detection Unit 58 Film Thickness Measurement Unit 59 Data Unit 60 Thin Film Generation / Processing Device 61 Complex Reflectance Measurement Device 62 Process Control System 63 Data Unit 64 Resist Coating Device 65 Stepper 66 Process Control system

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshihiko Aiba 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Within the Production Engineering Laboratory, Hitachi, Ltd. No. 1 Hitachi, Ltd. Musashi Factory (56) References JP-A-4-269643 (JP, A) JP-A-5-346309 (JP, A) JP-A-2-96640 (JP, A) Hei 2-503115 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 G01B 11/00-11/30 ESPACENET

Claims (6)

(57) [Claims] 1. A method of irradiating a coherent and highly directional parallel light onto a surface of an object to be measured set at a reference height position from a vertical and almost horizontal oblique direction, and irradiating the surface of the object to be measured. The interference light between the reflected light of the vertical irradiation light and the reference light, and the phase difference between the reflected light of the irradiation light and the interference light between the reference light and the irradiation light from an oblique direction nearly horizontal to the surface of the device under test. A complex reflectance measurement method comprising: detecting a phase term of a complex reflectance of an object to be measured; and detecting an amplitude of the complex reflectance of the object to be measured from an intensity of reflected light of the vertical irradiation light. 2. The method according to claim 1, wherein the object to be measured is formed of a multilayer object. 3. The refractive index of the object to be measured, the first complex reflectance before the thin film formation and processing of the object to be measured, and the second complex reflection after the thin film formation and processing of the object to be measured. In the film thickness measuring method for detecting the film thickness of the thin film from the ratio, the parallel light having coherence and high directivity is perpendicularly and substantially perpendicularly to the surface of the measured object set at the reference height position. Irradiation is performed from a nearly horizontal oblique direction, 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 irradiation light from the oblique line nearly 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 between the reference light, and the amplitude of the complex reflectance of the DUT is detected from the intensity of the reflected light of the vertical irradiation light. And obtaining said first and second complex reflectances. 4. A process for forming a thin film on an object to be measured and a process condition of a processing apparatus based on information on optical characteristics such as a refractive index of the object to be measured and a complex reflectance of the object to be measured. In a thin film generation and processing system, a coherent and highly directional parallel light is irradiated on a surface of an object to be measured set at a reference height position from a vertical and almost horizontal oblique direction, and the object to be measured is The phase difference between the interference light between the reflected light of the vertical irradiation light from the surface of the object and the reference light, and the interference light between the reflected light of the irradiation light from an oblique direction almost horizontal to the surface of the device to be measured and the reference light. Detecting the phase term of the complex reflectance of the device under test, detecting the amplitude of the complex reflectance of the device under test from the intensity of the reflected light of the vertical irradiation light, and obtaining the complex reflectance. Complex reflectance measurement method. 5. A means for setting an object to be measured at a reference height position, and irradiating a coherent and highly directional parallel light to a surface of the object to be measured from an oblique direction which is nearly vertical and almost horizontal. Means, 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 reflected light of the parallel light irradiated to the surface of the object to be measured from a nearly horizontal oblique direction. Means for detecting the phase term of the complex reflectance of the device under test from the phase difference between the light and the interference light; and the intensity of the reflected light of the vertical irradiation light from the surface of the device under test. Means for detecting the amplitude of the complex reflectance, and obtaining the complex reflectance of the device under test from the detected phase term and the amplitude. 6. The complex reflectance measuring apparatus according to claim 5, wherein the object to be measured is formed of a multilayer object.