JP2724025B2 - Measurement method of optical constant of thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring an optical constant of a thin film and an apparatus for measuring the same, and more particularly to a nondestructive, simple and accurate measuring method. Further, the present invention relates to an optical integrated circuit or a semiconductor element formed by feeding back a measured value of an optical constant by the above-described measuring method to a thin film forming process.

[Conventional technology]

2. Description of the Related Art Conventionally, as methods for measuring thin film optical constants, 1) ellipsometry, 2) interference microscopy and the like are well known. First,
Ellipsometry has the disadvantage that the refractive index cannot be quantified unless the film thickness is known to some extent, since a relatively thick film (3000 °) has a periodic solution in the measured values. In addition, the measurement accuracy of the refractive index is generally as low as about 1 × 10 ⁻³ . Further, there is a disadvantage that the method cannot be applied as a method for measuring the refractive index distribution.

Next, the interference microscope needs to make the measurement medium thin and optically polished. Therefore, a great deal of time is required for sample preparation. In addition, there is a drawback that the sample cannot be regenerated because it is a destructive inspection. In addition, when an interferometer such as Michelson et al. Is used, a refractive index × thickness, that is, an optical distance can be obtained as a measured value, so that there is a disadvantage that any one of them is known as a precondition.

On the other hand, with the progress of research on semiconductor lasers in recent years,
Research on an optical integrated circuit in which a light receiving / emitting element such as a laser and various waveguide type optical elements are integrated on a single substrate has been actively conducted. One of the most basic components of the optical integrated circuit is an optical waveguide. As a method for measuring the effective refractive index of an optical waveguide, see Journal of the Optical Society.
Of America, 60, 10 (1970) J. of the OSAVol6
0, No10 (1970) and the like, the prism coupler method is generally widely known.

[Problems to be solved by the invention]

The above prior art, the prism refractive index n _P is adhered across the air layer on the optical waveguide. Then, exciting the guided light by the phase matching between the optical waveguide is incident light beam to the prism bottom surface at a predetermined angle theta _P, the second prism taking out guided light to the outside. In this case, the effective refractive index of the optical waveguide is calculated using the principle that the angle of the emitted light varies depending on the waveguide mode of the optical waveguide. However, in this method, since the bottom surface of the prism is flat, the coupling efficiency is low, and moreover, since two or more prisms are always used, there is a disadvantage that the SN is reduced and high-precision measurement cannot be performed. Further, when the refractive index of the optical waveguide changes continuously, there is a disadvantage that it cannot be used. Furthermore, when applied to the measurement of the propagation loss of an optical waveguide, there is a problem that the coupling efficiency varies greatly and is not practical.

Therefore, there has been no method of measuring the refractive index, which is a basic parameter of the optical integrated circuit, with high accuracy, and it has been necessary to optimize the device by trial and error in manufacturing the device.

In the semiconductor device manufacturing process, Si used as a chip passivation film or an interlayer insulating film of a multilayer wiring is used.
The physical properties of various dielectric thin films such as O ₂ , Si ₃ N ₄ , PSG, etc.
Evaluating and managing in situ is a very important issue in ensuring the reliability of a semiconductor device.

Conventionally, as a monitoring device in a thin film manufacturing process, a film thickness meter is mainly used. Therefore, there is a disadvantage that the physical property value at the time of film formation cannot be measured and fed back to the film formation conditions.

An object of the present invention is to measure optical values such as a refractive index, a film thickness, and a refractive index distribution propagation loss of a thin film with high accuracy.

Another object of the present invention is to easily and nondestructively measure the above optical values.

Another object of the present invention is to form a thin film with high accuracy,
An object of the present invention is to provide an optical element having excellent performance.

In the present invention, the optical measuring device includes a light source, a prism placed in close contact with the sample, and a light receiving device for detecting light reflected from the bottom of the prism. In the present invention, using a prism integrated with a light receiving element, the relationship between the incident angle of a light incident beam from a light source on the prism and the intensity of reflected light at the bottom of the prism is continuously measured using the incident angle as a variable.
Then, from the relationship between the incident angle of the light incident beam and the intensity of the reflected light at the bottom of the prism, the effective refractive index of a number of media (optical thin films, optical waveguides) corresponding to the above variables is calculated. Here, it is necessary to calculate two or more effective refractive indices for at least two or more incident angles.

In the above measurement, coupling efficiency is improved by processing the prism bottom surface into a spherical surface, and measurement accuracy is improved. Next, 2
For the above variables (incident angle), the reflected light intensity is measured, and the refractive index and the film thickness are simultaneously quantified by numerical calculation.
When the refractive index is distributed, the refractive index distribution can be obtained by using the inverse WKB method.

[Action]

The measurement accuracy of the optical constant according to the present invention depends on the measurement accuracy of the incident angle of the beam. That is, the measurement accuracy of the refractive index is ΔN
Then Given by Here, Δn _p , Δα, and Δθ _P are measurement errors of the prism refractive index, prism apex angle, and laser beam prism incident angle, respectively. Assuming that Δn _P = 1 × 10 ⁻⁵ and Δα = 0.5 seconds, when Δθ _P is measured with an accuracy of ± 3 seconds, the refractive index measurement accuracy is 1 × 10 ^{−5, which} is an extremely high value in principle. can get. Therefore, the optical constant according to the present method can be measured as a monitor of various thin film forming processes and can be fed back to the film forming conditions. Further, by adding two more prisms, it can be applied as a method for measuring the propagation loss of the optical waveguide. In this case, since the third prism is used as a monitor, there is a feature that the coupling efficiency is not affected by the measurement accuracy of the loss even when the second prism is moved.

The measuring method of the present invention is applied to sputtering, vacuum deposition, CVD
(Chemical Vapor Deposition), ion plating and other thin film forming methods can improve the controllability of the performance of the formed thin film and provide high performance optical devices, optical integrated circuits, and semiconductor devices. Will be possible.

In this specification, the term thin film is used in a broad sense. Conductive thin film (metal thin film etc.), dielectric thin film (optical waveguide, glass, SiN, LiNbO ₃ etc.), semiconductor thin film (S
i, Ge, GaAs, etc.) and polymer thin films (resist, passivation of polyimide, etc.). The thin film is formed by a sputtering method, a vacuum deposition method, a CVD method, an ion plating method, a thermal oxidation method, or the like. It is assumed that the thin film includes a layer continuously formed on the substrate surface by a method such as ion plating. The thin film is an optical integrated circuit,
It includes a constituent material that functions as an optical waveguide in a semiconductor element and an optical element.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail.

Embodiment 1. FIG. 1 shows an embodiment of the present invention, in which, for example, a LiNbO ₃ crystal is used for a substrate 1 and an optical waveguide 2 whose refractive index continuously changes in the depth direction of the substrate 1. 4 shows an example of measuring a refractive index distribution. The optical waveguide 2 was formed by a thermal diffusion method of metal Ti. The preparation conditions were as follows: Ti was deposited on the substrate 1 by a 1000 ° sputtering method and then thermally diffused at 1000 ° C. in an O ₂ atmosphere for 20 hours. Next, a prism 3 whose bottom is spherically processed is brought into close contact with the optical waveguide 2 via an air layer. By performing spherical processing, the optical coupling efficiency between the optical waveguide 2 and the prism 3 is improved. It is appropriate that the radius of curvature is 150 to 400 mm.
Here, the prism 3 is made of TiO ₂ (rutile) and has an apex angle of 55.
The degree and the prism refractive index n _P = 2854 and the radius of curvature of the bottom surface of 250 mm were used. The light beam is incident on the prism 3 by using, for example, a He—Ne laser having a wavelength of 0.633 μm as the light source 4, and adjusting the incident angle by using a driving device, for example, a pulse motor (not shown). 5 was performed.
FIG. 2 shows an example of a method of supporting the prism 3. The prism 3 is fixed to the holder 6, and the degree of close contact with the substrate 1 is adjusted by a push screw 7. The driving device may be controlled by a computer (not shown).

FIG. 3 (a) shows the trajectories of the light beam which is incident on the prism 3 at various angles and which propagates through the optical waveguide 2 and the light beam which is reflected at the bottom of the prism. Here, as described above, the light beam propagating through the optical waveguide 2 has a discrete value of m = 0, 1, 2,... With respect to the incident angle of the light beam.
Therefore, the incident angle of the light beam and the light intensity reflected on the bottom surface of the prism 3 are continuously measured by the light receiving element 8. The light receiving element 8 may be formed integrally with the prism 3 and the holder 9.

Here, the measurement principle will be described with reference to FIG. When measuring the refractive index _nf and the film thickness h of the thin film (optical waveguide) 2 formed on the substrate 1 (refractive index n _s ), a prism integrated with a light receiving element and having a spherical bottom is adhered to the thin film 2, Laser light is made incident on the prism. Then, the incident angle θ _P is changed to read the incident angle θ _{P at} which the intensity of the reflected light from the bottom surface of the prism is minimized, and the effective refractive index N corresponding to the propagation mode is calculated by equation (1).

Here, α is the prism apex angle and the refractive index of the prism.

Here, the prism to be used needs to be appropriately selected according to the refractive index of the thin film to be measured. As the prism material, BK-7 glass _{(n P = 1.52), GGG} (n P = 1.965), TiO 2
(N _P = 2.584) and GaP (n _P = 3.314).

Next, substituting N into the eigenvalue equation (2) of the next guided mode derived from Maxwell's wave equation,
The refractive index _nf and the film thickness h are calculated by making the equation (2) simultaneous.

Here, m is a mode number, and m = 0, 1, 2... K _X , γ
_S and γc are propagation constants in the incident direction of the laser light, Wave number k ₀ = 2π / λ λ: wavelength.

Next, a case where the refractive index in the depth direction of the medium changes continuously will be described with reference to FIG. In FIG. 3 (b), an optical waveguide 2 whose refractive index changes continuously is formed above the substrate 1. The light beam propagating through the optical waveguide 2 draws a locus of an arc, and draws a different locus depending on the propagation mode. Therefore, the effective refractive index N corresponding to the propagation mode is calculated by equation (1) as described above.

Next, the wave equation of the TE mode in the two-dimensional optical waveguide having the refractive index distribution of n (y) is obtained from Maxwell's equation: It is expressed as

Here, β: propagation constant in the x direction, μ ₀ : magnetic permeability in vacuum,
ω: angular frequency of light.

Using the effective refractive index N described above, equation (4) gives: Becomes When n (y) is known, finding an equivalent refractive index that satisfies equation (7) is an eigenvalue problem. Where WKB
According to the approximation method, the following eigenvalue equation is obtained.

Here, ytm: transition point of the m-order mode, n ₀ : surface refractive index.

Next, the inverse WKB method calculates the respective transition points yt ₁ , yt _2, ..., Yt from the effective refractive indices N ₁ , N ₂ ,.
This is a method of obtaining m and obtaining a sequence of points (Nt, yt ₁ ) and (Ntm, yTm). By connecting the dot sequence, the refractive index distribution can be obtained.

Further, when the refractive index of the substrate is larger than the refractive index of the thin film, the refractive index _nf and the thin film h of the thin film can be measured by simultaneously establishing the following eigenvalue equation, which is generally called a leaky mode.

FIG. 4 shows an example of the measurement data. The horizontal axis is a prism incident angle theta _P of the light beam, and the vertical axis represents the intensity of reflected light by the light receiving element. In the figure, the incident angle at which the reflected light intensity shows the minimum value corresponds to the effective refractive index Nm of each propagation mode (m, 0, 1, 2,...), And the value is calculated by the equation (1). Next, measurement data Nm of the effective refractive index corresponding to the above-described propagation mode
Is used to calculate a point sequence between the effective refractive index and the transition point according to the equation (8). Table 1 shows an example of the calculation results of the effective refractive index and the transition point.

When the effective refractive index Nm shown in Table 1 and the transition point, that is, the distance x from the substrate surface, are plotted, * shown in FIG. 5 is obtained. Next, when the refractive index distribution of the Ti diffused optical waveguide 2 is estimated from the diffusion theory and assumed to be a Gaussian distribution, and curve fitting is performed, a solid curve shown in FIG. 5 is obtained. The refractive index distribution n (y) is expressed as _{n (y) = n s +} Δn · exp- (y / dy) 2 ...... (10).

Here, n _s : substrate refractive index, Δn: refractive index change, dy: diffusion depth. As shown in Table 1, both the surface refractive index n ₀ and the diffusion depth dy are in good agreement between the analysis results and the values predicted by the diffusion experiment. The theoretical curve (solid line) shown in FIG.
And the calculated value * corresponded well, confirming the effectiveness of this method.

Also, the reproducibility by repeated measurement was 3σ = 0.00.
1 was good.

The above-described method of measuring the refractive index distribution is used as an application other than the metal diffusion type optical waveguide, in the process of manufacturing a semiconductor element,
The measurement of impurity concentration distribution by impurity diffusion or ion implantation into the Si substrate and the measurement of the thickness of the epitaxial growth layer can be performed by using infrared light as a light source.

Example 2 Next, an example of measuring the refractive index and the thickness of a TiO ₂ thin film used as a light-wave control loading layer on an optical waveguide in forming an optical integrated circuit will be described. Using BK-7 glass as the substrate 1, a TiO ₂ film 2 was formed by a reactive sputtering method. In order to control the composition of the TiO ₂ thin film, O ₂ gas is added to Ar gas to perform sputtering. Table 2 shows the measurement results of _nf and h of the films manufactured by changing the partial pressure ratio of O ₂ / Aγ as the sputtering conditions. As a result, a remarkable correlation is observed between the O ₂ / Aγ partial pressure ratio and n _f . Therefore, to measure the value of n _f as a monitor at the time of film formation, it can be stabilized in the film forming process by feeding back the film forming conditions.

As the above-mentioned monitoring method, there are a method of (1) sampling inspection of a sample, a method of providing a monitor chamber in a vacuum chamber, appropriately introducing a sample into the monitor chamber, and measuring in-process. Further, the above method can be applied to various thin film forming methods such as a vacuum evaporation method and a CVD method, and various thin films formed using the same.

Example 3 FIG. 6 shows a measurement example of a Si thermal oxide film important in a manufacturing process of a semiconductor element or an optical integrated circuit. Sample preparation is 400μ thick
The m single Si crystal substrate was heated at 1200 ° C. for about 30 hours in a flowing oxygen atmosphere humidified with steam using a quartz tube electric furnace to form a SiO ₂ film having a thickness of about 5 μm. Figure 6 is a horizontal axis like the fourth diagram described in Example 1 is the incident angle theta _P of the prism of the laser beam, and the vertical axis represents the intensity of reflected light from the prism bottom surface by the light receiving element. Table 3 shows the measurement results of the incident angle θ _P corresponding to each mode. Table 4 shows the calculation results of the refractive index _nf and the thickness h of the SiO ₂ film using the equation (9). Generally, the refractive index of SiO ₂ is 1.46. On the contrary,
In this method, 1.458981 was obtained. The standard deviation of n _f calculated for each mode was 2.46 × 10 ^−5, which was a good value. On the other hand, the measurement result of the film thickness was 3.28 × 10 ⁻³ μ with a standard deviation.
Although slightly lower than m and _nf , it is considered that the precision is sufficient for forming an optical integrated circuit or a semiconductor element.

The above-described measurement method can be applied to various thin films such as a resist and a passivation film.

Embodiment 4 FIG. 7 (a) shows another embodiment of the present invention, and FIG. 7 (b), FIG. 8 (a), FIG. 8 (b), and FIG. A method for measuring propagation loss of an optical waveguide which is important in forming an integrated circuit will be described. FIG. 7A is a perspective view of an apparatus for measuring a propagation loss. FIG. 7 (b) is a perspective view illustrating a case where the measuring device is viewed from another angle. Fig. 8 (a)
FIG. 8 (c) is a diagram for explaining a measuring method and a measuring principle of the propagation loss. The device shown in FIG. 7 (a) has a movable second prism 32 for taking out guided light propagating through the optical waveguide 2 to the outside in addition to the basic structure shown in the device shown in FIG.
And a third prism 33 for monitoring. Here, the method of measuring the propagation loss will be described in detail with reference to FIG. In FIG. 8, the position of the prism 3 is taken as the origin, the position of the prism 32 is x ₂ , the position after the movement of the prism 32 is x ₂ ′, and the position of the prism 33 is x ₃ . Fig. 8 (a)
In the above, if the power of the light guided to the optical waveguide 2 by the prism 3 is P ₀ and the intensity of the light emitted from the prism 33 is P ₃ , Becomes Here, γ is the coupling coefficient of the prism 33, and L is the propagation loss of the optical waveguide. Next, install the prism 32 to the position of the x _2, the emitted light intensity from the prism 32 and P _2, the prism
If the intensity of the emitted light from 33 is P ₃ ′, Becomes Further, assuming that the prism 32 is moved to x ₂ ′ and the radiated light intensities of the prisms 32 and 33 are respectively P ₂ ′ and P ₃ ″, Becomes Therefore, from (11) to (13), the propagation loss L of the optical waveguide 2 is Becomes

An example of the above-described propagation loss measurement is shown in Example 1.
As a result of measuring L of the Ti diffused LiNbO ₃ optical waveguide, L = 0.5 dB /
cm was obtained. In addition, good results were obtained with a repeat measurement error of 0.5% or less. According to this method, by providing the third monitoring prism 33, the measurement efficiency is improved because the coupling efficiency of the second prism 32 does not affect the measurement.

Embodiment 5 FIG. 9 shows another embodiment of the present invention, and shows a sputtering apparatus 11 as an example of a thin film forming apparatus necessary for forming an optical integrated circuit or a semiconductor element. In FIG. 9, after the chamber 12 is evacuated to a vacuum, a gas such as Ar is introduced from the flow control valve 13 and a high voltage is applied between the target 14 and the substrate holder 15 to ionize Ar and collide with the target. Let it. Then, the atoms on the target surface are repelled by Ar ions and deposited on the substrate 1. here,
In order to evaluate the physical property value, the film thickness, and the like of the thin film 3 in-sita, the film formation is temporarily stopped, and the prism holder 16 having the vertical mechanism is brought into contact with the monitor substrate 1. Next, chamber 12
Laser beam 17 from outside via mirrors 18 and 19
And the photodiode 8 detects the intensity of the reflected light.
Here, the mirror 19 can be rotated in 0.1 second units by a pulse motor (not shown), and the prism incident angle can be adjusted. Therefore, the film thickness and the refractive index can be measured with high accuracy of 1 × 10 ⁻⁵ without taking the sample into the atmosphere. Further, as described above (Example 2), since the refractive index of the formed thin film and the film forming conditions have a strong correlation,
By feeding back the refractive index measurement data to the film forming conditions, a thin film of stable quality can be formed. The present thin film forming apparatus can be applied to various thin film forming apparatuses such as a vacuum deposition apparatus, a CVD apparatus, and an ion plating apparatus in addition to a sputtering apparatus. In addition, this thin film forming apparatus is used for GaAs, ImP, TiO ₂ , ZnO, PL
It can be applied to film formation of any material such as ZT, Si ₃ N ₄ and SiO ₂ .

Embodiment 6. FIGS. 10 (a) and 10 (b) show another embodiment of the present invention, in which an optical pickup for an optical disk device is taken as an example of an optical integrated circuit and is necessary for forming the same device. The following shows an indispensable application example as a process monitor for measuring the refractive index and film thickness of various thin films.

Optical integrated circuit (OIC) shown in FIGS. 10 (a) and 10 (b)
In other words, the light emitted from the semiconductor laser 4 coupled to the glass block 20 is diffracted by the diffraction grating 21 and further refracted at the interface between the glass block and the substrate.
Is coupled to the optical waveguide 2. The guided light 23 is deflected by the SAW light deflector 24, enters the grating coupler 22 ', and is diffracted into the substrate. The light diffracted into the substrate is refracted at the interface between the substrate and the glass block, and then the diffraction grating 21 '
The light is diffracted by the glass block, is reflected by the end surface of the glass block, is emitted upward, and is condensed by a lens 25 having a mechanism for moving perpendicularly to the optical disk, and the bit (information) of the optical disk 26
Is collected. The light reflected by the optical disk 26 passes through the lens 25, the glass block 20 ', and the diffraction grating 21', is coupled to the waveguide again by the grating coupler 22 ', and then is incident on the condensing beam splitter 27.
The light is divided and condensed on the two-division photodiodes 28 and 28 'to read the bit information.

Hereinafter, a method for manufacturing the above-described OIC will be described in detail. Using an optically polished LiNbO ₃ crystal as the substrate 1, Ti was deposited to a thickness of 24 nm by sputtering, and thermal diffusion was performed to form an optical waveguide 3. The sputtering conditions were as follows: high frequency power 300 W, argon gas pressure 0.35 Pa, sputtering rate 0.4 nm / se
c. The thermal diffusion was performed by using an electric furnace, heating to 1000 ° C., flowing an argon gas atmosphere for 2 hours, and subsequently flowing an oxygen gas for 0.5 hours.

Here, the refractive index of the optical waveguide 2 was measured in the same manner as in the method described in Example 1, and as a result, the surface refractive index n ₀ = 2.220.
It was a TE single-mode waveguide having an effective refractive index N = 2.209.
These measured values are compared with the optical design values, and if there is an error, it can be accurately controlled by feeding back to the process conditions. Next, the optical waveguide 2
In order to form various gratings thereon, TiO ₂ was formed to a thickness of 100 nm by reactive sputtering. The sputtering conditions were as follows: using a TiO ₂ target, using argon and oxygen as the sputtering gas, a flow ratio of O ₂ and Ar of 0.7, and a sputtering gas pressure of
0.42 Pa, high frequency power 500 W, sputtering rate 0.1 nm / sec. The thickness and refractive index of TiO ₂ were measured in the same manner as in Example 2. Next, in order to finely process the TiO ₂ layer into a predetermined grating shape, a resist was formed on the TiO ₂ layer by a spin coating method. Here, chloromethylated polystyrene (CMS-EX) which is an electron beam resist is used as the resist.
R: Toyo Soda). Here, as a result of measuring the resist film thickness in the same manner as described above, it was 500 nm. After pre-baking the resist at 130 ° C. for 20 minutes, an electron beam was applied to a predetermined greeting shape. The irradiation conditions were an electron beam diameter of 0.1 μm and an irradiation amount of 16 μc / cm ² . After electron beam exposure, development was performed to form a resist mask. Thereafter, the grating layer was finely processed by ion etching. Conditions of the ion etching, a CF ₄ as an etching gas, and the pressure 3.8Pa, a high-frequency power 200 W, and etching time 15min. After the etching, the resist mask was removed to form a grating element. Then 21,2
C with respect to the diffraction grating, using the BK-7 glass as the substrate, in which the SiO ₂ to about 8μm thereon, the SiCl ₄ and O ₂ as a raw material 1 '
It was formed by a VD method, a vapor deposition method, sputtering, or the like. Next, in order to process SiO ₂ into a predetermined lattice shape by photolithography, a photoresist (OFPR800) was formed by a 1 μm spin coating method. After pre-baking the resist at 85 ° C. for 30 minutes, the resist was contact-exposed using a UV exposure apparatus using a photomask having a predetermined lattice shape. After the exposure, the film was immersed in chlorobenzene at 40 ° C. for 5 minutes and developed. Cr was vapor-deposited on the resist lattice pattern, and ultrasonic cleaning was performed in acetone to remove the resist, thereby forming a Cr mask. Thereafter, SiO ₂ was finely processed by ion etching using CF ₄ gas, and Cr was removed to form a lattice pattern. This photolithography technique can also be applied to the aforementioned fine processing of the grating layer. Substrate on which the above elements are formed, diffraction gratings 21, 21 'and BK-7
The glass blocks 20, 20 'are cut and polished at their respective end faces at a predetermined angle, and bonded with an adhesive having substantially the same refractive index as BK-7. (A), the optical IC of FIG. 10 (b) was formed. In order to evaluate the performance of the above-described OIC, a search for embedded data was performed in a read-only optical disk device. As a result, it was confirmed that the operation performed almost as designed. It was also confirmed that the test passed a predetermined durability test. Further, the above process monitor for measuring the refractive index and the film thickness for forming an optical integrated circuit can be applied to various optoelectronic components including optical communication products.

Embodiment 7 FIG. 11 shows another embodiment of the present invention, in which a MOS transistor is taken as an example of a semiconductor element, and an application example as a process monitor for measuring a film thickness in various semiconductor thin film forming processes is shown.

In FIG. 10, a silicon substrate 1 was a (100) n-type silicon wafer, the surface of which was mirror-finished, and a donor impurity concentration = 1 × 10 ¹⁵ cm ⁻³ (low efficiency of 4 to 6 Ω · cm). Next, as a gate insulating film, SiO ₂ 129 by thermal oxidation is used.
And SiN130 was formed by CVD. The conditions of the thermal oxidation were such that steam was sent as an oxidizing atmosphere, and oxidation was performed at 1000 ° C. for 100 minutes. VCD conditions are as follows: a gas mixture of 99% NH _{3 and} 1% SiH ₄ is supplied as a gas, the substrate temperature is 850 ° C., and the furnace vacuum degree is 0.5 Torr.
And 20 analyzes were performed.

Here, the thickness of the SiO ₂ thermal oxide film was measured in the same manner as in Example 3, and as a result, it was 600 nm. The thickness of the SiN film was measured in the same manner as in Example 2, and was found to be 500 nm. In the case where there is a variation in the film thickness, accurate control can be performed by feeding back to the process conditions.

Next, a window is formed in the drain-source region. First, a photoresist is applied to the entire surface, and the resist in the drain-source region is removed by a normal photolithography technique. Next, windows of the SiN film are opened by a plasma etching method using the resist as a mask. Furthermore, HF: NH ₄ F = 12: 100
A window of SiO ₂ is formed with the etching solution of SiN using SiN as a mask. Next, after removing the resist, B ₂ H ₆ -NH ₃
Using a system gas, a BN film 131 is deposited at about 1500 nm at a substrate temperature of 700 ° C.

Next, a diffusion heat treatment is performed at 1150 ° C. for 6 hours in an N ₂ atmosphere to form a P-type diffusion layer in the drain 132 and the source 33 region 133.
Further, Al electrodes 134 and 135 are formed on the gate insulating film. A
The electrodes 134 and 135 are formed by processing Al into a predetermined electrode shape by using vacuum deposition and ordinary photolithography and etching techniques as a film forming method.

In order to evaluate the characteristics of the MOS transistor described above, a drain voltage (V _D ) -drain current (I _D ) characteristic was measured. As a result, I _D of saturation region without depending on V _D, becomes a constant value, was found to show good saturation characteristics. Further, the process monitor of the semiconductor device described above can be applied to the manufacturing process of various microcomputers and memories including bipolar transistors in addition to MOS transistors.

The present invention has been described based on the embodiments. In the measurement of the refractive index of the thin film described above, when the thickness of the thin film is small, or when the refractive index difference between the thin film and the substrate is small, it is generally called a single mode waveguide, and in the equation (2), the mode number m = 0. Only light is guided. Therefore, the eigen equation (2) of the waveguide mode cannot be simultaneously established, and it is assumed that one of the refractive index _{nf and the} film thickness h is known.

Therefore, a method for solving the above-described problem will be described in detail below. Laser light, which is a light source, generally emits linearly polarized light. Also, two types of linearly polarized light, S-polarized light and P-polarized light, are known. Further, it is known that the refractive index of a medium used as a thin film is slightly different depending on the above-mentioned polarized light. Therefore, when measuring the refractive index of the thin film described above, the polarization plane of the laser beam is rotated, and the incident angle θ _{P at} which the intensity of the reflected light from the prism bottom surface with respect to each of the S-polarized light and the P-polarized light is measured. I do. Next, by calculating the effective refractive index N for each polarized light by the formula (1), it is possible to simultaneously measure the refractive index and the film thickness of the single mode waveguide by the formula (2).

〔The invention's effect〕

As described above, according to the present invention, optical constants (refractive index, film thickness, refractive index distribution, etc.) of a thin film can be measured with high accuracy. By feeding back these measured values to the thin film forming process, a high-performance optical integrated circuit or semiconductor device can be stably produced with good reproducibility. Further, by adding two prisms to the above-described method of measuring the optical constant of the thin film, the propagation loss of the optical waveguide can be measured with high accuracy, thereby improving the performance of the optical integrated circuit and optimizing the optical design. There is.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a thin film optical constant measuring apparatus according to the present invention. FIG. 2 is a sectional view showing an example of the prism holding method. FIG. 3 (a) shows one embodiment of the present invention, and is a diagram for explaining the trajectory of a light beam propagating to a medium via a prism. FIG. 3 (b) shows an embodiment of the present invention and is a diagram for explaining the trajectory of a light beam propagating through a prism to a medium whose refractive index changes continuously. FIG. 4 is a diagram showing the relationship between the incident angle of the prism by the measurement of the present invention and the intensity of the light reflected by the light receiving element. FIG. 5 is a diagram showing a refractive index distribution characteristic obtained by measurement according to the present invention. FIG. 6 is a diagram showing a relationship between the prism incident angle and the reflected light intensity by the light receiving element according to the measurement of the present invention. FIG. 7 (a) shows another embodiment of the present invention, and is a perspective view showing an optical waveguide propagation loss measuring device. FIG. 7 (b) shows the seventh embodiment.
It is a perspective view showing the case where the measuring device of Drawing (a) is seen from another angle. FIGS. 8 (a) to 8 (c) are diagrams for explaining a measuring method and a measuring principle of the propagation loss. FIG. 9 shows another embodiment of the present invention and is a view showing a thin-film manufacturing apparatus provided with a thin-film optical constant measuring apparatus. FIG. 10 (a) shows another embodiment of the present invention and is a plan view of an optical integrated circuit prepared by monitoring the optical constants of the thin film. FIG. 10 (b) is a front view of the optical integrated circuit of FIG. 9 (a). FIG. 11 shows another embodiment of the present invention and is a view for explaining a thin film manufacturing process including a process of monitoring a thin film optical constant. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Optical waveguide, 3 ... Prism, 4 ... Light source, 5 ... Rotary table, 6 ... Holder, 7 ... Push screw, 8 ... Light receiving element, 9 ... Holder.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazumi Kawamoto 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd. Production Technology Laboratory Co., Ltd. (56) References JP-A-2-244106 (JP, A) JP-A-57-120844 (JP, A) JP-A-64-35306 (JP, A) JP-A-53 JP-A-136886 (JP, A) JP-A-60-236004 (JP, A) JP-A-53-130061 (JP, A)

Claims (18)

(57) [Claims] 1. A prism having a bottom surface in close contact with a thin film, light from a light source is incident on the prism while changing the incident angle, and the light is incident on the thin film from the bottom surface of the prism. The light intensity of the reflected light from the bottom surface of the prism is measured, the incident angle at which the light intensity is minimized is determined, and the effective refractive index is calculated using the determined incident angle, the vertex angle of the prism, and the refractive index as parameters. A method of calculating a plurality of effective refractive indices for a plurality of propagation modes, and calculating an optical constant of the thin film based on the plurality of calculated effective refractive indices. 2. The method according to claim 1, wherein the calculated optical constant is a refractive index or a film thickness of the thin film. 3. The method according to claim 1, wherein the calculated optical constant is calculated based on the effective refractive index using a WKB method or an inverse WKB method. 4. The accuracy of the calculated effective refractive index is 1 × 10.
^{2. The} method for measuring optical constants of a thin film according to claim 1, wherein the value is not less than ^-5 . 5. The method for measuring the optical constant of a thin film according to claim 1, wherein a laser beam having a different wavelength is used as the light source, and a refractive index dispersion as an optical constant of the thin film is calculated. 6. The method according to claim 1, wherein a laser beam having a different polarization state is used as the light source, and a refractive index, which is an optical constant of the thin film, is calculated. 7. A first prism, a second prism, and a bottom surface of a third prism are placed in close contact with a thin film, and first light from a light source is incident on the first prism. The first light is incident on the thin film from the bottom surface of the prism, the first light is propagated in the thin film, and the first propagated light is emitted by the third prism,
A first light intensity of the first emitted light is measured, a second light is incident on the first prism from a light source, and the second light is applied to the thin film from a bottom surface of the first prism. Incident, and propagates the second light into the thin film;
Is emitted by the second prism, a second light intensity of the second emitted light is measured, third light is incident on the second prism from a light source, and the second light is emitted from the light source. The third light is incident on the thin film from the bottom surface of the prism, and the third light is propagated in the thin film.
Is emitted by the third prism, a third light intensity of the third emitted light is measured, the second prism is moved, and the first prism is moved from the light source to the first prism. 4, the fourth light is incident on the thin film from the bottom surface of the first prism, the fourth light is propagated in the thin film, and the fourth propagated light is moved in the thin film. The fourth emitted light is measured by the second prism, the fourth light intensity of the fourth emitted light is measured, and the fourth propagated light is reflected at the interface of the thin film. The fifth propagating light is emitted by the third prism, the fifth light intensity of the fifth emitted light is measured, and the fifth light intensity is converted to the first to fifth light intensities. Calculating the propagation loss of light propagating in the thin film based on the thin film optical constant. Measurement method. 8. A first prism, a second prism, and a bottom surface of a third prism are placed in close contact with a thin film, and first light from a light source is incident on the first prism. The first light is incident on the thin film from the bottom surface of the prism, the first light is propagated in the thin film, and the first propagated light is emitted by the third prism,
A first light intensity of the first emitted light is measured, a second light from a light source is incident on the first prism, and the second light is applied to the thin film from the bottom surface of the first prism. , The second light is propagated in the thin film, and the second propagated light is emitted by the second prism,
Measuring a second light intensity of the second emitted light; reflecting the second propagated light at an interface of the thin film; propagating the second light as a third light in the thin film; The third light is emitted by the third prism, the third light intensity of the third emitted light is measured, the second prism is moved, and the fourth light from the light source is sent to the first prism. Light is incident, the fourth light is incident on the thin film from the bottom surface of the first prism, the fourth light propagates in the thin film, and the fourth propagated light is moved. The light is emitted by the second prism, the fourth light intensity of the fourth emitted light is measured, the fourth propagated light is reflected at the interface of the thin film, and the fifth light is reflected in the thin film as the fifth light. The fifth propagating light is emitted by the third prism, and the fifth emitted light is emitted by the third prism. Measuring a fifth light intensity of said light, and calculating a propagation loss of light propagating in said thin film based on said first to fifth light intensities. 9. A thin film, a light source, a prism disposed in close contact with the bottom surface of the thin film, and light from the light source propagates through the prism and enters the thin film from the bottom surface of the prism. A light-receiving device that receives reflected light generated by being reflected at the bottom surface of the prism through the prism and measures the light intensity of the reflected light; and a holding driving unit that holds the thin film and the prism and displaces a relative position of each other. And a calculation control means for controlling the holding and driving means and calculating the optical constant of the thin film based on the light intensity. 10. The apparatus according to claim 9, wherein said calculation control means calculates a refractive index, a film thickness, or a refractive index distribution.
The optical measuring device as described in the above. 11. An apparatus according to claim 9, wherein the bottom surface of said prism is spherically processed. 12. A radius of curvature of the spherical processing is 150 to 400 nm.
12. The apparatus for measuring a thin film optical constant according to claim 11, wherein: 13. An apparatus according to claim 9, wherein said prism and said light receiving device are integrally formed. 14. An apparatus according to claim 9, wherein said light is laser light having a different wavelength, and said optical constant is refractive index dispersion. 15. An apparatus according to claim 9, wherein said light is laser light having a different polarization state. 16. A computer system comprising: a plurality of prisms for emitting light incident on the thin film by the prism; and a plurality of light receiving devices for receiving light emitted from the plurality of prisms, respectively. The apparatus for measuring a thin film optical constant according to claim 9, wherein the means calculates a propagation loss. 17. An apparatus according to claim 16, wherein at least one of said plurality of prisms is movable. 18. An apparatus for measuring the optical constant of a thin film according to claim 9, further comprising a holding drive means for holding said thin film and said prism and displacing a relative position between said thin film and said prism.