JPH0394104A - Film thickness measuring method and film thickness measuring device and film forming device using it - Google Patents

Abstract

PURPOSE:To measure with high accuracy the film thickness of an optical thin film which is being formed by using a monochromatic photometric method, and also, to execute the film thickness control with high accuracy by executing simultaneously the photometry by the combination of plural wavelength and an incident angle. CONSTITUTION:An electron beam vapor deposition device is provided with a chamber 15 for containing a substrate 14 to be processed, a vacuum pump 18, a vapor deposition source 19, etc., and by radiating an electron beam from the vapor deposition source 19, a vapor deposition substance is emitted, reaches the lower face of the substrate 14 and forms an accumulated film 13. Also, this device is provided with two photometric systems, provided with characteristic X-ray sources 11a, 11b for radiating a monochromatic light from the oblique direction to the substrate 14, and also, X-ray detectors 16a, 16b using a proportional counter tube for detecting independently each reflected light from the substrate 14. The X-ray sources 11a, 11b and the X-ray detectors 16a, 16b consist of a structure being capable of varying an angle against the substrate 14. In this state, since the photometry in the monochromatic photometric method is not executed by the combination of one wavelength and an incident angle but executed simultaneously by the combination of plural wavelength and the incident angle, the accuracy for measuring the film thickness can be improved.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Application in Industry) The present invention relates to film thickness measurement technology, and in particular to a film thickness measurement method and film thickness measurement method for measuring film thickness in a film shape. The present invention relates to an apparatus and a film forming apparatus equipped with this film thickness measuring apparatus.

(Prior Art) Conventionally, methods for measuring the thickness of a thin film can be divided into two types: those that can be measured during film formation, and those that can be measured after film formation. Film thickness a that can be measured during film formation
The 1st determination method includes the crystal oscillator method and the 1st optical method.
Examples include 11-color Allj photometry, two-color photometry, wavelength scanning method, and ellipsometry. Film thickness measurement methods that can be measured after film formation include the stylus method, multiple beam interference method as an optical method, phase contrast microscope, and ellipsometry.

Each has its advantages and disadvantages, and the film material to be formed,
The film is formed using an appropriate film thickness measurement method depending on the film thickness and film structure.

For example, when the film material to be formed is a 111-layer film with a film thickness of several microns, the film is optically opaque, so methods such as the stylus method and multiple beam interference method are effective, and optical methods Monochromatic photometry is not suitable. Further, when the film to be formed is a multilayer film, methods such as a stylus method that can be measured only after the film is formed are not suitable, and methods that can perform measurements during the film formation are effective. However, among these methods, the crystal oscillator method has the drawback of accumulating film thickness errors.

Furthermore, when the thickness of the film to be formed is on the order of several tens of layers, the measurement limits of multiple beam interference method, stylus method, etc. are exceeded. In addition, in two-color photometry, since the wavelength is in the X-ray region, one wavelength is an integral multiple of the other wavelength.
There is no filter to extract different wavelengths (two colors), and therefore characteristic X-rays may be used.

However, using characteristic
It is extremely difficult to find one wavelength. Therefore, in the case of such ultra-thin films, monochromatic photometry is used. Eribsometry and quartz crystal methods are used.

Incidentally, in the current semiconductor industry, research and development of X-ray lithography is active as integrated circuits become more highly integrated, and on the other hand, X-ray microscopes and the like are also being developed. As research and development in the X-ray wavelength region progresses,
Rapid progress is also being made in the development of X-ray reflectors, which are radiation optical elements.

The X-ray reflecting mirror is made by alternately laminating two materials with greatly different optical constants, and the thickness of each layer is one-fourth of the wavelength used, and is several to several hundred λ. The crystal oscillator method, ellipsometry, and monochromatic photometry are used to measure the film thickness in forming this X-ray multilayer film reflector (M.Ya
mamotoat. SPIEvo1.68g, 99(
198G), E. Spillcr SPIE5 vol. 563.387 (1985)). Among them, as mentioned above, the crystal resonator method has the disadvantage that film thickness errors are accumulated when forming a multilayer film. Furthermore, it is unstable against temperature changes and is not suitable for vapor deposition of high melting point metals. On the other hand, i11. Color photometry does not accumulate film thickness errors and is very stable against temperature changes. Furthermore, since the measurement is performed at the wavelength and incident angle actually used in the reflector, it has the advantage of being able to measure reflectance and other properties of the reflector at the same time as measuring the film thickness, making it extremely effective for forming X-ray reflectors. It is a means.

This monochromatic photometry method is used within the film forming system (for example, inside the vapor deposition equipment).
By installing a monochromatic photometry system in the λ
/4 film, 3λ/4 film, etc. can be obtained. The basic configuration is shown in Figure 4. It is assumed that raw material vapor is supplied from the evaporation source 46 to the lower surface of the substrate 42 to be processed, and thereby the thin film 43 is deposited on the lower surface of the substrate 42 . Light 41 from a monochromatic light source 40 is obliquely irradiated onto a substrate 426 , and the reflected light is detected by a light receiver 44 . The output of the light receiver 44 is supplied to a waveform memory 45 and stored therein. Then, the thickness of the thin film 43 is measured based on the contents stored in the waveform memory 45.

In the case of an X-ray multilayer film, λ/4 layers are stacked, and the wavelength for photometry is also X-ray. Figure 5 shows the wavelength of 44.7 (C - Kα) of a tungsten film formed on a silicon substrate.
) shows the change in X-ray reflectance.

It can be seen that as the film thickness increases, the reflection intensity changes in a sine curve. By stopping film formation at this extreme value of strength, a λ/4 film (film thickness 200 in this case) can be obtained.

Note that the peak of the reflection intensity is determined by the refractive index of the film as n and the film thickness as d.
2nd cos θ: mA (m is a positive integer) is obtained when the angle of 2-person incidence is θ and the wavelength of the incident light is A.

However, this type of method has the following problems. That is, it is very difficult to accurately detect the extreme value of the reflected light intensity as an extreme value during film formation, and even if the film formation is stopped after detecting the extreme value, the film will always be thicker. 2 colors fl
The ll light method is a method that reduces the errors of the color photometry, but as described above, in the X-ray wavelength region, it is impossible to obtain suitable two-color wavelengths that can be used for photometry.

(Problems to be Solved by the Invention) As described above, as a film thickness measurement method for forming optical thin films such as multilayer film formation for X-ray reflecting mirrors and reflective rib film formation, H effect is not suitable for non-'J:9. There are monochromatic photometry and two-color photometry that can simultaneously measure the optical properties (reflectance, etc.) of an optical thin film being formed during film formation. Furthermore, in a wavelength region such as X-rays where no suitable filter exists, two-color photometry cannot be used, and only monochromatic photometry is used as an effective method for measuring film thickness. However, the monochromatic photometry method has a problem in that the accuracy of film thickness control is poor in principle as described above, and the film thickness always ends up being too thick.

The present invention has been made in consideration of the above circumstances.
The purpose of the present invention is to provide a film thickness determination method that can measure the film thickness of an optical thin film that is being formed using the photometric method, and that enables highly accurate film thickness measurement. It's about doing.

Another object of the present invention is to provide a film thickness measuring device for carrying out the above method, and a film forming device that enables highly accurate thickness control.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to convert 7lll1 light into 1 in monochromatic photometry.
The purpose of this method is to improve the accuracy of film thickness measurement by simultaneously performing photometry using multiple combinations of wavelengths and angles of incidence, rather than using a single combination of wavelength and angle of incidence.

That is, in the present invention, an electromagnetic wave is incident on a substrate to be used for forming a thin film, and the thickness of the thin film being formed is determined from the extreme value of the reflected intensity.
1111 In the crotch thickness i'llll standard method, the same II. When the electromagnetic waves of 9 combinations of two or more wavelengths and incident diagonals are detected in 7, and the wavelength of the incident electromagnetic waves is 8 and the angle of incidence is θ, it is defined as D-A-'eosθ, then the film to be measured is D of the combination of wavelength and human 1J angle that gives the first extreme value of the thickness value
In this method, the value of DA is used, and the incident angle and wavelength are used such that the value of D of other electromagnetic waves is an integral multiple of DA.

The present invention also provides at least two single-wavelength radiation sources that irradiate electromagnetic waves onto a substrate to be subjected to thin film formation, a receiver that independently detects reflected waves from the substrate, and a receiver that independently detects reflected waves from the substrate. A film thickness measuring device comprising a means for measuring the thickness of a thin film formed on a substrate from the extreme value of wave intensity, wherein D is the wavelength of the electromagnetic wave irradiated to the substrate and θ is the incident angle.
= Λ-1 cos θ, one of the single wavelength radiation sources is set to the value DA of the combination of wavelength and incidence angle that yields the first extreme value at the film thickness value to be measured, and the other The incident angle and wavelength are set so that the value of D of the single wavelength radiation source is an integral multiple of DA.

10 Furthermore, the present invention is such that the film thickness measuring device is incorporated into a film forming apparatus comprising a chamber containing a substrate to be subjected to film formation and means for supplying a film forming material to the surface of the substrate. It is.

(Function) According to the present invention, the change in reflectance obtained with one photometric system is as shown by the dashed line in FIG.
The reflection skew change obtained with another photometric system in which the value of D is, for example, 5 times (the period is 1/5) is as shown by the solid line in the figure.

Comparing the dash-dotted line and the solid line, the film thickness corresponding to the first extreme value (λ/4) of the curve shown by the dash-dotted line is the same as the film thickness corresponding to the third extreme value of the curve shown by the caustic line. Match. Therefore,
In the conventional method, to form a λ/4 film, it was necessary to detect the first extreme value of the reflectance from the curve shown by the dashed line in Figure 6, but the change in reflectance with respect to the change in film thickness was can be detected from the third extreme value of the curve shown by the solid line with a short cycle, thereby making it possible to improve the accuracy of film thickness measurement. Here, in order to detect the third extreme value of reflectance only from the curve shown by the solid line, it is necessary to count the extreme values, and the circuit configuration becomes complicated. By using two curves, the dashed line and the solid line, the extreme value of the dashed line can be easily determined from the extreme value of the large line. In addition, the dashed line 2
The film thickness corresponding to the extreme value after the second extreme value (3λ
/4) is the 8th point on the solid line, and the 3rd extreme value is the 13th point on the length line, and so on, from one value to the next extreme value on the dashed-dotted line, there are 5 extremes on the solid line. value will exist.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing a film forming apparatus according to an embodiment of the present invention. This device is a combination of an electron beam evaporation device and a film thickness measuring device using monochromatic photometry.

The electron beam evaporation apparatus includes an electron beam gun (not shown) that irradiates an electron beam onto a chamber 15 that accommodates a substrate 14 to be processed, a vacuum pump 18 that evacuates the inside of the chamber 15, an evaporation source 19, and a deposition layer 19. ), etc. Then, a deposition material is emitted from one deposition source by irradiation with an electron beam, and this reaches the lower surface of the substrate 4 to form a deposited film 13.

Two fflll optical systems were provided as film thickness measuring devices.

That is, two characteristic X-ray sources 11a and 1lb of the electron beam excitation type are provided to uniformly illuminate monochromatic light from an oblique direction to the substrate 14, and a proportional coefficient tube is provided to independently detect each reflected light from the substrate 14. Two X-ray detectors 16a and 16b were provided. These X-ray sources 11a, llb and X-ray detector 1
6a16b has a structure that allows its angle to be changed with respect to the substrate 14. In other words, it is possible to change the incident angle of X-rays. Further, each detection output of the X-ray detectors 16a and 16b is stored in a waveform memory 17, and the film forming operation is controlled based on the stored contents.

13 Next, a film forming method using this apparatus will be explained.

An X-ray multilayer film reflector using tungsten (W) and silicon (St) that can obtain the highest reflectance at a wavelength of 44.7λ (C-Kα) and an angle of 1114 of 85 degrees was formed on a silicon substrate. .

The thickness of one layer is 139λ for W and 200 for Si.

First, for comparison, a case will be shown in which an X-ray multilayer film reflecting mirror is formed using one of the two photometric systems using the conventional lj color AIII light method.

Naturally, the photometry was performed using the wavelength and incidence angle used by the reflector. The results of reflectance changes at this time are shown in Figure 2 (
Shown in a). Each time the first extreme value appeared, the deposition was stopped and the next film material was deposited.

It can be seen that the reflectance increases as the number of layers increases, and the increase stops at the IOth layer. Also, its reflectance is 1
It was 5%. In addition, from FIG. 2(b), which shows the reflectance of the second to fourth layers enlarged in order to see in detail the vicinity of the extreme value of the change in reflectance, it can be seen that the vapor deposition is stopped after the extreme value has been passed. On average, an amount of about 14 liters of 10% was deposited. This is an error that occurs because an extreme value cannot be detected as an extreme value until after the extreme value has passed. In other words, it's a trick! This is a problem with the 11-color photometry method.

Next, a case will be shown in which the same multilayer film is formed using two photometric systems according to the present invention, and the film thickness is measured at the same time using two different combinations of wavelengths and angles of incidence.

Here, if the refractive index of the film is n, the film thickness is d, the incident angle is θ, and the wavelength of the incident light is A, then an extreme value appears in the detection signal at 2ndcosθ=mA (m is a positive integer). From this equation, it becomes, and if ( A /eosθ) of photometric system B is set to l/3 with respect to photometric system A, then photometric system B
The third extreme value of i5111 coincides with the first extreme value of optical system A, and when (A/cos θ) is set to 1/5, the fifth extreme value of optical system B becomes the first extreme value of optical system A. coincides with the extreme value of

In other words, D = Λ - cos θ is defined, and the first extreme value is the film thickness that should be determined by i'llll. By doubling it, the plurality of extreme values of photometric system B can be matched with the first extreme value of photometric system A. In this example, one wavelength and incidence angle combination (photometry system A) is the wavelength 44.7 and the incidence angle 8, which are actually used in the reflecting mirror.
5 degrees, and the value of D is 1cosθ=1.95X 10
-3.

The second is a combination of a wavelength and an incident angle that have a D value that is an integral multiple of this D value, so each value can be appropriately selected. In the same case, the wavelength was the same at 44.7 degrees, the incident angle was set at 64 degrees, and a combination of wavelength and incident angle (7TllI optical system B) with a D value of 5 times was used.

The change in reflectance of the δIl1 optical system A is shown in FIG. 3(a).

Further, FIG. 3(b) shows changes in reflectance of the allj optical system A and the δIl1 optical system B between the second to fourth layers.

From Figure 3(b), photometric system B is exactly one-fifth of photometric system A.
It can be seen that it changes with the period of . In other words, the reflectance change of photometric system B is more sensitive to the increase in film thickness than that of photometric system 8.
By stopping the vapor deposition at the extreme value of this photometric system B, it becomes possible to control the film thickness with higher accuracy. If we look closely at the vicinity of the extreme value of the AIII optical system A in FIG. 3(b), we can see that the deposition is successfully stopped almost at the extreme value. The error is within about 2 points. Compared to the case of monochromatic photometry, which had an error of about 10 in, the accuracy of film thickness control was significantly improved. The meaning of measuring at the same time with photometric system A is that the ratio of 8.1 at the wavelength and angle of incidence actually used for the reflecting mirror in optical system A is 1', so the characteristics of the reflecting mirror cannot be measured. It has the advantage of being able to be fixed during formation, and furthermore, as the number of layers increases, 4I
This is because if only the lj optical system 2 is used, the number of extreme values of reflectance becomes enormous, making it difficult to recognize the intended extreme value of film thickness.

It can be seen from the rapid change in reflection of photometric system A in FIG. 3(a) that the highest reflectance of 28% was obtained with eight layers. This value requires fewer layers than when measuring film thickness using monochromatic photometry.
Moreover, it shows that a higher ratio of 1.1 was obtained, which is the result of higher precision in film thickness control.

17 Thus, according to this embodiment, two photometric systems are used, and the value of D (=Λ' cosθ) in one photometric system is set to DA, and the value of D in the other illll optical system is set to an integral multiple of DA. By doing so, the thickness of the optical thin film being formed can be measured with high precision.

By controlling the vapor deposition operation based on this measurement, the thickness of the thin film formed on the substrate can be set with high precision. Therefore, an X-ray multilayer film reflecting mirror or the like can be formed with high precision, and its usefulness is tremendous. Furthermore, since the D-DA photometry system sets the wavelength and incidence angle that are actually used for the reflecting mirror, it has the advantage that the characteristics of the reflecting mirror can be measured while the film is in the form of a film.

Note that the present invention is not limited to the length examples described above. In the embodiment, the wavelength of the photometric system was X-rays, but the wavelength is not limited to X-rays as long as the wavelength is selected according to the characteristics of the thin film to be formed.

In addition, the combination D (=Λ-'cosθ) of wavelength A and incident angle θ in the two photometric systems was determined so that one was five times that of the other, but it may vary depending on the film material to be formed, film thickness, etc. You can multiply it by an appropriate integer. Furthermore, 2
Although the film thickness i11l1 was determined using two illumination optical systems, it is conceivable to simultaneously measure the film thickness using three or more ap+ optical systems in order to further improve accuracy.

For film formation, an electron beam evaporation device may be used, or a film forming device using any other method may be used as long as it can be equipped with a photometric system. Furthermore, the film to be formed is not limited to multilayer reflective mirrors, but can also be used for other purposes, such as antireflection films and thin films completely unrelated to optics. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention! 11 The thickness of the optical thin film being formed is measured by simultaneously performing photometry using multiple wavelengths and angles of incidence, rather than using a combination of one wavelength and angle of incidence in monochromatic photometry. It is possible to measure the film thickness with high accuracy. Also, if this is applied to film thickness formation, highly accurate film thickness control can be achieved in one step.
9. It becomes possible to realize a film forming apparatus that is possible.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing a film forming apparatus according to a major embodiment of the present invention, and Fig. 2 is a characteristic showing reflectance changes when film thickness is measured using one of the monochromatic δII light systems. Figures 3 and 3 are characteristic diagrams showing changes in reflectance when film thickness is measured using both monochromatic photometry systems, and Figures 4 and 5 are for explaining the problems with the conventional method. , Figure 4 is a diagram showing the basic principle of 01 color photometry, Figure 5 is! The wavelength of the tungsten film formed on the silicon substrate when using 11-color photometry is 44,
Figure 6 is a diagram showing the change in reflectance for a 7-input system, and is for explaining the effect of the present invention, and is a diagram showing changes in reflectance for a photometry system where the value of D is 1 and a photometry system where the value of D is 5 times. be. 1 1 a, 1 1 b - X-ray source, 13... thin film, 14... substrate to be processed, 15... chamber, 20 6a, 16b-=X-ray detector, 7... waveform memory, 8 ...vacuum pump, 9...evaporation source,

Claims (3)

[Claims] (1) In a film thickness measurement method in which electromagnetic waves are incident on a substrate to be used for forming a thin film, and the thickness of the thin film being formed is measured from the extreme value of the reflected intensity, two or more wavelengths are incident on the substrate at the same time. When electromagnetic waves of a combination of angles are incident, and the wavelength of the incident electromagnetic waves is Λ and the angle of incidence is θ, it is defined as D=Λ^-^1cosθ, the wavelength at which the first extreme value is obtained in the film thickness value to be measured. A method for measuring film thickness, characterized in that the value of D of the combination of and angle of incidence is set to D_Λ, and the value of D of other electromagnetic waves is used such that the value of D is an integral multiple of D_Λ. (2) at least two single-wavelength radiation sources that irradiate electromagnetic waves onto a substrate to be subjected to thin film formation; a receiver that independently detects each reflected wave from the substrate; and reflections obtained by these receivers. and means for measuring the thickness of the thin film formed on the substrate from the extreme value of the wave intensity, and where the wavelength of the electromagnetic wave irradiated to the substrate is Λ and the angle of incidence is θ, D=Λ^-^1cosθ is defined. Then, one of the single wavelength radiation sources is set to the value D_Λ of the combination of wavelength and incident angle that yields the first extreme value of the film thickness value to be measured, and D of the other single wavelength radiation source is set to D_Λ. A film thickness measuring device characterized in that the incident angle and wavelength are set such that the value of D_Λ is an integral multiple of D_Λ. (3) a chamber containing a substrate to be subjected to film formation; means for supplying a film-forming material to the surface of the substrate; at least two single-wavelength radiation sources that irradiate the surface of the substrate with electromagnetic waves; A film forming apparatus equipped with a receiver that independently detects each reflected wave from the receiver, and means for stopping the film forming operation or changing the type of film to be formed based on the extreme value of the reflected wave intensity obtained by these receivers. When the wavelength of the electromagnetic waves irradiated to the substrate is Λ, and the angle of incidence is θ, it is defined as D=Λ^-^1cosθ, then one of the single wavelength radiation sources is used at the first film thickness value to be measured. The value of D for the combination of wavelength and incident angle that yields an extreme value is set to D_Λ, and the value of D for other single wavelength radiation sources is set to an incident angle and wavelength that are an integral multiple of D_Λ. A film forming device characterized by: