JPH0479405B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the angle of incidence of an ellipsometry monitor.

Conventionally, emission spectroscopy, atomic absorption spectrometry, voltage change method, reflectance change method, mass spectrometry, etc. have been widely used to monitor the film thickness of film forming equipment, but recently, the above-mentioned methods have been used from the viewpoint of obtaining higher measurement accuracy. Ellipsometry has been replaced by ellipsometry. Ellipsometry is a method that can accurately determine the thickness and optical constants of thin films by measuring changes in the state that occur when polarized light is reflected on the sample surface. The device usually has a light source section, a light receiving section, and a sample holder integrally formed on a precision-machined pedestal, and the incident angle is set on this pedestal. Therefore, when incorporating such a device into a vacuum process device, it is actually difficult to integrate the entire device and adjust it, and if the entire monitor device is integrated and installed, the incident angle setting angle accuracy also deteriorates.

Therefore, this invention provides a new method for measuring the angle of incidence that allows the angle of incidence of the polarization analysis monitor to be roughly set without being precisely set in advance, and the angle of incidence can be easily and accurately determined when the monitor is installed in a vacuum process device. It is about providing law.

By the way, considering the reflection of light by a thin film, as shown in Figure 1, the refractive index of the substrate is ns, the refractive index of the thin film is n, and the film thickness is d. If it is incident on
The direction parallel to the plane containing the incident ray and the normal, i.e. p
The reflectance of each component in the direction and the direction perpendicular to the above plane, that is, the s direction, is It is expressed as δ=2π/λ・2nd cos ₁ (λ: wavelength of light, ₁ : angle of refraction within the thin film).

r ₁ p, r ₁ s are the Fresnel reflection coefficients in vacuum and thin film, r ₂ p, r ₂ s are Fresnel reflection coefficients in thin film and substrate, respectively. , where ₂ is the refraction angle within the substrate. It is the ratio of 1Rp and Rs that determines the change in the polarization state between the incident light and the reflected light, that is, the ratio of the reflectance of the polarization p component and s component is 1Rb/1Rs=Rpe ⁱ 〓 ^p /Rse ⁱ 〓 ^s = r ₁ p + r ₂ pe ^-2i 〓/1 + r ₁
pr ₂ pe ^-2i 〓/r ₁ s＋r ₂ se ^-2i 〓／1＋r ₁ sr ₂ se ^-2i 〓≡tan
Ψe ⁱ 〓(3) Therefore, it can be expressed as tanΨ ^- = Rb/Rs, Δ=δp−δs (4) These Ψ and Δ are called ellipsometry parameters, and these parameters are It is recognized that a certain relationship holds between the optical constants of the surface, the film thickness, and the angle of incidence. Therefore, if the film thickness d and refractive index n of the thin film are known, the ellipsometry parameters Ψ and Δ can be determined by calculating in the order of the above equations (2), (1), and (3).

Therefore, in the incident angle measurement method according to the present invention, the angle of incidence is first roughly set, and then the optical axis is adjusted using a sample whose optical constants are known and whose surface has a thin layer with a different optical constant. The polarization analysis parameters Ψ and Δ of the sample are measured using the polarization analysis monitor based on the above equations, and the angle of incidence is accurately determined from these values.

An embodiment of the present invention will be described below with reference to FIG. 2 of the accompanying drawings.

In the illustrated embodiment, a case will be considered in which the angle of incidence is determined using a raw silicon wafer as a sample. Silicon He-Ne laser wavelength (6.328Å)
The optical constant n in is n=3.85−0.02i. The ellipsometry parameters Ψ and Δ of this sample are the incident angle =
Measure near 70°. Considering that there is a natural oxide film on the raw silicon wafer, and assuming that the film has a refractive index of n = 1.45 and has a thickness of d, calculate the ellipsometry parameters Ψ and Δ for each incident angle of 0.1°, The results are shown in the diagram of FIG. Second
In the figure, the arrows indicate the accuracy range of Ψ and Δ obtained with a normal polarization analyzer, and the accuracy is set to ±0.05° for the parameter Ψ and ±0.1° for the parameter Δ.

Therefore, as can be seen from FIG. 2, the incident angle and the thickness d of the natural oxide film can be determined from the values of the measured polarization analysis parameters Ψ and Δ. Also, even if there is an error of ±0.1 in the refractive index n of the natural oxide film, n = 1.35 for the =70.0° curve in Figure 2, and n =
As shown in 1.55, the error in the angle of incidence determined is extremely small.

As described above, according to the method of the present invention, ellipsometric analysis can be performed by measuring the ellipsometric parameters Ψ and Δ using a sample having a known optical constant and having a thin layer on the surface with a different optical constant. The angle of incidence of the monitor can be easily and accurately determined.

[Brief explanation of drawings]

Figure 1 shows the interference of light by a single layer film, Figure 2
The figure is a graph showing one embodiment of the method of the present invention.

Claims (1)

[Claims] 1. Measure the ellipsometric parameters Ψ and Δ of a sample that has a known optical constant and a thin layer with a different known optical constant on the surface using an ellipsometric monitor with optical axis adjustment, and measure the ellipsometric parameters Ψ , Δ, the incident angle of the ellipsometry monitor whose optical axis has been adjusted is calculated from the values of Δ.