JPH02168102A - Measuring method of film thickness of semiconductor multilayer thin film - Google Patents

Abstract

PURPOSE:To enable accurate measurement of the film thickness of each layer of a semiconductor multilayer thin film by making a monochromatic light of a prescribed long wavelength incident vertically while varying the wavelength continuously and by measuring the spectrum of a transmitted light. CONSTITUTION:A white light being used as a prober, the light incident vertically on a multilayer thin film is reflected in a multiple way by each layer and then emitted as a transmitted light from the back of a crystal. The intensity of this transmitted light is detected as a superposition of an oscillation spectrum corresponding to the film thickness of each layer as shown in a Figure (b) in a transmission area of a semiconductor constituting the thin film. By subjecting this spectrum to Fourier transform in an appropriate range of wavelength, the spectrum at a position proportional to the film thickness of each layer can be known exactly as shown in Figure (c). From the value of this spectrum, the film thicknesses of a plurality of thin films can be determined simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring the film thickness of a multilayer heteroepitaxial wafer stacked on a conductor substrate.

(Conventional technology) Semiconductor J! The thickness of a semiconductor thin film on a plate has conventionally been measured as follows.

0) A method in which a substrate having a semiconductor thin film is etched to reveal boundaries between different materials, and the step difference therebetween is measured using a step measuring device.

(2) A method of measuring the thickness of each thin film by polishing it into a flat surface at a small angle to the surface of the thin film and observing the flat surface with a microscope.

■A method in which white light is incident perpendicularly to the surface of a thin film, the maximum and minimum values of the vibration spectrum of multiple reflections in the thin film that appear in the spectra of transmitted light and reflected light are determined, and the film thickness is detected from the wavelength difference. .

(Special Publication No. 62-223609, Special Publication No. 62-16
Publication No. 5103) (Problem to be Solved by the Invention WJ) In the measurement methods (1) and (2), etching and angle polishing are performed, so no elements can be formed on the wafer used for measurement. Furthermore, although the measurement method (2) is a non-destructive measurement method, it is not possible to determine the thickness of each layer in a multilayer film.

The present invention aims to eliminate the above-mentioned drawbacks and provide a method for accurately measuring the thickness of each layer of a semiconductor multilayer thin film by a non-destructive measurement method.

(Means for Solving the Problems) The present invention provides monochromatic light with a wavelength longer than the wavelength corresponding to the energy gap of the semiconductor, to be applied to a semiconductor multilayer thin film in which a large number of semiconductor thin layers with different refractive indexes are laminated in a Jλ plate. The transmitted light is incident perpendicularly while changing the wavelength continuously, the transmitted light is measured, and by Fourier transform, it is separated into vibrational spectra corresponding to each thin layer, and based on this spectrum, each thin layer is determined. This is a method for measuring the thickness of a semiconductor multilayer thin film, which is characterized by detecting the film thickness.

(Function) FIG. 1 is an explanatory diagram schematically showing the measurement principle of the film thickness measurement method of the present invention. Using white light as the blow μ, the light directly incident on the multilayer thin film is reflected by each layer and then exits from the rear of the crystal as transmitted light, as shown in FIG. 1(a). The intensity of this transmitted light is 111 which forms the thin film.
In the 00 transmission region, it is detected as a superposition of vibration spectra corresponding to the film thickness of each layer as shown in Fig. 3(b). By performing Fourier transform on the stiffness spectrum in an appropriate wavelength range, it is possible to accurately grasp the spectrum at a position proportional to the film thickness of each layer, as shown in Figure (c). This mo? (The thicknesses of multiple thin films can be determined simultaneously from

The light incident on a multilayer film is -r'I' at the interface between each layer.
, is reflected, and the remaining components are transmitted, so the final transmitted light must be multiplied by 4 r [reflection at the interface of each layer]. First, the light that directly enters the t1111 layer film has one optical axis, as shown in Figure 2.1, but the optical axis is shifted and shown in Figure 3 to make it easier to understand.2 Let the two boundary surfaces be '' and U, let the transmission coefficients at the boundary surfaces be t and U, the reflection coefficients k and Q, and the reflection coefficients at the opposite angle be k and Q, then L, u.

t can be written as follows using the refractive index n in the crystal.

Note that each E is an electric field vector in the direction shown in FIG. 3, and the subscripts distinguish different layers.

Here, Er+n1ll is the boundary surface T compared to E r+ 11.

There is one extra reflection each at U, and E r1+, -+ = Q, KEr, net tlO.
(5) Also, the incident light E, and the first transmitted light E, . The relational expression with is shown as follows.

lshi r, t,: turshi,
(6)
By the way, the transmitted light Er is E t* jn”o, l,
, , al), the required transmitted light is 17 times.

Next, the case of transmitting light to a multilayer film in which two thin layers are laminated on a crystal substrate will be described with reference to FIG. 4. The light that has passed through the 41-layer film mentioned above directly passes through the second layer 11 film (
r), the same consideration can be made using the result of equation (7) as a new incident light. X instead of u, Q, k as transmission and reflection coefficients
.

When m and Q are used, transmitted light 1>, is obtained. The transmitted light given as a superposition of these ¥/ep reflected lights transmits through the substrate S and its intensity 1 (
is measured, so if the absorption coefficient in the substrate is α, the transmitted light intensity for measurement is the square of the electric field vector, and 1': l a m t l −e −”
It is expressed as "l E m l '.

Therefore, if we perform this Fourier transform, A,! 1 with 3 as a constant, (I + 111 NII”) = ^l t 6 (u-
2Ld, +) ' 1δ (m42, d,)j4^II
δ(to i+-2, dr) ``δ(to u+2, d,)l
'B2jδ(ω) From this, the wave number 1, k, in each layer is
If is known in advance, the film thicknesses dq and d can be determined.

(Effects of the Invention) The present invention makes it possible to non-destructively, easily and accurately measure the film thickness of a multilayer heteroepitaxial wafer stacked on a semiconductor substrate by employing the configuration described in ``-''. Therefore, it can be effectively used for film thickness inspection and film thickness control.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing the measurement principle of the present invention, (
(a) Figure is a cross-sectional view of the thin film for which the film thickness is to be determined, (b) Figure is an explanatory diagram showing that it is expressed by the superposition of the vibration spectra of the q layer and r layer, (c) Figure is the same as that of (b). Figure 2 is an explanatory diagram schematically showing the principle of multiple reflection in a thin film. Figure 3 is an explanatory diagram showing multiple reflection by shifting the optical axis of incident light. Figure 4 is a diagram showing the Fourier transform of the spectrum. 1 is a cross-sectional view of a two-layer thin film crystal showing multiple reflections in the layers with the optical axis shifted.

Claims (1)

[Claims] Monochromatic light with a wavelength longer than the wavelength corresponding to the energy gap of the semiconductor is applied perpendicularly to a semiconductor multilayer thin film made by laminating a large number of semiconductor thin layers with different refractive indexes on a substrate while continuously changing the wavelength. The spectra of the transmitted light are measured, and this is Fourier transformed to separate vibrational spectra corresponding to each thin layer, and the film thickness of each thin layer is detected based on the spectra. A method for measuring the thickness of semiconductor multilayer thin films.