JPH03283615A - Etching monitor method - Google Patents

Abstract

PURPOSE:To enable detection of etching velocity and end point by radiating white light for spectrum processing of reflection light from both surfaces of a thin film and by displaying intensity distribution of spectrum of interference wave by interfering both spectrums. CONSTITUTION:White light 5 from a light source 5a is reflected by a half mirror 14 and radiated to a thin film 2 during etching through a glass window 13b of a reflection furnace 13, and reflection wave from both sides is transmitted through a half mirror 14 and input to diffraction grating 7. Both reflection waves are spectrum-dispersed by the diffraction grating 7, focus and interfer per wavelength by a lens 8 and input to CCD9 to output intensity distribution of spectrum of interference wave. An output voltage is processed by data processing part 10 and figures of processing results are output to an output part 12 simultaneously with display of spectrum on a display 11. According to this constitution, it is possible to detect etching velocity readily and to acquire accurate end point by data processing since the detailed state of etching near end point can be observed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application on M Beams] The present invention relates to an etching φ monitoring system, and more specifically to a system for detecting the speed and end point during etching of a thin film.

[Conventional technology] In the manufacture of semiconductor devices, a thin film of oxide is deposited on a wafer of silicon or the like using a CVD device. Etching is performed on this to form a predetermined pattern. Etching is an important process in order to improve the quality of the product, and it is necessary to know its speed and end point in order to set the optimum conditions. Various methods have been used for this purpose, and one that uses optical interference waves is well known.
No. 8, "Method of imaging by laser interference and laser interferometer for carrying out this method".

Figures 4(a) and (b) show the above patent application publication.
This explains the principle of detecting the speed and end point of etching. In Figure (a), a substrate 1 on which a thin film 2 is deposited is placed in a reactor (not shown), and a laser beam of a single wavelength is applied to the thin film 2. 3 is irradiated.

A reflected wave 41 is reflected from the surface of the thin film 2, and if the thin film is transparent, a reflected wave 42 is also reflected from the back surface, and both reflected waves 42 interfere with each other. As is well known, when the wavelength of the interference wave is λ, the intensity is maximum when the phase difference between the two interference waves is an even multiple of λ/2, and is minimum when the phase difference is an even multiple of λ/2. As the etching progresses, the thickness d of the thin film 2 gradually decreases, so the phase difference between both reflected waves continuously changes between odd and even multiples of λ/2, and therefore the intensity of the interference wave is at its maximum. Vary between the value and the minimum value. When such an interference wave is received by a photoelectric converter and the waveform of its output voltage is displayed on a display, the curve shown in FIG. 3(b) is observed. 1 in the figure is the average value of the intensity, and the waveform is centered around this and the maximum value I
It changes between ax and the minimum value Is+In according to time t. When the etching reaches the end point, the intensity changes no longer and settles to the maximum value I, and this time point 11 is detected as the end point. Furthermore, since the time interval Ts between the two maximum values of 1 wax corresponds to an even multiple of λ/2 (an integral multiple of λ), the etching rate can be measured from this. In addition, in the above patent application publication, the etching state of the required range of the thin film to be processed is captured by scanning with a laser beam, and the interference wave intensity in that range is displayed on a display using a data processing device. be.

[Problem to be solved] In the interference wave system disclosed in the above patent application, the curve in FIG. 4(b) has a maximum value of 1 before reaching the end point 11
wax and the minimum value of 1 min, it changes multiple times corresponding to the initial thickness, and suddenly reaches the maximum value of 1 min at the end point.
It settles on wax. Therefore, the progress of etching before the end point cannot be grasped in detail, and the end point cannot be predicted in advance.

The present invention has been made in view of the above, and provides an etching monitor method that can be used in-line in the production process, allows detailed observation of the progress of etching, especially near the end point, and detects the speed and end point of etching. The purpose is to

[Means for Solving the Problems] The present invention is an etching monitor system in which a thin film being etched is irradiated with white light, and the reflected light from the front and back surfaces of the thin film is separated into spectra using a diffraction grating. The two separated spectra are interfered and received by a CCD sensor, and the intensity distribution of the interference wave spectrum is displayed on a display to observe the progress of etching.
The etching speed and end point are also detected through data processing.

[Operation] In the etching monitor system of the present invention having the above configuration, a thin film is irradiated with white light, and the reflected light from both the front and back surfaces of the thin film is separated into spectra by a diffraction grating. Both spectra are continuous spectra spread over a wide range of wavelengths included in white light, and since the same wavelengths of both reflected lights interfere with each other, the spectra of the interference waves are changed. This interference wave spectrum is received by a CCD sensor, and the intensity distribution with respect to wavelength is displayed two-dimensionally on a display and observed. Here, the intensity of the interference wave depends on the phase difference between both reflected waves, that is, the thickness of the thin film, and as the thin film becomes thinner as etching progresses, the wavelength showing the maximum or minimum value gradually shifts on the display. Since this moving speed is the etching speed, the etching speed can be easily detected by waveform observation or data processing.

Furthermore, when the thickness of the thin film becomes thinner than one-fourth of the minimum wavelength of the continuous spectrum (the phase difference is one-half), the maximum and minimum intensity values of the interference wave spectrum decrease as the thickness decreases. The difference gradually decreases, and the intensity distribution settles to its maximum value at the end of etching.

In this way, as the thickness of the thin film decreases and approaches the end point,
Since the intensity distribution of the interference wave spectrum gradually approaches the maximum value in a peculiar manner, the etching situation near the end point can be observed in detail, and the end point can be accurately determined through data processing.

[Embodiment] FIG. 1(a) shows an embodiment of an optical system in an etching monitor according to the present invention. A thin film 2 of oxide or the like is deposited on the surface of a silicon wafer 1, and white light 5 is irradiated onto the thin film 2. The white light 5 is preferably one with a continuous spectrum that does not have any particular line spectrum. The white light 5 is reflected by the front and back surfaces of the thin M2, respectively.
62 is reflected and separated into spectra by the diffraction grating 7. In this case, a reflection type diffraction grating 7 is shown, but a transmission type may also be used. Although the spectroscopic principle of a diffraction grating is well known, it will be briefly explained with reference to FIG. 1(b) for reference.

When white light 5 is incident on the reflective diffraction grating 7 at an incident angle α, due to the diffraction effect, diffracted light 50, 51, 52, etc. with a reflection angle β corresponding to λ in the following equation are obtained. be ejected.

d (s in α+s in β)=nλ (1) where n is the order of the diffracted light and d is the thickness of the thin film.

The reflection angle β0 of the 0th order diffracted light 50 for n=o is the wavelength λ
It is the same as the angle of incidence α regardless of the angle of incidence, that is, specular reflection occurs. On the other hand, the first-order diffracted light 51,5 for n=1
2.53... are separated by the size of the wavelength λ, and their reflection angles β1. β2. β3... are larger than β0 in this order, that is, the white light 5 is divided into spectra corresponding to the wavelength λ.

Incidentally, although there are diffracted lights of second order and higher order, their intensities are small, so they are not considered a problem here.

Referring again to FIG. 1(a), each of the diffracted lights of both reflected waves GO, 61 separated by the diffraction grating 7 is received by the lens 8 with each wavelength focused on the CCD sensor 9. Here, since there is a phase difference between the two reflected waves [il, 82, the same wavelength of the diffracted light of both reflected waves also has a phase difference, these interfere with each other to produce an interference wave spectrum, and the interference wave The output voltage of each element of the CCD sensor 9 with respect to the spectrum is input to the data processing section 0.

Changes in the intensity 41 of the interference wave spectrum displayed on the display will be explained with reference to FIGS. 2(a) to 2(f). In each figure, the horizontal axis is the wavelength λ, and the wavelength range of white light is λ1n.
~λWaX, λ1 close to λ1n, and λ3 twice that
(λ3〈λ■aX), and their center λ
Let's focus on point 2. Here, d is the same as above for the thin film 2
When the thickness is , and ε is the refractive index of the thin film, 2d/ε corresponds to the phase difference between both reflected waves (however, for the sake of simplicity, the incident angle α with respect to the thin film 2 is assumed to be O). Figure (a) shows the case where the phase difference 2dl/ε due to the thin film thickness dl is an even multiple of λt/2 (n 2 * 3...), and therefore this phase difference is It is also an even multiple of λ3/2, and λ
1 and λ3 is the maximum value 1 set aX. Also, the central λ2
Then, the minimum value lm1n is obtained. Figure (b) shows a case where the phase difference due to the thickness d2 is an odd multiple of λl/2, with the minimum value at λl and λ3 and the maximum value at λ2. As the etching progresses, the above-mentioned maximum value or minimum value moves, and the etching speed can be detected by observing this or by data processing. The above changes are regular, but as the etching progresses and the phase difference in the thickness dp becomes equal to λl/2 as shown in Figure (e), the minimum value ■1n is reached at λ1, but between λ2 and λ
3, the phase difference is less than λ/2, so it does not reach ll1a× or I min. In Figures (d) and (e), the thicknesses dQ and dr become even thinner, and the respective phase differences are λl/4 or λt/8, and the curves gradually rise and at the end point, the figure ( f) such that the maximum value I
I settled on sax. In this way, the intensity distribution undergoes a peculiar change near the end point, and this change can be observed in detail.

FIG. 3 shows an embodiment of the overall configuration when the etching monitor system according to the present invention is applied to a plasma CVD apparatus. A sample stage 13a is provided at the bottom of the reactor mouth, on which a silicon wafer 1 to be processed is placed. A thin oxide film 2 is deposited on the surface of the wafer 1, and an etching action is performed by injecting an etching gas such as fluorine thread into a reactor. On the other hand, the white light 5 from the light source 5a
is reflected downward by the half-mirror eye and irradiated onto the thin film 2 through the glass window 13b of the F section of the reactor, and the reflected waves from both the front and back surfaces pass through the half-mirror 14 and enter the diffraction grating 7. Both reflected waves are spectrally separated by a diffraction grating, focused and interfered by a lens 8 for each wavelength, input to a CCD sensor 9, and a voltage corresponding to the intensity distribution of the spectrum of the interference wave is output from each element. The output voltage is processed in the data processing section 10, the spectrum is displayed on the display H, and at the same time, the numerical value of the data processing result is outputted to the output section 12. Data processing section 1
0 is configured by a microprocessor and! - The processing and display of the notes are automated.

[Effects of the Invention] As is clear from the above explanation, according to the etching monitoring method according to the present invention, a thin film to be etched is irradiated with white light, and reflected waves from both the front and back sides are detected by a diffraction grating. The interference wave spectrum between the same wavelengths of both spectra is received by a CCD sensor and displayed on a display to observe the change in intensity, or data processing is performed to automatically determine the etching speed and its end point from the change in intensity. In the conventional method using a single wavelength laser beam, the intensity change is detected one-dimensionally along the time axis, but in the case of this invention, the intensity distribution with respect to wavelength is detected. Since it is displayed two-dimensionally on the display, changes in etching speed and etching conditions near the end point can be grasped in more detail, and data can be changed to set optimal conditions, which has a great effect on etching management. be.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1(a) and 1(b) are diagrams of the configuration of an optical system in an embodiment of the etching fist monitor system according to the present invention and an explanatory diagram of the action of a known diffraction grating, and FIG. a) ~ (f)
1A is a curve diagram illustrating changes in the intensity distribution of the interference wave spectrum in FIG. Figures (a) and (b) are
FIG. 2 is a schematic explanatory diagram of a method for detecting etching speed and end point using a single wavelength laser beam as disclosed in a patent application publication. DESCRIPTION OF SYMBOLS 1... Silicon wafer, 2... Thin film, 3... Laser beam, 41.42... Reflected wave, 5... White light, 5a... Light source, 61... Surface reflected wave,
62...Back surface reflected wave, 7...Diffraction grating,
8... Lens, 9... CCD sensor, 1G... Data processing section, ■... Display, 12... Output section, ■... Reactor, 13a... Sample stage, 13b.・・・
Glass window, 14...Half mirror - Figures (a) (b) Figure 1.2

Claims (1)

[Claims] (1) Irradiate the thin film being etched with white light, separate the reflected light from the front and back surfaces of the thin film into spectra using a diffraction grating, and receive the interference waves of both of the separated spectra with a CCD sensor, An etching method characterized by displaying the intensity distribution of the spectrum of the interference wave on a display to observe the progress of the etching, and detecting the etching rate and end point by data processing.
Monitor method.