JPH01320408A - Thin film monitor using laser and film thickness measuring method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus and method for measuring changes in the thickness of thin films, including electronic materials, during production or etching.

[Conventional technology]

Conventionally, when trying to monitor the thickness of a thin film during thin film formation or etching, optical technology] Vol.
1 1 (1973) N(L9 Page
Methods for measuring reflectance or transmittance with monochromatic light, methods for comparing reflectance or transmittance at two different wavelengths, spectral reflectance or spectroscopy as disclosed in 7-2 2 (Hidetsugu Yokota) Methods such as monitoring transmittance were used. Among these methods, the method of measuring reflectance or transmittance using monochromatic light is widely used due to the simplicity of the device configuration. It was used in terms of performance, output strength, etc.

[Problem to be solved by the invention]

In the oscillation wavelength range (633n*) of the conventionally used gas laser (lie-Ne gas laser), the light absorption coefficient of the thin film is large (if you try to monitor the thickness of the thin film with the gas laser, it will be difficult to detect a certain thickness). When the thickness of the thin film reaches a certain height (for example, about 111 m in the case of an amorphous silicon thin film), the light absorption coefficient of the thin film is large, which weakens the effect of multiple interference and makes it difficult to determine the film thickness.

In view of these problems, the present invention reduces the thickness of the thin film to 2 μm.
The aim is to provide a technology that can monitor up to m.

[Means to solve the problem]

The present invention is an apparatus consisting of a laser, a detector, a digital voltmeter, and a control computer that measures the thickness of a thin film by irradiating a laser onto a substrate installed in a vacuum chamber of a thin film forming or etching apparatus. The wavelength of the laser used is 700 nm to 800 nm+, and the change in film thickness is monitored simultaneously with the formation or etching of a thin film by the multiple interference effect of light.

[For production]

The effects of the present invention will be explained in detail by taking as an example an amorphous silicon thin film that the inventors took up as an example. In order to solve the above problems, the inventors conducted experiments and theoretical studies on the wavelength dependence of the absorption coefficient of an amorphous silicon thin film and the multiple interference effect used for film thickness monitoring. An example of the measurement results of the wavelength dependence of the absorption coefficient is shown in FIG.

Generally, when trying to monitor a film thickness of 1 μm to 2 μm, the absorption coefficient is approximately 3000 cm or less, depending on the optical arrangement of the measuring device, according to the results of various experiments conducted by the inventors. It has been found that it is possible to measure film thicknesses exceeding 1 pm. Also, in order to easily adjust the optical system, visible light is necessary, and considering the above, it is recommended to monitor the thickness of thin films with a large light absorption coefficient, such as amorphous silicon thin films, from 1n to 2μl. In this case, the wavelength of light to be used from Figure 1 is 700n.
The wavelength is required to be between m and 800 nm. Typical lasers suitable for film thickness monitoring that oscillate in this wavelength range include A7CaAs, GaAsP, and I.
Semiconductor lasers such as nGaAs and A/Ga1nP are preferably used.

Semiconductor lasers can oscillate in the wavelength range of 700 nm to 800 nm, but their application has heretofore been considered difficult due to the instability of their oscillation modes. However, recent advances in semiconductor laser technology have made stable oscillation possible, and in the present invention, a highly stable semiconductor laser is used as a light source for monitoring the thickness of a thin film with strong absorption. By using a semiconductor laser with an oscillation wavelength of 700 nm to 800 nm, the absorption coefficient is large (200 nm) in the measurement wavelength range of conventional technology (Ile-Ne laser; 633 nm).
Even for thin films that are difficult to measure up to a film thickness of about 1 pta (approx. becomes. Calculating the effect on the optical arrangement of the measuring device used by the inventors, the film thickness IInn and 2p for the amorphous silicon thin film were calculated.
The ratio of signal intensity due to multiple interference to the total light amount at m (signal/background ratio) is 630 r++
++ (He-Ne laser) at 1 pm; 0.0
13 and 21'm i 3 X I Q-4,700n
m (semiconductor laser) 1 μm; 0.292 and 2
μm: 0.143. In order to accurately determine the film thickness, the signal/background ratio must be 0.1 or more, and the above calculation shows that it is possible to monitor film thickness up to 2 μm using a laser with an oscillation wavelength of 700 nm. It shows.

Furthermore, as a secondary effect, the light intensity of semiconductor lasers can be easily changed electrically, so it is possible to adjust the light intensity by taking into account the influence on the film formation or etching process, the S/N ratio, etc. Easy to improve the S/N ratio of the monitor signal by light intensity modulation Also, since semiconductor lasers are smaller, lower cost, consume less energy, and have a longer lifespan than gas lasers, film thickness monitoring systems can be used for film formation or etching. It has a high degree of freedom in terms of where it can be installed on the device, and is easy to install. ・Low cost. ・Easy to manage, resulting in low maintenance costs.

[Example] Fig. 2 is a schematic diagram of a film thickness monitoring device incorporated into a thin film forming or etching apparatus used in the present invention (other auxiliary devices related to the thin film forming or etching apparatus are not shown).
shows. As the semiconductor laser 2, IV Ga A
A semiconductor laser (oscillation wavelength: 750 nm) is used, and its laser light is introduced into a vacuum chamber (thin film growth chamber) through an input quartz window 3 and reflected by the substrate surface (film growth surface) 4. At this time, the laser beam undergoes intensity changes due to multiple interference effects and absorption by the thin film. The laser beam that has undergone the intensity change passes through the output quartz window 5, exits the vacuum chamber, and enters the detector (silicon photodiode) 6. Detector output (current)
is converted into a digital signal by the digital voltmeter 7 and sent to the control computer 8.

Figure 3 shows the present invention in an amorphous silicon film (absorption coefficient;
1.8 x 10'cm-' at 633 nm, 750n
The vertical axis shows the output current (unit: ++A) of the detector (silicon photodiode), and the horizontal axis shows the deposition time (unit: ++A). minutes) (corresponding to the film thickness). It can be seen that as the deposition time increases, that is, as the film thickness increases, the output of the photodiode changes periodically due to the multiple interference effect. Angle (P polarization); 7
7”, refractive index of l film (amorphous silicon film),
3.43), the film thickness corresponding to one period of periodic change is 0.114μ, so in this experiment, approximately 12 periods (
Film thickness: 12 times of 0.114fm to approximately 1.4 arm)
This means that the film thickness could be measured without significantly changing the signal/background ratio. Further, other results show that the present invention was able to adequately monitor the film thickness even when the film thickness reached 2n.

〔Effect of the invention〕

To summarize the effects of the present invention, as a result of using a semiconductor laser with an oscillation wavelength in the visible light range and as long as possible in the wavelength range of 700 nm to 800 nm as a light source for the film thickness monitor, l) the measurement wavelength range of the conventional technology ( For example, with a He-Ne laser (S630 nm), the thickness of a thin film with a large absorption coefficient is approximately 2
It is now possible to measure in the visible light range, where the optical system can be easily adjusted down to μm.

Furthermore, as a secondary result, 2) since the light intensity can be easily changed electrically, it is easy to adjust the light intensity taking into account the influence on the film formation or etching process, the S/N ratio, etc. ■It is easy to improve the S/N ratio of the monitor signal by light intensity modulation. 3) Compared to gas lasers, semiconductor lasers are smaller, lower cost, consume less energy, and have a longer lifespan. It has the following effects: it has a large degree of freedom in terms of where it can be installed on the etching device, it is easy to install, ■ it is low cost, and ■ it is easy to manage and has low maintenance costs.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the wavelength dependence of the absorption coefficient of the amorphous silicon thin film taken up in the examples of the present invention. The vertical axis is the absorption coefficient (unit: cm-) of the amorphous silicon thin film.
'), and the horizontal axis represents the wavelength of light (unit: nm). The curve shows the decrease in the absorption coefficient as the wavelength of light increases: 633nm, 700n+a, 750n+a, 80nm.
The absorption coefficients at 0 nm are 1.8×10' and 3.
IXLO', 6.7XIO", 3.3X10". Figure 2 is a schematic diagram of the film thickness monitoring device used in the present invention.
1 is a vacuum chamber (film growth chamber), 2 is a semiconductor laser (#JG
aAs semiconductor laser (50 nm), 3 is an incident quartz window, 4 is a substrate, 5 is an output quartz window, 6 is a detector (silicon photodiode), 7 is a digital voltmeter, and 8 is a control computer. Figure 3 is a diagram showing the relationship between the output current of the detector (silicon photodiode) and the deposition time (corresponding to film thickness), where the vertical axis is the output current of the detector! (unit: mA), and the horizontal axis represents deposition time (unit: minutes). The curve represents a periodic change in the output current as the film thickness increases (1 cycle = film thickness 0.114 μm). Fo-h-diode-p shivering output (mA)

Claims (2)

[Claims] (1) Measure the thickness of a thin film by irradiating a laser onto a substrate installed in the vacuum chamber of a thin film forming or etching device. A film thickness monitor using a laser, characterized in that the wavelength of the laser is 700 nm to 800 nm. (2) Film thickness using a laser, characterized in that the film thickness monitor according to claim 1 is used to monitor changes in film thickness simultaneously with thin film formation or etching using the multiple interference effect of light. Measuring method.