JPS6250610A - Plasma monitoring method - Google Patents

Abstract

PURPOSE:To evaluate the filming state on the surface of a sample by monitoring light from a specific chemical species in plasma which is reflected by the surface of the sample during a plasma treatment by a photodetector. CONSTITUTION:An Si substrate 2 which has Si3N4 on the surface is put in a reaction chamber 1, CF4+O2 is flowed to maintain about 0.4Torr, and high frequency electric power is supplied to etch the Si3N4. Then, N2 is produced on the start of the etching to cause light emission 3 and the light is reflected by the substrate 2. The reflected light is converted by a sensor 4 photoelectrically and the variation in light intensity is recorded 5. The light intensity is varies periodically owing to interference as the film thickness of the Si3N4 film decreases. The film thickness (t) is determined according to the interference rule t=lambda/4cosgamma.mu, where lambda is wavelength, gamma is the angle of refraction of the reflected light, and mu is the refraction of the Si3N4. Sensors 4-4''' are fitted at the periphery of the reaction chamber 1 at equal intervals and reflected light from parts 6-9 are monitored to compare variation in thickness from variation in the light intensity of each part, thereby evaluating the uniformity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the monitoring of equipment for manufacturing semiconductors, solar cells, etc. by plasma processing. The present invention relates to a monitoring method that can evaluate the state of film removal or film formation.

[Background of the invention]

In the conventional film microfabrication process using plasma etching and film formation process using plasma deposition, the film thickness has been evaluated by measuring with a film thickness measuring device (ellipsometer), surface roughness meter, etc. after plasma processing. In addition, as a method for evaluating during plasma processing, there has been a method in which monochromatic light such as a laser is applied to the sample surface and the film thickness is measured using the interference phenomenon between the base and the thin film of the reflected light.

In the former case, the evaluation is performed after plasma treatment, so even if there is an abnormality in the process conditions, it cannot be evaluated until after a certain amount of plasma treatment has been performed, and even if something abnormal occurs, it can only be dealt with after the fact. I couldn't get it. Therefore, the latter method has been used to evaluate the film thickness during plasma processing, but since it uses extra equipment such as a laser, there are problems with process safety, increased running costs, etc.

As a related technique, there is one described in in-process monitoring of thin film formation in a semiconductor process (Nikkei Electronics, July 1978, p. 111 to p. 114).

[Purpose of the invention]

An object of the present invention is to provide a method for monitoring a film thickness state by utilizing light emission of a specific chemical species in plasma without irradiating a sample undergoing plasma treatment with monochromatic light such as laser light from the outside. .

[Summary of the invention]

It has been found that the light intensity of the emission spectrum of a specific chemical species in the plasma reflected from the surface of a plasma-treated sample periodically increases or decreases due to interference as the film thickness of the sample surface changes due to plasma treatment. Ta. Therefore, the present invention was developed based on the idea that the film thickness state of the sample could be accurately determined by monitoring the period of increase and decrease of the light intensity.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. FIG. 1 shows a schematic configuration of the present invention. Flow CF, 102 into plasma etching chamber 1 JIL4oSC
CM is supplied, the internal pressure is maintained at about 0.4 Thrr, and a radio frequency power of 150 W is applied to etch a wafer 2t on which a 3i3N film has been formed on an 8i substrate, which is the material to be etched. 8i3N and CF4 at the start of etching
Nitrogen (N, ), which is a reaction product of +Ot, is produced,
Emits light. The light of the plasma emission 3 from the wafer 2 is reflected on the surface of the wafer 2. This reflected light 3 is received by an optical sensor 4, converted into an electrical signal, and changes in the light intensity of the reflected light during etching are recorded on a recorder 5.

The light intensity of the reflected light 3 is determined by the Si, N of the wafer 2.

As the thickness of the film decreases due to etching, the amount of interference it receives increases and decreases periodically as shown in Figure 2. From the period of increase and decrease in the light intensity of this reflected light, the law of light interference t--- and m-(t: Film thickness (^) 4 ・CO8 γ ・ μ 28 Wavelength of reflected light ('A), γ: Refraction angle of reflected light.

μ: refractive index of Si, N4), it is possible to determine the film thickness as the light intensity attenuates. Therefore, four optical sensors 4 are arranged around the double-inching chamber 1 at equal intervals.
By attaching ~4'# and monitoring the reflected light in 6 to 9 local areas on the surface of the sea urchin as shown in Figure 3, we can obtain the temporal changes in the light intensity in 5 local areas as shown in Figure 4. be able to. The change in film thickness can be compared from the change in light intensity at each part 6 to 9 on the surface of the sea urchin, making it possible to evaluate the uniformity of etching.

〔Effect of the invention〕

According to the present invention, since the surface condition of a sample can be monitored and evaluated during plasma processing, product defects can be reduced, and there is no need to use a laser beam or the like, which is advantageous in terms of economy.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing changes in reflected light over time during etching, FIG. 3 is an explanatory diagram of a monitoring method using a plurality of photodetectors, and FIG. Figure 4 is the third
FIG. 3 is an explanatory diagram of changes over time in reflected light locally on the sample surface obtained by the monitoring method shown in the figure. 1... Plasma etching device, 2... Sample, 3... Reflected light, 4-4
/l... Optical sensor, 5... Recorder.

Claims (1)

[Claims] 1. In semiconductor manufacturing process equipment that uses low-pressure gas plasma, during plasma processing, the emission of specific chemical species in the plasma reflected from the sample surface is monitored using multiple photodetectors, thereby detecting the surface of the sample. A plasma monitoring method characterized by evaluating the state of film formation.