JPH04142735A - Etching abnormality monitor - Google Patents

Abstract

PURPOSE:To enable the abnormality in the shape of trenches to be accurately detected by a method wherein the intensity of the reflective diffraction beams from the substrate to be etched away is detected and the detection signals are spectrum-analyzed so as to detect the etching abnormality by the width of the spectrum. CONSTITUTION:A reflector 16 for almost vertically irradiating a substrate 13 to be etched on the other electrode 12 with a laser beam Q through an observation window 14 is arranged on the optical path of the laser beam Q emitted from a laser oscillator 15. The intensity of a part of the partial reflective diffraction light Q' is detected by a detector 17 so as to transmit the detection signals by a spectrum-analyzer 18. This spectrum analyzer 18 monitors the existence of microtrenches 4 by spectrum-analyzing the detection signals. That is, the width of the intensity distribution 22 when the microtrenches 4 are detected is wider than that when the microtrenches 4 are not detected at all.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) This invention provides an etching abnormality monitoring system capable of detecting an abnormal shape of a trench formed in a substrate to be etched housed in a vacuum container during etching. Regarding equipment.

(Conventional technology) In general, etching in the semiconductor manufacturing process includes wet etching and dry etching, but in microfabrication of ultra-precision semiconductors, a fine photoresist pattern is faithfully transferred onto a substrate to be etched consisting of a silicon wafer. Dry etching is widely used. In a dry etching device that performs ultra-fine processing, it is difficult to set process conditions because processing accuracy on the micron level is required. On the other hand, even once set, the process conditions change over time due to subtle changes in the composition of the reaction gas due to reaction products adhering to the etching chamber wall surface due to long-term etching.

As a result, the etched shape may become abnormal. Further, slight fluctuations in reaction gas pressure and applied power also cause abnormalities in the etching results.

Usually, as shown in FIG. 4, an etching mask 2 having a certain pattern is formed on the upper surface of a silicon wafer 1.
Then, the silicon wafer 1 is etched on the part of the silicon wafer l that is not covered by the etching mask 2.
A trench 3 is formed substantially perpendicularly from the surface. but,
If the etching conditions cannot be properly controlled as described above, small notch-shaped microtrenches 4 may be formed along the wall surface of the trench 3 and at the bottom wall of the trench 3, as shown in FIG. In addition, the micro trench 4
may occur at the center of the bottom wall of trench 3. When a microtrench 4 is formed on the bottom wall of the trench 3 in this way,
When this trench 3 is used as a capacitor, this micro-trench 4 causes an electric withstand voltage failure. Therefore, even during etching, the presence or absence of this microtrench 4 must be constantly monitored, and when a microtrench 4 is discovered, the silicon wafer 1 must be rejected as a defective product.

As an etching abnormality monitoring device for detecting such an abnormality in etching of a substrate to be etched, the conventional etching abnormality monitoring device was
A structure disclosed in Japanese Patent No. 1-241923 is known. This etching abnormality monitoring device includes a laser light source, a means for irradiating the laser light emitted from the laser light source to an arbitrary point on a wafer being processed by a dry etching device, and a means for irradiating the laser light emitted from the laser light source to an arbitrary point on a wafer being processed by a dry etching device, My,
A structure comprising a light detection means for detecting a specific diffracted light, and an abnormality detection means for determining a contrast from a change in the intensity of the detection light detected by the light detection means and detecting an etching abnormality from the magnitude of the contrast. It has become.

The etching abnormality monitoring device configured as described above constantly determines the maximum and minimum of the light intensity change, calculates the contrast from the latest maximum and minimum values, and when the contrast becomes smaller than the threshold, It was determined that the shape of trench 3 was abnormal. However, in the actual detection signal, as the trench 3 becomes deeper, the mask 2 is also etched, and the intensity of the reflected diffracted light from the surface of the mask 2 changes depending on the amount of etching. Therefore, the intensity signal of the reflected diffracted light obtained from the substrate to be etched is a signal obtained by combining the intensity change of the reflected diffracted light from the bottom wall of the trench 3 and the intensity change of the reflected diffracted light from the surface of the mask 2. Therefore,
The positions of the maximum and minimum points of the intensity signal are greatly affected by changes in the thickness of the mask 2, and the contrast between the maximum and minimum values is affected not only by changes in the condition of the bottom wall of the trench 3 but also by the thickness of the mask 2. Since the change component is also included, even if the contrast mentioned above is smaller, it is still the same in trench 3.
It is difficult to accurately determine that this is due to an abnormal shape.

(Problem to be Solved by the Invention) In this way, the conventional etching abnormality monitoring device detects an abnormality in the shape of a trench based on a change in the contrast between the maximum and minimum intensity of the reflected diffracted light from the substrate to be etched. Ta. Such a measurement method does not take into account the effect of a decrease in mask thickness, making it difficult to accurately detect abnormalities in the trench.

This invention was made to solve the above problems,
It is an object of the present invention to provide an etching abnormality monitoring device that can accurately detect an abnormality in the shape of a trench by eliminating the influence of changes in mask thickness on reflected and diffracted light from a substrate to be etched.

[Structure of the Invention] (Means for Solving the Interval Point) The present invention provides a dry etching apparatus in which a substrate to be etched is etched in an etching chamber in which a light-transmitting window member is provided on the wall. Measurement light irradiation means disposed outside the etching chamber for passing measurement light through the window member and irradiating the substrate to be etched; and detection means for detecting the intensity of reflected diffracted light from the substrate to be etched. and spectrum analysis means for analyzing the spectrum of the detection signal and detecting an etching abnormality based on the width of the spectrum.

With such a configuration, even if the detection signal is affected by a change in the thickness of the mask, this effect can be removed and the presence or absence of a microtrench can be accurately determined.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an etching abnormality monitoring device showing an embodiment of the present invention.

In the figure, 11 is an etching chamber. In this etching chamber 11, one electrode (not shown) and the other electrode 12 are arranged below.

The substrate to be etched 13 is placed on the upper surface of the other electrode 12, and is connected to a high frequency power source (not shown). The wall of the etching chamber 11 corresponding to the other electrode (
There is an observation window 14 made of quartz light-transmitting window material on the earthen wall).
is located. Note that the etching chamber 11
A gas supply pipe (not shown) for supplying reactive gas into the etching chamber 11 and an exhaust pipe (not shown) for exhausting the gas inside the etching chamber 11 are provided, respectively.

Further, a laser oscillator 15 is arranged outside and above the etching chamber 11. In the optical path of the laser beam Q emitted from the laser oscillator 15, there is a reflecting mirror 1 for irradiating the laser beam Q through the observation window 14 almost perpendicularly to the substrate 13 to be etched on the other electrode 12.
6 is placed. The intensity of some of the reflected diffraction lights Q'' among the plurality of reflected diffraction lights Q obtained from the substrate to be etched 13 is detected by a detector 17, and the detection signal is sent to a spectrum analysis section 18.

The spectrum analysis unit 18 monitors the presence or absence of the microtrench 4 by performing spectrum analysis on the detection signal. The monitoring method will be explained below with reference to the drawings.

In Figure 4, the trench depth is D1 and the mask 2 thickness is T.
Then, the trench depth D and the intensity of the diffracted light reflected from the substrate to be etched 13 detected by the detector 17 are
The relationship with is expressed by equation (1).

1- C1+ C2cos2(4πn+T/λ)-y(
d, λ, D) Icos (4πn, Tc) 1cos (4r
(DOT) C) (1) Equations C and C2 are arbitrary constants, λ is the wavelength of the laser beam, and nl is the refractive index of the mask 2. The mask thickness T gradually decreases as the trench depth increases, that is, as the etching depth D progresses, so it can be treated as a function of the trench depth D. γ(d
, λ, D) are attenuation coefficients determined by the trench diameter d, the wavelength λ of the laser light, and the trench depth D. If the trench diameter d and the wavelength λ of the laser light are constant, λ is also a function of the trench depth D. That is, equation (1) is expressed as a function of trench depth D. The second term in equation (1) is mask 2
The third term is a term due to the intensity change of the reflected diffracted light from the surface of the trench 3, and the third term is a term due to the intensity change of the reflected diffracted light from the bottom wall of the trench 3. Therefore, the reflected diffracted light Q detected by the detector 17
' is a composite light of the reflected diffracted light from the mask 2 and the reflected diffracted light from the trench bottom wall. Therefore, if we graph the relationship between the trench depth D and the intensity I of the reflected diffracted light Q- in equation (1), we will see a large undulation as shown in Figure 2.
It becomes a composite curve of small undulations. That is, among the curves in FIG. 3, large undulations are a signal due to a change in light intensity due to a change in the thickness of the mask 2, and small undulations are a signal due to a change in light intensity due to a deepening of the trench 3.

By the way, equation (1) is an equation that holds true when the bottom wall of the trench 3 is flat as shown in FIG. When the microtrench 4 is formed in the bottom wall of the trench 3, the depth of the trench 3 varies depending on the location as shown in FIG. 5, and the trench depth D in equation (1) does not take a constant value. Therefore, the intensity change of the intensity signal when the microtrench 4 is generated is (1
), it is necessary to transform equation (1). That is, the light intensity ! of the reflected diffracted light Q'' at a certain time t is expressed by equation (2).

I l−C++C2cos2(4πn+T/λ)−ft
(d, λ, D) cos (4yr n+T/λ)・eo
st4π(D(x)+T)/λl dx = (
2) In equation (2), the third term in equation (1), the intensity of the reflected diffracted light from the bottom wall of trench 3, is made into an integral term in consideration of the intensity change due to the change in trench depth D. As shown in Figure 5, X is the distance from the - side of trench 3, D (x)
is the depth of trench 3 at position X. If D (x) in the third term of equation (2) changes, the phase of the light will shift, so when the microtrench 4 is formed on the bottom wall of the trench 3, the reflected diffracted light from the bottom wall of the trench 3 It can be seen that the light is a composite light of light whose phase is slightly shifted.

Furthermore, as the etching becomes deeper, the microtrench 4 also becomes deeper, but if the microtrench 4 becomes deeper,
The phase shift shown in the third term of equation (2) also increases. This phase shift can be seen in the shape of the maximum or minimum point of the light intensity I in FIG. That is, when the microtrench 4 is present, the maximum intensity of the detection signal does not occur noticeably, and the curves near the maximum and minimum points become gentler than when the microtrench 4 is not present.

In the present invention, spectrum analysis of reflected diffracted light is performed to objectively view such changes. When the reflected diffraction light from the substrate to be etched is analyzed spectrally and the signal is decomposed into single frequency components, spectral lines as shown in FIGS. 3(a) and 3(b) are obtained. FIG. 3(a) shows the spectrum line when the microtrench 4 is present, and FIG. 3(b) shows the spectrum line when the microtrench 4 is not present.

In the spectrum line thus obtained, the frequency component of the diffracted light reflected from the surface of the mask 2 and the frequency component of the diffracted light reflected from the bottom wall of the trench 3 are separated. As shown in FIGS. 3(a) and 3(b), among the intensity distributions of the spectral lines, the first intensity distribution 20 having the apex at point 19 is due to reflected diffracted light from the mask surface, A second intensity distribution 22 having a peak at point 21 is due to reflected diffracted light from the trench bottom wall.

Therefore, if we extract only the second intensity distribution and compare its shape in FIGS. 3(a) and (b), we find that FIG. 3(a), that is, the intensity distribution 22 with the micro trench 4, is However, the width of the intensity distribution is wide. This spread is caused by the fact that the phases of the reflected and diffracted light from the bottom wall of the trench 3 are not aligned due to the formation of the microtrench 4. That is, for the second intensity distribution of the spectrum of the reflected diffracted light Q-, the half-width H of the spectrum width is taken and compared with the half-width H8 of the second intensity distribution 22 in the case where there is no microtrench 4, and H ＞Ha
If so, it can be determined that a microtrench 4 has been formed on the bottom wall of the trench 3.

Note that this invention is not limited to the above embodiments.

For example, in this example, a laser oscillator was used as a means for emitting monochromatic light as the measurement light, but a /Xlogen lamp,
Using a light source that emits white light such as a xenon lamp or a mercury lamp, filter the white light emitted from the light source,
The light may be converted into monochromatic light using a spectroscopic means such as a diffraction grating.

[Effects of the Invention] As described above, in the present invention, the spectrum of the reflected diffracted light from the substrate to be etched is analyzed, and the shape abnormality of the trench is determined based on the spectrum width.

With this configuration, it is possible to eliminate the influence of changes in mask thickness and accurately determine abnormalities in trench shape.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, FIG. 2 is a graph showing the intensity signal of the reflected diffracted light from the substrate to be etched when etching is performed normally, and FIG.
) is a graph showing the spectrum line of the intensity signal when etching is abnormal, and Figure 3(b) is a graph showing the spectrum line of the intensity signal when etching is normal.
FIG. 4 is a longitudinal sectional view of a trench formed by etching, and FIG. 5 is a longitudinal sectional view of a trench in which a microtrench is formed in the bottom wall. 11... Etching chamber, 13... Etching target substrate, 14... Window member, 15... Laser oscillator,
17...Detector, 18...Spectrum analysis section. Applicant's agent Patent attorney Takehiko Suzue Figures (a) (b) Figures Figures Figures Figures

Claims (1)

[Claims] In a dry etching apparatus in which a substrate to be etched is etched in an etching chamber provided with a light-transmissive window member on the wall, the dry etching apparatus is disposed outside the etching chamber and allows measurement light to pass through the window member. measurement light irradiation means for irradiating the substrate to be etched; detection means for detecting the intensity of the reflected and diffracted light from the substrate to be etched; and a spectrum analysis of the detection signal to identify etching abnormalities based on the width of the spectrum. An etching abnormality monitoring device characterized by comprising a spectrum analysis means for detecting