JPH0624188B2 - Etching completion point detection method - Google Patents

Description

The present invention relates to a dry etching process for a semiconductor device,
In particular, the present invention relates to an etching completion point detection method suitable for detecting the processing completion point during the etch back processing.

[Conventional technology]

In a manufacturing process of a semiconductor device such as an LSI, various etching processes are often required. At this time,
Especially in etch back (flattening process),
It is necessary to accurately detect when the processing is completed.

By the way, as a detection method at the time of completion of the etch-back, conventionally, for example, a method of changing the emission spectrum intensity due to the material of the substrate to be etched or the component of the etchant, or the like, for example, JP-A-56-50515. As disclosed in, a diffraction grating pattern is set on the surface of the substrate to be etched, or an interference light measurement area is set and a predetermined light is irradiated from the outside to diffract the light and interfere with the light. A method of knowing the completion time point by detecting the film thickness of the etched portion by measuring light, or, for example, as disclosed in JP-A-57-28334, the pattern and the surface state of the film (of the crystal grains). A method is known in which the completion time is judged by a change in scattered light intensity due to a difference in size, etc.).

[Problems to be solved by the invention]

However, each of these conventional examples has the following problems.

First, with the method that detects changes in the emission spectrum intensity, it is difficult to eliminate the effect of plasma light associated with the etching process, which complicates the configuration, and when the change in the etching area is small, complete There is a problem that it is difficult to detect the time point.

In addition, in the method using diffracted light or interference light, it is necessary to set a pattern or a predetermined measurement area on the surface of the substrate to be etched, and irradiate the area where the pattern or area is set with light accurately. However, there is a problem that a special device is required for this purpose, and further, the indefiniteness of the film thickness on the upper part of the pattern is directly reflected in the indetermination of the planarization.

In addition, the method based on the change of the surface state similarly has the problem of positioning the irradiation light, and also has the problem that there are restrictions on the application depending on the film on the substrate surface and the material of the pattern.

It is an object of the present invention to provide an etching completion point detecting method capable of sufficiently addressing the problems of these conventional examples and always obtaining the detection of the etching completion point.

[Means for solving problems]

According to the present invention, the above-mentioned object is achieved by optically detecting a step generated on the surface of the substrate due to the etch back by utilizing scattered light from the side surface, and thereby determining the etching completion time. .

[Work]

Since a step on the surface of the substrate to be etched suddenly occurs immediately after the etching back is completed and as the etching of the part other than the pattern proceeds subsequently, it is possible to reliably detect the completion time of the etching back by detecting this.
And it can be detected easily.

〔Example〕

Hereinafter, the etching completion point detecting method according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows the present invention in which a wiring electrode is formed by patterning an aluminum (Al) layer on the surface of a certain layer existing on the surface of a semiconductor substrate by a dry etching method in a manufacturing process of a multilayer wiring semiconductor device. After the formation, a coating film such as an insulating material is applied to the entire surface, baked, and etched back to form a desired wiring layer. To do.

In FIG. 1, reference numeral 1 denotes a parallel plate type plasma etching apparatus having a lower electrode 2 and an upper electrode 3, and a high frequency voltage is supplied from a high frequency power source 5 to these electrodes 2 and 3 and a predetermined amount is supplied from a gas introduction pipe 6. The exhaust gas is exhausted from the exhaust pipe 7 at a predetermined flow rate while supplying an etching gas such as oxygen (O ₂ ) so that the gas pressure in the etching apparatus 1 becomes a predetermined value such as 10 [Pa]. Keep
By supplying a high frequency voltage from the high frequency power source 5, the substrate to be etched 4 placed on the lower electrode 3 is etched. As the frequency of the high frequency voltage at this time, for example, 13.6 [MHz] is used.

Reference numeral 8 is a laser light source, 9 is a condenser lens, 10 is an optical filter, 11 is a photodetector including a photodiode, and 12 is a signal recording device.

For example, a laser light source 8 including a He-Ne laser having an oscillation wavelength of 633 [nm] and an optical output of about 1 [mW].
When the etching apparatus 1 starts etching the substrate 4, the laser beam Li is irradiated from the side of the substrate 4 at an angle of about 5 degrees with respect to the surface of the substrate 4. The irradiation region of the substrate 4 by the laser light Li at this time has, for example, a long axis of about 1
It has an oval shape of 0 [mm] and a short axis of about 0.8 [mm].

Next, the reflected light Lr from this elliptical irradiation area is made incident on the photodetector 11 through the condenser lens 9 and the optical filter 10 and converted into an electric signal corresponding to its intensity, and then the signal recording device. 12 is input. At this time, the condenser lens 9 functions to efficiently collect the reflected light Lr, and the optical filter 1
0 works so that only the light having the same wavelength as the laser light Li, that is, 633 [nm] is incident on the photodetector 11.

Next, the operation of this embodiment will be described.

As described above, when the intensity R of the reflected light Lr is measured by the signal recording device 12 while continuing the dry etching of the substrate 4 by the etching device 1, the change of this intensity R with respect to time t is as shown in FIG. become.

In FIG. 2, S is the time when etching is started, and the intensity P remaining at this time is the intensity detected by the light component of wavelength 633 [nm] contained in the plasma generated in the etching apparatus 1. , D shows the step difference due to the progress of the etch back, and the detected intensity at the time point E when the step height reaches about 50 [nm], and F shows the case when the film on the substrate 4 is completely etched. The detection intensity is shown.

Therefore, when the etching of the substrate 4 is started, the intensity R of the reflected light Lr is continuously monitored by the signal recording device 12, and in the beginning, the intensity R gradually increases from the intensity P at the start point S. The reason is that, after a change in the rising state, the strength suddenly increases and the etching process is terminated at the time E when the strength reaches the predetermined strength D, the substrate etched back to a predetermined flatness is obtained. 4 can be obtained.

Next, the reason for this will be described with reference to FIG.

FIG. 3 shows a cross section of the wiring pattern 40 and the coating film 41 formed on the surface of the substrate to be etched 4 in FIG. 1, and initially, in the state where there is no step d,
The reflected light Lr due to the incident laser light Li is hardly generated. Therefore, at this time, from time S to time E in FIG.
As shown in the period in which the intensity does not reach, the level of the intensity R of the reflected light Lr hardly increases from the initial intensity P.

Then, as the etch-back progresses, the surface of the wiring pattern 40 appears, and eventually the etch-back of only the surface of the coating film 41 progresses, whereupon a rising portion almost vertical to the side surface of the wiring pattern 40 occurs, and the step d Appears. Then, due to the step d, the reflected light Lr, which has hardly existed until then, appears. As a result, after the step d appears, the intensity R of the reflected light Lr sharply increases, and the step d
When E reaches a predetermined value, a predetermined strength D is obtained almost in steps, and the time when etching back is completed can be surely and easily known.

According to this embodiment, the value of the intensity D in FIG. 2 is about 1/4 of the intensity F when the saturation state is finally reached, and S / N of 3 [dB] is obtained. As a result, it was possible to detect the etching completion point with sufficient accuracy.

By the way, in the above embodiment, the laser light is used as the light to be incident on the surface of the substrate 4, but instead of this, the light from the point light source is converted into a single light by an appropriate optical system such as a reflecting mirror or a lens. It may be used as a directional one. Needless to say, even when laser light is used, it is not limited to the above-mentioned He-Ne laser.

In the present invention, any light may be used as the incident light, but as described above, it is effective to use unidirectional light. When laser light is used as this unidirectional light, the output per unit area is large, so the intensity of the reflected light from the irradiation surface at that wavelength of the laser light is the plasma light at that wavelength. Remarkably larger than the strength of.

Therefore, according to this embodiment, it is possible to detect the change in reflected light intensity with high sensitivity and accuracy with almost no influence of plasma light, and it is possible to sufficiently improve the detection accuracy at the etching completion time. .

On the other hand, the photodetector 11 is not limited to the photodiode, and any photoelectric converter such as a photomultiplier tube can be used. Further, the optical filter 10 can be a cut filter or a monochromator. Needless to say.

〔The invention's effect〕

As described above, according to the present invention, the etching completion time can be detected by the height of the step caused by etching and the change in the reflected light intensity that appears in response to the change in the tilt angle on the side surface of the step. Therefore, the problems of the prior art can be sufficiently dealt with, high-precision detection can always be easily obtained, and etching with good flatness can be performed. Further, according to the present invention, the substrate to be etched,
Since it is possible to detect any step in the irradiation surface due to the incident light due to etching, when applied to etch back, it is easy to position the light irradiation portion on the substrate surface.
No special device is required on the surface of the siding plate, it can be easily applied with simple equipment, and the substrate for the preceding test can be eliminated.

Further, as described above, the present invention uses the height of the step generated by etching and the monitor of the reflected light intensity due to the change of the tilt angle at the side surface as the detection principle, and therefore is not limited to the above-mentioned etch back. The same action and effect as in the case of etchback can be obtained by applying it to etching for forming the side wall of the oxide film at the time of forming the gate electrode of the semiconductor device, or a processing step for finishing the etching at a desired etching depth. It goes without saying that you can do it.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an etching completion point detecting method according to the present invention, and FIG. 2 is a characteristic diagram for explaining the operation,
FIG. 3 is a sectional view of the substrate for explaining the operation. 1 ... Plasma etching device, 2 ... Lower electrode, 3 ...
... Upper electrode, 4 ... Substrate to be etched, 5 ... High frequency power source, 6 ... Gas introduction tube, 7 ... Exhaust tube, 8 ... Laser light source, 9 ... Condenser lens, 10 ... Optical filter, 11 …
Photo detector, 12 Signal recording device.

Claims (2)

[Claims] 1. A first layer having a predetermined pattern formed on a base, and a second layer made of a material different from the first layer and the first layer formed on the base. A work piece having a
In the process of etching the surface of the layer to expose the first layer, the processed surface of the workpiece is irradiated with light from a certain direction at a predetermined inclination angle, and the processed surface is formed by the light. The reflected light returning from the reflected light returning from the same direction as the irradiation direction of the light is detected by the step generated on the processed surface, and the completion of etching is determined when the light amount of the reflected light sharply increases. A method for detecting an etching completion point, characterized in that 2. A method of detecting an etching completion point according to claim 1, wherein the light radiated to the workpiece is a laser light.