JP2656869B2 - End point detection method in dry etching - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting whether or not an object to be etched has been completely etched when dry-etching the object to be etched (this is referred to as an end point of the object to be etched). is there.

[0002]

2. Description of the Related Art When a semiconductor device or the like is manufactured, a dry etching method is frequently used. At this time, if the object to be etched is not completely etched and remains, a desired pattern cannot be obtained, and the etching is continued even after a lower component (hereinafter, “base”) of the object to be etched is exposed. Also, a desired pattern cannot be obtained because side etching of the object to be etched proceeds. Therefore, various methods for detecting an etching end point of an object to be etched so as to perform desired patterning have been conventionally proposed.

[0003] For example, a document ("Integrated Circuit Process Technology Series, Semiconductor Plasma Process Technology", Takuo Sugano (Showa 60), published by Sangyo Tosho Co., Ltd., p. 112) discloses a conventional method of detecting an etching end point, A spectroscopic method and a method of irradiating an object to be etched with light, for example, a laser beam, and using the reflected light are disclosed.

[0004] The emission spectroscopy is a method for detecting the end point of etching by monitoring the light emission of constituent atoms or reaction products of an object to be etched in plasma.

The detection method using reflected light is a method in which, for example, a laser beam is applied to an object to be etched, and the end point of etching is detected from an interference waveform or a time differential waveform of light reflected from the object. FIG. 3 is a diagram showing an example in which an etching end point is detected based on a time-differential signal waveform of a current obtained by photoelectrically converting reflected light from an object to be etched. The vertical axis indicates the time derivative of the current (dI / dt), and the horizontal axis indicates the time. In this method, dI / dt fluctuates when the etching of the object to be etched progresses, but dI / dt varies when the object to be etched is completely etched.
Since / dt continues to indicate zero, the time a (see FIG. 3) is set as the end point of the etching.

In the emission spectroscopy, since the emission of constituent atoms of an object to be etched or the emission of a reaction product is monitored, if the area to be etched is narrow, the above emission becomes weak, so that sufficient sensitivity cannot be obtained. On the other hand, in the detection method using reflected light, measurement was relatively easy even when the region to be etched was narrow.

[0007]

However, in the etching end point detection method using reflected light, which is described with reference to FIG. 3, when the etching rate of the object to be etched is extremely low, dI / Since the time during which dt continues to exhibit a constant value near zero (including zero) is longer than when the etching rate is high, it is difficult to determine whether the etching of the object to be etched has been completed. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and accordingly, it is an object of the present invention to provide a conventional method for performing an etching end point of an object to be etched in dry etching using reflected light from the object to be etched. An object of the present invention is to provide a method capable of reliably detecting an etching end point.

[0009]

In order to achieve this object, according to the present invention, the end point of etching when etching an object to be etched by dry etching is determined by irradiating the object with light and reflecting the light. In the method using light, an end point of an object to be etched is detected based on a signal obtained by adding an absolute value of a time derivative of an intensity of at least two lights having different wavelengths among reflected lights. .

In the present invention, the at least two lights having different wavelengths from each other include not only ideal at least two monochromatic lights but also at least a practically narrow spectral width within a range in which the object of the present invention can be achieved. This includes the case of two lights (quasi-monochromatic light).

In practicing the present invention, the light to be applied to the object to be etched may be obtained from separate monochromatic light sources having the above-mentioned lights having different wavelengths as main wavelengths, or at least the lights having the above-mentioned wavelengths different from each other. It may be obtained from a single light source (including a white light source and the like) containing both lights. It is desirable that the light source used be capable of outputting light of the corresponding wavelength at a constant intensity.

Further, in practicing the present invention, it is desirable that the base of the object to be etched can reflect at least two lights having different wavelengths as described above.

[0013]

According to the structure of the present invention, of the reflected light from the object to be etched, for example, the first reflected light having a wavelength of λ _{1 and} the second reflected light having a wavelength of λ ₂ (for example, λ ₁ = 2λ
Considering the example using ₂ ), the first
The changes in the intensity of the reflected light and the second reflected light associated with the etching of the object to be etched occur in different phases as shown in FIG. And these first
Since the absolute value of the time derivative of the intensity of the second reflected light and the intensity of the second reflected light are obtained, the intensity change of each reflected light is as shown in FIG. A signal as shown in FIG. As is apparent from FIG. 1C, in the present invention, the signal for detecting the etching end point always indicates a level on the plus side from the zero level as long as the etching is in progress. It is easier to determine that the etching rate of the object is very slow and that the etching of the object has reached the end point.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for detecting an etching end point according to the present invention will be described below with reference to the drawings. It is to be noted that the drawings used in the description are only schematically shown to the extent that the present invention can be understood.

First, an example of a detection apparatus suitable for carrying out the etching end point detection method of the present invention will be described with reference to FIG. In FIG. 2, reference numeral 11 denotes a dry etching apparatus, and a substrate 15 having an object to be etched 13 is provided at a predetermined position in the dry etching apparatus 11. Here, the substrate 15 is, for example, a silicon substrate or GaAs.
A semiconductor substrate such as a substrate can be used, and the object 13 to be etched can be an insulator such as a SiO ₂ film.

This detecting device comprises a light source 21 capable of irradiating the etching target 13 with a first irradiation light having a wavelength of λ _{1 and} a second irradiation light having a wavelength of λ ₂ , and the first and second irradiation lights. A photodetector 23 for measuring the first reflected light intensity of the wavelength λ _{1 and} the second reflected light intensity of the wavelength λ ₂ of the reflected light from the object 13 to be etched, and the measured first reflected light A differentiating circuit 25 for differentiating the intensity of each of the reflected light and the second reflected light with time, an absolute value circuit 27 for calculating the absolute value of the differentiated signal, and an addition for adding the absolute signal A circuit 29 and a monitor 31 for monitoring the added signal and detecting the etching end point from the signal are provided.

Here, the light source 21 may have a light source that mainly emits the first irradiation light having the wavelength λ _{1 and} a light source that mainly emits the second irradiation light having the wavelength λ ₂ . Any of those that emit light including the above light may be used. However, it is preferable to emit light of these wavelengths at a constant intensity.

The photodetector 23 is preferably composed of a filter or a device having a spectroscope and a photoelectric conversion unit. Further, the differentiating circuit 25, the absolute value circuit 27, the adding circuit 29 and the monitor unit 31 can be constituted by conventionally known circuits. In particular, it is preferable that the monitor section 31 be configured to output an etching stop control signal to the dry etching apparatus 11 immediately after detecting the etching end point. It is preferable that the differentiating circuit 25, the absolute value circuit 27, the adding circuit 29, and the monitor unit 31 are constituted by a computer.

Next, an embodiment of the etching end point detecting method according to the present invention will be described with reference to an example using the apparatus described with reference to FIG. 1 (A) to 1 (C) are diagrams for explanation thereof. In particular, FIG. 1A shows the intensity of the first reflected light and the second reflected light detected by the photodetector 23 from the start of the etching of the object to be etched until the end point of the etching is detected (specifically, FIG. FIG. 1B is a diagram showing the change of the photoelectrically converted current value I, and FIG. 1B is a signal obtained by differentiating the signal of FIG. / Dt |, FIG. 1 (C) is FIG.
FIG. 3B is a diagram illustrating an addition signal of the respective signals in FIG. 2B, that is, a signal (etching end point detection signal S) obtained by the addition circuit 29. In each of the figures, the horizontal axis represents time, and the vertical axis represents intensity. In FIGS. 1A and 1B, a signal P indicated by a solid line is a signal derived from the first reflected light of the wavelength λ ₁ , and a signal Q indicated by a broken line is the second reflected light of the wavelength λ ₂ It is a signal derived from light.

In the method of detecting an etching end point according to the present invention,
When the first reflected light and the second reflected light are measured by the photodetector 23 when the thickness of the object to be etched is reduced due to the etching, as shown in FIG. Two changing signals P and Q are obtained. However, since the wavelength λ ₁ of the first reflected light is different from the wavelength λ _{2 of} the second reflected light, the period T ₁ of the intensity change of the first reflected light and the intensity change of the second reflected light Is different from the period T _{2 of} Assuming that λ ₁ and λ ₂ have a relationship of, for example, λ ₁ = 2λ ₂ , the period T ₁ of the intensity change of the _first reflected light and the period T ₂ of the intensity change of the second reflected light are T ₁ = 2T ₂ .

Therefore, when the first and second reflected lights (electrically converted currents) whose intensity is changed as described above are processed by the differentiating circuit 25 and the absolute value circuit 27, as shown in FIG. The signal | dI / dt | is obtained. Further, when this signal is processed by the adder circuit 29, as shown in FIG. 1 (C), the intensity does not become zero during the etching of the object to be etched, and the intensity becomes low when the etching of the object to be etched is completed. Is zero, that is, a signal S for detecting the etching end point. For this reason, even when the etching rate is extremely slow, the addition circuit 29 outputs a signal having an intensity on the plus side from zero, which can be clearly distinguished from the case where the etching of the object to be etched is completed.

In the above, the embodiment of the method for detecting the end point of the dry etching according to the present invention has been described. However, the present invention is not limited to the above embodiment.

For example, in the above embodiment, two lights having different wavelengths among the reflected lights from the object to be etched are used, and the wavelength relationship between the two reflected lights is λ ₁ = 2λ _2. The wavelength relationship of light is not limited to this, and other wavelength relationships may be used as long as the object of the present invention can be achieved. For example, even when the wavelength relationship between the two reflected lights is λ ₁ = 4λ ₂ , the same effect as in the embodiment can be expected.

In the above embodiment, two lights having different wavelengths among the reflected lights are used. However, depending on the design, three or more lights having different wavelengths among the reflected lights from the object to be etched are used. May be.

The object to be etched is not limited to an insulating film, and may be any object as long as the end point of etching can be detected using reflected light.

If necessary, the added value output from the adding circuit may be multiplied by a coefficient.

[0027]

As is clear from the above description, according to the method for detecting the etching end point in dry etching of the present invention, a signal on the positive side from zero is always obtained while the object to be etched is being etched. The signal becomes zero level only after the etching of the etching object is completed. Therefore, even when the etching rate is extremely low, it is possible to clearly distinguish the state of the etching of the object to be etched from the state where the etching of the object to be etched is completed.

For this reason, for example, the etching control for forming a contact hole in an interlayer insulating film of a semiconductor device can be performed accurately, so that the dry etching process can be automated, and the quality of the semiconductor device can be improved. Can be expected.

[Brief description of the drawings]

FIGS. 1A to 1C are explanatory diagrams of an etching end point detecting method according to an embodiment.

FIG. 2 is an explanatory diagram of a detection device suitable for implementing the present invention.

FIG. 3 is an explanatory diagram of a conventional technique and its problems.

[Explanation of symbols]

 11: Dry etching apparatus 13: Object to be etched 15: Substrate 21: Light source 23: Photodetector 25: Differentiator circuit 27: Absolute value circuit 29: Adder circuit 31: Monitor section

Claims (1)

(57) [Claims] 1. A method of irradiating an object to be etched with light and using the reflected light to detect the end point of the etching when etching the object to be etched by dry etching, wherein the reflected light has different wavelengths from each other. An end point detection method in dry etching, wherein an end point of an object to be etched is detected based on a change in a signal obtained by adding an absolute value of at least two light intensity time derivatives.