JPH0669165A - Method for detecting end point of plasma dry etching - Google Patents

Abstract

PURPOSE:To obtain an emission spectrum intensity curve for judging an end point stably by completely receiving a luminous spectrum from the inside of gas plasma at a wavelength band which a photomultiplier in a specific wavelength range has. CONSTITUTION:A luminous spectrum from the inside of a gas plasma 11 in a reaction chamber 1 is taken into a photomultiplier 4 with a wavelength of 300-650nm and the sensitivity is adjusted by a sensitivity adjusting circuit 9, thus converting to an electrical signal and enabling the signal to be multiplied by the amplification circuit 6. After a gain and an offset are added to the signal by a gain circuit 8 and an offset circuit 7, the signal is taken into a microcomputer 5 and it is processed arithmetically, thus obtaining a target luminous spectrum intensity curve. Therefore, by further increasing the difference between the amount of luminous spectrum of Al of the luminous spectrum intensity curve and the amount of luminous spectrum of TiN, a displacement point becomes clear, thus detecting an end point positively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching endpoint detection method for semiconductor devices, and more particularly to a plasma dry etching endpoint detection method for a multilayer metal wiring layer.

[0002]

2. Description of the Related Art In recent years, a plasma dry etching method utilizing a reaction component in a gas plasma has been used as an etching method of a thin film capable of forming a fine pattern with high precision in a manufacturing process of a semiconductor device. There are various methods in the plasma dry etching method, but as a general method, high frequency power is applied to an electrode arranged in a reaction chamber which is a vacuum container, and a reaction gas introduced into the reaction chamber, for example, Cl. ₂ , HBr or the like is converted into a gas plasma, and radicals or the like which are active components in the gas plasma are utilized to etch a multilayer metal wiring layer or the like on a semiconductor wafer into a desired pattern with high accuracy.
In addition, problems such as stress migration have arisen with the recent trend toward finer wiring such as metal wiring films in semiconductor elements. As a countermeasure against this, multi-layered structures of metal wiring films have been developed. -Si-Cu alloy film / TiN-Ti film About 300 angstrom / 9000
It has a film structure of angstrom / 1000 angstrom.

As shown in FIG. 2, the spectrum intensity curve generated by the conventional method for detecting the end point of dry etching shows the emission spectrum from the gas plasma 11 in the reaction chamber 1 through the filter 10 capable of capturing the wavelength of 396 nm band. Photomultiplier
Then, the sensitivity is adjusted by the sensitivity adjusting circuit 9, and the sensitivity is adjusted by the sensitivity adjusting circuit 9, whereby the signal is converted into an electric signal and the signal is amplified by the amplifier circuit 4. Gain circuit 8 for this signal
After the gain and the offset have been added by the offset circuit 7, the gain is taken into the microcomputer 5 to obtain the emission spectrum curve as shown in FIG.

A method of actually detecting the end point using this emission spectrum curve will be described. The end point detection method for plasma dry etching is to determine the end point by finding the transition point where the emission spectrum intensity changes from a small change area to a large change area and then to a large intensity change area again.
In order to make the transition point of the emission spectrum curve obtained from the emission spectrum clearer and to ensure the detection of the end point, the calculation processing of the primary differential processing or the secondary differential processing is performed. When the Al-Si-Cu alloy film / TiN-Ti film is actually etched, for example, an emission spectrum curve as shown in FIG. 4 is obtained, and when the secondary differential processing is performed, a differential curve as shown in FIG. 7 is obtained. A simulation is performed in advance by setting process conditions, and the primary judgment level is set to the point where the Al film shifts to the TiN film for this differential curve.
The secondary judgment level is set at the point where the TiN film moves to the base. Actually, when the emission spectrum is obtained by etching the semiconductor wafer, the differential curve passes through the primary judgment level downward when moving from the Al film to the TiN film,
When the TiN film is again transferred to the base, the time when the secondary judgment level is passed in the upward direction is judged as the end point of the TiN-Ti film etching, and the Ti film / Al-S which is the metal wiring layer is judged.
As the end point of the etching of the i-Cu alloy film / TiN-Ti film, the gas plasma discharge is stopped and the etching is stopped.

[0005]

The emission spectrum intensity curve used in the above-described end point detection method is the emission spectrum in the wavelength band of 396 nm in which the emission spectrum of Al appears as a peak from the graph of the emission spectrum and wavelength shown in FIG. By capturing the spectrum as the emission spectrum intensity by the filter, the intensity change becomes the largest when the Al film etching is finished and the peak value of the emission spectrum intensity decreases. However, since the filter that can capture the wavelength of 396 nm band captures the emission spectrum with a certain haunch width, the Al film and TiN
At the point where the films are mixed and etched, A
l and the emission spectrum of TiN are almost at the same level,
The emission spectrum amount of N is slightly reduced. Therefore, 39
When the emission spectrum is taken into the photomultiplier through a 6 nm band filter, as shown in FIG. 4, when the etching of the Al film starts to shift to the etching of the TiN—Ti film, the shift of the emission spectrum curve is so-called “ It appears as a "hump". Fluctuation of the emission spectrum when the gas plasma discharge state is unstable, attenuation of the emission plasma due to contamination of the window provided in the reaction chamber, variation in etching rate, variation in thickness of the metal wiring film, etc.
Disturbance occurs in the emission spectrum curve from the point A to the point B where the film is etched, and the amount of change in the differential value when the emission spectrum curve is differentiated becomes an extremely small change. For this reason, there is a case where the differential curve does not pass the preset primary determination level in the downward direction and the primary determination is not performed, so that the end point determination is not applied. Further, when there is variation in the shift of the emission spectrum curve when the TiN film is transferred to the base, the secondary judgment level may not be passed in the upward direction, and the end judgment of the TiN-Ti film may not be made without making the secondary judgment. There were cases where it did not take place. As a result, overetching of the underlying layer causes a problem in the next process, and a residue of the TiN-Ti film remains, which causes an electrical short when actually operating as a semiconductor element. Yield was significantly reduced.

[0006]

A method for detecting the end point of plasma dry etching according to the present invention receives all emission spectra from a gas plasma in a wavelength band possessed by a photomultiplier, and calculates emission spectrum intensity curves The transition point is clarified by making the difference between the emission spectrum amount of Al and the emission spectrum amount of TiN larger, thereby ensuring the end point detection.

[0007]

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an embodiment for obtaining an emission plasma curve in a plasma dry etching endpoint detection method according to the present invention. The emission spectrum from the gas plasma 11 in the reaction chamber 1 was measured in the wavelength range of 300 to 6
The signal is taken into the photomultiplier 4 of 50 nm, and the sensitivity is adjusted by the sensitivity adjusting circuit 9, whereby the electric signal is converted into an electric signal and the signal is amplified by the amplifier circuit 4. After gain and offset are added to this signal by the gain circuit 8 and the offset circuit 7, the signal is taken into the microcomputer 5,
This is processed by arithmetic processing to obtain an emission spectrum intensity curve as shown in FIG. FIG. 9 is a cross-sectional view of an example of multilayer wiring to be etched. There is an oxide film 12 as an underlying insulating film of the multi-layer wiring, and a multi-layer wiring is formed on the oxide film 12 in order.
Ti film 13 with a thickness of 300 Å, thickness 100
TiA film 14 which is a barrier metal of 0 angstrom
(Although it may be a TiW film), an Al-Si-Cu alloy film 15 having a thickness of 9000 angstroms (may be an Al-Cu alloy film), and a TiN film 16 as an antireflection film having a thickness of 250 angstroms.

FIG. 6 is a graph showing the relationship between the emission spectrum intensity during the etching of the Al film, the emission spectrum intensity during the etching of the Ti film, and the emission spectrum intensity of the base and the wavelength. The emission spectra of the Al film and the TiN film are 300 nm, which is the constant wavelength band of the photomultiplier.
Al during etching when viewed in the range of up to 650 nm
It can be seen that the emission spectrum amount of TiN is larger than the emission spectrum amount of the film and the underlying layer, which makes the difference between the emission spectrum amount of Al and the emission spectrum amount of TiN larger. The relationship between the amount of Al emission spectrum collected by the photomultiplier and the etching time gives a graph as shown in FIG. Initially stable Al
Of the emission spectrum intensity curve, the slope of the emission spectrum curve is in the upward direction from the point A when the Al film is transferred to the TiN film, and has a peak value at the point B when the TiN film is completely etched. In addition,
Since the TiN film-Ti film is as thin as about 1000 angstroms, the etching ends immediately, so a downward curve is drawn up to the emission spectrum intensity level of the base.

An end point detecting method according to the present invention will be further described with reference to FIG. The emission spectrum curve obtained as described above is further subjected to second-order differential processing to obtain a differential curve. A simulation is performed in advance by setting process conditions, and a primary determination level is set at the point where the Al film shifts to the TiN film, and a secondary determination level is set at the point where the TiN film shifts to the base for this differential curve. When the emission spectrum is obtained by actually etching the semiconductor wafer, the differential curve passes upward from the primary judgment level when moving from the Al film to the TiN film, and the secondary curve passes when moving from the TiN film to the base again. The time point at which the judgment level passes upward is judged as the TiN film-Ti film end point, and is a metal wiring film such as Ti film / Al-Si-Cu alloy film / TiN film-
When the etching of the Ti film is completed, the gas plasma discharge is stopped and the etching is stopped.

Another embodiment of the end point detecting method according to the present invention will be described with reference to FIG. With respect to the emission spectrum curve obtained by the present invention, the level of the point B, which is the peak point of the rise of the emission spectrum intensity of TiN, is set to A by the simulation of the emission condition intensity of Al in advance.
It is set as the end point of the etching of the l film. Also, T
The over-etching time is calculated from the film thickness of the iN-Ti film and the etching rate, and is preset as a parameter. Thereby, the semiconductor wafer is actually etched to obtain the emission spectrum, and when the emission spectrum intensity reaches the point B, the TiN-Ti film overetching timer is started, and the time-over time point is determined as the end point of TiN. When the etching of the Ti film / Al—Si—Cu alloy film / TiN film—Ti film which is the metal wiring film is completed, the gas plasma discharge is stopped and the etching is stopped. According to the present embodiment, it is not necessary to perform complicated differential processing, and it is possible to provide a simple end point determination function. Capture of emission spectrum by photomultiplier Even if a wide wavelength band is used, there is quantum efficiency (expressed in%) that is the efficiency of the photomultiplier to convert the emission spectrum into current, and capture over a certain wavelength band. However, it cuts this, so a photomultiplier suitable for the present invention should be selected.

[0011]

As described above, according to the present invention, by receiving all the emission spectra from the gas plasma in the wavelength band of the photomultiplier, the emission spectrum intensity curve of Al and the emission spectrum amount of Al obtained are obtained. The difference in the emission spectrum amount of TiN becomes larger, and the transition point becomes clearer. This makes it possible to detect the end point more reliably and accurately. As a result, the influence of the change in the slope of the emission spectrum intensity curve due to the variation in the film thickness of the metal wiring film, which is the object to be etched, and the variation in the etching rate is almost eliminated, and as shown in one example and other examples. In the endpoint detection method,
It is possible to provide stable end point determination by eliminating variations in end point determination due to the fact that the end point cannot be found. As a result, the end point of plasma dry etching can be detected more reliably, and problems such as problems in the next process due to overetching of the base, which has been a problem in the past, and semiconductor elements due to residues of the TiN film-Ti film can be obtained. There is no problem of electrical short when operated,
The product yield can be significantly improved.

According to the present invention, if the film structure under the Al-Si-Cu alloy film is a TiN film-Ti film structure, Al-Si
Even if the film structure on the —Cu alloy film is a Si film other than the Ti film or another film structure, there is no particular problem. Also, T
Even if the film thickness of i film / Al-Si-Cu alloy film / TiN film-Ti film changes, there is no problem.

Ti film / Al-Si-Cu alloy film / TiN
Even in the wiring in which the other film is formed on the TiN film-Ti film having the film-Ti film structure, if the emission spectrum is higher than the emission spectrum intensity of the Al-Si-Cu alloy, the endpoint detection method according to the present invention can be used. is there.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of the present invention.

FIG. 2 is a schematic view of an embodiment according to a conventional method.

FIG. 3 is a graph of emission spectrum intensity and etching time according to the present invention.

FIG. 4 is a graph of emission spectrum intensity and etching time by a conventional method.

FIG. 5 is a graph of emission spectrum intensity by a conventional method and received wavelength by a photomultiplier.

FIG. 6 is a graph of the emission spectrum intensity according to the present invention and the received wavelength by a photomultiplier.

FIG. 7: Second derivative curve diagram of emission spectrum intensity by the conventional method

FIG. 8 is a second derivative curve diagram of emission spectrum intensity according to the present invention.

FIG. 9 is a cross-sectional view of a multilayer wiring according to an example.

[Explanation of symbols]

 1 Reaction Chamber 2 High Frequency Power Supply 3 Semiconductor Wafer 4 Photomultiplier 5 Microcomputer 6 Amplifier Circuit 7 Offset Circuit 8 Gain Circuit 9 Sensitivity Adjustment Circuit 10 Filter 11 Gas Plasma 12 Oxide Film 13 Ti Film 14 TiN Film 15 Al ・ Si ・ Cu Film 16 TiN film

Claims (1)

[Claims] 1. A Ti film, an Al-Si-Cu alloy film, and a Ti film.
A method for detecting the end point of plasma dry etching of a multilayer metal wiring layer by an N film and a Ti film, which is obtained by receiving all emission spectra from gas plasma in the wavelength band of a photomultiplier having a wavelength range of 300 to 650 nm. A method for detecting the end point of plasma dry etching, which uses an emission spectrum intensity curve.