JPH02234427A - Method and apparatus for detecting terminal point of dry etching of tantalum film - Google Patents

Abstract

PURPOSE:To detect a terminal point of dry etching of a tantalum film by a method wherein transition due to time in intensity of light (electromagnetic wave) emitted from bromine atoms in plasma generated by high frequency discharge or rate of change in the intensity due to time is used. CONSTITUTION:The intensity of beam emitted from bromine (Br) atoms in plasma is rapidly raised at the time of discharge start, after a temporary pause the intensity again increases to be the maximum, then it starts to decrease, and after a point where the rate of decrease largely changes the intensity gradually decreases with a constant decreasing rate. Since etching completion time of a tantalum (Ta) film (just etching time) decreases with a constant decreasing rate with Ten (n=1, 2, 3) as a turning point before and after it, it can be determined by the time where two lines cross each other in the figure, and the just etching time of the tantalum (Ta) film certified matches this point well. Thus the just etching time of the tantalum (Ta) film can be obtained with real time objectively and accurately based on variation due to time by detecting the emitted beam of bromine.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for etching patterns of fine tantalum (Ta) films used in the manufacture of X-ray exposure masks and semiconductor integrated circuits, and in particular, The present invention relates to a method and apparatus for detecting the end point of dry etching of a film.

[Conventional technology]

As the density of semiconductor integrated circuits becomes higher, the line width of a pattern required for forming an element is becoming less than 1 μm.

In recent years, as an alternative to the conventional ultraviolet exposure method, an X-ray exposure method that is capable of forming finer patterns has been actively researched. The X-ray exposure method requires a so-called X-ray mask in which a pattern made of a material that absorbs X-rays is formed on an X-ray transparent thin film.

X&? I-absorbers include tantalum (Ta), tungsten (W). Heavy metals such as gold (Au) are commonly used. Among these, tantalum (Ta) JP-A-59-146
As described in Publication No. 38, since batten formation is possible by reactive ion etching using CBrF3 (carbon trifluoride bromide) gas, it is possible to form battens by using ion milling or sputter etching. Gold (Au)
It has the advantage that it is easier to obtain vertical sidewalls than other patterns. However, depending on the etching conditions, vertical sidewalls can be obtained up to just etching, but the sidewalls are extremely unstable when over-etched, and undercuts rapidly progress after just etching. .

Generally, when depositing a thin film, there is a variation in film thickness within a substrate of about ±5%, and there is also a similar variation in etching uniformity. Therefore, even in dry etching of tantalum (Ta), the just etching time varies by about 20% in total within the substrate, and correspondingly, overetching by about 20% is automatically performed.

For this reason, it is desired to develop an etching method that does not cause undercuts even when overetched by about 20%, and as described in Japanese Patent Application No. 62-3 2266, tantalum (Ta) is used. As the etching gas, fluorine (F), bromine (Br). Tantalum (T) is removed during etching using a gas containing carbon (C) and hydrogen (H).
a) A dry etching method has been developed that protects the sidewalls of the pattern with a polymeric film to reduce undercuts.

[Problem to be solved by the invention]

However, under etching conditions that completely prevent etching of the sidewalls, the deposition rate of the polymer film exceeds the etching rate even in the areas to be removed due to plasma polymerization, making it difficult to etch the tantalum (T a ) film with good reproducibility. becomes difficult. On the other hand, the time from the start of etching until the portion of the tantalum (Ta) film to be removed is removed in just the right amount and the underlying material appears is called the just etching time, but the just etching time for the tantalum (Ta) film is Speed (film thickness removed/time)
It is usually estimated from the film thickness. This method requires knowing accurate values of film thickness and etching rate, and is susceptible to changes in etching rate due to non-uniformity of film thickness, errors in estimation, or changes in plasma conditions. especially,
In dry etching of tantalum (T a ) films that are prone to undercuts, X, v! Necessary for masks. This becomes an obstacle in the formation of the necessary submicron fine patterns. Therefore, it has been desired to establish a method for detecting just etching time that does not depend on changes in film thickness or etching conditions.

[Means to solve the problem]

The purpose of the present invention is to provide a method and apparatus for detecting the just etching time of a tantalum (Ta) film during etching in real time without being affected by changes in the initial film thickness or etching conditions of the tantalum (Ta) film. It is about providing.

In order to achieve the above object, the present inventors have developed tantalum (Ta).
). Fluorine (F) and Bromine (B
The etching gas is a gas mixed with the element r), and the elements carbon (C) and hydrogen (H), which have the effect of inhibiting etching and suppressing undercut.
) We experimentally investigated the spectrum of light emitted from plasma during film etching and its temporal changes in the wavelength range from near-ultraviolet to near-infrared, and obtained the following results.

That is, (1) to provide a point where the time dependence of the intensity of the emission line emitted by the bromine (Br) element among various emission lines emitted from plasma corresponds one-to-one with the just etching time of the tantalum (Ta) film. , (2) Is the time dependence of the emission intensity from bromine (Br) element due to hydrogen (H) in the etching gas? Although the etching time changes with the degree of M, it has become clear that there is a method of obtaining just the etching time based on the time dependence in this case as well. Therefore, the present invention detects the luminescent radiation emitted from the bromine (Br) element in plasma using a photoelectric converter such as a photodiode or photomultiplier tube, and detects the time change of the luminescent radiation by using a photoelectric converter such as a photomultiplier tube. The main feature is that the time can be obtained objectively and accurately in real time. Conventionally, tantalum (T
a) In film etching, no method has been proposed to mechanically and objectively obtain the just etching time;
For example, a method has been used in which the just etching time is determined from the change in contrast of the etched surface of the tantalum (T a ) film with the naked eye.

Against this. However, in the present invention, the just etching time is determined from the time dependence of the emission intensity of the emission line of the bromine (Br) element, so the just etching time can be accurately obtained and unnecessary overetching can be prevented. Advantages exist.

〔Example〕

Among the light emitted from plasma, the emission lines from Br atoms are 444.2, 447.3,
447.8, 452.6, 457.6, 4
78.0. 497.98, 614.9, 63
5.1, 663.2, 668.2, 669
．． 2,679.0,679.1,700.5
, 734.9 , 751.3 , 780.3 ,
793.9 798.99, 813.2, 8
15.4, 827.2, 833.5, 844
．． 7, 847.8, 856.6, 863.
9, 882.5. It is known that the maximum intensity is exhibited at a wavelength around 889.3 nm. Kuntal (T a ) focused on the temporal changes in the emission intensity of these emission lines.
A method for detecting the end point of dry etching of a film is an important feature of the present invention. Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram explaining the first embodiment of the present invention, in which a tantalum (Ta) film deposited by a sputtering method is
rF. 827.4, 844.7, and 863.9 nm, respectively, emitted from the bromine (Br) element obtained when etching with gas at a pressure of 50 mTorr and a high-frequency power density of 0.27 W/cm2.
This is the etching time dependence of the emission line intensity with a peak in the vicinity. The light emitted from the plasma is guided to a spectrometer using an optical fiber, and the separated light is photoelectrically converted by a photomultiplier tube, and the time dependence of the light emission intensity is output to a plotter. The time dependence of each emission line shows almost the same time course, although there are differences in emission intensity. That is, the intensity of the luminescent line rises rapidly with the start of discharge, temporarily stagnates, and then increases again to reach its maximum value. After that, it begins to decrease, and after passing a point where the rate of decrease changes significantly, it gradually decreases at a constant rate of decrease. The etching end time (just etching time) of the tantalum (Ta) film is given by Te+ + Te2 and Te3 as shown in FIG. The etching end time is Ten (n=1.2.
Before and after 3) is a turning point, the emission intensity decreases at different constant decreasing rates, so it can be determined by the time when two straight lines intersect, as shown in FIG. This time corresponds well to the just etching time for etching the tantalum (Ta) film, which was confirmed by visual observation or scanning electron microscope. Here, three of the luminescent lines emitted by the bromine (Br) element are illustrated, but bromine (Br) emitted from plasma
The above-mentioned 4, which is observed in the air as an emission line from atoms.
44.2, 447.3, 447.8, 45
2.6, 457.6, 478.0. 497
．． 98,614.9, 635.1, 663.2
, 668.2 , 669.2 , 679.0
, 679.1 , 700.5 , 734.9 ,
751.3, 780.3. 793.9. 7
98.99, 813.2, 815.4, 827
．． 2,833.5, 844.7,
847.8, 856.6, 863.9
, 882.5. It was confirmed that all the emission intensities showing the maximum intensity at wavelengths around 889 and B nm showed the same etching time dependence as in FIG. 1.

Figure 1 shows the case where only CBrF3 (carbon trifluoride bromide) gas is used as the etching gas for the tantalum (Ta) film, but the time dependence of the emission intensity is due to the inclusion of etching gas hydrogen (H). It changes with However, even in this case, the just etching time can be obtained from the dependence of the emission intensity on the etching time. FIG. 2 shows a second embodiment of the present invention, in which the etching gas composition ratio is CB rF3 : CHF3 = 3.
This is the etching time dependence measured using a gas having a component ratio of 2 and focusing on the intensity of the emission line with a wavelength of 827.4 nm emitted from the plasma during etching.

When hydrogen (H) is present in the etching gas, the intensity of the emission line increases rapidly immediately after plasma generation, reaches a maximum value, then decreases and maintains a minimum, almost constant intensity for a certain period of time. Then it increases again and shows a constant intensity. It has been found that the etching end time in this case is the time Te in FIG. 2 which shows good agreement with the actual etching end time observed by SEM observation. Although the emission line with a wavelength of 827.4 nm is shown here, bromine (B) emitted from plasma is
r) The aforementioned 444.2, 447.3, 447.8, observed in the air as emission lines from atoms.
452.6, 457.6. 478.0, 49
7.98, 614.9, 635.1, 663
．． 2, 668.2, 669.2, 679.
0, 679.1, 700.5, 734.9
, 751.3 , 780.3 , 793.9 ,
798.99, 813.2, 815.4,
827.2, 833.5. 844.7 84
7.8, 856.6, are obtained.

Which type (type) does the time dependence of the emission line intensity belong to, the first embodiment or the second embodiment? Does it depend on the hydrogen (H) in the etching gas? It depends on the a degree, but for example CB
When mixing rF3 with 10% or more CHF3, CH
Fs? As m degrees increase, the time dependence rapidly shifts from the type of the first embodiment to the type of the second embodiment. Also, CBrF. When the etched area of tantalum (T a ) is large in a -rich (excessive) gas composition, the time dependence of the emission intensity shows the same transition as the type of the second embodiment.

In the above embodiment, a photomultiplier tube was used as the photoelectric conversion device, but instead of this, a wavelength containing at least one or more noteworthy emission lines from bromine (Br) atoms emitted from the plasma described above may be used. A photodiode having sensitivity within the region may also be used, and in this case, the end point of etching can be detected with a cheaper device configuration. Further, in the example, since a spectroscope with high resolution was used, the dependence of the emission intensity on the etching time for each emission line was shown, but such resolution is not necessarily necessary. Furthermore, from the relationship between the emission line and the emission intensity, if an appropriate photodetector is used, 916.6, 91, which exists in the near-infrared region, can be detected.
7.4, 917.8, 926.5, 932
．． 1, 989.6 and 1045. It is easily inferred that the emission line from the bromine (Br) element around 8 nm can also be used.

FIG. 3 shows tantalum (
This is an example of the configuration of an apparatus for detecting the end point of dry etching of a Ta) film. The etching end point detection device includes a photoelectric converter 31,
It consists of an m divider 32, an end point detection control device (output monitoring/end point detector) 33, and a storage device 34 that stores an end point detection algorithm or program, and is particularly characterized by being equipped with a differentiator 32. be. In this example, the differentiator 32 is arranged as an independent device, but the differentiator 32 may also be realized by program processing by a computer within the output monitoring/end point detector 33. Finally terminal 35
An end point detection signal output is obtained at . FIGS. 4 and 5 are fourth and fifth embodiments of the present invention, respectively, and are diagrams illustrating an etching end point mechanism as an operating principle of dry etching of Kuntal (T a ) by this apparatus. That is, the time dependence (a) of the signal obtained by converting the intensity of the emission line with a wavelength of 827.4 nm emitted from the bromine (Br) element in the plasma into an electrical signal by a photoelectric converter, and the differential processing of this signal by a differentiator. The signal (b) obtained by

Figure 4 corresponds to the time dependence of the luminescence intensity in Figure 1, and
The figure corresponds to the time dependence of the emission intensity in FIG. In FIG. 4, the etching end time of the tantalum (Ta) film is determined by the fact that the output from the signal processing device takes an almost constant negative minimum value for a certain period of time, then decreases and transitions to a second negative constant value. The etching end time can be detected either at the starting time T, or in FIG. 5, at the time T4 when the output from the signal processing device goes from a negative value to a maximum positive value and then becomes zero again.

〔Effect of the invention〕

As explained above, by using the method and apparatus for detecting the end point of tantalum (Ta) film dry etching according to the present invention, bromine (Br), which is found in the near-ultraviolet region to the near-infrared region, can be detected.
) The etching end point of the tantalum (Ta) film can be determined objectively and accurately from the etching time dependence of the emission line from the element. The present invention can also be applied to automatic etching of multiple samples using automatic detection of etching end time and detection of abnormal conditions through automatic monitoring of plasma conditions (or etching conditions).
The effects of using the device according to the present invention are wide-ranging.
This results in an industrially extremely effective method and device.

By using the dry etching end point detection method and apparatus according to the present invention, tantalum (T) in X-ray exposure method can be used.
a) In the formation of submicron fine patterns on masks, it is possible to detect just the etching time that does not depend on changes in film thickness or etching conditions, and there is no undercut, and moreover, tantalum (Ta) 39
can be etched with good reproducibility. The present invention provides a method and apparatus for detecting the just etching time of such a tantalum (Ta) film in real time, and has extremely high utility value, such as in a method for manufacturing fine semiconductor devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment according to the present invention,
CB r F. 827.4, 844.7, 86 when tantalum (Ta) film is etched with gas
FIG. 3 is a diagram showing the relationship between the etching time dependence of the emission intensity of the emission line from the bromine (Br) element appearing around 3.9 nm and the etching end point. FIG. 2 is a diagram showing a second embodiment of the present invention, in which CBrF, 10CHF. Bromine (
This is the relationship between the etching time dependence of the emission intensity of the emission line from the element Br) and the etching end point. FIG. 3 is a block diagram of a tantalum (Ta) film dry etching end point detection apparatus as a third embodiment of the present invention. FIGS. 4 and 5 are fourth and fifth embodiments of the present invention, and are diagrams for explaining the etching end point detection mechanism as the operating principle of tantalum dry etching by this apparatus, respectively.
The relationship between the differentiator output and the etching end point corresponding to FIG. 1 (first embodiment) and FIG. 2 (second embodiment) is shown. Te, Te. ,Te,,Te3, .--Etching end time T+. Tz. T3. Ta, Ts... Time a when the time course of the emission intensity changes... Time course of the emission intensity b... Time course of the differentiation result of the emission intensity with respect to time 31... Photoelectric converter 32... Differentiation Device 33...Output monitoring/end point detector 34...End point detection algorithm storage device 35...End point detection signal output terminal Patent applicant: Nippon Telegraph and Telephone Corporation Agent, Patent attorney: Kugoro Tamamushi This invention's first part Relationship between time dependence of emission intensity and etching end point as an example Figure 1 Relationship between differentiator output and etching end point as a fourth example of the invention ↑ Principle explanatory diagram Chicken 4 Figure

Claims (1)

[Claims] 1. A reactive gas is introduced into a vacuum container equipped with a vacuum evacuation device, a high frequency power source, an electrode, and a gas supply device, and high frequency power is applied to the electrode to cause discharge. In an apparatus for etching a tantalum (Ta) film, the reactive gas to be supplied contains at least bromine (Br) and fluorine (F).
), and focused on the time course of the intensity of light (electromagnetic waves) emitted from the bromine (Br) element in the plasma generated by high-frequency discharge in the vacuum container, and found that the emission intensity reached the maximum. After that, the etching end point is set at time T at which the rate of decrease with respect to time decreases significantly, or the time rate of change of the emission line intensity shows a positive maximum value and then a negative maximum value as the etching progresses. A method for detecting the end point of dry etching of a tantalum (Ta) film, characterized in that the end point of etching is set at a time T when the after-reduction rate decreases and shows a constant time reduction rate. 2. A reactive gas is introduced into a vacuum container equipped with a vacuum evacuation device, a high-frequency power source, an electrode, and a gas supply device, and high-frequency power is applied to the electrode to generate a discharge to form a tantalum (Ta) film. In an etching device, the reactive gas supplied is at least bromine (Br), fluorine (
Bromine (Br) in the plasma generated by high-frequency discharge in the vacuum chamber, which contains the hydrogen (H) element in addition to the element F)
By focusing on the temporal changes in the intensity of light (electromagnetic waves) emitted from elements, we can determine the concentration of hydrogen (H) or bromine (H) in reactive gases.
Br) When the change in the luminescence intensity of the element with respect to time shows the minimum value of the luminescence intensity and the rate of change becomes almost zero, it starts to increase again and the rate of change in the luminescence intensity reaches almost zero at time T,
Either the end time of etching is set at time T, or the time rate of change of the emission line intensity shows a negative minimum value as etching progresses, then shows a positive maximum value, and then the time rate of change becomes approximately A method for detecting the end point of dry etching of a tantalum (Ta) film, characterized in that the end point of etching is set to a time T which becomes zero. 3. Light of a single or multiple emission lines (electromagnetic waves) having a predetermined wavelength within the wavelength range of 400 nm to 1100 nm
A photoelectric converter having a sensitivity to and in particular a differentiator producing a time rate of change of an electrical output signal of the photoelectric converter and monitoring output changes from the differentiator; A storage device storing an algorithm for the method for detecting the end point of dry etching of a tantalum (Ta) film as described above, or a program for realizing the same, in a form readable by a machine or a human; and an output device that outputs an electrical signal indicating that the end point of etching has been detected according to a program.
Film dry etching end point detection device.