JP2000077388A - Method and system for dry etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce subtrenches at the time of fine patterning by applying a sine wave bias subjected to amplitude modulation by a saw-tooth wave to a sample setting electrode. SOLUTION: At the time of etching a sample 113 set on an electrode 112 applied with an AC bias voltage by touching the surface of the sample 113 to a plasm generated above the sample 113, the AC bias voltage is subjected to amplitude modulation by a saw-tooth wave by an amplitude modulation bias generating mechanism 116 comprising a sine wave oscillator 110 and a saw-tooth wave generator 109. For example, a sine wave (AC bias) of about 800 kHz is subjected to amplitude modulation by a triangular wave or a saw- tooth wave. Frequency of the sine wave is about 2 MHz or below, preferably 2-100 kHz, more preferably 2-400 kHz and one cycle of the waveform used for amplitude modulation is preferably set t about 10 ms or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method and a dry etching apparatus by a plasma process used in a manufacturing process of various fine patterns such as a semiconductor element and an electronic circuit, and more particularly to a method of applying a bias to an object to be processed. The present invention relates to a dry etching method and a dry etching apparatus for performing a plasma treatment by using a dry etching method.

[0002]

2. Description of the Related Art At present, in an etching process used for manufacturing a semiconductor device, a method using etching by plasma processing is mainly used to realize fineness and anisotropic processing. In the etching process by the plasma treatment, as a means for generating plasma, a method of irradiating a gas introduced into a vacuum vessel with an electromagnetic wave and dissociating the gas with the energy is generally used.

As a plasma source for generating this plasma, for example, a capacitively coupled plasma (CCP) is used.
plasma), inductively coup (ICP)
ledplasma) and ECR (electron cyclotron resonance) plasma. In addition, there are ECR plasmas that use UHF-band electromagnetic waves instead of conventional micro (μ) waves.

When etching is performed using a plasma source having a relatively low plasma potential, such as ICP or ECR plasma, a high frequency (RF) bias is applied to the processing sample to accelerate the processing on the processing sample. The technology to make it work has been established. This RF bias includes 13.56MHz, 2MHz, 800k
Frequencies such as Hz are commonly used.

For example, in the step of forming a gate of a field effect transistor (MOS device), when these RF biases are applied and gate etching is performed, local side etching (notching) occurs between a gate oxide film and a gate electrode. ) Occurred. This is because the electrons incident on the sample have low energy, so that the electrons cannot reach the etching bottom surface, the bottom surface is charged positively, and the path of the incident ions is bent by Coulomb repulsion. To solve this problem, there is known a "pulse bias" (JP-A-6-61182) technique in which a positive voltage is applied sooner than the electron attraction time to attract electrons to the etching bottom surface.

[0006]

However, as the thickness of the gate oxide film is reduced to 5 nm or less due to the miniaturization of ULSI, the problem of destruction of the gate insulating film due to the sub-trench shape is newly closed rather than the problem of notching. I've been up. The destruction of the gate insulating film by the sub-trench shape means that a conductive film formed on the gate insulating film for forming a gate electrode is etched using a resist mask to form a pattern of minute electrodes (gate electrodes). In this case, an unnecessary groove (subtrench shape) is formed in the insulating film around the gate electrode, and the gate insulating film is destroyed.

Therefore, an object of the present invention is to provide the above ICP, E
Using a plasma source with a relatively small plasma potential such as CR,
To provide.

More specifically, in a dry etching method and apparatus for applying a bias to a processing sample setting electrode using high density plasma of about 10 ¹¹ to 10 ¹² cm ^-3 , the number of sub-trenches can be reduced. An object of the present invention is to provide an improved dry etching method and dry etching apparatus.

[0009]

As a cause of the above-mentioned sub-trench, reflection of ions on a side wall of an electrode pattern is generally said. According to the experimental studies by the present inventors, 10 ¹¹ to 10 ¹²
When an RF bias of, for example, 800 V and 150 Vpp is used in a high-density plasma of cm ⁻³ , the energy distribution of ions incident on the sample spreads to about 0 to 150 V as shown in FIG. It is considered that the ions in the high-energy portion 402 are reflected on the pattern side wall, and a subtrench is generated.

Therefore, it has been noticed that a bias application method in which a high energy portion of the ion energy distribution does not exist may be employed. In order to realize this, for example, an 800 kHz sine wave (AC bias) may be amplitude-modulated by a sawtooth wave such as a triangular wave or a sawtooth wave.
In that case, the frequency of the sine wave is 2 MHz or less, preferably 2M
Hz to 100 kHz, more preferably 2 MHz to 400 kHz,
It was found that it is desirable that one cycle of the waveform used for amplitude modulation should be 10 ms or less.

The present invention has been made based on such knowledge, and the invention according to the above-mentioned dry etching method has a plasma etching method in which an AC bias voltage is applied to an electrode on which the sample is placed. In the dry etching method, the AC bias voltage is amplitude-modulated and applied with a sawtooth wave when etching is performed by causing the sample surface to come into contact with the plasma and performing the etching process.

Further, according to the invention relating to the dry etching apparatus of the above object, there are provided means for introducing a gas into a vacuum discharge part container, means for radiating electromagnetic waves into the discharge part container to generate plasma, and installing a processing sample. And a means for applying an AC bias voltage to the applied electrode, wherein the means for applying the AC bias voltage to the electrode on which the processing sample is placed is subjected to amplitude modulation by applying a sawtooth wave to the AC bias voltage. The present invention is achieved by a dry etching apparatus characterized by comprising means.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the above dry etching method, the sawtooth wave for amplitude-modulating an AC bias voltage is, for example, a waveform having a predetermined rising inclination angle with respect to a time axis t, and a typical waveform is a triangular wave or a triangular wave. Although it is a sawtooth wave, the vertices of these waveforms are rounded,
The waveform may be missing or slightly deformed. However, it does not include a rectangular wave whose rise is vertical.

In the above-mentioned dry etching apparatus, the means for applying a sawtooth wave to the AC bias voltage and modulating the amplitude includes, for example, a sine wave oscillator and a sawtooth wave generator. May be amplitude-modulated.

As the plasma used for dry etching, high-density plasma of, for example, about 10 ¹¹ to 10 ¹² cm ^-3 is used. Various types of electronic components that require the formation of various fine patterns, such as various etching processes in the manufacturing process of semiconductor devices that require processing (eg, gate electrode forming process for MOS devices) and various fine pattern forming processes in the manufacturing process of thin-film magnetic heads. It can be widely used in the manufacturing process.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic explanatory view schematically showing a specific configuration example of a dry etching apparatus according to the present invention. This apparatus is an example of a UHF band ECR etching apparatus, and the feature of the apparatus configuration is that, when an AC bias voltage is applied to the sample setting electrode 112, an amplitude modulation bias generation mechanism 116 that amplitude-modulates the AC bias with a sawtooth wave. It is in the point with.

The present apparatus is configured such that the discharge vessel 1
After the gas is introduced into the chamber 05, the pressure in the vessel can be controlled by a variable opening valve (not shown) attached to the evacuation device 106.

A UHF wave oscillated from a UHF power supply 101 is transmitted by a coaxial tube or a waveguide, and is matched with a load impedance by a UHF wave matching device 102 to form an electromagnetic wave radiating electrode 103.
Is discharged into the discharge part container 105.

The gas in the discharge part container 105 is dissociated by the energy of the emitted electromagnetic wave. At this time, the magnetic field formed by the electromagnet 104 causes the electrons to undergo electron cyclotron motion, so that the plasma 115 can be generated at a low pressure of about 0.5 to 2 Pa. The processing sample 113 is a sample setting electrode 112
It is installed above and has a structure in contact with the plasma 115.

The amplitude modulation bias generating mechanism 116 for realizing the present invention includes a sine wave oscillator 1 having an amplitude modulation function.
It comprises 10, a triangular wave generator 109 and a linear amplifier 108. Then, the oscillation frequency from the sinusoidal oscillator 110 (800 kHz
In order to perform the matching in z), power is supplied to the installation electrode 112 on which the sample 113 is mounted using the matching device 107. When using a sine wave other than 800 kHz, use the linear amplifier 108 and matching unit 1
07 can be dealt with by changing according to the frequency of the sine wave used.

Further, as the amplitude modulation bias generating mechanism 116 for realizing the present invention, an oscillator in which the sine wave oscillator 110, the amplifier 108 and the triangular wave generator 109 are integrated may be used. Blocking capacitor 1
When measured at a point between 11 and the sample setting electrode 112, it is observed as shown in FIG. It can be seen that the present apparatus did not employ the electrostatic adsorption type sample fixing method, so that a negative DC component was generated by bias application.

Using the UHF band ECR plasma shown in FIG.
Fig. 3
FIG. 3B shows an etching result when a sample having a gate structure in a MOS device as shown in FIG.
Shown in

FIG. 3C shows an etching result when a bias whose amplitude is modulated to the triangular wave of the present invention is applied. The structure of the sample used was such that resist 30
1. Conductive film (poly-Si) 30 for forming gate electrode
2. Insulating film (SiO ₂ ) 303 and Si substrate 304. When an RF bias is used without conventional amplitude modulation, a subtrench 305 is generated as shown in FIG. 3B, but when the present invention is applied, as shown in FIG. The sub-trench was sufficiently improved without any occurrence.

This is because the energy distribution of the incident ions is controlled according to the present invention. FIG. 4 (a) shows the results of simulating the energy distribution of ions incident on a processing sample when a conventional 800 kHz RF bias is applied without amplitude modulation and when a bias is applied by amplitude modulation with a triangular wave according to the present invention. ) And FIG. 4 (b).

From this result, it can be seen that the conventional 800 k
Fig. 4 (a) shows the incident ion energy distribution 401 in the case of Hz.
It can be seen that the high energy portion 402 exists as shown in FIG.

On the other hand, the maximum amplitude is constant and the period is 100 k.
The incident ion energy distribution in the case of the present embodiment in which the RF of 800 kHz was modulated by the triangular wave changed to Hz and 1 kHz changed as curves 404 and 403 shown in FIG. 4B. As the amplitude period is reduced, the high energy component 402 decreases, and 1
When the amplitude is modulated by the triangular wave of kHz, the high energy portion does not exist as shown by the curve 403.

It has been found that the sub-trench can be eliminated by eliminating the high energy component. Since a similar ion energy distribution can be obtained even with a sawtooth wave, a similar effect can be obtained even when the amplitude modulation waveform is a sawtooth wave.

The amplitude modulation bias generation mechanism 116 of the present embodiment.
This modulated waveform oscillated from is, as shown in FIG.
The one in which the time derivative near the peak of the lowest voltage 202 which is a main factor of high energy is discontinuous (specific examples, a triangular wave and a sawtooth wave) is effective. In FIG. 2, reference numeral 203 is an enlarged view of the vicinity 202 of the lowest voltage peak. As described above, the same effect can be obtained with the waveform 204 in which waveforms having different periods are superimposed without being affected by the noise component or the amplitude of the amplitude waveform, instead of the accurate triangular wave.

These effects are not limited to the UHF band ECR plasma etching apparatus, and the same effects can be obtained when ICP plasma or magnetron plasma is used.

From the experimental results, it was found that the resist selectivity was 2 to 2.
The effect of improving the selectivity from 3 to 3 to 4 and SiO ₂ from 50 to 70 was also obtained. This is also considered to be the result of the elimination of high energy components. Also, in a plasma having a density of 10 ¹¹ cm ^-3 , ions cannot follow the frequency of the applied sine wave when the frequency is 2 MHz or more, and the ion energy distribution is
Since the distribution is centered on V _DC , the present invention is more effective when the frequency is lower than this frequency.

The amplitude modulation bias generating mechanism 116 of the present embodiment
In the above, the triangular wave generator 109 was used as a means for generating a sawtooth wave in order to amplitude-modulate a sine wave, but the sawtooth wave generator is not limited to the triangular wave generator, and further these triangular waves,
It is needless to say that the same effect can be obtained even if the top of the sawtooth waveform generates a distorted waveform.

Example 2 FIG. 5 shows the results of an experiment in which the metal etching rate was measured when the period of the triangular wave used for amplitude modulation of the sine wave bias was changed. In the figure, the white circles indicate the etching rate 501 when the peak voltage of the triangular wave is 500 V, and the black triangle points indicate the etching rate 502 at 300 V. Thus, a result was obtained in which the etching rate decreased as the triangular wave cycle became slower than 100 Hz.

From this, it can be seen that the period of the triangular wave must be 100 kHz or more, that is, one cycle time is 10 ms or less in order to obtain the effect of the first embodiment while maintaining the etching rate in the practical range. Was.

From the above simulation results, it is needless to say that the cycle of the waveform for amplitude-modulating the sine wave bias needs to be equal to or less than the frequency of the sine wave (RF).

[0036]

As described in detail above, the intended object has been achieved by the present invention. That is, in a dry etching method and apparatus in which high-density plasma is used and a bias is applied to a sample setting electrode, a sinusoidal bias is amplitude-modulated with a sawtooth wave, which is the biggest problem in forming a fine pattern. The reduced sub-trench could be reduced or completely eliminated. Further, an effect of improving selectivity with respect to resist and oxide film can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of a UHF band ECR plasma etching apparatus according to one embodiment of the present invention.

FIG. 2 is a waveform diagram of a bias used when an effect of the present invention is tested.

FIG. 3 is a process cross-sectional view of the present embodiment showing an etching effect in a gate electrode pattern forming step in manufacturing a MOS device in comparison with a conventional comparative example.

FIG. 4 is a graph showing the energy distribution of ions incident on a sample in comparison with a conventional example.

FIG. 5 is a graph showing a change in metal etching rate when the cycle of a triangular wave used for amplitude modulation is changed.

[Explanation of symbols]

101 ... UHF power supply, 102 ... UHF wave matching device, 10
3 ... electromagnetic radiation electrode, 104 ... electromagnet, 105 ... discharge part container, 106 ... vacuum exhaust device, 107 ... RF matching device, 108 ... linear amplifier, 109 ... triangular wave generator, 110 ... sine wave oscillator, 111 ... blocking capacitor 112… Sample setting electrode, 113… Processed sample,
114… Gas inlet pipe, 115… Plasma, 116…
Amplitude modulation bias generation mechanism, 201: bias waveform used in the present invention, 301: resist, 302: poly-
Si, 303: SiO ₂ , 304: Si substrate, 305: Subtrench, 401: 800 kHz incident ion energy distribution (no amplitude modulation), 402: high energy portion, 403: incident ion energy distribution of the present embodiment, 501
... Characteristic diagram showing change in etching rate at 500 Vpp, 502
... Characteristic diagram showing change in etching rate at 300 Vpp.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kazunori Tsujimoto 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. F term in the Central Research Laboratory of the Works (reference) 4K057 DA02 DA13 DB01 DB06 DD01 DD08 DG20 DM02 DM18 DM20 DN01 5F004 AA02 AA05 AA06 BA04 BA08 BA09 BA14 BB11 BB18 BD07 CA06 CA09 DB00 DB02 DB08 EB02

Claims (10)

[Claims] 1. An AC bias voltage is applied to an electrode on which a sample is placed, and a plasma is generated on the sample and the sample surface is brought into contact with the plasma to perform an etching process. A dry etching method characterized by modulating and applying. 2. The frequency of the AC bias voltage is 2 MHz.
A dry etching method wherein the frequency is set to 100 kHz. 3. The dry etching method according to claim 1, wherein the sawtooth wave used for amplitude modulation of the AC bias voltage is a triangular wave. 4. The dry etching method according to claim 1, wherein the sawtooth wave used for amplitude modulation of the AC bias voltage is a sawtooth wave. 5. The dry etching method according to claim 1, wherein a cycle of one cycle of the saw-tooth wave used for amplitude modulation of the AC bias voltage is 10 ms or less. 6. Means for introducing a gas into a vacuum discharge vessel, means for radiating electromagnetic waves into the discharge vessel to generate plasma, and means for applying an AC bias voltage to an electrode on which a processing sample is placed. Wherein the means for applying an AC bias voltage to the electrode on which the processing sample is placed is constituted by a means for applying a sawtooth wave to the AC bias voltage to modulate the amplitude. apparatus. 7. A dry etching apparatus according to claim 6, wherein said means for applying a saw-tooth wave to said AC bias voltage and modulating the amplitude comprises a sine wave oscillator and a saw-tooth wave generator. 8. The sine wave oscillator has a frequency of 2 MHz to
7. An oscillator of 100 kHz.
Or the dry etching apparatus according to 7. 9. The dry etching apparatus according to claim 6, wherein the saw-tooth wave generator is a saw-tooth wave generator having one cycle of 10 ms or less. . 10. A dry etching apparatus according to claim 6, wherein said means for applying a saw-tooth wave to said AC bias voltage and modulating the amplitude comprises a sine wave oscillator and a saw-tooth wave generator.