JPH09186136A - Plasma processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excessive dissociation of process gas and increase the rate of selected Si to a matrix in plasma processing using a helicon plasma source. SOLUTION: The method is implemented as follows: Source power is applied through antenna 12 to a source chamber 11 that is constructed by utilizing a helicon plasma source and produces a plasma. The plasma produced by discharge due to the source electrode is used in necessary processes, such as etching, on a substrate 14. This plasma processing is performed at a source power below the value of source power corresponding to the portion of discontinuous variation in the ratio of the intensities of two if specific wavelength of beams of emitted light due to the above-mentioned plasma relative top the source power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method, and more particularly to a plasma processing method in which a semiconductor element is subjected to an etching process or a film forming process with plasma generated using a helicon wave plasma source.

[0002]

2. Description of the Related Art In recent plasma processing, it has been required to be performed at a low pressure as the processing size of a semiconductor element becomes finer and the processing accuracy becomes higher. Particularly, low-pressure processing is required for plasma etching. On the other hand, there arises a problem that the processing speed decreases as the processing pressure becomes lower. This is because when the processing pressure becomes low, the density of ions and neutral active species decreases. As a method of compensating for such a decrease in processing speed, there is a method of utilizing high density plasma.
As one of the plasma generation methods for obtaining high-density plasma, a method using a helicon wave plasma source has been conventionally proposed.

[0003]

A feature of the conventional plasma processing method utilizing a helicon wave plasma source capable of generating high density plasma at low pressure in plasma processing is that the dissociation degree of process gas is high. The feature of high dissociation degree poses the following problems.

For example, when high density plasma is applied to the etching of a silicon oxide film, the dissociation of the fluorocarbon gas, which is the process gas, proceeds too much, and fluorine atom radicals are generated. Since the fluorine atom radical is also an etchant of silicon (Si) which is the base of the silicon oxide film, even the base silicon is etched. When a helicon wave plasma source is used as a means for generating plasma, when a large source power is applied, the underlying silicon is etched, which causes a problem that a high selection ratio cannot be obtained with respect to the underlying silicon.

The above problem will be described in detail with reference to FIG. FIG. 4 is a graph showing the etching characteristics of the silicon oxide film when a high source power is applied, and the apparatus used in the experiment for obtaining these graphs is a plasma etching apparatus using a helicon wave plasma source. In this plasma etching apparatus, a plasma process for etching a silicon oxide film formed on a silicon substrate is performed under specific process conditions. Incidentally, in a conventional plasma etching apparatus using a helicon wave plasma source, it is common to apply high power as the source power, and in this example as well, the source power of the specific process condition is as high as 1500 W, for example. Power is on.

Regarding the coordinate system of the graph shown in FIG.
The horizontal axis is the size of the contact hole (diameter φ: unit is μ
m), the vertical axis on the left side represents the etching rate (angstrom / min (min)) of the silicon oxide film and the underlying silicon, and the vertical axis on the right side represents the selection ratio of the silicon oxide film to the underlying silicon (selectivity ratio to underlying silicon). ) Means. FIG. 4 is a graph 5 showing changes in the etching rate of silicon.
1, a graph 52 showing changes in the selection ratio, and a graph 53 showing changes in the etching rate of the silicon oxide film are drawn.

According to FIG. 4, as is clear from the graph 52, for example, the selectivity ratio to the underlying Si obtained in the contact hole having the diameter φ of 0.5 μm is 23 at most.
This selection ratio is an inadequate value because the selection ratio of Si to the underlying silicon is required to be 40 or more in the device manufacturing under the sub-half micron design rule. As described above, the conventional plasma etching apparatus using the helicon wave plasma source has a problem that only a low selectivity ratio of Si to the underlying layer can be obtained.

An object of the present invention is to solve the above problems. When plasma processing is performed using a helicon wave plasma source, plasma processing is performed by suppressing excessive dissociation in the process gas, and Si against the underlying substrate is used. It is to provide a plasma processing method capable of increasing the selection ratio.

[0009]

A plasma processing method according to a first aspect of the present invention (corresponding to claim 1) is configured by using a helicon wave plasma source, and an antenna is provided in a source chamber for generating plasma. This is a method in which the source power is input via the plasma and the necessary processing is performed on the substrate with the plasma generated by the discharge based on this source power.
It is configured to perform plasma processing with a source power that is less than or equal to a source power value that corresponds to a portion of the emission characteristics of the plasma that changes in the ratio of the emission intensity of two specific wavelengths with respect to the source power and that changes discontinuously. It

In the first aspect of the present invention, the source power supplied corresponds to a portion of the light emission by the plasma which changes discontinuously due to the change characteristic of the ratio of the emission intensity of two specific wavelengths to the source power. Since the value is less than or equal to the electric power value, excessive dissociation of the process gas is suppressed, and when this plasma processing method is applied to etching of a silicon oxide film, for example, the selection ratio of underlying Si can be increased.

A plasma processing method according to a second aspect of the present invention (corresponding to claim 2) is the dry etching of a thin film containing silicon oxide as a main component using fluorocarbon gas according to the first aspect of the present invention. Characterize.

A plasma processing method according to a third aspect of the present invention (corresponding to claim 3) is the plasma processing method according to the second aspect of the present invention, wherein the ratio of the emission intensities of the two specific wavelengths is the emission intensity of the F radical wavelength. It is characterized in that it is the ratio of the emission intensity of the wavelength of CyFx.

A plasma processing method according to a fourth aspect of the present invention (corresponding to claim 4) is the plasma processing method according to the third aspect of the present invention, wherein the ratio of the emission intensities of the specific two wavelengths is equal to the emission intensity of the F radical wavelength. It is characterized in that it is the ratio to the emission intensity of the wavelength of CF ₂ .

[0014]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 schematically shows a plasma etching apparatus using a helicon wave plasma source as a typical example of the plasma processing apparatus in which the plasma processing method according to the present invention is implemented. In FIG. 1, a pair of antennas 12 for generating a helicon wave excitation electric field and an external magnetic field necessary for exciting a helicon wave are formed around a source chamber 11 for generating plasma, which is formed of a dielectric material. The generating coil 13 is arranged. Source chamber 1
1 generates plasma by the action of discharge. The source chamber 11 is provided on the upper wall of the diffusion chamber 15 in which the substrate 14 to be processed is arranged. The internal spaces of the source chamber 11 and the diffusion chamber 15 are connected to each other. Therefore, the plasma generated in the source chamber 11 is diffused inside the diffusion chamber 15 and etches the surface of the substrate 14 disposed inside. The substrate 14 is made of silicon and is placed on the substrate holder 16.

Diffusion chamber 15 and source chamber 11
When the etching process is performed on, for example, a silicon oxide film formed on the substrate 14 by generating plasma, the inside thereof is depressurized to a required level by an exhaust mechanism (not shown). Further, the process gas is introduced into the diffusion chamber 15 in which the plasma processing is performed on the substrate 14 by a gas introduction mechanism (not shown) at a required pressure.

High frequency power is supplied from a high frequency power supply 17 to a helicon wave excitation antenna 12 formed in a loop shape via a matching box 18. The high frequency power supplied from the high frequency power supply 17 is supplied to the source chamber 1
1 is the source power input. In addition, the substrate holder 16
The other high-frequency power source 19 supplies high-frequency power. The high frequency power supplied from the high frequency power supply 19 is a bias power for controlling the energy of the ions entering the substrate 14.

In order to prevent the plasma generated in the source chamber 11 from colliding with the inner wall surface of the source chamber 11 and the inner wall surface of the diffusion chamber 15 and causing the plasma to be lost, the plasma is generated outside the diffusion chamber 15. It is also preferable to form the cusp magnetic field on the inner wall surface of each chamber by alternately arranging the magnetic poles of rod-shaped permanent magnets (not shown).

A viewing port 20 is formed on the side wall of the diffusion chamber 15. A glass 21 made of synthetic quartz having a sufficient transmission wavelength band is attached to the inside of the viewing port 20, and the viewing port 20 is spectroscopically exposed to the atmosphere. A light receiving probe 22 is attached. Light emission caused by the plasma in the diffusion chamber 15 is generated by the viewing port 20.
Then, it is taken out via the glass 21 and the spectroscope light receiving probe 22. The emitted light is extracted by the optical fiber 2
At 3, the light is guided to the spectroscope 24, and the emission intensity of a specific wavelength is measured.

Next, a characteristic operation for performing plasma processing in the plasma processing apparatus having the above-mentioned structure will be described.

First, in order to perform the plasma processing method according to the present invention, process parameters other than the source power applied to the antenna 12, that is, gas flow rate, internal pressure,
The external magnetic field strength, bias power, etc. generated by the coil 13 are fixed to specific values set by the conventional device. Next, the source power is appropriately applied to generate plasma discharge in the source chamber 11, and the plasma generated by this discharge is diffused toward the substrate 14 in the diffusion chamber 15. Light emission caused by the plasma diffused into the diffusion chamber 15 is taken out through the viewing port 20, the glass 21, and the spectroscope light-receiving probe 22, and is further guided to the spectroscope 24 by the optical fiber 23. The spectroscope 24 measures the emission intensity of a specific wavelength, that is, the emission intensity of two specific wavelengths as described below, and thereby measures the ratio of the emission intensity of the specific two wavelengths. Then, by changing the value of the source power, a change characteristic of the ratio of the emission intensities of the specific two wavelengths (source power dependence characteristic) is observed.

As the above-mentioned two specific wavelengths, one is a wavelength related to light emission from a radical in a high dissociation state that serves as an indicator of progress of dissociation, and the other is a wavelength in a low dissociation state. It is desirable to select each wavelength associated with the emission from a radical.

Taking the etching of the silicon oxide film as an example, 704 nm which is related to the emission from the fluorine atom radical which is the final dissociation product of the fluorocarbon gas which is the process gas is selected as one wavelength, and the other wavelength is selected. Is selected as 276 nm which is related to the emission from CF ₂ which is a typical deposition species in the low dissociation state. as a result,
The change in the emission intensity of the light having a wavelength of 704 nm and the emission intensity of the light having a wavelength of 276 nm is measured, and the ratio of the emission intensities of these two lights is measured.

FIG. 2 shows CF ₂ obtained as described above.
Source power dependence characteristic of ratio of emission intensity of emission of F radical to emission intensity of emission of radical 31
And the source power dependence characteristics 32 of the measured silicon oxide film-to-underlying Si selection ratio are shown. In the graph of FIG. 2, the horizontal axis represents the source power, and the left vertical axis represents the CF ₂ radical and F.
The emission intensity ratio of radicals and the vertical axis on the right side show the selection ratio of Si to the base. According to this graph, it can be seen that the emission intensity ratio changes discontinuously at the boundary of the source power value of 1000 W. Further, the emission intensity ratio increases discontinuously 10
It can also be seen that the selection ratio to Si of the base is drastically reduced near 00W. This suggests that when the silicon oxide film is etched with a source power whose emission intensity ratio of F to CF ₂ is less than or equal to the source power value at which it discontinuously changes, a high selectivity ratio to the underlying Si layer can be obtained. doing. Therefore, in the plasma processing method according to the present embodiment, the plasma processing is performed using the source power having a value equal to or lower than the source power value corresponding to the discontinuously changing portion in the change characteristic of the emission intensity ratio. .

Next, an example in which the plasma processing method according to the present embodiment is applied to etching of a silicon oxide film will be described.

To operate the helicon wave plasma source shown in FIG. 1, the source chamber 11 and the diffusion chamber 1
5 is evacuated to a predetermined decompression level by a well-known evacuation mechanism (not shown). Then, a gas supply mechanism (not shown) supplies a fluorocarbon gas (fluorocarbon) such as CHF ₃ , C ₂ F ₆ , C ₄ F ₈ with a flow rate controlled by a mass flow controller (not shown). Next, the diffusion chamber 1
A variable orifice (not shown) located between the No. 5 and the exhaust mechanism is controlled by a pressure controller (not shown) to control the pressure within the range of 1 to 100 mTorr. At that time, on the electrode holder 16, the silicon substrate 14 in which a desired pattern is formed on the silicon oxide film with a resist is placed. Next, source power is supplied from the high-frequency power source 17 for plasma generation to the pair of antennas 12 via the matching box 18. At the same time, the substrate holder 16 is supplied with required bias power from the high frequency power source 19 for high frequency bias in order to control the incident energy of ions.

In the above operation, the source power supplied to the antenna 12 is set to a value equal to or lower than the source power value corresponding to the discontinuously changing portion in the source power dependence characteristic of the emission intensity ratio of F to CF ₂ . By doing
It is possible to suppress excessive dissociation of the process gas supplied to the diffusion chamber 15.

FIG. 3 shows the etching characteristics of the silicon oxide film obtained by satisfying the above conditions with respect to the value of the source power to be input. In FIG. 3, the horizontal axis represents the size of the contact hole (diameter: unit is μm), the left vertical axis represents the etching rate of the silicon oxide film and the underlying silicon (angstrom / min (min)), and the right vertical axis represents the selection ratio to silicon. Means In FIG. 3, a graph 41 showing changes in the etching rate of silicon, a graph 42 showing changes in the selection ratio, and a graph 43 showing changes in the etching rate of the silicon oxide film are drawn. As described in the section of the prior art, when etching is performed with a source power higher than the source power value corresponding to the portion where the change characteristic of the emission intensity ratio with respect to the source power changes discontinuously, the obtained anti-base S
The i selection ratio was at most 23 even in the hole having a diameter of 0.5 μm, but in the etching by the processing method of the present embodiment, as shown in the graph of FIG. It was 83, and a sufficiently large selection ratio could be obtained.

As described above, according to the plasma processing method of the present embodiment, etching can be performed at a high source power, that is, at a high plasma density immediately before the selection ratio of the silicon oxide film to the underlying Si is sharply reduced. A high etching rate can be obtained, and at the same time, since the dissociation state is low, there is an advantage that a sufficient selectivity ratio to the underlying Si layer can be obtained.

In the above embodiment, the example of etching the silicon oxide film by the helicon wave plasma source is explained.
The plasma processing method according to the present invention is not limited to the above example. It is needless to say that the present invention can be applied to all plasma treatments in which excessive dissociation is suppressed and high-density plasma is required. As such plasma treatment, in addition to dry etching, surface treatment by plasma, plasma CVD, or the like can be given. High-density plasma generating means other than the helicon wave plasma source, such as ECR, T
Of course, it can be applied to CP, ICP and the like.

[0031]

As is apparent from the above description, according to the present invention, in the plasma processing method in the plasma processing apparatus configured by using the helicon wave plasma source, the value of the source power among the process conditions Of the emission intensity of two specific wavelengths of the emission due to the source power value corresponding to the discontinuously changing portion of the source power value, the excessive dissociation of the process gas is suppressed, It is possible to obtain a high-density plasma gas in which the dissociation state is appropriately controlled, that is, the etching species are appropriately generated. As a result, when plasma processing is performed using a helicon wave plasma source, it is possible to suppress excessive dissociation in the process gas and increase the Si-to-base Si selection ratio.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a plasma processing apparatus including a helicon wave plasma source to which a plasma processing method according to the present invention is applied.

FIG. 2 is a graph showing source power dependence characteristics of the ratio of the emission intensity from the F radical to the emission intensity from the CF ₂ radical and the selection ratio of the silicon oxide film to the underlying Si.

FIG. 3 shows the etching characteristics of the silicon oxide film when the silicon oxide film is etched below the source power value corresponding to the portion where the ratio of the emission intensity from the F radical to the emission intensity from the CF ₂ radical changes discontinuously. It is a graph which shows a contact hole diameter dependence characteristic.

FIG. 4 is a graph showing silicon oxide film etching characteristics when a conventional plasma processing method using high source power is applied.

[Explanation of symbols]

 11 Source Chamber 12 Antenna 13 Coil 14 Substrate 15 Diffusion Chamber 16 Substrate Holder 17 Source Power High-Frequency Power Supply 19 Bias Power Supply High-Frequency Power Supply 20 Viewing Port 21 Glass 22 Spectrometer Receiving Probe 23 Optical Fiber 24 Spectrometer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI technical display location // C23C 14/35 C23C 14/35 F 16/50 16/50 (72) Inventor Yoneichi Ogawara 5-8-1 Yotsuya, Fuchu-shi, Tokyo Within Anerva Co., Ltd. (72) Inventor Tsutomu Tsukada 5-4-1 Yotsuya, Fuchu-shi, Tokyo Within Anerva Co., Ltd.

Claims (4)

[Claims] 1. A plasma processing method for generating plasma using a helicon wave plasma source, wherein the ratio of the emission intensity of two specific wavelengths of the emission by the plasma changes discontinuously with respect to the source power. A plasma processing method, characterized in that the plasma processing is performed with a source power having a value equal to or lower than a source power value corresponding to the portion. 2. The plasma processing method according to claim 1, wherein the plasma processing is dry etching of a thin film containing silicon oxide as a main component using a fluorocarbon gas. 3. The plasma processing method according to claim 2, wherein the ratio of the emission intensities of the two specific wavelengths is the ratio of the emission intensity of the F radical wavelength to the emission intensity of the CyFx wavelength. . 4. The plasma processing according to claim 3, wherein the ratio of the emission intensities of the two specific wavelengths is the ratio of the emission intensity of the F radical wavelength to the emission intensity of the CF ₂ wavelength. Method.