JP3350973B2 - Plasma processing method and plasma processing apparatus - Google Patents

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 a plasma apparatus, and more particularly to a technique for satisfying conflicting demands for high speed and low damage.

[0002]

2. Description of the Related Art Etching using plasma and film formation are indispensable for high-precision microfabrication techniques represented by the production of semiconductor integrated circuits and liquid crystal devices.
FIG. 2 shows a plasma processing apparatus that is currently mainstream. In the figure, 1 is an RF power supply, 2 is a chamber, 3 is a cathode, 4 is an anode, 5 is a gas inlet, 6 is plasma, 7
Denotes an exhaust pump, 8 denotes an object to be processed, and 9 denotes an insulator.

A cathode 3 which is two parallel electrodes held in a vacuum and a cathode 3 of one electrode on an anode 4
An object to be processed 8 is set on the top, and an active gas is introduced to apply an RF voltage to generate a plasma 6. Etching or film formation is performed using radicals or ions in the plasma 6 as active species. One of the two electrodes is grounded (grounded), and a high frequency (RF) voltage is applied to the other. Utilizing the self-bias voltage generated by the plasma 6, anisotropy can be obtained and the processing speed can be increased. The object 8 is placed on the RF application electrode side (usually called a cathode couple). The self-bias voltage independently changes depending on various parameters such as an RF applied voltage, a gas pressure, and a gas type. Since the processing speed and processing characteristics greatly depend on the self-bias voltage, controlling the self-bias voltage is an important technique for plasma processing.

[0004] An RF frequency is a parameter that greatly changes the self-bias voltage. The generation density of the plasma 6 depends on the RF frequency, and the higher the frequency, the higher the plasma density and the lower the self-bias voltage. In the cathode couple, a frequency of 13.56 MHz is usually used. On the other hand, in ECR (Electron Cyclotron Resonance), 2.45 GHz is used, and the value of the self-bias voltage is 10 times or more the voltage difference in the case of the RF frequency. If it is necessary to use the ion bombardment reaction particularly in the cathode couple, the frequency is set to 300 k instead of 13.56 MHz.
It is also practiced to increase the self-bias voltage using a frequency of about 1 Hz to 1 MHz.

In this case, the self-bias voltage is 13.5
Since 2-5 times more voltage can be obtained compared to 6MHz,
The anisotropy becomes stronger and the reaction rate likewise increases.

[0006]

However, in the case of using the above-mentioned conventional cathode-coupled plasma processing apparatus, if the RF frequency is lowered for the purpose of increasing the anisotropy and increasing the reaction speed, it is likely to suffer from ion bombardment. The processed object is damaged. Further, since the self-bias voltage is high, damage due to electrostatic breakdown is caused by a high voltage generated between the object to be processed and the electrode or the plasma 6.

[0007] In order to avoid the above problems, there are inconveniences such as the limitation of processing conditions, the limitation of the object 8 to be processed, and the limited effective use of the advantage of low frequency.

[0008]

[MEANS FOR SOLVING THE PROBLEMS]
The plasma processing method of the present invention,On the substrateProcessedLayer
The substrateOn the first electrode in the chamberInstallation
Then, a predetermined gas is introduced into the chamber, and the first gas is introduced.
electrodeBetween and the second electrode facingFirsthigh frequencyPower supply
Connect,SaidInside the chamberToFirstGenerated plasma
LetMost of the layer to be processed is etched with the first plasma.
And the first plasma damages the surface of the substrate.
Forming a remaining film of the layer to be processed to a thickness not giving
AboutThen, the first electrodeAnd between the second electrode
In addition, a frequency higher than that of the first high frequencySecondHigh lap
waveElectricSourceConnectionTo generate a second plasma,
Etching the remaining film of the layer to be processed with the plasma
It is provided with.

In the process of applying the first and second power supplies, the degree of vacuum in the chamber is processed at a lower degree of the frequency of the first and second power supplies.

[0010] An object to be processed having an oxide film formed on a semiconductor substrate is grounded on a first electrode in a chamber, a predetermined gas is introduced into the chamber, and a first gas is applied to the first electrode. To generate plasma between the first electrode and the second electrode, and to provide a plasma between the first electrode and the first power supply in a state where the thickness of the oxide film is greater than 30 nm. The first electrode and the second power supply are connected by the provided switch.

[0011] The plasma processing apparatus of the present invention to solve the above problems, provided the processed layer on a substrate, and placing the substrate on the first electrode <br/> chamber, the chamber
A predetermined gas is introduced into the second electrode and the second electrode facing the first electrode.
A first high frequency power supply is connected between the
A first plasma is generated in the chamber and the first plasma is generated.
Etching the majority of the layer to be processed with
To a film thickness that plasma does not damage the surface of the substrate
Wherein forming a residual film of the processed layer, followed by a switch for switching a plurality of power supply, and the first electrode and the second
Between the first high-frequency power source and the electrode;
Generating of a second plasma by connecting a second high-frequency power
And etching the remaining film of the layer to be processed with the second plasma.
It is provided with a means for carrying out .

[0012]

According to the present invention, when processing is performed using plasma, damage occurs at the start of processing or at the end of processing. From a stable plasma state, the plasma becomes transiently unstable at the start and end of plasma application, and ion bombardment and electrostatic destruction instantaneously increase. Which one causes fatal damage to the object to be processed changes depending on the processing method and the state of the object to be processed. In the present invention, at the start or end of plasma application, plasma is applied to a high-frequency state which is a condition of low damage, thereby minimizing damage to an object to be processed.

[0013]

1 is a conceptual diagram of the structure of a plasma processing apparatus according to the present invention. In FIG. 1, reference numerals 11 and 12 denote RF power supplies having different frequencies, and reference numeral 13 denotes a switch for switching the RF power supplies 11 and 12. The structure can be further simplified by using a two-frequency power source in which the RF power sources 11, 12 and the switch 13 are combined into one. 13.56 MHz was used for the RF frequency of the RF power supply 11, and 400 kHz was used for the RF power supply 12. This frequency is not limited to the above value, and other frequencies can be used according to the type of desired plasma processing. The range of use is 100 kHz with the current cathode couple plasma generation technology.
From about 50 MHz.

An example in which a silicon oxide film of a semiconductor integrated circuit is used in an etching process in this plasma processing apparatus will be described in detail. In the etching of the silicon oxide film, a mixed gas of CHF ₃ and O ₂ is introduced into the gas-tight chamber 14 through the gas inlet 17 and exhausted by the vacuum pump 19 to keep the pressure constant. The cathode 1
RF is applied between 5 and anode 16. The insulator 14 is electrically insulated between the chamber 14 and the cathode 15. RF power is supplied from the RF power source 11 to the cathode 1
5 is supplied. In the conventional example, the RF frequency is 13.5.
Although the frequency is 6 MHz, in this embodiment, two different frequencies of the RF power sources 11 and 12 are connected to the cathode 15 via the changeover switch 13. Switching of the frequency is performed by an instruction from a controller of the device.

The voltage applied between the cathode 15 and the anode 16
Plasma between the electrodes 15 and 16 due to the generated RF electric field.
18 occurs. Between the plasma 18 and the cathode 15
In between, CF_Three ⁺, CF_Two ⁺, F⁺Mobility of ions and electrons such as
A potential difference occurs due to the difference in degrees. This is called the cathode drop voltage
It is. This cathode drop voltage causes CF_Three ⁺, CF_Two ⁺, F ⁺
Ions such as enter the cathode 15. Cathode 15
The silicon substrate, which is the object to be processed 20 placed on the
The ions react and etch the silicon oxide film.
You.

The silicon oxide film is etched by a cathode
It is performed with fluorine gas plasma using
You. To promote the reaction between fluorine and silicon oxide film
Requires ion bombardment. Diagram of ion energy
The cathode drop voltage, which is a standard, needs to be 100 V or more.
100V or more using 13.56MHz RF frequency
In order to obtain the cathode drop voltage of
Or 5W / cm ^TwoThe above high power is required.
When the degree of vacuum is reduced, the absolute number of fluorine ions
And the reaction rate decreases. If the RF power is large,
High temperature consumption due to high power consumption of plasma
The resist which is a mask is burned. Therefore, the degree of vacuum
At 10 Pa and RF power of 3 W / cm^TwoDon't use
I have to. For this purpose, an etching rate of 20
0nm / min, slow processing speed several minutes compared to other processes
Must be less than or equal to 1.

On the other hand, when the RF frequency of 400 kHz is used, the degree of vacuum is 30 Pa, the RF power is 3 W / cm ² , and the etching rate is 500 nm / min. However, fluorine and carbon atoms contained in the plasma gas are knocked into the etching region, the surface is deteriorated, and ohmic contact with the wiring metal cannot be obtained, which is not practical.

In this embodiment, the RF frequency is set to 13.56 M
The power supplies of two different frequencies of Hz and 400 kHz are used. 400 at the beginning of the etching of the silicon oxide film
The frequency was changed to 13.56 MHz when the remaining silicon oxide film became 50 nm,
Continue etching. If the remaining film is 50 nm or more,
The depth of the impurity to be beaten at 400 kHz is 30 nm.
Therefore, impurities are not knocked into the silicon substrate. Thereafter, since etching is performed at 13.56 MHz, no damage occurs. 1 compared to 400 kHz
At a frequency of 3.56 MHz, the etching rate is reduced by a factor of 2.5. However, since most of the silicon oxide film is etched at a high speed of 400 kHz, the actual processing time is only 13.56 MHz. This is about 40% shorter than the conventional frequency.

Regarding the damage at this time, 13.5
There is no problem as before with 6MHz single frequency,
No resist burn. In this embodiment, 13.56 MHz
And two frequencies of 400 kHz are used, but the frequency is not limited to this frequency.
MHz, and the lower limit of the frequency is 1
It can be practically used from 00 kHz to 1 MHz.

In this embodiment, two frequencies are used.
It is also possible to perform more sophisticated plasma processing using three or more types of frequencies.

In the embodiment of the present invention, conditions other than the frequency are not changed. However, other conditions such as the type of gas, pressure, and RF power may be performed simultaneously with the change of the frequency.

In the case of plasma film formation, the film is grown at a high frequency of 13.56 MHz in order to reduce damage to the underlying substrate, and when a film of 100 to 300 nm is grown on the entire surface of the underlying substrate, the film is formed at a low frequency of 800 kHz. Do. 800 kHz
, An anisotropic film can be formed, so that a uniform and flat film can be grown even on a base step portion having a large aspect ratio of 2 or more, and the base layer has a thickness of 100 to 300 nm.
Since a film having a thickness of m is formed, it is not damaged. In this embodiment, two frequencies of 13.56 MHz and 800 kHz are used. However, the present invention is not limited to these frequencies. High frequencies can be used from about 1 MHz to about 50 MHz, and low frequencies can be used from 100 kHz to 1 MHz. It is practical.

In this embodiment, two frequencies are used.
It is also possible to perform more sophisticated plasma processing using three or more types of frequencies.

When ending the plasma processing at a low frequency,
Depending on the conditions, electric charges accumulated on the surface of the object may be instantaneously discharged, and the object may cause dielectric breakdown.
In order to avoid this problem, the frequency can be returned to a high frequency immediately before the end of the plasma processing, and the electric charge accumulated on the surface of the processing object can be gradually discharged into the plasma to avoid the dielectric breakdown.

In the embodiment of the present invention, conditions other than the frequency are not changed. However, other conditions such as the type of gas, pressure, and RF power may be performed simultaneously with the change of the frequency.

In this embodiment, the switching of the frequency is performed continuously, but the effect is not lost even if the switching between the low frequency and the high frequency is interrupted.

[0027]

According to the present invention, low damage and high speed processing can be achieved.
In addition, only the advantages of the opposite properties of anisotropy can be used, and high-performance plasma processing has become possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a plasma processing apparatus according to one embodiment of the present invention.

FIG. 2 is a schematic diagram of a conventional plasma processing apparatus.

[Explanation of symbols]

 11, 12 RF power supply 13 Switch 14 Chamber 15 Cathode 16 Anode 17 Gas inlet 18 Plasma 19 Exhaust pump 20 Workpiece 21 Insulator

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23F 4/00 H01L 21/3065

Claims (5)

(57) [Claims] 1. A provided the processed layer on a substrate, the substrate was placed on the first electrode in the chamber, introducing a predetermined gas into the chamber, a second facing the first electrode
Connect the first high frequency power supply between the electrodes, the tea
To generate a first plasma in members, the first plug
Etching the majority of the layer to be processed with
To a film thickness that plasma does not damage the surface of the substrate
Forming a residual film of the layer to be processed,
Between the first electrode and the second electrode.
And connecting the second high-frequency power having a frequency higher than the source second
Generating a plasma, and performing the processing with the second plasma;
A plasma processing method including a step of etching a remaining film of a layer . Wherein in said first and second plasma generation, plasma treatment according to claim 1, the vacuum degree in the chamber, characterized in that it held a degree of vacuum in said first plasma Method. Wherein an object to be processed where the oxide film is formed on a semiconductor substrate is placed on the first electrode in the chamber, introducing a predetermined gas into the chamber, opposite to the first electrode
Connecting the first high-frequency power supply between the second electrode and
To generate a first plasma in the chamber, the first
And etching most of the oxide film with the plasma of
The first plasma does not damage the surface of the substrate
Forming a remaining film of the layer to be processed to a thickness, and thereafter, applying the first height between the first electrode and the second electrode.
And connecting the second high-frequency power having a frequency higher than the frequency power source
A second plasma is generated, and the second plasma
A plasma processing method including a step of etching a remaining film of a layer to be processed . 4. The frequency of the first high frequency power supply is 100
In KHz～1MHz, the second frequency of the high frequency power source is I 1MHz~50MHz der, initial thickness of the remaining film
4. The plasma processing method according to claim 3 , wherein the thickness is larger than 30 nm . 5. A substrate provided with an object to be processed is placed in a chamber.
A predetermined gas in the chamber
Introducing, between the second electrode facing the first electrode
Connected to the first high-frequency power supply,
The first plasma is generated, and the plasma is generated by the first plasma.
Etching most of the processing layer and before the first plasma
The layer to be processed has a thickness that does not damage the surface of the substrate.
Is formed between the first electrode and the second electrode by a switch for switching a plurality of power supplies.
A second high frequency having a frequency higher than that of the first high frequency power supply.
Generating a second plasma by connecting a wave power, the second
Flop plasma processing apparatus having a means for etching the remaining film in plasma the processed layer <br/>.