JPH0160913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to improvements in a microwave processing method and a microwave processing apparatus for processing a sample by generating plasma using microwaves.

(b) Background of the technology As an example, when forming semiconductor devices such as ICs and LSIs, a silicon dioxide (SiO ₂ ) film is generally formed on a silicon (Si) substrate, and the SiO ₂ film is apertured in a predetermined pattern. Then, a method is adopted in which impurity atoms for semiconductor element formation are introduced into the windowed opening portion to form a semiconductor device.

By the way, when etching such a SiO ₂ film into a predetermined pattern to form openings, a resist film is applied on the SiO ₂ film, and after the resist film is formed into a predetermined pattern by photolithography. Using the resist film to be patterned as a mask, a dry etching method using a mixed gas plasma of carbon tetrafluoride (CF ₄ ) gas and oxygen (O ₂ ) gas, etc. is used.

In such a dry etching method, the Si substrate on which the SiO ₂ film to be etched has recently been formed is introduced into a reaction chamber, and after the reaction chamber is evacuated, reaction gases of CF ₄ gas and O ₂ gas are introduced into the chamber. A method has been adopted in which the reactant gas is introduced and irradiated with microwaves to form a microwave plasma of the reactant gas, and the SiO ₂ film on the substrate is formed in a predetermined pattern using this microwave plasma. ing.

Etching using microwave plasma generates a higher density of plasma particles than the plasma etching method in which a reactive gas is excited with high-frequency power, and the equipment is simple because it does not require a complicated impedance matching circuit. This method has recently been attracting attention because the degree of collision of ion radicals of the etching gas with the substrate is gentler than in plasma etching, and the degree of damage to the substrate surface is less.

Further, as an example, dry etching technology using microwave plasma is also applied to etching polysilicon and ashes of photoresist films.

(c) Prior art and problems By the way, as a conventional microwave generation method for forming such a microwave plasma, as shown in FIG. A high voltage of 5kV is made, and then it is double-wave rectified using rectifier circuit 2. This high-voltage double-wave rectified current is input to the magnetron, and the output waveform of the magnetron's anode current is as shown in Figure 2. I was getting .

Here, the vertical axis in FIG. 2 shows the anode current of the output of the magnetron, and the horizontal axis shows the drive time of the magnetron.

As shown in the figure, when the magnetron is operated using the conventional method, the output anode current value increases rapidly with the operating time of the magnetron, and after that,
It drops rapidly with operating time, and there is no steady state point.

Furthermore, the output anode current becomes intermittent at twice the cycle of the AC power supply compared to the operating time, and there is a stop time t in which the output anode current value becomes zero.

In such a conventional method of operating a magnetron, the above-mentioned reaction gas is irradiated with the output microwave of the magnetron to form a microwave plasma of the reaction gas, and this microwave plasma is used to generate a reaction gas.
When removing the SiO ₂ film, a drawback arises in that it takes too long to remove the SiO ₂ film by etching.

Furthermore, in the above-mentioned driving method, since the magnetron is driven by a pulsating current that is twice the frequency of the AC power source, the number of electron bombardments against the anode and cathode of the magnetron is large, resulting in a drawback that the magnetron deteriorates quickly.

(d) Purpose of the Invention The present invention eliminates the above-mentioned drawbacks, makes the anode current waveform of the magnetron output constant or pulsed, and shortens the time required for etching a SiO ₂ film using microwave plasma. The object of the present invention is to provide a new microwave processing method and a microwave processing apparatus that extend the life of a magnetron.

(e) Structure of the Invention In order to achieve the above object, the microwave processing method of the present invention generates plasma by irradiating microwaves, and processes a sample using the plasma. This method is characterized in that the state of plasma particles is controlled as intermittent rectangular pulses in which at least the pulse height and the pulse generation interval are changed, and the sample is processed by the plasma particles. .

Furthermore, the method includes a microwave generation means and an output waveform control means for making the microwave output waveform into an intermittent rectangular pulse shape in which at least the pulse height of the pulse width, pulse height and pulse generation interval is changed. This is a characteristic microwave processing device.

(f) Embodiments of the invention Examples of the invention will be described in detail below with reference to the drawings.

FIG. 3 is a schematic diagram of a device showing an example of application when this embodiment is used, FIG. 4 is a block diagram of a magnetron drive circuit used in the microwave generation method of the present invention, and FIG. FIG. 6 is a related diagram of an example of the output waveform and operating time of the magnetron according to the method of the embodiment, and FIG. 6 is a related diagram of another example, and FIG.
The figure is a schematic diagram of an apparatus showing another application example using this embodiment.

An example of application using this embodiment is to use microwaves to form a microwave plasma of a reaction gas of CF ₄ gas and O ₂ gas to etch an SiO ₂ film on a Si substrate into a predetermined pattern. This is a plasma etching apparatus, and a schematic diagram of the apparatus configuration is shown in FIG.

As shown in the figure, on the Si substrate installation stand 21,
A Si substrate 22 having a SiO ₂ film and a patterned resist film is installed, and the substrate installation stand 21 is installed on a movable belt 23 so that it can be taken out one by one from the insertion rack 24 of the substrate installation stand 21. ing.

The substrate 22 on the substrate installation stand 21 is placed in the decompression chamber 2.
The opening/closing lids 28 and 29 between 5, 26, and 27 are moved by opening and closing, and when the substrate installation table 21 arrives at the decompression chamber 26, the substrate installation table 21 moves into the microwave plasma processing chamber 30. I'm starting to do that.

The inside of the microwave plasma processing chamber 30 is
The chamber is evacuated to a vacuum level of 10 ^-2 Torr or higher, and a reaction gas is introduced into the chamber through a gas introduction pipe 31.
Microwaves are irradiated from the magnetron 32 and introduced into the plasma processing chamber 30 via the waveguide 33 to turn the introduced reaction gas into microwave plasma.

Here, by operating the magnetron 32 and irradiating microwaves using the method described later, the
Etching the SiO ₂ film has the advantage of shortening the etching time and prolonging the life of the magnetron 32.

The drive circuit for the magnetron 32 used in the microwave processing method of this embodiment is as shown in FIG.
A high voltage DC power supply 41 is used to convert an AC voltage of 200 V into a high voltage DC voltage of 4 to 7 kV, and a high voltage pulse generation circuit 42 is used to generate high voltage DC pulses from the high voltage DC thus obtained.

On the other hand, pulses are repeatedly applied to the grid circuit of the tetrode constituting the high-voltage pulse generation circuit 42 at 10 to 500 pulses/s with a pulse width of 1 to 10 ms, and -20 to -
A grid bias voltage of 140V is applied by the pulse generator 43, the output current value is changed to a desired value, and the output current value is turned on and off in a desired pulse state in a predetermined time unit. Enter.

The output current value of the magnetron 32 thus constructed is as shown in FIG. 5 as an example, and as shown in FIG. 6 as another example, and the pulse width and pulse generation interval are set to predetermined values while changing the pulse height. Alternatively, the generation of microwaves output from the magnetron can be precisely and freely controlled by setting and controlling the microwaves to vary over time.

Figure 5 shows the case where the pulse height is changed over time, and Figure 6 shows the case where the pulse height, pulse width, and pulse generation interval are all changed over time. Plasma etching must be performed with precision and by freely adjusting the output.

Next, another application example of a plasma etching apparatus using this embodiment will be described with reference to the schematic diagram of FIG. 7.

A Si substrate 53 coated with a photoresist film is placed on a substrate installation stand 52 in a reaction chamber 51 of a quartz container shown in FIG.
It is evacuated to a vacuum level of 10 ^-2 Torr or higher. The reaction chamber 51 is irradiated with microwaves generated in the application example of the present invention as described above from the magnetron 54, and the resist film on the substrate 53 is baked at a predetermined temperature by the microwaves.

If the magnetron 54 is operated in the manner described above, the output current value can be easily controlled, so the substrate 53 can be gradually heated with an arbitrary temperature gradient, and the solvent dissolving the resist film can be sufficiently gradually heated. Baking can be performed in the discharged state, and it is possible to avoid a phenomenon in which the resist film changes in quality due to rapid evaporation of the solvent in the resist film.

Thereafter, when the resist film has been sufficiently baked, the resist film is exposed and developed, and the substrate 53 is introduced into the reaction chamber 51 again. After exhausting the reaction chamber 51, CF ₄ gas is introduced from the gas introduction pipe 55. The SiO ₂ film is etched away in a predetermined pattern.

This has the advantage that the SiO ₂ film can be patterned with high precision.

(g) Effects of the invention As described above, if microwaves are generated using the method of the present invention and a film such as an SiO ₂ film is plasma etched using the generated microwaves,
Etching time can be shortened and the life of the magnetron can be extended.

Furthermore, if the resist film is baked using the microwaves generated by the method of the present invention, the resist film can be baked without deterioration, and therefore, an accurate SiO ₂ pattern can be obtained afterward.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram used in a conventional microwave generation method, FIG. 2 is an output waveform by the conventional microwave generation method, and FIG. 3 is a schematic diagram of a device showing an example of application using this embodiment. FIG. 4 is a block diagram of a magnetron drive circuit used in the microwave generation method of this embodiment, and FIG. 5 is a relationship diagram of an example of the magnetron output waveform and operating time according to the method of this embodiment. FIG. 6 is a related diagram of another example, and FIG. 7 is a schematic diagram of an apparatus showing another application example using this embodiment. In the figure, 1 is a transformer, 2 is a rectifier, 21,
52 is a substrate installation stand, 22 and 53 are substrates, 23 is a belt, 25 to 27 are decompression chambers, 28 and 29 are opening/closing lids, 30 is a plasma processing chamber, 31 and 55 are gas introduction tubes, 32 and 54 are magnetrons, 33 is a waveguide, 41 is a DC power supply, 42 is a high-voltage pulse generation circuit, 43 is a pulse generator, and 51 is a reaction chamber.

Claims (1)

[Claims] 1. A microwave processing method in which plasma is generated by irradiating microwaves and a sample is processed using the plasma, the microwave output waveform being controlled by pulse width, pulse height, and pulse generation interval. A microwave processing method comprising: controlling the state of plasma particles as intermittent rectangular pulses with at least varying pulse heights, and processing a sample with the plasma particles. 2. A microwave processing device that generates plasma by irradiating microwaves and processes a sample using the plasma, which sets the microwave output waveform to at least the pulse height among the pulse width, pulse height, and pulse generation interval. 1. A microwave processing device comprising: an output waveform control means for generating an output waveform in the form of a varied intermittent rectangular pulse.