JPH0570930B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a plasma processing method and apparatus suitable for manufacturing semiconductor devices.

[Background of the invention]

Plasma processing involves introducing a processing gas into a vacuum-evacuated processing chamber, applying a high frequency voltage to parallel plate electrodes provided in the processing chamber to generate plasma, and performing processing. The processing includes dry etching, which uses ions and radicals from the processing gas generated by plasma to etch the film according to the pattern formed in the resist, plasma CVD, which uses plasma to decompose the processing gas and form a film, and plasma CVD, which uses plasma to decompose the processing gas and form a film. This includes plasma polymerization, which causes a polymerization reaction to form a film.

In recent years, these plasma treatments have rapidly come to be used in production as semiconductor devices become more highly integrated and solar cells become less expensive. Therefore, in order to improve production yield, more advanced processing characteristics are required. For example, in dry etching, it is necessary to increase the etching rate to increase productivity, to increase the etching rate ratio between the target film and the underlying material, that is, to increase the etching selectivity, and to increase the etching rate of fine patterns. It is required to be able to perform etching with precision.

Conventionally, in plasma processing, the characteristics of etching and film formation have been controlled by controlling the type of gas, gas pressure, gas flow rate, high frequency power, etc.

However, with conventional control factors, taking dry etching as an example, there are the following problems, and sufficient characteristics cannot be obtained.

First, there was a problem in that increasing the gas pressure improved the selectivity, but the etching accuracy deteriorated.

Second, there was a problem in that when the high frequency power was increased, the etching rate increased, but the selection ratio deteriorated.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the problems of the prior art, it is an object of the present invention to provide a plasma processing method and an apparatus for the same, which improve both contradictory plasma processing characteristics such as film formation rate, film quality, etching rate, selectivity and etching accuracy.

[Summary of the invention]

In the present invention, a processing gas is introduced into a plasma processing chamber to generate discharge plasma, and a high frequency voltage is periodically modulated to control the ion energy distribution or electron temperature distribution to perform plasma processing. be.

[Embodiments of the invention]

As examples according to the present invention, several plasma processing methods and apparatuses will be described below.

In the conventional dry etching method in which a high frequency voltage of approximately 5 to 20 MHz (13.56 MHz) is applied to parallel plate electrodes, the ion energy distribution and electron temperature distribution are determined by gas pressure and high frequency power. Therefore, when etching an aluminum film or the like, high-energy ions are not necessary for etching the aluminum itself, but ion energy is required for etching the underlying oxide film or silicon film. Therefore, the selection ratio can be improved by reducing the ion energy.

However, in order to remove the oxide film on the aluminum surface and perform high-precision etching, it is necessary to form a sidewall to prevent side etching by the gas released by striking the resist surface with ions, and high-energy ions are essential.

Therefore, the ion energy distribution according to the conventional method is schematically shown in FIG.

Since the ion energy of part A is essential, there are ions of part B that etch the underlying material, making it impossible to make the selection ratio sufficiently large.

Therefore, an etching method by applying an AM modulated high frequency voltage shown in FIG. 3 according to the present invention in contrast to the conventional high frequency applied voltage shown in FIG. 2 will be explained.

Gas pressure is set higher than conventional processing conditions.

In the _t1 portion, a high frequency voltage of _V2 , which is lower than the conventional _V1 , is applied. At this time, since the gas pressure is high, the incident ion energy decreases in the t ₁ portion, but the discharge current increases. Therefore, the energy of electrons flowing from the electrode to the plasma decreases, but the number increases, and the generation of radicals contributing to etching increases.

In the t ₂ part, a high frequency voltage of V ₃ higher than V ₁ is applied even under high pressure. Therefore, sufficient ion energy can be obtained for removing the oxide film and forming the sidewall. The ion energy distribution at this time is schematically shown in FIG.

During the discharge in the _t1 portion, the amount of low-energy ions and radicals as shown in D increases, so that the etching rate can be increased.

In the discharge during the t ₂ portion, high-energy ions shown in C are generated, and the amount and energy of the ions can be controlled by the time ratio between t ₁ and t ₂ and the applied voltage V ₃ .

Therefore, the C portion can be controlled to the minimum necessary yen energy and ion amount, and the etching rate of the underlying layer can be minimized.

Although the case where AM modulation is applied has been described above, the same effect can be obtained with FM modulation shown in FIG. In the t ₄ part, compared to 13.56MHz in the t ₃ part
By lowering the frequency to 1MHz, the discharge voltage becomes higher and the incident ion energy becomes higher.

FIG. 6 shows the etching characteristics according to the modulation method of FIG. 3 of the present invention and the conventional etching characteristics.

Next, as another example of etching, a case where a silicon oxide film of a semiconductor wafer is etched will be described. There is a silicon surface under the silicon oxide film, and the difference between the etching speed of the silicon oxide film and the etching speed of silicon should be as large as possible so that the etching of the silicon surface does not proceed after etching of the oxide film is completed. At this time, silicon is etched with lower ion energy than the oxide film, so in order to increase the selectivity between the oxide film and silicon, the ion energy distribution must be higher than the level required for etching the oxide film. In order to increase this ion energy, it is necessary to lower the gas pressure or increase the high frequency power.

However, under conditions of low gas pressure, although the ion energy increases, the ionization rate decreases and the etching rate decreases. Furthermore, under conditions where the high frequency power is increased, the amount of heat generated increases as the ion energy increases, and the temperature of the wafer also increases.

In order to form a pattern on the wafer surface of a wafer used to make semiconductor products, a resist pattern is formed before etching. This resist softens when the wafer temperature exceeds approximately 120°C, distorting the pattern shape, and making it impossible to perform high-precision etching.
In some cases, the resist deteriorates and cannot be completely removed after etching, resulting in problems.

In the present invention, as shown in FIG. 7, a high frequency voltage V ₄ higher than the conventional voltage is applied for t ₅ seconds, and then the applied voltage is reduced for t ₆ seconds, thereby applying a periodically modulated high frequency voltage. This applied high frequency power is t ₅ ,
When the t ₆ part is averaged, it becomes the same as the conventional high frequency power.

As mentioned earlier, etching of SiO ₂
It requires ions with higher energy than Si, etc., and in order to increase the etching rate and selectivity, the ion energy must be distributed higher than the level required for SiO ₂ etching.

However, in the discharge according to the present invention, V ₄ at t ₅
is increased, high-energy ions are incident on the wafer, and at t ₆ the discharge is performed at a low power that does not have enough energy to etch the Si.

Since the high-frequency power supplied is the same as conventional ones, the resist formed on the wafer surface does not soften, and only the ion energy distribution is increased, increasing the etching rate by 2.5 times and the selectivity by 1.8 times. I was able to do it.

Although the etching method has been described above, similar effects can be obtained by plasma polymerization or plasma CVD. The properties of the produced film are related to the electron temperature within the plasma, the incident ion energy, and the ions and radicals produced near the sheath.

In addition, by modulating the electron temperature and these ions and radicals as explained earlier in the etching process, the distribution, types, and ratios of ions and radicals can be controlled. Therefore, it is clear that once conditions for obtaining better film characteristics are clarified, discharge plasma can be controlled using the method of the present invention to improve processing characteristics.

In the above embodiments, 13.56 MHz is used as the frequency of the high-frequency applied voltage, but basically any frequency that generates and sustains discharge may be used.

The modulation frequency may be a sufficiently small value for the current plasma processing time of 1 minute to several tens of minutes, that is, to the extent that no difference occurs in the processing conditions even if the plasma processing is stopped at an arbitrary time. From the above, it is sufficient that the frequency of the high-frequency applied voltage is 10 ² Hz or more, and the modulation frequency is one order of magnitude smaller than that, 10 Hz or more.

In addition, in this example, etching using parallel plate electrodes, CVD, and plasma polymerization were explained.
It is clear that the present invention is not limited to this, but can also be applied to plasma processing using external capacitance type and inductance type electrodes, and plasma generation using microwaves or electron cyclotron resonance. These discharges do not have electrodes in the processing chamber, but by modulating the applied high frequency or microwave, it is possible to control the electron temperature distribution within the plasma and the types and amounts of generated ions and radicals, making it possible to control plasma processing characteristics.

Furthermore, although modulation is performed using a rectangular wave in this embodiment, it is clear that the modulation waveform is not limited to this. In other words, when the optimal distribution and ratio of ion energy distribution, electron temperature distribution, amount and type of ions and radicals are known, the modulated wave is determined in a manner corresponding to them.

Next, an embodiment of a plasma processing apparatus that implements the plasma processing method described so far will be described.

FIG. 8 shows a cathode coupling type plasma processing apparatus used for etching the aluminum film and silicon oxide film mentioned above by AM modulated discharge.

The processing chamber 10 is provided with a processing gas supply port 11 and an exhaust port 12 . Furthermore, there are a grounded earth electrode 13 and a high-frequency electrode 14 inside the processing chamber, and the high-frequency electrode is fixed to the processing chamber via an insulating pusher 15, and a shield case 16 is provided around the processing chamber to prevent electrical discharge with the inner wall of the processing chamber. There is. Also, high frequency electrode 1
4 is connected to a high frequency power amplifier 19 via a matching box 18. The signal from the 13.56MHz standard signal generator 21 is transmitted to the modulation signal generator 22.
According to the signal from , the AM modulator 20 performs AM modulation and supplies the signal to the high frequency power amplifier 19 .

The modulation signal generator 22 can generate arbitrary waveforms such as rectangular waves and sine waves with different periods and amplitudes.

The modulation signal generator 22 generates a modulation signal that modulates the waveform shown in FIG. 3 or FIG. input.

The high frequency power amplifier 19 outputs waveforms as shown in FIGS. 3 and 7, and is applied to the high frequency electrode 14 through the matching box 18.
For AM modulation, the frequencies are the same, so
Matching can be performed using a matching box for 13.56MHz.

As described above, the discharge plasma described in the plasma processing method can be generated and plasma processing can be performed.

An anode coupling type plasma processing apparatus used for plasma etching, plasma CVD, etc. can be realized by exchanging the positions of the ground electrode 13 and the high frequency electrode 14 of this embodiment.

Figure 9 shows a plasma processing apparatus for anode coupling electrodes using the FM modulation method.

The processing chamber 25 has a processing gas supply port 26 and an exhaust port 27, a high frequency electrode 28 provided with an insulating bush 30 and a shield case 31 at the top, and a ground electrode 29 at the bottom.

The wafer 32 is placed on a ground electrode 29, and the high frequency electrode 28 is connected to a high frequency power amplifier 35 via a 13.56 MHz matching box 33 and a 1 MHz matching box 34 provided in parallel.

The signal from the 13.56MHz standard signal generator 37 follows the signal from the modulation signal generator 38, and the signal is sent to the FM modulator 3.
6, it is modulated into a 13.56MHz part and a 1MHz part.

The ratio between 13.56MHz and 1MHz can be set arbitrarily by the modulation signal. The modulated signal is amplified by the high frequency power amplifier 35, the 13.56MHz frequency part passes through the 13.56MHz matching box 33, and the 1MHz part passes through the 1MHz matching box 3.
4 and is transmitted to the high frequency electrode 28. This generates a modulated high-frequency discharge between the electrodes,
Plasma treatment can be performed.

In the above embodiment, the modulation signal is generated by a modulator, but the present invention is not limited to this, and the embodiment shown in FIG. 10 can also be used.

The signals from the standard signal generator 40 are input to different frequency dividers 41, and the output from each frequency divider can be changed individually by an attenuator 42.

The outputs from each attenuator are added by an adder 43. In this device, although it depends on the number of frequency dividers 41, a signal equivalent to the modulation waveform can be obtained by setting each attenuator 42.

FIG. 11 shows an embodiment of an electron cyclotron resonance type plasma processing apparatus.

The signal from the 2.45 GHz standard signal generator 44 is modulated by the AM modulator 45 according to the signal from the modulation signal generator 46, amplified by the power amplifier 47, and enters the waveguide 48.

The modulated microwave is guided into a waveguide 48 and enters a processing chamber 50 made of quartz. This processing chamber 50
Coils 49 and 51 that generate a magnetic field are provided around the , and plasma is generated by the resonance of electrons caused by the magnetic field and microwaves. Since the energy of the electrons at this time is related to the intensity of the input microwave, the electron temperature distribution can be controlled by modulation, and the type and amount of ion radicals generated accordingly can be controlled.

Therefore, the etching characteristics and film quality of electron cyclotron resonance type etching equipment and CVD equipment can be controlled.

Note that 54 is a processing gas introduction pipe, 55 is an exhaust pipe,
52 is a stage, and 53 is a substrate.

The embodiments of the plasma processing method and plasma processing apparatus have been described above, but as will be clear from the description of this embodiment, it can be easily inferred from the description of this embodiment that the present invention can be applied to all processing methods and processing apparatuses that apply plasma. It is possible.

[Effects of the Invention] As explained above, according to the present invention, it is possible to control the electron temperature distribution, the types and amounts of ions and radicals, and the ion energy distribution in plasma, thereby improving the performance of plasma processing, that is, etching processing. This has the effect of improving the etching rate, selectivity, etching accuracy, film formation speed, and film quality in the process.

[Brief explanation of the drawing]

Fig. 1 shows the ion energy distribution in conventional parallel plate plasma processing, Fig. 2 shows the applied voltage in conventional plasma processing, and Fig. 3 shows an example of the applied voltage by AM modulation according to the present invention. 4 shows the ion energy distribution in the case of the applied voltage shown in FIG. 3, FIG. 5 shows an example of the applied voltage by FM modulation according to the present invention, and FIG. 6 shows the ion energy distribution according to the present invention. A comparison diagram of etching characteristics and conventional etching characteristics, FIG. 7 is a diagram showing an embodiment of the silicon oxide film etching according to the present invention, FIG. 8 is a diagram showing an embodiment of the AM modulation type device according to the present invention, Fig. 9 is a diagram showing an embodiment of the FM modulation device according to the present invention, Fig. 10 is a diagram showing an embodiment of modulated wave generation, and Fig. 11 is a diagram showing an embodiment applied to an electron cyclotron resonance type plasma processing apparatus. FIG. 10... Processing chamber, 14... High frequency electrode, 19...
...High frequency power amplifier, 20...AM modulator, 3
6...FM modulator.

Claims (1)

[Scope of Claims] 1. Processing gas is introduced into a plasma processing chamber containing a workpiece, high frequency power is applied to generate discharge plasma, and the high frequency power is periodically modulated to change the ion energy distribution or A plasma processing method characterized in that the object to be processed is subjected to plasma processing by controlling electron temperature distribution. 2. The plasma processing method according to claim 1, characterized in that the high frequency power is modulated at a cycle sufficiently smaller than the processing time. 3 A gas introducing means for introducing a processing gas into a plasma processing chamber, a high frequency power supply section, and a power supply section, and high frequency power is supplied from the high frequency power supply section to the inside of the plasma processing apparatus via the power supply section. The plasma processing apparatus preferably includes a plasma generation means for generating plasma, and a modulation section connected to the high frequency power supply section to periodically modulate the high frequency power, and ion energy distribution or electron temperature distribution in the plasma. 1. A plasma processing apparatus comprising: plasma control means for controlling. 4 The periodic modulation of the high frequency power by the modulation section of the plasma control means may be AM modulation or
4. The plasma processing apparatus according to claim 3, wherein the plasma processing apparatus is FM modulated. 5. The plasma processing apparatus according to claim 3, wherein the power supply section of the plasma generating means is constituted by parallel plate electrodes. 6. The high-frequency power supplied from the high-frequency power supply section of the plasma generation means is microwave power, and the microwave power is introduced into the plasma processing chamber from the pre-electromotive force supply section to generate electricity in the plasma processing chamber. 4. The plasma processing apparatus according to claim 3, wherein the plasma processing apparatus generates plasma.