JPS58186937A - Dry etching method - Google Patents

Abstract

PURPOSE:To change a ratio between ions applied to substrate and to obtain a dry etching method which assures high etching speed and superior in the selectivity by changing a discharge frequency with time. CONSTITUTION:A frequency has been divided on the time sharing basis and the etching has been conducted by periodically changing the frequencies of 13.56MHz and 300kHz. As a result, the etching speed of Si has been improved for about 3-5 times in that of a single frequency. A selection ratio of Si and SiO2 is about 10 and selection ratio of Si and photo resist has been about 3-5. When the etching is carried out with a high frequency, the etching rate of Si is high because a large amount of CF<+3> is contained. However, on the contrary, frequency becomes 100kHz, amount of CF<+> increases and therefore the etching rate is lowered. There is no large change of etching rate in the SiO2 or photo resist. When period and frequency are changed, both etching rate and selectivity change. Therefore it is an effective method for high speed etching.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry etching method. More specifically, the present invention relates to an etching method in which the ion ratio and energy are variable and suitable for high-speed etching and selective etching.

Conventional dry etching equipment includes a low-wavelength parallel plate plasma etching equipment of about IQQkHz, 13.56M
Hz high frequency parallel plate plasma etching equipment, cylindrical plasma etching equipment, and 2.45Gt (z
There are microwave plasma etching apparatuses, and ion beam etching apparatuses in which the ion chamber and etching chamber are separated. Furthermore, the 10 flat plate type h= includes a sword couple type in which high frequency is applied to the table on which the wafer is placed and an anode couple type in which high frequency power is supplied from a counter electrode. The high frequency discharge parallel plate cathode couple method etching surface is usually a reactive ion etching coating IM.
It is also called, and is often used conveniently.

Conventionally, in the dry etching equipment described above, #
A method was used in which discharge was performed at a single wave frequency (for example, 13.56 MH2) and etching was performed. but,
It is known that when the discharge frequency is constant, the ratio between ion species in the plasma does not change even if the input is changed.

Therefore, when the input power is small, the proportion of ions that are likely to cause deposition increases, resulting in a decrease in the etching rate, and furthermore, etching may not occur at all. Conventionally, as a countermeasure for this, it was necessary to introduce an additive gas in order to improve selectivity.

In view of the above points, an object of the present invention is to change the ratio of ion species incident on a substrate by a discharge method that changes the discharge frequency over time, and to increase the etching rate.
An object of the present invention is to provide a dry etching method with excellent selectivity.

The present inventors have newly discovered that among the ions generated in plasma, there are ions that are effective for etching and ions that suppress etching.

It has also become clear that this effect is due to the energy of the incident ions. From these results, the present invention makes it possible to freely control the etching characteristics by changing the ion ratio and energy, and has achieved a significant improvement in performance compared to the conventional dry etching method. be.

For example, when CF gas is discharged, five types of ions are generated in the plasma. Figure 1 shows CF, 5 in plasma.
This figure shows the dependence of Si etching rate on incident ion energy for different types of ions. Figure (al is CP
In the case of n (n=0 to 4) (7), Figure (b) shows the case of F+. In addition, the vertical axis of the figure is the Si etching rate deposit.
A positive value indicates the extent of etching. From the same figure,
The ease of deposition by ions ranges from F to CF3. C.F.
2. For example, at an ion energy of Q, 5 keV, F'', cp
;2 cF; etches Sl, and then cp; c+
, material deposition occurs on the surface. Furthermore, as can be seen from the figure, the ratio of depositing ions to etching ions changes greatly depending on the ion energy. Therefore, like the conventional equipment 7, a certain amount of energy (1
When each ion from 00 to fjO (J eV) is incident,
It can be seen that deposition and etching compete at a certain rate and determine the overall etching rate.

It is thought that the change in the composition ratio of the incident ion species due to the discharge frequency is due to the energy and density of the electrons that ionize the gas. Figure 2 is 100kHz.

It is an electrogram showing the ion composition ratio obtained when CF4 discharge is performed at 13.56 MHz and 2.45 GHz. As the frequency increases, the ratio of C
F+ decreases. That is, when etching is performed at a high frequency, there are many C points, so the etching speed is 81, which is high, and conversely, when the frequency is 100kHz, CF+ increases, so the etching speed becomes low. On the other hand, in SiO□ and photoresist, the C in the ion molecules combines with the oxygen in the material to form CO or Co2, which evaporates. Therefore, when ions with the same energy are incident, the etching rate of both is greatly affected. no change. Therefore, Sl and 5i02
．． This means that the etching rate ratio between Si and photoresist can be changed by changing the discharge frequency. Furthermore, in reality,
The energy of incident ions also changes depending on the discharge frequency.

For example, in microwave plasma etching at 2.45 GHz, it is 10 to 20 eV, and at 13.56 MHz
For reactive ion etching, lOO ~ 400 eV
, and 400 to 20 for 100kHz noise
00 eV. SiO□ and photoresist have low incident ion energy and are difficult to be etched at about 200 eV. In particular, in microwave plasma etching, 5IO2 is no longer etched. Therefore, when the discharge frequency is decreased, the ion composition ratio increases by CF4, and the energy changes to become larger.
The etching rate of Sl is lower than that of SiO2 and photoresist. In addition, conversely, the frequency can be changed (then, Sl
will be etched faster.

The present invention will be explained in detail below using examples.

Skilled secondment].

FIG. 3 shows temporal changes in the frequency of the voltage applied for gas plasma generation in this example. That is, in this embodiment, the frequency melting is time-divided into 13
．． Etching was performed by periodically displaying 56 MHz and 300 kHz. As a result, the etching rate of Sl was approximately 3 to 5 times faster than with a single frequency. Also,
The selectivity ratio between Si and SiO2, Si/5in2, is approximately 10,
Selection ratio of Si/photoresist is 3~
It was about 5. Here, if we change the N4 period and frequency,
Etching speed and selectivity are tabulated. Therefore, the method of this embodiment is effective for crystal speed etching and selective etching.

Example 2 FIG. 4 is a diagram showing the discharge frequency (solid line) and the accompanying change in ion energy (broken line) in this example. As shown in the figure, by changing the discharge frequency aperiodically,
When changing briefly from a 13.56 MHz discharge to a 100 kHz discharge, the energy of the ions typically increases by 20
The voltage changes from 0 eV to 1000 eV, increasing the ion sputtering effect and removing etching residue. Also,
Since the ion energy is large, the ions are incident perpendicularly to the substrate, making it suitable for precise processing according to the mask. Furthermore, since the etching speed becomes faster during this period, deeper etching can be performed than etching at only 13.56 MHz.

Next, the discharge frequency was changed aperiodically as shown in FIG. 5, and SiO□ was etched.

As a result, the ion energy is high in the early stage and the etching rate is 1000 A/m+n, and in the latter half the etching rate is 100 A/min.
This is effective when etching is performed at high speed in the early stage of etching and at low speed in the latter half of etching.

By combining aperiodic and periodic discharge frequency changes,
Etching with good processing accuracy and selectivity is possible.

Embodiment 3 The present invention can also be implemented using an amplitude modulated wave as shown in FIG. The k6 diagram is hypothetically 13. at 300kHz.
It shows him changing over time by overlapping 56 MHz high frequency waves. Plasma has image frequency effects. The composition ratio of ions can also be achieved by temporally changing the frequency to dK&.

From what has been explained above, the present invention has the following effects.

If the discharge frequency is continuously changed from low frequency to high frequency, the energy of the ions involved in etching will continuously change from about 1000 eV to 100 eV. As for the etching shape, the higher the ion energy, the more it will be etched according to the mask.
It is effective to increase the etching effect of ions first, or to improve processing accuracy. On the other hand, if the frequency is changed continuously from high to low frequency, etching will occur under the mask first, and then etching will take place in the shape of the mask, making it easier to cover the stepped portions during film formation in the later process. There is.

Note that the present invention requires manual power to vary the frequency. As for circuits that automatically match power supplies and devices, it is also possible to match one frequency and not match another frequency. This can also be achieved by using multiple or more power supplies with different frequencies.

[Brief explanation of the drawing]

Figure 1 shows CF'h (n=0~4) (Figure (a))
Figure 2 is an electrogram showing the ion composition ratio of CF4 when the discharge frequency is changed; Figures 3 to 6 are diagrams showing the dependence of Si etching rate on incident ion energy for
The figure is a diagram showing temporal changes in power supply input frequency. Representative Patent Attorney Junnosuke Nakamura 2 figures, 13 figures, 4 figures

Claims (1)

[Claims] 1. In a dry etching method using high-frequency gas discharge, by temporally changing the frequency of the discharge, the ratio and energy of ion species incident on the material to be etched are temporally changed. A dry etching method characterized by etching an etching material.