JPS60126835A - Plasma etching device - Google Patents

Abstract

PURPOSE:To perform an etching at higher speeds and with no undercut in a plasma etching device by a method wherein a discharge by fluorine-containing gas and a discharge by NH3 gas are alernately performed. CONSTITUTION:A vacuum chamber 6 is exhausted to a high-vacuum state, and after that, SF6 gas or NH3 gas is introduced in the vacuum chamber 6 at a prescribed gas pressure as a discharge gas. A magnetic field is formed at the discharge tube part by an electromagnet 5, a microwave is made to generate by a magnetron 1, and an etching is started. During the etching time, the supplies of the discharge gas SF6 and NH3 are alternately performed in a time- division manner, and at the same time, the output of the microwave and a voltage, which is impressed RF on a sample 10, are adjusted. By this method, NH3 is added into the SF6 gas and as the lower sidewall of the mask results in being protected with a silicon nitride, a fine processing can be performed. Moreover, as the SF6 gas and the NH3 gas have been alternately supplied, the silicon nitride on the sidewall can be firmly formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a surface treatment apparatus using plasma, and particularly to a plasma etching apparatus for semiconductor integrated circuits.

[Background of the invention]

Surface treatment technology using plasma is actively used industrially. This plasma surface treatment apparatus consists of a vacuum chamber, a means for evacuating the vacuum chamber, a means for introducing gas into the vacuum chamber, a means for generating plasma in the vacuum chamber or a part thereof, and a sample and a means for holding the sample. be done. The characteristics of plasma surface treatment vary drastically depending on the type, composition, and concentration of the plasma generating gas (discharge gas).

FIGS. 1 and 2 show the configuration of a conventional etching apparatus using plasma (plasma etching apparatus W). FIG. 1 shows an apparatus using a magnetic field mask wave discharge. The means for generating magnetic field microwave discharge includes a microwave discharge oscillator (usually a magnetron) 1, a waveguide 3, a discharge tube 4,
It is composed of an electromagnet 5 and a permanent magnet 12. In some cases, both an electromagnet and a permanent magnet are not necessary, and only one of them is sufficient. The device shown in FIG. 2 utilizes RF discharge, and means for generating RF discharge is comprised of an RF power source 15, a capacitor 16, and upper and lower RF electrodes 13,14. Here, in the example of FIG. 2, the RF electrodes 13.14
is located inside the vacuum chamber, but in some cases the RF electrode may be installed outside the vacuum chamber.

In order to apply a plasma etching apparatus to a semiconductor device manufacturing process, the following issues are important.

(1) High etching speed.

(2) When the film to be etched 24 shown in FIG. 3(a) is etched using the mask 25, there is no undercut or as little vertical etching as possible (etching according to the mask) as shown in FIG. 3(c). Be possible. In other words, it has good microprocessability. (Usually accompanied by an undercut 26 as shown in FIG. 2(b)) In order to increase the etching speed, for example, when the material to be etched is Si (or poly-S i ), SF6 or F2 is used. It is good to use it as a discharge gas.

However, with this discharge gas, the undercut is large and condition (2) is not satisfied. In other words, the cross-sectional shape after processing is the third
It should look like figure (b).

As will be shown later, according to the present invention, the above (1) can be achieved by alternately performing the discharge using SF6 or F2 and the discharge using NH,l (furthermore, the discharge using SF or a mixed gas of F2 and NHB).

It becomes possible to satisfy condition (2) at the same time.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus that enables high-speed and fine plasma etching processing, which has been impossible with conventional plasma etching apparatuses.

[Summary of the invention]

In plasma etching, the type and composition of discharge gas,
Concentration is the parameter that most effectively changes its properties. For example, SF6 gas and F2 gas are
This gas is suitable for etching s i at an extremely high speed, and the etching speed is approximately 1000 nm/m.
becomes in. However, when using SF, gas, or F2 gas alone, the undercut at the bottom of the mask (see FIG. 3) is large and the microfabrication performance is poor. When N2 or NH is added to SF6 gas or F2 gas, the sidewall of the lower part of the mask is protected by Si nitride, so that microfabrication properties are slightly improved. However, this alone is not sufficient. This is because silicon nitride on the sidewalls cannot be formed sufficiently firmly by simply mixing N2 or N2)f3 into SF or F2.

In order to strengthen this silicon nitride, N2 or N
■-I, cut off the supply of SFl or F2 during gas discharge.

I need to do it. Based on this idea, the present invention combines SF6 or F2 gas discharge and N2 or NH,
The present invention provides a high-speed and fine plasma etching method and an apparatus suitable for carrying out the method by alternately repeating gas discharge in a time-division manner.

[Embodiments of the invention]

The present invention will be explained in detail below. FIG. 4 shows an example of the configuration of a plasma etching apparatus using the present invention. A magnetic field microwave discharge is used as the plasma generation means, and Si (or poly-S i ) is used as the material to be etched.
Here is an example. The differences from the configuration in FIG. 1 are as follows.

(1) There are two gas supply systems, one for SF and one for NH3.

(2) Gas supply flow rate control valve (or on/off valve)
8a, 8b, a power source 15 for applying an RF voltage to the sample, and a microwave oscillator power source 2 are electrically controlled by a controller 18;

In this example, first, the vacuum chamber was set to a high vacuum (approximately 1 x 10-'
Torr), and then SF6 or NH3 is introduced as a discharge gas at a predetermined gas pressure. Next, a magnetic field is formed in the energized tube section by the electromagnet 5, and microwaves (frequency: 1 to 10 GHz, usually frequency = 2.
When a microwave (45 GHz) is introduced into the discharge tube, a magnetic field microwave discharge is generated and etching begins. The features of this embodiment include the supply of discharge gas during etching, the microwave output,
and changing the RF voltage applied to the sample (hereinafter expressed as PP, which represents the difference between the maximum peak voltage and the minimum peak voltage). FIG. 5 shows an example of how to change these quantities. SF6 and NH.

Gas supply is performed alternately, and the respective supply time intervals are τ1. It is τ2. The gas pressure in the vacuum chamber at the time of supply is, for example, SF, the gas partial pressure is P+=2X10-jTorr,
P, = OT orr, NH, gas partial pressure is P, =
4 X 10-BT orr, P, =0 'I'o
It can be rr. The RF voltage is applied for only 3 hours from the end of NH gas discharge. The RF electricity at this time is, for example, vPpl=80v and vpP2=Ov. The microwave output is, for example, during SF6 gas discharge (15
time) is 200W, NH, gas discharge time (12 o'clock) is 500W.
It can be set as W. The reason for increasing the microwave output during NH3 gas discharge is to sufficiently decompose N)(3 gas in the plasma and sufficiently nitriding St. τ).

τ2. The conditions for determining τ will be described later, but for example, c
,=13sec, f2=2sec, fi=3s
It can be ec. By doing this -
, high-speed etching (etching speed > 400 nrn/win) of Si (or polySi) is achieved without undercut. It will be described below that the present invention has made high-speed, fine etching possible for the first time.

SF in the first period τ after the start of etching.

Etching progresses due to a large amount of F+ ions and F radicals generated in the plasma. The sample has a negative floating potential v r (v tx =about −20 V) with respect to the plasma, and the F+ ions are incident perpendicularly to the sample surface. Therefore, etching by F+ ions is perpendicular to the sample surface, and no undercut occurs. On the other hand, since F radicals are electrically neutral, they are isotropically incident on the sample surface and cause undercuts. However, in St etching using SF and gas, the effect of F+ ions is greater than that of F+ ions.
The effect of radicals is larger and the etching shape is the 6th one.
The force shown in Figure (a) is particularly low. That is, when the St etching layer 24 is etched to a depth of d perpendicularly to the surface during τ1, the etching depth is also approximately d in the lateral direction with respect to the mask 25.
An undercut has occurred. Next, the discharge gas is
F, gas to NH.

When switching to gas, F+ ions and F radicals in the plasma are exhausted, and N+ ions and N radicals are formed in the plasma instead. As a result, the surface (both the horizontal surface and side surfaces) of the St layer 24 is nitrided by these N+ ions and N radicals, and an SiN film 27 is formed as shown in FIG. 6(b). Next, perform 5FII gas discharge again and RF
When a voltage is applied for 13 hours, both accelerated ions (including F''') and neutral radicals are incident on the horizontal plane, and only neutral radicals are incident on the side surfaces. However, when only F radicals are present, silicon nitride Since the film is hardly etched, the side surfaces covered with the silicon nitride film are hardly etched, and etching is performed in the vertical direction (horizontal plane) and the newly appeared side surfaces.The size of the undercut at this time is still d. (Figure 6(C)) The reason for applying the RF voltage is to quickly remove the silicon nitride film formed on the horizontal plane, and it is not always necessary depending on the conditions. (b) ~ (e
) By repeating the process shown in FIG. 6(d), the cross-sectional shape shown in FIG. 6(d) is etched.

τ. If the above operation is repeated n times with =τ and +τ2 as one cycle, the total etching time tεtε=nτ.
(1) The etching speed d in the vertical direction and the amount of etching (undercut amount) dV in the horizontal direction are d, =: nd, = - (2) dv = d, ... (3 ). For vertical etching, dP/dV >10
Since n>10 (4) is necessary. In addition, SF6 gas and NHB in a vacuum chamber
For sufficient gas exchange, @, , (,)τ
, ...(5) τr: Requires the residence time of gas molecules and atoms existing in the vacuum chamber. τ1 is the volume of the vacuum chamber V(Q),
If the exhaust speed is S (Q /5ec), fr=V/
It is S. In normal equipment, V=40Q, S=500Q
Since it is 7 sec, τ, = 80 m5 ec.

Therefore, from equation (5), τ+ + τx )80'm5eG .=(5) is required. On the other hand, according to experiments, the etching depth dl during τ1 was required to be 1100n or less in order to maintain the fine processing process. That is, assuming that the final etching speed in the vertical direction is ε (n m /m1n), τ,<(100/ε)N60 (7) is required. For example, assuming ε=400 nm/min, r<'15 sec is required. Further, since etching is not performed during τ2, τ2 (τ1 is also practically necessary).

Through the experimental verification described above, τ, = 13 sec + τ2
It has become clear that =12 sec, τ, =3 sec are suitable. However, these time constants are not exact;
Almost the same results can be obtained even if the above values are changed little by little. For example, if the ratio τ1/τ2 is increased, the etching speed ε will increase slightly, and on the other hand, undercuts will also appear slightly. These time constants can be varied depending on the required etching characteristics.

In this example, NH,
was used, but similar effects can be obtained by using N2 gas. However, the N-N bond energy in N2 gas molecules is larger than the NH2-H bond energy in NH and gas molecules, so in order to achieve sufficient nitriding, it is necessary to further increase the microwave output during N2 discharge. 1 or τ2 needs to be made longer.

Similar effects can be expected by using other F-containing gases such as F2 and CF4 instead of the SF gas of this embodiment.

Furthermore, in this embodiment, St (or polysi) was described as the material to be etched, but other materials (for example, W,
The present invention has similar effects on Mo, Ta, Nb, and their silicides.

Further, in this embodiment, the exchange of SF6 and NH, l gas discharge is repeated many times, but it does not necessarily have to be many times. For example, if the surface of the sample substrate has a two-layer structure of SiO2 and W films (W on the top surface) and it is desired to etch only W, the following procedure may be used. That is, first, SF,
Almost the entire W film is etched by the discharge, and when a part of the surface of the Sin film appears, the discharge is switched to an NH3 discharge.

Next, when the remaining W is etched again by SF6 discharge, high-speed etching with less undercut is realized.

Also, in the middle of the method of this embodiment. , the ratio of /τ2, the value of V PP l 9 V PP 2, Pwttpw
By appropriately changing the value of z, etc., it is possible to obtain an etched cross-sectional shape with an appropriate amount of undercut.

Although this embodiment describes an apparatus using magnetic field microwave discharge, similar effects can be obtained even if the present invention is applied to a plasma etching apparatus using RF discharge.

〔Effect of the invention〕

As described above, by using the present invention, high-speed and fine plasma etching (without undercuts) can be easily performed.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional plasma etching apparatus (using magnetic field microwave discharge), Figure 2 is a schematic diagram of a conventional plasma etching apparatus (using RF discharge), and Figure 3 is a vertical An explanatory diagram of etching and non-vertical etching, Fig. 4 is a schematic diagram of an etching apparatus according to an embodiment of the present invention, and Fig. 5 shows gas pressure, microwave output, and RF applied voltage in the embodiment of Fig. 4. FIG. 6 is a graph showing an example of control, and is an explanatory diagram of the progress of etching. DESCRIPTION OF SYMBOLS 1... Microwave oscillator, 2... Power supply for microwave oscillator, 3... Waveguide, 4... Discharge tube, 5... Electromagnet, 6... Vacuum chamber, 7... Piping, 8... Gas flow control valve, 9... Cylinder, 10... Sample, 11
... Sample holding means (sample stand), 12... Permanent magnet,
13... Upper electrode, 14... Lower electrode, 15...
High frequency (RF) power supply, 16... Capacitor, 17.
...Insulator, 18...Controller. Agent Patent attorney Akira Takahashi ← 'f13 Figure 4 Figure 5 (2) Peeling title shouting darkness g ward <b) Continued from page 1 ■ Inventor Oka 1) Shinshin Kokubunji City Mooro Research Institute

Claims (1)

[Claims] 1. Consisting of a vacuum chamber, means for evacuating the vacuum chamber, means for introducing gas into the vacuum chamber, means for generating plasma in the vacuum chamber or a part thereof, and a sample and means for holding the sample. A plasma etching apparatus characterized in that a discharge using a gas containing fluorine and a discharge using an NH gas are performed alternately. 2. A plasma etching apparatus according to claim 1, characterized in that 5FII or F2 is used as the fluorine-containing gas.゛