JPS6056231B2 - plasma etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved plasma etching method.

Recently, radio frequency (RF)
) A plasma etching method in which a gas plasma is formed from a reactive gas between the electrodes by applying electric power, and etching is performed on the electrodes. It is attracting attention in the IC and LSI fields because it can also etch.

By the way, Al films are widely used as electrodes and wiring in ICs and ICs, but Si and SiO.

Selective etching of the Al film is an important issue in its introduction. For example, Al is deposited over the entire surface of the substrate on which elements have been formed, and electrodes and wiring are formed from the Al film using an appropriate pattern as an etching mask. However, since the effective thickness of the Al film becomes larger at the step portion (measured perpendicular to the substrate surface), the N film etching at the flat portion is completed before the etching at this portion is completed. Therefore, if the etching selectivity is poor, the surface of the field oxide film may be etched, or A may be etched in the contact hole.
The substrate surface that deviates from the l film pattern is etched.
The n-junction may be damaged and cause leakage current. In other words, in order to increase the density of contact holes formed in opposite conductivity type regions on the substrate surface, when the openings are 1 to 2μ square, it is no longer necessary to form an Al pattern to cover the entire contact hole for mask alignment. It is difficult to do so, and it is now possible to allow a part of the contact hole to come into contact with the contact hole. CCI is less toxic and easier to handle as a gas introduced during conventional N etching. (carbon tetrachloride) has been widely tried, but the etching rate is slow and Al/SiO
2 In particular, the Al/Si etching selectivity is poor, and it has not yet been put to practical use. The present invention has been made in view of the above-mentioned circumstances, and includes applying high-frequency power to electrodes provided facing each other to form gas plasma between the electrodes, and performing etching on the electrodes using CCl4 gas. to Cl2
Cl2/CCl4+Cl2 pressure ratio with gas added is 0.8
The gas plasma is formed using a gas that is 0
．． The present invention provides a plasma etching method characterized by etching an aluminum film under a high vacuum of 1T0rr or less.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view schematically showing the plasma etching apparatus used in this example.

A vacuum container 1 made of stainless steel is provided with gas inlets 2 and 3, through which CCl4 gas and Cl2 gas are introduced, respectively. Both electrodes 4 and 5 have a parallel plate shape and are insulated from the container by insulators (Teflon in this case) 6 and 6'', respectively.
Electrode 4 is connected to R of 13.56MHz through vacuum seal 7.
The F power source 8 is connected via a matching box 9, and the electrode 5 is grounded. In this way, 200W is applied to the electrodes 4 and 5.
(7) RF power is applied.

Both electrodes 4 and 5 are cooled by water-cooled vibrators 10 and 1'', and gas is introduced after the container 1 reaches 0.01T0rr or less by an exhaust means 11 such as a diffusion pump, Roots pump, or rotary pump, and a conductance valve 12 ,1
2'' adjusts the degree of vacuum in the vacuum container 1, that is, the etching pressure.A liquid nitrogen trap 13 is provided between the conductance valves 12 and 12''. In this way, gas plasma is formed between the electrodes 4 and 5 by glow discharge, and the sample 14 on the electrode 4 is etched under reduced pressure.

Figure 2 shows the chlorine gas mixture ratio, Cl2/CCl4:
, +Cl2 pressure ratio is changed to show the relationship between etching rate and etching selectivity.

Here, the degree of vacuum in the vacuum container 1, that is, the etching pressure is set to 0.
．． It was kept constant at 1T0rr. Curves A, b, and c are the etching rates of Al, Si, and SiO2 calculated from the etching depth and etching time of 4 hours after the completion of etching, and curves D and e are the etching rates of A1/Si and Al, respectively, calculated using the results.
/SiO2 etching selectivity. As the mixing ratio of Cl2 gas increases, the etching rate of Al, Si, and SlO2 decreases to 0.7 when the Cl2/CCl4+Cl2 ratio is 0.7, respectively.
5 is the maximum, but the rate of change in N is particularly large. And as shown in curves D and e, A1/S
The etching selectivity of i, Al/SIO, is both Cl2/
When the CCl4+Cl2 ratio is below 0.8, Cl2/CCl
4+Cl2 ratio is zero, that is, the selectivity and etching rate of the Al film are improved compared to etching with CCl4 gas alone.

Figure 3 shows the etching rate and etching selection by changing the Cl2/CCl, +Cl2 pressure ratio when etching Al, Si, and SiO2 films in the same way as explained in Figure 2 with the etching pressure kept constant at 0.04T0rr. FIG. 2 is a characteristic diagram showing the relationship with the ratio obtained in the same manner as explained in FIG. 2.

Curves a″, b″, and c″ are the etching rates of Al, Si, and SiO2, respectively, and curves d″ and e″ are the etching rates of Al, Si, and A1/Si, respectively.
The etching selectivity ratio of l/SiO2 is shown. As the mixing ratio of Cl2 gas increases, the aforementioned Cl2/CCl4+C
When the l2 ratio is 0.8 or less, the etching rate of the A1 film and Al/Si,
The etching selectivity of Al/SiO2 was improved.

The A1 film was no longer etched at all at 0.9.
FIG. 4 is a characteristic diagram showing the relationship between etching pressure, etching rate, and etching selectivity when etching N film, Si film, and SiO2 film.

The etching pressure was 0.025T0rr.CCl4 gas.
．． While introducing C12 gas at a pressure of 0.015T0rr, using the conductance valve described above,
5,0.07,0.085,0.1,0.11,0.1
2 pressures were set. Here Cl2/CCl4+C
The l2 ratio is 0.015/0.4. Curves A, b, and c are the etching rates of Al, Sj, and SiO2, respectively, and curves D,
e represents the etching selectivity of A1/Si and Al/SiO2, respectively. As shown in the figure, as the etching pressure was increased, the etching selectivity ratios of A1/Si and Al/SiO2 also increased, reaching 5,100 at 0.1 T0rr.

Incidentally, at 0.15T0rr, A1 was no longer etched at all. In addition, experiments were conducted under various conditions, and in all cases, Cl2/CC was judged to be superior to etching with CCl4 gas alone, judging comprehensively from the etching selectivity and Al film etching speed.
The l4+Cl2 ratio was found to be within a range of 0.8 or less.

For example, the results were the same even though the high frequency power was varied.

Figure 5 a shows high frequency power of 100W (0.12W/Clt)
, 200W (0.24W/Cfi), 300W (0.3
Cl2/CCl4+Cl at 6W/C7lf).

The relationship between pressure ratio and cathode drop voltage ■Dc is shown. Cathode refers to the electrode to which the RF power source is connected. In other words, electrons in the plasma flow into the cathode during the positive half cycle of the high frequency, and positive ions in the plasma flow into the cathode during the next negative half cycle, but since the mobility of the electrons is greater than that of the positive ions, both The potential of the cathode is lowered and self-corrected so that the difference disappears. This decrease in potential is called cathode drop voltage/■DC (VdC=ψ), and an explanatory diagram is shown in FIG. 4b. (V,: maximum value, V2 minimum value)
. In Figure 5 a, curves F, g, and h are 100W and 200W, respectively.
, 300W, and remained almost unchanged with respect to the amount of CI2 added.

By the way, the change in the etching rate of the film shown in the results shown in FIGS. 2 and 3 is inferred as follows.

That is, as the Cl2/CCl4+Cl2 ratio increases, the CCI
While there is a lot of 4, excessive C covers the AI film surface and Al
The etching rate of the film is low, and by adding Cl2, this C
becomes CCl4 with Cl2 and is removed, Cl2/CCl
N film etching is best at a 4+Cl2 ratio of 0.75, but after that, the etching rate rapidly increases as the ring element by CCl3+ of the thin Al2O3 layer on the N surface formed in the atmosphere becomes difficult to perform due to the lack of CCl4 gas. It is thought that this has decreased. In addition, the effect of Cl2 addition is Cl2/C
Cl4+Cl.

The ratio begins to appear clearly from 0.1, especially from 0.2. Among them, 0.4 to 0. The range of 0.6 to 0.8 was particularly significant. In addition, the etching rate of the A1 film and A]/Si, AI/
To remove sudden changes in SlO2 selection ratio, Cl2/CCl4+
The Cl2 ratio is preferably 0.7 or less, particularly 0.6 or less. Furthermore, the selectivity effect was remarkable when the etching pressure ranged from a lower limit of 0.01, especially 0.0rr', to an upper limit of 0.06T0rr.

In addition, when considering damage during etching of the A1 film of a pattern used as an etching mask deposited on the N film and undercuts under the mask, at least 100 (0.
12W/d) ~ 300W (a). High frequency power of about 36W/c#i), cathode drop voltage -20 to -220V
It was necessary to do so.

These will be explained in detail. FIG. 6 shows the change in Vdc for each d power when the etching pressure is changed. Here, CCl4 gas 0.025T0rr
', the pressure was adjusted as described above while flowing Cl2 gas at 0.015T0rr. Curve a is d power 100W (0.12W/
Clt), b is 200W (0.24W/d), c is 30
0W(4). 36W/C7lf), the larger the d power, the larger Vdc, and the lower the etching pressure, the larger Vdc. As shown in FIG. 7a, aluminum 32 with a thickness of 1 μm is deposited on a wafer 31 coated with SiO2, a positive resist mask 33 is formed, and 0.1T
Etching was performed at 0rr and 200W, but as shown in the figure, a large undercut 34 occurred, and the underlying SiO
Polymer 35 was deposited on 2.

Also, 0.04T0rr-(CCl4O.O25TOrr
, Cl. O. 100W under the pressure of
Etching was carried out in the same manner with Rf powers of 200 W and 300 W, but undercutting occurred with 100 W. FIG. 8 shows the relationship (solid line) between etching pressure and undercut amount (lateral etching depth).

CCl4O. O25TOrr', Cl2O. Ol5TO
The pressure was adjusted while flowing with rr, and the Rf power was 200W. As a result, at 0.1T0rr, a significantly large undercut larger than the N film thickness occurred. In this way, undercut is closely related to ■Dc, and at least Vdc is -20
Etching below V was necessary to avoid significant undercuts.

■When Dc approaches 0V, CCl enters the sample perpendicularly.
It is presumed that etching by ion species such as 3+ is reduced and etching by neutral species is increased, making it impossible to obtain directionality in etching. 0.04T0rr(CCl
4O. O25TOrr, Cl2O. Under the conditions of Rf power of 200 W and under a pressure of 200 W (Ol5 TOrr), the resist mask was hardly etched, and almost no undercut was observed.

This situation is shown in FIG. 9a.

That is, deposits 51 were observed on the sidewalls of the etched A1 film. This deposit is made of EPMA (ElectrOnP
rObeMicrO. (Arlalysis) measurements revealed that it was a substance mainly composed of crab. It is believed that during Al etching, deposits are attached to the sidewalls of the Al, and this deposit prevents undercuts. The resist in the state shown in FIG. 9a is ashed by oxygen plasma, but the deposits remain un-ashed as shown in FIG. 9b. However, when the wafer in the state of a is used in a resist stripping solution (J-100 manufactured by Tokyo Ohka Co., Ltd.) under resist stripping conditions (11CfC, 5 minutes), not only the resist but also the deposit 51 is etched at the same time as shown in c. , a microfabricated pattern of A1 film without undercuts appeared. The 1μ thickness made like this is 1μm.
A pattern of wide lines and spaces was achieved. Figure 10 shows the change in undercut amount (solid line) with respect to the Cl2 addition amount, that is, the Cl2/CCl4 + Cl2 pressure ratio,
Etching pressure 0.04T0rr,. rf power 200W
This is the condition. Cl2/CCl4+Cl2 pressure ratio is 0.
3 to 0.35, almost no undercut was observed.

This is the effect of the sidewall deposits mentioned above. The effect weakens as the ratio deviates from the above, but Cl2/CCl4+
If the CI2 ratio is 0.6 or less, CCl4 alone, that is, Cl2
/CCl4+Cl2 ratio was less than that of zero.

Especially when the Cl2/CCl4+Cl2 pressure ratio is 0.2 to 0.4
If it is 5, the undercut will be substantially zero.

The present invention is also effective in preventing deformation of resist masks.

200W, C12/CCl, +Cl2 ratio of 0.3 to 0.
In Fig. 35, the resist after etching remains in its original form, but in Fig. 10 (Rf power 200W, 0.04T0r
Cl as shown in r) (dashed line).

/CCl4+Cl. Depending on the pressure ratio, large swelling occurred in the resist after etching (the amount of swelling appeared as a spread in the lateral direction).For example, Cl2/CCl4+Cl
When the 2 ratio is 0.7, as shown in FIG. 7b, large swelling is exhibited and a polymer is formed on the base SiO2. In this way C
l2/CCl, +Cl2 ratio is 0.61). C if below
The deformation of the resist is smaller than when using Cl alone. stomach.

The broken line in FIG. 8 also indicates the amount of resist swelling.

It should be noted that when Vdc is lower than -220V, particularly -330V, the resist mask is damaged by the large kinetic energy of the etching species.

In addition, the etching rate of the aluminum film, A1/Si,
Considering Al/SiO2 etching selectivity, the above Cl
The 2/CCl4+Cl2 ratio is preferably 0.2 to 0.6. or,
When Vdc is lowered from -20V or lower to -50V or lower, it is more effective in preventing undercuts and resist swelling. Incidentally, the above results are similar even for aluminum films containing several percent of copper or silicon, and the present invention also includes these. In particular, the undercut after exposing the base progressed more slowly in the aluminum film containing several percent Si than in the case of pure N.
In addition, Cl. to CCl4. The addition does not stop at the above effects, but also has 7
It has the additional effect of recirculating substances that cause contamination, such as C in CCI and the polymer C2Cl, into CCl4, improving etching reproducibility, and preventing deterioration of exhaust system oil and pumps. It has been found.

The present invention is suitable for etching an aluminum film on a silicon or silicon oxide layer. Furthermore, both polycrystalline and single-crystalline silicon exhibit similar effects.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of a plasma etching device.
Figure 2 shows Cl2 at an etching pressure of 0.1T0rr.
A characteristic diagram of etching rate and etching selectivity with respect to mixing ratio, FIG. 3 shows Cl at an etching pressure of 0.04T0rr.

Claims (1)

[Claims] 1. When high-frequency power is applied to electrodes provided facing each other to form gas plasma between the electrodes and etching is performed on the electrodes, Cl_4 gas is added to CCl_4 gas.
A plasma etching method characterized in that the gas plasma is formed using a gas having a pressure ratio of Cl_2/CCl_4+Cl_2 of 0.8 or less, and the aluminum film is etched under a high vacuum of 0.1 Torr or less. . 2. The plasma etching method according to claim 1, wherein the Cl_2/CCl_4+Cl_2 pressure ratio is 0.6 or less and the cathode drop voltage is -20 volts or less.