JPS58100684A - Dry etching method - Google Patents

Abstract

PURPOSE:To enable accurate working by plasma-etching the surface of a material in a gaseous compound prepared by substituting Br or I for part of F in CF4 or a gaseous mixutre of the gaseous compound or the like with CF4. CONSTITUTION:A gas having a molecular structure obtd. by substituting Br or I for part of F in CF4 or a gaseous mixture of said gas, Br or I with CF4 is prepared. The gas is introduced into a composite plasma and sputter etching apparatus or a parallel electrode type plasma etching apparatus. Ions in the gas in a plasma state are allowed to collide against the surface of a material to etch a layer of a volatile substance such as Si. Thus, the surface of the material is accurately worked.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry etching method for selectively etching the surface of a material using the chemical reactivity of plasma or ions, and in particular to a dry etching method that is suitable for the etching process in the manufacturing process of semiconductor integrated circuits. - Concerning etching methods.

In the etching process of semiconductor integrated circuit manufacturing workers @tc:fd, from the point of view of the target material to be etched,
81(
Step of patterning polycrystalline silicon) or 8isN4 (silicon nitride) or metal glands etc. as photoresist v mask and 8[)l+ 8iBN4 on 81 substrate.
The two steps of forming a pattern using a photoresist such as phosphor glass as a mask are superimposed.

In these steps, 810. The characteristic that 81 or 81 is hardly etched, that is, the selective etching characteristic is important. 8 further deposited on top of the 8i01 gland on the 8i substrate
Plasma etching technology using freon gas such as OF as an etching gas has conventionally been used as a dry etching method for patterning 1 or 86N4 or metal wires using a photoresist V mask. . This technique is based on the principle of turning OF gas into a plasma state by high-frequency discharge, and etching using the chemical action of neutral fluorine radicals that are dissociated and generated. Because of this, the etching progresses isotropically, so if you try to form a pattern of 81, 8i, Na, etc. as a photoresist mask, the etching process will be uneven, as shown in Figure 1. This results in a so-called undercut, which is removed to the same depth as the bottom of the photoresist pattern.

In the figure, l is the photoresist, ko is the target material to be etched, here 5101.3 is the base material, here 8I or 8i, N, '1. For this reason, there was a drawback that pattern accuracy was significantly deteriorated.

On the other hand, as a dry etching method that can be applied to the process of patterning 8101 + 811 N4 + phosphor glass on an 81 substrate using photoresist as a mask, the recently developed plasma sputter combined etching (reactive sputter etching) ) or parallel electrode type plasma etching technology.

The former technique is, for example, % open/close No. 32-//Hirohiro≠Hiroshi, and the latter technique is 1, for example, I.E.I.E.
International Electron Devices e-Meeting (IgBFi International
Electron Devices Meeting
) R-G Pakuru Ryuun 1 (R-G, Poulse
Plasma glcbing of aluminium
It is described in a paper entitled um). These techniques, like plasma etching techniques, are OF, 0!
Freon gas such as F6 is used as an etching gas, but W and coral are completely different. That is, O
Ions such as Fo are incident and bombarded perpendicularly to the surface of the material to be etched using the same principle as raw salt in sputter etching equipment, and the chemical reactions that occur at this time (aFn+o,→8iFm+Co,
Etching of 5IO1 is performed using ft (co, etc.). For this reason, the etching has directionality, and as shown in FIG. 2, it is possible to form a pattern with high precision without causing an IC or undercut.

However, +S such as St deposited on 8i01
There has been no known method for patterning an 8i substrate using V photoresist as a mask or using 8i01 as a mask without causing undercuts.

The present inventor used plasma sputter composite processing yf7/equipment (reactive sputter etching equipment) to
0. The results of investigating the relationship between the etch rate ratio and pattern formation characteristics are described below. The exhaust system of the experimental apparatus used by the present inventor is composed of an oil diffusion pump (/ 000 L/sec) and an oil rotary pump (j 00 L/+nin). An etching gas introduction system is connected to the vacuum w1, and an electrode (diameter 200 mas) for generating plasma is arranged inside, and the electrode is water-cooled. A sample to be etched is placed on an etching table set above the electrodes. When high wave power (frequency t j, jA MHz) is applied to the electrode and plasma is generated between it and the opposing plate at a grounded potential, Wi, which is the same as the high frequency sputtering device,
As a result of the process, the sample surface and the exposed etching table surface are bombarded with ions. The chemical reaction caused at this time is utilized in the 8i0. It is etching.

In this case, as mentioned before, without undercut,
Highly accurate pattern formation is possible.

The present inventors first studied a method of mixing oxygen with fluorocarbon gas to determine whether such pattern forming characteristics can be maintained for Si when the etch rate of 8i is increased. Mixing oxygen with fluorocarbon gas (Freon gas) is a method commonly used in plasma etching techniques to increase the etch rate, such as 81. As a result, 81 and 8i0. When the etch rate ratio of 81 is less than l:l-λ:l, it is possible to form a pattern without undercutting, but when the etch rate of 81 is increased to an etching rate ratio of l:l-coni of 1 or more, It has been found that undercuts occur exactly as in the case of plasma etching. This result is OF4 * 01 F@ + 04 Fg gas and 02
+001 was established for all gas combinations.

It is therefore an object of the present invention to provide a dry etching method which makes it possible to selectively etch layers of typically fluoride volatile materials, such as 81, deposited over a %8i01 substrate, without undercutting. It is to propose.

In order to achieve the above object, the dry etching method according to the present invention uses, as an etching gas, a gas having a molecular structure in which part of the fluorine in fluorocarbon is replaced with bromine or iodine, or a fluorocarbon. and bromine, iodine, or a gas having a molecular structure in which part of the fluorine in carbon fluoride is replaced with bromine or iodine.

As a reminder of the inventor's experimental results mentioned above,
0 If a large amount of snow is mixed, OF, + 0. →■、oo
, +$F reactions occur in the plasma, generating a large amount of neutral fluorine radicals, and forming an etching machine (Si+44F→8iFa) similar to plasma etching.
It can be interpreted that this is because the effect of ion injection becomes extremely small. In addition, when the etch rate of 8i is the same as or lower than StO, %old is also undercut (the reason why it is etched is O3
Since the concentration of 8i is not so high, the action is mainly on the material surface, and the 0 snow that reaches the 8i surface becomes %81 + OFn + 0.7' due to ion bombardment from CF.
→Reactions such as 5tFfr, +oo, co are triggered, and the F of OFn reacts with 8i, and the remaining 0 and OF are removed from the 81 surface by O, resulting in 81
The etching progresses, resulting in undercuts)'lk-
It is thought that this will not occur.

According to the findings of the present inventors, the reaction within the plasma does not generate fluorine radicals, and the ion bombardment surface rcm is only 0. [If a halogen element with low reactivity is used as a mixed species that plays a similar role, 8& can be efficiently etched using ions such as CF score without anodacut.

The results of experiments conducted by the present inventor using iodine and bromine are shown below.

OF, gas or 08F, gas with iodine (processing io ~ 20
- By mixing and using quartz glass and carbon as etching table material, 81 is efficient without undercut (
Etched with an etch rate ratio of 8i:8i0. Φj
:l was found to be realized. Gas pressure condition is 0.
It was 0.03 to 0.07 Torr. High frequency power sow<
o, itw7♂), 81 is approximately j O(7A 7m
It was efficiently etched at an etch rate of i n . Figure 3 shows the flow rate of OF, Y / j et / m
The relationship between high-frequency power and etch rate when etching is performed for 10 minutes with the gas flow rate at J cc/min and the gas pressure at 0.02 Torr is 81. Photoregis) k's, 1310J1 and 8IO1.

Bromine (Brl) also showed almost the same effect as iodine.

Mixing Is or Brl not only increases the etch rate of St but also increases the etch rate of 8i0. It was also found to be effective in reducing the etch rate. Furthermore, the etch rate of the photoresist is also low. This result shows that the binding energy of ■ or Br is 0.0 and 8I. It is thought to be based on the weaker reactivity, which is smaller than the bond energy of Hl and N, and weaker than the C-0 bond.

The etching reaction mechanism of 81 when OF or OtF gas is mixed with If, Br, or tt is that when ions such as OFn bombard 5i11o, OFn
Since F in is more stable when combined with 81 than with 0, it is 5
iit'n is formed, and the remaining 0 and CF combine with the 2 or Br attached to the surface and volatilize, resulting in the same situation as in the case of a small amount of 01 mixture. Also, the parts that are not subjected to ion bombardment! It is presumed that it is not etched due to the low reactivity of 0Ffi or B.The fact that fluorine-containing components such as 0Ffi plays an important role in I.

It was confirmed from the results of 5 trials that Br, single gas, or Ar mixed gas has a small effect.

0 as a gas that is expected to show the same effect as a mixed gas of OF, IO, gas and Br, sI, gas.
BrF110Br, F, *OIF, , OI,
PQ Noyo 5rc, a trace of fluorine in fluoride carbon OnF@ is B
Or gases having a molecular structure in which I is substituted.Among these gases, %OB, F, and OBr
, HalonF-/JB/ (0BrFi), which is known as a gas for extinguishing agents and is extremely safe.
It is known under the trade name Halon 1'-/JBJ (OBr, F,).

The results of experiments conducted by the inventor on these gases are 0
Taking BrF@ as an example, the following is explained. 0B
When the rF@ gas enters a plasma state, Br, which has the smallest binding energy, is dissociated from the 0BrF@ molecule, and it is thought that it exhibits the same effect as a mixed gas of OF and Br.

Figure 8 shows a single crystal 81.0% obtained using quartz glass as the etching table material, a flow rate of 0BrFH/j cc/min, and high-frequency power jOW. Polycrystalline silicon:z
y, 8i, N,, photoresist kz/90J,
Figure 5 shows the moderate relationship between 0BrFB gas pressure and gills for 0.0 and 8 lO. OJ Torr
using the same OB r
The relationship between high frequency power and etch rate is shown in k'g ft for the same material as in Figure 1. As is clear from the figure, even with a relatively small high frequency power such as 5OW (0, / 4 W/cxh), the 8-shift is 700JL/win.
The etch rate was as follows. Further, the etch rate ratio of %S1 to S-imprint snow was 8i:5lo==+:/ or more. Furthermore, 81. N.

is also efficiently etched, S import N4: at O*
An etch rate ratio of :Hu : / or more was obtained. Further, the etch rate of the photoresist was also low, and an etch rate ratio of 8i:photoresist-321 or higher was obtained.

To further confirm the selective etching characteristics and undercut-free pattern formation characteristics of 81 and 8101.

As a result of etching the 81 substrate as a patterned stow mask with a thickness of 015 μm, patterns -〇, f
It was possible to obtain a vertical / (turn) with a vertical sidewall at a height of 3 μm. The mirror state was maintained.

With 0BrFs gas, 6-cell glass gave better results than carbon as an etching table material. If the etching table material is carbon and 0BrF@gas is used, or if the amount of I or Br8 is increased too much, deposits may occur on the %81 surface.
p4+0@F@gas, OBrF,,OB et al.F@*
By mixing 0IFI * OI gas, etc., the ratio (concentration) of %B' or !! can be adjusted to correspond to conditions such as the type of etching table material and gas pressure.

Gas pressure is 0. / = / Parallel polar plasma etching equipment used in the Torr region is also basically a plasma sputter composite etching equipment (reactive sputtering).
Since it has the same effect on wood as the etching device (etching device), the method described above can be applied equally well.

Due to its reaction type, the dry etching method according to the present invention can form patterns with high precision without undercuts on materials at temperatures as low as 5°C to which conventional OF and gas plasma etching can be applied. I can do it. This makes Mo'P Mo8i, which is important as a wiring material for semiconductor integrated circuits.

Furthermore, it is possible to form a pattern with a high nyt on other metals such as TI and Tm+W, which generally have volatile fluorides. However, in the case of metal, 0BrF@OF
4 gases or a small amount of 0. Better results can be obtained by mixing the two gases and using a slightly higher gas pressure.

As can be seen from the etching reaction mechanism, even if the above-mentioned gases are introduced into an ion beam etching device or an ion Java etching device, the plasma sputter combined etching device (reactive sputter etching device) will not work.
Alternatively, as in a parallel electrode plasma etching system, fluoride-volatile materials can be selectively etched with high precision.

Since the present invention is an etching method that utilizes a chemical reaction caused by ion injection, it has better uniformity and reproducibility than conventional plasma etching methods, and also has no dependence of etching rate on pattern shape. There is.

Carbon tetrachloride (C
By applying o14) to 81 etching,
A certain sF! Experimental results showed that the L undercut could be reduced; The method according to the present invention is far superior in each respect.

According to the present invention, it is possible to process a substrate with high precision using the 8-crystal fake as a mask, so it is possible to process semiconductor materials sensitive to impurity contamination such as metals without using a metal mask. The advantage of being able to process it is significant.

In addition, the gases used in the present invention, such as 0BrP'', are superior in terms of safety and ease of handling, and are completely different from conventional plasma sputter combined etching equipment (reactive sputter etching equipment) that uses Freon gas. It has the advantage that similar equipment, configuration, and handling are possible.

[Brief explanation of the drawing]

FIG. 1 shows 8i or 81.8i deposited by conventional plasma etching and photoresist as a mask on a flat surface. N
, 4 etched to form a pattern, FIG. 2 is a cross-sectional view of the 810. A cross-sectional view when etched, or a hole 810 according to the present invention, 81 coated on top
or 81. A cross-sectional view of a pattern formed by Not' etching, Figure @3 is a diagram showing the relationship between high frequency power and etching rate when a mixed gas of OF and I is used, Figures 3 and 5 are OB r FIG. 4 is a diagram showing the relationship between 0BrF, gas pressure and etch rate, and between high frequency power and etch rate when F@2 gas is used, respectively. l: Photoresist, λ: Target material to be etched, 3: Base material. Designated agent Ya 2 Figure 0 25 60 75 t00 high rt”+=
Voice electric power W) t, 6234s') t.

Claims (3)

[Claims] (1) As an etching gas, a gas having a molecular structure in which part of the fluorine in carbon fluoride is replaced with bromine or iodine, or carbon fluoride and bromine. A mixed gas containing iodine or a gas having a molecular structure in which part of the fluorine in carbon fluoride is replaced with bromine or iodine is used. The sample to be etched is placed so as to be bombarded by ions in the gas in a plasma state. Fluoride etches a layer of volatile substances'Ik
Dry etching method with 4I characteristics. (2) The above gas is introduced into a plasma sputter combined etching device (reactive sputter etching device) or a parallel electrode type plasma etching device to etch the material surface. dry etching method. (3) A dry etching method according to claim 1, characterized in that the gas is introduced into an ion beam etching device or an ion Java etching device to etch the surface of the material.