JPH0521397A - Photoetching method - Google Patents

Abstract

PURPOSE:To etch an SiO2 layer at high speed by using chemical species which are created by applying light to a compound, which has sulfur and fluorine, and gas, which contains O2. CONSTITUTION:A wafer, where an insulating SiO2 interlayer film is stacked on a single-crystal silicon substrate, and an etching mask is made of a fluorine- resistant resist material, is set in a reaction cell, which has a high vacuum exhaust mechanism and a light application mechanism, and S2F2/O2 mixed gas also, is irradiated with an ArF excimer laser. SF created from S2F2 reacts with O2, and generates intermediate product SFO, and pulls out the O atoms in SiO2, and proceeds with etching. Since it does not go through the phased reaction for dissociating F, the process can be made high-speed as compared with the conventional case of generating the intermediate product NFO from NF3/O2 mixed gas. Since SFO does not reacts upon Si, selectivity to base becomes infinite.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photo-etching method, and more particularly to a method for high-speed etching a silicon oxide (SiO ₂ ) -based material layer while maintaining high selectivity with respect to an underlying silicon-based material layer.

[0002]

2. Description of the Related Art As seen in recent VLSI, ULSI, etc., the design rules of semiconductor devices have already been put to practical use at the submicron level, and research is proceeding at the half micron and even quarter micron levels. .. Needless to say, what has played a leading role in such microfabrication technology is reactive ion etching (RIE) utilizing the directionality of ions in plasma. However, in RIE, accelerated reactive ions collide with the substrate, and etching proceeds by a mechanism that promotes reaction with active species, so that it is essentially difficult to increase the selectivity to the underlayer. Further, collision of charged particles having such kinetic energy causes various irradiation damages such as generation of crystal defects in the silicon substrate and generation of fixed charges and neutral traps in the oxide film. Further, the mask may be charged with negative charges in plasma, so that a thin oxide film such as a capacitor film or a gate insulating film may cause dielectric breakdown.

Under these circumstances, in recent years, a magnetron RIE apparatus which enables a process with lower damage than that of the conventional RIE, a magnetic field microwave plasma etching apparatus using ECR discharge, or the like has been used. .. These devices can generate high-density plasma even under a low gas pressure, and can perform anisotropic processing even under conditions of relatively low ion incident energy. Therefore, defects due to kinetic energy of ions can be significantly reduced by using these devices. On the other hand, regarding damage by charged particles, the phenomenon itself has not been fully understood. However, the damage is unavoidable as long as etching is performed by using the chemical species generated in plasma, and if the design rules of the semiconductor device are further miniaturized in the future, there is a great possibility that the damage will be seriously affected.

One of the promising techniques for realizing a low damage or no damage process is photoetching. Focusing on the fact that the electron impact energy required to cause a chemical reaction is only a few eV, a mercury lamp (5 to 6 eV) and an ArF excimer laser (6.4 eV) are used.
V), KrF excimer laser (5 eV), XeCl excimer laser (4 eV) or the like is used to directly cut the chemical bond of the reaction gas. A feature of the present invention is that charged particles are not included in the reaction system because plasma discharge such as in conventional RIE is unnecessary.

In the photo-etching at the beginning of development, the main research object was the etching of the silicon-based material layer. But,
If the process did not help but rely by conventional ion-assisted reaction to allow a light etching, it is considered a significant advantage for low damage and selection improvement occurs, the etching of the SiO ₂ based material layer also Research is in progress. For example, Mat. R
es. Soc. Symp. Proc. , Vol. 47,
p. 112 (1985), a method of using CF ₂ Br ₂ as an etching gas, Appl. Phys.
Lett. , Vol. 47, p. In 398 (1985), methods using an NH ₃ / H ₂ mixed gas are reported.

[0006]

By the way, the above-mentioned CF
_The method using ₂ Br ₂ or NH ₃ / H ₂ mixed gas is an extension of the conventional way of thinking that the generation of etching species is performed by photoreaction, and the problem of low etching rate cannot be avoided. This is because the light absorption cross section of a molecule with respect to a photon is smaller by 1 to 2 digits than the electron collision dissociation cross section of a molecule in plasma. In the field of dry etching, single-wafer type dry etching apparatuses are becoming mainstream as the diameter of wafers becomes larger, and it is indispensable to greatly improve the etching rate in order to maintain the same productivity as conventional ones. Therefore, the low speed is one of the factors that practically prevents the practical use of photoetching.

On the other hand, the method using NF ₃ was reported in the 38th Joint Lecture on Applied Physics (Spring 1991) Proceedings, 2nd Volume, 530 pages, Abstract No. 29p-ZB-12. There is. This is a method in which residual O ₂ in the reaction cell is reacted with NF ₃ by irradiation of ArF excimer laser light to generate an intermediate product NFO, and the O atom of SiO ₂ is extracted using the deoxidation reaction of NFO. Is. In other words, the idea is different from the conventional photo-etching that generates etching species by photoreaction.
The slowness can be improved to some extent. By the way, the simplest NFO generation mechanism is expressed by the following equation. ^{_{NF 3 → NF 2 + F *}} NF 2 → NF + F * NF + (1/2) O 2 → NFO In other words, in order to generate a NFO requires a gradual reaction to dissociate the F ^* from NF _3. However, it is possible that this stepwise reaction is rate limiting in the process. Therefore, it is an object of the present invention to further improve the etching rate in order to put into practical use the photo-etching based on the O atom abstraction reaction by the intermediate product.

[0008]

The photoetching method according to the present invention is proposed to achieve the above-mentioned object, and contains at least a compound having sulfur and fluorine as constituent elements and O _2. It is characterized in that the etching gas is irradiated with light and the generated chemical species are used to etch the SiO ₂ -based material layer.

[0009]

The present inventor selects a compound having a small number of elementary reactions until an intermediate product is obtained as a means for accelerating the photoetching, or a large amount of F ^* even if the number of elementary reactions is large ^. Based on the policy of selecting compounds that can generate As a result, it has been found that a compound having sulfur (S) and fluorine (F) as constituent elements is suitable as the above compound. The most typical of the above compounds is sulfur fluoride. As sulfur fluoride, five kinds of compounds having different S atom oxidation numbers are known. For example, if S ₂ F ₂ having the lowest oxidation number in sulfur fluoride is used, SF is generated by breaking the S—S bond without dissociating F ^* . This SF
Is reacted with O ₂ , SFO can be promptly obtained as an intermediate product. Further, if SF ₆ having the highest oxidation number in sulfur fluoride is used, a stepwise reaction for dissociating F ^* is required until SF is generated,
During this period, theoretically, 5 F ^* can be produced from one molecule. However, F ^* has a relatively short life and disappears by recombination when the light irradiation is stopped. Therefore, in this case, if the irradiation time is set longer than in the conventional case, it is possible to effectively use a large amount of F ^* to be generated and to increase the speed. In any case, in the present invention, the advantage of photoetching that does not use charged particles is utilized as it is, and it is possible to perform a process with low damage and high underlayer selectivity at high speed.

Specific examples of the present invention will be described below.

Example 1 This example is an example in which the present invention is applied to the processing of contact holes, and the SiO ₂ interlayer insulating film is etched using an S ₂ F ₂ / O ₂ mixed gas. In this example, etching
The sample wafer has a SiO ₂ interlayer insulating film laminated on a single crystal silicon substrate in which an impurity diffusion region is formed in advance, and an etching mask made of a fluorine-resistant resist material is further formed on the SiO ₂ interlayer insulating film. It is formed by predetermined patterning. This wafer is set in a reaction cell having a high vacuum evacuation mechanism and a light irradiation mechanism, the wafer temperature is controlled at 20 ° C., the atmosphere in the cell is taken as an example, S ₂ F ₂ flow rate 50 SCCM, O ₂ flow rate ₂ SCC.
M, gas pressure was adjusted to 13.3 Pa (100 mTorr). In this state, the wafer was irradiated with ArF excimer laser light under the condition of an energy density of 40 mJ / cm ² and 2,000 shots.

In this process, S ₂ F is irradiated by laser light irradiation.
SF was decomposed from ₂ reacts with O _2, which is an intermediate product SFO was formed. A typical reaction at this time is shown in the following formula. S ₂ F ₂ → 2SF 2SF + O ₂ → 2SFO S ₂ F ₂ is more unstable than SF ₆ etc. even with the same sulfur fluoride, and efficiently absorbs light energy to facilitate S-
The S bond was cleaved to generate SF. Here, the stepwise release process of F ^* is not included. The SFO has a relatively long life, and stayed in the etching reaction system even after the irradiation of the laser beam was stopped to proceed with the following reaction with the SiO ₂ interlayer insulating film. 4SFO + SiO ₂ + O ₂ → SiF ₄ ↑ + 4SO ₂ Here, SFO has a function of extracting O atoms from SiO ₂ . Ion bombardment is not involved in this extraction reaction, but only the mechanisms such as SFO adsorption on the SiO ₂ surface, formation of SiF ₄ and SO ₂ by surface reaction, and desorption of reaction products are involved. .. Therefore, no damage due to charged particles occurs. When the etching of the SiO ₂ interlayer insulating film progressed and the impurity diffusion region which was the underlying silicon-based material layer was exposed, SFO did not react with Si at all, so the etching was stopped. Although F ^* is also generated during the light irradiation, the F ^* is recombined and disappears soon after the light irradiation is stopped, so that there is no fear that the selectivity with respect to the silicon underlayer is lowered. As a result, the selectivity to the substrate becomes infinite. The etching rate in this embodiment is about 2
It was 5 nm / min, which was much higher than about 10 nm / min when the conventional NF ₃ / O ₂ mixed gas was used.

Embodiment 2 This embodiment is an example in which the present invention is also applied to the processing of contact holes, and the SiO ₂ interlayer insulating film is etched using SF ₆ / O ₂ mixed gas. The wafer and reaction cell used as the etching sample in this example are the same as those used in Example 1. The above-mentioned wafer is set in a reaction cell, the wafer temperature is controlled at 20 ° C., and the atmosphere in the cell is taken as an example, S ₂ F ₂ flow rate 100 SCCM, O ₂ flow rate 2
The SCCM and the gas pressure were adjusted to 13.3 Pa (100 mTorr). In this state, ArF excimer
Laser beam energy density of 40 mJ / cm ² , 10, 0
Irradiation was performed under the condition of 00 shots.

In this process, SF _{6 is} irradiated by laser light irradiation.
Stepwise F ^* is generated while being dissociated SF from the O ₂
And an intermediate product SFO was produced. A typical reaction at this time is shown in the following formula. SF ₆ → SF ₅ + F ^* SF ₅ → SF ₄ + F ^* ……… SF _n → SF _n-1 + F ^* SF _n-1 + (1/2) O ₂ → SFO + (n-2) F ^* (n is Natural number, 2 ≦ n ≦ 4) Here, a large amount of F ^* is released into the etching reaction system until the SFO is generated. Therefore,
In order to effectively use this F ^* , in this embodiment, light irradiation is performed until immediately before the underlying impurity diffusion region is exposed, and the light irradiation time is five times as long as the number of shots as compared with the above-described first embodiment. Extended. As a result, the etching of the SiO ₂ interlayer insulating film progressed at high speed due to the contribution of SFO and F ^* during light irradiation, and after the light irradiation was stopped, infinite selectivity was achieved due to the contribution of SFO alone. The etching rate in this example is 30 nm / min, which is also the same as the conventional NF ₃
This is a significant improvement over the case of using the / O ₂ mixed gas.

Although the present invention has been described above based on two embodiments, the present invention is not limited to these embodiments. For example, as a compound having at least sulfur and fluorine as constituent elements, The above S ₂ F ₂
In addition to SF ₆ and SF ₆ , SOF ₂ (thionyl fluoride) or the like can be used. Since SOF ₂ also contains O atoms in the molecule, it is expected that SOF ₂ is excellent in SFO generation efficiency. Also, it goes without saying that the structure of the sample wafer, the type of light source, the etching conditions, etc. can be changed as appropriate.

[0016]

As is apparent from the above description, when the present invention is applied, the number of elementary reactions until an intermediate product for extracting O atoms in a SiO ₂ -based material layer is reduced, or It is possible to improve the etching rate by either using the by-produced F ^* effectively. Moreover, the advantages of photo-etching such as no damage and high selectivity can be obtained as before. Therefore, the present invention can provide photoetching as a truly highly practical process.

Claims (1)

Claims: 1. A light is irradiated to an etching gas comprising a compound and O ₂ having at least a sulfur and fluorine as constituent elements, the generated chemical species silicon oxide-based material layer by using a An optical etching method characterized by etching.