JPH05102095A - Dry etching method - Google Patents

Abstract

PURPOSE:To anisotropically etch an Al group material layer excellent in resist and base material selectivity without using BCl3. CONSTITUTION:After removing natural oxide film 7 on the surface of Al-1%Si layer 6, Al-1%Si layer 6 and barrier-metal 5 are etched using S2F2/Cl2 mixed gas. Cl* generated dissociation from Cl2 acts as main etching seed and S generated from S2F2 acts as a component for a side wall protective film 9, anisotropic working possible even under low bias. Since above stated mixed gas does not contain reducing substances such as BCl3, etc., the selectivity against a SiO2 interlayer insulating film 1 which is a base material improves. The deposited S can be easily removed through sublimation when a wafer is heated, thus can not be the cause for particle pollution. Only in the removal process of natural SiO2 film 7, reducing substances may be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method applied in the field of semiconductor device manufacturing, etc., and particularly to improvement of resist selectivity and underlayer selectivity in etching of aluminum (Al) -based material layer, and apparatus. It is intended to facilitate the maintenance of.

[0002]

2. Description of the Related Art Aluminum (Al) or an Al--Si alloy in which 1 to 2% of silicon (Si) is added as an electrode wiring material of a semiconductor device, and 0.5 to 1 as a stress migration countermeasure. % Copper (C
Al-based materials such as Al-Si-Cu alloys containing u) are widely used.

Dry etching of the Al-based material layer is generally performed using a chlorine-based gas. For example, BCl ₃ / Cl disclosed in JP-B-59-22374.
_A mixed gas is a typical example. The chemical species contributing as the main etching species in the etching of the Al-based material layer is C.
Since it is l ^* (chlorine radical), only Cl ₂ should be used originally. However, a natural oxide film is present on the surface of the actual Al-based material layer, and unless this is reduced, etching does not proceed promptly. Further, since the etching proceeds isotropically only with Cl ^* , some kind of ion contribution is required for performing anisotropic processing.
BCl ₃ has been added in view of this need. That is, since BCl ₃ produces a chemical species BCl _x having a strong reducing action in plasma, it is possible to reduce the natural oxide film on the surface of the Al-based material layer and to promptly advance the etching reaction. Ions such as BCl _x ⁺ generated from BCl ₃ promote forward sputtering of the resist mask and deposit carbonaceous decomposition products on the pattern side wall portion, so that the side wall protection effect of this deposit is anisotropic. It is possible to process the material.

[0004]

However, the above B
The addition of Cl ₃ / Cl ₂ mixed gas, especially BCl ₃ , has the following problems. The first is deterioration of maintainability. BCl ₃ reacts with oxygen during exhaust to generate B ₂ O ₃ (boric acid), and this white powder clogs the piping of the exhaust system of the etching apparatus, resulting in frequent maintenance and high throughput. It causes a decrease.

The second problem is that since BCl ₃ has a strong reducing property, when the underlying insulating film made of silicon oxide or the like is exposed, it is reduced and is susceptible to etching by Cl ^*. is there. This means that the over-etching significantly decreases the selectivity to the underlayer.
The third problem is that a certain amount of ion incident energy is required to expect forward sputtering of the resist mask, which inevitably reduces the resist selectivity. Further, when the underlying insulating film is exposed and sputtered by the ions having high energy, the insulating film is deposited on the pattern side wall portion to form a redeposition layer. Since this redeposited layer is porous, it easily absorbs residual chlorine, which causes aftercorrosion. Particularly in recent years, a barrier metal is provided on the lower side of the Al-based material layer, or Cu is added to the Al-based material layer.
In many cases, the formation of a redeposition layer which provides a residual field of chlorine must be avoided, because it is often added and the conditions are disadvantageous from the viewpoint of preventing after-corrosion.

As described above, many problems in the conventional etching of Al-based materials are caused by the use of BCl ₃ . Therefore, it can be said that it is not preferable to use the etching gas added with BCl ₃ throughout the etching process of the Al-based material layer. Therefore, the present invention solves the above-mentioned problems and improves the resist selectivity.
It is an object of the present invention to provide a dry etching method which is excellent in selectivity to base and maintainability and which enables anisotropic processing of an Al-based material layer while effectively preventing after-corrosion.

[0007]

The present invention is proposed to achieve the above objects. That is, the dry etching method according to the first invention of the present application, while controlling the temperature of the substrate to be etched to room temperature or lower,
It is characterized in that the Al-based material layer is etched using an etching gas containing at least one kind of sulfur fluoride selected from ₂ F ₂ , SF ₂ , SF ₄ , and S ₂ F ₁₀ and a chlorine-based compound.

Further, the dry etching method according to the second invention of the present application is characterized in that at least the natural oxide film on the surface of the Al-based material layer is removed before the above-mentioned etching.

[0009]

In order to avoid deterioration of maintainability and deterioration of resist selectivity and underlayer selectivity among the above-mentioned three problems, the present inventor has proposed a process which does not use BCl ₃ as much as possible. The study was conducted with the recognition that it is necessary and that a process capable of achieving high anisotropy is required even if the ion incident energy is low in order to prevent sputter removal of the underlying interlayer insulating film. Here, reducing the ion incident energy means that it is not possible to expect the supply of the resist decomposition product under the low bias condition, and therefore it is necessary to perform the sidewall protection with a material which is an alternative thereto.

In the present invention, an etching gas comprising a chlorine-based compound to which sulfur fluoride having a high S / F ratio (ratio of the number of S atoms to the number of F atoms in the molecule) is added is used, and etching is performed. It is based on this recognition that etching is performed while controlling the temperature of the substrate (wafer) below room temperature. Needless to say, the above chlorine-based compound is
It is a supply source of Cl ^* which is the main etching species of the Al-based material layer.

On the other hand, sulfur fluoride is a compound proposed by the applicant of the present application in a series of applications including Japanese Patent Application No. 2-198045 and is an S (sulfur) source. The sulfur fluoride used in the present invention, unlike sulfur hexafluoride SF ₆ which has been conventionally used as an etching gas, can release free S (sulfur) into plasma under discharge dissociation conditions. .. Generated S
Easily adsorbs on the surface of the wafer whose temperature is controlled below room temperature. Of these, S adsorbed on the vertical incidence plane of ions
Will be immediately sputtered away if there is an appropriate incident ion energy, but will be deposited as it is on the side wall of the pattern where the vertical incidence of ions does not occur in principle to form a side wall protective film. In other words, since the side wall protective film is formed by the product from the gas phase, it is not necessary to cause forward sputtering of the resist mask with ions such as BCl _x ⁺ having a high incident energy as in the conventional case. ..
This means that highly anisotropic processing is possible without applying high bias power. Therefore, not only the selectivity to resist is improved, but also the underlying interlayer insulating film is not sputtered and redeposited on the pattern side wall during overetching, and after-corrosion can be suppressed.

Moreover, in the present invention, the S deposited on the side wall of the pattern has a thickness of about 90 after the etching.
It can be easily sublimated and removed by heating it at a temperature of not less than 0 ° C, so that it does not cause any particle contamination.

Of course, in the present invention, the wafer temperature is controlled to be room temperature or lower, so that the merit of general low temperature etching is also obtained. The term low temperature etching is often used especially for a process of controlling the wafer temperature at 0 ° C. or lower. However, in the normal dry etching process, unless the wafer is cooled, the temperature of the wafer is usually raised to 100s of tens of degrees Celsius due to plasma radiation heat or reaction heat. It can be included in the etching. The low-temperature etching freezes or suppresses the radical reaction in the lateral direction on the pattern sidewall while keeping the etching rate in the depth direction at a practical level by the ion-assisted reaction, so that the ion incident energy is relatively low. However, this is a technology that aims to achieve high anisotropy.
In the case of etching the Al-based material layer, the main etching species is Cl ^*, which is generated by dissociation from a chlorine-based gas, but its reactivity is suppressed in the temperature range below room temperature as compared with that in normal etching, and it has high anisotropy. It is advantageous to achieve.

The sulfur fluoride may also react with residual oxygen in the etching system during the exhaust process to generate sulfur oxide SO _x . However, unlike the above-described B ₂ O ₃ , SO _x is a gas and can be easily exhausted by installing a desulfurization device, so that maintenance of the device does not become complicated. Further, it seems that S dissociated and produced from sulfur fluoride is also deposited on the inner wall of the etching chamber, etc. However, since such a portion is heated by plasma radiant heat, the actual deposition amount is small and particle contamination does not occur. Not so worrisome.

Further, in the present invention, the reducing gas is not contained in the etching gas in the step of etching the Al-based material layer. Therefore, even if the Al material layer is over-etched after a part of the base insulating film is exposed, the base insulating film is not reduced, and the base selective resistance is improved.

The above is the basic idea of the two inventions of the present application. In the second invention, the natural oxide film is removed (so-called breakthrough) prior to the etching of the Al-based material layer.
I do. This is the etching proposed in the first invention.
This is because the gas does not contain a reducing substance, so that the etching rate may be significantly reduced in some cases. However, if the natural oxide film is removed in advance, the subsequent etching of the Al-based material layer can proceed smoothly.

[0017]

EXAMPLES Specific examples of the present invention will be described below. This embodiment applies the second invention of the present application, and Ar /
After removal of the natural oxide film on the surface of the Al-1% Si layer using a S ₂ F ₂ / Cl ₂ mixture gas, the Al-1% Si layer and barrier metal using a S ₂ F ₂ / Cl ₂ mixture gas This is an example of etching. This process will be described with reference to FIG.

First, as an example, as shown in FIG. 1A, a first Ti layer 2 having a thickness of about 0.03 μm and a TiON layer 3 having a thickness of about 0.07 μm are formed on a SiO ₂ interlayer insulating film 1. ,
A barrier metal 5 is formed by sequentially laminating a second Ti layer 4 having a thickness of about 0.03 μm, and further, a barrier metal 5 having a thickness of about 0.
A 3 μm Al-1% Si layer 6 is formed by sputtering or the like, and a resist layer is formed on the Al-1% Si layer 6.
A wafer having the mask 8 formed thereon was prepared. Al above
On the surface of the -1% Si layer 6, a natural oxide film 7 mainly composed of Al ₂ O ₃ is formed.

The above-mentioned wafer was set on the wafer mounting electrode of the magnetic field microwave plasma etching apparatus. Here, the wafer mounting electrode has a built-in cooling pipe,
The wafer can be cooled to a predetermined temperature by receiving the supply of the cooling medium from a cooling equipment such as a chiller installed outside the etching apparatus. Here, an ethanol refrigerant was used. An example of etching conditions is shown below.

Ar flow rate 90 SCCM S ₂ F ₂ flow rate 30 SCCM Cl ₂ flow rate 10 SCCM Gas pressure 2.1 Pa (16 mTorr) Microwave power 800 W (2.45 GHz) RF bias power 50 W (2 MHz) Wafer temperature -60 ° C. As shown in FIG. 1B, the native oxide film 7 was promptly removed by the reverse sputtering action of Ar ^{+ in} the region not masked by the resist mask 8.

Next, the Al-1% Si layer 6 and the barrier metal 5 were etched by switching the etching conditions as follows, for example. S ₂ F ₂ flow rate 60 SCCM Cl ₂ flow rate 120 SCCM Gas pressure 2.1 Pa (16 mTorr) Microwave power 800 W (2.45 GHz) RF bias power 30 W (2 MHz) Wafer temperature -60 ° C. In this process, ECR discharge from Cl ₂ The etching reaction using Cl ^*, which is generated by dissociation, as the main etching species
Etching proceeded by a mechanism assisted by ions such as l _x ⁺ , S ⁺ and SF _x ⁺ , and the Al-1% Si layer and the barrier metal were removed in the form of AlCl _x and TiCl _x, respectively.

At the same time, S generated from S ₂ F ₂ is deposited on the side wall of the pattern on the wafer, and the side wall protection film 9 is formed.
Was formed. Moreover, the reactivity of radicals is suppressed by cooling the wafer at a low temperature. The above effects appear synergistically, and as shown in FIG. 1C, the Al-1% Si layer pattern 6a having a good anisotropic shape and the barrier metal pattern 5a are formed. However, in the drawing, each material layer after patterning is represented by adding a subscript a to the reference numeral of the corresponding original material layer.

The role that the present invention expects from S ₂ F ₂ is to serve as an S supply source, but F ^* produced from S ₂ F ₂ contributes to the formation of a reaction product AlF _x having a low vapor pressure, It also works to enhance the side wall protection effect. Alternatively, the above F ^* contributes to the suppression of aftercorrosion by substituting residual chlorine in the vicinity of the pattern with fluorine.

After this, over-etching of about 50% was performed, but since the side wall protection by S is continued,
Even if Cl ^* was relatively excessive, the barrier metal 5 did not undercut. Also, RF bias
Since the etching is performed in the region where the power is relatively low, the underlying SiO ₂ interlayer insulating film 1 was not sputtered and redeposited on the pattern side wall portion, and the early generation of after-corrosion was suppressed.

Further, the sidewall protection film 9 was easily sublimated and removed by heating the wafer to about 90 ° C. after the etching was completed, and did not cause any particle contamination. The heating at this time can be performed by using a wafer mounting electrode having a built-in heater or by carrying the wafer to a preheating chamber or the like and mounting it on a heating stage.

Alternatively, the side wall protective film 9 is formed by a conventional O
₂ Resist mask 8 depending on plasma ashing conditions
Can also be removed at the same time.

By the way, the present invention is not limited to the above embodiments. For example, in the step of removing the natural oxide film, the addition of Ar is not always necessary if the sputtering action of ions such as S ⁺ and SF _x ⁺ generated from sulfur fluoride is used under the condition that the ion incident energy is increased. Alternatively, in this step, in addition to the conventionally well-known reducing substances such as BCl ₃ and SiCl ₄ , Si ₂ S previously proposed by the present inventor in Japanese Patent Application No. 3-81008 is proposed
₂ Cl ₄ (tetrachlorocyclodisylthiane) or the like may be used.

The reducibility of BCl ₃ is as described above. When BCl ₃ is used, the production of B ₂ O ₃ in the exhaust system is unavoidable. However, since the time required to remove the native oxide film is much shorter than the etching of the Al-based material layer in the main process, the amount of BCl ₃ produced is far greater than that of the conventional method in which BCl ₃ is used throughout the process. Very few, maintenance frequency and labor is greatly reduced.

SiCl ₄ and Si ₂ S ₂ Cl ₂ generate a highly reducing chemical species SiCl _x in plasma by discharge decomposition. Since these gases do not produce any solid compounds in the exhaust system, problems such as when using BCl ₃ can be avoided. Alternatively, these reducing substances may be appropriately added with the sulfur fluoride used in the present invention.

Further, although S ₂ F ₂ was used as the sulfur fluoride in the above-mentioned embodiments, substantially the same result can be obtained when other sulfur fluoride limited in the present invention is used. Furthermore, in the sense that the etching gas is expected to have a sputtering effect, a dilution effect, a cooling effect, etc., Ar, H
A rare gas such as e may be appropriately added.

[0031]

As is clear from the above description, in the present invention, a chlorine-based compound that supplies Cl ^* , which is the main etching species of the Al-based material layer, and S, which is the main component of the sidewall protection film, are supplied. An etching gas containing sulfur fluoride is used. Since this etching gas does not contain a reducing substance, there is no fear that the selectivity with respect to the underlying insulating film will decrease. Further, it is possible to perform highly anisotropic processing even under a low bias condition, improve the selectivity ratio to resist and the selectivity ratio to underlying layer, and expect an effect of suppressing after-corrosion.
Moreover, since S that has contributed to the protection of the side wall can be easily sublimated and removed, it does not cause particle contamination.

Therefore, the present invention is extremely effective in manufacturing a semiconductor device which requires high performance and high reliability based on fine design rules.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the present invention in the order of steps, (a) showing a state where a resist mask is formed on an Al-1% Si layer, and (b) showing Al-1. %
The state in which the native oxide film on the surface of the Si layer is removed is shown, and (c) shows the state in which the Al-1% Si layer and the barrier metal are anisotropically etched.

[Explanation of symbols]

1 ... SiO ₂ interlayer insulating film 2 ... first Ti layer 3 ... TiON layer 4 ... second Ti layer 5 ... barrier metal 6 ... Al-1% Si layer 6a · ..Al-1% Si pattern 7 ... Natural oxide film 8 ... Resist mask 9 ... Side wall protective film (S)

Claims (2)

[Claims] 1. At least one sulfur fluoride selected from S ₂ F ₂ , SF ₂ , SF ₄ , and S ₂ F ₁₀ and a chlorine-based compound are contained while controlling the temperature of the substrate to be etched below room temperature. A dry etching method comprising etching an aluminum-based material layer using an etching gas. 2. A dry etching method, characterized in that the etching according to claim 1 is performed after at least the natural oxide film on the surface of the aluminum-based material layer is removed.