JP3385679B2 - Anisotropic etching method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anisotropic dry etching method, and in particular, for example, in a multilayer resist process, incident ions required when anisotropically processing a lower layer resist which is an organic material layer to form a resist pattern. The present invention relates to a method for reducing the energy to improve the selectivity ratio to the underlayer and prevent the redeposition of the underlayer material by sputtering.

[0002]

2. Description of the Related Art As semiconductor device design rules such as LSI are miniaturized from a half micron level to a quarter micron level, requirements for fine processing techniques such as photolithography and dry etching are becoming more severe. . In photolithography technology, the exposure wavelength has been shortened in recent years in order to obtain high resolution, and since the surface step of the underlying substrate has increased due to the adoption of a multilayer wiring structure, the adoption of a multilayer resist process is becoming essential. is there. The multi-layer resist process consists of a thick intermediate layer resist that is thick enough to absorb the surface step of the underlying substrate and form a flat surface, and a thin intermediate layer consisting of an inorganic material to form a substantial mask pattern when etching the underlying layer resist. A so-called three-layer resist process, which uses a combination of layers and a thin upper layer resist sufficient to achieve high resolution, has been described by JM Morran et al. In J. Vac. Sci. Technol., 16 , 1620.
(1979).

In the three-layer resist process, the upper layer resist is first exposed to a predetermined shape, developed and patterned, and the intermediate layer is patterned by RIE (reactive ion etching) using this as a mask, and the patterned upper layer resist is further patterned. And the intermediate layer as a mask,
The lower layer resist is patterned by dry etching using O ₂ gas or the like.

By the way, in the step of anisotropically patterning the lower layer resist which is an organic material layer with O ₂ gas, a high gas pressure condition is set in order to improve the etching rate, and oxygen radicals (hereinafter referred to as O ^{*) are used.} When the etching is performed mainly by the radical reaction, the O ^* wraps around to the bottom of the intermediate layer pattern,
Undercut occurs due to isotropic oxidation reaction and the pattern shape deteriorates.

On the other hand, in order to prevent undercutting of the lower layer resist and achieve highly anisotropic etching, conditions such as low gas pressure and high bias power that increase the mean free path of ions and the substrate bias are adopted. Will be required. That is, by utilizing the vertical incidence of O ⁺ (oxygen ions) and the large kinetic energy, the ion mode etching is performed while the sputtering is used together, so that the highly anisotropic etching is performed. However, the adoption of such etching conditions causes a reduction in the selection ratio between the underlying material layer and the intermediate layer, which is one of the factors that hinder the practical use of the multilayer resist. This problem will be described with reference to FIG.

FIG. 3A shows a sectional shape of the substrate to be etched on which the upper layer resist pattern 15 is formed in the three-layer resist process. That is, first, the underlying material layer 12 following the step is formed on the interlayer insulating film 11 having the step, and the lower resist layer 13 having a sufficient thickness to absorb the step and form a flat surface, and For example, a SiO ₂ -based intermediate layer 14 made of spin-coated glass (SOG), and a thin upper resist layer are sequentially formed on the intermediate layer 14 in this order. This upper resist layer is patterned by photolithography and development,
The resist pattern 15 described above is obtained. Since the photolithography at this time is exposure on a flat surface, the resolution is high,
The upper layer resist pattern 15 has a clear edge with a width of 0.35 μm, for example.

Next, the intermediate layer 14 is patterned by RIE using the upper resist pattern 15 as a mask, and as shown in FIG.
As shown in (b), the intermediate layer pattern 14a is formed.
The intermediate layer pattern 14a also has a clear shape with a width of 0.35 μm.

Next, the lower resist pattern is etched using O ₂ gas. In this etching process, the thin upper layer resist pattern 15 disappears halfway, and thereafter the exposed intermediate layer pattern 14a functions as an etching mask. Here, the lower resist layer 13 is a layer formed to have a thickness sufficient to absorb the surface step difference of the substrate to be etched based on the purpose of the three-layer resist process. And the time required for etching is naturally different.
For example, as shown in FIG. 3C, in the region corresponding to the upper part of the step of the underlying material layer 12, the lower layer resist pattern 13a is just-etched and completed at the early stage of the etching process, and the underlying material layer 12 is exposed.

Subsequently, over-etching is performed to remove the remaining portion 13b of the lower layer resist in the region corresponding to the lower portion of the step of the underlying material layer. At this time, in the region corresponding to the upper part of the step, the exposed underlying material layer 12 is irradiated with ions having large incident energy and is sputtered. A part of the sputtered product is redeposited on the side wall of the lower resist pattern 13a to form a redeposited layer 12a as shown in FIG. 3 (d). In particular, when the underlying material layer 12 is a metal wiring material layer, this redeposited material layer 1
2a is difficult to remove and becomes a source of particle contamination.
The redeposited material layer 12a is the lower layer resist pattern 1
Since the substantial line width of 3a is thickened, a dimensional conversion difference easily occurs.

The problem of the reattachment layer described above has been pointed out, for example, in Proceedings of the 33rd Joint Lecture on Applied Physics (Spring Annual Meeting 1986) p.542, Lecture No. 2p-Q-8. ,
Well known. It is obvious that the reduction of the incident ion energy is effective for suppressing the formation of the redeposited layer 12a, but in this case, the above-mentioned isotropic reaction becomes dominant and the anisotropy decreases, Undercut occurs.

Therefore, the incident ion energy is reduced, and
A dry etching method for a lower resist layer that can achieve both high anisotropy and compatibility has been earnestly desired.

As a technique for responding to such a demand, the present applicant has not hitherto depended only on the reduction of the radical component and the enhancement of the ionic component to achieve high anisotropy, but to protect the side wall by the reaction product of etching. An application has been filed for an invention based on the idea of using a membrane together. That is, if the side wall protective film is also used, it is possible to reduce the ion incident energy while ensuring the etching rate to the extent that there is no practical problem.

For example, Japanese Patent Laid-Open No. 2-244625 discloses O
By using an etching gas in which Cl-based gas is added to ₂ , anisotropic etching of the lower resist layer is performed while depositing CCl _x , which is a reaction product of the lower resist layer and Cl-based gas, as a sidewall protective film. Demonstrated technology.

Further, Japanese Patent Laid-Open No. 4-084414 proposes a technique of controlling the substrate temperature at 50 ° C. or lower and etching the resist material layer using an etching gas mainly composed of NH ₃ . According to this method, the reaction product containing N, C, and O as constituent elements plays the role of a sidewall protective film.

Further, Japanese Patent Laid-Open No. 4-171726 discloses O ₂
A technique for anisotropically etching the lower resist layer while depositing CBr _x , which is a reaction product of the lower resist layer and the Br gas, as a side wall protective film by using an etching gas to which Br-based gas is added. Was disclosed.

[0016]

The above-mentioned dry etching methods previously filed by the applicant of the present invention ensure that a practical etching rate is ensured and that anisotropic etching by low ion energy is carried out in a practical temperature range. This is an epoch-making technology in that By these techniques, reattachment of the base material layer to the side wall of the lower resist pattern by sputtering has been greatly suppressed.

However, as devices are highly integrated in the future,
As the surface step increases, sometimes 100% overetching is required. In the process of receiving ions for such a long time, it is still difficult to prevent the redeposition of sputter depending on the kind of the base material layer. It is possible to further reduce the incident ion energy, but for this purpose, in order to secure anisotropy, C
There is no choice but to increase the proportion of l-based gas or Br-based gas added,
There is a risk of lowering the etching rate and particle contamination.

Further, depending on the type of the base material layer,
-It has been pointed out that the pollution of the particles will become more serious. This
This is especially because the underlying material layer is a Cu wiring layer or Al-Si-Cu.
It becomes remarkable in the case of an alloy wiring layer. That is, Cu
The lower resist layer on the underlying material layer containing the Cl-based gas
Etching with a Br-based gas or
Cu supplied from the exposed surface is Cu₂Cl₂And Cu₂Br
₂Etc., and reapply it on the sidewall surface of the lower resist pattern.
To wear. In addition, the main component of the etching gas is O ₂To gas
Copper oxide is generated by this, and this is also the lower resist pattern
Redeposit on the sidewall surface. All these redeposits are steam
It is difficult to remove due to low pressure,
Become.

When the underlying material layer contains Cu, if it is exposed to over-etching for a long time, oxidation may progress from the surface of the underlying material layer to the inside thereof, and the wiring bulk resistance may increase. The merit of the Cu-containing wiring material originally intended for low resistance wiring may be impaired.

Therefore, the object of the present invention is to prevent the deterioration of the anisotropic shape due to undercutting based on O ^* while ensuring a practical etching rate, to eliminate the dimensional conversion difference due to the receding of the intermediate layer, and to improve the base material. Avoids particle contamination and pattern shift caused by redeposited matter due to spatter from the layer, and does not excessively depend on the CCl _x or CBr _x side wall protective film to deteriorate the particle level, and is practical. It is to provide a clean anisotropic etching method for an organic material layer (resist layer) that achieves an etching rate.

A further object of the present invention is to prevent the deterioration of the particle level due to redeposits such as CuO when the base material layer is a material containing Cu and to increase the wiring bulk resistance due to oxidation. It is also a solution.

[0022]

The dry etching method of the present invention has been devised to solve the above-mentioned problems, and an organic material layer formed on a base material layer is formed from alcohol, ether and ketone. Etching was performed using an etching gas containing at least one compound selected from the group consisting of

Further, according to the present invention, the etching gas further contains a sulfur-based compound capable of releasing free sulfur into plasma under discharge ionization conditions, and etching is performed while sulfur is deposited on the substrate to be etched. .

Further, according to the present invention, the organic material layer formed on the base material layer is treated with at least one compound selected from the group consisting of alcohols, ethers and ketones, and sulfur released in plasma under discharge ionization conditions. A sulfur-based compound capable of releasing sulfur, and a just etching step in which sulfur is deposited on the substrate to be etched while etching is performed substantially until just before the underlying material layer is exposed.
_An etching gas containing ₃ is used, and an overetching step of etching the remaining portion of the organic material layer while heating the substrate to be etched is adopted.

Furthermore, in the present invention, the base material layer is C
It is characterized in that it contains u, and is characterized in that it exerts a particularly advantageous effect when used in this case.

Examples of alcohols, ethers and ketones used in the present invention include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol and t-butanol.
It is possible to use butanol, methyl ethyl ether, diethyl ether, acetone, methyl ethyl ketone, methyl isobutyl ketone and the like.

Although these alcohols, ethers and ketones cannot constitute the etching gas by themselves,
Since only one oxygen atom is contained in the molecule, it is preferable to use it in combination with O ₂ or a halogen-based gas in order to obtain a practical etching rate.

As the sulfur-based compound used in the present invention and capable of releasing free sulfur into plasma under discharge ionization conditions, an SX-based gas having an X / S ratio of less than 6 (X is a halogen element or hydrogen) ), For example S ₂ Cl ₂ , S ₃
Sulfur chloride gas such as Cl ₂ and SCl ₂ , S ₂ Br ₂ and S
Sulfur bromide gas such as ₃ Br ₂ and SBr ₂ , S ₂ F ₂ and S
Illustrative examples are sulfur fluoride gas other than SF ₆ , such as F ₂ , SF ₄ , S ₂ F ₁₀ , and H ₂ S. SF ₆ gas, which is well known as a sulfur fluoride compound, is F /
Since the S ratio is 6, it does not release free sulfur into plasma under the conditions of discharge ionization, which is not suitable for the purpose of the present invention.

As a prior application similar to the present invention, a method of ashing and removing a resist pattern with an etching gas prepared by adding about 5% of alcohol to O ₂ is disclosed in, for example, Japanese Patent Laid-Open No. 05-134929. . This method is intended to improve the ashing rate and prevent ashing residues, and is different from the mechanism of the present invention in which the sidewall protection film is strengthened to achieve anisotropic etching to form a resist pattern. .

[0030]

The point of the present invention is to enhance the film quality of the carbon-based plasma polymer, which is an etching reaction product that contributes as a side wall protective film, to achieve sufficient anisotropic processing even if the deposition amount is reduced. It is to realize the selectivity to the intermediate layer and the selectivity to the base.

The alcohols, ethers and ketones (all represented by the general molecular formula C _x H _y O _z ) used as etching gas in the present invention are C--H bonds and C-- which are dissociated and formed in discharge plasma. The atomic group having an O-bonded isopolarized structure increases the degree of polymerization of the carbon-based plasma polymer, which is a plasma polymerization product, and enhances resistance to ion injection and radical attack.

Further, H atoms and CO that are liberally generated in the discharge plasma can trap the halogen radicals introduced at the same time as the etching species to reduce the concentration of the halogen element in the carbon-based plasma polymer, and also to reduce the carbon-based plasma polymer. An atomic group having the above-mentioned polarization structure is introduced into the plasma polymer molecular chain. Recent studies have revealed that the carbon-based plasma polymer having such a structure has chemical and physical stability higher than that of the conventional carbon-based plasma polymer having only a repeating unit structure of-(CX) _n-. (Here X
Represents a halogen element and n represents a natural number). This is because the C—O bond (1077 kJ / mol) has a C—C bond (607 kJ / mol) when compared with the binding energy between two atoms.
It is also supported by the fact that it is larger than (mol).

By thus strengthening the film quality of the carbon-based plasma polymer itself, it is possible to reduce the incident ion energy required for anisotropic etching, and SO
The selectivity with respect to the intermediate layer made of G or the like and the underlying material layer is improved, and the redeposition on the side wall due to the underlying sputtering and the plasma damage to the underlying material layer are reduced. Further, even if the deposition amount of the carbon-based plasma polymer is reduced, anisotropic processing can be sufficiently achieved, so that particle contamination can be reduced.

Although the present invention is based on the principle as described above, a method aiming at further anisotropic processing, reduction of particle contamination and low damage is also proposed.

One of the methods is to add a sulfur compound capable of releasing free sulfur (S) into plasma under discharge ionization conditions to the above etching gas, and perform etching while depositing sulfur on the substrate to be etched. Is. In this case, in addition to the carbon-based plasma polymer that is the etching reaction product, sulfur can also be used as the sidewall protective film. Therefore, the incident ion energy can be further reduced, and a high selection ratio and low plasma damage can be thoroughly achieved. In addition, the amount of carbon-based plasma polymer deposited can be relatively reduced, and particle contamination can be reduced accordingly. Sulfur can be deposited on the surface of the substrate by controlling the temperature of the substrate to be etched to room temperature or lower, for example 25 ° C. or lower. Moreover, the deposited sulfur can be easily removed by sublimation by heating the substrate to be etched to approximately 90 ° C. or higher after the etching is completed, so that it does not remain on the substrate to be etched.
Sulfur itself does not become a source of particle contamination.

In the present invention, the oxidation of the base material layer is effective.
To prevent the above-mentioned etching just
Two-step etching of the etching process and the over-etching process
However, in the latter over-etching process, etching
O from gas system₂To eliminate NH ₃Etching gas containing
Over etching is performed. This allows the base
Vapor pressure, which has occurred conventionally when the material layer contains Cu
Of small oxide copper oxide on the side wall of pattern and etching
It is possible to prevent the problem of particle contamination due to the residual residue.
Furthermore, during overetching, the
Problem of increase in wiring bulk resistance due to oxidation progressing to the bottom
It has become possible to improve significantly.

The etching mechanism of the organic material layer when NH ₃ is used is as disclosed in the above-mentioned Japanese Patent Laid-Open No. 4-084414.

[0038]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 In this example, Al-1% was used in a three-layer resist process.
Example in which a lower resist layer formed on a base material layer made of a Si-0.5% Cu alloy was etched using a mixed gas of O ₂ / Cl ₂ / CH ₃ OH (methanol, bp = 64.6 ° C.). Is. This process will be described with reference to FIG.

First, as shown in FIG. 1A, as a substrate to be etched, on a SiO ₂ -based interlayer insulating film 1 having a step formed on a Si wafer having a diameter of 5 inches, for example,
The Al-1% Si-0.5% Cu alloy layer 2 having this step difference is formed by O.D. It is formed to a thickness of 7 μm and is used as a base material layer. It should be noted that the lower layer wiring and the like below the interlayer insulating film 1 are omitted here. Next, as an example, a novolac-based positive photoresist (manufactured by Tokyo Ohka Kogyo Co., Ltd., trade name OFPR-800) is applied thereon to form the lower resist layer 3. Here, the thickness of the lower resist layer 3 corresponding to the lower part of the step is about 1.0 μm, and the surface is formed so as to absorb the step and become a flat surface. On the lower resist layer 3, SOG (trade name OCD-Type2 manufactured by Tokyo Ohka Kogyo Co., Ltd.) was spin-coated to a thickness of about 0.
A 2 μm SiO ₂ -based intermediate layer 4 is formed. Further, an upper layer resist pattern 5 patterned into a predetermined shape is formed on the intermediate layer 4. The upper resist pattern 5 is, for example, a negative chemically amplified resist (made by Shipley, trade name SAL-601) and has a thickness of about 0.7 μm.
The coating film of m is subjected to KrF excimer laser exposure and development processing to be formed. The pattern width of the upper layer resist pattern 5 is 0.35 μm, for example.

Next, this substrate to be etched is set in, for example, a hex type dry etching apparatus, and the intermediate layer 4 is etched using the upper layer resist pattern 5 as a mask. The etching conditions at this time are as follows, for example. CHF ₃ 75 sccm O ₂ 8 sccm Gas pressure 6.5 Pa RF bias power 1350 W (13.56 MH
z) As a result, as shown in FIG. 1B, the intermediate layer pattern 4a was formed immediately below the conditional resist pattern 5.

Next, this substrate to be etched was transferred to an RF bias application type ECR plasma etching apparatus, and the lower resist layer 3 was etched under the following conditions as an example. O ₂ 40 sccm Cl ₂ 10 sccm CH ₃ OH 20 sccm Gas pressure 1.5 Pa Microwave power 900 W (2.45 GHz) RF bias power 300 W (2 MHz) Substrate temperature Room temperature where the above CH ₃ OH is at room temperature H because it is a liquid
It was bubbled with e gas to be vaporized and introduced into the etching chamber so that the saturated vapor pressure at room temperature was converted to a predetermined flow rate.

In the above etching process, the etching proceeds by a mechanism in which the isotropic oxidation reaction by O ^* is assisted by ions such as O ⁺ and Cl ⁺ . In addition, conventional O ₂ / C
As in the case of using the l ₂ -based gas, CCl _x is generated due to the carbon-based decomposition product supplied from the lower layer resist 3, but the C—O bond and C—H bond based on CH ₃ OH are generated. While being incorporated into the structure, a strong carbon-based plasma polymer was generated due to the decrease in the ratio of Cl contained in the constituent elements. This carbon-based plasma polymer is deposited on the side wall of the pattern to form the side wall protection film 6 and contributes to anisotropic etching. As a result, as shown in FIG. 1C, a lower layer resist pattern 3a having an anisotropic shape was formed.

In this example, the etching selectivity to the SOG intermediate layer 4 was improved as compared with the conventional one, and the mask receding during the etching hardly occurred. Therefore, the dimensional conversion difference after the etching was not recognized.

Example 2 In this example, the lower resist layer is also O ₂ / HBr / CH.
_This is an example of etching using a mixed gas of ₃ OCH ₃ (dimethyl ether, bp = −24 ° C.). First, the substrate to be etched shown in FIG.
The lower resist layer 3 was etched under the following conditions by setting it in an R plasma etching apparatus. O ₂ 40 sccm Cl ₂ 10 sccm CH ₃ OCH ₃ 10 sccm Gas pressure 1.5 Pa Microwave power 900 W (2.45 GHz) RF bias power 300 W (2 MHz) Substrate temperature Room temperature

In the above etching process, CBr _x having a small Br composition ratio and carbon-based plasma polymer in which C—O bonds and C—H bonds are incorporated are generated, and the sidewall protective film 6 is formed by these deposits. It As a result,
As shown in (c), a lower layer resist pattern 3a having an anisotropic shape was formed. Particularly, in this embodiment, Cl
B has a larger atomic radius and lower reactivity with Si than
By using the r-type chemical species, the selection ratio with respect to the intermediate layer 4a is further improved as compared with the first embodiment.

Example 3 In this example, the lower resist layer was similarly O ₂ / S ₂ Cl ₂
This is an example in which a substrate to be etched is etched while being cooled to room temperature or lower using a mixed gas of / CH ₃ COCH ₃ (acetone, bp = 56.5 ° C.). First, Figure 1 above
The substrate to be etched in (b) is an RF bias application type ECR
The lower resist layer 3 was set in a plasma etching apparatus under the following conditions as an example. O ₂ 30 sccm S ₂ Cl ₂ 10 sccm CH ₃ COCH ₃ 10 sccm Gas pressure 1.5 Pa Microwave power 900 W (2.45 GHz) RF bias power 180 W (2 MHz) Substrate temperature −20 ° C. Here, the above CH _{Since 3} COCH ₃ is a liquid at room temperature, it was bubbled with He gas to be vaporized, and introduced into the etching chamber so as to have a predetermined flow rate converted from the saturated vapor pressure at room temperature.

In the above etching process, the lower resist 3
CCl _x due to carbon-based decomposition products supplied from
Is generated, but C-based on the dissociation of CH ₃ COCH ₃
While O-bonds and C-H bonds are incorporated into the structure,
A strong carbon-based plasma polymer was generated due to the decrease in the ratio of Cl contained in the constituent elements. Further, the sulfur generated in the plasma and the above-mentioned carbon-based plasma polymer,
A side wall protective film 7 is formed by being deposited on the side wall of the pattern to form a composite, which contributes to anisotropic etching. Furthermore, since the substrate to be etched is cooled at a low temperature, the oxidation reaction due to O ^* is suppressed in the pattern side wall portion where the number of incident ions is small. As a result, undercut was not generated even under a lower bias condition than in Examples 1 and 2 described above, and as shown in FIG. 1C, the lower layer resist pattern 3a maintaining the anisotropic shape was formed. Been formed. As a matter of course, the selection ratio with respect to the intermediate layer 4a was further improved, and redeposition from the underlying material layer was not confirmed at all.

After the low-temperature etching is completed, before the substrate to be etched is carried out of the etching apparatus into the atmosphere, it is kept at 90 ° C. or higher in a reduced pressure atmosphere for the purpose of preventing dew condensation.
When heated at 00 ° C., sulfur in the side wall protective film 7 is easily sublimated and removed. Therefore, even if the number of processed wafers is increased in the same etching apparatus, the particle level in the chamber does not deteriorate.

Example 4 In this example, the lower resist layer on the copper-based metal material layer was O ₂
/ S ₂ Br ₂ / CH ₃ OH mixed gas is used for just etching while cooling the substrate to be etched to room temperature or below, then switched to Cl ₂ / NH ₃ mixed gas and overetched while heating the substrate to be etched. It is an example of performing. This process will be described with reference to FIG. Note that the reference numerals in FIG. 2 are partially common to those in FIG.

The substrate to be etched used as the etching sample in this embodiment is, as shown in FIG. 2A, a pure Cu layer as an underlying material layer 8 conforming to this step on the interlayer insulating film 1 having the step. Is formed to have a thickness of 0.7 μm, for example, and a lower layer resist layer 3, an intermediate layer pattern 4a and an upper layer resist pattern 5 are further formed in this order by a three-layer resist process. Here, the patterning method of the intermediate layer pattern 4a and the upper layer resist pattern 5 is the same as that described in the first embodiment, and thus the description thereof is omitted.

This substrate to be etched has a substrate stage equipped with a cooling mechanism capable of controlling the temperature below room temperature.
The FCR bias type ECR plasma etching apparatus is set, and as an example, the lower layer resist is just etched under the following conditions. O ₂ 40 sccm S ₂ Br ₂ 10 sccm CH ₃ OH 10 sccm Gas pressure 1.5 Pa Microwave power 900 W (2.45 GHz) RF bias power 180 W (2 MHz) Substrate temperature −20 ° C. where CH ₃ OH The method of introducing is the same as in Example 1.

In this just etching process, as shown in FIG.
As shown in (b), the etching was stopped when the lower layer resist pattern 3a on the step was formed. In the above etching process, CBr _x is generated due to the carbon-based decomposition products supplied from the lower layer resist 3,
_{While the} C—O bond and C—H bond based on ₃ OH were incorporated into the structure, the ratio of Br contained in the constituent elements was reduced, so that a strong carbon-based plasma polymer was formed. Further, sulfur generated in the plasma and the above-mentioned carbon-based plasma polymer are deposited on the pattern side wall portion to form a composite side wall protective film 7, which contributes to anisotropic etching. At this time, the residual portion 3b of the lower resist layer remains in the region corresponding to the lower portion of the step.

Therefore, in order to remove the residual portion 3b, overetching is performed by changing the etching conditions as described below as an example. HBr 15 sccm NH ₃ 45 sccm Gas pressure 1.5 Pa Microwave power 900 W (2.45 GHz) RF bias power 120 W (2 MHz) Substrate temperature 150 ° C. Here, the substrate to be etched is built in the substrate stage. This was done by operating the heater. In this over-etching process, a carbon-based plasma polymer containing C, Br, N, O, and H as constituent elements is deposited, and etching proceeds while forming the sidewall protective film 6. Although the sulfur in the composite side wall protection film 7 formed in the just etching step is sublimated and removed in the overetching step, the carbon-based plasma polymer in the side wall protection film 7 remains and the side wall protection film 7 remains. The function as a membrane was maintained.

By the way, the important feature of this embodiment is that the bulk resistance of the Cu wiring pattern formed in the subsequent step does not increase and the original electric resistivity of the Cu wiring is 1.4 μΩ / cm.
That is, it is possible to form a low resistance wiring pattern that maintains the value of. In the over-etching process,
By eliminating oxygen from the etching reaction system, Cu
This is because the progress of oxidation from the exposed surface of the layer 8 is prevented.

In this embodiment, a low temperature process (just etching) and a high temperature process (over etching)
Since this is continuously performed, it takes some time to cool and heat the substrate to be etched. Therefore, it is preferable to use a multi-chamber type etching apparatus in which the low temperature process chamber and the high temperature process chamber are connected by a gate valve and the substrate to be etched can be transported under a high vacuum from the viewpoint of improving the throughput. Further, as proposed in Japanese Patent Application Laid-Open No. 5-114590 filed by the present inventor, an etching apparatus equipped with a substrate stage including a fixed electrode having a cooling means and a movable electrode having a heating means is used. Thus, a method of continuously processing in the same chamber is also extremely effective.

Although the present invention has been described with reference to the four examples, the present invention is not limited to these examples.

For example, in addition to methanol, dimethyl ether, and acetone used in the above-mentioned examples as alcohols, ethers, and ketones, ethanol (bp = 7) is used.
8.3 ° C), n-propanol (bp = 97.4 ° C),
i-propanol (bp = 82.7 ° C.), n-butanol (bp = 117 ° C.), i-butanol (bp = 108)
C), sec-butanol (bp = 100 ° C.), t-butanol (bp = 83 ° C.), methyl ethyl ether, diethyl ether (bp = 36.6 ° C.), methyl ethyl ketone and methyl isobutyl ketone, etc.
A compound having a large vapor pressure up to about 0 ° C. can be preferably used.

The above compound may be introduced into the etching chamber by bubbling with a rare gas such as He gas. However, it is also effective to heat the bubbler and maintain it at a constant temperature so that heat is not dissipated by the latent heat of vaporization and the vaporization efficiency is not reduced. Instead of bubbling with a rare gas, it is also possible to heat the container of the above compound to near the boiling point temperature to evaporate and vaporize. This is effective when using a higher-order compound having a higher boiling point. At this time, the gas introduction pipe to the etching chamber may be heated by a ribbon heater or the like so that the compound gas is not condensed in the pipe.

Examples of sulfur compounds include S ₃ C ₂ in addition to S ₂ Cl ₂ and S ₂ Br ₂ used in the above-mentioned examples.
l ₂ , SCl _2, etc., sulfur chloride, S ₃ Br ₂ , SBr ₂
Sulfur bromide such as S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀
Sulfur fluoride other than SF ₆ , and H ₂ S can be used. When sulfur fluoride is used, F ^* (fluorine radical) is generated, so it is necessary to consider the etching selection ratio with the intermediate layer.

Although the SiO ₂ material using SOG was used for the intermediate layer, it is possible to use an inorganic thin film such as Si ₃ N ₄ based, SiON based, Al ₂ O ₃ based or various metals. As a film forming method, sputtering, vapor deposition, various types of CVD, or the like can be used.

As the organic material layer on the base material layer, the novolac-based positive photoresist was used in each of the above-mentioned embodiments, but various other resist materials can be used. The organic material layer does not need to be photosensitive because it suffices to flatten the step underlayer, and various organic materials such as polyimide can be used.

In addition, the structure of the substrate to be etched, etching conditions, etching apparatus, etc. can be changed as appropriate. A rare gas such as He or Ar may be added to the etching gas composition, and N ₂ , H ₂ , CO, CO ₂ and various Br are added.
System, I type, NO _x systems may be added SO _x based gas or the like.

[0064]

As is clear from the above description, according to the present invention, in etching an organic material layer such as a resist, a plasma that functions as a sidewall protective film can be obtained by using an etching gas containing one of alcohol, ether and ketone. Even if the polymer film is strengthened and its deposition amount is reduced, undercut does not occur, and a highly anisotropic etching can be achieved while ensuring a practical etching rate. Further, since the film quality of the side wall protective film is strong, the incident ion energy required for anisotropic etching can be reduced, and the selection ratio with respect to the intermediate layer made of SOG or the like is improved. Since the difference can be avoided and the selectivity for the underlying material layer is also improved, redeposition on the side wall due to underlying sputtering and plasma damage to the underlying material layer can be reduced.

While a sulfur compound capable of releasing free sulfur into plasma under discharge ionization conditions is further added to an etching gas containing any one of alcohol, ether and ketone, while sulfur is deposited on the substrate to be etched. By etching, higher anisotropy, higher selection ratio, and lower damage can be achieved.

The base material layer is Cu or Al-Si-C.
In the case of copper-containing material layers such as u alloys, by using a gas system that excludes oxygen during over-etching, it is possible to prevent an increase in wiring bulk resistance, and to prevent particles from re-sputtering copper or copper oxide. It is possible to reduce pollution.

Due to the above effects, for example, the practicability of the three-layer resist process can be enhanced, and it is effective in manufacturing a semiconductor device having a multilayer wiring structure based on a fine design rule, which requires high integration and high reliability. Is. The present invention is not limited to the above semiconductor device, and exhibits a high effect in patterning an OEIC, a bubble domain memory device, and a thin film magnetic head coil that require patterning on a high step substrate.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining Examples 1, 2 and 3 to which the present invention is applied, in the order of steps, in which (a) is a lower layer resist on an Al—Si—Cu alloy base material layer having steps A state where the intermediate layer and the upper layer resist pattern are sequentially formed, (b) a state where the intermediate layer pattern is formed,
(C) is a method of etching the lower resist layer using the upper layer resist pattern and the intermediate layer pattern as a mask,
The underlying resist pattern has been formed, and the upper layer resist pattern has been etched off and disappeared.

FIG. 2 is a schematic cross-sectional view for explaining Example 4 to which the present invention is applied in the order of steps, in which (a) is a lower resist layer, an intermediate layer pattern, and an upper resist on a Cu base material layer having steps. The pattern is formed in sequence,
(B) is a state where the lower resist layer is just etched, (c) is a state where the lower resist layer is over-etched and a lower resist pattern is formed, and the upper resist pattern is etched off and disappeared. .

FIG. 3 is a schematic cross-sectional view for explaining a problem in the conventional three-layer resist technology, FIG. 3A is a state in which a lower layer resist, an intermediate layer and an upper layer resist pattern are sequentially formed on a base material layer having a step; (B) shows a state in which an intermediate layer pattern is formed, (c) shows a state in which the lower resist layer is just etched, and (d) shows a redeposited layer made of a sputtered material of the base material layer during overetching. The respective states are shown.

[Explanation of symbols]

1 Interlayer insulation film 2 Al-Si-Cu alloy layer (base material layer) 3 Lower layer resist layer 3a Lower layer resist pattern 3b Remaining part of lower resist layer 4 Middle class 4a Intermediate layer pattern 5 Upper layer resist pattern 6 Side wall protection film (carbon-based plasma polymer) 7 Side wall protection film (carbon-based plasma polymer + sulfur) 8 Cu layer (base material layer)

Claims (2)

(57) [Claims] 1. An organic material layer formed on a base material layer containing copper , and at least one compound selected from the group consisting of alcohols and ethers and sulfur that is liberated in plasma under discharge ionization conditions. An anisotropic etching method characterized by etching while depositing sulfur on a substrate to be etched using an etching gas composed of a sulfur-based compound that can be released. 2. An organic material layer formed on a base material layer containing copper, at least one compound selected from the group consisting of alcohols and ethers , and sulfur liberated in plasma under discharge ionization conditions. A sulfur-based compound that can be released is used to etch sulfur while depositing sulfur on the substrate to be etched until the base material layer is substantially exposed, and an etching gas containing NH ₃ is used. And an overetching step of overetching the remainder of the organic material layer while heating the etching substrate.