JPH05182937A - Dry-etching method - Google Patents

Abstract

PURPOSE:To avoid the deterioration in aniosotropical shape during over-etching step in the etching step of an Al base material layer. CONSTITUTION:An Al base multiple layer film 7 comprising a barrier metal 4, an Al-1%Si layer 5 and a reflection preventive film (a suffix (a) is added to either one in Figure) is just etched away using ordinary chlorine base gas further to be plasma-processed using CHF3/CO (carbon monomer) mixed gas to cover the whole wafer surface with an organic polymer layer 9. At this time, this organic polymer layer 9 containing >C=O radical in the molecules thereof to improve the chemical and physical stability, polymerization degree etc., can offer excellent resistance to radical attack. Accordingly, even if the residue 7b is over-etched away, the anisotropical shape of an Al base wiring pattern 7a can be retained by the sidewall protective effect of the organic polymer layer 9 presumably effective as an after-corrosion measures.

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 to the manufacture of semiconductor devices and the like, and more particularly to a method for preventing deterioration of an anisotropic shape during overetching when etching an aluminum (Al) -based material layer. ..

[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 disclosed in JP-B-59-22374.
A mixed gas of / Cl ₂ is a typical example.

In the etching using the chlorine-based gas, it has been a problem that the anisotropic shape of the Al-based wiring pattern is deteriorated during overetching. This problem will be described with reference to FIG. Figure 6 (a)
Shows a state in which the Al-based multilayer film formed on the SiO ₂ interlayer insulating film 11 is etched (just-etched) through the resist mask 18 by almost the thickness of the layer to form the Al-based wiring pattern 17a. ing. The Al-based wiring pattern 17a includes a barrier metal 14a having a two-layer structure including a Ti layer 12a and a TiON layer 13a, and an Al-based wiring pattern 17a.
The -1% Si layer 15a and the TiON antireflection film 16a are laminated. Al-1 with chlorine gas
Since the etching of the% Si layer 15a layer isotropically proceeds due to the contribution of Cl ^* , a condition in which the incident ion energy is increased is usually employed to achieve anisotropic processing. Therefore, in the steps up to just etching, the ion assist mechanism and the resist mask 18 are used.
Due to the side wall protection effect of the decomposition products of Al, the Al-based wiring pattern 17 has a good anisotropic shape as shown in the figure.
a is formed.

By the way, at the end of just etching, the nonuniformity of the plasma density, the wafer temperature, the film thickness of the Al-based multilayer film, etc., or the effect of the natural oxide film remaining on the surface of the Al-1% Si layer 15a. As a result, a large amount of the residue 17b is generated. Therefore, it is usually necessary to perform over-etching to remove the residue 17b. However, since the Al-based multilayer film to be etched is extremely small during over-etching as compared with just-etching, relatively excessive Cl ^* causes lateral migration on the wafer surface, resulting in Al-1.
The pattern side wall surface of the% Si layer 15a is attacked. As a result, as shown in FIG. 6B, the Al-1% Si layer 1
The cross-sectional shape of 5a becomes an inverse taper shape surrounded by the inclined side wall surface 19. Further, since the incident ion energy is still high, the amount of the SiO ₂ interlayer insulating film 11 removed by the ion sputtering also increases.

Since the device structure has become complicated as in recent years,
When the l-based multilayer film is formed on a substrate having a high step, the amount of overetching also increases. Therefore, the deterioration of the cross-sectional shape of the Al-based wiring pattern 17a becomes a major factor that deteriorates the reliability of the wiring. ..

In order to prevent the deterioration of this anisotropic shape,
Several measures have been conventionally proposed. Typical examples are: (a) decrease the flow rate of etching gas during overetching, (b) increase incident ion energy during overetching, (c) plasma using CHF ₃ before overetching. A method is known in which the surface of the Al-based wiring pattern is covered with a CF _x polymer layer by treatment.

[0007]

However, the fact is that the conventional measures have not yet effectively prevented deterioration of the anisotropic shape of the Al-based material layer during overetching. First, in the method (a) of reducing the flow rate of the etching gas, the etching rate is naturally lowered, so that the over-etching time is inevitably lengthened and the reverse taper cannot be prevented. ..

In the method (b) of increasing the incident ion energy, the reverse taper can be prevented, but the resist selectivity and the underlayer selectivity are deteriorated. Deterioration of the resist selectivity increases deposits on the pattern side wall surface due to forward sputtering of the resist material. On the other hand, the deterioration of the underlayer selectivity is as expressed in FIG. 6B, which promotes the removal of the SiO ₂ interlayer insulating film and the like by sputtering and the reattachment of the SiO ₂ interlayer insulating film to the pattern sidewall surface. In any case, the re-deposited matter is deposited while taking in residual chlorine, which causes a problem that after-corrosion is easily promoted.

The method of performing plasma treatment using CHF ₃ described in (c) above is described in Proceedings of the 36th Joint Lecture on Applied Physics (Spring Annual Meeting 1989) p. 571, Abstract No. 1p-L-4, or Monthly Semiconductor World, October 1990, p. 44 etc.
In this method, the lateral attack of excessive radicals is blocked by the CF _x polymer layer, so that some effect can be expected in maintaining the anisotropic shape, and the after-corrosion resistance is also improved. However, since the formed CF _x polymer layer itself is relatively fragile, if the amount of overetching increases, the side wall protection effect may be insufficient again. The side wall protection effect can be enhanced by forming a thick CF _x polymer layer, but this increases particle contamination and is not a practical process.

Therefore, an object of the present invention is to provide a dry etching method for an Al-based material layer capable of maintaining an anisotropic shape without causing a decrease in selectivity and an increase in particle contamination even during overetching. And

[0011]

The dry etching method of the present invention is proposed in order to achieve the above-mentioned object, and an Al-based material layer on a substrate to be etched is formed substantially by its layer thickness. Having a step of etching, a step of covering the entire surface of the substrate to be etched with an organic polymer layer by performing plasma treatment using a mixed gas containing a fluorocarbon compound and carbon monoxide, and a step of performing overetching Is characterized by.

[0012]

The point of the present invention is that when the organic polymer layer is formed, a mixed gas obtained by adding carbon monoxide (CO) in addition to the fluorocarbon compound is used. Above the organic polymer mixed gas is generated in the plasma discharge conditions, -CF ₂ - repeatedly in addition to the carbonyl group (> C = O) are included in the structure of, and superior to conventional CF _x polymer Recent studies have shown that it exhibits chemical and physical stability. Further, considering that the high reactivity due to the carbon-oxygen unsaturated bond is widely used in the field of synthetic chemistry, it is possible that CO itself promotes the polymerization reaction of the organic polymer. That is, the organic polymer layer formed by the present invention corresponds to the one in which the conventional CF _x polymer is modified, the degree of polymerization is increased, and / or both are achieved. And shows excellent resistance.

As described above, if the side wall can be protected by the strong organic polymer layer, the incident ion energy required for anisotropic processing can be reduced, so that the resist mask and the underlying oxide film can be selected. There is no risk of deterioration of the sex. Therefore, the present invention can be applied to a process that requires excessive overetching. Moreover, since it is not necessary to thicken the organic polymer layer, particle contamination can be reduced. Further, since the organic polymer layer having such excellent strength is also excellent in passivation property, covering the entire surface of the substrate to be etched with such an organic polymer layer before overetching is from the viewpoint of suppressing after-corrosion. Is also effective.

[0014]

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

Example 1 In this example, an Al-based multilayer film composed of a barrier metal, an Al-1% Si layer, and an antireflection film was just-etched using a BCl ₃ / Cl ₂ mixed gas, and then CHF ₃ / CO mixed. The surface of the wafer is covered with an organic polymer layer by plasma treatment using gas, and further BCl ₃ / Cl _{2 is} added.
In this example, overetching is performed using a mixed gas. This process will be described with reference to FIGS.

As shown in FIG. 1, the wafer used as an etching sample in this embodiment has a Ti layer 2 having a thickness of about 0.03 μm and a thickness of about 0.08 μm on the SiO ₂ interlayer insulating film 1. Barrier metal 4 consisting of TiON layer 3,
Al-1% Si layer 5 having a thickness of about 0.4 μm, thickness of about 0.0
An Al-based multilayer film 7 in which a TiON antireflection film 6 having a thickness of 3 μm is sequentially laminated is formed, and a resist mask 8 having a thickness of about 1.0 μm which is patterned into a predetermined shape is further formed on the Al-based multilayer film 7. It has been done. Here, the resist mask 8 is, for example, a novolac-based positive photoresist (manufactured by Tokyo Ohka Kogyo Co., Ltd., trade name TSMR-).
V3) and a g-line stepper are used to form a pattern width of about 0.5 μm.

The above-mentioned wafer was set in an RF bias application type magnetic field microwave plasma etching apparatus, and as an example, the Al-based multilayer film 7 was just-etched under the following conditions. BCl ₃ flow rate 60 SCCM Cl ₂ flow rate 90 SCCM Gas pressure 2.1 Pa (16 mTorr
r) Microwave power 850 W (2.45 GHz) RF bias power 60 W (2 MHz) In this process, the radical reaction by Cl ^* is B ⁺ , BC
Etching progressed by a mechanism assisted by ions such as l _x ⁺ and Cl _x ⁺ , and an Al-based wiring pattern 7a having an anisotropic shape was formed as shown in FIG. In addition,
In the drawing, the pattern of each material layer formed after etching is represented by adding the subscript a to the original code.

This just etching was terminated when the underlying SiO ₂ interlayer insulating film 1 was exposed on most of the wafer. The base selection ratio at this time was about 8. The residue 7b remained on a part of the wafer.

Next, as an example, plasma treatment was performed under the following conditions. CHF ₃ flow rate 40 SCCM CO flow rate 110 SCCM Gas pressure 4.0 Pa (30 mTorr
r) Microwave power 850 W (2.45 GHz) RF bias power 0 W Wafer temperature −30 ° C. Here, the wafer is cooled by cooling pipes built in the wafer mounting electrodes of the etching apparatus, which are installed outside the apparatus. It was performed by supplying an ethanol refrigerant from a chiller.
In the process of this plasma treatment, an organic polymer having a> C═O group in the molecular structure and having a high degree of polymerization was deposited on the entire surface of the wafer, and the organic polymer layer 9 was formed as shown in FIG.

The side wall surface of the Al-based wiring pattern 7a in a state where different types of material layers are in contact with each other and exposed is covered with the organic polymer layer 9 in this manner in order to suppress the occurrence of after-corrosion. Is also extremely advantageous.

Next, as an example, over-etching was performed under the following conditions to remove the residue 7b. BCl ₃ flow rate 60 SCCM Cl ₂ flow rate 90 SCCM Gas pressure 2.1 Pa (16 mTorr
r) Microwave power 850 W (2.45 GHz) RF bias power 10 W (2 MHz) In this over-etching step, the organic polymer layer 9 and the residue 7b were removed at the ion normal incidence surface.
At this time, the organic polymer layer 9 remaining on the side wall of the pattern serves as the side wall protective film 9a and exhibits excellent resistance to radical attack. Therefore, even if the RF bias power is reduced to 1/6 of the just etching step. The anisotropic shape of the Al-based wiring pattern 7a could be maintained. Further, by lowering the bias, the selection ratio to the underlying SiO ₂ interlayer insulating film 1 was also improved to about 15.

The above sidewall protection film 9a was removed at the same time as the resist mask 8 by performing ordinary O ₂ plasma ashing after the etching was completed. As a result, the Al-1% Si layer pattern 5a was not inversely tapered, but the Al-based wiring pattern 7a having a good anisotropic shape was formed.

In this embodiment, the wafer is not particularly cooled in the step of etching the Al type multilayer film 7, but the wafer is cooled to -30 ° C. in the step of forming the organic polymer layer. In this way, in the case of continuously carrying out the steps having different wafer temperatures, when a multi-chamber type apparatus in which two etching chambers having different temperature settings of wafer mounting electrodes are connected under high vacuum, This is advantageous from the viewpoint of improving throughput.

Example 2 This example is an etching example of an Al-based multilayer film as in Example 1, but the plasma treatment is performed using a mixed gas of c-C ₄ F ₈ (octafluorocyclobutane) / CO. It is an example. First, the same wafer as that shown in FIG. 1 was set in a magnetic field microwave plasma etching apparatus, and the Al-based multilayer film 7 was just etched under the same conditions as in Example 1.

Next, as an example, plasma treatment was performed under the following conditions. c-C ₄ F ₈ flow rate 30 SCCM CO flow rate 100 SCCM H ₂ flow rate 20 SCCM gas pressure 4.0 Pa (30 mTorr)
r) Microwave power 850 W (2.45 GHz) RF bias power 0 W Wafer temperature -30 ° C. The gas system in which CO is added to c-C ₄ F ₈ was previously filed by the applicant of the present application in Japanese Patent Application No. 3-280373. Although it was proposed as an etching gas for the silicon compound-based material layer in this document, this is utilized in the formation of the organic polymer layer in this embodiment. H added to the above gas system
₂ contributes to trapping excess F ^* and increasing the C / F ratio (ratio of the number of C atoms and the number of F atoms) of the gas system to promote the deposition of the organic polymer. By this plasma treatment, as shown in FIG. 3 described above, the entire surface of the wafer was covered with the strong organic polymer layer 9.

Further, over-etching and resist ashing were performed under the same conditions as in Example 1 to complete an Al type wiring pattern 7a as shown in FIG.

Although the present invention has been described above based on two embodiments, the present invention is not limited to these embodiments. For example, an etching gas used for etching an Al-based material layer can be used. In order to expect a cooling effect, a sputtering effect, a dilution effect, etc., a rare gas such as He or Ar may be appropriately added. As the fluorocarbon compounds used to form the organic polymer layer, another _{CHF 3, CH 2 F 2,} CH 3 fluorocarbons having one carbon atom having H as an element in the molecule as F, etc. A high-order fluorocarbon having 2 or more carbon atoms having H as a constituent element in the molecule, or a high-order fluorocarbon having 2 or more carbon atoms not containing H as a constituent element can be used. However, in the case of using a higher order fluorocarbon having 2 or more carbon atoms that does not contain H as a constituent element, as described in Example 2, an additive gas such as H ₂ is used and the C / F ratio of the gas system is It is desirable to raise the value to some extent in order to promote the formation of the organic polymer layer.

[0028]

As is apparent from the above description, according to the present invention, prior to over-etching of the Al-based material layer, a> C═O group is contained in the molecular structure, and the chemical structure is higher than that of the conventional CF _x polymer. A with an organic polymer layer with excellent physical stability
Cover the 1-system wiring pattern. As a result, even in a process that requires excessive overetching, highly anisotropic processing can be performed while maintaining high resist selectivity and high underlayer selectivity under relatively low incident ion / energy conditions. Moreover, since it is not necessary to increase the thickness of the organic polymer layer, particle contamination can be reduced and after-corrosion resistance is improved.

Therefore, the present invention is extremely suitable for manufacturing a semiconductor device which is designed based on a fine design rule and which requires high integration, high performance and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a state in which a resist mask is formed on an Al-based multilayer film in a process example to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view showing a state in which the Al-based multilayer film of FIG. 1 is just-etched to form an Al-based wiring pattern having an anisotropic shape and a residue is generated.

FIG. 3 is a schematic cross-sectional view showing a state where an organic polymer layer is formed by covering the entire surface of the wafer of FIG.

4 is a schematic cross-sectional view showing a state in which a part of the organic polymer layer of FIG. 3 and a residue are removed by overetching.

5 is a schematic cross-sectional view showing a state where the resist mask and the side wall protective film made of an organic polymer layer in FIG. 4 are removed.

FIG. 6 is a schematic cross-sectional view for explaining a problem in dry etching of a conventional Al-based multilayer film. FIG. 6A is an Al-based wiring pattern having an anisotropic shape by just-etching the Al-based multilayer film. Is formed and a residue is generated, (b) is Al-
The 1% Si pattern is inversely tapered and the underlayer selectivity is deteriorated.

[Explanation of symbols]

1 ... SiO ₂ interlayer insulating film 2 ... Ti layer 3 ... TiON layer 4 ... barrier metal 5 ··· Al-1% Si layer 5a ··· Al-1% Si pattern 6 ... TiON antireflection film 7 ... Al-based multilayer film 7a ... Al-based wiring pattern 7b ... Residue 8 ... Resist mask 9 ... Organic polymer layer 9a ... Side wall protective film

Claims (1)

[Claims] 1. A step of etching an aluminum-based material layer on a substrate to be etched substantially by the thickness of the layer, and a plasma treatment using a mixed gas containing a fluorocarbon compound and carbon monoxide. A dry etching method comprising: a step of covering the entire surface of an etching substrate with an organic polymer layer; and a step of performing overetching.