JPH01279782A - Reactive ion etching method for laminated metal - Google Patents

Abstract

PURPOSE:To reduce the amt. of a barrier metal undercut when a laminated metal consisting of a wiring metal forming an upper layer and the barrier metal forming a lower layer is etched, by using a gaseous mixture of gaseous SF6 with a gas contg. at least Cl atoms in the molecule as an etching gas for the barrier metal. CONSTITUTION:When a laminated metal consisting of a wiring metal 13 forming an upper layer and a barrier metal 11 forming a lower layer is etched by reactive ion etching in a process of producing a super-LSI, a gaseous mixture of gaseous SF6 with a gas contg. at least Cl atoms in the molecule, preferably BCl3 is used as an etching gas for the barrier metal 11. The concn. of BCl3 in the etching gas is regulated to about 20-60%. The amt. 12(mum) of the barrier metal 11 undercut is reduced, a proper ratio in etching rate (barrier metal 11/base film 10) is obtd. and the amt. of a deposit (dust) stuck on a substrate is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to reactive ion etching of laminated metals in a VLSI manufacturing process.

<Conventional technology> Conventionally, aluminum alloys such as AtSi and At5iCu have been used as wiring metals in the VLSI manufacturing process, but in recent years, the use of barrier metal layered as a lower layer and wiring metal layered as an upper layer has been increasing. Ta. The effect of barrier metal is to intervene between the wiring metal and the semiconductor substrate at the point of contact between the wiring and the semiconductor substrate (contact area), suppress reactions between the two, and stabilize the electrical characteristics of the contact area. That's true. Usually, aluminum alloy is used as the wiring metal. Furthermore, in this application, barrier metal is a general term for tungsten and titanium, which are generally classified as high-melting point metals, as well as alloys, silicides, and nitrides thereof.

Microfabrication of laminated metals with barrier metals is performed using photolithography technology using reduction projection exposure and reactive ion etching (RIE).
This is carried out by making full use of dry etching techniques such as etching (Etching), but in particular, the following four conditions must be satisfied in the dry etching technique.

(Condition 1) Etching of each layer of the laminated metal is performed continuously in the same reaction vessel.

...This is necessary to increase process throughput and reduce equipment costs.

(Condition 2) In the etching of the lower barrier metal, the barrier metal and its underlying film, a silicon oxide film (Borophosphosilicat) doped with phosphorus or poron, are etched.
The etching rate ratio (at least 2.5 or more) with eglass1 (hereinafter referred to as BPSG) must be sufficient.

...If this etching rate ratio is insufficient, the base film (BPSG) will be etched, causing defects. Second
The figure shows the difference in processed shape depending on the etching rate ratio (barrier metal/base film) using a cross-sectional view.

In the figure, 21 is a semiconductor substrate, 22 is a gate electrode, 2
3 is a base film (BPSG), 24 is a barrier metal, 2
5 is a wiring metal. If the etching rate ratio (barrier metal/BP SG ) is appropriate, a desirable processed shape as shown in FIG. 2(a) can be obtained. On the other hand, if the etching rate ratio is insufficient, the base film 23 will be etched as shown in FIG. Condition 3) No undercut occurs in the barrier metal during etching of the lower layer barrier metal.

. . . If a/da cut occurs, the desired wiring resistance cannot be obtained and the wiring metal is likely to break. In addition, the protective film that protects the LSI chip is likely to crack, reducing reliability.

Figure 3 shows a cross-sectional view of the occurrence of cracks in the protective film due to undercutting of the barrier metal.
is a base film, 32 is a barrier metal, 33 is a wiring metal, 34
is a protective film.

If there is no undercarriage in the barrier metal 32, the same figure (a
), the protective film 34 has a normal processed shape. On the other hand, if there is an undercut 35 in the barrier metal 32, a crack 36 will occur in the protective film 34.

(Condition 4) There is little dust adhering to the substrate during etching.

...If dust adheres during etching, it will cause a short circuit in the wiring and cause defects. As described below, there is no conventional technology that satisfies all of the above conditions. 0 Conventional laminated metal (wiring) The reactive ion etching technology for membranes was successfully realized through a process consisting of the following three steps.

(Step 1) Reactive ion etching of upper layer wiring metal Since aluminum alloy is usually used as the wiring metal, reactive ion etching of aluminum alloy will be described.

Reactive ion etching of aluminum alloys is performed on SiC14, B Ct3 + containing at least chlorine in the molecule.
This is carried out using a gas such as CL2. In addition to these gases, CHF3 is also used to improve the etching characteristics.
．． A fluorocarbon gas such as CF4 or an inert gas such as He or Ar may be added, but the details are omitted since they are not directly related to the present invention.

Reactive ion etching of aluminum alloys generally proceeds through the following reaction.

At+3C1--→AtC43 As a by-product of the above reaction, AtIC,F, BISt.

A polymer formed by a complex reaction of H, etc. is formed and adheres to the wall of the reaction vessel. These reaction products may react again depending on the etching conditions in the post-process, and may greatly affect the amount of dust attached to the substrate during etching.

(Step 2) Reactive ion etching of the underlying barrier metal The etching conditions for this barrier metal are the technology related to the present invention.

Table 1 shows conventional barrier metal etching methods and problems associated with each method.

(Afternoon & Meji Table 1 (In the table, ○ indicates appropriate, X indicates inappropriate) Table 1 (A
) reactive ion etching using CF4+02 gas is a method in which a fluoride of barrier metal (WFa, etc.) is formed by fluorine radicals and then etched.

Since this method uses fluorine radicals, undercurrent of the barrier metal is large, making it unsuitable for microfabrication required for VLSI.

The gas system shown in Table 1 (CB) is a method in which a barrier metal oxychloride (WC4xOy, etc.) is formed by chlorine radicals, oxygen radicals, and appropriate ion bombardment for etching. Generally, oxychloride has a higher vapor pressure than chloride, so the reaction product removal rate is faster. Furthermore, no undercaution occurs as seen in etching using fluorine radicals. However, when etching is performed continuously using this method, a problem arises in that as etching is repeated, the amount of dust adhering to the substrate increases as shown in Table 2.

Table 2 This shows that the reaction products (described above) attached to the wall of the reaction vessel during etching of aluminum alloy are decomposed by the effect of oxygen radicals and become non-volatile compounds such as A4z03+ B2O5+ S io2, which are deposited on the substrate. It is thought that this is because it sticks.

In reactive ion etching of aluminum alloys,
Adhesion of the reaction product to the wall surface of the reaction vessel cannot be prevented by current technology, as shown above (step 1). Therefore, it is impossible to etch a laminated metal layer including a barrier metal using this method.

The gas system in Table 1 (C) etches the barrier metal using the sputtering effect caused by ion bombardment (CF3, etc.), and the chlorine-based additive gas promotes the removal of reaction products and improves the etching rate. used for However, in this method, since the effect of sputtering is large, the etching rate of BPSG as the base film is also large, and the etching rate ratio of the barrier metal and BPSG becomes small to nearly 1.

There are problems with any of the methods shown in Table 1 (1, (BJ, CC)). Super LS metal wiring
It could not be applied to I.

<Problems to be Solved by the Invention> The conventional technology has the disadvantage that it is difficult to microfabricate laminated metals with barrier metals using reactive ion etching technology, and it is difficult to fabricate interconnects using laminated metals with barrier metals in VLSI manufacturing. The problem is that it cannot be applied. The present invention aims to solve the problems of the prior art described above.

Means for Solving the Problems> The present invention provides a reactive ion etching method for a laminated metal consisting of an upper wiring metal (particularly an aluminum alloy) and a lower barrier metal, using at least SFs gas as an etching gas for the lower barrier metal. This method uses a reactive ion etching method for laminated metal, which is characterized by using a mixed gas consisting of a gas containing chlorine atoms in its molecules, as a means to solve the problem. This is a particularly effective means when metal etching is carried out continuously in the same reaction vessel. As an etching gas for the lower barrier metal, a mixture consisting of SFaF2 gas or at least a gas containing chlorine gas in its molecules is used. By using gas, the amount of underlayer of barrier metal can be reduced and a reasonable etching rate ratio (barrier metal/
It is possible to realize the base g) and also to reduce the amount of non-volatile compounds generated by decomposition of the reaction products that adhered to the wall surface of the reaction vessel in the previous step.

<Example> The inventors of the present invention conducted experiments with various combinations of gases and examined whether the problems shown in Table 1 could be solved.

As a result, it has become clear that it is appropriate to use ÷-← gas as the main etching gas and as the additive gas in barrier metal etching. This will be explained in detail below. Although the results obtained when titanium tungsten alloy (TiW) is used as the barrier metal will be described, the etching method of the present invention can be easily applied to etching other barrier metals.

First, when selecting a gas, we first considered reducing the amount of dust adhering to the substrate, and decided to use a gas that does not contain oxygen. Etching rate and base film (BPSG) of titanium tungsten alloy in an oxygen-free gas system
Table 3 shows the results of examining the ratio of the etching rate of I found out that it can be done. However, 5Fa
When 100% gas was used for etching, it became clear that undercutting of the barrier metal occurred in the titanium-tungsten alloy film due to the effect of fluorine radicals, and further studies were conducted to solve this problem.

It is extremely difficult to prevent the above-mentioned undercutting and maintain a good etching rate ratio to the base film (BPSG), and this cannot be solved by changing and optimizing parameters such as the operating pressure and high-frequency power of the etching equipment. There wasn't.

The inventors of the present application thought that it would be possible to add a second etching gas, SFaF2 gas, and use this mixed gas to prevent undercutting of the barrier metal, and as a result of examining various gases, they decided to add SFaF2 gas as the second etching gas.
It has been found that by adding it to the gas, it is possible to prevent undercurrent of the barrier metal without significantly impairing the selectivity with the underlying film (BPSG).

Figure 1 shows the etching characteristics (b) of a titanium-tungsten alloy using a mixed gas of SF6 gas and BCL3 gas, and a cross-sectional view of the etching shape (b) for explaining the etching characteristics.
a) is shown.

In the same figure, although it is not clear why the undercoat 12 of the titanium-tungsten alloy film 11 formed on the base film 10 is prevented, chlorine contained in the added gas promotes the polymerization reaction in the plasma. This is thought to be because it adheres to the side surfaces of the titanium-tungsten alloy film 11 and protects the side surfaces from attack by radicals. 13 is an upper layer wiring metal (aluminum alloy), and 14 is a mask material (resist).

It is assumed that carbon and hydrogen supplied from boron and etching mask materials simultaneously contribute to the polymerization reaction. The amount of Cl3 required to prevent undercurrent of the barrier metal is approximately 20 to 60% in concentration of the total etching gas, as shown in Figure ('b). In particular, for the equipment, pressure, and high-frequency power density used in this experiment, the optimum concentration of BCl3 was 40%. The etching rate of the titanium tungsten alloy at this time was 1000 A/m1o1 and the etching rate ratio (TiW/BPSG) was 4.0. It was confirmed that fine patterns of laminated metal can be processed with sufficient precision for VLSI manufacturing.

Furthermore, since the present invention does not contain oxygen in the etching gas, there is little increase in the amount of dust adhering to the substrate, and continuous two-step etching, which was impossible with conventional etching containing oxygen, is possible.
It was also confirmed that etching treatment could be performed 00 times.

In addition, as the second etching gas in the present invention,
It is possible to use not only BCl3 but also CCt4 and 5iC1<, and the effect of the present invention can be achieved as long as the gas contains at least a chlorine atom in its molecule.

<Effects of the Invention> By using a mixed gas consisting of SF6 gas as an etching gas for the lower barrier metal and a gas containing at least chlorine atoms in the molecule, the underlayer amount of the barrier metal can be reduced and a reasonable etching rate ratio (barrier metal/underlying film] and can further reduce the amount of deposits (dust) on the substrate, allowing microfabrication of laminated metal consisting of barrier metal and metal wiring as VLSI wiring with high precision at the mass production level. .

As a result, the reliability of VLSIs such as large-capacity dynamic memories has improved, and production with high yields has become possible.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the etching characteristics according to an embodiment of the present invention, Fig. 2 is a cross-sectional view showing the difference in processed shape depending on the etching rate ratio (barrier metal/base film), and Fig. 3 is an undercut of barrier metal. FIG. 3 is a cross-sectional view showing the occurrence of cracks in the protective film due to the formation of cracks in the protective film. In the figure, 10 is a base film, and 11 is a barrier film 13 is a wiring metal. Agent Patent Attorney Takeshi Sugiyama (and 1 other person) (Kame) 0! lo W's /W't
f's4aBCj'sIμT("l)<'o) The engineering is then 7' buttocks now 1st Figure 1.

Claims (1)

[Claims] 1. In a reactive ion etching method for a laminated metal consisting of an upper wiring metal and a lower barrier metal, the etching gas for the lower barrier metal is composed of SF_6 gas and a gas containing at least chlorine atoms in its molecules. A reactive ion etching method for laminated metal characterized by using a mixed gas.