JP3032244B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for removing a titanium silicide film.

(Prior Art) As a method of reducing the resistance of polycrystalline silicon (hereinafter referred to as polysilicon) or a diffusion layer generally used in a semiconductor integrated circuit, various methods of forming silicide thereon have been considered. One of the methods is to selectively form titanium silicide only on the polysilicon or the like. For example, literature ELECTORPNICS & DIELECTRICS &
INSULATION DIVISIONS, VOL. 86-4, issued in 1986 (USA), SEMICONDUCTOR SILICON 1986, P297, 309, 313
However, the outline will be described with reference to FIG.

First, as shown in FIG. 1A, a field oxide film (SiO ₂ ) is formed on a silicon substrate 1 by a normal method of manufacturing a semiconductor device.
2, a diffusion layer 3, a polysilicon 4 for wiring and the like are formed, and a titanium film 5 is deposited on the entire surface by sputtering or vapor deposition.

Thereafter, when heated at about 600 to 800 ° C. in an atmosphere of an inert gas such as helium or nitrogen, the polysilicon film 4 and the titanium film 5 on the diffusion layer 3 react with silicon to form titanium silicide as shown in FIG. It becomes a film 6. However, since titanium on the silicon oxide film (SiO ₂ ) 2 hardly reacts, it remains titanium. Thereafter, unreacted titanium on SiO ₂ 2 is selectively removed by etching with respect to titanium silicide, and titanium silicide is formed only on wiring polysilicon 4 and diffusion layer 3 as shown in FIG.

(Problems to be Solved by the Invention) However, in the method described above, the titanium film 4 on SiO ₂ 2 actually reacts slightly with SiO ₂ to form a thin titanium silicide layer at the interface. Therefore, if this layer is not removed when titanium is removed, electrical leakage occurs between the wiring polysilicon 4 and between the polysilicon 4 and the diffusion layer 3 through the titanium silicide thin film formed on the SiO ₂ 2. Would. The present invention solves this problem and provides a method for forming a titanium silicide of a semiconductor device having a titanium silicide wiring having no electric leakage.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a semiconductor substrate having a silicon region and a silicon oxide film region on a surface thereof, wherein a titanium layer is formed on the silicon region and the silicon oxide film region. Forming a titanium silicide film on the silicon region by subjecting the titanium layer to a heat treatment and reacting with the silicon, and removing the unreacted titanium layer with H ₂ SO ₄ and H _2. Selectively removing with a mixed solution of ₂ O ₂ , and thereafter, removing a titanium silicide film remaining on the silicon oxide film region with a mixed solution of NH ₄ OH and H ₂ O ₂ , It is characterized by the following.

(Operation) As described above, the present invention provides an etching solution of H ₂ SO ₄ having a large etching selectivity of titanium to titanium silicide.
And H ₂ O ₂ to remove only unreacted titanium, followed by NH ₄ O
Titanium silicide on SiO ₂ is removed with a mixture of H and H ₂ O ₂ , so there is room for etching conditions, it is easy to control, and a method suitable for mass production can be realized. Unnecessary titanium silicide can be removed without adversely affecting the silicide, and an extremely reliable semiconductor device without electric leakage can be obtained.

(Example) First, a selective etching liquid for titanium silicide will be described. As mentioned in the above-mentioned literature, examples of this liquid include a mixture of aqueous hydrogen peroxide (H ₂ O ₂ ) with ammonia water (NH ₄ OH) and a mixture of sulfuric acid (H ₂ SO ₄ ). There is. FIG. 2 shows the result of evaluating the state of etching of titanium and titanium silicide of both mixed solutions. Here, the sample is formed by depositing titanium on a silicon wafer by a sputtering method, and heating at 600 ° C. for 30 minutes in an N ₂ atmosphere. That is, since heating is performed at a relatively low temperature and in N ₂ , not all of the deposited titanium is silicide, and the vicinity of the surface remains titanium containing a large amount of N. That is, the sample has a structure in which titanium silicide is superposed on silicon (Si), and titanium is superimposed thereon.
(See inset (a) and FIG. 1 (b) in FIG. 2).
FIG. 2 shows the etching time dependency of the thickness of a film (a film of titanium silicide and titanium or a film of titanium silicide only) remaining on Si when the sample is etched. From this we can see the following.

Titanium is very soluble in the liquid of H ₂ O ₂ system, NH ₄ OH and H ₂ O ₂
The mixed solution of (1) considerably etches not only titanium but also titanium silicide. That is, the etching selectivity of titanium and titanium silicide is poor. This is especially true when the liquid temperature is high.
Or, it is remarkable when the ratio of NH ₄ OH is large. Also, H ₂ S
A mixture of O ₄ and H ₂ O ₂ has better selectivity than a mixture of NH ₄ OH and H ₂ O ₂ . That is, only titanium is etched and silicide is hardly etched. This is more apparent, especially when H ₂ SO ₄ is high. Therefore, when titanium is selectively etched with respect to titanium silicide,
If a mixture of NH ₄ OH and H ₂ O ₂ is used, silicide remaining on the wiring may be etched. Therefore, the etching conditions (liquid structure, temperature, time) must be strictly controlled, which is not optimal for mass production. Conversely, in the case of a mixed solution of H ₂ SO ₄ and H ₂ O ₂ , titanium is etched because the selectivity is good, but a thin silicide layer is formed on SiO ₂ (2 in FIG. 1, ie, a portion where titanium silicide is unnecessary). Remains, resulting in electrical leakage between the wiring layers or between the wiring and the diffusion layer.

From the above, it can be understood that the above problem does not occur if etching is performed by the following method. This is the present embodiment.

That is, first, only the unreacted titanium is etched with a liquid having a high selectivity, and then the silicide on SiO ₂ is removed with a liquid having a lower selectivity than the liquid. Specifically, after the titanium silicide 6 was formed by heat treatment as in Fig. 1 (b), first, a mixed solution of H ₂ SO ₄ large H ₂ SO ₄ in ratio and H ₂ O ₂ to initially (for example, composition ratio H ₂ SO ₄ : H ₂ O ₂ = 3: 1 to 5: 1, temperature 60 to 90
C.) for 5-10 minutes to remove unreacted titanium.
After that, dip into a mixture of NH ₄ OH and H ₂ O ₂ under conditions where the etching rate of silicide can be easily controlled (can be reduced)
The silicide remaining on SiO ₂ ( _{2 in} FIG. 1) is removed. (For example, composition ratio NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 1: 5 to 1: 1: 1
0, room temperature (20 to 25 ° C), immersion for 30 seconds to 2 minutes (Fig. 1 (c)
reference). In this way, the necessary parts (the wiring polysilicon 4 and the diffusion layer 3) are required based on the conditions of the above-mentioned mixed solution.
The titanium silicide thin film remaining in unnecessary portions (on SiO ₂₂ ) can be completely removed without exerting an adverse effect on titanium silicide (the effect of being removed up to that point). Further, the etching conditions described above can be set to have a sufficient margin as can be understood from the numerical values shown.

(Effects of the Invention) As described above, in the method of the present invention, the etching of unreacted titanium and unnecessary titanium silicide are performed by using the optimum etching solutions, respectively. It can be completely removed without exerting any effects, and has a margin of etching conditions, so that a highly reproducible manufacturing method suitable for mass production can be obtained. This also makes it possible to realize a highly reliable semiconductor device having a titanium silicide wiring in which no electric leakage occurs.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a manufacturing process of a titanium silicide wiring, and FIG. 2 is a graph showing a change in thickness of titanium silicide and titanium on Si by etching. 2 ... SiO ₂ film, 3 ... diffusion layer, 4 ... polycrystalline silicon, 5 ... titanium film, 6 ... titanium silicide film.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21 / 306,21 / 308 C23F 1/00-3/06

Claims (1)

(57) [Claims] A step of forming a titanium layer on the silicon region and the silicon oxide film region on a semiconductor substrate having a silicon region and a silicon oxide film region on a surface, and performing a heat treatment on the titanium layer. Forming a titanium silicide film on the silicon region by reacting with the silicon, and selectively removing an unreacted titanium layer with a mixed solution of H ₂ SO ₄ and H ₂ O _2. Removing the titanium silicide film remaining on the silicon oxide film region with a mixed solution of NH ₄ OH and H ₂ O ₂ , and thereafter.