Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – Insulated gate formation
Reexamination Certificate
2001-01-31
2003-01-07
Chaudhuri, Olik (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Insulated gate formation
C438S773000
Reexamination Certificate
active
06503819
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for the fabrication of a semiconductor integrated circuit device, particularly to a technique effective when applied to gate processing of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having a poly-metal gate.
Japanese Patent Application Laid-Open No. H5-152282 (which will hereinafter be called “Ohmi”), dicloses an oxide film forming device for oxidizing a semiconductor wafer, or the like, with water synthesized using a catalyst, such as nickel.
On pages 128-133 of Papers of the Lecture addressed at the 45-th Symposium of Semiconductor Integrated Circuit Technique held on Dec. 1-2, 1992 (which will hereinafter be called “Nakamura”), oxide film formation under a strong reducing atmosphere, which contains water vapor synthesized by a stainless catalyst is disclosed.
Japanese Patent Application Laid-Open No. S59-132136 (which will hereinafter be called “Kobayashi”), discloses a process, in a silicon semiconductor integrated circuit device having a refractory metal (high-melting point metal) gate, for carrying out auxiliary thermal oxidation (which will hereinafter be called “light oxidation” or “auxiliary oxidation after gate formation”) not of the gate metal itself, but necessary portions other than the gate metal, under a mixed atmosphere of water vapor and hydrogen after gate patterning, thereby adjusting an insulation film at the periphery below the gate.
Similarly, Japanese Patent Application Laid-Open No. H3-119763 (which will hereinafter be called “Katada”) and Japanese Patent Application Laid-Open No. H7-94716 (which will hereinafter be called “Muraoka”), discloses a process for forming a gate having a three-layered structure made of tungsten, titanium nitride and polysilicon, and then subjecting it to oxidation treatment under a mixed atmosphere of hydrogen, water vapor and nitrogen.
It is presumed that for a device having a circuit formed of a minute MOSFET, whose gate length is 0.25 &mgr;m or smaller, such as a DRAM (Dynamic Random Access Memory) of the type available since the development of the 256 Mbit (megabit) memory, a gate processing step using a low-resistance conductive material including a metal film will become indispensable to reduce the parasitic resistance of a gate electrode.
As such a low-resistance gate electrode material, so-called poly-metal (which generally means a refractory metal formed directly or indirectly over a polycrystalline silicon electrode) having a refractory metal film stacked over a polycrystalline silicon film is regarded as promising. The poly-metal can be used not only as a gate electrode material, but also as an interconnection material because it has a sheet resistance as low as 2 &OHgr;/□. According to an investigation by the present inventors, W (tungsten) Mo (molybdenum), Ti (titanium) or the like, which exhibits a good low resistance even in a low temperature process not higher than 800° C. and has a high electro-migration resistance, can be used as the refractory metal. Since the stacking of such a refractory metal film directly on a polycrystalline silicon film lowers the adhesion between these two films or tends to form a high-resistance silicide layer at the interface between these two films by a high-temperature heat treatment process, the poly-metal gate is practically formed of a three-layered structure having, between the polycrystalline silicon film and the refractory metal film, a barrier layer made of a metal nitride film, such as TiN (titanium nitride) or WN (tungsten nitride).
Based on an investigation by the present inventors, gate processing is conventionally carried out as follows. First, a semiconductor substrate is thermally oxidized to form a gate oxide film on its surface. Although a thermally oxidized film is generally formed in a dry oxygen atmosphere, wet oxidation is employed for the formation of a gate oxide film because the defect density in the film can be reduced. In wet oxidation, a pyrogenic method is employed in which water is formed by the combustion of hydrogen in an oxygen atmosphere and then fed to the surface of a semiconductor wafer together with oxygen.
The pyrogenic method, however, is accompanied with the drawback that combustion is effected by igniting hydrogen jetted from a nozzle attached to the tip of a quartz-made hydrogen gas inlet tube, but heat generated upon combustion melts the nozzle and generates particles, which presumably become a contamination source for the semiconductor wafer. For the formation of water, therefore, a method using a catalyst without combustion also has been proposed.
The above-described Ohmi publication discloses a thermal oxidation apparatus having a hydrogen gas inlet tube formed at its inside from Ni (nickel) or a Ni-containing material and is equipped with means for heating the hydrogen gas inlet tube. In this thermal oxidation apparatus, Ni (or a Ni-containing material) inside of the hydrogen gas inlet tube heated at 300° C. or higher is brought into contact with hydrogen to generate a hydrogen activated species and then, the hydrogen activated species is reacted with oxygen (or an oxygen-containing gas), whereby water is generated. Water is thus generated in such a catalytic manner without combustion so that neither melting of the quartz-made hydrogen gas inlet tube at its tip point nor generation of particles occurs.
Over the gate oxide film formed by such a wet oxidation method, a gate electrode material is deposited, followed by patterning of the gate electrode material by dry etching with a photoresist as a mask. After the photoresist is removed by ashing treatment, the dry etching residue or ashing residue on the surface of the substrate is removed using an etching solution, such as hydrofluoric acid.
By the above-described wet etching, the gate oxide film in a region other than that below the gate electrode is etched and, at the same time, the gate oxide film at the side wall end portions of the gate electrode are etched isotropically and undercuts are formed, which brings about inconveniences, such as lowering in pressure resistance of the gate electrode. With a view to improving the profile having undercuts formed at the side-wall end portions of the gate electrode, the substrate is subjected to light oxidation treatment, that is, it is subjected to thermal oxidation again to form an oxide film on its surface.
The above-described refractory metals, such as W and Mo, are considerably prone to oxidation under a high-temperature oxygen atmosphere so that the application of the above light oxidation treatment to a gate electrode of a poly-metal structure oxidizes the refractory metal film, thereby increasing its resistance or partially peeling off the film from the substrate. In the gate processing using a poly-metal, it is therefore necessary to take countermeasures against the oxidation of a refractory metal film upon light oxidation treatment.
The above-described Kobayashi publication discloses a technique of selectively oxidizing Si without oxidizing a W (Mo) film by forming over a Si (silicon) substrate a gate electrode of a W- or Mo-film-containing poly-metal structure and then carrying out light oxidation in a mixed atmosphere of water vapor and hydrogen. This technique makes use of the difference between W (or Mo) and Si in a water vapor/hydrogen partial pressure ratio which brings about equilibrium in redox reaction. In this technique, selective oxidation of Si is realized by setting the partial pressure ratio within a range where W (or Mo) once oxidized by water vapor is reduced rapidly by coexisting hydrogen, but Si remains oxidized. The mixed atmosphere of water vapor and hydrogen is generated by the bubbling system which feeds hydrogen gas in pure water carried in a container and the water vapor/hydrogen partial pressure ratio is controlled by changing the temperature of the pure water.
The above-described Katada and Muraoka publication disclose a technique of forming a gate electrode of a poly-metal structure, more specifically, forming a metal
Asano Isamu
Natsuaki Nobuyoshi
Saito Masayoshi
Tanabe Yoshikazu
Yamamoto Naoki
Antonelli Terry Stout & Kraus LLP
Chaudhuri Olik
Hitachi , Ltd.
Peralta Ginette
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