JPS628512B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved plasma etching method.

In recent years, radio frequency (RF) power has been applied to parallel plate electrodes to discharge introduced fluorocarbon-based reactive gases such as CF ₄ and C ₂ F ₆ to form gas plasma between the electrodes. Etching of a film on the surface of a semiconductor wafer (substrate) placed on the electrode is performed under reduced pressure using positive ions.

However, during plasma etching, the surface of the semiconductor substrate is exposed to a considerably reactive etching atmosphere because over-etching is performed depending on the margin of completion of etching. As a result, a defective layer is formed on the silicon surface, and it is also contaminated with organic substances such as C and F, as well as heavy metals such as Fe, Ni, and Cr originating from the device, resulting in PN junction leakage, poor field current, source, drain, and metal wiring. This may lead to an increase in contact resistance with the

In particular, stacking faults (OSF) occur due to thermal oxidation of the surface after plasma etching.
This induces a huge number of crystal defects called induced stacking faults.

In particular, when boron ions are implanted into a plasma etched area or a thick thermal oxide film such as a field oxide film is formed at a plasma etched area, significant crystal defects occur.

The present invention has been made in view of the above circumstances, and involves discharging a reactive gas such as a gas containing carbon and fluorine or a gas containing chlorine under reduced pressure to form a gas plasma, which is a step in the manufacturing of semiconductor devices. After plasma etching the film on the surface of the semiconductor substrate as
The present invention provides a plasma etching method characterized in that the etched area is subjected to high-temperature heat treatment at 650° C. or higher in an atmosphere containing an inert gas, and electrical characteristics can be improved.

Embodiments of the present invention will be described in detail below with reference to the drawings.

First, a silicon oxide film 2 with a thickness of 700 Å is formed as a buffer oxide on a silicon substrate 1 by thermal oxidation.
Furthermore, a 2000 Å thick silicon nitride film 3 for selective oxidation
and a resist mask 4 is formed (FIG. 1a).
Next, use the parallel plate plasma etching apparatus mentioned above.
Plasma etching is performed by discharging CF ₄ +H ₂ gas at 10 ^-3 Torr and 180 W to etch the silicon nitride film 3 and silicon oxide film 2 in the field portion (FIG. 1b). At this time, although the etching rate of the substrate 1 is extremely slow at several tens of angstroms per minute, it is exposed to a plasma atmosphere, receives ion bombardment, forms a defective layer, and at the same time becomes contaminated with the aforementioned organic substances and heavy metals. After this, when field boron ions are implanted and the field is wet oxidized, an OSF with a high density (approximately 10 ⁷ ions/cm ² ) is generated.

After plasma etching, inert gas e.g.
When high temperature heat treatment was performed at 1050°C for 60 minutes in a N ₂ atmosphere, the OSF could be reduced to ~10 ³ /cm ² .

Figure 2 shows one without _N2 heat treatment (A);
1050℃ 30 minutes _N2 heat treatment (B), 1050℃ 60 minutes _N2 heat treatment (C)
shows the OSF density of

In addition to _N2 , Ar or He gas may also be used.

Good OSF reduction was observed when the heat treatment temperature was higher than 650℃, especially higher than 1000℃.

Further, it is more effective if this inert gas treatment is performed before or both before and after the boron ion implantation.

After inert gas treatment, a CVDSiO ₂ film 5 of 0.5 μm was deposited and subjected to high-temperature heat treatment in POCl ₃ gas (Fig. 1c), the SiO ₂ film 5 was removed, and a field boron film of 1×10 ¹³ cm− ₂ was deposited. An ion implantation layer 6 is formed (FIG. 1d).

CVDSiO ₂ film 5 deposition and Pocl ₃ shown in Figure 1c
Processing is not necessarily required.

After this, a field oxide film 7 with a thickness of 1 μm is formed by thermal oxidation by wet oxidation (Fig. 1e), and films 2 and 3 are formed by thermal oxidation.
(FIG. 1f), a gate oxide film 8, polycrystalline silicon 9, and a resist mask 10 are formed (FIG. 1g), and the polycrystalline silicon film is etched using the resist mask 10 as an etching mask in the same manner as described above. 9,
Gate oxide film 8 is plasma etched to form n ⁺ ion implantation layers 11, 11' (FIG. 1h).
The plasma etching conditions here are CF ₄ +H ₂ , 2
×10 ^-2 Torr, RF output 150W. This plasma etching also causes damage and contamination as described above.

Therefore, high-temperature heat treatment is performed in an N ₂ + H ₂ atmosphere.

Figure 3 shows 30 minutes in a gas containing 10% _H2 in _N2 .
(B), 60 minutes (C) N ⁺ ion implanted layer 1 with and without heat treatment at 700°C, respectively.
The contact resistance between layers 1 and 11' and the Al electrode formed on this layer is shown. The contact hole is 3μ.

This treatment significantly reduces contact resistance,
A value comparable to that obtained by etching contact holes with an ammonium fluoride solution (solid line), which is not a dry process or isotropic etching, was obtained.
The heat treatment was preferably performed at 650 to 1000°C for 30 minutes or more.

Next, a CVDSiO ₂ film 12 is deposited (Fig. 1i),
The BPSG film 13 is deposited (Fig. 1j) and the contact hole is opened using the resist 14 (Fig. 1k).
An electrode 15 is formed (FIG. 1l) to form a MIS transistor with 11 and 11' serving as a source and a drain, respectively.

In addition to silicon oxide films, silicon nitride films, polycrystalline silicon films, and even metal silicon alloy films can be used as the film on the surface of the semiconductor substrate to be plasma etched.If Al is included, plasma etching may be performed with CCl ₄ . .

[Brief explanation of the drawing]

Figures 1a to 1 are cross-sectional views showing the embodiment of the present invention according to each step; Figure 2 is a characteristic diagram showing the effects of the present invention;
FIG. 3 is a characteristic diagram showing the effects of the present invention.

Claims (1)

[Claims] 1. A gas containing carbon and fluorine, or a gas containing chlorine is discharged under reduced pressure to form a gas plasma, and a film on the surface of a semiconductor substrate is etched as a step of manufacturing a semiconductor device, and then the etched portion is etched. 650℃ in an atmosphere containing inert gas
A plasma etching method characterized by performing the above-mentioned high-temperature heat treatment.