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Content archived on 2024-04-15

Physical-Chemical Characterisation of Silicon Oxynitrides in relation to their Electronic Properties

Objective

The objective of this project was to investigate the feasibility of implementing a process step based on silicon oxynitrides by establishing:
a)the relationship between the physical-chemical and the electrical properties of silicon oxynitride films
b)the relationship between physico-chemical properties and growth parameters.
Work on oxynitrides is important in view of the possible applications of these films in IC technology, for instance in MNOS-based non-volatile memories and in submicron MOS devices.
The objective of this project was to investigate the feasibility of implementing a process step based on silicon oxynitrides by establishing:
the relationship between the physical chemical and the electrical properties of silicon oxynitride films;
the relationship between physico-chemical properties and growth parameters.

A large number of material characteristics of silicon oxynitrides were evaluated.

Extensive studies into the basic understanding of the growth and characteristics of low pressure chemical vapour deposition (LPCVD) and thermally grown silicon oxynitrides were carried out.

Emphasis was given to the preparation of oxynitrides by rapid thermal nitridation (RTN) of silicon oxide films, because of the shortened process times which allow prevention of the redistribution of impurities, otherwise induced in a conventional high temperature process step. Optimum nitridation conditions for thin (15 nm) layers to be used in submicron metal oxide semiconductor (MOS) transistors were established.
Towards a), a large number of material characteristics of silicon oxynitrides were evaluated. This knowledge is very important for assessing the improvement of the cost/performance ratio and the reliability of future generations of integrated circuits.Towards b), extensive studies into the basic understanding of the growth and characteristics of LPCVD and thermally grown silicon oxynitrides were carried out.
Concerning the LPCVD films, the following three technologically important conclusions were drawn:
-The stress in the silicon oxynitrides is lowered by the introduction of oxygen into the nitride lattice, whereas the oxidation resistance is comparable or even better than that for the nitride. Accordingly, the "bird'sbeak" length in a LOCOS process, using a single oxynitride layer instead of the conventional nitride/pad oxide structure, is considerably shortened without any increase in the number of defects.
-For applications in MNOS-type devices, oxynitrides with the ratio of O/(O+N)=0.1 0.2 have been proved to be the most suitable films.
-The hydrogen chemistry in the films is extremely important for various electrical and optical properties.
In the last year emphasis was given to the preparation of oxynitrides by Rapid Thermal Nitridation (RTN) of silicon oxide films, because of the shortened process times which allow prevention of the redistribution of impurities, otherwise induced in a conventional high-temperature process step. Optimum nitridation conditions for thin (15nm) layers to be used in submicron MOS transistors were established.
Exploitation
A 64KSRAM with a lateral isolation scheme, consisting of an RTN silicon oxide film capped with a LPCVD Si3N4 layer, has been put into production at Matra. A decrease in bird's beak length from 0.5micron to 0.2micron was achieved.
Non-volatile memory devices have been fabricated at IMEC. In particular, SONOS structures with better retention and endurance have been prepared. Application of oxynitrides as tunnel dielectrics in EEPROM cells has also been performed; the results confirmthe improvement in yield associated with nitridation.

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Coordinator

UNIV VAN UTRECHT
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PRINCETONPLEINWEG 5 Postbus 80000
3508 TA UTRECHT
Netherlands

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Participants (4)