This invention relates to methods for producing silicon nitride films and silicon oxynitride films by chemical vapor deposition (CVD).
Silicon nitride films exhibit excellent barrier properties and an excellent oxidation resistance and for these reasons are used for, for example, etch-stop layers, barrier layers, gate insulation layers, and ONO stacks in the fabrication of microelectronic devices.
The main technologies in use at the present time for the formation of silicon nitride films are plasma-enhanced CVD (PECVD) and low-pressure CVD (LPCVD).
In PECVD, a silicon source (typically a silane) and a nitrogen source (typically ammonia but more recently nitrogen) are introduced between a pair of parallel-plate electrodes and high-frequency energy is applied between the two electrodes at low temperatures (about 300° C.) and intermediate pressures (0.1 to 5 Torr) in order to generate a plasma from the silicon source and nitrogen source. Active silicon species and active nitrogen species in the generated plasma react with each other to produce a silicon nitride film. The silicon nitride films produced by PECVD generally do not have a stoichiometric composition and are also hydrogen rich. As a result, these silicon nitride films have a low film density and a high etch rate and are of poor quality.
LPCVD, which does not employ a plasma, is used in order to deposit high-quality silicon nitride films. LPCVD as it is currently practiced uses low pressures (0.1 to 2 Torr) and high temperatures (750-900° C.) and produces silicon nitride films of a quality superior to that of the silicon nitride films produced by PECVD. Silicon nitride films have generally been produced by this LPCVD technology by the reaction of dichlorosilane (DCS) and ammonia gas. However, the existing LPCVD technology requires fairly high temperatures in order to obtain acceptable deposition (film formation) rates (≧10 Å/minute) for silicon nitride films. For example, temperatures of 750 to 800° C. are typically used for the reaction of DCS and ammonia In addition, the reaction of DCS and ammonia produces large amounts of ammonium chloride, which can accumulate in and clog the exhaust plumbing system of the CVD reaction apparatus.
A number of silicon nitride precursors have been introduced for the purpose of obtaining satisfactory silicon nitride film deposition rates at low temperatures. Hexachlorodisilane (HCDS) is one example of such precursors. HCDS produces SiCl2 at relatively low temperatures by the reaction Si2Cl6→SiCl2+SiCl4 and this SiCl2 reacts well with ammonia The use of HCDS can provide silicon nitride film deposition at film formation rates of approximately 10 Å/minute at 600° C.
Another example of these precursors is the is(tert-butylamino)silane (BTBAS) described in U.S. Pat. No. 5,874,368. Use of BTBAS can also provide silicon nitride film deposition at lower temperatures than for the use of DCS. As in the case of HCDS, BTBAS enables the deposition of silicon nitride films at a film formation rate of approximately 10 Å/minute at 600° C.
While both HCDS and BTBAS can achieve film formation rates of approximately 10 Å/minute at 600° C., this performance level also means that commercially acceptable film formation rates will not be obtained at lower temperatures ≦550° C., or in specific terms that a film formation rate of at least 10 Å/minute will not be obtained at lower temperatures ≦550° C. These two precursors are also associated with the disadvantages described below.
HCDS, being a completely chlorinated disilane, has a high chlorine content, and the Si—Cl bond is also very strong. As a consequence, the chlorine content in the resulting silicon nitride film will increase as the reaction temperature declines, and it has been found that the chlorine content reaches as high as about 2 atom % at a 600° C. reaction temperature. In addition, HCDS also leads to the production of large amounts of ammonium chloride just as in the case of DCS.
BTBAS has an activation energy of 56 kcal/mole, with the result that its silicon nitride film formation rate declines drastically when the reaction temperature is reduced. It is estimated that its film formation rate drops to a quite small 3 Å/minute at a reaction temperature of 550° C.
The same problems appear when the aforementioned prior art precursors are used to produce silicon oxynitride films, which have the same physical properties and applications as silicon nitride films.
The issue addressed by this invention, therefore, is to provide a method for the production of silicon nitride and silicon oxynitride films by CVD technology, wherein said method provides acceptable film formation rates even at lower temperatures and is not accompanied by the production of large amounts of ammonium chloride.