Process for Thermally Depositing Silicon Nitride and Silicon Dioxide Films Onto a Substrate

The following examples further illustrate the present invention. All parts and percentages are by weight unless explicitly stated otherwise.

Tert-butyllithium, (CH.sub.3).sub.3 CLi, [1.12 liters, (1.9 moles)] in pentane was added to a 2 liter flask containing hexane (about 200 ml) under a nitrogen atmosphere at room temperature. The flask was then cooled to -5.degree. C. Dichlorosilane, Cl.sub.2 SiH.sub.2, [65.53 g (1.0 mole)] was slowly added to the mixture in the cooled flask by means of cold finger. An immediate exothermic reaction and a white solid precipitate occurred.

Subsequent to addition, the mixture was stirred for two hours at -5.degree. C. and then for two hours at room temperature. The white solid, lithium chloride, by-product was then removed by filtration and washed three times with pentane. The washings were combined with the filtrate. The combined filtrate and washings were then fractional distilled (pentane and hexane removed at about 70.degree. C. and the desired product DTBS at about 126.degree. C.) to recover the DTBS in about a 90% yield.

The recovered product was identified as di-tert-butylsilane by proton NMR and infrared spectroscopy.

Tert-butyllithium, (CH.sub.3).sub.3 CLi [0.30 liters, (0.51 moles)] in pentane was added to an empty 500 milliliter flask under a nitrogen atmosphere at 0.degree. C. Tetrachlorosilane, SiCl.sub.4, [42.5 g (0.25 moles)] was then added to the cooled flask. The mixture was stirred for 30 minutes at 0.degree. C. No immediate reaction was observed. Next, the reaction mixture was stirred for 12 hours at room temperature. A white solid precipitate was then observed. Next, the majority of the pentane was removed by vacuum distillation and then replaced with 300 ml of heptane. This new reaction mixture was heated to reflux for a 48 hour duration. After this time, the cooled solution was combined with lithium aluminum hydride, LiAlH.sub.4, [9.5 g (0.25 moles)] while maintaining the nitrogen atmosphere. This reaction solution was heated at reflux for 5 hours, then cooled to room temperature and the reaction mixture filtered to remove by-product salts. The resulting filtrate was slowly poured onto ice and a two phase solution resulted. The organic phase was separated from the aqueous phase and then dried using magnesium sulfate. The dried organic phase was then fractional distilled (heptane removed at 98.degree. C. and the desired product DTBS at about 126.degree. C.) to recover the DTBS in about an 80% yield.

The recovered product was identified as di-tert-butylsilane by proton NMR and infrared spectroscopy.

For this and the following Example, a Lindberg three zone horizontal tube furnace (Model 54657 manufactured by the Lindberg Furnace Co. of Watertown, Wis.) equipped with a quartz tube, quartz wafer boat, vacuum pumping system and gas supply system was used. The quartz wafer boat was fitted inside the quartz tube and held two inch silicon wafers in a vertical orientation. The loaded quartz wafer boat was placed in the second zone of the furnace.

After loading the furnace (previously heated to 600.degree. C., 650.degree. C. and 600.degree. C. in three zones) with the quartz boat and about 5 wafers, the vacuum pumping system was turned on and the heated furnace evacuated to a base pressure of 0.050 Torr.

Anhydrous ammonia vapor at a flow rate of 18 sccm was introduced into the furnace through a mixing manifold attached to the door at the first zone of the furnace. Soon after the ammonia flow was started, DTBS vapor was simultaneously introduced into the mixing manifold at a flow of 68 sccm. The DTBS was vaporized before entering the manifold by slightly warming (about 30.degree. C.) under vacuum.

While in the mixing manifold, the two vapors were intimately mixed, then entered the furnace through the first zone. The introduction of the gases into the furnace established the deposition pressure in the furnace at 1.7 Torr.

Reaction and decomposition of the gases formed silicon nitride films on the surfaces of the silicon wafers in the quartz wafer boat. After 30 minutes, the gas mixture was shut off and nitrogen gas introduced to purge the system. The system was vented and the loaded quartz boat removed.

The silicon nitride films on the silicon wafers were examined. The average nitride film thickness was 2844 Angstroms as determined by means of an ellipisometer. The average refractive index was 1.956 as determined by the ellipisometer. The dielectric constant of one random film was determined to be 4.34. The dielectric strength was 2.74.times.10.sup.6 V/cm. A sputtered AUGER profile indicated less than 5 atomic percent carbon in the film.

These results indicate that a good silicon nitride film was deposited on the silicon wafers.

Using the same equipment as in Example 3, the three zones of the furnace were heated to 450.degree. C., 500.degree. C. and 550.degree. C., respectively. The furnace was evacuated to a base pressure of 0.050 Torr.

Oxygen was introduced into the mixing manifold at a flow rate of 35 sccm and then DTBS vapor was introduced into the same manifold at 68 sccm. Again, the DTBS was vaporized prior to the introduction into the manifold by slightly warming (30.degree. C.) under vacuum.

The gas mixture then entered the furnace through the first zone. The introduction of the gases into the furnace established the deposition pressure in the furnace at 1.8 Torr. Reaction and decomposition of gases formed silicon dioxide films on the surfaces of the silicon wafers in the quartz wafer boat. After 10 minutes, the gas mixture was shut off and nitrogen gas was introduced to purge the system. The system was vented and the loaded quartz boat removed.

The silicon dioxide films on the silicon wafers were examined. The average silicon dioxide film thickness was 937 Angstroms as determined by means of an ellipisometer. The average refractive index was 1.44 as determined by the ellipisometer. A sputtered AUGER profile indicated less than 5 atomic percent of carbon.

These results indicate that good silicon dioxide films were deposited on the silicon wafers.