Document Type
Thesis
Date of Award
12-31-1991
Degree Name
Master of Science in Electrical Engineering - (M.S.)
Department
Electrical Engineering
First Advisor
Roland A. Levy
Second Advisor
James M. Grow
Third Advisor
Kenneth Sohn
Fourth Advisor
Durgamadhab Misra
Abstract
Ditertiary-butyl silane (DTBS) and ammonia have been used to deposit silicon nitride films by plasma enhanced chemical vapor deposition (PECVD) with ammonia. The films were deposited in the temperature range of 150 to 300 °C with 0.15 watts/cm2 plasma power density at 100 KHz. The NH3/DTBS ratio was varied from 1 to 18, the total flow rate was varied between 195 and 570 sccm with total pressure ranging from 0.2 to 0.6 torr.
The deposition rate of these films was found to increase as total pressure or total flow rate increases, but was found to decrease as the deposition temperature or the NH3/DTI3S ratio increases. If the total flow rate or the total pressure is incrased, the density of the films decreases. But an increase of the deposition temperature or the NH3/DTBS ratio, decreases the density of the films. The refractive index of these films was found to be influenced by their (Si + C)/N atom ratio, increasing this ratio increases the refractive index.
The infrared spectra of these films showed strong absorption at 850 cm-1 which was assigned to the Si-N and Si-H vibrations. As the hydrogen concentration decreases, the absorption peak shifts from 850 cm-1 to 860 cm-1. The N-H and Si-H absorptions were centered at 3340cm-1 and 2170 cm-1.
The composition and properties of the deposited films varied over a large range depending upon the deposition condition. These films have relatively large concentrations of carbon and hydrogen as determined by RBS analysis. The presence of carbon in the deposited films reduces the breakdown voltage. Whereas at subsequent high deposition temperatures, the presence of the hydrogen causes blistering and poor adhesion. The carbon content in the plasma silicon nitride film is controlled by the reactant ratio, and can be decreased by increasing the NH3/DTBS ratio. The increase of the deposition temperature also reduces the hydrogen content in the films but increases the carbon content.
To obtain the best quality of plasma deposited silicon nitride film using DTBS and ammonia, the following deposition parameters were suggested:
- Deposition temperature of about 300 °C to 350 °C
- High NH3/DTBS ratio ( > 18 )
- Low total flow rate
- Low total pressure
- Plasma power density 0.15 watts/cm2 at 100 KHz.
The films deposited under above conditions (DTBS = 15 sccm, NH3/DTBS = 18, Total pressure = 0.3 torr, Deposition temperature = 300 °C, Plasma power = 0.15 watts/cm2 at 100 KHz ) had 13 % (atomic percent) hydrogen and a Si/N ratio of 0.5, indicating that these films are superior to the plasma silicon nitride films deposited using silane and ammonia. However, the carbon content ( 8% atomic percent) is still the major drawback of the silicon nitride films deposited by PECVD using DTBS and ammonia.
Recommended Citation
Shih, Kei-Turng, "Synthesis and characterization of silicon nitride film deposited by plasma enhanced chemical vapor deposition from ditertiary-butyl silane" (1991). Theses. 2620.
https://digitalcommons.njit.edu/theses/2620
