Silicon nitride from bis(tertiarybutylamino)silane

A process for the low pressure chemical vapor deposition of silicon nitride from ammonia and a silane of the formula: (t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 provides improved properties of the resulting film for use in the semiconductor industry.

BACKGROUND OF THE INVENTION 
The present invention is directed to the field of low pressure chemical 
vapor deposition of silicon nitride films using 
bis(tertiarybutylamino)silane, a novel organosilicon source material for 
silicon nitride. 
In the fabrication of semiconductor devices, a thin passive layer of a 
chemically inert dielectric material such as, silicon nitride (Si.sub.3 
N.sub.4) is essential. Thin layers of silicon nitride function as 
diffusion masks, oxidation barriers, trench isolation, intermetallic 
dielectric material with high dielectric breakdown voltages and 
passivation layers. Many other applications of silicon nitride coatings in 
the fabrication of semiconductor devices are reported elsewhere, see 
Semiconductor and Process technology handbook, edited by Gary E. McGuire, 
Noyes Publication, New Jersey, (1988), pp 289-301; and Silicon Processing 
for the VLSI ERA, Wolf, Stanley, and Talbert, Richard N., Lattice Press, 
Sunset Beach, Calif. (1990), pp 20-22, 327-330. 
The present semiconductor industry standard silicon nitride growth method 
is by low pressure chemical vapor deposition in a hot wall reactor at 
&gt;750.degree. C. using dichlorosilane and ammonia. 
Deposition of silicon nitride over large numbers of silicon wafers has been 
accomplished using many precursors. The low pressure chemical vapor 
deposition (LPCVD) using dichlorosilane and ammonia requires deposition 
temperatures greater than 750.degree. C. to obtain reasonable growth rates 
and uniformities. Higher deposition temperatures are typically employed to 
get the best film properties. There are several drawbacks in these 
processes and some of these are as follows: 
i) Deposition under 850.degree. C. gives poor hazy films with chlorine and 
particle contamination; 
ii) Silane and dichlorosilane are pyrophoric, toxic compressed gases; 
iii) Films formed from dichlorosilane result in the formation of less 
uniform films; and 
iv) Films from dichlorosilane have contaminants, such as chlorine and 
ammonium chloride, which are formed as byproducts. 
Japanese Patent 6-132284 describes deposition of silicon nitride using 
organosilanes with a general formula (R.sub.1 R.sub.2 N).sub.n SiH.sub.4-n 
(where R.sub.1 and R.sub.2 range from H--, CH.sub.3 --, C.sub.2 H.sub.5 
--C.sub.3 H.sub.7 --, C.sub.4 H.sub.9 --) by a plasma enhanced chemical 
vapor deposition and thermal chemical vapor deposition in the presence of 
ammonia or nitrogen. The precursors described here are tertiary amines and 
do not contain NH bonding as in the case of the present invention. The 
deposition experiments were carried out in a single wafer reactor at 
400.degree. C. at high pressures of 80-100 Torr. The Si:N ratios in these 
films were 0.9 (Si:N ratios in Si.sub.3 N.sub.4 films is 0.75) with 
hydrogen content in the deposited films. The butyl radical is in the form 
of isobutyl. 
Sorita et al., J. Electro. Chem. Soc., Vol 141, No 12, (1994), pp 
3505-3511, describe deposition of silicon nitride using dichlorosilane and 
ammonia using a LPCVD process. The major products in this process are 
aminochlorosilane, silicon nitride and ammonium chloride. Formation of 
ammonium chloride is a major drawback of using Si--Cl containing 
precursors. The formation of ammonium chloride leads to particle formation 
and deposition of ammonium chloride at the backend of the tube and in the 
plumbing lines and the pumping system. Processes which contain chlorine in 
the precursors result in NH.sub.4 Cl formation. These processes require 
frequent cleaning and result in large down time of the reactors. 
B. A. Scott, J. M. Martnez-Duart, D. B. Beach, T. N. Nguyen, R. D. Estes 
and R. G. Schad., Chemtronics, 1989, Vol 4, pp 230-234., report deposition 
of silicon nitride using silane and ammonia by LPCVD in the temperature 
region of 250.degree.-400.degree. C. Silane is a pyrophoric gas and is 
difficult to control for the deposition of clean silicon nitride due to 
partial gas phase reaction. 
J. M. Grow, R. A. Levy, X. Fan and M. Bhaskaran, Materials Letters, 23, 
(1995), pp 187-193, describe deposition of silicon nitride using 
ditertiarybutylsilane and ammonia by LPCVD process in the temperature 
range of 600.degree.-700.degree. C. The deposited silicon nitride films 
were contaminated with carbon impurities (10 atomic %). This is mainly due 
to the presence of direct Si--C bonds in the precursor. 
A. K. Hochberg and D. L. O'Meara, Mat. Res. Soc. Symp. Proc,. Vol. 204, 
(1991), pp 509-514, report deposition of silicon nitride and silicon 
oxynitride by using diethylsilane with ammonia and nitric oxide by LPCVD. 
The deposition was carried out in the temperature range of 650.degree. C. 
to 700.degree. C. The deposition is limited to deposition at 650.degree. 
C. and the deposition rate drops to below 4 .ANG./min at lower 
temperatures. In the LPCVD process, precursors which contain direct Si--C 
carbon bonds result in carbon contamination in the films. Carbon free 
deposition requires greater than 5:1 NH.sub.3 to precursor ratios. At 
lower ammonia concentrations, the films were found to contain carbon. 
Diethylsilane+ammonia processes typically require covered boats or 
temperature ramping to improve uniformities across the wafers. 
U.S. Pat. No. 5,234,869 and R. G. Gordon and D. M. Hoffman, Chem. Mater., 
Vol. 2, (1990), pp 482-484 disclose other attempts to reduce the amount of 
carbon involved aminosilanes, such as tetrakis(dimethylamino)silane. The 
temperature of deposition is in the range of 300.degree.-1000.degree. C. 
with pressures in the range of 1 mTorr-10 Torr. The presence of direct 
Si--N bonds and the absence of Si--C bonds were expected to give lower 
carbon concentrations in the films. However, there are three main 
disadvantages with precursors of this class. 
1) They contain N-methyl groups, the methyl groups tend to migrate to the 
silicon surface readily and contaminate the films with carbon during a CVD 
process. In order to reduce the amount of carbon, the process involves 
high temperatures (&gt;700) and high ammonia ratios (&gt;10:1). With increased 
ammonia ratios the deposition rates dramatically reduce due to reactant 
depletion. 
2) They do not contain NH bonding and they do not involve secondary 
silanes. 
3) At lower temperatures the deposition rates and uniformities are very 
poor (&gt;5%). 
The prior art has attempted to produce silicon nitride films at low 
temperatures, at high deposition rates and low hydrogen and carbon 
contamination. However, the prior art has not been successful in achieving 
all these goals simultaneously with one silicon precursor. The present 
invention has overcome the problems of the prior art with the use of a 
precursor unique to the formation of silicon nitride which avoids the 
problems of plasma deposition, operates at low thermal conditions, avoids 
Si--C bonds to reduce carbon contamination of the resulting films, has low 
hydrogen contamination, as well as avoiding chlorine contamination and 
operates at low pressures (20 mTorr-2 Torr) in a manufacturable batch 
furnace (100 wafers or more), as will be described in greater detail 
below. 
BRIEF SUMMARY OF THE INVENTION 
The present invention is a process for the low pressure chemical vapor 
deposition of silicon nitride on a substrate using ammonia and a silane of 
the formula: 
EQU (t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 
Preferably, the temperature of the substrate is in the range of 
approximately 500.degree. to 800.degree. C. 
Preferably, the pressure is in the range of approximately 20 mTorr to 2 
Torr. 
Preferably, the molar ratio of ammonia to silane is greater than 
approximately 2:1. 
Preferably, the substrate is silicon. 
Preferably, the substrate is an electronic device. 
Alternatively, the substrate is a flat panel display. 
In a preferred embodiment the present invention is a low temperature 
chemical vapor deposition of silicon nitride in a reaction zone, 
comprising the steps of: 
a) heating a substrate to a temperature in the range of approximately 
500.degree.-800.degree. C. in said zone; 
b) maintaining the substrate in a vacuum at a pressure in the range of 
approximately 20 mTorr-2 Torr in said zone; 
c) introducing into said zone ammonia and a silane of the formula: 
(t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 ; and 
d) maintaining the conditions of a) through c) sufficient to cause a film 
of silicon nitride to deposit on the substrate. 
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
Not Applicable

DETAILED DESCRIPTION OF THE INVENTION 
A large variety of "thin films" are used in the fabrication of Very Large 
Scale Integration (VLSI) devices. These deposited thin films can be of 
metals, semiconductors, or insulators. The films may be thermally grown or 
deposited from the vapor phase using LPCVD). VLSI technology requires very 
thin insulators for a variety of applications in both microprocessors and 
random-access memories device fabrication. Silicon dioxide has been 
predominantly used as a dielectric material because of its ease of 
deposition and excellent properties at the SiO.sub.2 /Si interface. 
Silicon nitride has other advantages over silicon dioxide, some of these 
include impurity and dopant resistant diffusion barriers, high dielectric 
breakdown voltages, superior mechanical and inherent inertness of Si.sub.3 
N.sub.4. 
In VLSI fabrication a large set of rigorous chemical, structural, process 
and electrical requirements need to be satisfied. Purity of the film, 
thickness, uniformity and deposition rates are some of the strictly 
controlled parameters to facilitate fabrication of submicron features in a 
device. It is a major advantage in the fabrication and performance of a 
device if the deposition process can be carried out at temperatures lower 
than 850.degree. C. Silicon source materials for depositing silicon 
nitride under LPCVD conditions at these temperatures are limited to silane 
and dichlorosilane. A safe, reliable low temperature silicon nitride 
source material has applications in other technologies, such as; flat 
panel display devices, other electronic and non-electronic substrates or 
compound semiconductor device fabrication. 
The present invention is directed to bis(tertiarybutylamino)silanes as a 
class of aminosilanes that deposit silicon nitride at unexpectedly low 
temperatures with superior uniformities. 
The bis(tertiarybutylamino)silane meets the following formula: 
EQU (t-C.sub.4 H.sub.9 NH).sub.2 Si(H).sub.2. 
The deposited films have superior uniformities and are free of ammonium 
chloride and chlorine contamination. The bis(tertiarybutylamino)silane 
apparently has the property to deposit silicon nitride at 
250.degree.-300.degree. C. below that of the dichlorosilane+ammonia 
process by LPCVD. Analogous aminosilanes which contain ligands, such as 
n-butylamines and tetrakis(dimethylamino)silane, do not deposit carbon 
free films at such low temperatures by LPCVD, and the film uniformities 
are poorer. 
The remarkable advantages of bis(tertiarybutylamino)silane may be 
attributable to the inherent property of t-butyl amine ligands in 
bis(tertiarybutylamino)silane. During pyrolysis of 
bis(tertiarybutylamino)silane, the t-butyl amine ligand may eliminate 
readily as isobutylene. Isobutylene is a very stable, good leaving group 
and thus does not contaminate silicon nitride films during deposition. In 
comparison to the dialkylaminosilanes, tertiarybutylamino groups are more 
basic than dialkylamines due to the presence of the nitrogen-hydrogen bond 
(N--H) in the tertiarybutylamino group. The presence of the N--H bond may 
facilitate labile .beta.-hydride transfer to form diaminosilane and 
cleavage of the tertiarybutyl group as isobutylene. 
Other advantages of bis(tertiarybutylamino)silane can be summarized as 
follows: 
1) It is a non-pyrophoric volatile stable liquid with a vapor pressure of 
7.5 Torr at 40.degree.-45.degree. C. 
2) It does not have any chlorine in the precursor. The Si--Cl bonds in 
dichlorosilane leads to the formation of ammonium chloride which deposits 
in the back end of the tube and requires frequent cleaning. 
3) The precursor does not contain direct Si--C bonds, and the resulting 
silicon nitride films were carbon free, as indicated by auger 
spectroscopy. 
4) The t-butyl amino ligands behave as good leaving groups to form 
isobutylene and are readily eliminated during pyrolysis. This is thought 
to be in part because the compound has a N--H bond. This additional 
advantage helps in removing all the carbon cleanly without contaminating 
the deposited films. 
5) When compared to the dichlorosilane and ammonia process 
bis(tertiarybutylamino)silane gives superior uniformities. This may be due 
to the presence of bulky t-butyl amino ligand. The steric bulk of these 
ligands helps in increased mobility of the molecules on the surface of the 
substrate which results in higher uniformity. 
6) When compared to other amines, such as; diamino, dimethylamino and other 
alkylamines, the deposition temperature using these precursors can be 
lower by 250.degree.-300.degree. C. 
A comparison of other precursor deposition temperatures, precursor and film 
properties are given in Table 1 
TABLE 1 
______________________________________ 
Vapor Deposi- 
Pressure 
tion 
(Torr Temp. Precursor and Film 
Precursors @ .degree.C.) 
(.degree.C.) 
Properties 
______________________________________ 
SiH.sub.4 + NH.sub.3 
Gas at 200-400 Pyrophoric gas. Gas phase 
ambient Plasma reaction. Silicon rich at 
process lower temperatures. 
Films may contain 
hydrogen. 
Cl.sub.2 SiH.sub.2 + NH.sub.3 
Gas at &gt;750 Corrosive gas. Direct 
ambient Si--Cl bonds. Chlorine 
contamination. Ammonium 
chloride as byproduct. 
(C.sub.2 H.sub.5).sub.2 SiH.sub.2 + NH.sub.3 
100 at 650-725 Poor uniformities. 
20 Direct Si--C 
bonds. Direct Si-Cl bonds. 
Carbon impurities in the 
films &gt;2%. May require 
cage boats and 
temperature ramping. 
(t-C.sub.4 H.sub.9).sub.2 SiH.sub.2 + NH.sub.3 
20.5 at 600-700 Direct Si--C bonds. 
20 Carbon content (10 at %) 
in the films. 
(CH.sub.3).sub.2 N!.sub.3 SiR + NH.sub.3 
16 at 25 
700-1000 Direct Si--C bonds. 
R.dbd.H or CH3 Carbon content in the films 
&gt;2% and require high 
ammonia to source ratios 
(30:1). Poor uniformities 
of &gt;5%. 
(t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 
7.5 at 500-1000 No Si--C bonds, no carbon 
(present invention) 
45 contamination, good 
uniformity and high 
deposition rate. 
(t-C.sub.4 H.sub.9).sub.2 Si(NH.sub.2).sub.2 + 
2.1 at 600-700 Direct Si--C bonds. 
NH.sub.3 39 Carbon contamination in 
the films. 
______________________________________ 
The bis(tertiarybutylamino)silane compound is also more desirable than 
ditertiarybutylamino analog for the N--H bonding properties discussed 
above, and bis(tertiarybutylamino)silane is more desirable than the mono, 
tri or tetrakis (tertiarybutylamino) analog because the mono analog is 
unstable, the tri substituted analog has significant delivery problems, 
the tetrakis (tertiary butylamino)silane analog has much lower vapor 
pressure and cannot be readily synthesized due to steric bulk of the 
ligands on a single silicon atom and therefore, inappropriate for 
commercial use. 
To form silicon nitride films, the bis(tertiarybutylamino)silane and 
ammonia are allowed to react in the reactor tube at an elevated 
temperature (preferably 500.degree. C.-800.degree. C., but the temperature 
could be less or greater than this range). Reaction may occur either on 
the surface or very close to the wafer surface to deposit a thin silicon 
nitride film. If the reaction occurs in the gas phase (a homogeneous 
reaction) then clusters of silicon nitride are formed. Such cases are 
typical in silane and ammonia process. When the reaction occurs close to 
the wafer surface then the resulting films are of superior uniformities. 
Thus, one important requirement for CVD application is the degree to which 
heterogeneous reactions are favored over gas phase reactions. 
The CVD process can be grouped into a) a gas-phase process and b) a surface 
reaction process. The gas phase phenomenon is the rate at which gases 
impinge on the substrate. This is modeled by the rate at which gases cross 
the boundary layer that separates the bulk regions of flowing gas and 
substrate surface. Such transport processes occur by gas-phase diffusion, 
which is proportional to the diffusivity of the gas and concentration 
gradient across the boundary layer. Several surface processes can be 
important when the gases reach the hot surface, but the surface reaction, 
in general, can be modeled by a thermally activated phenomenon which 
proceeds at a rate which is a function of the frequency factor, the 
activation energy, and the temperature. 
The surface reaction rate increases with increasing temperature. For a 
given surface reaction, the temperature may rise high enough so that the 
reaction rate exceeds the rate at which reactant species arrive at the 
surface. In such cases, the reaction cannot proceed any more rapidly than 
the rate at which reactant gases are supplied to the substrate by mass 
transport. This is referred to as a mass-transport limited deposition 
process. At lower temperatures, the surface reaction rate is reduced, and 
eventually the concentration of reactants exceeds the rate at which they 
are consumed by the surface reaction process. Under such conditions the 
deposition rate is reaction rate limited. Thus, at high temperatures, the 
deposition is usually mass-transport limited, while at lower temperatures 
it is surface-reaction rate-limited. In actual processes, the temperature 
at which the deposition condition moves from one of these growth regimes 
to the other is dependent on the activation energy of the reaction, and 
the gas flow conditions in the reactor. Thus, it is difficult to 
extrapolate process conditions or results from one pressure regime or 
temperature regime to another. 
In processes that are run under reaction rate-limited conditions, the 
temperature of the process is an important parameter. That is, uniform 
deposition rates throughout a reactor require conditions that maintain a 
constant reaction rate. This, in turn, implies that a constant temperature 
must exist everywhere on all wafer surfaces. On the other hand, under such 
conditions, the rate at which reactants reach the surface is not 
important, since their concentration does not limit the growth rate. Thus, 
it is not as critical that a reactor be designed to supply an equal flux 
of reactants to all locations of a wafer surface. It should be appreciated 
that in LPCVD reactors, wafers can be stacked vertically and at very close 
spacing because such systems operate in a reaction rate limited mode. The 
reason for this is as follows: Under the low pressure of an LPCVD reactor 
.about.1 torr, the diffusivity of the gas species is increased by a factor 
of 1000 over that at atmospheric pressure, and this is only partially 
offset by the fact that the boundary layer, the distance across which the 
reactants must diffuse, increases by less than the square root of the 
pressure. The net effect is that there is more than an order of magnitude 
increase in the transport of reactants to and byproducts away from the 
substrate surface, and the rate-limiting step is thus the surface 
reaction. 
The presence of the tertiary-butyl group in bis(tertiarybutylamino)silane 
apparently helps the surface reaction pathways and hence the deposited 
films have a superior uniformity when compared to other processes, even at 
lower temperatures. These films were deposited using an LPCVD hot walled 
reactor, as described below. 
Low pressure chemical vapor deposition processes (LPCVD) involve chemical 
reactions that are allowed to take place in the pressure range of 20 mTorr 
to 2 Torr. The chemical vapor deposition (CVD) process can be described in 
the following sequence of steps at a given temperature, pressure and ratio 
of the reactants: 
1) Reactants are introduced into the reaction chamber and may be diluted 
with inert gases, if needed; 
2) The reactants are allowed to diffuse to the substrate; 
3) The reactants are adsorbed on the substrate, and the adsorbed molecules 
undergo migration; and 
4) Chemical reactions occur on the surface, and the gaseous byproducts of 
the reaction are desorbed, leaving behind the deposited film. The 
reactions are initiated by several methods; e.g., thermal or photons. 
Thermal energy is used in the LPCVD process. 
Horizontal tube hot wall reactors are the most widely used for LPCVD in 
VLSI manufacturing. They are employed for depositing poly-Si, silicon 
nitride, undoped and doped silicon dioxide films. These reactors are used 
extensively because they are economical, have high throughputs, their 
deposited films are uniform and they can accommodate large diameter wafers 
(6"-12"). Their main disadvantages are susceptibility to particulate 
contamination and low deposition rates. 
The vertical flow isothermal LPCVD reactor may also be used for deposition 
of silicon dioxide. Here, the reactor configuration can avoid the 
wafer-to-wafer reactant depletion effects. They require no temperature 
ramping, produce highly uniform depositions and reportedly achieve low 
particulate contamination. 
To induce the low pressure conditions in the reactor, an appropriate vacuum 
system is necessary. For the present experiments, the vacuum system 
consisted of a rotary vane pump/roots blower combination and various cold 
traps. The reactor pressure is controlled by a capacitance manometer 
feedback to a throttle valve controller. Reactor loading consisted of 
eighty 100 mm diameter silicon wafers at 9 mm spacing in standard 
diffusion boats. The boats were positioned on a sled, so that the wafers 
centers were slightly above the center of the reaction tube. This produces 
a uniform conductance around the wafer peripheries by compensating for 
conductance restrictions caused by the boats and the sled. The temperature 
uniformity across the wafer load for the data presented was .+-.1.degree. 
C. as measured by an internal multi-junction thermocouple. Deposition 
uniformity down the wafer load is improved by a temperature ramp. 
Our deposition experiments were carried out in a horizontal tube reactor, 
but the deposition with this precursor will occur even in a vertical tube 
reactor. The precursor was fed through an open port near the load door. 
Ammonia was also fed from a port near the door of the furnace separately. 
The present invention of a method of depositing substantially pure thin 
silicon nitride films on silicon wafers by using a 
bis(tertiarybutylamino)silane precursor has been demonstrated 
experimentally. The bis(tertiarybutylamino)silane is a non-pyrophoric 
volatile liquid which is safer to handle than silane and dichlorosilane. 
The deposition process is carried out at preferably 20 mTorr-2 Torr in the 
temperature range of preferably 500.degree. C. to 800.degree. C. using 
vapors from bis(tertiarybutylamino)silane and ammonia. Optionally, an 
inert gas diluent, such as nitrogen or argon, can be used to dilute and 
control the rate of reaction. The molar feed ratio of ammonia to 
bis(tertiarybutylamino)silane and ammonia is preferably greater than 2:1. 
EXAMPLE 1 
The process involves reaction of bis(tertiarybutylamino)silane with ammonia 
under LPCVD conditions (low pressure range of 20 mTorr-2 Torr). The 
precursor and ammonia are introduced into the heated reactor 
(500.degree.-800.degree. C.) via injectors placed at the door. The 
reactants are flowed over wafers into the evacuated chamber. The ammonia 
to silicon source is kept at a ratio in the range of 2:1-10:1. A 
continuous film of silicon nitride is deposited upon the surface of a 
silicon wafer. These films are suitable for integrated circuit 
manufacture. A typical run was carried out in a 150 mm hot wall LPCVD 
horizontal tube reactor, although the apparatus configuration is not 
critical. The process involves loading the quartz reactor with 75 to 100 
silicon wafers; evacuating the system; letting the wafers come to a 
desired temperature at which the deposition will be carried out. The 
energy required for this reaction can be supplied by simple resistive 
heating. However, simple, resistive heating is advantageous because the 
equipment is less expensive, and one avoids radiative film damage often 
associated with plasma reactors. 
The films are characterized by infrared spectroscopy and refractive index. 
FT-IR spectrum is consistent with silicon nitride films deposited from 
other known nitride precursors e.g. dichlorosilane+ammonia. There are 
moderate absorption bands in the Si--H stretching region at 2100 cm.sup.-1 
and a strong Si--N stretch at 834 cm.sup.-1. Refractive indices for these 
films were measured by ellipsometry at 632.4 nm and the refractive indices 
ranged from 1.95-2.01 for these films. Silicon nitride films were 
characterized by Auger depth profile analysis. Silicon, carbon, nitrogen 
and oxygen content for these films were determined. The composition of 
silicon nitride was 43% silicon and 57% nitrogen. The composition of these 
films was uniform throughout the depth of the films. Oxygen and carbon 
were below the detection limits (&lt;2 atomic %) of the auger spectroscopy. 
Comparative data of several analogous precursors and the 
bis(tertiarybutylamino)silane of the present invention is set forth below 
in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Vapor 
V. Press 
at T 
Source 
Temp 
Press 
NH3/ 
Dep Rte 
Refr 
Precursors Formula Mol Wt 
Torr 
.degree.C. 
sccm 
.degree.C. 
mTorr 
source 
ang/min 
index 
__________________________________________________________________________ 
Bis(dimethylamino)silane 
H.sub.2 Si(NCH.sub.3 !.sub.2).sub.2 
118.25 
&gt;10 27 600 
22.0 
650 
600 6.0 5.5 2.00 
Tris(dimethylamino)silane 
HSi(NCH.sub.3 !.sub.2).sub.3 
161.32 
8 29 21.6 
600 
600 6.0 0 
21.6 
650 
600 6.0 12 1.75 
21.6 
700 
600 6.0 22 1.89 
Bis(diethylamino)silane 
H.sub.2 Si(NC.sub.2 H.sub.5 !.sub.2).sub.2 
174.36 
14 65.4 
48.3 
550 
300 0 15 1.65 
38.6 
600 
500 0 16 2.00 
Bis(t-butylamino)silane 
H.sub.2 Si(NHC.sub.4 H.sub.9).sub.2 
174.36 
7.5 45 22.0 
600 
600 6.0 14 1.96 
22.0 
650 
600 6.0 58 1.95 
22.0 
700 
600 6.0 124 1.96 
Di-t-butyldiaminosilane 
(C.sub.4 H.sub.9).sub.2 Si(NH.sub.2).sub.2 
174.36 
2.1 39 21.0 
600 
600 6.3 12 1.87 
18.6 
650 
600 7.1 43 1.93 
26.0 
650 
600 5.1 57 1.94 
21.0 
700 
600 6.3 130 1.99 
Tris(ethylamino)ethylsilane 
C.sub.2 H.sub.5 Si(NHC.sub.2 H.sub.5).sub.3 
189.38 54 11.0 
600 
600 4.0 9 1.73 
11.0 
650 
600 4.0 30 1.87 
23.0 
650 
600 6.0 47 1.88 
11.0 
700 
600 4.0 62 1.93 
23.0 
700 
600 6.0 105 1.94 
Tetrakis(dimethylamino)silane 
Si(NCH.sub.3 !.sub.2).sub.4 
204.39 
7.3 51 34.3 
600 
500 0 0 
__________________________________________________________________________ 
Based upon this data, vapor pressure of the precursors for easy delivery, 
deposition rates, carbon impurities in the deposited films, temperature of 
deposition, silicon to nitrogen ratios and refractive indices were used as 
criteria to compare the different precursors. The highest deposition rates 
were obtained using chemicals that had N--H bonds; 
bis(tertiarybutylamino)silane, di-t-butyldiaminosilane, and 
tris(ethylamino)ethyl silane. Of these, the silicon nitride films having 
the lowest carbon impurities in the deposited films were obtained using 
chemicals that did not have direct Si--C bonds, namely; 
bis(tertiarybutylamino)silane and t-butylaminosilane dimer. The most 
uniform depositions were obtained using chemicals that had t-butyl groups, 
namely; bis(tertiarybutylamino)silane and di-t-butyidiaminosilane. In 
light of this criteria, bis(tertiarybutylamino)silane is unexpectedly a 
superior silicon nitride precursor. 
The present invention has been described with regard to a preferred 
embodiment, however the full scope of the present invention should be 
ascertained from the claims which follow.