NASA Technical Memorandum 10230 1 

F! 

Ion Beam and Plasma Methods 

of Producing Diamohdlike 

Carbon Films 

Diane M. Swec, Michael J. Mirtich, 

and Bruce A. Banks 

Lewis Research Center 

Cleveland, Ohio 

Presented at the 

32nd Annual International Technic41 Symposium on Optical and 

Optoelectronic Applied Science and Engineering 

sponsored by the Society of Photo-Qptical Instrumentation Engineers 

San Diego, California, August 14-19, 1988 

* 

(NASA-Tb-1023Of) ION BEAH AND PLASf!A' 

flEfHODS OF PRODUCING DIAHDNDLIKE CAEBOI 

FILMS [NASA.. Lewis Besearch Center) 17 P 

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ION BEAM AND PLASMA METHODS OF PRODUCING DIAMONDLIKE CARBON FILMS 

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Diane M. Swec, Michael J. Mirtich, and Bruce A. Banks 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135 

SUMMARY 

At the NASA Lewis Research Center a variety of plasma and ion beam techniques have been employed to generate diamondlike carbon films. 

include the use of RF sputtering, DC glow discharge, vacuum arc, plasma gun, 

ion beam sputtering, and both single and dual ion beam deposition. Since the 

films have been generated using a wide variety of techniques, the physicochemical properties of these films vary considerably. In general, these films 

have characteristics that are desirable in a number of applications. 

example, the films generated using both single and dual ion beam systems were 

evaluated for applications including power electronics as insulated gates and 

protective coatings on transmitting windcws. These films were impervious to 

reagents which dissolve graphitic and polymeric carbon structures. Nuclear 

reaction and combustion analysis indicated hydrogen to carbon ratios to be 

1.00, which allowed the films to have good transmittance not only in the infra 

red, but also in the visible. Other evaluated properties of these films 

include band gap, resistivity, adherence, density, microhardness, and intrinsic stress. 

for depositing diamondlike carbon films are presented in this paper. 

These methods 

For 

The results of these studies and those of the other techniques 

INTRODUCTION 

The deposition of carbon films possessing diamondlike properties has been 

reported by numerous researchers. A variety of plasma and ion beam techniques 

have been employed to generate the carbon films. 

reported to produce diamondlike carbon films include: vacuum evaporation 

(ref. 1>, RF sputtering using inert gas and carbon targets (ref. 2>, RF plasma 

decomposition of hydrocarbon gases (refs. 3 to 61, DC glow discharge of predominantly hydrocarbon gases with a small fraction of argon (ref. 7>, coaxial 

pulsed plasma acceleration using methane gas (ref. 8>, vacuum arc using a 

graphite cathode (ref. 9), ion beam deposition with argon and hydrocarbon scission fragment ions (refs. 10 to 121, and deposition using pure carbon ion 

beams (ref. 13). Combinations of varicus techniques have 3lso Seen utilized 

such as argon ion bombardment of evaporated carbon films (ref. 141, vacuum carbon arc plasma in conjunction with DC or RF potentials applied to the silbstrate 

(ref. 9>, and dual ion beam deposition and sputtering techniques (refs. 12,1S, 

and 16). 

Processes which have been 

These diamondlike carbon films may be hard, transparent, chemically 

inert, electrically insulating, and have been reported to range from amorphous 

to polycrystalline in structure. Thus they would find wide use in a number of 

applications, including, power electronics as insulating gates for field effect 

transistors or as doped semiconductors, protective coatings for optical components, integral coatings for solar cells or laser windows in the infrared, 

etc. Successful realization of these applications is contingent on effective 
production of these films, and tailoring their characteristics to meet the 

needs of the particular application. Therefore, NASA Lewis Research Center 

has employed a variety of plasma and ion beam methods to generate diamondlike 

carbon (DLC) films. These methods include the use of RF sputtering with hydrocarbons, DC glow discharge, vacuum arc, coaxial carbon plasma gun, ion beam 

sputtering, and both single and dual ion beam deposition. This paper presents 

the process techniques and associated characteristics of the films. Film characteristics include density, hydrogen content, band gap, resistivity, microhardness, dielectric constant, adherence, intrinsic stress, transmittance, and 

chemical resistance. Some application evaluations will also be presented. 

APPARATUS AND PROCEDURE 

Diamondlike carbon films were ion beam sputter deposited using an 8 cm 

diameter source (ref. 17). A 100 eV, 55 mA argon ion beam was produced for 

sputter cleaning and deposition. An ion beam current density of -1 .O rnA/cm2 

resulted in the vicinity of the sputter target and substrates which were located 20 cm downstream of the ion source. The ion source was operated with a 

hot filament neutralizer in a vacuum facility which maintained a pressure of 

2x10-5 torr during operation. The target was made of pyrolytic graphite and 

films up to 0.15 pm thick were deposited on various substrates. 

A 30 cm dlameter ion source with its optics masked to 10 cm in diameter 

was used to directly deposit DLC films (ref. 18). The ion source used argon 

(Ar) gas in the hollow cathode, located in the main discharge chamber, as well 

as in the neutralizer. After a discharge was established between the cathode 

and the anode, methane gas (CH4) was introduced through a manifold into the 

discharge chamber. For the depositions reported, the molar ratio of CH4 to Ar 

was 0.28. For this system, the total ion beam energy was the sum of the discharge voltage and the screen grid voltage. Typically, current densities were 

1 mA/cm2 at a distance of 2.5 cm axially downstream of the grids. Films were 

deposited at rates as high as 71 A/min to film thicknesses as great as 1.5 pm. 

It is believed that the amorphous carbon films are produced under conditions where both growth and sputtering occur simultaneously, whereby increased 

sputtering may decrease the number of graphitic precursors incorporated in the 

films and hence improve the quality. In addition, Marinow and Dobrew have 

found that active sites for nucleation are created and the growth and coalescence of the nuclei are enhanced due to an increased mobility of the condensing atoms when film structures are bombarded by inert gas beams (ref. 19). 

With these factors in mind, a dual beam system was created by adding an 8 cm 

diameter argon ion source (ref. 18). This system, shown in figure 1, was used 

to generate another set of DLC films. The 8 cm source, using a filament cathode, was located at a 12" angle with respect to the 30 cm source. This source 

was used to direct a beam of 200-600 eV argon ions with a current density of 

25 pa/cm2 on the substrate while the deposition from the 30 cm source was 

occurring. 

The plasma gun, shown in figure 2, consisted of two coaxial carbon electrodes (ref. 20). The outer electrode was a hollow cylinder with a large 

inside diameter along one half of its length and a smaller inside diameter 

along the other half. The inner electrode was a carbon rod of similar shape, 

2 
supported by a polytetrafluoroethylene cylinder which centered it within the 

outer electrode and allowed it to slide axially. To fire the gun, the inner 

electrode was drawn forward by two solenoids until the two tapered surfaces 

came into contact. Current was fed into the system creating an arc which 

caused the resulting plasma to be accelerated forward and deposited onto the 

substrate. During operation the belljar. pressure was -10-6 torr. 

-1800 V produced currents on the order of 100 kA which resulted in a power 

level of about 73 MW being dissipated by the gun. One firing event lasted 

between 0.6 and 0.8 msec. 

Voltages of 

Figure 3 illustrates a vacuum arc using a graphite cathode to provide a 

source of high temperature carbon. The cathode, made of spectroscopic grade 

graphite, was held in a water cooled copper sleeve. A tungsten tipped striker, 

supplied with current from a 200 A DC welder supply, contacted the cathode and 

an arc was created. The resulting plasma, consisting of carbon atoms and ions, 

was accelerated forward through a water cooled copper anode and deposited onto 

the substrate in a background pressure of 10-5 torr. 

RESULTS AND DISCUSSION 

Compositional characteristics. - Auger analysis of both the single and 

dual ion beam deposited DLC films showed no evidence of any elements other 

than carbon and small amounts of argon and oxygen. After argon ion sputtering, the oxygen signal disappeared, but the argon signal was enhanced. High 

resolution Auger spectra obtained from a single crystal of pyrolytic graphite, 

an ion beam deposited carbon film, and natural diamond are shown in figure 4. 

The lineshape for the carbon film lies somewhere between those of pyrolytic 

graphite and diamond. The shoulder in the graphite spectrum at 250 eV is 

present in the film spectrum, but not so pronounced, whereas natural diamond 

shows no shoulder. It should also be noted that due to the escape depth of 

the 270 eV Auger electrons, only the outermost surface layers were sampled in 

all cases. These would be the most prone to graphitization. Therefove, it 

was significant that differences between the ion beam deposited film and graphi te were observable. 

An example of a Secondary Ion Mass Spectroscopy (SIMS) spectrum from a 

single ion beam deposited DLC film on a silicon substrate is given in figure 5. Note the cluster of peaks at 12, 13, 14 and 15 AMU from the hydrocarbon fragments C+, CH+, CH2+ and CH3+. 

assigned to N+, however, Auger analysis indicated no nitrogen. There is a 

strong H+ peak at 1 AMU and a cluster of hydrocarbon peaks at 26, 27, 28, and 

29 AMU. It is believed that when multiatomic ionic clusters are emitted from 

the surface, e.g., CH2+, these atoms were bound together in the original solid 

(ref. 21). Therefore it appears likely that the ion beam deposited DLC films 

contained chemically combined hydrogen. 

The peak at 14 AMU could also be 

Nuclear reaction and combustion analysis for hydrogen was also performed 

on the DLC films (ref. 22). There was a variation in hydrogen content which 

depended upon the method used for deposition of the DLC film as indicated by 

the ratios listed in table I. A hydrogen to carbon (H/C) ratio of 0.91 existed 

for DLC films made by single ion beam deposition. 

second ion source (dual beam) this ratio was reduced to 0.62. Thus, the second source removed some of the hydrogen. The films generated by ion beam sputter deposition from a graphite target had a H/C ratio of 0.22. 

By adding the energy of the 

It has been 

3 
I’ 

shown that for the ion beam deposited DLC films, using semiquantitative infrared spectroscopy, the ratio of chemically bonded hydrogen to carbon was 

between 0.03 and 0.44 (ref. 16). The difference between the two hydrogen 

analysis techniques indicated the presence of nonbonded hydrogen in the films. 

The electron diffraction pattern of the DLC films generated using either 

single or dual ion beam deposition was found to be characteristic of an amorphous solid. Films deposited by the coaxial carbon plasma gun method were 

also primarily amorphous as determined by x-ray diffraction. 

Optical properties. - The transmittance, reflectance and absorptance of 

the DLC films on fused silica were obtained using an integrating sphere and 

the technique described in reference 23. Shown in figure 6(a> is the spectral 

transmittance for DLC films varying in thickness from 0.08 to 0.33 pm. These 

films were generated using dual ion beam deposition. Figures 6(b) and 6(c> 

show the corresponding spectral reflectance and absorptance. At short wavelengths the films all show a large decrease in transmittance while there is a 

large increase in absorptance. For film thicknesses between 0.08 and 0.15 pm 

there are only small differences in transmittance a t a l l wavelengths. Increasing the DLC film thickness to 0.33 pm has only a small effect on the transmittance for wavelengths greater than 0.8 pm, but reduces the transmittance to as 

low as 10 percent at 0.4 pm. Most of this transmittance loss for the 0.33 pm 

thick film is due to the corresponding increase in absorptance. The thinner 

films looked clear to yellowlike in appearance, while the thicker DLC film was 

brown. 

The spectral transmi ttance, ref 1 ec tance and absorptance for the DLC f i lms 

obtained from the single ion beam deposition method are similar to those generated using the dual beam source, but have lower spectral transmittance for 

films greater than 0.12 pm thick. This is evident in figure 7 where the spectral transmittance’is shown for DLC films, 0.15 pm thick, generated using both 

methods. The 0.15 pm thick dual beam film has greater transmittance at all 

wavelengths when compared to the single beam film of the same thickness. The 

increased absorption most likely arises from the presence of systems of conjugated double bonds within the film, although the presence of oxygen could play 

a role. Both the graphitic precursors and oxygen would be expected to be 

reduced by the increased sputtering from the second source. A dual ion beam 

deposited DLC film, 0.05 pm thick displays spectral transmittance values 

greater than 90 percent at wavelengths greater than 0.7 pm. Also shown in figure 7 is the spectral data for an ion beam sputter deposited DLC film 0.17 pm 

thick. The transmittance was measured only between 0.4 and 0.8 pm for this 

film, and is very low when compared to the DLC films which were direct 

deposited. The low transmittance of the sputtered film may be due to its low 

hydrogen content. 

Chemical and physical properties. - A solution of 3 parts H2SO4 and 1 

part “03 (concentrated acids, by volume) at 80°C was used as the solvent in 

the chemical dissolution studies. This reagent rapidly dissolves graphitic 

and polymeric materials, but does not dissolve diamond. Diamondlike carbon 

films from the single and dual ion beam deposition methods were subjected to 

the reagent at 80°C for periods up to 20 hr. The films on silicon were unaffected. However, the films on fused silica showed varied behavior. In some 

cases they were untouched, in others the film was removed from the substrate, 

but not fully dissolved. These results clearly indicate that the DLC films 

4 
generated by direct deposition, especially on silicon, were far more resistant 

to chemical etching than normal polymeric hydrocarbons or graphite. 

Scanning transmission electron microscopy (STEM) showed the single and 

dual ion beam deposited DLC films to be smooth and essentially free of features. For the vacuum arc and 

coaxial carbon plasma gun deposited films, STEM showed that particles and 

inclusions were randomly dispersed throughout the film. 

No pinholes or other defects were observed. 

The densities of the DLC films were measured by either the sink or float 

measurement of flakes or by direct determination of thickness, area and mass. 

The density of the sputter deposited films was 2.1 g/cm3, and 1.8 g/cm3 for 

the dual ion beam deposited DLC films. The densities were less than either 

diamond (3.51 g/cm3> or graphite (2.26 g/cm3>. It is clear from these results 

that the long range structure of the films was not that of diamond. However, 

since the films were typically amorphous, one would expect to observe densities much below 2.26 g/cm3. Therefore, there must be a reasonable fraction of 

tetragonal bonded carbon. The observed high densities were an indicator of 

the degree to which the films were diamondlike. The densities were also measured for the DLC films deposited by the other methods and are listed in 

table I. On the average the densities were 2.0 g/cm3 for these methods. 

The DLC films were deposited on silicon (Si) and intrinsic stress measurements were made using a stress gauge. All of the DLC films exhibited a cornpressive stress which varied depending on the deposition method. 

shows that the stress in the CH4 single beam films can be reduced to values as 

low as 4x109 dynelcm2 by decreasing the deposition energy to 90 eV. 

pressive stress for an ion beam sputter deposited film was 1 .6x1O10 dyne/cm2 

which was higher than that of direct ion beam deposition, single or dual, with 

CH4. Listed in table I are the stress levels for the various DLC films. The 

data indicates that the film stress does not depend on the'hydrogen content, 

but on other parameters such as deposition technique and conditions. 

Figure 8 

The comThe adherence of the DLC films on fused silica (Si021 was measured following the procedure used by Mirtich (ref. 15). Methane films up to 1.0 pm 

thick, deposited using either single or dual beam systems, were at least as 

adherent as the maximum measurable adherence of the adherence tester, namely, 

5.5~10~ N/m2 or 8000 psi. These films were so adherent that, for some of the 

films, portions of the Si02 gave way with the film still intact. Films which 

were sputter deposited from a graphite target began to spa11 at 0.2 pm, indicating an upper limit of allowable thickness of the film. This was expected, since the stress level of this type of film was greater than those made 

by direct ion beam deposition. 

the DLC films from the various methods are listed in table I. 

A qualitative description of the adherences of 

Some DLC films deposited by the dual ion beam system on Si have shown no 

visible signs of deterioration, even after 4 years. However, a film 1.75 pm 

thick deposited using the single ion beam source spalled within several weeks. 

Microhardness was measured by the Vickers diamond indentation method 

(ref. 24). The DLC films were either single or dual ion beam deposited, vacuum 

arc or RF sputter deposited on (100) silicon substrates. Figure 9 shows the 

microhardness as a function of load and thickness for RF sputtered DLC films. 

5 
The film hardness Increases with decreasing indentor load, and indicates a 

slight increase with increasing film thickness. The DLC films deposited by 

the vacuum arc technique had many inclusions, but microhardness data collected 

from the clear regions indicated a comparable hardness to the RF sputtered 

films. It was found that the single or dual ion beam deposited DLC films had 

a hardness half that of diamond. 

Electronic properties. - Listed in table I are the values for the optical band gap of the DLC films from the various methods. The DLC films from 

the single and dual ion beam systems have similar band gaps, but the films 

which were ion beam sputtered from a graphite target had a higher band gap. 

Diamondlike carbon films which were Rf sputtered or deposited by DC glow discharge had even higher band gaps which were in the range of 1.5 to 3.0 eV. 

The coaxial carbon plasma gun films had a band gap of -0 eV, which was indicative of a graphitic (0 eV) as opposed to a diamond (5.0 eV> structure. The 

differences in the band gaps between the films was most likely due to the difference in hydrogen content of the films. 

The resistivity of the various DLC films on silicon was measured and is 

also listed in table I. Electrical contacts to the film were made with sputtered gold and silver paint. The resistivities for DLC films which were ion 

beam sputtered, direct ion beam deposited or coaxial carbon plasma gun deposited were all on the order of 106 SZ-cm. The DLC films which were RF sputter 

or DC glow discharge deposited had resistivities in the range of lo8 to 10l2 

Q-cm. However, all of the DLC films had resistivities higher than graphite 

(0.017 SZ-cm), but lower than diamond Q-cm). 

Applications. - Two of the materials most often used as optical windows 

due to their high transmittance at infrared (IR) wavelengths are zinc selenide 

(ZnSe) and zinc sulfide (ZnS). However, these materials are soft and often 

degrade when subjected to a particle-impacting environment (ref. 25). DLC . 

films have the potential to protect these window materials from rain and particle erosion as well as chemical attack. Therefore, DLC films were ion beam 

sputter deposited and also direct deposited with either the single or dual ion 

beam on ZnS and ZnSe. The DLC coated window surfaces were then exposed to aluminum oxide (A12031 particles in a microsandblaster, and water droplets at 

speeds up to 400 mph. 

In order to improve the adherence of the DLC films on ZnS and ZnSe, a 

thin intermediate coating of germanium (Gel was used prior to deposition of 

the DLC film (ref. 26). Ion implantation of the ZnS and ZnSe surfaces with 

helium (He) at energies of 100 keV and at doses to 2x1017 particles/cm2 prior 

to the deposition of the DLC/Ge film also helped to improve the adherence but 

as a bonus improved the physical hardness of the substrate. The DLC films 

plus an intermediate coating of 0.05 pm Ge deposited on the window materials 

and also windows He ion implanted showed adherence values equal to the 

strength of the substrate. 

A spectrophotometer was used to measure the IR transmittance of the DLC 

films deposited on the ZnS and ZnSe substrates. for the DLC films, 0.1 pm 

thick, deposited on ZnS or ZnSe and measured between 2.5 and 25 pm, the spectral transmittance of the material did not change in this wavelength region. 

The use of an intermediate Ge coating or ion implantation also did not seem 

6 
to alter the IR transmittance of the ZnS and ZnSe. Shown in figure 10 is the 

IR specular transmittance of a ZnSe substrate coated with a 0.1 pm thick DLC 

film from the single beam plus an intermediate layer of 0.03 pm Ge along with 

the transmittance of an uncoated ZnSe. Although there is a reduction in the 

IR specular transmittance due to the DLC/Ge film at shorter wavelengths, only 

a 1 percent loss occurs at 10 pm. 

In order to determine the protection the DLC films afforded the ZnS and 

ZnSe, the surfaces were first exposed to 27-pm-diam A1203 particles with an 

estimated stream velocity of 1100 ft/sec in a microsandblaster (ref. 27). The 

protective quality of the film was then characterized by the change in specular transmittance due to the particle erosion with the Perkin-Elmer spectrophotometer between 2.5 and 50 pm. Figure 11 indicates the change in specular 

transmittance at 10 pm due to total erosion time for various surfaces of ZnS 

coated with the DLC/Ge films. In the figure there is an envelope which portrays the erosion rate of the uncoated surface, which is necessary because 

each ZnS substrate had a slightly different initial transmittance due to the 

substrate thickness. As the figure indicates, neither the DLC/Ge films or ion 

implantation plus the DLC/Ge films afforded the ZnS surfaces any extension in 

particle erosion lifetime after exposure to the A1203 particles. The same was 

true for the ZnSe surfaces. 

The ZnS surfaces were also evaluated for rain erosion performance at 

Wright Patterson Air Force Base. 

rotating arm apparatus with speeds to 470 mph and a simulated rainfall of 

1 in./hr. Zinc sulfide, DLC/Ge coated ZnS, and ZnS first implanted with He 

ions at doses to 2x1017 particles/cm2 and then coated with the DLC/Ge films 

were subjected to the rain erosion. It was apparent from optically viewing 

the ZnS surfaces exposed to the water droplets at 400 mph, that there was an 

improvement in the performance in the ZnS surface which was ion implanted and 

coated with a 0.1 pm DLC film from'the single beam plus an intermediate layer 

of 0.04 pm Ge. The ion implantation plus the DLC/Ge coating resulted in a 

decrease in the number of new pits in the ZnS surface, and an increase in 

resistance to the formation of subsurface ring fractures. This could be 

expected since the ion implantation improved the physical hardness at the 

surface to a depth of -1.0 pm of the ZnS (ref. 26). There were no changes in 

the IR specular transmittance for the ZnS surface ion implanted and DLC/Ge 

coated after exposure to the rain erosion. 

The rain erosion facility consisted of a 

Although He ion implantation plus a DLC/Ge film did not afford any protection to the ZnS and ZnSe windows exposed to the simulated particle erosion, it 

did however, improve the performance of ZnS exposed to rain erosion. Hardening of the window surface by ion implantation plus the addition of a thick 

stress-free DLC film, may be a surface which would protect, thereby increasing 

the lifetime of infrared transmitting windows from both rain and less severe 

particle erosion. 

A systematic attempt to study the electrical characteristics of the DLC 

films on compound semiconductors and to explore their potential as a gate 

dielectric for insulated-gate technology for very high (1 to 00 GHz) speed 

integrated circuits was also performed (ref. 28). The DLC fi ms were direct 

deposited on indium phosphide (InP), gallium arsenide (GaAs), and Si semiconductor wafers to evaluate their potential as a new electronic material in a 

metal-insulator (carbon>-semiconductor (MIS) device configura ion for solid 

state power devices for space applications. 

7 
After directly depositing the DLC films, using both single and dual ion 

beams, on the p-type wafers, circular 0.5 pm aluminum (Al) gate electrodes were 

deposited on the DLC films from a resistance heated boat at 10-6 torr to form 

the MIS system. Ohmic contacts were formed by depositing 0.5 pm A1 on the Si 

back surface and 0.5 pm 5 percent Au-Zn alloy on fhe InP and GaAs back surfaces 

The contact metalization was then sintered at 375 C for 5 min. in forming gas. 

The fixed insulator charge number density of the MIS system was evaluated 

The analysis of 

This figure displays the variation of fixed insulator charge number 

by high frequency 1 MHz capacitance-voltage C-V measurements. 

the C-V data is shown in figure 12 for DLC films on InP, Si, and GaAs substrates. 

density as a function of the ion beam energy at which the DLC film was deposited 

on the substrates. The lower x-axis shows the energy of the single ion beam 

system, while the upper x-axis shows the energy of the dual ion beam system. 

The results show that the fixed insulator charge number density increases with 

ion beam deposition energy for all of the InP, GaAs, and Si substrates. 

Analysis of the quasistatic C-V data yielded a U-shaped distribution of 

interface state density for InP, GaAs, and Si substrates. Figure 13 shows the 

minimum interface state density in the middle of the band gap of the substrate 

as a function of ion beam energy of the deposition source. The lower and the 

upper x-axis are the same as in figure 12. The interface state density as a 

function of ion beam deposition energy increases dramatically for DLC films 

deposited on GaAs, increases slightly for DLC films deposited on InP, and 

remains essentially unchanged for DLC films deposited on Si substrates. 

Diamondlike carbon films do not appear to be a promising new electronic 

material as a gate dielectric for insulated-gate technology for application in 

microelectronics. This is due to low optical band gaps, low resistivity, very 

high fixed insulator charge number density, and high interface state deasity. 

In addition, these films generally decomposed at temperatures above 450 C, and 

therefore are not suitable for use in microelectronics processing. 

CONCLUSIONS 

A variety of plasma and ion beam methods were employed to generate diamondlike carbon films. These methods included RF sputtering, DC glow discharge, 

vacuum arc, coaxial carbon plasma gun, ion beam sputtering, and both single and 

dual ion beam deposition. Auger analysis of the single and dual ion beam deposited DLC films showed no evidence of any elements other than carbon and small 

amounts of argon and oxygen. SIMS analysis indicated that these ion beam deposited DLC films contained chemically combined hydrogen. Nuclear reaction and 

combustion analysis for hydrogen showed there was a variation in hydrogen content which depended upon the method used for deposition of the DLC film. 

hydrogen to carbon ratio of nearly one existed for single ion beam deposited 

films, while the ratio was reduced to 0.62 for the dual ion beam films. Films 

generated by ion beam or RF sputtering though, had low H/C ratios. The spectral transmittance for DLC films obtained from the single ion beam deposition 

method was similar to those generated using the dual beam source, whereas, the 

spectral transmittance of the ion beam sputtered DLC films was much lower than 

the direct deposited films. The low transmittance of the sputtered films may 

be due to ts low hydrogen content. Electron and x-ray diffraction patterns 

were found to be characteristic of an amorphous solid for DLC films either single or dua ion beam deposited, and for those films which were plasma gun 

depos i ted. 

A 

8 
Diamondlike carbon films from the single or dual ion beam deposition methods were impervious to reagents which dissolve graphitic and polymeric materials. 

other defects as determined by STEM. 

films though, STEM showed that particles and inclusions were randomly dispersed 

throughout the films. 

either diamond or graphite, therefore indicating that the long range structure 

of the films was not that of diamond. The ion beam sputtered and deposited 

films both exhibited a compressive stress, which did not depend on hydrogen content, but on other parameters such as deposition technique and conditions. 

The adherence of most of the DLC films was very good, but the films generated 

by the vacuum arc and plasma gun had poor adherences which was most likely due 

to the poor surface quality of these films. The microhardness of the RF sputtered and vacuum arc DLC films was comparable, but lower than the direct deposited films. All of the microhardness values were lower than diamond. The band 

gaps for the single and dual ion beam deposited DLC films were similar, while 

the RF sputtered, DC glow discharge, and ion beam sputtered films had band gaps 

which were higher. The coaxial carbon plasma gun DLC films had a band gap of 

-0 eV which was indicative of a graphitic structure. The DLC films had similar 

resistivities with the RF sputtered and DC glow discharge films somewhat higher, 

but all still lower than the resistivity of diamond. 

These direct deposited films were also smooth and free of pinholes or 

For the vacuum arc and plasma gun DLC 

The densities of the various DLC films were less than 

Although the physico-chemical properties of the DLC films varied, the 

films in general had characteristics which were desirable for certain applications. Therefore, the DLC films were evaluated as protective coatings for optical windows, and as a gate dielectric for insulated-gate technology. The DLC 

film did not afford any protection to the infrared windows exposed to simulated 

particle erosion, however, they improved the performance of ZnS exposed to rain 

erosion. Therefore, a thick stress-free DLC film may have the potential to 

increase the lifetime of an IR transmitting window. In the second application 

evaluation the DLC films were found to be deficient in electrical properties 

conducive to microelectronics. It can be seen from the properties, as well as 

the advantages and disadvantages of each DLC film deposition technique, there 

is the potential to tailor the characteristics of the DLC film to meet the 

needs of a particular application. 

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9 
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Khoroshikh, Sov. Phys. Tech. Phys., 25, 1164-1166 (1980). 

in Ion Implantation, S. Picraux and W. Choyke, eds., Proc. Materials Res. 

SOC. Meeting, Boston, MA, 433 (1981). 

17. B.A. Banks and S.K. Rutledge, NASA TM-82873 (1982). 

18. M.J. Mirtich, D.M. Swec, and J.C. Angus, NASA TM-83743 (1984). 

19. M. Marinov and D. Dobrev, Thin Solid Films, 42 267-268 (1977). 

20. D.M. Sater, D.A. Gulino, and S.K. Rutledge, NASA TM-83600 (1984). 

21. A. Benninghoven, Surf. Sci., 53, 596-625 (1975). 

22. J.C. Angus, J.E. Stultz, J.R. MacDonald, M.J. Mirtich, S. Domitz, and P.J. 

23. R.L. Bowman, M.J. Mirtich, and A.J. Weigand, NASA TMX-52687 (1969). 

24. J.C. Kolecki, NASA TM-82980 (1982). 

25. M.J. Mirtich, D. Nir, D.M. Swec, and B.A. Banks, NASA TM-87083 (1985). 

26. M.J. Mirtich, D. Nir, D.M. Swec, and B.A. Banks, J. Vac. Sci. Technol. A, 

27. D.M. Swec, M.J. Mirtich, D. Nir, and B.A. Banks, J. Vac. Sci. Technol. A, 

Shiller, Thin Solid Films, 118, 311-320 (1984). 

4, 2680-2681 (1 986). 

4, 3030-3031 (1 986). 

10 
28. V.J. Kapoor, M.J. Mirtich, and B.A. Banks, J. Vac. Sci. Technol. A, 4, 

1013-1017 (1986). 

TABLE I. - EVALUATION OF DIAMONDLIKE CARBON FILM DEPOSITION TECHNIQUES 

Property 

Adherence 

H/C ratio 

Density, g/cm3 

Band gap, eV 

Stress, dyne/cm2 

Microhardness, 

k g/rnn? 

ohm-cm 

Resistivity, 

Deposition rate, 

ithi n 

Major advantages 

Major 

disadvantages 

Ion beam 

sputter 

Very good 

0.22 

2.1 

0.909 

1 .6x1010 

5.29~10~ 

20 

Uniform films, 

good adhesion 

Low deposition 

rate 

Single ion 

beam 

Very good 

0.91 

1.8 

0.382 

0.9x1010 

5000 

8 .66x106 

60 

Uniform films, 

good adhesion 

Low deposition 

rate 

Deposition technique 

Dual ion 

beam 

Very good 

0.62 

1.8 

0.343 

0.9x 1010 

5000 

3.35~10~ 

60 

Uniform films, 

good adhesion 

Low deposition 

rate 

Vacuum 

arc 

Very poor 

1 ow 

2.75 

1050 

----______ 

-10,000 

Rapid 

deposition 

rate 

Inclusions 

RF sputter 

108 to 1012 

-1000 

Uniform films, 

simplicity 

Poor adhesion 

on metals 

ArI,A 

ION SOURCE 

!I Ar+*Ar - 

7 

\ 

\ 

\ 

\ 

\ 

\ 

I 

dc Glow 

discharge 

-600 

Simplicity 

Nonuniform 

films 

P1 ama 

Gun 

Figure 

-- 

I. - Schematic of dual ion beam deposition system. 

11 
-+ TO INSTRUMENTATION 

CURRENT-TRANSFORMER' 7 

CAPACITOR BANK, 

14 CAPACITORS AT 

400 pF EACH lOOOX VOLTAGE PROBE' 

H IG KVOLTAGE 

1 -*, - I '-COAXIAL RAILGUN 0-4 kV dC 

VOLTAGE Il 

CLAMPING PLUNGER 

REVERSAL L SOLENOID-OPERATED RELAY CONTACTS 

DIODE' 

'THESE COMPONENTS WERE CONTAINED WITHIN THE BUSBAR ASSEMBLY. WHICH IS NOT EXPLICITLY SHOWN 

IN THIS SCHEMATIC. 

Flgure 2. - Bask elements of coaxial carbon plasma gun deposition system. 

r WATER SUBSTRATE 

HEATER 7 

SUBSTRATE - 

Figure 3. - Vaarum arc deposition system. 

1. 12c 

12 
.8 ' 

W 

2 .6. a 

L 

f 

$ .4 

- 

t 

.2 - 

/ 

/ -- .15 

.- 71- 

0. 

(b) REFLECTANCE. 

.2 .4 .6 .a 1.0 1.2 1.4 1.6 

WAVELENGTH, pn 

(c) ABSORPTANCE. 

Figure 6. - Transmittance, reflectance and absorptance as a function 

of wavelength for various thicknesses of DLC films from the dual 

ion beam deposition system. 

'.O r 

THICKNESS, 

Cun 

A 0.15 DUALBEAM 

.15 SINGLEBEAM 

P 0 .05 SINGLEBEAM 

0 .17 SPUTTERED 

.4 .6 .8 1 .o 1.2 1.4 

WAVELENGTH, pn 

Figure 7. - Transmittance as a function of wavelength for 

DLC films deposited with the single or dual ion beam 

system and sputtered from a graphite target. 

13 
16 

01 

6 

f 

V x 

v) 

w 

U 

w 

v) 

v) 

W 

12 

kl 

2 

0 

E 

20x19 

- 

- 

8- 

4- 

1200 

01 

E 

E 

p 1100 

I I I 1 

ma 

v) 

W 

2 

U 

2 

g 1000 Y 

c 

A 25 

050 

0 100 

0 200 

900 

0 .1 .2 .3 .4 .5 

THICKNESS, p 

Figure 9. - Microhardness as a function of film thickness 

and load for DLC films RF sputter deposited. 

UNCOATED ZnSe - 

0.03 prn Ge + 0.1 p DLC \ 

2.5 4.0 5.0 6.0 10.0 20.0 

WAVELENGTH, prn 

Figure 10. - Specular transmittance of a DLC film from the single ion beam deposition system plus an intermediate layer of Ge on ZnSe and uncoated ZnSe. 
ION BEAM ENERGY, DUAL BEAM, eV 

8c 

s 

8 w 70 

n 

W 

a 

< 

I 5 

40 

n 

u) 

30 

- ...................................................... 

............ ............................ ..... . ,...................... _... UNCOATED ZnS 

------ He IMPLANTEDAT~x~O~~/C~~+ DLC 

- - - He IMPLANTED AT 2~10~~/cm~+ DLC 

---- SPUITERED 

--- SINGLE BEAM 

- 

0 2 4 6 8 lo 

EXPOSURE TIME, min 

Figure 11. - Change in specular transmitrance at 10 pm due to total 

erosion time for various surfaces of ZnS coated with DLClGe films. 

136 205 

I I - 

I I 

133 200 

ION BEAM ENERGY, SINGLE BEAM, eV 

Figure 12. - Variation of me flxed insulator charge number 

density as a function of ion beam deposltion energy for 

DLC films on GaAs. InP, and Si. 

E 

ION BEAM ENERGY, DUAL BEAM, eV 

133 200 

ION BEAM ENERGY, SINGLE BEAM, eV 

function of ion beam depwitlon energy for DLC films on Gals, InP and SI. 

Figure 13. - Variation of the interface state density as a 

T 

si 

15 
National Aeronautics and 

Space Administration 

1. Report No. 

NASA TM-102301 

Report Documentation Page 

2. Government Accession No. 

7. Author(s) 

Diane M. Swec, Michael J. Mirtich, and Bruce A. Banks 

9. Performing Organization Name and Address 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135-3191 

2. Sponsoring Agency Name and Address 

National Aeronautics and Space Administration 

Washington, D.C. 20546-0001 

3. Recipient's Catalog No. 

5. Report Date 

6. Performing Organization Code 

8. Performing Organization Report No. 

E-4980 

IO. Work Unit No. 

506-4 1-42 

11. Contract or Grant No. 

13. Type of Report and Period Covered 

Technical Memorandum 

14. Sponsoring Agency Code 

5. Supplementary Notes 

Presented at the 32nd Annual International Technical Symposium on Optical and Optoelectronic Applied Science 

and Engineering sponsored by the Society of Photo-Optical Instrumentation Engineers, San Diego, California, 

August 14-19, 1988. 

6. Abstract 

At the NASA Lewis Research Center a variety of plasma and ion beam techniques have been employed to generate 

diamondlike carbon films. These methods include the use of RF sputtering, DC glow discharge, vacuum arc, 

plasma gun, ion beam sputtering, and both single and dual ion beam deposition. Since the films have been 

generated using a wide variety of techniques, the physico-chemical properties of these films vary considerably. In 

general, these films have characteristics that are desirable in a number of applications. For example, the films 

generated using both single and dual ion beam systems were evaluated for applications including power electronics 

as insulated gates and protective coatings on transmitting windows. These films were impervious to reagents 

which dissolve graphitic and polymeric carbon structures. Nuclear reaction and combustion analysis indicated 

hydrogen to carbon ratios to be 1.00, which allowed the films to have good transmittance not only in the 

infrared, but also in the visible. Other evaluated properties of these films include band gap;' resistivity, adherence, 

density, microhardness, and intrinsic stress. The results of these studies and those of the other techniques for 

depositing diamondlike carbon films are presented in this paper. 

7. Key Words (Suggested by Author(s)) 

Diamondlike carbon films 

Ion beam and plasma deposition 

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