Gross R., Sidorenko A., Tagirov L. Nanoscale Devices

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392 B. Z. Mansurov

Estimation of electrostatic field effects on the energy

conditions for diamond and graphite

The estimation of the effects of electrostatic and magnetostatic fields on the

energy state of diamond and graphite nuclei located in these fields, is

completed by the limited version of the simulation program ELCUT (see

http://www.tor.ru/elcut).

On Fig. 3 the schematic model of the installation is presented.

Fig. 3. Schematic model of the installation: 1 - quartz; 2 - anode; 3 - nuclei; 4 -

substrate-cathode.

Under the above-mentioned conditions of electrode mounting, the energy

of the electrostatic field is concentrated in the center of the substrate.

Putting a diamond and graphite nuclei of various shapes in the center of the

substrate, the following results were obtained. In the Fig. 4 the

characteristic distribution of the energy density of the electrostatic field is

shown. In the Table 1 the density of the electrostatic field energy in the

volume limited by nuclei of diamond, graphite and in the same volume

without any nuclei in the vacuum is presented.

Fig. 4. Distribution of the energy density of the electrostatic field.

The Influence of Applied Field on the Nucleation and Growth 393

As shown in Table 1, for a columnar growth the energy density in

volume in comparison with vacuum increases both for graphite and for

diamond. For a platelet type growth parallel to the surface the energy

density decreases in both cases, however, it decreases stronger for diamond

nuclei. Thus, the growth along the substrate surface is the most favourable

for diamond. The columnar growth is unfavourable both for graphite and

diamond.

Table 1. Density of the electrostatic field energy in the volume limited by nuclei of

Material Shape

density of electrostatic field energy, ×10

-10

J/m

Vakuum 2.667

Graphite 2.684

Diamond

5.807

Vakuum 2.504

Graphite 2.501

Diamond

1.288

Estimation of magnetic field effects on the energy conditions

for diamond and graphite

Similar estimations have been made also for magnetic fields. The

calculations showed that a constant magnetic field does not have a

significant influence on the energetics of the state of the nuclei due to the

tiny difference of the magnetic susceptibilities for various carbon

modifications (for diamond

= -1.726.10

-12

, for graphite

= -51.665.10

= -0.906.10

-12

[7]). However, it has significant influence on the carbon

ions deposited on the substrate. As shown in ref. [8], the hardness of carbon

films may be considerably increased, if a magnetic field is applied in the

deposition process.

Not only the strength of the applied magnetic field has influence on the

magnitude of thermodynamic functions but also the symmetry of the field

with respect to the structure of crystalline film and its nuclei. The copper

structure saturated with hydrogen determines the symmetry of surface

forces which is appropriate for a diamond structure. The distribution of

electrodes and their shapes should therefore form the symmetry of diamond

structure.

diamond, graphite and in the same volume without any nuclei in the vacuum.

394 B. Z. Mansurov

Method of Differential Magnetron Sputtering

The pressure of the saturated carbon vapours at a temperature of 500 K is

P = 10

-35

Torr. In contrast, the typical background pressure in the deposition

chamber in the process of plasma-chemical vapour deposition is P ≈ 10

-5

Torr. This pressure should be lower than the pressure of the carbon vapour

(a molecular stream) by 2 to 3 order of magnitude, i.e. P

≈ 10

-2

-10

-3

Torr.

Then, mass chaotic crystallization occurs at such (10

) oversaturation.

For the artificial reduction of the carbon oversaturation the essentially

new technique of the differential magnetron sputtering, which is based on

the balancing of streams of carbon from two magnetrons, is offered. This

technique will allow to solve the basic problem of the gas-phase synthesis

of diamond - the problem of irreversibility of the diamond growth process.

It will enable to grow diamond and diamond-like films with instrument

quality. Moreover, such tool enables the improvement of recipes for

epitaxial film growth in the presence of passivating gases with methods of

hydrocarbon decomposition, and also technological methods used for the

doping of film with well defined doping concentration.

On the basis of our theoretical calculations the technological apparatus

for the growth of carbon films by the method of differential magnetron

sputtering has been developed and designed. Figure 5 show a cross-

sectional view of the deposition apparatus. Two magnetrons (1) are located

symmetrically with respect to the copper anode (6). The experimental study

of the influence of the symmetry of external fields on the nucleation and

growth of the carbon films is carried out with three forms of anodes, which

have various axes of symmetry (3-fold, 4-fold, ∞). Laser irradiation of the

substrate comes from a source (7) located outside of the chamber by means

of the window VUP-5M (Vacuum Universal Post) and the mirror (9).

At the first stage, for depositing a copper buffer layer, copper atoms are

sputtered from the target (8) by Ar ions. On the second magnetron the

substrate (3) is located. The electrostatic field determines the energy of the

surface bombardment of a nucleus and a film, and, hence, it determines the

temperature of an adsorption layer and the speed at which the film is etched

away. The heaters (2) set the substrate temperature.

The deposition process of copper has to be performed in a mixed argon -

hydrogen atmosphere.

the second stage there is a change from the copper target to a

graphite one and then the carbon deposition is carried out in an argon

atmosphere.

Change of the voltage applied between the target and the

anode as well as between the substrate and the anode controls the streams

of carbon onto the substrate and from it.

The Influence of Applied Field on the Nucleation and Growth 395

Fig. 5. Cross-sectional view of the apparatus used for the growth of carbon films

by the method of differential magnetron sputtering: 1 - magnets: 2 - heaters: 3 - the

substrate - cathode: 4, 5 - a quartz: 6 - the anode: 7 - light source: 8 - cathode -

target: 9 - a mirror.

Calculation of the differential magnetron sputtering system

parameters

In order to define the optimum modes for the growth of carbon films on a

copper buffer layer the following calculations have been carried out:

1. Calculation of the analytical dependences of technological parameters

396 B. Z. Mansurov

for the deposition process of a copper buffer layer in the atmosphere of

argon - hydrogen:

• Dependence of the sputtering coefficient of copper on the applied an-

ode – target voltage

• Dependence of the sputtering coefficient of copper on the concentra-

tion of hydrogen in an argon – hydrogen gas mixture

• Dependences of the sputtering and deposition velocities of copper on

the applied voltage and the concentration of hydrogen

2. Calculation of the analytical dependences of the technological

parameters of the deposition process of a carbon film in an argon

atmosphere:

• Dependence of the sputtering coefficient of graphite on the anode –

target voltage

• Dependence of the sputtering and deposition velocities of carbon on

the applied voltage and the discharge current density.

The results of the calculations are presented in Figures 6 and 7:

Fig. 6. Dependence of the sputtering coefficient of graphite on the target – anode

voltage.

The Influence of Applied Field on the Nucleation and Growth 397

Fig. 7. Dependence of the deposition velocity of a carbon film on the discharge

current and the applied voltage.

The algorithm of deposition process of carbon films on a copper buffer

layer developed on the basis of the obtained analytical dependences of

deposition parameters is presented in the scheme shown in Fig. 8.

398 B. Z. Mansurov

Fig. 8. The scheme of the deposition process.

Conclusion

We have shown that the conditions for the preferential nucleation and

growth of a diamond film might be created through changing the magnitude

and shape of applied fields. It was proven that to obtain high quality

diamond films it is necessary to create an intermediate buffer layer with

diamond-like physical-chemical properties. It was found that copper

saturated with hydrogen is an appropriate material for the buffer layer with

atomic hydrogen in tetrapores of the lattice acting as crystallisation centers

for the diamond film. The distribution of tetrapores on the copper (111)

surface and, respectively, of the atomic hydrogen located in them, creates

the conditions for preferential formation of tetragonal carbon bonds. We

developed a mathematical algorithm for modelling the deposition process

on the basis of theoretical calculations carried out earlier. This allows us to

offer a theoretical model for the essentially new technological method of

differential magnetron deposition of carbon films.

References

1. May PW (2000). Phil Trans R Soc Lond A358:473-495

2. Martorell IA, Partlow WD, Young RM, Schreurs JJ, Saunders HE (1999).

Diamond and Related Materials 8:29-36

The Influence of Applied Field on the Nucleation and Growth 399

3. Cui JB, Shang NG, Liao Y, Li JQ, Fang RC (1998). Thin Solid Films 334:156-

160

4. Takeyasu Saito, Masanori Kameta, Katsuki Kusakabe et al. (1998). Journal of

Crystal Growth 191:723-733

5. Bartsch K, Waidmann S et al. (2000). Thin Solid Films 377-378:188-192

6. Mansurov BZ, Aknazarov SKh, Grinev VP, Lezbaev BT (1997) International

Symposium “Chemistry of Flame Front”. Proceeding, Almaty, Kazakhstan pp

144-149

7. Samsonov GV (ed) (1965) Physical – Chemical Properties of Elements.

Naukova Dumka, Kiev

8. Hou QR, Gao J (1998). Applied Physics A: Materials Science & Processing

A67:417-420

9. Mansurov BZ, Kalykova G, Myasnikova N, Mikhailov L (2001). Eurasian

Chemico-Technological Journal 3:211-214

Gross R., Sidorenko A., Tagirov L. Nanoscale Devices - Fundamentals and Applications

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