‘‘Diamondlike’’ carbon films: Optical absorption, dielectric properties, and hardness dependence on deposition parameters

Natarajan, V.; Lamb, Joel D.; Woollam, John A.; Liu, David C.; Gulino, Daniel A.

doi:10.1116/1.573280

Cited by 29 publications

(3 citation statements)

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“…A marked decrease in ER vs. P is apparent, denoting a harder and/or denser film with increasing deposition power. A qualitatively similar result was reported earlier for hardness vs. deposition power (17).…”

Section: Resultssupporting

confidence: 91%

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Ellipsometric and Optical Study of Amorphous Hydrogenated Carbon Films

Alterovitz

Warner

Liu

et al. 1986

J. Electrochem. Soc.

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A low-frequency plasma deposition system was used to prepare amorphous hydrogenated carbon (a-C;H) films. The growth energy was varied by changing the power and/or pressure of the plasma. Ellipsometry and optical absorption were used to obtain the optical energy gap, the density of states, and the refractive index. Ion sputtering was used in conjunction with ellipsometry and Auger electron spectroscopy to get absolute sputtering rates. The plasma deposited a-C:H is amorphous with optical energy gap of approximately 2.0-2.4 eV. These a-C:H films have higher density and/or hardness, higher refractive index, and lower optical energy gaps with increasing energy of the particles in the plasma, while the density of states remains unchanged. These results are in agreement and give a fine-tuned positive confirmation to an existing conjecture on the nature of a-C:H films (1).Insulator films on semiconductors have a wide variety of applications, including passivation, insulation, capping, etc. In the case of silicon, the silicon based films SiO2 and Si3N4 have been successfully used for all the required applications. However, the need for high-speed devices and integrated circuits requires the use of Group III-V semiconductor devices and substrates. SiO~ and Si3N4 proved to be inadequate for some of these applications for Group III-V semiconductors. Thus, new types of insulator films for one or more of the required applications are needed. In this study we have chosen a-C:H for the insulator film. Some of the attractive properties of a-C:H are: (i) it is easily prepared as a homogeneous film (2): (it) it is very hard mechanically and chemically: (iii) it has a high breakdown voltage (3) and resistivity: (iv) it has a relatively low interface density of states on Si (4) and InP (3): (v) it has a variable energy gap (1, 5); and (vi) it can be used in metal-insulator-metal (MIM) structures (6).However, not all the desirable properties are achieved in a single sample, i.e., the highest energy gap sample will have a rather low mechanical hardness (1). It was suggested in Ref.(1) that the growth energy environment controls the energy bandgap, the hardness, the hydrogen concentration, and bond type. Thus, it may not be possible to optimize all the desirable parameters simultaneously. This conjecture was made using samples made by different deposition methods having very large variations in growth environment energy. In the present work, we report a study of a-C:H films made by varying the growth energy in a continuous way, i.e., varying the plasma power, and/or pressure, and/or the substrate temperature during deposition. We have used ellipsometry, UV-visible absorption, and Auger electron spectroscopy (AES) profiling for sample characterization. These techniques give us energy gaps, density of state parameters, indexes of refraction, and sputtering rates. We have correlated these results with the growth environment energy in order to check the conjecture of Ref.(1). ExperimentalThe sample preparation will be discussed only very ...

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Section: Resultssupporting

confidence: 91%

“…Thus the density of states is not changing as a function of the deposition power in this case. The value of B is 300 cm ~/2 eV-~/s, vs. 750 cm -~/2 ev -w~ for a-Si~C~_~ (16) an d in good agreement with results deduced from plasma deposited a-C:H films (17,18). The optical gap, Eo, found from Fig.…”

Section: Resultssupporting

confidence: 87%

Ellipsometric and Optical Study of Amorphous Hydrogenated Carbon Films

Alterovitz

Warner

Liu

et al. 1986

J. Electrochem. Soc.

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“…As a consequence, the optical gap of the films decreases and their conductivity increases with growing ion impact energy. For intermediate and high values of the energy, the optical gap can change from 2.7 to 1.0 eV, and the conductivity from 10 -13 to 10 2 S/ m. − These differences, which are commonly attributed to sp 2 sites, resemble those characteristic of the a-I and a-S forms of the a-Ge X C Y :H films under discussion.…”

Section: Introductionmentioning

confidence: 95%

Transition from Amorphous Semiconductor to Amorphous Insulator in Hydrogenated Carbon−Germanium Films Investigated by Raman Spectroscopy

Kazimierski¹,

Tyczkowski²,

Kozanecki

et al. 2002

Chem. Mater.

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Amorphous hydrogenated carbon-germanium films (a-Ge X C Y :H) were fabricated by plasma chemical vapor deposition in an audio frequency (af) three-electrode reactor using tetramethylgermane (TMGe) as a source compound. Two types of the material, namely semiconducting (a-S) and insulating (a-I) films characterized by quite different electronic properties, were produced. For example, electrical conductivity at room temperature, T room , amounts to approximately 10 -18 S/m (with activation energy E A ≈ 0.9 eV) and 10 -4 S/m (E A ≈ 0.3 eV) for a-I and a-S, respectively. This very drastic change in the electronic structure of the a-Ge X C Y :H films can be caused by a very small variation of the plasma deposition conditions and therefore it is termed a-I-a-S transition. The previous attempts to explain the nature of the a-I-a-S transition from the molecular and supermolecular point of view (quantitative chemical microanalysis, XPS and IR spectrscopies, TEM, SEM, electron diffraction, and AFM) have failed. In this paper Raman spectroscopy has been used to this end. It has been found that the carbon structure does not determine the electronic properties of the films and sp 2 sites are not responsible for the a-I-a-S transition. This conclusion is supported by investigations on a-Ge X C Y :H films, in which sp 2 sites are purposely created. On the other hand, a drastic difference in the Ge atoms dispersion in the a-I and a-S has been found. In the a-I films a great amount of Ge atoms is molecularly dispersed, whereas in the a-S films the vast majority of Ge atoms is in the form of a-Ge several-nanometersized clusters. It is suggested that these clusters play a crucial role in the formation of the amorphous semiconductor network and they are responsible for the a-I-a-S transition.

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Surface modification of plastics by plasma treatment and plasma polymerization and its effect on adhesion

Carlsson¹,

Johansson²

1993

Surface & Interface Analysis

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The adhesion between plasma-modified polyethylene (PE) and Merent polar polymers, as well as aluminium and steel, has been studied. The PE was modified by either oxygen plasma treatment or plasma polymerization of acrylic acid. The results show the importance of introducing polar groups on the surface of the non-polar PE in order to improve the adhesion to polar polymers as well as metals. Laminates made of plasma-modi6ed PE and polyamide 6 (PA-6) or poly(ethy1ene vinyl alcohol) (EVAL-G) showed failure in P A 4 or EVAGG when delaminated. Poly(ethy1ene terephthalate) (PET), which is not as polar as P A 4 or EVAIPG, showed an adhesive failure when the PE was treated with either of the plasma methods. However, when both the PET and the PE were modified, the failure occurred in the PET upon delamination. Oxygen plasma treatment of PE resulted io an increased adhesion when laminated with cellophane, with no observed material failure. The laminates composed of plasma-mdied PE and aluminium or steel showed cohesive failure in the PE.

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‘‘Diamondlike’’ carbon films: Optical absorption, dielectric properties, and hardness dependence on deposition parameters

Cited by 29 publications

References 0 publications

Ellipsometric and Optical Study of Amorphous Hydrogenated Carbon Films

Ellipsometric and Optical Study of Amorphous Hydrogenated Carbon Films

Transition from Amorphous Semiconductor to Amorphous Insulator in Hydrogenated Carbon−Germanium Films Investigated by Raman Spectroscopy

Surface modification of plastics by plasma treatment and plasma polymerization and its effect on adhesion

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