Titanium containing DLC coatings from a PACVD process using titanium (IV) isopropylate as a precursor

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Abstract

We report here the plasma activated deposition of Ti-DLC films using titanium (IV) isopropylate as a precursor. Gas phase processes during film deposition were analyzed using a differentially pumped quadrupole mass spectrometer (QMS). The film composition and the chemical nature of the film elements Ti, C and O were obtained using X-ray induced photoelectron spectroscopy (XPS). These measurements were complemented by the determination of the film growth rate. With decreasing USB (increasing rf power) the QMS measurements demonstrated a change in the fragmentation pattern of the precursor, especially in the range of USB between −100 and −300 V. These gas phase changes correlate with changes in the film composition, film hardness and adhesion behavior. With XPS we determined for USB=−900 V the film composition of Tisingle bondOsingle bondC:H coatings to be: 48 at% C, 29 at% O and 23 at% Ti. We note that the Ti content of the film is significantly higher than that of the precursor (5.9 at% Ti). With decreasing self-bias voltage (−100 to −400 V) the C/Ti ratio in the films decreases from 2.5 to below 2. Further, we note also a slight decrease of the O/Ti ratio with decreasing USB. Analyzing the Ti 2p doublet with XPS we find that for USB=−100 to −200 V, TiO2 is the predominant Ti species. For USB≤−200 V a second Ti doublet evolves at lower binding energy which is related to the presence of TiC. The development of Tisingle bondC bonding is also detected in the C 1s spectra.

Introduction

Titanium and titanium oxide are well known materials with good biological compatibility. This is also the case for the DLC material. Therefore, titanium containing DLC coatings is of interest for applications in medical implantation.

Recently, we reported on Ti-DLC film deposition from titanium ethoxide [1]. In this investigation we showed that the Ti content of the deposited films, depending on the experimental conditions, was much higher than that of the MO precursor. Further, we observed the formation of Tisingle bondC bonding for decreasing self-bias voltage. In the present paper these investigations with Ti containing precursors are expanded to the titanium (IV) isopropylate compound in order to detect common behavior.

Section snippets

Experimental

For the deposition of Ti containing DLC films we used a plasma activated process (PACVD). Experimental details have recently been published elsewhere [2]. We reported on the deposition of Fe and Ti containing amorphous carbon films from various solid volatile iron–organic chemicals such as ferrocene [Fe(C5H5)2] [2], [3], [4], [5], cyclooctatetraen-iron-tricarbonyl [C8H8single bondFe(CO)3] [4], [5], methyl-cyclopentadienyl-iron-dicarbonyl [Cpsingle bondFesingle bondCH3single bond(CO)2] [5] and fluid titanium ethoxide [1].

In the present

Film growth rates and simple mechanical testing

The growth rates determined with a profilometer (alpha-step 200, Tencor Instruments) as a function of the self-bias voltage USB during deposition are shown in Fig. 2. We observe a steep decrease of the growth rate in the self-bias voltage regime from 0 to about −300 V (referred to as region 1, from about 3.5 to about 1.5 μm/h). For self-bias voltages of −400 to −1000 V (region 2) the growth rate is within the scattering bars (Fig. 2) constant. The decreasing growth rate with decreasing self-bias

Conclusions

We briefly summarize the main conclusions of our present study.

  • 1.

    We successfully deposited hard Ti containing films from the Ti(IV) isopropylate using a plasma activated process. The film composition is in the range of Ti:O:C=23:29:48 at%. The Ti content in the film is much higher than in the MO precursor.

  • 2.

    In order to deposit films with high hardness and good adhesion to the Si substrate, negative self-bias potential below −300 V had to be applied.

  • 3.

    The increased hardness and better adhesion for high

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1

Present address: Institute of Physics, University of Basel, Klingelbergstr. 82, CH-4056 Basel, Switzerland.

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