Evaluation of Surface Cleaning Procedures for CTGS Substrates for SAW Technology with XPS.

Erik Brachmann,Marietta Seifert,Steffen Oswald,Siegfried Menzel,Thomas Gemming

doi:10.3390/ma10121373

Erik Brachmann, Marietta Seifert + Show 3 more

Open Access

https://doi.org/10.3390/ma10121373

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Abstract

A highly efficient and reproducible cleaning procedure of piezoelectric substrates is essential in surface acoustic waves (SAW) technology to fabricate high-quality SAW devices, especially for new applications such SAW sensors wherein new materials for piezoelectric substrates and interdigital transducers are used. Therefore, the development and critical evaluation of cleaning procedures for each material system that is under consideration becomes crucial. Contaminants like particles or the presence of organic/inorganic material on the substrate can dramatically influence and alter the properties of the thin film substrate composite, such as wettability, film adhesion, film texture, and so on. In this article, focus is given to different cleaning processes like SC-1 and SC-2, UV-ozone treatment, as well as cleaning by first-contact polymer Opticlean, which are applied for removal of contaminants from the piezoelectric substrate CaTaGaSiO. By means of X-ray photoelectron spectroscopy, the presence of the most critical contaminants such as carbon, sodium, and iron removed through different cleaning procedures were studied and significant differences were observed between the outcomes of these procedures. Based on these results, a two-step cleaning process, combining SC-1 at a reduced temperature at 30 C instead of 80 C and a subsequent UV-ozone cleaning directly prior to deposition of the metallization, is suggested to achieve the lowest residual contamination level.

Highlights

For the preparation of high-quality thin films on substrates a clean surface of the substrates is indispensable
Since one aim of this work is to compare the results of the cleaning procedures on Ca3 TaGa3 Si2 O14 (CTGS) with those obtained on Si substrates, in each figure the results for Si are presented
Six different substrate-cleaning procedures for CTGS substrates have been evaluated with respect to the residual contamination by means of X-ray photoelectron spectroscopy (XPS) measurements

Summary

Introduction

For the preparation of high-quality thin films on substrates a clean surface of the substrates is indispensable. The high surface sensitivity (information depth below 5 nm) allows the detection of surface contamination monolayers as well Another advantage of XPS is it is possible to investigate electrically insulating samples like CTGS substrate, since no charged particles are used for excitation. The use of both acetone and ethanol for cleaning samples is common in laboratory settings, since both solvents are commonly available in laboratories and are quite easy to handle compared to use of acids in the RCA procedure This cleaning method is included in our investigations to study its suitability for removal of contaminants. Menon et al developed a cleaning procedure for removing inorganic particles using a mixture of acetone and ethanol (volume ratio 1:1) in an ultrasonic bath for 15 min at room temperature [16] After this cleaning step, the sample was rinsed twice with ultrapure water followed by an ultrasonic bath for 15 min. The samples are flushed with isopropanol, followed by further cleaning by rinsing the samples in isopropanol in an ultrasonic bath for 15 min at room temperature

RCA Clean Procedure

Modified RCA-Cleaning Procedure

Cleaning in UV-Ozone Atmosphere

Cleaning by Use of Opticlean First-Contact Polymer

Results and Discussion

Summary and Conclusions