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Evaporation of Adherent Al-Films on Single Crystalline LiNbO3 Substrates

Evaporation of Adherent Al-Films on Single Crystalline LiNbO3 Substrates Active and Passive Elec. Comp., 1992, Vol. 14, pp. 245-249 Reprints available directly from the publisher Photocopying permitted by license only () 1992 Gordon and Breach Science Publishers S.A. Printed in the United Kingdom EVAPORATION OF ADHERENT AI-FILMS ON SINGLE CRYSTALLINE SUBSTRATES LiNbO3 E. SCHIPPEL Department Electrotechnics, Technical University 0-2400 Wismar, Germany of is used as a single crystalline substrate material for the manufacturing of surface acoustic wave LiNbO3 devices as frequency selective components. On the polished substrate wafer, AI with a film thickness of about 400 nm is evaporated in a high vacuum. The difficulties of the inadequate adhesion of the structured Al-film were eliminated by systematical investigations. Films that were adherent to the total surface could be prepared by evaporating an intermediate film of Cr or or, otherwise, a mixed film of AI with Si. SiOx was an assessment of local and An ultrasonic test for adhesion strength developed that results in also large-area film adhesion. I. INTRODUCTION is material. For electronics, Lithium niobate a very interesting Because (LiNbO3) of its is and It is a ferroelectric material crystal class 3m, trigonal polar. LiNbO3 and coefficients. with large pyroelectric, piezoelectric, electro-optic, photo-elastic static occur on the substrate surface because of Therefore, electric charges may detailed of the structure and the temperature variations. A description crystal characteristics of the are WEIS and GAYLORD 1. physical given by LiNbO3 The of the can be made the Czochralski method. growth single crystals by LiNbO3 To avoid areas of different in a the the of polarity crystal, polarity during growing 2,3. a above the of 1140C can be set an electric field crystal Curie-temperature by A field of of is the of surface acoustic wave application manufacturing LiNbO3 devices. For that a metal film is onto a purpose evaporated polished single crystalline substrate wafer vacuum. An structure is then in high interdigital generated by means of The structure consists of two "combs" of photolithography. interdigital different and size. The structural widths of electrodes of the shape interdigital structure are less than 15 The of the filters on the frequency range depends tm. structural of more than 300 electrode widths of width; frequencies MHz require about The electrical contact is created of Al-wires to the structured 1/zm. by bonding metal film. A adhesion of the metal film on the surface good strength evaporated vibrating is for the function of the filters. the cut there absolutely necessary Concerning yz were of adhesion bonds with the 38-cut. problems 245 246 E. SCHIPPEL II. EXPERIMENT In production, the polished wafers are given a short treatment with various LiNbO3 chemicals. Therefore, tests of various pretments of the wafers were made. LiNbO3 After a standard cleaning with acetone in an ultrasonic bath, the wafers were treated at 20C and 50C for 5 min and 20 min with the following chemicals: 1. HF, 20% solvent NH3 2. Chromium-sulphuric acid 3. NaOH, 20% solvent 4. PO4, concentrated solvent H3 5. F2, concentrated solvent H2 An assessment of the efficiency of the chemicals with respect to the surface of wafers resulted from electron microscopic photographs. LiNbO3 In another test series, standardized cleaned and pre-treated glass and LiNbO3 substrates were coated under the same conditions with A1 by evaporization. These tests should show differences between the adhesion of A1 films to amorphous glass and crystalline LiNbO3. In general, the evaporation was done from W-boats on the substrates in vacuum with and without a glow discharge. For the manufacturing of a mixed film, AI and the additives Cu, Si and Ni were evaporated from separate boats. The thickness of the mixed film was 20 nm to 50 nm. Above it, pure A1 was evaporated up to a thickness of 400 nm. Cr For the manufacturing of intermediate films, as an insulator or as a SiOx metal first a were evaporated to maximum thickness of 30 nm, followed by pure of nm. AI evaporated up to a total thickness 400 To investigate the adhesion of the evaporated films a test method was developed. The are immersed into a solvent and samples (e.g., acetone, xylene) ultrasonically 4. The test method is to the extent of adherence of the to the agitated sensitive film substrate. The test method can be into a incorporated production process because it is non-distructive of adherent films. fully this test non-adherent or not adherent films removed By method, sufficiently are from the and obscure a film. substrate visually as spots without By the proper choice of solvent for ultrasonic and sound-transmission, frequency treatment time, the test method can be to the adhesion bond 4. adapted necessary for the product For the assessment of the a screen of 1 mm x 1 was to investigations, mm used measure the area of substrate without a film. III. RESULTS From electron microscopic investigations, the surface of the wafer appears LiNbO3 to be affected in different ways by different chemicals. There is no surface effect due to HE The largest which are to the NH3 etching pits, arranged according crystal symmetry, are produced by 1 shows the classification of the chemicals Fig. H2 F2. EVAPORATION OF ADHERENT AI-FILMS 247 Effect of Etching 1 2 3 4 5 FIGURE Classification of chemicals to the effect on the wafer. according etching LiNbO3 HF (20% solvent), lmNH3 acid 2mChromium-sulphuric 3--NaOH (concentrated solvent) 4---H3 PO4 (concentrated solvent) 5--H_, (concentrated solvent). F2 to the effect on the wafer. It was found that the treat- according etching LiNbO3 ments of the wafer with acid and will chromium-sulphuric improve LiNbO3 H3 PO4 the adhesion of the A1 film. 2 shows that the adhesion of the A1 film is worse on Fig. clearly essentially than on After a test time of 10 min the A1 film has been 60% glass. nearly LiNbO3 dissolved from the while it is still on the surface to more than LiNbO3, glass up 90%. For the film with an film on the substrate, it was found that systems underlying the adhesion of the A1 film with an A1Si mixed film is excellent as 3 along Fig. shows. AI films with an mixed film of A1Cu have better adhesion than underlying with AINi mixed films or films of AI. To retain the filter function of the pure the thickness of the mixed film must not succeed 30 to 40 nm5. component, An excellent adhesion is also to be found with the A1 films with an intermediate 6O Substrate 2O ’1 2 3 4 5 6 7 8 9 10 rain Time for Ultn3scic Test FIGURE 2 Area without after ultrasonic test of on and layer pure AI film glass- in LiNbO3-substrate percent. 248 E. SCHIPPEL AINi 8O 6O AtCu z, 0 2 3 9, 5 6 7 10 min Time for Ultrasonic Test FIGURE 3 Area without after ultrasonic test of AI film and AI films with below mixed films of layer AISi, AICu and AINi on in LiNbO3 percent. of the materials or Cr. After a test time of 10 min there are no dissolutions layer SiOx of the A1 film to be seen. A is before the glow discharge necessary evaporization of A1 on the intermediate 6. The is not at the layer glow discharge necessary SiOx of A1 on the intermediate Cr The excellent adhesion of the evaporization layer. AI film can be reached with thin intermediate of less than 20 nm. With very layers thicker intermediate determined of the filter can be layers, changes component 7,8. reached to the according patents IV. CONCLUSION The of the adherent metallization of substrates with A1 investigation by LiNbO3 show that a suitable combination of substrate film evaporization by pretreatment, and methods, total-area well-adhered films can be system, technological evaporated in a For film AI films with films reproductible way. composite systems, underlying of A1Si, SiOx, or Cr are suitable. To get results of the adhesive bond of films, a test ultrasonic agitation, was The test method is methodemploying developed. applicable in the manufacturing process, as well as for testing the adhesion of films that have been structured by a method. photolithographic REFERENCES 1. R.S. Weis and T.K. Gaylord: Lithium niobate: summary of physical and crystal structure properties Appl. Phys. A37 191-203. (1985) 249 EVAPORATION OF ADHERENT AI-FILMS 2. P.W. and P.D. Townsend: A method of and below Haycock poling LiNbO3 LiTaO3 Tc Appl. Phys. 48 698-700. (1986) 3. P. Reiche, J. Bohm, B. Hermoneit, P. and D. Schulze: von Rudolph Wachstumsmorphologie bei der nach dem Czochralski-Ver-fahren unter der Einwirkung LiNbO3-Einkristallen Ziichtung eines elektrischen Feldes Cryst. Res. Technology 23 467-474. (1988) 4. E. and A. Piech: Verfahren zur Priifung der Haft-festigkeit von aufgedampften Schichten Schippel Patent (application 1989) 5. E. T. V61ker and A. Breitlauch: Schichtsystem zur haftfesten Metallisierung piezoelek- Schippel, trischer Substratmaterialien Patent DD 276 697. 6. E. Schippel and M. Schmidt: Verfahren zur haftfesten Metal-lisierung von piezoelektrischen Ma- terialien Patent DD 264 943. 7. Akustisches Oberflichenwellenwandler-System Patent D 2238 925.9. 8. Schallwandler for akustische Oberflichenwellen Patent D 2431 620.0. International Journal of Rotating Machinery International Journal of Journal of The Scientific Journal of Distributed Engineering World Journal Sensors Sensor Networks Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Volume 2014 Journal of Control Science and Engineering Advances in Civil Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Submit your manuscripts at http://www.hindawi.com Journal of Journal of Electrical and Computer Robotics Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 VLSI Design Advances in OptoElectronics International Journal of Modelling & Aerospace International Journal of Simulation Navigation and in Engineering Engineering Observation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2010 Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com http://www.hindawi.com Volume 2014 International Journal of Active and Passive International Journal of Antennas and Advances in Chemical Engineering Propagation Electronic Components Shock and Vibration Acoustics and Vibration Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Active and Passive Electronic Components Hindawi Publishing Corporation

Evaporation of Adherent Al-Films on Single Crystalline LiNbO3 Substrates

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Publisher
Hindawi Publishing Corporation
Copyright
Copyright © 1992 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ISSN
0882-7516
eISSN
1563-5031
DOI
10.1155/1992/20790
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See Article on Publisher Site

Abstract

Active and Passive Elec. Comp., 1992, Vol. 14, pp. 245-249 Reprints available directly from the publisher Photocopying permitted by license only () 1992 Gordon and Breach Science Publishers S.A. Printed in the United Kingdom EVAPORATION OF ADHERENT AI-FILMS ON SINGLE CRYSTALLINE SUBSTRATES LiNbO3 E. SCHIPPEL Department Electrotechnics, Technical University 0-2400 Wismar, Germany of is used as a single crystalline substrate material for the manufacturing of surface acoustic wave LiNbO3 devices as frequency selective components. On the polished substrate wafer, AI with a film thickness of about 400 nm is evaporated in a high vacuum. The difficulties of the inadequate adhesion of the structured Al-film were eliminated by systematical investigations. Films that were adherent to the total surface could be prepared by evaporating an intermediate film of Cr or or, otherwise, a mixed film of AI with Si. SiOx was an assessment of local and An ultrasonic test for adhesion strength developed that results in also large-area film adhesion. I. INTRODUCTION is material. For electronics, Lithium niobate a very interesting Because (LiNbO3) of its is and It is a ferroelectric material crystal class 3m, trigonal polar. LiNbO3 and coefficients. with large pyroelectric, piezoelectric, electro-optic, photo-elastic static occur on the substrate surface because of Therefore, electric charges may detailed of the structure and the temperature variations. A description crystal characteristics of the are WEIS and GAYLORD 1. physical given by LiNbO3 The of the can be made the Czochralski method. growth single crystals by LiNbO3 To avoid areas of different in a the the of polarity crystal, polarity during growing 2,3. a above the of 1140C can be set an electric field crystal Curie-temperature by A field of of is the of surface acoustic wave application manufacturing LiNbO3 devices. For that a metal film is onto a purpose evaporated polished single crystalline substrate wafer vacuum. An structure is then in high interdigital generated by means of The structure consists of two "combs" of photolithography. interdigital different and size. The structural widths of electrodes of the shape interdigital structure are less than 15 The of the filters on the frequency range depends tm. structural of more than 300 electrode widths of width; frequencies MHz require about The electrical contact is created of Al-wires to the structured 1/zm. by bonding metal film. A adhesion of the metal film on the surface good strength evaporated vibrating is for the function of the filters. the cut there absolutely necessary Concerning yz were of adhesion bonds with the 38-cut. problems 245 246 E. SCHIPPEL II. EXPERIMENT In production, the polished wafers are given a short treatment with various LiNbO3 chemicals. Therefore, tests of various pretments of the wafers were made. LiNbO3 After a standard cleaning with acetone in an ultrasonic bath, the wafers were treated at 20C and 50C for 5 min and 20 min with the following chemicals: 1. HF, 20% solvent NH3 2. Chromium-sulphuric acid 3. NaOH, 20% solvent 4. PO4, concentrated solvent H3 5. F2, concentrated solvent H2 An assessment of the efficiency of the chemicals with respect to the surface of wafers resulted from electron microscopic photographs. LiNbO3 In another test series, standardized cleaned and pre-treated glass and LiNbO3 substrates were coated under the same conditions with A1 by evaporization. These tests should show differences between the adhesion of A1 films to amorphous glass and crystalline LiNbO3. In general, the evaporation was done from W-boats on the substrates in vacuum with and without a glow discharge. For the manufacturing of a mixed film, AI and the additives Cu, Si and Ni were evaporated from separate boats. The thickness of the mixed film was 20 nm to 50 nm. Above it, pure A1 was evaporated up to a thickness of 400 nm. Cr For the manufacturing of intermediate films, as an insulator or as a SiOx metal first a were evaporated to maximum thickness of 30 nm, followed by pure of nm. AI evaporated up to a total thickness 400 To investigate the adhesion of the evaporated films a test method was developed. The are immersed into a solvent and samples (e.g., acetone, xylene) ultrasonically 4. The test method is to the extent of adherence of the to the agitated sensitive film substrate. The test method can be into a incorporated production process because it is non-distructive of adherent films. fully this test non-adherent or not adherent films removed By method, sufficiently are from the and obscure a film. substrate visually as spots without By the proper choice of solvent for ultrasonic and sound-transmission, frequency treatment time, the test method can be to the adhesion bond 4. adapted necessary for the product For the assessment of the a screen of 1 mm x 1 was to investigations, mm used measure the area of substrate without a film. III. RESULTS From electron microscopic investigations, the surface of the wafer appears LiNbO3 to be affected in different ways by different chemicals. There is no surface effect due to HE The largest which are to the NH3 etching pits, arranged according crystal symmetry, are produced by 1 shows the classification of the chemicals Fig. H2 F2. EVAPORATION OF ADHERENT AI-FILMS 247 Effect of Etching 1 2 3 4 5 FIGURE Classification of chemicals to the effect on the wafer. according etching LiNbO3 HF (20% solvent), lmNH3 acid 2mChromium-sulphuric 3--NaOH (concentrated solvent) 4---H3 PO4 (concentrated solvent) 5--H_, (concentrated solvent). F2 to the effect on the wafer. It was found that the treat- according etching LiNbO3 ments of the wafer with acid and will chromium-sulphuric improve LiNbO3 H3 PO4 the adhesion of the A1 film. 2 shows that the adhesion of the A1 film is worse on Fig. clearly essentially than on After a test time of 10 min the A1 film has been 60% glass. nearly LiNbO3 dissolved from the while it is still on the surface to more than LiNbO3, glass up 90%. For the film with an film on the substrate, it was found that systems underlying the adhesion of the A1 film with an A1Si mixed film is excellent as 3 along Fig. shows. AI films with an mixed film of A1Cu have better adhesion than underlying with AINi mixed films or films of AI. To retain the filter function of the pure the thickness of the mixed film must not succeed 30 to 40 nm5. component, An excellent adhesion is also to be found with the A1 films with an intermediate 6O Substrate 2O ’1 2 3 4 5 6 7 8 9 10 rain Time for Ultn3scic Test FIGURE 2 Area without after ultrasonic test of on and layer pure AI film glass- in LiNbO3-substrate percent. 248 E. SCHIPPEL AINi 8O 6O AtCu z, 0 2 3 9, 5 6 7 10 min Time for Ultrasonic Test FIGURE 3 Area without after ultrasonic test of AI film and AI films with below mixed films of layer AISi, AICu and AINi on in LiNbO3 percent. of the materials or Cr. After a test time of 10 min there are no dissolutions layer SiOx of the A1 film to be seen. A is before the glow discharge necessary evaporization of A1 on the intermediate 6. The is not at the layer glow discharge necessary SiOx of A1 on the intermediate Cr The excellent adhesion of the evaporization layer. AI film can be reached with thin intermediate of less than 20 nm. With very layers thicker intermediate determined of the filter can be layers, changes component 7,8. reached to the according patents IV. CONCLUSION The of the adherent metallization of substrates with A1 investigation by LiNbO3 show that a suitable combination of substrate film evaporization by pretreatment, and methods, total-area well-adhered films can be system, technological evaporated in a For film AI films with films reproductible way. composite systems, underlying of A1Si, SiOx, or Cr are suitable. To get results of the adhesive bond of films, a test ultrasonic agitation, was The test method is methodemploying developed. applicable in the manufacturing process, as well as for testing the adhesion of films that have been structured by a method. photolithographic REFERENCES 1. R.S. Weis and T.K. Gaylord: Lithium niobate: summary of physical and crystal structure properties Appl. Phys. A37 191-203. (1985) 249 EVAPORATION OF ADHERENT AI-FILMS 2. P.W. and P.D. Townsend: A method of and below Haycock poling LiNbO3 LiTaO3 Tc Appl. Phys. 48 698-700. (1986) 3. P. Reiche, J. Bohm, B. Hermoneit, P. and D. Schulze: von Rudolph Wachstumsmorphologie bei der nach dem Czochralski-Ver-fahren unter der Einwirkung LiNbO3-Einkristallen Ziichtung eines elektrischen Feldes Cryst. Res. Technology 23 467-474. (1988) 4. E. and A. Piech: Verfahren zur Priifung der Haft-festigkeit von aufgedampften Schichten Schippel Patent (application 1989) 5. E. T. V61ker and A. Breitlauch: Schichtsystem zur haftfesten Metallisierung piezoelek- Schippel, trischer Substratmaterialien Patent DD 276 697. 6. E. Schippel and M. Schmidt: Verfahren zur haftfesten Metal-lisierung von piezoelektrischen Ma- terialien Patent DD 264 943. 7. Akustisches Oberflichenwellenwandler-System Patent D 2238 925.9. 8. Schallwandler for akustische Oberflichenwellen Patent D 2431 620.0. International Journal of Rotating Machinery International Journal of Journal of The Scientific Journal of Distributed Engineering World Journal Sensors Sensor Networks Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Volume 2014 Journal of Control Science and Engineering Advances in Civil Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Submit your manuscripts at http://www.hindawi.com Journal of Journal of Electrical and Computer Robotics Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 VLSI Design Advances in OptoElectronics International Journal of Modelling & Aerospace International Journal of Simulation Navigation and in Engineering Engineering Observation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2010 Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com http://www.hindawi.com Volume 2014 International Journal of Active and Passive International Journal of Antennas and Advances in Chemical Engineering Propagation Electronic Components Shock and Vibration Acoustics and Vibration Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014

Journal

Active and Passive Electronic ComponentsHindawi Publishing Corporation

Published: Jan 1, 1992

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