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Anodic Bonding of Glass-to-Glass through Magnetron Spattered Nanometric Silicon Layer
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Procedia Engineering
Procedia Engineering 00 1629 (2011)– 000–000 Procedia Engineering 25 (2011) 1632 www.elsevier.com/locate/procedia
Proc. Eurosensors XXV, September 4-7, 2010, Athens, Greece
Anodic bonding of glass-to-glass through magnetron spattered nanometric silicon layer Pawel Knapkiewicza, Bartlomiej Cichyb, Witold Posadowskia, Katarzyna Tadaszaka, Patrycja Sniadeka, Jan Dziubana a
Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland b Polish Academy of Science, Wroclaw, Poland
Abstract
We described the glass-to-glass anodic bonding through thin p-Si layer. The applied here p-Si forming procedure allows to achieve high quality, strong connection between two glass plates. The p-Si forming procedure have been never reported before. Several test structures of different shape and size were done. Simple microfluidic device were fabricated as well. Crash test of test structure and pneumatic test of the microfluidic device proved high quality of the assembling method. © 2011 Published by Elsevier Ltd. "Keywords: anodic bonding, glass-to-glass"
1. Motivation Glass as chemically resistive, easy to clean and transparent material is widely used for microfluidic chips developing [1-5]. Microfluidic chips consist of two glass plates, usually. After proper processing of that plates (chemical etching or mechanical treatment of micro-channels, via-holes, etc.), the plates are assembled used of the fusion bonding process at high temperature close the melting temperature depended on type of glass. Fusion bonding process ensured strong and tight connection, but several disadvantages can be pointed out. High temperature of assembling process conducts to volumetric degradation of glass, diffusion of some contaminations into glass structure is possible. Surface development of glass plates caused by outgassing of residual gasses from the surface (micro-blisters, micro-craters) were observed. Smooth surface of glass plates is strongly required from chemical point of view and possible sensors integration [6]. That is why alternative assembling method of glass plates has been inquired. Several requirements for an alternative glass-to-glass assembling method has been defined: connection must be strong, tight, chemically resistance against aggressive compounds (except HF acid). Technology must be relatively cheap and easy to apply for chip-scale fabrication of micro-fluidic chips. Assembling methods utilized glue (photohardened glue, epoxy glue), Kapton® or Teflon foil (glass-to-glass adhesive bonding through foil) can not be used. Glues are chemically unstable; glass-foil interface can be easy penetrate by chemicals (eg. nitric acid) toward delamination of chip. Glass-to-glass anodic bonding through thin film as intermediate layer seems to be only solution (Table. 1).
1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.12.403
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PawelKnapkiewicz/ KnapkiewiczProcedia et al. / Procedia Engineering 25000–000 (2011) 1629 – 1632 Pawel Engineering 00 (2011)
Table 1. Several assembling methods test against mixture of concentrated nitric and sulphuric acids .
2. Experiment Some works have been done by Berthold and all [7]. Several material used as intermediate layer, deposited onto one or two glass wafers anodically bonded on last step have been investigated (Fig. 1a). Anodic bonding forming strong chemical connection between intermediate layer and glass wafer or between two thin intermediate layers. The weakest point of proposed technique is that at least one connection between intermediate layer and glass is realized by adhesive forces only. We proposed modified method of glass-to-glass assembling use of two steps anodic bonding process (Fig. 1b). The thin film polysilicon (p-Si) layer have been used as intermediate layer. During experiments borosilicate glass Borofloat 3.3 (Shott) were used. The p-Si layer was magnetron-spattered onto one glass wafer. During experiment 100 nm thick p-Si layer have been defined as optimal. Thinner p-Si layer ware not continues; thicker were decorticated. After p-Si spattering onto glass wafer, the p-Si layer have been treated thermally and electrically – anodic bonding of the p-Si layer to glass wafer (t = 300°C, U = 750 V) called later as p-Si forming. The p-Si forming is a key technological step of the modified glass-to-glass assembling method. It increasing adhesion of the p-Si layer athwart replacing adhesive forces by chemical connection of p-Si layer and glass. Finally, the second glass wafer is anodically bonded to previously prepared glass – p-Si structure at standard conditions (t = 450°C, U = 1 kV). a)
b)
Fig. 1. Flow chart of glass-to-glass assembling: a) follow the [7]: 1 – preparation of two glass wafers, 2 – thin film layer/layesr deposition onto glass wafer/wafers, 3 – glass-to-glass anodic bonding, b) newly developed process: 1 – preparation of two glass wafers, 2 – thin p-Si layer deposition onto one glass wafer, 3 - thermal treatment of the p-Si layer (anodic bonding), 4 – glass-to-glass anodic bonding.
Pawel Knapkiewicz et al.Procedia / Procedia Engineering (2011) 1629 – 1632 Pawel Knapkiewicz/ Engineering 0025 (2011) 000–000
1631 3
Use of the described here method of glass-to-glass assembling method through thin p-Si layer, square glass plates of 35 x 35 mm2 (Fig. 2b), as well as round 3” glass plates (Fig. 2a) were successfully bonded. High quality bonding interface similar to glass-to-silicon anodic bonding has been achieved. The high quality bonding were proved during crash test (Fig. 2c). Bonded structure brakes as bulk material. We estimated, that the bonding force is minimum 40 MPa and it is similar to bonding force of silicon-glass anodic bonding.
Fig. 2. Glass-to-glass assembling method using anodic bonding through PSi as intermediate layer: a) 3” assembled glass wafers, b) 35 x 35 mm2 bonded glass wafers, c) crash test – breakthrough – bonded glass wafers breaking as bulk material.
Simple microfluidic device have been fabricated use of the glass-to-glass anodic bonding through thin p-Si layer (Fig. 3). Two borosilicate glass plates (Borofloat 3.3) of 35 x 17.5 mm2 and 1.1 mm thick were used. Straight microfluidic channel (30 µm depth, 300 µm width) were isotropic etched in one of the glass plates. In parallel, 100 nm thick p-Si layer were magnetron spattered onto second glass plate. Following, p-Si forming were done and through holes were mechanically drilled. Finally, hydrophilization treatment were applied and glass-to-glass anodic bonding were done. During a test water of 4 bar pressure were inserted into the channel. No leakages or delamination of the structure were observed.
Fig. 3. All glass microfluidic chip utilized described here assembling method: a) top-side: microchannel is visible, b) inlet and outled are visible.
41632
PawelKnapkiewicz/ KnapkiewiczProcedia et al. / Procedia Engineering 25000–000 (2011) 1629 – 1632 Pawel Engineering 00 (2011)
4. Summary The glass-to-glass integration method using anodic bonding technique through thin polysilicon layer (p-Si) as intermediate layer has been presented. The method is characterized by high quality bonding cause of unique p-Si forming procedure. Breaking tests of test samples has shown bonding force higher than 40 MPa, what corresponds to bonding force of glass and silicon assembled by anodic bonding process. The method described in this paper can be used for integration of glass wafers with different shape and size. Till now 3” glass wafers (as maximum) has been successfully assembled. However, there is no limits to assemble large scale glass plates. The glass-to-glass assembling method has been used for fabrication simple microfluidic chip. The method opens a way to fabricate cheap, large scale, all glass microfluidic chips, as well as another glass structures, using microengineering technology. 5. References [1] Microchemical Engineering in Practice. Edited by Thomas R. Dietrich. WILEY 2009. [2] T. Dietrich, A. Freitag, R. Scholz: Production and characteristics of microreators made from glass. Chemical Engineering Technology 28. No. 4. 2005. 477 – 483. [3] R. E. Oosterbroek, D. C. Hermes, M. Kakuta, F. Benito-Lopez, J. G. E. Gardeniers, W. Verboom, D. N. Reinboudt, A. van der Berg: Fabrication and mechanical testing of glass chips for high-pressure synthetic or analytical chemistry. Microsystem Technology 12. 2006. 450 – 454. [4] M. Masuda, K. Sugioka, Y. Cheng, T. Hongo, K. Shihoyama, H. Takai, I. Miyamoto, K. Midorikawa: Fabrication of 3-D microreactor structures embedded in photosensitive glass by femtosecond laser. International Microprocesses and Nanotechnology Conference. Japan Society of Applied Physics. 2003. Tokyo. Japonia. materiały konferencyjne. 198 – 199. [5] S. Mukherjee, M. K. Hatalis, M. V. Kothare: Water Gas Shift Reaction in a glass microreactor. Catalysis Today 120. 2007. 107 – 120. [6] P. Knapkiewicz, R. Walczak, J. Dziuban: The method of integration of silicon micromachined sensors and actuators to microreactor made of Foturan glass. Optica Applicata. 2007, vol. 37, no 1/2, 65-72. [7] A. Berthold, L. Nicola, P. M. Sarro, M. J. Vellekoop: Glass-to-glass anodic bonding with standard IC technology thin films as intermediate layers. Sensors and Actuators 82. 2000. 224-228.
Procedia Engineering
Procedia Engineering 00 1629 (2011)– 000–000 Procedia Engineering 25 (2011) 1632 www.elsevier.com/locate/procedia
Proc. Eurosensors XXV, September 4-7, 2010, Athens, Greece
Anodic bonding of glass-to-glass through magnetron spattered nanometric silicon layer Pawel Knapkiewicza, Bartlomiej Cichyb, Witold Posadowskia, Katarzyna Tadaszaka, Patrycja Sniadeka, Jan Dziubana a
Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland b Polish Academy of Science, Wroclaw, Poland
Abstract
We described the glass-to-glass anodic bonding through thin p-Si layer. The applied here p-Si forming procedure allows to achieve high quality, strong connection between two glass plates. The p-Si forming procedure have been never reported before. Several test structures of different shape and size were done. Simple microfluidic device were fabricated as well. Crash test of test structure and pneumatic test of the microfluidic device proved high quality of the assembling method. © 2011 Published by Elsevier Ltd. "Keywords: anodic bonding, glass-to-glass"
1. Motivation Glass as chemically resistive, easy to clean and transparent material is widely used for microfluidic chips developing [1-5]. Microfluidic chips consist of two glass plates, usually. After proper processing of that plates (chemical etching or mechanical treatment of micro-channels, via-holes, etc.), the plates are assembled used of the fusion bonding process at high temperature close the melting temperature depended on type of glass. Fusion bonding process ensured strong and tight connection, but several disadvantages can be pointed out. High temperature of assembling process conducts to volumetric degradation of glass, diffusion of some contaminations into glass structure is possible. Surface development of glass plates caused by outgassing of residual gasses from the surface (micro-blisters, micro-craters) were observed. Smooth surface of glass plates is strongly required from chemical point of view and possible sensors integration [6]. That is why alternative assembling method of glass plates has been inquired. Several requirements for an alternative glass-to-glass assembling method has been defined: connection must be strong, tight, chemically resistance against aggressive compounds (except HF acid). Technology must be relatively cheap and easy to apply for chip-scale fabrication of micro-fluidic chips. Assembling methods utilized glue (photohardened glue, epoxy glue), Kapton® or Teflon foil (glass-to-glass adhesive bonding through foil) can not be used. Glues are chemically unstable; glass-foil interface can be easy penetrate by chemicals (eg. nitric acid) toward delamination of chip. Glass-to-glass anodic bonding through thin film as intermediate layer seems to be only solution (Table. 1).
1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.12.403
21630
PawelKnapkiewicz/ KnapkiewiczProcedia et al. / Procedia Engineering 25000–000 (2011) 1629 – 1632 Pawel Engineering 00 (2011)
Table 1. Several assembling methods test against mixture of concentrated nitric and sulphuric acids .
2. Experiment Some works have been done by Berthold and all [7]. Several material used as intermediate layer, deposited onto one or two glass wafers anodically bonded on last step have been investigated (Fig. 1a). Anodic bonding forming strong chemical connection between intermediate layer and glass wafer or between two thin intermediate layers. The weakest point of proposed technique is that at least one connection between intermediate layer and glass is realized by adhesive forces only. We proposed modified method of glass-to-glass assembling use of two steps anodic bonding process (Fig. 1b). The thin film polysilicon (p-Si) layer have been used as intermediate layer. During experiments borosilicate glass Borofloat 3.3 (Shott) were used. The p-Si layer was magnetron-spattered onto one glass wafer. During experiment 100 nm thick p-Si layer have been defined as optimal. Thinner p-Si layer ware not continues; thicker were decorticated. After p-Si spattering onto glass wafer, the p-Si layer have been treated thermally and electrically – anodic bonding of the p-Si layer to glass wafer (t = 300°C, U = 750 V) called later as p-Si forming. The p-Si forming is a key technological step of the modified glass-to-glass assembling method. It increasing adhesion of the p-Si layer athwart replacing adhesive forces by chemical connection of p-Si layer and glass. Finally, the second glass wafer is anodically bonded to previously prepared glass – p-Si structure at standard conditions (t = 450°C, U = 1 kV). a)
b)
Fig. 1. Flow chart of glass-to-glass assembling: a) follow the [7]: 1 – preparation of two glass wafers, 2 – thin film layer/layesr deposition onto glass wafer/wafers, 3 – glass-to-glass anodic bonding, b) newly developed process: 1 – preparation of two glass wafers, 2 – thin p-Si layer deposition onto one glass wafer, 3 - thermal treatment of the p-Si layer (anodic bonding), 4 – glass-to-glass anodic bonding.
Pawel Knapkiewicz et al.Procedia / Procedia Engineering (2011) 1629 – 1632 Pawel Knapkiewicz/ Engineering 0025 (2011) 000–000
1631 3
Use of the described here method of glass-to-glass assembling method through thin p-Si layer, square glass plates of 35 x 35 mm2 (Fig. 2b), as well as round 3” glass plates (Fig. 2a) were successfully bonded. High quality bonding interface similar to glass-to-silicon anodic bonding has been achieved. The high quality bonding were proved during crash test (Fig. 2c). Bonded structure brakes as bulk material. We estimated, that the bonding force is minimum 40 MPa and it is similar to bonding force of silicon-glass anodic bonding.
Fig. 2. Glass-to-glass assembling method using anodic bonding through PSi as intermediate layer: a) 3” assembled glass wafers, b) 35 x 35 mm2 bonded glass wafers, c) crash test – breakthrough – bonded glass wafers breaking as bulk material.
Simple microfluidic device have been fabricated use of the glass-to-glass anodic bonding through thin p-Si layer (Fig. 3). Two borosilicate glass plates (Borofloat 3.3) of 35 x 17.5 mm2 and 1.1 mm thick were used. Straight microfluidic channel (30 µm depth, 300 µm width) were isotropic etched in one of the glass plates. In parallel, 100 nm thick p-Si layer were magnetron spattered onto second glass plate. Following, p-Si forming were done and through holes were mechanically drilled. Finally, hydrophilization treatment were applied and glass-to-glass anodic bonding were done. During a test water of 4 bar pressure were inserted into the channel. No leakages or delamination of the structure were observed.
Fig. 3. All glass microfluidic chip utilized described here assembling method: a) top-side: microchannel is visible, b) inlet and outled are visible.
41632
PawelKnapkiewicz/ KnapkiewiczProcedia et al. / Procedia Engineering 25000–000 (2011) 1629 – 1632 Pawel Engineering 00 (2011)
4. Summary The glass-to-glass integration method using anodic bonding technique through thin polysilicon layer (p-Si) as intermediate layer has been presented. The method is characterized by high quality bonding cause of unique p-Si forming procedure. Breaking tests of test samples has shown bonding force higher than 40 MPa, what corresponds to bonding force of glass and silicon assembled by anodic bonding process. The method described in this paper can be used for integration of glass wafers with different shape and size. Till now 3” glass wafers (as maximum) has been successfully assembled. However, there is no limits to assemble large scale glass plates. The glass-to-glass assembling method has been used for fabrication simple microfluidic chip. The method opens a way to fabricate cheap, large scale, all glass microfluidic chips, as well as another glass structures, using microengineering technology. 5. References [1] Microchemical Engineering in Practice. Edited by Thomas R. Dietrich. WILEY 2009. [2] T. Dietrich, A. Freitag, R. Scholz: Production and characteristics of microreators made from glass. Chemical Engineering Technology 28. No. 4. 2005. 477 – 483. [3] R. E. Oosterbroek, D. C. Hermes, M. Kakuta, F. Benito-Lopez, J. G. E. Gardeniers, W. Verboom, D. N. Reinboudt, A. van der Berg: Fabrication and mechanical testing of glass chips for high-pressure synthetic or analytical chemistry. Microsystem Technology 12. 2006. 450 – 454. [4] M. Masuda, K. Sugioka, Y. Cheng, T. Hongo, K. Shihoyama, H. Takai, I. Miyamoto, K. Midorikawa: Fabrication of 3-D microreactor structures embedded in photosensitive glass by femtosecond laser. International Microprocesses and Nanotechnology Conference. Japan Society of Applied Physics. 2003. Tokyo. Japonia. materiały konferencyjne. 198 – 199. [5] S. Mukherjee, M. K. Hatalis, M. V. Kothare: Water Gas Shift Reaction in a glass microreactor. Catalysis Today 120. 2007. 107 – 120. [6] P. Knapkiewicz, R. Walczak, J. Dziuban: The method of integration of silicon micromachined sensors and actuators to microreactor made of Foturan glass. Optica Applicata. 2007, vol. 37, no 1/2, 65-72. [7] A. Berthold, L. Nicola, P. M. Sarro, M. J. Vellekoop: Glass-to-glass anodic bonding with standard IC technology thin films as intermediate layers. Sensors and Actuators 82. 2000. 224-228.