Micro-masonry for 3D Additive Micromanufacturing

The aim of this procedure is to demonstrate a transfer printing based micro assembly termed micro masonry for three dimensional additive micro manufacturing. This is accomplished by first preparing silicon or gold micro objects called inks on donor substrates, such that they are suspended on patterned photo resist supporters. The second step is to precisely align an elastomeric microtip stamp on an ink and apply a preload of predefined force on the stamp to form an adhesive contact area.

In between, the stamp has then rapidly retracted to retrieve the ink. Next, the stamp and the retrieved ink are transferred to a receiver substrate where the ink is gently printed on the target area. With the small preload, the stamp is then slowly retracted, leaving the ink on the receiver substrate.

The final step is the rapid thermal eeling of the receiver substrate to bond the printed ink and the substrate permanently. Ultimately, this transfer printing procedure is repeated until a desired 3D microstructure is completed. In this case, a micro teapot is fabricated solely through micro masonry to demonstrate its capability.

The main advantage of this micro masonry technique over conventional monolithic microfabrication is that it can create heterogeneous three dimensional microstructures in a very simple way as children play with Legos, which would be otherwise very challenging to achieve. Visual demonstration of the method is very critical due to its parallel steps. Visually observing this technique should clarify any ambiguities that the viewers may have To begin this procedure.

Design three masks for fabrication of inks on a donor substrate. As detailed in the text protocol On an SOI wafer with a three micron device layer and a one micron box oxide layer spin coat photo resist AZ 5 2 14 at 3000 RPM for 30 seconds. To achieve a 1.5 micron thickness of the photo resist heat the wafer on a 110 degrees Celsius hot plate for one minute, and using mask aligner, expose using mask one and develop using MIF 3 2 7 developer using a reactive IN etching instrument pattern.

The device layer of the SOI wafer and remove the photo resist mask. After this step, the etched region has exposed the box oxide layer. Next spin coat the photo resistors before and pattern with mask two.

Then heat the wafer at 125 degrees Celsius for 90 seconds On a hot plate, immerse the wafer into 49%hydrogen fluoride for 50 seconds to etch the exposed box oxide layer. After completely drying, remove the masking photo, resist spin coat again and pattern with mask three. Then heat the wafer at 125 degrees Celsius on a hot plate.

After 90 seconds, immerse the wafer into 49%hydrogen fluoride for 50 minutes. This step etches the box oxide layer remaining underneath the pattern device layer silicon resulting in suspended silicon. Individual units on the photo resist.

The next step is to make the mold for a micro tip stamp and duplicate a micro tip stamp as described in the text protocol. To begin the printing process, place the donor substrate onto the motorized, rotational and XY translation stages equipped with the microscope. Then attach the microtip stamp to an independent vertical translational stage.

Once the donor substrate and the microtip stamp are loaded, operate the motorized translation stages under the microscope. Align the microtip stamp with the silicon ink on the donor substrate using translational and rotational stages. Afterwards, bring the microtip stamp down to make contact.

Slowly bring the microtip stamp down further after initial contact so that the small tips are fully collapsed and the whole surface is in contact with the silicon ink on the donor substrate. Next, quickly raise the Z stage, breaking the anchors due to the large contact area between the microchip stamp and the silicon ink. To retrieve the silicon ink from the donor substrate and attach it to the microtip stamp, place the receiver substrate onto an XY translation stage and align the retrieved silicon ink under the microtip stamp at the desired location to send the Z stage until the retrieved silicon ink barely makes contact with the receiver substrate.

After making contact slowly raise the Z stage to release the silicon ink, printing it on the desired location. Next program, a rapid thermal, a kneeling furnace to cycle from room temperature up to 950 degrees Celsius in 90 seconds. Remain at 950 degrees Celsius for 10 minutes, and then cool down to room temperature.

Place the printed receiver substrate the furnace in an ambient air environment and a kneel at 950 degrees Celsius for 10 minutes for silicon silicon bonding. To demonstrate its capability, a micro teapot is fabricated solely through micro masonry. This optical microscopic image reveals fabricated silicon inks on a donor substrate.

The designed inks are discs with different dimensions made of single crystalline silicon, which are the building blocks of the micro teapot. Once a donor substrate is independently prepared, discs are transfer printed onto a receiver substrate and a kneeled layer by layer utilizing a micro tip stamp. The inner region of the micro teapot is hollow as can be seen from each assembled disc.

The delicateness of micro mason reprocesses is also tested by transfer printing and a kneeling, a rather exquisite photonic crystal platelet photonic surfaces are patterned with nano imprint lithography and made as transferable inks on a donor substrate. Once the ink is fully prepared, the photonic crystal platelet is transferred onto four silicon rings with 50 micron thickness forming a table like configuration shown. Here are examples of micro masonry adopted to assemble thin gold films.

This optical microscopic image reveals the prepared 400 nanometer thick gold films on a donor substrate. These inks are further processed and tested to transfer print onto a gold surface as well as on a silicon surface. After watching this video, you should have a good understanding of how to assemble microstructures using micro mason D and you should be able to apply this technique to building more appealing three dimensional micro device structures.

Once mastered, this technique should reduce overall fabrication time through its parallel process character compared with other sequential micro manufacturing processes. We would Like to thank New Mattered and Professor Ferreira for their help with automated transfer printing processes and Mickey Dki for help in the MNMS clean room at UIUC.