The SiC nano for PicoGeo consortium visited the CNR-IMM Clean Room in Bologna
On the occasion of the first progress meeting in November, the SiC nano for PicoGeo consortium members were hosted by the Institute for Microelectronics and Microsystems of the Italian National Research Council (CNR-IMM) – i.e. the project coordinator – in its Bologna UNIT (IMM-BO). During this meeting, partners had the chance to visit the laboratories of IMM-BO, which has ...
On the occasion of the first progress meeting in November, the SiC nano for PicoGeo consortium members were hosted by the Institute for Microelectronics and Microsystems of the Italian National Research Council (CNR-IMM) – i.e. the project coordinator – in its Bologna UNIT (IMM-BO).
During this meeting, partners had the chance to visit the laboratories of IMM-BO, which has the biggest publicly funded facility for silicon micro-machining in Italy, capable of producing different non-VLSI devices, in particular micro-electro-mechanical-systems (MEMS), using micro-machining techniques for Si, SiC and Quartz substrates, and 3rd generation solar cells and photovoltaic devices. Here, the CNR-IMM researchers perform activities on carbon-based materials, like carbon nanotubes (CNTs), graphene and Silicon Carbide.
The facility is located in a clean room with a total area of 500m2, including laboratories and service corridors. Half of the area is class 100000 rated, whereas the remaining have a class 100 rating (i.e. less than 100 particles larger than 0.5 microns for a cubic foot of air). Air is recirculated approximately 20-30 times per hour, depending on room class and cooling. Class 100 area is characterized by a constant laminar airflow from ceiling to floor. Air which enters the clean room is continuously filtered to remove dirt and dust particles. The efficiency of the filtering system is automatically monitored to ensure constant performance over time. The clean room is positively pressurized with respect to the adjacent areas, to prevent the accidental introduction of contaminants through possible leaks.
SiC nano for PicoGeo partners were guided on the visit by Dr. Alberto Roncaglia and Dr. Matteo Ferri, both working on the project. The two researchers explained to the partners the structure of the clean room and described the rooms into which it is divided, highlighting what project-related activities are done in each of them.
In the Photolithography Room, photo masking is performed. Researchers work with a spinner to evenly distribute the photoresist, which is then heat-treated to activate it. Next, two mask aligners are used to develop the mask: a pattern is "transported" onto the photoresist by light and shadow. The precision obtained is about 1 µm. Bounding machines are later used to bind (precisely weld) the different devices obtained. Fusion bonding is used for bonding silicon and glass or glue, using a photoresist, but depending on the requirements, different techniques can be used. At this stage of the process, researchers usually work with samples as small as 4 inches in size, but some can be as large as 6 inches.
In the Metallization Room are the deposition machines, where the metal can be deposited on the device for subsequent fabrication. Metal deposition can be done in two different ways, by sputtering or by evaporation. Obviously, the different processes require different machines, and in the Bologna laboratory, there are 2 for the former and 1 for the latter. Through the process of evaporation, the metal is evaporated and the particles reach the sample on which they are deposited, creating a thin layer, of thickness in the nm range. Usually, this is not an isotropic process, so the walls of the resist, which have been previously etched, may be less covered by the materials. Through this process, many materials (metal, oxides, etc.) can be deposited. On the other hand, the sputtering process is isotropic, so it can cover the sample more evenly. Depending on the cleanliness of the process, two different machines are available. Usually, metals such as gold, platinum, copper, etc., are deposited.
The Furnace Room contains ovens for heat treatment and deposition of materials. There are eight heat treatment furnaces here, each for specific utilization. One is reserved only for microelectronics, so that dirt is not carried from one to another (for example, so that zirconia is not found on silicon chips). Wet oxidation (very hot and moist, so that oxygen can react quickly and deeply) is also possible, and its choice is dictated by the precision one wants to achieve. Low-temperature oxidation can be performed in two other devices, one gas-fired and the other liquid-fired. One is used to deposit oxide layers for relatively thick films (1-5 µm) while the other is used for very thin and precise films on the order of nm. The heat treatment to which the silicon wafer is subjected is very rapid: it is placed and is then heated by 2 tungsten matrices that can reach 1500 °C in 2 seconds, a rather short time, but rapid annealing is achieved in another machine that can easily reach 2000 °C.
It was an exciting experience for all partners who were able to see up close some of the research process being carried out within the SiC nano for PicoGeo project.