Research and Curriculum Development Project at Clarkson University for
Particle Transport, Deposition, and Removal
CAMP Professor Goodarz Ahmadi (Mechanical and Aeronautical Engineering Department) in collaboration with Professors John McLaughlin (Chemical Engineering Department), Cetin Cetinkaya ( Mechanical and Aeronautical Engineering Department) and Stephen Doheny-Farina (Technical Communications), is working on a combined Research and Curriculum Development project. This work is supported by a grant from the National Science Foundation for Particle Transport, Deposition, and Removal. The objective of this project is to develop a sequence of courses to bring the recent advances in particle transport processes to the classroom for the benefit of undergraduate and graduate students.
CAMP Professor Daryush Aidun's research objectives are to design and develop an alternative method to CMP that is an optical process for the polishing and/or planarization of wafers. In an attempt to accomplish this objective, he will investigate the use of excimer lasers to remove materials by breaking their chemical bonds and vaporizing them. The first and most important part of this research will be to determine the feasibility and the practicality of a laser polishing/planarization (LPP) process. The next step will be to make conceptual designs of the LPP processes and to finally construct a "prototype" process using the excimer lasers to polish Si wafers. Figure 3 shows a possible design for the LPP of semiconductor wafers. The advantages of a LLP would be lower cost and higher productivity.
Figure 3. This illustrates various views of the designed optical system. The four lenses shown are not to scale and the thin cylinder on the upper right represents the wafer. The red beam demonstrates how the laser beam will be diffracted through the lenses and focused on the wafer.
speed of the vaporization (Sv) using the LPP process can be written as:
If one uses a laser capable of producing 1000 W of power with a rectangular beam 3.8 cm x 1.3 cm producing an area of 4.94 cm2 resulting in a power density of about 202 W/cm2, then the time of vaporization (t) for removing 100 nm of Cu and Al will be about 3.8 and 0.7 seconds, respectively. See Table 1.
The LPP process requires no chemicals, has no wastes, and is environmentally friendly.
Professor Cetin Cetinkaya and his group have been conducting analytical, computational and experimental work in the area of laser-based particle removal. There is an immense need in various industries for dry removal of submicron particles from substrates and trenches. Professor Cetinkaya's group has developed a novel dry cleaning method to remove micron and submicron particles from a 25Ám diameter pinhole and the surrounding surface. This is a noncontact method and the removal efficiency is an order of magnitude higher than the traditional laser cleaning methods. This work involved a surface that was polished copper with gold plating. The particles were a mixture of 0.46, 0.71, 0.99, and 1.58 Ám diameter glass spheres. A Nd:YAG laser, with a fundamental wavelength l= 1064 nm and a pulse energy/width equal to 370 mJ and 5 ns respectively, was used in the dry laser cleaning process. Before and after SEM images of a pinhole sample are shown in Figure 4. A total of 5 laser pulses were used during this test. The dry laser cleaning method is being used to remove micron and submicron particles from varying substrates as well as from small (D~10-6 m) holes and semiconductor trenches. The new cleaning method has demonstrated a great potential in the area of submicron particle removal. Various applications of this technology are being investigated by Professor Cetinkaya's group. Professor Cetinkaya is also characterizing thin polymer layered structures with acoustic waves and performing computational studies on surface acceleration for nanoparticle removal.
Figure 4. Before and after images of a 25 Ám gold coated pinhole that has been through a dry laser cleaning process.