Satomi Hamada

Measurement of the Frictional Force between PVA Roller Brushes and Semiconductor Wafers with Various Films Immersed in Chemicals

To better understanding the lubrication condition between a polyvinyl acetal (PVA) brush and cleaning surfaces, we measured the frictional force between the PVA roller brushes and the semiconductor wafers with various films immersed in chemicals. The frictional force showed different tendencies depending on the combination of chemicals and surface films. Especially, the large fluctuation of friction force was observed under the combination of Cu and NH4OH.

Cu corrosion in laminar flow using microfluidic channels

Increases in the sizes of silicon wafers and the degree of circuit integration has led to a requirement for a reduction in the size and number of defects, including defects caused by corrosion during the Cu-chemical mechanical polishing (CMP) or cleaning processes.

Structures of Cu surfaces developing in benzotriazole solutions: Effect of pH

The effect of pH on layer formation onto clean Cu surfaces in benzotriazole (BTA) aqueous solutions was studied by in situ spectroscopic ellipsometry. The effect of H2O2 addition was also investigated. Time changes in the ellipsometric parameters Ψ and Δ, which correspond to the structural changes of the layers on Cu, were discussed. In acidic solutions, a BTA or a Cu–BTA complex layer grows directly on Cu. The out-diffusion of Cu is suppressed at the Cu layer interface. When H2O2 was mixed, the Cu surface is eroded in acidic solutions. In alkaline solutions, the BTA layer grows on the oxidized Cu layer, or no growth occurs, depending on the composition of the solutions. In neutral solutions, the Cu–BTA complex layer forms on Cu, and the uncovered part is oxidized in the presence of H2O2.

Metrologies of abrasive behaviors for understanding and upgrading CMP process

Laser scanning confocal fluorescent microscopy and the friction mode of Atomic Force Microscopy were adopted as metrologies of abrasive behaviors and removal force during polishing and cleaning processes As small as a diameter of 50nm silica particle can be individually detected and spatial distribution of particles in three dimensional space also clearly observed using the fluorescent microscopy. The fine particle removal force was able to measure using the friction mode of AFM. Accurate force was quantified by calibrating torsion spring constant of an AFM cantilever using a MEMS micro-force sensor with the particles attached to the sensor probe.

In situ ellipsometry of Cu surfaces immersed in benzotriazole–hydrogen peroxide solutions

In the chemical mechanical polishing (CMP) of Cu, the Cu surface is oxidized and is concurrently removed by the mechanical function of an abrasive. Surface oxidation can lead to severe surface corrosion, and to prevent this, a corrosion inhibitor is added to slurries. Accurate understanding of the competition between oxidation and passivation is essential for advanced Cu CMP technologies. In this work, layer formation on clean Cu surfaces in benzotriazole (BTA), H2O2, and BTA–H2O2 aqueous solutions was studied by in situ spectroscopic ellipsometry. Time changes of ellipsometric parameters are discussed with respect to BTA and H2O2 concentrations. It was found that the BTA adsorbs onto the Cu surface and the adsorbed BTA transforms into a Cu–BTA complex in about 3 min after the onset of adsorption. The BTA/complex layer passivates the Cu surface against oxidation by H2O2.

Effect of pH and chemical mechanical planarization process conditions on the copper–benzotriazole complex formation

Benzotriazole (BTA) has been used to protect copper (Cu) from corrosion during Cu chemical mechanical planarization (CMP) processes. However, an undesirable Cu–BTA complex is deposited after Cu CMP processes and it should be completely removed at post-Cu CMP cleaning for next fabrication process. Therefore, it is very important to understand of Cu–BTA complex formation behavior for its applications such as Cu CMP and post-Cu CMP cleaning. The present study investigated the effect of pH and polisher conditions on the formation of Cu–BTA complex layers using electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy) and the surface contact angle. The wettability was not a significant factor for the polishing interface, as no difference in the contact angles was observed for these processes. Both electrochemical techniques revealed that BTA had a unique advantage of long-term protection for Cu corrosion in an acidic condition (pH 3).

Characterization of Cu-BTA Organic Complexes on Cu during Cu CMP and Post Cu Cleaning

Although copper have better electrical properties than aluminum such as low resistivity and high electro-migration resistivity, aluminum has been used as an interconnect material due to the difficulty in Cu dry etching. Since CMP process has been adapted to the semiconductor fabrication, Cu became the choice of materials for interconnection. However, copper CMP process introduces new defects on the surface such as slurry particle, organic residue, scratch and corrosion [1].

Surface potential change with droplet formation and Cu watermark growth by electrochemical oxidation resulting therefrom

To reveal the mechanism of watermark formation on a Cu film, the Volta potential in a droplet area on Cu was evaluated using the scanning Kelvin-probe method. The droplet area on Cu exhibited an upward convex potential profile, indicating that the electrochemical reactions were more active in the areas around the droplet than at the center of the droplet. On the other hand, Si exhibited a profile converse to that of Cu: electrochemical reactions were more active at the center of the droplet area than in the areas around it. These evaluations revealed that the pinning and ring-shaped watermark formation at the droplet area on a Cu film resulted from the said Volta potential profile.

Investigation of Cu-BTA complex formation and removal on various Cu surface conditions

The effect of Cu surface conditions on Cu-BTA complex was investigated using ex-situ electrochemical impedance spectroscopy method. Cu-BTA complex is generated during Cu CMP process because BTA which is the most common corrosion inhibitor in Cu CMP slurry react with Cu and form a strong complex. Then it is very important to remove Cu-BTA complex during post-Cu CMP cleaning because Cu-BTA complex cause severe problem such as particle contamination and watermark due to its hydrophobic characteristic. The Cu-BTA complex formation at various Cu surfaces was investigated to understand its behavior, so the effective development will be possible in post-Cu CMP cleaning process.

Fundamental study of air flow effects on liquid removal from wafer surface

Effects of air flow on droplet removal from wafer were investigated as the fundamental study of CMP cleaning. Deformation and movement of droplet on wafer by air flow were visualized by a high speed camera, and characteristics of droplet behavior were evaluated. Effects of wafer film types (Two types of wafer, Type-A and Type-B were used in this study) on droplet behavior were also investigated. Droplet on Type-A wafer was moved by the air flow with relatively large deformation. However in Type-B wafer, the droplet was moved with almost no deformation. Critical air velocity of droplet movement for Type-B wafer was lower than that of Type-A wafer. From these results, it was confirmed that the liquid removal processes by the air flow was strongly influenced by the property of the wafer surface.