Tomonori Saeki

Controlling Ambient Gas in Slot-to-Slot Space Inside FOUP to Suppress Cu-Loss After Dual Damascene Patterning

We investigated a Cu-loss problem after dual-damascene patterning during manufacturing; that is, more than a dozen wafers were stored in a FOUP. We found that a decreased yield due to the Cu-loss strongly depended on the wafer position in a FOUP and on the queue time between etching and wet cleaning. We developed a Cu-oxidation model to explain what happens in a FOUP during the queue time; that is, the F content, which catalyze Cu-oxidation, in the post-etch residue gradually evaporate into the slot-to-slot space. The ambient gas analysis in a FOUP showed that F-containing gas evaporates from the post-etch wafers, and that the evaporation is gradual, which is consistent with our model. On the basis of our model, we controlled ambient gas in the slot-to-slot space. The increased yield showed that the Cu-loss problem was successfully suppressed.

The cleaning at a back surface and edge of a wafer for introducing Cu metallization process

Cu metallization has been introduced in high-speed complementary metal-oxide-semiconductor (CMOS) large scale integration (LSI) in order to achieve low electrical resistivity. This means Cu contamination can be spread all over semiconductor equipment by the wafers, even though Cu has been thoroughly eliminated from semiconductor manufacturing for a long time. To protect the other wafers without Cu from Cu cross-contamination, we have demonstrated a method that can clean the back surface and selectively clean the edge of a wafer simultaneously without any masks. This method performs the cleaning by optimizing the overhang of chemicals in the single-wafer system with the Bernoulli chuck. We have also demonstrated a new edge extractor that can be used to perform the quantitative evaluation of Cu contamination at the wafer edge. The combination of the edge cleaning and the edge evaluation is useful for introducing not only Cu, but also new exotic materials such as Ta/sub 2/O/sub 5/ and BST.

Ambient gas control in slot-to-slot space inside FOUP to suppress Cu-loss after dual damascene patterning

We investigated a Cu-loss problem after dual-damascene patterning during manufacturing; that is, more than a dozen wafers were stored in a FOUP. We found that a decreased yield due to the Cu-loss strongly depends on the wafer position in a FOUP and on the queue time between etching and wet cleaning. We developed a Cu-oxidation model to explain what happens during the queue time; that is, the F content, which catalyze Cu-oxidation, in the post-etch residue gradually evaporate into the slot-to-slot space. On the basis of our model, we applied ambient gas control in the slot-to-slot space to suppress the decrease in yield due to the Cu-loss.

The cleaning at a back surface and edge of a wafer for introducing Cu metalization process

Cu metalization has been introduced in high-speed CMOS LSIs in order to achieve low electrical resistivity. This means Cu contamination can be spread all over semiconductor equipment by the wafers. To protect the other wafers without Cu from Cu cross-contamination, we have demonstrated a method that can clean the back surface and selectively clean the edge of a wafer simultaneously without any masks. This method performs the cleaning by optimizing the overhang of chemicals in the single-wafer system. We have also demonstrated a new edge extractor that can be used to perform the quantitative evaluation of Cu contamination at the wafer edge. The combination of the edge cleaning and the edge evaluation is useful for introducing not only Cu but also new exotic materials such as Ta/sub 2/O/sub 5/ and BST.

Wastewater treatment with acoustic separator

Acoustic separation is a filter-free wastewater treatment method based on the forces generated in ultrasonic standing waves. In this report, a batch-system separator based on acoustic separation was demonstrated using a small-scale prototype acoustic separator to remove suspended solids from oil sand process-affected water (OSPW). By applying an acoustic separator to the batch use OSPW treatment, the required settling time, which was the time that the chemical oxygen demand (COD) decreased to the environmental criterion (<200 mg/L), could be shortened from 10 to 1 min. Moreover, for a 10 min settling time, the acoustic separator could reduce the FeCl3 dose as coagulant in OSPW treatment from 500 to 160 mg/L.

Recovery of Rare Earth Metals in Used Magnets by Molten Magnesium

We report here Hitachi’s approach to recycle rare earth (RE) metals in used magnets by using molten magnesium (Mg). The process consists of 3 steps; (1) extraction of RE metals from magnets into molten Mg, to form Mg-RE melt, (2) mechanical separation of magnets from the Mg-RE melt, (3) collection of RE metals by evaporation of Mg in the Mg-RE melt. In the step 1, extraction of RE metals proceeds rapidly and completes in about 3 h. The efficiency strongly depends on the temperature (T) and Mg/magnet ratio (r)). One of the optimal conditions is T=1273 (K) and η is 10, where the efficiencies for Nd and Dy extraction are almost 100 % and 60 %, respectively. Further increase of Dy extraction efficiency is possible by addition of Ca to suppress the oxidation of Dy.

Prototyping and evaluation of ultrasonic particle filter considering water flux and sound propagation direction

The water supply market is growing rapidly worldwide, and low-cost, energy-efficient water purification technology is becoming an important consideration. Filtering using acoustic radiation force (ARF) is a promising method that works without consumables. In the present paper, we propose a novel design for a water filtering apparatus that operates by means of ARF. An ultrasonic transducer was arranged such that the direction of the ultrasound propagation was parallel to the flow of water in the proposed apparatus. Since suspended particles have a higher chance of encountering the nodes in the ultrasonic standing waves, the filtering performance should be enhanced. The efficiency of turbidity reduction using the proposed apparatus reached 80%.