Preparation and analysis of amorphous carbon films deposited from (C6H12)/Ar/He chemistry for application as the dry etch hard mask in the semiconductor manufacturing process

Amorphous carbon layers (ACL) were deposited on Si (100) wafers by plasma enhanced chemical vapor deposition (PECVD) by using 1-hexene (C₆H₁₂) as a carbon source for dry etch hard mask of semiconductor devices manufacturing process. The deposition characteristics and film properties were investigated by means of ellipsometry, Raman spectroscopy, X-ray photo electron spectroscopy (XPS) and stress analysis. Hardness, Young's modulus, and surface roughness of ACL deposited at 550 °C were investigated by using nano-indentation and AFM. The deposition rate was decreased from 5050 Å/min to 2160 Å/min, and dry etch rate was decreased from 2090 Å/min to 1770 Å/min, and extinction coefficient was increased from 0.1 to 0.5. Raman analysis revealed a higher shift of the G-peak and a lower shift of the D-peak and the increase of I(D)/I(G) ratio as the deposition temperature was increased from 350 °C to 550 °C. XPS results of ACL deposited at 550 °C revealed a carbon 1s binding energy of 284.4 eV. The compressive film stress was decreased from 2.95 GPa to 1.28 GPa with increasing deposition temperature. The hardness and Young's modulus of ACL deposited at 550 °C were 5.8 GPa and 48.7 GPa respectively. The surface roughness RMS of ACL deposited at 550 °C was 2.24 Å, and that after cleaning in diluted HF solution (H₂O:HF = 200:1), SC1 (NH₄OH:H₂O₂:H₂O = 1:4:20) solution, and sulfuric acid solution (H₂SO₄:H₂O₂ = 6:1) was 2.28 Å, 2.30 Å and 7.34 Å, respectively. The removal amount of ACL deposited at 550 °C in diluted HF solution, SC1 solution and sulfuric acid solution was 6 Å, 36 Å and 110 Å, respectively. These results demonstrated the viability of ACL deposited by PECVD from C₆H₁₂ at 550 °C for application as the dry etch hard mask in fabrication of semiconductor devices.     

Optimization of the number of quantum well pairs for high-brightness AlGaLnP-based light emitting diodes

We investigated high-brightness light emitting diodes (LEDs) appropriate for general lighting applications in terms of their temperature dependent photoluminescence characteristics and device performance according to the change of quantum well pairs (QWs). As the number of QWs was increased from 2 to 35 pairs, radiative recombination efficiency and device performances significantly improved, due to the suppression of carrier overflow by decreasing the carrier density in the active region and shortening the carrier transfer time from barrier to well. At a further increase in the number of QWs to 50 pairs, however, the optical and device performances started to degrade because of the increase in internal loss in the active region, such as the well volume itself acting as light absorbing layer and due to the aluminum oxide complexes in the barrier.     

Popular Ethnic Foods in the United States: A Historical and Safety Perspective

In recent years, a dramatic increase in the demand for ethnic foods in the United States has been observed. Interestingly, with their rise in popularity, more foodborne illness outbreaks associated with ethnic foods have also been reported. Despite a more than 200‐y history of ethnic foods in the United States, there is a paucity of information about them. Furthermore, there is also a lack of research on food safety issues involving ethnic foods. Therefore, this paper provides a comprehensive overview of ethnic foods, including the history, types, popularity, characteristics, ingredients, and consumer attitudes toward them. Importantly, this review provides an analysis of the statistics of foodborne illness outbreaks associated with ethnic foods based on data from the Centers for Disease Control and Prevention (CDC). The breakdown of etiology of ethnic foods identified the number of total outbreaks, the causative microorganisms, the food vectors, and the locations where foodborne disease outbreaks have occurred. Also covered is a review of the Hazard Analysis Critical Control Point (HACCP) system implementation, food safety training, and inspection score systems related to ethnic foods and how these can serve as effective tools for the prevention of foodborne illness outbreaks. This study contributes to the body of food safety literature by providing helpful information about ethnic foods in the United States.     

Diversity analysis of lactic acid bacteria in Korean rice wines by culture-independent method using PCR-denaturing gradient gel electrophoresis

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was used to determine the presence and diversity of lactic acid bacteria (LAB) in takju, a traditional Korean rice wine. Bacterial DNAs were extracted from 15 commercial rice wines and amplicons of partial 16S rRNA genes were separated by DGGE and intense bands were sequenced. Lactobacillus (Lb.) paracasei, Lb. plantarum, and Leuconostoc pseudomesenteroides were detected in all samples and Lb. harbinensis and Lb. parabuchneri were found with above 80% frequency of occurrence. Unknown species of Lactobacillus were also widely detected. This result revealed that, regardless of products and raw materials, the distribution profiles of LAB in takju products have a common pattern comprising of above predominant species and, furthermore, takju can be regarded as a LAB-rich fermented food providing various probiotics.