Etching characteristics of high dielectric constant HfO 2 films have been studied in high-density BCl 3 -containing plasmas without rf biasing. Emphasis was placed on plasma conditions and etch chemistries to achieve a high selectivity over Si and SiO 2 and to enhance the etch rates. The HfO 2 etch rate was $5 nm/min at a pressure P 0 ¼ 10 mTorr in a BCl 3 plasma, giving a selectivity of >10 over Si and SiO 2 . At lower P 0 6 mTorr in BCl 3 , the deposition of boron-chlorine compounds B x Cl y was observed on all sample surfaces of HfO 2 , Si, and SiO 2 to inhibit etching. The addition of O 2 to BCl 3 was found to suppress the deposition and significantly enhance the HfO 2 etch rate, which was $50 nm/min at P 0 ¼ 5 mTorr in a BCl 3 / 30%-O 2 plasma; at higher O 2 addition !40%, the heavy deposition of boron-oxygen compounds B x O y occurred on surfaces to inhibit etching. The mechanisms underlying the phenomena observed are discussed based on plasma and surface diagnostics.
A bstTact-Superconducting Fault Current Limiters (SCFCLs) are expected to improve the reliability of power systems. An SCFCL of a transformer type with adjustable trigger current level was proposed. Three SCFCLs of this type for 3-phase A C power source were designed and made. The trigger current level of each trial SCFCL can be adjusted to equal value, and the SCFCLs can be used as a 3-phase SCFCL. As preliminary tests, sudden-short circuit tests with a 20kVA synchronous generator are carried out.Limiting tests of the 3-phase SCFCL at fault are carried out with the synchronous generator. The effect of 3-phase SCFCL and the characteristics of the synchronous generator are studied experimentally.
The recovery time of a transformer type SC-FCL (Superconducting Fault Current Limiter) with adjustable trigger current level, is studied experimentally. The recovery time is defined as the required time of zero current period of SCFCL for recovery from its current limiting mode to its waiting mode. A trial SCFCL, which was designed and made, is tested to measure the recovery time with various fault time. The experimental results show that the recovery time depends on the fault time. When the fault time is longer than 200 ms, the recovery time becomes shorter and approaches a certain value (a few ten ms) as the fault time is longer.
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