Preparation of Ge 2 Sb 2 Te 5 Thin Film for Phase Change Random Access Memory by Magnetron Sputtering on Small Hole Patt
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Preparation of Ge2Sb2Te5 Thin Film for Phase Change Random Access Memory by Magnetron Sputtering on Small Hole Patterns Shin Kikuchi, Yutaka Nishioka, Isao Kimura, Takehito Jimbo, Masahisa Ueda, Yutaka Kokaze, and Koukou Suu Institute for Semiconductor Technologies, ULVAC,Inc., 1220-1 Suyama, Susono, Shizuoka, 410-1231, Japan
ABSTRACT Ge2Sb2Te5 (GST) thin films were prepared on the small hole patterned wafer by a new concept sputtering tool which designed developed to fill a hole. The structure of GST film was observed with cross section SEM and the film composition was measured with XRF. It was observed an overhang was suppressed and a GST film was filled in a small hole with a new concept tool. In addition, the uniformity of the GST film composition was good at almost 1% in 200mmφ substrate. Key words; GST; Magnetron sputtering; Hole filling INTRODUCTION Phase Change Random Access Memory [PRAM] is one of the candidates for next generation memory due to its non-volatility, high speed, high density and compatibility with Sibased semiconductor process. Ge2Sb2Te5 [GST] thin film, an active layer in this device, is utilized because it has the well-known property of rapid crystallization without phase separation in erasable compact discs industry.1) In order to integrate PRAM to beyond 512Mbit, a high writing current and degradation of cell transition at small cell size become a problem. To resolve these problems, Confined Cell structure PRAM was suggested.2〕 However, it was difficult to fill GST layer in a small hole with a conventional sputtering tool because a big overhang occurred. In this work, we prepared GST films on the small hole patterned wafer by a new concept sputtering tool which designed developed a new concept sputtering tool. The structure of GST film was observed with cross section SEM and the film composition was measured with XRF. It was observed an overhang was suppressed and a GST film was filled in a small hole with a new concept tool. In addition, the uniformity of the GST film composition was good at almost 1% in 200mm φ substrate. EXPERIMENT A multi-chamber sputtering system ULVAC ENTRONTM-EX (Figure 1) was used for GST deposition on φ200mm hole patterns substrates. GST films were deposited at R.T. by magnetron sputtering with a φ 300mm sintered target. The GST deposition conditions are shown
in Table.1. A scanning electron microscope (SEM) was used to observe the filling profile of GST. XRF analysis was used to evaluate the composition of the films. The Sheet resistances of the GST films are measured by Omnimap RS-100 (KLA tencore). A test phase-change device was fabricated by the process shown in Figure 2. The fabricated device was reversibly switched between crystalline (set) and amorphous (reset) phases using a pulse generator. The voltage and the width of set and reset pulse were 3.0V ñ100nsec and 5.0V ñ 50nsec respectively. Figure1. multi-chamber sputtering system ULVAC ENTRONTM-EX Table l. Sputtering conditions Sputtering condition ï Sputtering tool ï Target ï Substrate ï
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