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The simplest stacked capacitor with BST thinner films (about 50nm-thick) grown by a novel low temperature growth [ 11 was demonstrated. The storage node without sidewall spacer was constructed by thinner Ru-layer, sputtered-TiN diffusion barrier, TiSix electrical contact layer and poly-Si plug. The low temperature BST growth prevented the leakage current increase of BST films as thin as 25nm. Therefore, 50% step coverage BST-capacitor was performed as sidewall-less simple stacked capacitors with large storage charge. Introduction(Ba, Sr)TiO, film with high dielectric constant has been extensively investigated in view of its applications to simple stacked capacitors for high density DRAMS. Recently, Ru and/ or RuO, as storage node has been applied on the capacitor structure, on the point of view in dry-etching and electrical conduction [2]. However, Ru is not so stable for oxygen at high temperatures which causes of increase in roughness at the surface. Therefore, low temperature BST growth processes has been required for the capacitor fabrications. Chemical vapor deposition using metalorganic sources [2] or mist sources [3] have recently been proposed for the low temperature deposition with excellent step coverage, however, the deposition temperature was considered higher for Ru-layer. Therefore, in the case of CVD process for BST deposition, RuO,/Ru multilayer must be used [2].This paper is to demonstrate the simplest stacked capacitor with Ru storage node using a novel lower temperature BST growth enhanced crystallization by reactive sputtering.

Phone: +81-44-548-5359 ' Toshiba Intelligent Technology Corporation Phone: +81-44-548-5710 1. Introduction A high density recording was investigated by using a mark-edge recording method forAgTe-C hlm [l], where an ablative recording was carried out to form a pit. The tracking servo control was pointed out to be influenced by the decrease of reflectivity, which was brought about by the long length pits formed repeatedly. Ge-Sb-Te/Bi-Te write-once disk was developed as a nonablative type media, where data were recorded by the alloying process between the two layers, to keep the tracking servo controlbeing stable.We will report the mark-edge recording charicteristics and the reliability of the disk using an alloying process 2. Experimental Figure 1 exhibits the cross sectional view of the recording layers. These two layers were prepared by an rf-magnetron sputtering onto a polycarbonate substrate having a pregrmve of 1.6 um track pitch. The surface of Bi-Te layer was covered with a layer of W light cured resin. The laser beam of 830 nm in wavelength was focused by an objective lens with a numerical aperture (NA) of 0.55. Carrier to noise ratio (CNR) was measured at a recording frequency of 3.7 M H z and a linear velocity of 5.7 m/s. The measurements of byte erorr rate (BER) were carried out for the random data recorded by using a (1,7)RLL code without waveform equalization. 3. Results and Discussion Figure 2 shows the dependencre of the CNR on the recording power. With 50 ns pulse width, the CNR reached 50 dB at 5 mW; the CNR of more than 50 dB was obtained up to 15 mW. With 100 ns pulse width, 50 dB was obtained at 4 mW; the CNR reached the peak level of 56 dB, then decreased to less than 50 dB because of the readout interference. Figure 3 indicates the dependence of the BER on the recording power at the linear velocity of 5.7 m/s. For the linear density of 0.68 um/bit, the BER was about 2E-5 in the recording power region from 7 to 14 mW. It is recognized that the Ge-Sb-Te/Bi-Te disk has a wide recording power tolerance of +33% at the center power of 10.5 mW. The leveled off value of the BER curve, 2E-5, for 0.68 um/bit was approximately equal I uv light curing resin I I I Polycarbonate substrate Fig.1 Cross sectional view of the disk 60 -0-lOOnsec t-50nsec Linear Velocity : 5.7 m/s Recording Frequency : 3.7 ,WIZ 5 10 15 Recording Power (mW) Fig.2 CNR vs. recording power