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据《Semiconductor World》1992年第8期报道,日本日立制作所制作了世界上最小的256M DRAM存储单元。 该存储单元的设计规格为0.25μm,尺寸为0.6μm×1.2μm(0.72μm~2)。原准备使用准分子激光光刻来实现规模生产,但由于投资庞大而用i线+移相掩模技术来进行尝试。难点是焦深问题。一般在NA=0.5情况下,i线的焦深约为±0.25μm,结合使用移相掩模技术其极限约为±0.6μm。此外,圆筒形电容存储器的存储阵列与周边电路的段差为1.0μm。
According to “Semiconductor World” No. 8, 1992 reported that Japan’s Hitachi produced the world’s smallest 256M DRAM memory cell. The memory cell has a design size of 0.25μm and a size of 0.6μm × 1.2μm (0.72μm ~ 2). The original preparation for the use of excimer laser lithography to achieve the scale of production, but because of huge investment with i-line + phase shift mask technology to try. Difficult point is the depth of focus. Generally at NA = 0.5, the i-line has a depth of focus of about ± 0.25 μm, and the limit in combination with phase-shift masking techniques is about ± 0.6 μm. In addition, the difference between the memory array of the cylindrical capacitor memory and the peripheral circuit is 1.0 μm.