U. Glaeser

FIGURE 1.1
by using PMOS technology in which threshold voltage control was easier, but soon the PMOS was replaced
by NMOS, which was suitable for high speed operation. It was the middle of 1980s when CMOS became
the main stream of Silicon LSI technology because of its capability for low power consumption. Now
CMOS technology has realized 512 Mbit DRAMs and 1.7 GHz clock MPUs, and the gate length of
MOSFETs in such LSIs becomes as small as 100 nm.
Figure 1.2 shows the cross sections of NMOS LSIs in the early 1970s and those of present CMOS LSIs.
The old NMOS LSI technology contains only several film layers made of Si, SiO2,
and Al, which are
basically composed of only five elements: Si, O, Al, B, and P. Now, the structure becomes very complicated,
and so many layers and so many elements have been involved.
In the past 30 years, transistors have been miniaturized significantly. Thanks to the miniaturization,
the number of components and performance of LSIs have increased significantly. Figures 1.3 and 1.4
show the microphotographs of 1 kbit and 256 Mbit DRAM chips, respectively. Individual tiny rectangle
units barely recognized in the 16 large rectangle units of the 256 M DRAM correspond to 64 kbit
DRAM. It can be said that the downsizing of the components has driven the tremendous development
of LSIs.
Figure 1.5 shows the past and future trends of the downsizing of MOSFET’s parameters and LSI chip
properties mainly used for high performance MPUs. Future trend was taken from ITRS’99 (International
Technology Roadmap for Semiconductors) [2]. In order to maintain the continuous progress of LSIs for
future, every parameter has to be shrunk continuously with almost the same rate as before. However, it
was anticipated that shrinking the parameters beyond the 0.1 µ m generation would face severe difficulties
due to various kinds of expected limitations. It was expected that huge effort would be required in research
and development level in order to overcome the difficulties.
In this chapter, silicon technology from past to future is reviewed for advanced CMOS LSIs.
© 2002 by CRC Press LLC
TABLE 1.1
Year
Past and Current Status of Advanced LSI Products
Min.
( µ m) Ratio DRAM Ratio MPU Ratio
L
g
1970/72 10 1 1 k 1 750 k 1
2001 0.1 1/100 512 M 256,000 1.7 G 2,300
Year 2001 New Century for Solid-State Circuit
73 years since the concept of MOSFET
20th C 1928, J. Lilienfeld, MOSFET patent
54 years since the 1st Transistor
1947, J. Bardeen, W. Bratten, bipolar Tr
43-42 years since the 1st Integrated Circuits
1958, J. Kilby, IC
1959, R. Noice, Planar Technolgy
41 years since the 1st Si-MOSFET
1960, D. Kahng, Si-MOSFET
38 years since the 1st CMOS
1963, CMOS, by F. Wanlass, C. T. Sah
31 years since the 1st 1 kbit DRAM (or LSI)
1970 Intel 1103
16 years since CMOS became the major technology
1985, Toshiba 1 Mbit CMOS DRAM
History of LSI in 20th century.