Abstract-Readily available process, device, and circuit simulation programs have been integrated into an effective system for enhancing semiconductor product ...
554
IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN. VOL.
CAD-4. NO. 4. OCTOBER 1985
Practical Integration of Process, Device, and Circuit Simulation RALPH J. S OKEL,
MEMBER, IEEE,
AND
DONALD B. MACMILLEN,
Abstract-Readily available process, device, and circuit simulation
MEMBER,
IEEE
found that the use of simulation is cost effective, espe cially when compared with silicon wafer processing costs, semiconductor product development. In this paper, the system will be and provides quantitative results when used jUdiciously. discussed with particular emphasis on the problems encountered in Realization of the benefits of using simulation is not easy making simulation tools accessible to users. Each of the primary pro in practice. We have identified three major attributes which grams is reviewed, and the modifications and enhancements which have been made to adapt the programs to our requirements are discussed. must exist, either in each of the individuals using the sim The problem of interpolating impurity concentration profiles between ulation programs or in a closely coupled group of users, process simulation grids and device simulation grids is discussed. The to utilize the simulation tools effectively. Most important link between device simulation and circuit simulation is parameter ex is a good understanding of the process or system being traction. The application of optimization techniques for parameter ex simulated. This includes an appreciation of the models traction is considered. used and their range of applicability and their limitations. Secondly, one must understand the computing environ 1. I NTRODUCTION ment and be able to adapt to or modify this environment UCH W ORK has been done in the area of applying so that the simulation tools can be used efficiently. Finally, numerical analysis techniques to simulate the behav an understanding of the numerical techniques employed is ior of physical processes and systems. For example com needed so that problems can be structured or defined to puter programs for simulating silicon device fabrication improve the chances of obtaining accurate results. Also processes, for calculating electron transport in bipolar and understanding the numerical algorithms along with the metal-oxide-semiconductor (MaS) transistors, and for relevant physics is required for interpreting results espe simulating complex circuits containing these transistors are cially when questions of convergence arise. All problems readily available. Less emphasis has been placed, how and pitfalls encountered while working with numerical ever, on the problems encountered when one tries to in simulation programs can be traced to one of these attri tegrate these software tools to enhance semiconductor butes. product development activities by reducing the time re In what follows each of the major simulation compo quired for technology development and circuit design and nents-process, device and circuit-is discussed. Next the by eliminating costly iterations which result from trial interfaces between the programs are discussed. The prob and-error approaches. Computer-aided design of circuits lem of grid matching between process and device simu has been a necessity for some time, and the software and lation is considered, and the problem of extracting param hardware developed for this purpose are fairly well ad eters from the results of device simulation for use in vanced. Although process and device simulation tools are subsequent circuit simulation is treated. In Fig. I the sim available, they have not been utilized to the extent that ulation system which is discussed is shown for subsequent circuit simulation tools have been. This situation, espe reference. We emphasize that the following treatment is cially for advanced memory products like the 4-Mbit dy not meant to be exhaustive. Our intent is to extract from namic RAM, is changing quickly as silicon device struc practical experiences some of the areas which need con tures are developed to cope with the demand for more sideration for simulation to acquire credibility in a product highly integrated circuits. Therefore, the emphasis of this development environment. paper is the integration of process and device simulation tools and parameter extraction for circuit simulation. II. P ROCESS SIMULATION A simulation program, to be practical, must approxi The primary purpose of process simulation is to obtain mate the physics which describes the system to be simu impurity concentration profiles in silicon which can be lated. By definition, therefore, all simulation programs used in device simulation programs to predict the terminal have limitations and fail to give correct answers under all current-voltage characteristics of the fabricated device. conditions. Despite this fundamental limitation we have These programs simulate, at various levels of sophistica tion, the important silicon fabrication steps such as im Manuscript received January 17, 1985; revised April IS, 1985. purity diffusion and ion implantation. The primary pro R. 1. Sokel is with INMOS Corporation, Colorado Springs, CO 80935. cess simulation program which we use is SUPREM [1]. D . B. Mac Millen was with INMOS Coroporation, Colorado Springs, CO. He is now with Sierra Semiconductor, Sunnyvale, CA 94086. We also use SUPRA [2] for special modeling purposes.
programs have been integrated into an effective system for enhancing
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