Simulation parameter effects on critical dimension and sensitivity of 193 nm Chemically Amplified Resist
It is helpful in lithography process and developing resist to know the relationship between the critical dimension variation and simulation parameters such as aerial image parameters, the Dill exposure parameters, PEB (Post Exposure Bake) parameters, and development parameters. In this paper the profiles of a 193 nm CAR (Chemically Amplified Resist) were simulated with those various parameter, and those results were analyzed by the response surface methodology (RSM) approach to know the influence of independent factors on a dependent response and to optimize each process. Both the parameter effects of each process and the simulation process effects of the whole process were described about critical dimension and side wall angle so that the sensitivity of lithography process could be assumed. The development parameters were modified with those of flood exposure experiment according to the pattern density and pattern size for more accurate lithography simulation. Also those effects on critical dimension and side wall angle were analyzed. For the validity of our results the quantitative comparison between our results and those of a commercial tool was shown.
Characterization of solvent-rich resist coating process
This paper studies the characteristics of a solvent-rich coating process which has demonstrated its abilities to provide wider resist thickness range and better coating uniformity on square substrates. The coating recipe being studied consists three spin steps, spread spin (1st spin), snap spin (2nd spin), and dry spin (3rd spin). A two-level, six-factor fractional factorial design of experiment (the screening test) is conducted first to determine which process parameters the film thickness and coating uniformity is sensitive to. A response surface model is then built for those significant factors. The screening test found that 3rd spin speed and time do not affect film thickness significantly, but should not be ignored in controlling coating uniformity. On the other hand, both 1st and 2nd spin speed and time are important to film thickness as well as coating uniformity. This is contrary to traditional coating systems where spin time is typically not an important factor in determining coating thickness. The central composite design was used to obtain the response surface model (RSM). Analysis shows that the model is adequate to represent the characteristics of a solvent-rich coating system. The four major factors, i.e., 1st spin speed and time, and 2nd spin speed and time are the dominant independent variables in determining film thickness. The first-order interactions between these major factors are weak. It is interesting to notice that the response surface model for coating uniformity is very unreliable, represented by poor model fitting statistics and high p values for individual factors. This is possibly due to the exclusion of 3rd spin speed and time in the central composite design.
Electron‐beam direct writing system EX‐8D employing character projection exposure method
An electron‐beam direct writing system which adopts character projection methods in addition to conventional variable‐shaped beam methods, has been constructed for 0.15 μm class ultra‐large scale integration pattern fabrication. This system is a modified version of our variable‐shaped beam machine. The electron optical system adopts a three stage octapole deflector for a 2 mm field and installs an aperture plate exchange mechanism for character projection. The objective lens system was designed so that the beam resolution is 0.04 μm. An optimization study to write a 1G‐dynamic random access memory pattern with 0.15 μm design rules showed that a preferable character size and number are 2.5 μm and 48, respectively. The writing speed of this system is designed to be 110 s a chip, using the characters for memory cells as well as peripheral circuits. An advanced beam calibration method has been developed for beam current density and for character size, direction, and position. This method effectively adjusts the current density for each character to be the same on wafers. The beam position is accurately corrected by analyzing the obtained beam intensity distribution.