A simulator for aluminum etching was developed in order to analyze the microloading effect. We have adopted the procedure that the flux rates (gas particles, ions, and sputtered mask fragments) are calculated independently as a function of trench aspect ratio; then the etching rate is calculated with these flux rates at each aspect ratio. The simulator can be operated on a personal computer by this simple procedure and the characteristics of aluminum etching can be obtained quickly. The surface reaction parameters were determined by fitting the calculated result to the basic experimental etching rate data. By using these surface reaction parameters the simulator can predict the characteristics of aluminum etching such as etching rate, selectivity, etc. The difference of the microloading effect between photoresist and oxide mask was also analyzed. It was confirmed by this simulator that the microloading effect was affected by the sputtered photoresist fragments.