Abstract: A method for real-time monitoring the fabrication of magnetic memory units uses an ion beam milling machine, mainly using plasma to etch the films. The method for real-time measuring resistance during etching can acquire the charge carriers' transport characteristics of tunneling resistance with current perpendicular to the plane of film. By means of monitoring the etching end point by a module of tunneling magneto-resistance (TMR) memory unit on the chip, other tunneling magneto-resistance memory units on the chip can be fabricated in situ. By controlling applied voltage and etch time of the etch machine, samples of varying film thicknesses can be obtained. Different materials have different etch rates which depends on the amount of argon, applied voltage and accelerated voltage used in etching. This invention can modulate adequate parameters according to the requirements of different products, whose advantages include real-time management and analysis of non-conformities and causes.