The thermoacoustic sensors are getting more and more attention with the discovery of thermalinduced ultrasonic emission phenomenon from the porous silicon. The thermoacoustic sensors generate the alternating pressure in the surrounding air by changing the heat of the surface of the device, thereby emitting sound waves outward. The suspended metal film is the key component of the thermoacoustic sensor. However, it is difficult to prepare and release the largearea suspended film and it is necessary to consider the stress and adhesion effect of the metal film itself. In this paper, two methods based on the isotropic dry etching for fabricating metal thin films are proposed, and the suspended Al membrane is fabricated by XeF2/SF6. Because the XeF2 gas has a higher choice ratio for Al while etching silicon, and for silicon, it has a high etching rate for isotropic etching. By setting the parameters of ICP etching machine, SF6 can also be used for isotropic etching. The suspended Al membrane is fabricated based on the abovementioned characteristics. The corresponding preparation process is designed and the appropriate etching parameters of XeF2 etching machine and ICP etching machine are explored. The prepared suspended Al membrane has a smooth, free of impurities and has good morphology.