Patent Number: 
Section: claims

1. A method of preparing a sample for transmission electron microscopy (TEM), comprising:providing a sample with two pits and a failure region between the two pits, the failure region comprising a semiconductor device;milling a first surface of the failure region until the cross section of the semiconductor device is exposed;etching the first surface of the failure region;cleaning the sample; andmilling a second surface of the failure region until the failure region can be passed by an electron beam. 2. The method according to claim 1, wherein the first surface of the failure region is etched by a mixed acid solution. 3. The method according to claim 2, wherein the first surface of the failure region is etched for 7 s-9 s. 4. The method according to claim 2, wherein the mixed acid solution comprises nitrate acid, hydrofluoric acid, acetic acid, and copper sulfate. 5. The method according to claim 4, wherein the mass percentage of the nitrate acid is 45%-60%, and the mass percentage of the hydrofluoric acid is 4.5%-5%. 6. The method according to claim 5, wherein the nitrate acid is 10 ml-15 ml; the hydrofluoric acid is 5 ml-10 ml; the acetic acid is 80 ml-100 ml; and the copper sulfate is 0.2 g-0.5 g. 7. The method according to claim 1, wherein the first and second surfaces of the failure region are milled by FIB. 8. The method according to claim 1 or 7, wherein the first surface and the second surface of the failure region are milled by FIB with a current of 300 pA-500 pA. 9. The method according to claim 1, wherein the sample is cleaned by distilled water or deionized water for 60 s-120 s. 10. The method according to claim 1, wherein the second surface of the failure region is milled until the thickness of the failure region which can be passed by an electron beam is 80 nm-120 nm. 11. The method according to claim 3, wherein the mixed acid solution comprises nitrate acid, hydrofluoric acid, acetic acid, and copper sulfate. 12. The method according to claim 11, wherein the mass percentage of the nitrate acid is 45%-60%, and the mass percentage of the hydrofluoric acid is 4.5%-5%. 13. The method according to claim 12, wherein the nitrate acid is 10 ml-15 ml; the hydrofluoric acid is 5 ml-10 ml; the acetic acid is 80 ml-100 ml; and the copper sulfate is 0.2 g-0.5 g. 14. The method according to claim 7, wherein the sample is cleaned by distilled water or deionized water for 60 s-120 s. 15. The method according to claim 7, wherein the second surface of the failure region is milled until the thickness of the failure region which can be passed by an electron beam is 80 nm-120 nm.