9:45 AM - 10:00 AM
[15a-2Q-4] Self-limiting Cyclic Etching of SiN Using Formation and Desorption of (NH4)2SiF6
Keywords:etching,SiN
Recent progress in 3D devices is increasing demand for precisely controlled etching of various materials. One approach for achieving precise etching is cyclic etching, namely, repeated formation and removal of nonvolatile reaction products. Formation and sublimation of ammonium hexafluorosilicate ((NH4)2SiF6) has been used for cyclic etching of SiO2. To meet the requirements concerning a variety of materials to be etched, cyclic etching of SiN must be developed.
One important issue concerning the development of highly precise cyclic etching is to form protective and self-limiting reaction products. It has been reported that fluorocarbon-based plasmas produce protective (NH4)2SiF6 films as a reaction product on SiN. In this study, self-limited cyclic etching of SiN using formation and sublimation of (NH4)2SiF6 was developed.
Silicon nitride deposited by low-pressure CVD was used as the sample material. Several samples were exposed to radicals that were generated in fluorocarbon-based gas mixtures and were then annealed by using circulating fluid. The surface of the samples was analyzed by XPS.
Photoemission spectra obtained after radical exposure and after 100°C annealing of the SiN samples are compared. A nitrogen 1s peak (402.0 eV), which has previously been assigned as ammonium salt, is observed after radical exposure. A silicon 2p peak (103.0 eV), previously assigned as the Si4+ state, is observed simultaneously. Atomic concentrations of the sample surface are 0% carbon, 22.4% nitrogen, 0.1% oxygen, 67.7% fluorine, and 9.8% silicon after radical exposure. The ratio of nitrogen, silicon, and fluorine is roughly 2:1:6, which matches the compositional ratio of (NH4)2SiF6. These observations provide evidence that (NH4)2SiF6 is formed as a reaction product. After the samples were annealed at 100°C, the two peaks disappeared. A nitrogen 1s peak (397.5 eV) and a silicon 2p peak (101.7 eV), which are both attributed to SiN, appeared after the (NH4)2SiF6-related peaks disappeared. This phenomenon implies that the (NH4)2SiF6 sublimated.
The preliminary results of cyclic etching are plotted. Radical exposure time was 40 or 80 seconds, and annealing temperature was 120°C. The etching depth increases with increasing number of repetitions of the cycle. In one cycle of radical exposure and annealing, it is 2.6 nm. Because the etching depth does not depend on radical exposure time, it is concluded that the formation of the (NH4)2SiF6 film is self-limited. That is, self-limiting cyclic etching of SiN was successfully demonstrated.
One important issue concerning the development of highly precise cyclic etching is to form protective and self-limiting reaction products. It has been reported that fluorocarbon-based plasmas produce protective (NH4)2SiF6 films as a reaction product on SiN. In this study, self-limited cyclic etching of SiN using formation and sublimation of (NH4)2SiF6 was developed.
Silicon nitride deposited by low-pressure CVD was used as the sample material. Several samples were exposed to radicals that were generated in fluorocarbon-based gas mixtures and were then annealed by using circulating fluid. The surface of the samples was analyzed by XPS.
Photoemission spectra obtained after radical exposure and after 100°C annealing of the SiN samples are compared. A nitrogen 1s peak (402.0 eV), which has previously been assigned as ammonium salt, is observed after radical exposure. A silicon 2p peak (103.0 eV), previously assigned as the Si4+ state, is observed simultaneously. Atomic concentrations of the sample surface are 0% carbon, 22.4% nitrogen, 0.1% oxygen, 67.7% fluorine, and 9.8% silicon after radical exposure. The ratio of nitrogen, silicon, and fluorine is roughly 2:1:6, which matches the compositional ratio of (NH4)2SiF6. These observations provide evidence that (NH4)2SiF6 is formed as a reaction product. After the samples were annealed at 100°C, the two peaks disappeared. A nitrogen 1s peak (397.5 eV) and a silicon 2p peak (101.7 eV), which are both attributed to SiN, appeared after the (NH4)2SiF6-related peaks disappeared. This phenomenon implies that the (NH4)2SiF6 sublimated.
The preliminary results of cyclic etching are plotted. Radical exposure time was 40 or 80 seconds, and annealing temperature was 120°C. The etching depth increases with increasing number of repetitions of the cycle. In one cycle of radical exposure and annealing, it is 2.6 nm. Because the etching depth does not depend on radical exposure time, it is concluded that the formation of the (NH4)2SiF6 film is self-limited. That is, self-limiting cyclic etching of SiN was successfully demonstrated.