| AVS 61st International Symposium & Exhibition | |
| Selective Deposition as an Enabler of Self-Alignment Focus Topic | Wednesday Sessions |
| Session SD-WeA |
| Session: | Process Development for Selective Deposition and Self-Aligned Patterning |
| Presenter: | Gregory Parsons, North Carolina State University |
| Authors: | G.N. Parsons, North Carolina State University B. Kalanyan, North Carolina State University S.E. Atanasov, North Carolina State University |
| Correspondent: | Click to Email |
Selective area CVD has been heavily studied, and several strategies for selective growth are known, including sacrificial reactions, surface activation, nucleating species removal and passivation of non-growth surfaces. However, the success of selective deposition processes in manufacturing has been limited. Atomic layer deposition allows the partial pressure and exposure sequence of individual reactants to be independently adjusted, providing additional control in surface reaction sequence. Surface passivation layers can promote selective area ALD of metals and dielectrics, but integration into manufacturing can be a challenge. Recently, we have studied modified ALD process sequences as a means to control nucleation, without the need for pre-deposited nucleation blocking layers. For example, tungsten ALD using WF6/SiH4 onto SiO2 proceeds when surface Si-H (from SiH4) begins to form, allowing WF6 reduction to W and elimination of SiF4. We hypothesized that the introduction of a H2 or H-plasma exposure into the ALD sequence after the SiH4 dose may help remove Si from the SiO2, which could extend the nucleation delay on SiO2, while not affecting W growth on Si. Using ellipsometry, XPS, high resolution SEM and in-situ quadrupole mass spectrometry we found that a H2 exposure step after SiH4 during W ALD on ex-situ prepared SiO2 decreased the rate of W nucleation compared to growth without the H2 step, effectively increasing the selectivity window. At 220°C, one ALD cycle produced nm-scale nuclei on Si-H surfaces, and film coalescence after ~10 cycles, whereas growth on SiO2 showed no W nuclei after 10 cycles. After some nucleation, growth proceeded readily on the nuclei, with few new nuclei forming, producing rough surfaces that coalesced after 40 cycles. Including the H2 exposure step after SiH4 delayed nucleation by 5-10 cycles on SiO2, with no noticeable effect on Si-H. However, we found that removing surface carbon from the SiO2 prior to growth had a similar effect, indicating that C helped aid nucleation. Recent work with H2-plasma exposure also shows enhanced nucleation on SiO2, which likely depends on the extent of H exposure. In other studies, we are examining metal oxide nucleation using metal/metal alkoxide reaction sequences and comparing to similar reactions with water as a reactant. These results will help to define ALD nucleation sequences that are distinct from steady-state film growth, to achieve reliable selective area deposition.