In effort to further reduce the EOT scaling process while simultaneously maintaining low Ditand high mobility on III-V semiconductor surfaces, dry cleaning methods have been implemented to help create uniform and ordered semiconductor surfaces. The scaling of gate oxides on MOSFETs requires ALD oxide nucleation in every unit cell of the semiconductor channel surface, a process which depends having a highly ordered semiconductor with the minimization of surface defect sites which prevent ALD oxide deposition thereby inducing pihole formation. Through the use of in situ scanning tunneling microscopy (STM) and an atomic hydrogen cleaning technique, air exposed (001) InGaAs samples with an In/Ga rich 4x2 surface reconstruction and an As rich 2x4 surface have been restored to the order and cleanliness of MBE grown samples.

 

The InGaAs samples were exposed to air, containing NOx, ozone, and hydrocarbons, and returned to UHV for STM atomic imaging. Imaging confirmed the surfaces became amorphous upon air exposure. The samples were exposed to 150L dose of atomic hydrogen at 380°C. After atomic hydrogen dosing, STM revealed the restoration of the ordered pure In/Ga rich 4x2 surface reconstruction with highly flat atomic terraces. Atomic H cleaning results in formation of deep etch features but a subsequent anneal at 460 ˚C for 30 min can reduce this effect. Etch pit density has been quantified for samples both after hydrogen dosing and after the post annealing process. Results showed a 98% reduction in etch pit density following the post annealing process [1]. For formation of the pure As-rich 2x4 reconstruction with no group III rich regions, a relatively small processing window was found introducing the air exposed sample to a 1800L dose of atomic hydrogen at 285°C to form the pure 2x4 reconstruction. Etch pit formation occurred following hydrogen dosing and the samples were subsequently annealed to 290°C for 30 minutes. Etch pit density was quantified for samples before and after post deposition annealing and results showed a decrease in etch pit density by 55% following the post annealing process.

 

[1] W. Melitz, J. Shen, T. Kent, A. C. Kummel, and R. Droopad, " InGaAs surface preparation for ALD by hydrogen cleaning and improvement with high temperature anneal," J. Appl. Phys., vol. 110, p. 013713, 2011.