Nano-regime Length Scales Extracted from the First Sharp Diffraction Peak in Non-crystalline SiO2 and Related Materials: Device Applications

This paper distinguishes between two different scales of medium range order, MRO, in non-crystalline SiO2: (1) the first is similar to 0.4 to 0.5 nm and is obtained from the position of the first sharp diffraction peak, FSDP, in the X-ray diffraction structure factor, S(Q), and (2) the second is similar to 1 nm and is calculated from the FSDP full-width-at-half-maximum FWHM. Many-electron calculations yield Si-O third- and O-O fourth-nearest-neighbor bonding distances in the same 0.4-0.5 nm MRO regime. These derive from the availability of empty Si d pi orbitals for back-donation from occupied O p pi orbitals yielding narrow symmetry determined distributions of third neighbor Si-O, and fourth neighbor O-O distances. These are segments of six member rings contributing to connected six-member rings with similar to 1 nm length scale within the MRO regime. The unique properties of non-crystalline SiO2 are explained by the encapsulation of six-member ring clusters by five- and seven-member rings on average in a compliant hard-soft nano-scaled inhomogeneous network. This network structure minimizes macroscopic strain, reducing intrinsic bonding defects as well as defect precursors. This inhomogeneous CRN is enabling for applications including thermally grown similar to 1.5 nm SiO2 layers for Si field effect transistor devices to optical components with centimeter dimensions. There are qualitatively similar length scales in nano-crystalline HfO2 and phase separated Hf silicates based on the primitive unit cell, rather than a ring structure. Hf oxide dielectrics have recently been used as replacement dielectrics for a new generation of Si and Si/Ge devices heralding a transition into nano-scale circuits and systems on a Si chip.