Bird's Beak Configuration and Elimination of Gate Oxide Thinning Produced during Selective Oxidation

Abstract

In the selective oxidation scheme for processing Si MOS devices, Si3N4 is used to mask gate oxide areas against the isolation oxidation. After removing the Si3N4 , gate oxide is grown. This scheme produces three topographical features which have ramifications in subsequent processing and in device properties: a notch in the isolation oxide, penetration of the isolation oxide under the masking Si3N4 , and thinning of the gate oxide at the isolation oxide edge; the first two features form the bird's beak configuration. The transmission electron microscope was applied to thin film (<1 μm) cross sections through the bird's beak in order to obtain an accurate description of these features. The bird's beak extended typically 1.5 and 0.8 μm in the n‐ and p‐channel structures, respectively, leading to a corresponding decrease in the active device length of 3.8 and 2.3 μm for the 1.4 μm thick isolation oxide. Gate oxide at the edge of the bird's beak was thinned 35–100% in the n‐channel samples and 20–50% in the p‐channel samples. It was found that oxidation subsequent to the isolation oxidation and Si3N4 removal destroys the oxidation barrier (wet oxidation seemingly more effective than dry and more convenient). Thus, a method which incorporates an additional, short, sacrificial wet oxidation step between isolation and gate oxidations, in order to overcome the thinning phenomenon, is described.

Elasto-Capillary Folding Using Stop-Programmable Hinges Fabricated by 3D Micro-Machining

“…The stop-programmable hinge shown in Fig 10(c) is nearly identical to the schematic presented in the process flow, Fig 4(k) , except for the small bumps visible at the transitions between the thin and the thick parts of the smart hinges. These transitions are called ‘bird’s beaks’ because of their characteristic shapes [ 52 ], and originate from the oxidation step necessary to remove the polySi layer between steps (h) and (i) in Fig 4 .…”

“…This short oxidation step will consume the polySi material and slightly increase the radius of curvature of the mold. Moreover, the oxidation of the Si substrate will yield a specific shape, known as a bird’s beak, at the transition between the Si and the SiRN [ 52 ]. This shape is not visible in Fig 4 but will be shown in the results part of the paper ( Fig 10 ).…”

Recent developments of the two-dimensional technological process simulator OSIRIS

“…The parameters a,, bl, ai, bi, ... are functions of processing parameters eo x and en, and three characteristic features of the « bird's beak » : Eo x (given by Deal Grove's model [23]), Lbb (Length of lateral oxidation under the nitride layer) and H (lifting of the mask during oxidation) [21,24,25]. At the beginning of the oxidation cycle, we assumed that the initial pad-oxide was etched on the left side of the mask edge so :…”

Elastocapillary self-folding of micro-machined structures

“…This short oxidation step will consume the polySi material and slightly increase the radius of curvature of the mold. Moreover, the oxidation of the Si substrate will yield a specific shape, known as a "bird's beak", at the transition between the Si and the SiRN [111]. This shape is not visible in /12(1−ν 2 ) for thin plates, where E is Young's modulus and ν is Poisson's ratio [57].…”

“…However, the quality of the first SiRN layer should be checked at the beginning of the fabrication.The stop-programmable hinge shown inFigure 4.10-(c) is nearly identical to the schematic presented in the process flow,Figure 4.4-(k), except for the small bumps visible at the transitions between the thin and the thick parts of the smart hinges. These transitions are called "bird's beak" because of their characteristic shapes[111], and originate from the oxidation step necessary to remove the polySi layer between steps (h) and (i) inFigure 4.4. A nearly released tetrahedral pattern is presented in Figure 4.10-(d).…”