Surface Protection and Selective Masking during Diffusion in Silicon

Abstract

An apparatus is described for the vapor‐solid diffusion of donors and acceptors into silicon at atmospheric pressure. It consists essentially of a fused silica tube extending through one or more controlled temperature zones. A gas such as nitrogen carries the vapors from the heated impurity element or one of its compounds past the heated silicon.At temperatures above about 1000 °C, gases such as helium or nitrogen are shown to cause serious pitting or erosion of the silicon surfaces. A thin vitreous silicon dioxide envelope enclosing the silicon during the high temperature heating operation is shown to provide complete protection of the underlying surface against damage. Methods of obtaining surface passivation are described.In addition to surface protection, a silicon dioxide surface layer also is shown to provide a selective mask against the diffusion into silicon of some donors and acceptors at elevated temperatures. Data are presented showing the masking effectiveness of the silicon dioxide layer against the diffusion of several donors and acceptors into silicon.The application of the masking technique to produce precise surface patterns of both n‐ and p‐type is described. An example of its feasibility in device considerations is illustrated by the construction of a transistor by double diffusion. This transistor is unique in that both the emitter and base contacts are made at the surface in adjacent areas.Finally a new predeposition technique is described for controlling the impurity levels in diffused layers over wide ranges. Data are presented to illustrate this technique.

Physical and predictive models of ultrathin oxide reliability in CMOS devices and circuits

“…Gate oxide failure is a weakest-link type of problem because failure of the whole chip is defined by the failure of the first individual device, and a device fails if any small portion of the gate area of the device breaks down. From elementary statistics, if the probability of any one unit failing is then the probability of any one of independent units failing is (7) so that (8) The Weibull plot [ (6)] thus has the extremely useful property that if the area is increased by a factor then the curve shifts vertically by . Fig.…”

“…The reliability of SiO , i.e., the ability of a thin film of this material to retain its insulating properties while subjected to high electric fields for many years, has always been an important issue and has been the subject of numerous publications over the last 35 years [2]- [6], since the realization that SiO could be used as an insulating and passivating layer in silicon-based transistors [7], [8]. Oxide reliability and the experimental methods for accelerated testing have been the subject of earlier review papers [9]- [18].…”

Introduction to the History of Semiconductors

“…62 They also contributed their paper "Surface protection and selective masking during diffusion in silicon" in 1957. 63 Figure 1.3 shows the cross-sections of 2 double diffused silicon npn transistors according to Aschener et al (Bell Laboratories). 48 The area of the collector-base junction was defined by a mesa etch process.…”

Applications of Oxide Coatings in Photovoltaic Devices

“…Additionally thermally grown SiO x is used as a diffusion mask for common dopants of silicon such as boron, phosphorous, arsenic and antimony, and has long been used as a mask for spatially selective impurity doping on c-Si wafers [69]. TiO x has also been investigated as a phosphorus blocking barrier during the POCl 3 treatment to form a selective emitter in buried contact silicon PV cells [70].…”