Defect delineation

In the early days of silicon device manufacturing the need for surfaces with a low defect density led to the development of CP solutions. Defect etchants were developed at the same time in order to study the crystal quality for different crystal growth processes. The improvement of the growth methods and the introduction of chemo-mechanical polishing methods led to defect-free single crystals with optically flat surfaces of superior electronic properties. This reduced the interest in CP and defect delineation. 

Etchants for defect and junction delineation are usually composed of HF and an oxidizing agent such as HN03 [Dal, Gr4, Ka4, Nel], K2Cr207 [Se5] or Cr03 [Sil, Jel, Sc7, Ya4, Me5]. Alkaline solutions are rarely used for defect delineation [Mal2], An etch pit will form on a silicon surface if the dissolution rate is enhanced locally. Enhancement of the etch rate may occur for various reasons ... 

The successful fabrication of SiC based devices cannot be realized without reliable etching and cleaning processes for this material. The purpose of this Chapter is to review the developments and methods of etching silicon carbide for device applications. The term etching is used to describe the processes by which SiC material can be removed. It also includes chemical machining of a semiconductor as part of the fabrication process, as well as defect delineation. 

The defect question delineates solid behavior from liquid behavior. In liquid deformation, there is no fundamental need for an unusual deformation mechanism to explain the observed shock deformation. There may be superficial, macroscopic similarities between the shock deformation of solids and fluids, but the fundamental deformation questions differ in the two cases. Fluids may, in fact, be subjected to intense transient viscous shear stresses that can cause mechanically induced defects, but first-order behaviors do not require defects to provide a fundamental basis for interpretation of mechanical response data. 

The defect population in the doped solid under moist conditions then consists of V%, OHo, h, and Y /x. The domains over which each species is dominant for conductivity can be represented diagrammatically when data concerning the conductivity of the solid has been measured (Fig. 8.20). In this representation, the conductivity fields are bounded by lines tracing the locus where the transport number for a pair of defects is equal to 0.5. (The diagram could equally well be drawn in terms of domains delineating the defect species that predominate.)... 

Acidic silicon etchants are mainly used for two purposes for the delineation of crystal defects, as discussed in Section 2.5, or to remove silicon in an isotropic manner. Isotropic etching adds another degree of freedom to the design of micromechanical structures, because all alkaline etches are anisotropic. Most isotropic etchants for silicon were developed in the early days of silicon crystal technology and exhaustive reviews on this topic are available [Tu3, Rul]. A brief summary is given below. 

The rate of flow of electrons from such a charged particle depends on the availability of an accessible site for this transfer. Although it is known that lattice defects provide such sites and that conduction band electrons can trickle down through solid dislocation levels reduction sites for electron accumulation are usually provided by metallization of the semiconductor particle. This can be achieved through photo-platinization or by a number of vapor transfer techniques and the principles relevant to hydrogen evolution on such platinized surfaces have been delineated by Heller The existence of such sites will thus control whether single or multiple electron transfer events can actually take place under steady state illumination. 

Once an equivalent authority receives an inspection report from another equivalent authority (post- or preapproval reports), the receiving authority will normally endorse the report, except under specific and delineated circumstances (e.g., material inconsistencies or inadequacies in inspection report, quality defects identified in postmarket surveillance, and specific evidence of serious concern in relation to product quality or consumer safety [39]. In these exceptional cases, the importing country s regulatory authority may request clarification from the exporting country, which could result in a request for reinspection. In addition, the importing country might conduct its own inspection of the production facility if attempts at clarification are not successful [40]. 

Each of the four cases delineated [(ci), (cv), (ai), and (av)] is developed individually in such a way that it is self-contained. Each theoretical development is preceded by a formulation of the relevant equations for the defect solid-state reactions [63, 64] occurring at the phase boundaries separating the oxides. That is, balanced chemical equations involving... 

Thus, as is increasingly being recognised, the defects in some crystals are simply structures of another type and regular arrays of defects simply generate new structure types. In the present instance we have a new mode for generating more complex structures from simple prototypes, i.e. a new structure-building principle. Its delineation will, it is hoped, lead to the more complete elucidation of further examples. 

It has been found, however, that the etch rate of PBS can be reasonably controlled in both oxygen and CF4/O2 plasmas if the substrate temperature is kept below room temperature (9). This fact has been utilized to reduce the defect density in the manufacture of chrome photomasks by exposing the developed PBS pattern to a low-temperature oxygen plasma (descum) prior to wet-etching the chrome. We have now found that the plasma-etch resistance of PBS in a CF4/O2 plasma can be markedly enhanced at room temperature simply by exposing the resist to a short oxygen plasma pretreatment prior to exposure to the fluorinated plasma. This effect can be used in a variety of pattern transfer processes to controllably generate submicron features on wafers and masks. This paper examines the parameters associated with this effect, proposes a mechanism to account for the results and delineates some possible pattern transfer processes. 

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