Positive polyimide resists

Positive polyimide resists have also been developed. One example starts from a solnble polymer [60] with a formulation analogons to a novolac positive resist o-naphthoquinone diazide was used as a photoreactant linked to the polymer (Figure 6.25). 

Curing of epoxy resins can be initiated photochemically by release of imidazole from photolabile protected derivatives, such as AT-(2-nitrobenzyloxycarbonyl)imi-dazole. Positive working polyimide resists derived from 2-nitro-p-xylyleneoxy-amine have been synthesized and studied and 2-nitrobenzyloxy derivatives are included in a formulation for submicron imaging. ... 

High-performance polyimide-positive photosensitive heat resistance resins, (id, were prepared by Yamanaka et al. (3) and used in photosensitive compositions. 

Usually, dry etching of polyimide is performed by RIE with O2, CF, or their mixtures as an etchant gas, utilizing positive photoresist (2), metals such as aluminum (3), spin-on-glass (4), or SiN (5) as an etching mask. However, in the former case, it is difficult to define a fine via-hole as small as 2 pm or less because the resist thickness must be two or more times that of the polyimide as a result of the equal etching rates between photoresist and polyimide. In the latter case, though the fine pattern can be obtained the additional pattern transformation from the photoresist to the masking layer is necessary. 

Positive working silicon-containing resist with 0.8 jum resolution and O2 RIE selectivity greater than five was used for fine via hole formation in a polyimide film by O2 RIE process. 

Trilevel Schemes. Trilevel processing (6, 7) requires planarization of device topography with a thick layer of an organic polymer, such as polyimide or a positive photoresist that has been baked at elevated temperatures ( hard baked ) or otherwise treated to render it insoluble in most organic solvents. An intermediate RIE barrier, such as a silicon dioxide, is deposited, and finally, this structure is coated with the desired resist material. A pattern is delineated in the top resist layer and subsequently transferred to the substrate by dry-etching techniques (Figure 3). 

Initially, the experiments apply a commercially available polyimide coating, which is well known from many microelectronic applications. The polyimide (PI 2545, HD Microsystems GmbH) is a high-temperature coating that can be patterned by a positive photoresist. It is dissolved in the same process step as the exposed resist using an alkaline photoresist developer [6], but by different etching rates. 

Specifically for the passivation of temperature sensitive bubble memory devices,these ultrapure materials proved to be of great value. A cure process was optimized to obtain a reliable low temperature cure without affecting the magnetic coercivities of the bubble memory devices. A positive resist process, using a simple development step to pattern via holes in devices has been optimized and successfully used to fabricate devices. The devices fabricated using the the polyimide process have been compared with conventional SiC offers reliable passivations with thinner stress free films for passivations. The fabrications involve simple inexpensive process steps and are compatible with conventional resist processes. The reliability of the imide passivated devices can be considerably enhanced by the use of ultrapure starting materials to preclude harmful ionic mobilities through passivated layers. 

Auger electron spectroscopy with depth profiling via argon ion etching (position and thickness of near-surface layer), transmission electron microscopy of ultramicrotomed cross-sections (physical internal structure), elemental analysis (extent of metal salt conversion), and surface electrical resistivity versus temperature profiles (continuity of near-surface layer). The data from these techniques were used cooperatively to develop a model for these microcomposite polyimide films. The model represents the sample as three distinct regions. Fig. 1. The bulk of the film contains either converted (e.g. Ag) or nonconverted (e.g. C0CI2) additive in a predominately polyimide environment. An oxide-rich (e.g. 0 ) or metal-rich layer (e.g. Ag, Au) interspersed with polyimide accounts for the second region. 

The initial applications of polyimldes were as varnishes and overcoat enamels as wire Insulation. Polyimldes provided significant Improvement in high temperature cut through resistance as well as excellent dielectric properties. They continue In use today both as homopolymers and copolymers with amides and ester moieties. Paralleling this technology was the development by duPont of Kapton polyimide film. Kapton enjoys a strong position as a class 22 f organic film. These applications represent the major portion of polyimide consumption. 

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