Polyimides microelectronic applications

As previously stated, the rigid polyimides meet many of the requirements for microelectronics applications however, the presence of an ordered morphology, coupled with the lack of a softening transition results in extremely poor self-adhesion. Alternatively, thermally stable thermoplastics exhibit excellent self-adhesion, but often lack sufficiently high temperature dimensional stability and/or solubility and processability from common organic solvents. For instance, po-ly(phenylquinoxaline) (PPQ) has a T in the 370 °C range, thereby overcoming... 

Thermostability requirement for microelectronic applications basically involves only the thermo exposure during processing. Since the devices are not expected to operate at anywhere near the processing temperature. At 400°C in air, even with very thin films polyimide do not show any sign of degradation within the time (30-60 min) processing take place. We, therefore, conclude that fully aromatic polyimide is thermally sufficient for this application. 

Relative to microelectronic applications, the out-of-plane dielectric constant for BPDA-PFMB films measmed after aging at 50% relative humidity for 48 h at 23°C was between 2.8 and 2.9 (0.1 kHz to 1 MHz) (ASTM D-150-81These values are considerably lower than that of commercial polyimides such as PMDA-ODA (pyromellitic dianhydride, PMDA) (s = 3.5 at 1 kHz and 3.3 at 10 MHz). The dielectric constant and tan 8 (dissipation factor) were temperature- and frequency-dependent. The dielectric constant, which was independent of temperature until near 210°C increased above this point until a frequency-dependent maximum was reached at about 290°C. The dissipation factor, which was also independent of temperatme below 200°C, underwent a rapid increase with no maximum between 200 and 400°C owing to ion conductivity. The temperatme at which this increase occurred increased as the frequency increased. The films also... 

PFMB can be used to prepare aromatic polyimides that display solubility in ketone, ether, and polar aprotic solvents. This unusual solubility can be utilized in die facile preparation of thin films that display anisotropy in their structures and properties. The anisotropy in the optical properties of the films makes them promising candidates for use as compensation layers in liquid-crystal displays. Their low dielectric constants and CTEs in combination with their outstanding thennal and thermooxidative stabilities make diem candidates for dielectric layers in microelectronics applications. 

Because of the high functional values that polyimides can provide, a small-scale custom synthesis by users or toll producers is often economically viable despite high cost, especially for aerospace and microelectronic applications. For the majority of industrial applications, the yellow color generally associated with polyimides is quite acceptable. However, transparency or low absorbance is an essential requirement in some applications such as multilayer thermal insulation blankets for satellites and protective coatings for solar cells and other space components (93). For interlayer dielectric applications in semiconductor devices, polyimides having low and controlled thermal expansion coefficients are required to match those of substrate materials such as metals, ceramics, and semiconductors used in those devices (94). 

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. 

From the area of polymer dielectrics, a sample is presented here using a commercially available and (from many microelectronic applications) well-known high-temperature polyimide. The deposition and the subsequent curing process have been described in Section 18.2.3, resulting in a 190 nm thick insulating film that showed a good chemical resistance towards diluted developer solution and acetone, so that the cathode-sputtered Au drain and source contacts can be structured as described in Section 18.2.1. The 30 nm thick pentacene layer is thermally evaporated at a deposition rate of about 0.1 nm/s and a process pressure of 1 x 10 mbar. 

A number of different types of nanoporous materials for use in low dielectric constant iq lications have been developed in recent years, including nanoporous silica, polyimides, poly(arylefhers), and poly(methyl silsesquioxanes). Recently, much research has been done in die field of siqiercritical carbon dioxide (SCCO2) and its use in the synthesis of polymers for microelectronic applications. A variety of different methods using supercritical CO2 to form micro- and nanoporous materials towards applications in the microelectronic industry are described. 

Some requirements to use these polymers for interlayer and intermetal dielectrics in advanced microelectronic applications are high thermal stability, high glass transition temperature, good mechanical properties, low dielectric constant, low coefficient of thermal expansion and low moisture absorption. The dielectric constant of polyimides depends mainly on the... 

For specific applications, various specialty polyimides have been prepared. For example, polyimidesiloxanes are usefiil for screen printing a paste for microelectronic applications [27]. 

The methods used to synthesize poly(imide-siloxanes) have been reviewed by Lee who points out that electronic and microelectronic applications are key factors for the development of low-modulus, low-stress new materials [171]. The patent literature indicates that copoly(imide-siloxanes) have been synthesized with all available dianhydrides such as PMDA, BTDA, BPDA, OPDA, and the diether dianhydride used to produce the thermo-plastic polyimide Ultem 1000. These compounds were opposed to aromatic diamines in combination with siloxanediamine 113 with a degree of polycondensation m varying from 0 to 8 or more. Commercial polymers generally include only 5-10 mol% of siloxane units in order to maintain a glass transition temperature higher than 200°C. For example, preimidized thermoplastic copolymers have TgS in the range of 200-220°C and can be extruded at temperatures below 300°C... 

As mentioned earlier, siloxanes impart a number of beneficial properties to polymeric systems into which they are incorporated, including enhanced solubility, resistance to degradation in aggressive oxygen environments, impact resistance and modified surface properties. These particular advantages render polysiloxane-modified polyimides attractive for aerospace, microelectronic and other high performance applications (40-43). 

Fluorinated Polyimides for Optical, Microelectronic, and Fiber Applications... 

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