George Czornyj

Residual stress behaviour of isomeric PMDA-ODA polyimides

Poly(3,4′-oxydiphenylene pyromellitimide) (PMDA-3,4′-ODA), an isomer of poly(4,4′-oxydiphenylene pyromellitimide) (PMDA-4,4′-ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4′-oxydiphenylene diamine (3,4′-ODA). For these two polyimide isomers and their poly(amic acid) precursors in the condensed state on Si wafers, residual stress behaviour over the range 25–400°C was investigated by the dynamic measurement of wafer bending. During thermal imidization both isomers did not show any difference in stress versus temperature behaviour. Once imidized, however, one isomer exhibited a quite different stress behaviour from that of the other during cool-down: the stress of PMDA-3,4′-ODA increased rapidly from zero at 400°C to ≈45 MPa at 40°C, whereas that of PMDA-4,4′-ODA rose gradually from zero to ≈27 MPa. For both cured isomers, stress-temperature profile on heating was the same as that on cooling, with some deviation due to moisture uptake over the temperature range 25–150°C, indicating that their stresses were insensitive to thermal cycling or thermal annealing. From independently measured properties (thermal expansion coefficient, modulus, Poissons ratio of 0.34) of both polyimides, the thermal stresses were calculated and compared with the measured overall stresses. It is concluded that for both polyimides the overall residual stress results primarily from the thermal stress. In comparison with PMDA-4,4′-ODA, PMDA-3,4′-ODA showed a much higher stress despite its slightly lower thermal expansion coefficient. This leads to the conclusion that the large difference between the stresses of the isomers results from the large difference in their moduli (5.0 GPa for PMDA-3,4′-ODA and 3.0 GPa for PMDA-4,4′-ODA). This behaviour is further supported by the difference in morphological structures of these two isomers as determined by wide-angle X-ray diffraction: PMDA-3,4′-ODA showed a well-developed crystalline structure, whereas the PMDA-4,4′-ODA did not. In addition, the interfacial adhesion between polyimide film and Si wafer primed with A1100 was investigated.

Dual-Level Metal (DLM) method for fabricating thin film wiring structures

This paper describes a fabrication method for multilevel, thin film wiring in which each wiring level and a solid via or stud to the level below, are formed as one integral unit. The processing scheme described makes use of a photosensitive polyimide (PSPI) for defining the wiring channels and a non-photosensitive polyimide for the vias. The via opening in the non-photosensitive polyimide is formed by laser ablation while the wiring channels are formed in the PSPI layer by photolithography. The via hole and the channels in the PSPI are filled in the same metallization step consisting of electroplating copper over a sputtered seed layer. The wiring pattern is finally delineated when a planarization step removes the excess plated copper. This processing method, which we refer to as the Dual Layer Metallization (DLM) method, is found to be very economical, in terms of the number of process steps involved, for forming multilevel, polyimide-copper wiring structures.<<ETX>>

Materials in microelectronics

Abstract The technologies in computer electronics are very diverse and span the entire spectrum of engineering and scientific fields. Materials (metals, ceramics, and polymers) are at the heart of all leading-edge computers, for both semiconductors and packages. The material challenges for semiconductor devices include the materials for transistor formation as well as on-chip interconnection by extremely fine-line lithography. The role of packages, beyond being simply passive containers in the past, is viewed as setting limits to the ultimate performance of computers. In this role, the packages of the 1990s need to interconnect, power, cool, and protect devices in such a way that results in leading-edge performance and reliability. The materials to perform these functions include low-dielectric-constant ceramics, polymers, and high-conductivity metals.

Structure And Properties Of BPDA-PDA Polyimide From Its Poly(Amic Acid) Precursor Complexed With An Aminoalkyl Methacrylate

BPDA-PDA poly(amic acid) precursor was functionalized through its carboxylic acid groups being linked with a crosslinkable aminoalkyl methacrylate, 2-(dimethylamino)ethyl methacrylate (DMAEM), by acid/base complexation. BPDA-PDA polyimide films, which were thermally imidized from the precursors complexed with various amounts of DMAEM, were characterized by means of wide angle x-ray diffraction, stress-strain analysis, and residual stress analysis. The structure and properties of the BPDA-PDA polyimide film were dependent upon the history of the precursor, that is, the complexation of the poly(amic acid) precursor with DMAEM. The molecular packing order was enhanced with the history of DMAEM loading while the molecular order along the chain axis was disrupted. Overall, physical properties, such as mechanical properties and residual stress, were degraded with DMAEM loading. The moisture induced stress relaxation behavior was sensitive to the history of DMAEM loading, whereas the creep induced stress relaxation was varied little due to its high T g . These properties are understood in terms of structure/property relationships, as well as microvoids, which were possibly generated by outgassing the bulky DMAEM pendent groups during thermal imidization.