To lower the cost of multichip module packaging, hybridized substrate technologies have recently been reported which blend the desirable aspects of D and L fabrication (MCM-D/L). High performance dielectrics such as Cyclotene™ 3022 and photosensitive BCB have been shown to be compatible with laminate substrates used in MCM-D/L, however the cure levels of the dielectric on the laminates must be known for optimum processing. In this paper, the capability of attenuated reflection IR microscopy (micro-ATR-IR) to probe thin films of BCB polymers is demonstrated. This technique enables the polymer layer to be probed regardless of the characteristics of the substrate. Cure levels of both Cyclotene™ 3022 and photodefinable BCB polymer films are obtained with micro-ATR-IR on both silicon and laminate substrate. Micro-ATR-IR is also used to probe a rapid thermal cure of Cyclotene™ 3022 and photodefinable BCB layers on copper-clad polyimide laminate; these measurements cannot be made with transmission IR due to the high reflectivity of the substrate.

Large die such as SRAMs and DRAMs are subject to significant stresses resulting from the differences in the coefficient of thermal expansion (CTE mismatch) of the die and packaging materials. The use of polymers as a buffering medium between these two materials has been widely practiced in the industry to increase the reliability of these devices. This layer must be patterned to allow electrical connection to the bond pads (50 - 250 mu m openings). In many of the newer devices, smaller windows (<10 mu m) must also be opened up to allow access to other structures, such as ''fuse links'', which are used to reroute or reconfigure inactive circuits. This need for higher resolution polymer layers, as well as the desire for shorter processing cycles, has moved the industry away from the use of wet etch polymers toward photosensitive materials.Traditional wafer level processing of memory die has required a two mask operation for patterning features in the underlying primary passivation layer (commonly Si3N4) followed by coating and patterning of the polymer stress-buffer layer. A one mask manufacturing process has been developed using Photosensitive Benzocyclobutene (Photo-BCB) for opening up features (bond pads and fuse links) in both layers using the polymer layer as a permanent etch mask for the Si3N4. This results in a significant reduction in both the number of processing steps and the processing time, versus the traditional two mask process, and therefore, significantly lowers the cost of ownership for passivation/stress-buffer layers.In this paper, we will discuss the Photo-BCB processing steps and compare them to the steps in a two mask passivation/stress-buffer processes.

The Envision/spl TM/ cost model has been extended to allow an economic evaluation of Large Area Processing (LAP) techniques to fabricate MCM D and LD substrates. The model is based on the unit operation analysis of the capital, material, utilities and workforce requirements per thin film layer (dielectric and conductor layer pair). Comparisons are readily made between sputtered and plated metallurgy with and without metal barrier layers; and between dry etchable, and photosensitive dielectrics. Sensitivity analysis has been performed on coating tool cost, throughput and efficiency of the coating process and the type of tools and materials used to generate vias. More than a threefold cost differential exists between sow of the manufacturing scenarios, and more than a ten fold cost differential exists between IC MCM based fabrication and LAP MCM fabrication. This model is applicable to LAP MCM-D, MCM-CD and MCM-LD manufacturing.