A programmable anti-fuse, using amorphous silicon between levels of metal, is studied. The step coverage of the a-Si has the most significant impact on the anti-fuse characteristics. Other critical process parameters are also identified. The anti-fuse architecture is optimized to enhance its performance, yield and reliability with built-in process robustness.
Carbon based Spin on Glasses, used in intermetal oxides have been shown to cause field inversion in MOS circuits under certain process conditions. The problem has been shown to be caused by the interaction of H evolved from the plasma nitride interacting with the organic groups in the Spin on Glass.
.INTRODUCTIONSpin on Glasses have been utilized to planarize dielectrics for multilevel metallization schemes. Phosphosilicates are being used but suffer from the problem of excessive tensile stress and cracking especially when applied as layers thicker than 2000A. In order to alleviate this problem, carbon based SOGs were introduced that have less tensile stress and show more favorable resistance to cracking. Fig 1 shows the excellent planarization possible on a l u m double metal circuit using 3000A of the carbon based SOG. However, we have found that under certzit! conditions the carbon based SOGs can cause field oxide inversion in MOS circuits. By systematically changing various components in the multilevel metallization scheme we have shown that this field inversion is caused by charge developed in the SOG as a result of a complex interaction between the passivation and the SOG . A critical factor is played by the organic groups in the SOG and suggests that the presence of organic material in dielectrics can cause failures in MOS circuits under certain conditions.
EXPERIMENTAL DETAILS
ProcessDevices were fabricated using a l u m CMOS double metal process.The gate oxide and final field isolation oxide thicknesses were 200A and 4500A ,respectively . The metallization was a multilayer film incorporating a TiW barrier metal as described in Ref 1. After metal 1 definition, the lntermetal oxide (IMO) was deposited. This consisted of a thin layer ( 3 KA ) of PECVD oxide, two coats of a carbon based Spin on Glass(S0G) for planarization, followed by a thick Subsequent processing included via definition and etch,deposition and definition of metal 2 followed by passivation. The passivation consisted of two layers of dielectrics. The first was a PECVD oxide and the second layer was a plasma nitride . Each layer was about 9KA . The final step was a 460 C, 30 min alloy in forming gas.The PECVD oxide was deposited in a commercial single wafer 13.56MHz rf plasma reactor. The SOG was coated onto the wafers on a spin track which included a track bake at 220C . After each coat of SOG the wafers were baked in a furnace at 400C for 30 min in N2. A single coat of the carbon based SOG after a full cure gave a 1600A thick filmtwo coats gave a final thickness of about 3000A.Variations to the above baseline process focused on the SOG and passivation. SOGs with different carbon contents, similar carbon-based SOGs from different vendors and a non carbon SOG, a phosphosilicate glass, were tested. Several kinds of nitrides and a layer (6KA) of PECVD oxide.
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