Integrating TiN only bottom plate metal-insulator metal capacitor (MIMC) for contamination free manufacturing

Abstract

Metal-Insulator-Metal Capacitors (MIMCs) are used in many modern analog capable CMOS processes. MIMCs feature high capacitance per unit area, low parasitic capacitance, due to their distance from substrate, and low 1st and 2nd order voltage coefficients [1].It is very important to have lower defect density to manufacture highly reliable analog devices. Current practice of integrating MIMC has high defect density and thus poor reliability. There are many mechanisms by which reliability is affected. These are: (a) charging during dielectric deposition [2], (b) bottom plate roughness, and (c) dielectric thinning [3], [4], [5].In this work, MIM capacitors are integrated in a high-voltage capable CMOS process flow. MIM capacitors used in this work have MIMC area per die above 3 million m 2 /die, thus reliability must be proven at this level to <1 ppm fails for this mode. The electrical requirements for the MIMC are 1.5fF/um^2 capacitance/area, 3.6V maximum operating voltage, and less than 30ppm 1st order voltage coefficient. The capacitor is integrated using 2nd layer metal, a silicon nitride (SiN) dielectric layer, and a special top plate metal (metal 2.5).In addition to the electrical requirements, the MIMC must also meet applications reliability requirements. The reliability of a MIMC is determined by MIMC area, voltage, and temperature. In the case of our current implementation that uses metal as a MIMC's bottom plate, we observe a population of MIMCs, which have lower than expected voltage breakdown (vbd)-the source of this is identified as a bottom plate roughness.In this paper, we report the integration of TiN only (with no Aluminum layer) as a bottom plate for MIMC to improve the defect density and thus the reliability. MIMC bottom plate surface roughnessThe characterization of the bottom plate roughness of a MIMC was performed by atomic force microscopy (AFM). The difference between the roughness of a standard metal bottom plate and the new TiN bottom plate are shown in Figures 1. respectively. These results are shown in Table 1. Figure 1: (a) AFM images of 'standard metal' bottom plate MIMC with a RMS value of 42.2 Å, (b) AFM images of a TiN only bottom plate showing improved surface roughness RMS value of 10.3 Å. Figures 1 (a) and (b) clearly shows that the surface roughness of a TiN only bottom plate is four times better than the standard metal bottom plate. 978-1-4244-1892-3/07/$25.00 ©2007 IEEE