Overcoming the limitations of Al metal line patterning technology without damascene process
Etch patterning process using Al wiring is technical challenging in sub-280 nm pitch devices especially when Cu damascene process is not available in 8 inch wafer semiconductor fabrication facilities. However, some of the CMOS image sensors (CIS) at our company are designed to meet back end of layers (BEOL) minimum design rule (DR) of 200 nm pitch (Bar/Space 100/100nm) without damascene process. In addition to meeting the pitch requirement, the vertical profile of the metal 1 should be suitable for the characteristics of its optical sensor. If we cannot perform the metal 1 layer module process and patterning implementation, the optical attribute called Brightness(Y) Signal to Noise Ratio (YSNR) will decline, which is the most important part of the product. Moreover, electrical attributes and yield requirements cannot be achieved. Fig. 1. and 2. show the top and vertical view of the present CIS metal 1 profiles. In this paper, we optimized etch module process to realize fine metal pattern of CIS products which are based on Al wiring in 200nm pitch without using damascene process.
Effects of BCl3 gas on physical damage and Al residues in oxide hard-mask-based Al etching
This paper presents the effects of BCl3 additive gas on physical damage and the prevention against damage in oxide hard-mask-based Al etching. The BCl3 addition in the TiN/Ti break-through step effectively passivated the sidewall against the upper TiN/Ti notching damage; however, the TiN/Ti profile was easily distorted under excessive BCl3 added. The Al bottom notching depth decreased with decreasing BCl3/Cl2 ratio in the Al over-etch step. As the BCl3/Cl2 ratio is less than or equal to 0.625, the Al bottom notching was eliminated. Nevertheless, the low BCl3 addition in the Al over-etch step would result in increasing Al residues because insufficient passivation at low BCl3 flow cannot effectively protect the semi-iso Al sidewall from attack of Cl atoms, and insufficient ion bombardment at this low BCl3 cannot remove those residues around the damaged sidewall. An optimized condition achieves both notching-free and residue-free profiles.
Development of Aluminum Chemical Mechanical Planarization
The paper describes the development of an aluminum chemical mechanical planarization process that was successfully integrated into the dual damascene technology producing I Gb dynamic random access memory chips meeting all yield and sheet resistance requirements. Three of the major problems of chemical mechanical polishing of Al-0.5 Cu alloys, i.e., copper plate-out on titanium liners, array erosion, and slow polish rate were solved by adding Ce 4+ ions to the polishing slurry.