Curvature Correction Methodologies for Micromirror Platforms Deformed Due to Residual Stress


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Kumar, A and Ashudeep, Ms. and Anurop, Mr. and Kumar, P and Khushbu, Ms. and Rangra, K and Bansal, D (2019) Curvature Correction Methodologies for Micromirror Platforms Deformed Due to Residual Stress. In: xxth International Workshop on Physics of Semiconductor Devices: IWPSD 2019, Dec. 17-20, 2019, Kolkata, India.

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Micromachined devices are prone to post-release deformation due to the presence of residual stress in structural layers resulting, in poor performance and reliability issues. This paper presents the effects of residual stress on the flatness of a bilayer micromirror platform and different curvature correction methodologies fbr the same. The micromirror platform under investigation consists of a rectangular plate of area 500x500 pm' fabricated using 0.75 pm thick SiO, and 0.95 pm thick aluminum and suspended by a set of bimorph actuators. The presence of compressive stress in SiO (240 MPa) tensile stress in aluminum (35 MPa) manifests itself in curling of the platform after release. The extent of deformation depends on various factors that include constituent layer thickness. the dimension of the platform, location of anchoring points and magnitude of residual stress. the stress-induced deformation of the micromirror platform leaves the device unsuitable for any useful optical application. Finite Element Analysis of the platform is performed in CoventorwareR to access the nature and extent of post-release deformation at ambient temperature due to the presence of biaxial residual stress. The distribution of residual stress is assumed constant across the film thickness i.e. without stress uadient. In order to correct the platform deformation. two methods of stress counterbalancing i.e. metal reinforcement framing and deposition of a stress compensation layer are proposed and their effectiveness in curvature correction is investigated using FEM analysis. The simulation result shows that a 1 pm thick gold reinforcement frame results in a 13 um height difference between plat form center and platform corner, which improves to a height difference of 6 pm for reinforcement thickness of 3 pin. Improved curvature correction is obtained with a stress compensation layer in which maximum height difference between platform corner and platform center is reduced to 1 pm for a SiO, layer of thickness 0.75 pin deposited at the top of aluminum. FIN analysis confirms that presence of stress compensation layer at the top is more effective in curvature correction compared to metal reinforcement framing, however; post-release elevation of the stress-compressed platform is 5 poi below the post-release elevation of the reinforced platform and 25 um below the zero reference plane.

Item Type: Conference or Workshop Item (Paper)
Subjects: Semiconductor Devices > Sensors and Nanotechnology
Divisions: Semiconductor Devices
Depositing User: Mr. Jitendra Nath Bajpai
Date Deposited: 27 Aug 2021 07:04
Last Modified: 27 Aug 2021 07:04

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