*1.1.1 Cleaning of test wafer*

performance would be the key features required. Due to these features they improve the overall performance of the systems into which they are integrated. Hence, the focus of this work is on RF MEMS switches which are a superior

MEMS devices are fabricated by the use of special techniques called micromachining. Micro fabrication or micromachining or micro manufacturing is the use of a set of manufacturing tools based on thin and thick film fabrication techniques commonly used in the electronics industry. It is also a technology for creating small three dimensional structures with dimensions ranging from sub centimeters to sub micrometers. A vast majority of MEMS structures are fabricated using bulk micromachining process. This involves etching of bulk wafer leading to three dimensional structures such as beams, cantilevers and cavities. These processes can be realized on substrates such as Silicon, Glass and Gallium Arsenide etc. The thickness of the structures can range from a few micrometers to 200 mm. The resulting dimensions of microstructures are much larger compared to surface micromachining process. Surface micromachining is a process based on building up of material layers and then selectively retaining or etching by continued processing. The bulk of the substrate remains untouched. LIGA processes combine IC lithography and electroplating and molding to obtain depth. Patterns are created in a substrate and then electroplated to create 3D molds. These molds can be used as the final product, or various materials can be injected into them. This process has two advantages. Materials other than Silicon can be used e.g. metal, plastic and devices

This chapter provides the complete details of the unit step processes used for the fabrication and packaging of RF MEMS switches. The focus is on fabrication of low actuation voltage RF MEMS switches [7–10]. There are several challenges involved in the fabrication of MEMS switches such as, structural deformation, residual stress, non-release of structural layer to name a few. These challenges are overcome and addressed throughout the fabrication process by optimization of several unit processes. The unit processes used is discussed in each section of this

Surface micromachining process is used for fabricating the switches. In the

The sections below give the detailed description of the fabrication steps followed

The test wafers used in this work is P-type {100} low resistivity 4″ wafers with resistance ranging from 1 to 100 Ω. Using low resistivity wafers to fabricate RF MEMS switches has the advantage that integration with CMOS circuits is easier. However, use of low resistivity Silicon wafer leads to higher insertion loss due to

alternative to existing semiconductor switches.

*Nanofibers - Synthesis, Properties and Applications*

with very high aspect ratios can be built [6].

present work, fabrication costs were brought down by

• low resistivity Silicon wafers as substrate

• Use of only four masks for fabrication [11]

for successful fabrication of RF MEMS shunt switches.

The following are the process steps used for fabrication:

ii. Oxidation of the test wafer: Using wet oxide process

i. Cleaning of test wafer: Using RCA-1 and RCA-2 processes.

chapter.

**1.1 Fabrication process steps**

inherent parasitics.

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The cleaning of the Silicon wafer is the first process employed to removing any organic residue or films on the Silicon wafers. The cleaning process is performed in two parts [12]. The first part of the cleaning process is the famous RCA-1 named after the laboratory at which it was developed. In this process five parts of water is mixed with one part of Ammonium Hydroxide (NH4OH) and one part of Hydrogen Peroxide (H2O2). This mixture is then heated to 75°C on a hot plate. Once the solution bubbles vigorously the Silicon wafer is soaked in this solution for 15 minutes. The wafer is then dipped in a solution made of one part of Hydrofluoric acid (HF) and 50 parts of water for 30 seconds. This solution serves the purpose of etching out the thin oxide layer developed on the wafer. The wafer is again washed with DI water. The next step also called RCA-2 involves the use of Hydrochloric (HCl) acid, Hydrogen Peroxide (H2O2) and DI water in the ratio of 1:1:6. This solution is then heated to a temperature of 75°C for 15 minutes after which the Silicon wafer is placed in this solution. RCA-2 completely removes the traced of ionic contaminants from the wafer surface.
