Johannes F. C. M. Verhoeven

High-value MOS capacitor arrays in ultradeep trenches in silicon

A fully Si-compatible process has been developed to manufacture 6-inch silicon (100) wafers with patterns of trenches, several hundreds of @mm deep with a width and pitch of a few @mm. The hundred-fold enlarged silicon surface is used as a substrate for MOS (Metal-Oxide-Semiconductor) capacitor arrays with a capacitance of 1 nF to 1 @mF. The specific capacitance was as high as 100 nF/mm^2.

Etching of Deep Macropores in 6 in. Si Wafers

The process of photoanodic etching of deep pores in lightly doped n - -Si wafers was investigated. On a 6 in, wafer, more than 1 billion pores, regularly distributed over the wafer in a hexagonal array with a pitch of 3.5 μm, were obtained using an electrolytic back contact. The diameter of the pores was about 2 μm and depths up to 400 μm could be achieved. Kinetic experiments revealed that the etching process was diffusion controlled in a solution containing HF, H 2 O, and ethanol. Electrochemical experiments showed that H 2 evolution took place at the back side of the Si wafer and that H 2 and O 2 evolved at the Pt cathode and anode, respectively.

High-Density, Low-loss MOS Decoupling Capacitors integrated in a GSM Power Amplifier

High-density MOS capacitors have been fabricated with ∼ 30 nF/mm 2 specific capacitance on highly-doped Si-wafers with arrays of macropores with ∼ 2 μm diameter. Using the Bosch process [1] these pores were dry-etched to depths of ∼ 30 μm or more. The enlarged Si-surface thus obtained serves as a substrate for capacitors fabricated by fully MOS-compatible processing. Wafers were fabricated with a top electrode of poly-Si and Al and ‘ONO’ (i.e. oxide / nitride / oxide) dielectric stacks showing 7–10 MV/cm electrical breakdown field and leakage 2 @ 20 V. These wafers were thinned to 380 μm and sawn into dies, representing 40 nF capacitors. Typically low loss factors such as ESR 2 O 3 or laminate substrate as supply-line decoupling capacitors in complete GSM power amplifier test modules. RF decoupling and transmission were measured and compared to identical test modules with conventional discrete ceramic capacitors. The MOS capacitors showed very efficient decoupling, resulting in superior signal stability as measured in the 0 – 1 GHz range (less noisy, free from oscillations). The new capacitor is very suitable for integrated decoupling purposes, e.g. supply-line decoupling in RF wireless communication and analog and mixed-signal systems.