Fabrication of vertical sidewalls on (110) silicon substrates for use in si/sige photodetectors

Abstract

A method of fabricating vertical sidewalls on silicon (110) substrates for use in Si / SiGe photodetectors includes preparing a silicon (110) layer wherein the silicon (110) plane is parallel to an underlying silicon wafer surface. Masking the silicon (110) layer with mask sidewalls parallel to a silicon (111) layer plane and etching the silicon (110) layer to remove an un-masked portion thereof, leaving a patterned silicon (110) layer having vertical silicon (111) sidewalls. Removing the mask; growing SiGe-containing layers on the patterned silicon (110) layer; and fabricating a photodetector.

Description

FIELD OF THE INVENTION [0001] This invention relates to photodetectors, and particularly to near-infrared photodetectors integrated on silicon substrates. BACKGROUND OF THE INVENTION [0002] Photo detecting in the near infrared regime, i.e., having a wavelength of between 0.7 μm to 2 μm, has many applications, such as in fiber-optic communication, security applications, machine vision and night vision imaging. Although III-V compound semiconductors provide superior optical performance over their silicon-based counterparts, the compatibility of silicon based materials with current silicon-IC technology provides the possibility of making cheap, small and highly integrated optical systems. The following references provide additional background for the invention: Maiti et al., Strained Silicon Heterostructures: Materials and Devices, Chapter 10: Si / SiGe Optoelectronics, The Institution of Electrical Engineer, 2001; Murtaza et al., Room Temperature Electroabsorption in GexSi1-xPIN Photodi...

AI Technical Summary

Benefits of technology

The invention is a method for making vertical sidewalls on silicon substrates for use in photodetectors. This method improves the quantum efficiency of photodetectors and allows for the growth of strained SiGe and / or SiGe / Si multilayer structures. The process involves preparing a silicon layer, masking it with mask sidewalls, etching it to remove un-masked portions, and then growing SiGe-containing layers on the patterned silicon. The resulting photodetector has better performance and can detect near-infrared light.

Problems solved by technology

A high germanium concentration and high device process temperature result in a smaller critical thickness.

Once the SiGe thickness is grown above its critical thickness, lattice defects in SiGe are inevitable.

An IR photo detector built on SiGe containing lattice defects will have a high dark current and produce electronic noise.

However, this does not allow the device to be used in image detection.

However, referring to FIG. 2, reactive ion-etching (RIE) of silicon usually results in a sloped sidewall, shown generally at 10, and in poor crystal quality near the sidewall surface, as shown generally at 12, where a damaged area of silicon is formed near an RIE-etched sidewall.

Also, the surface is often rather rough.

However, such an etch process is not known in the prior art.

In addition, the use of a selective wet etch instead of RIE results in undamaged crystalline silicon at the sidewall surfaces.

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