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Trenches in SiO2 Substrate for Relaxation of SiGe Films on SOI Wafers

IP.com Disclosure Number: IPCOM000020343D
Original Publication Date: 2003-Nov-14
Included in the Prior Art Database: 2003-Nov-14
Document File: 4 page(s) / 67K

Publishing Venue

Motorola

Related People

Chun-Li Liu: AUTHOR [+4]

Abstract

Research and development to achieve fully relaxed SiGe buffer layer for strained Si technology has been very active in the past several decades. Utilization of SiGe mesa islands to further relax the SiGe films on silicon on insulator (SOI) has recently been proposed and demonstrated. In this publication, we describe an improved method by creating trenches in the SiO2 substrate surrounding the SiGe mesa islands to induce an augmented-relaxation of both substrate and SiGe. The trenches create open space (recesses) in the substrate so that SiO2 can undergo a viscous reflow during high temperature anneal, especially during the Ge condensation anneal. Relaxation of SiO2 substrate will, in turn, further relax SiGe mesa islands on the top by releasing the stress across the SiO2/SiGe interface. Results of continuum stress simulations confirmed the desired improvement: Trenches in the SiO2 substrate, sufficiently close to the mesa islands, accelerate indeed the relaxation process and at a given time during anneal more relaxation is achieved with trenches in SiO2 compared to the cases without trenches.

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Trenches in SiO2 Substrate for Relaxation of SiGe Films on SOI Wafers

Chun-Li Liu, Marius Orlowski, Shahid Rauf, and Vance Adams

                                         Abstract

Research and development to achieve fully relaxed SiGe buffer layer for strained Si technology has been very active in the past several decades. Utilization of SiGe mesa islands to further relax the SiGe films on silicon on insulator (SOI) has recently been proposed and demonstrated. In this publication, we describe an improved method by creating trenches in the SiO2 substrate surrounding the SiGe mesa islands to induce an augmented-relaxation of both substrate and SiGe. The trenches create open space (recesses) in the substrate so that SiO2 can undergo a viscous reflow during high temperature anneal, especially during the Ge condensation anneal. Relaxation of SiO2 substrate will, in turn, further relax SiGe mesa islands on the top by releasing the stress across the SiO2/SiGe interface. Results of continuum stress simulations confirmed the desired improvement: Trenches in the SiO2 substrate, sufficiently close to the mesa islands, accelerate indeed the relaxation process and at a given time during anneal more relaxation is achieved with trenches in SiO2 compared to the cases without trenches.

Problem and its Solution

It was a challenge for more than two decades to achieve fully relaxed SiGe films grown on Si substrates. A fully relaxed SiGe buffer layer is critical to achieving highest possible biaxial tensile strain in the strained Si layer which is deposited on the SiGe buffer layer. Recently, a Ge condensation approach has been proposed and successfully demonstrated by Toshiba [Tezuka et al, Applied Physics Letters, vol.79, p.1798, 2001

]. The approach produces a thin layer of SiGe film with high Ge content and high degree of relaxation. It is important, however, to note that full relaxation is still incomplete. [T.Tezuka, N. Sugiyama, S. Takagi, APL 80, 3560, 2002

; Tezuka et al, US20030006461A1

]. Subsequently, a structure of SiGe mesa islands was proposed and demonstrated to relax the remaining SiGe film even further [T.Tezuka, N. Sugiyama, S. Takagi, APL 80, 3560, 2002

; Tezuka et al, US20030006461A1]. The approach has several advantages over the continuous film case: It creates open space for the SiGe mesa islands allowing to relax sideways during a condensation anneal while the free surface of the SiGe mesa islands acts as a sink for extended defects such as dislocations. However, despite considerable improvement, full relaxation is still not being achieved. In this publication, we propose to create trenches in the SiO2 BOX layer, such that the trenches surround the SiGe mesa islands in close proximity and allow simultaneous relaxation of both SiG substrate and BOX and thus further relaxation of the SiGe mesa islands. A schematic for a spherical trench surrounding a mesa island is illustrated in Figure 1.

(a)

(b)

Figure 1 (a) Sectional view of a trench in the SiO2 substrate surrounding a spherical...