Growth of high-quality relaxed SiGe films with an intermediate Si layer for strained Si n-MOSFETs

P. S. Chen, S. W. Lee, Min-Hung Lee, C. W. Liu

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

An intermediate Si layer in Si 1-x Ge x film, replacing the conventionally compositional graded buffer layer, was used to fabricate a relaxed SiGe substrate of high quality. The intermediate Si layer changes the relaxation mechanism of the SiGe thin film via the generation of {3 1 1} dislocation loops. The {3 1 1} dislocation loops are formed in the intermediate Si layer to prompt a state of relaxation in the SiGe overlayer, provide the defects for trapping of threading dislocations (TDs) and leave a SiGe top layer with low dislocation density. For the SiGe/Si/SiGe samples, the residual strain and TDs on the top SiGe layer are independent of the SiGe underlayer thickness. With a 700 nm thick Si 0.8 Ge 0.2 overlayer, such a Si 0.8 Ge 0.2 /Si/Si 0.8 Ge 0.2 heterostructure with a smooth surface has a TD density of 8.9 × 10 5 cm -2 and 3% residual strain. Owing to the different main relaxation mechanisms in SiGe films, the surface root mean square roughness of this relaxed buffer with a low density of surface pits was measured to be about 3 nm, which is lower than that of the sample without any intermediate Si layer (13 nm). Relaxation of the SiGe overlayer depends on the thickness of the intermediate Si layer. Optimization on relaxation in the SiGe/Si/SiGe structure with an intermediate Si layer of 50 nm is done. Strained Si n-channel metal-oxide-semiconductor field effect transistors with various buffer layers were fabricated and examined. The effective electron mobility for the strained Si device with this novel substrate technology was found to be 80% higher than that of the Si control device. The SiGe thin films with the intermediate Si layer serve as good candidates for high-speed strained Si devices. The global strain in the Si channel with a SiGe/Si/SiGe buffer is still beneficial for short channel devices.

Original languageEnglish
Pages (from-to)479-485
Number of pages7
JournalSemiconductor Science and Technology
Volume21
Issue number4
DOIs
Publication statusPublished - 2006 Apr 1

Fingerprint

field effect transistors
Buffer layers
Buffers
Thin films
Electron mobility
MOSFET devices
Substrates
Heterojunctions
buffers
Surface roughness
Defects
control equipment
thin films
electron mobility
metal oxide semiconductors
roughness
trapping
high speed
optimization
defects

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering
  • Materials Chemistry

Cite this

Growth of high-quality relaxed SiGe films with an intermediate Si layer for strained Si n-MOSFETs. / Chen, P. S.; Lee, S. W.; Lee, Min-Hung; Liu, C. W.

In: Semiconductor Science and Technology, Vol. 21, No. 4, 01.04.2006, p. 479-485.

Research output: Contribution to journalArticle

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abstract = "An intermediate Si layer in Si 1-x Ge x film, replacing the conventionally compositional graded buffer layer, was used to fabricate a relaxed SiGe substrate of high quality. The intermediate Si layer changes the relaxation mechanism of the SiGe thin film via the generation of {3 1 1} dislocation loops. The {3 1 1} dislocation loops are formed in the intermediate Si layer to prompt a state of relaxation in the SiGe overlayer, provide the defects for trapping of threading dislocations (TDs) and leave a SiGe top layer with low dislocation density. For the SiGe/Si/SiGe samples, the residual strain and TDs on the top SiGe layer are independent of the SiGe underlayer thickness. With a 700 nm thick Si 0.8 Ge 0.2 overlayer, such a Si 0.8 Ge 0.2 /Si/Si 0.8 Ge 0.2 heterostructure with a smooth surface has a TD density of 8.9 × 10 5 cm -2 and 3{\%} residual strain. Owing to the different main relaxation mechanisms in SiGe films, the surface root mean square roughness of this relaxed buffer with a low density of surface pits was measured to be about 3 nm, which is lower than that of the sample without any intermediate Si layer (13 nm). Relaxation of the SiGe overlayer depends on the thickness of the intermediate Si layer. Optimization on relaxation in the SiGe/Si/SiGe structure with an intermediate Si layer of 50 nm is done. Strained Si n-channel metal-oxide-semiconductor field effect transistors with various buffer layers were fabricated and examined. The effective electron mobility for the strained Si device with this novel substrate technology was found to be 80{\%} higher than that of the Si control device. The SiGe thin films with the intermediate Si layer serve as good candidates for high-speed strained Si devices. The global strain in the Si channel with a SiGe/Si/SiGe buffer is still beneficial for short channel devices.",
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