Process-induced mechanical stress in isolation structures studied by micro-Raman spectroscopy

Abstract

Micro-Raman spectroscopy is used to study mechanical stress in local isolation structures on silicon substrates (poly-buffered local oxidation of silicon, called PBLOCOS or LOPOS). The influence of processing parameters such as nitride film thickness and width, pad oxide thickness, and field oxide thickness is studied. Also the change of the local stress during the successive processing steps of the isolation is investigated: deposition of the nitride mask, field oxidation, and removal of the nitride mask. The results are explained using a simple analytical model. It is found that stress varies very much during the different processing stages. After deposition of the nitride film, the stress is compressive under the mask lines and tensile outside the lines, close to the line border. The stress magnitude is highly dependent on the thickness of the nitride film. It can be described by edge forces. During field oxidation, this edge-force-induced stress nearly completely relaxes. In LOPOS structures with field oxide, the magnitude and distribution of the mechanical stress is mainly determined by the compressive forces exerted by the field oxide and the bird’s beak on the silicon, and tensile forces which are related to the bending of the nitride film at the edges. The influence of nitride film thickness on the stress at the center of the lines, ωc, is much smaller after field oxidation. For wide lines ωc is compressive and much higher than before field oxidation. For small widths ωc becomes tensile due to the influence of the vertical forces acting at the bird’s beak edge. The tensile stress due to the bending of the nitride film edge is much larger than the field-oxide-induced compressive stress, and dominates the stress picture at the bird’s beak. Only when very thick field oxides and thin nitride films are used, the field-oxide-induced compressive stress becomes visible. This becomes more clear when, in a further process stage, the nitride film is removed. The stress picture is then completely determined by the field oxide and the stress in the active area is always compressive.

Formation of compressively strained SiGe/Si(110) heterostructures and their characterization

“…Along with the formation of stress-induced crystalline defects during the growth, device fabrication processes also have significant influence on the lattice strain. For example, stress applied by surrounding materials [18][19][20][21][22][23] and change of strain as a result of micropatterning [24][25][26][27][28][29][30] affect the lattice strain and electronic properties. In this study, we investigated channel direction dependence of the strain in stripe-shaped SiGe-channel MOSFETs fabricated on Si(110) substrates.…”

Evaluation of local strain in Si using UV-Raman spectroscopy

“…Therefore, it is also necessary to establish reliable techniques of measuring strain, which are very important in the research, development, and production of all aspects of product management. Several technologies have been proposed to evaluate strain in Si crystal [9][10][11][12][13][14][15][16][17][18][19]. Of these, Raman spectroscopy is well known as a non-destructive and relatively high spatial resolution technique.…”

“…Strain has been managed passively such that the compressive strain induced by Shallow Trench Isolation (STI) has been minimized to suppress the deterioration in nMOSFET performance [10][11][12][13][14][15][16][17][18][19][20]. Controlled strain is presently intentionally introduced into the channel region in MOSFETs to enhance their carrier mobilities.…”

Spin-filter scanniing tunneliing microscopy : a novel technique for the analysis of spin polarization on magnetic surfaces and spintronic devices

“…Unfortunately the same arguments are valid if tunneling is done at low bias to attempt to determine spin polarization at Fermi level. In this case both LDOS and ILDOS have similar spin polarization and the compensation mechanism just described also washes out the SP-STS contrast or may even invert it [79].…”

“…The anomalous feature may also be a defect due to stress. Large tensile stress at the bird's beak edge due to bending of the nitride mask has been observed by micro-Raman spectroscopy [78,79] and x-ray diffraction imaging [80] which can generate defects or even break the pad oxide there. This tensile stress may be related to the anomalous profile.…”