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Strain state in silicon structures for microprocessor technology

100%

Hecker M. , Geisler H.

Materials Science Poland

2007

tom Vol. 25, No. 1

7--18

A promising approach to improve the performance of present CMOS devices is to introduce mechanical strain into the channel regions below the transistor gates. Strain can be generated as global strain on the whole wafer level (e.g., by growing strained silicon films on strain-relaxed silicon-germanium (SiGe) alloy layers or by using strained silicon films on an insulator), or as local strain on the transistor scale by applying specific technology processes (e.g., making use of embedded SiGe source-drain regions). The detection of strain in very thin silicon films requires sophisticated techniques with high depth sensitivity, whereas the measurement of the local strain state in thin Si structures with small lateral dimensions below 50 nm - such as the channels of current CMOS transistors - still remains to be mastered. A technique possessing the potential for solving this problem is Raman spectroscopy, where the diffraction limit for lateral resolution can be bypassed by near-field approaches. In the present paper, the occurrence of large strains in SiGe films and corresponding stresses in the GPa range are demonstrated by Raman spectroscopy, utilizing a simple approach for determining strain and composition separately. To estimate the strain distribution in a silicon channel structure due to embedded SiGe source-drain regions, a silicon strain calculation is applied based on a continuum-mechanical model utilizing a continuous distribution of virtual dislocations along the Si-SiGe boundaries. Within the framework of this model, the stress state in a 2D approximation is obtained by analytical expressions. Thus, the spatial distribution of channel strain and the impact of geometry on the strain state are obtained in a straightforward way.

Quantitative mapping of elastic properties of electron-beam damaged silica-based low-k films

80%

Jiang L. , Geisler H. , Zschech E.

tom Vol. 23, No. 3

643--651

A quantitative technique for mapping of elastic modulus performed on organosilicate glass (OSG) thin films with different surface conditions is described. This modulus mapping technique provides highly valuable information about the elastic properties at the very near-surface region of the films. The results show that low-k films can be modified by electron beams, leading to a near-surface region with increased stiffness. Compared with quasi-static nanoindentation, the modulus mapping technique is more surface sensitive, and therefore, it has a better capability to detect slight differences of elastic properties between ultra-thin films of different thickness on top of OSG films.

Experimental challenges for approaching local strain determination in silicon by nano-Raman spectroscopy

51%

Zhu L. , Atesang J. , Dudek P. , Hecker M. , Rinderknecht J. , Ritz Y. , Geisler H. , Herr U. , Geer R. , Zschech E.

Materials Science Poland

2007

tom Vol. 25, No. 1

19--31

Raman intensity enhancement induced by nanoprobes (metal particles and metallised tips) approached to a strained silicon sample surface is reported. With silver nanoparticles deposited onto a silicon surface, high enhancements in the vicinity of particles were observed. Furthermore, metallised tips were scanned inside the spot of the laser used for Raman measurements. Both silver-coated and pure silver tips, mounted onto a tuning fork, indicated high Raman signal enhancement for optimised tip position within the laser spot. Atomic force microscopy was performed on a structured sample to investigate the stability of these tips. Focused ion beam was utilized to refine and to re-sharpen pure silver tips after the measurements. Complementary measurements were performed using pure tungsten tips. Due to the high hardness of W wires, a special pre-etching technique was applied in this case.