Study of HCl and Secco Defect Etching for Characterization of Thick sSOI

Abstract

In order to continue improving strained silicon-on-insulator ͑sSOI͒ crystal quality, high-resolution defect monitoring needs to be developed and implemented for further defects reduction. The study presented in this paper evaluates and compares two techniques for revealing crystal defects in sSOI wafers produced by the Smart-Cut Technology. Two different etching techniques, based on the use of gaseous HCl in an epitaxy reactor or of a diluted Secco wet etching solution, were compared on their ability to delineate various defects. Both techniques should provide the required defects density resolution for analysis of thin and thick strained silicon layers. For the sake of analysis and discussion, samples with a high defects density were chosen in order to simplify the quantitative comparison ͑within the resolution of optical microscopy͒. We have observed a difference in etching selectivity between the two techniques. After a statistical comparison of defects delineated by the two techniques ͑in terms of threading dislocations, areal densities, and planar defect linear densities͒, we have demonstrated complementarities rather than a direct correlation between the HCl and Secco etch. The HCl etch seems quite suitable for revealing threading dislocations through etch pits and shows a higher sensitivity for pit delineation compared to Secco ͑difference corresponding to a factor of 10 in defects density͒. Meanwhile, the Secco chemical etching appears more appropriate to highlight the planar defects ͑linear density between 600 and 1000 cm −1 ͒. Moreover, a minimum etched thickness for sSOI defect revelation has been determined for both techniques ͑between 26 and 36 nm for HCl and between 20 and 30 nm for Secco for a 600 Å thick starting layer͒. Because the Secco etch is particularly sensitive for the delineation of various types of defects ͑isolated etch pits and planar defects͒, it is now used by us as a quality control method for SOI and sSOI. Thanks to it sSOI process improvements are tracked and current and next generations of this product evaluated.

Defect delineation by chemical etching techniques in silicon and engineered silicon substrates: Novel chemistries and basic aspects

“…There exists a large number of standard defect etching solutions and modified recipes to meet the requirements of progressing technology. In recent reviews the state‐of‐the‐art of preferential etching from a practical point of view 4 and some basic aspects 5 have been given. Most of the common preferential etching solutions contain Cr (VI) in the form of dichromate or CrO 3 as oxidizing agent.…”

“…Preferential etching solutions such as the one from Secco 6 provide superior defect delineation capability, excellent smooth and uniform surface quality and etch rates in the µm/min regime. For the application on thin films (50–200 nm) of SOI and sSOI (sSi film thickness 20–80 nm) dilute versions with adjusted etch rates have been developed with appropriate performance 4. However, hexavalent chromium (Cr (VI)) compounds are toxic and carcinogenic and their usage is or will be heavily restricted by law.…”

Decoration and preferential etching of crystal defects in silicon materials: influence of metal decoration on the defect etching process

“…Etching solutions such as a dilute Secco etch are used for the delineation of those crystal defects in SOI materials [3]. After etching a dip in HF solution (49 %) is accomplished to dissolve the buried oxide (BOX) below the etch pit producing a bright halo of several µm size which can be easily detected in an optical microscope.…”

“…[2] and Ref. [3] were annealed without decoration procedure in the copper or lithium tube, respectively, and then Secco etched. Figure 1 shows the results of the activation energies obtained for copper and lithium decorated and reference samples of SOI 1 material.…”

Copper Decoration and Etching for Delineation of Crystal Defects in Thick SOI

“…After Secco etching a dip in HF solution (49 %) is performed in order to dissolve the buried oxide (BOX) below the etch pits which were formed during preferential etching. This process enhances the visibility of those defects because of the bright halo easily discovered under an optical microscope (8). Copper decoration is a well-established procedure used to facilitate the delineation of crystal defects of a few nanometers in size which are scarcely revealed by preferential etching alone (9,10).…”