The Effects of Chemical Vapor Cleaning Chemistries on Silicon Surfaces
- PDF / 389,612 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 29 Downloads / 207 Views
ABSTRACT This study explores the effects of two chemical vapor cleaning chemistries on silicon surfaces. The silicon surfaces are not significantly roughened by exposure to either process. Trace amounts of fluorine are found on the surfaces exposed to 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (HFAC). A thin silicon nitride film forms on the silicon surface as a result of exposure to the HMDS process and is attributed to the H2 /N2 plasma treatment used in the first step of the process.
INTRODUCTION For any type of vapor phase cleaning process to become a viable technology it must meet certain criteria. These criteria include a proven capacity for removing surface contaminants to concentrations comparable to, or better than, wet cleans; it must occur at low temperatures and high throughput; it must not roughen the semiconductor surface; and it must not leave any residue that would be deleterious to device performance, reliability, or yield 1 . Examples of the various dry or gas phase cleaning methodologies that must meet these criteria include anhydrous HF, UV or downstream plasma enhanced halogen cleaning, and chemical vapor cleaning (CVC). CVC is the heterogeneous reaction of coordinating gas phase ligands with surface contaminants forming volatile coordination compounds or organometallic products. Our studies have focused on the removal of transition metals and mobile ions. The removal of trace levels of transition metals in the presence of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (HFAC) has been suggested2 . A typical reaction for the removal of a transition metal oxide is CuO + 2H+(HFAC)
-4
Cu(HFAC) 2 + H2 0
(1)
For the removal of mobile ion contamination a two step process has been suggested 3 . For example, to remove sodium from a native oxide surface the first step in this process is to convert the sodium to a more reactive state such as sodium amide ("NaNH 2 (s)"). This intermediate state is given in quotations as it has not been unequivocally identified as the stoichiometric material, but the sodium is known to be bound to nitrogen on the surface. Na2 0 + HI/NH 3 -> "NaNH 2(s)" + H20(vap)
(2)
The second step reacts the activated species with hexamethyldisilazane (HMMDS), HN[Si(CH 3 )3]2 , resulting in the formation of volatile sodium hexamethyldisilamide 3 . "NaNH12(s)" + HN[Si(CH 3)3] 2 (v7ap) -> NaN[Si(CH 3 )31 2(vap) + NH3(vap) 263 Mat. Res. Soc. Symp. Proc. Vol. 318. ©1994 Materials Research Society
(3)
The purpose of this work is to examine how the CVC processes mentioned above perform with respect to the last two criteria; i.e., do they roughen the silicon surface or leave a deleterious residue.
EXPERIMENTAL The samples used in this work were p-type (100) silicon with a resistivity of 0.1 fl-cm that were cut into 15 mm x 15 mm squares. Two methods of analysis were chosen for these experiments: Atomic Force Microscopy (AFM) and X-Ray Photoelectron Spectroscopy (XPS). Samples were cleaned by the standard RCA clean with an HF last step prior to initial AFM measurements and subsequent exposures t
Data Loading...
