Chlorine silicon etching

Fig. 3. Panorama of plasma etching using silicon etching with chlorine as an example. This figure also shows the disparate length scales involved from the reactor, to the sheath, to the microfeature, to the atomic scale. Cl radicals and CIJ ions are generated in the plasma by electron impact of gas molecules (a). Ions accelerate in the sheath and bombard the wafer along the vertical direction (b), thereby inducing anisotropic etching of microscopic features to yield SiCU, a volatile product (c). Ion bombardment creates a modified layer at the surface where Cl is mixed within the Si lattice (d).

Wafer temperature affects the rate of spontaneous etching and also polymerization reactions. Wafer temperature control is important in semiconductor manufacturing. The temperature is typically controlled by relatively high pressure (several torr) He cooling from the backside of the wafer. The model below refers to silicon etching in a chlorine plasma as a typical example [98]. 

Flamm, D.L. (1990), Mechanisms of Silicon Etching in Fluorine- and Chlorine Containing Plasmas, Report UCB/ERL M90/41, College of Engineering, University of California, Berkley. 

Barone M E and Graves D B 1995 Molecular dynamics simulations of direct reactive ion etching of silicon by fluorine and chlorine J. Appi. Phys. 78 6604-15... 

In order to prevent aluminum from spiking through shallow junctions, 1-2% silicon is often added to the film. Since SiCl4 is volatile at room temperature, aluminum-silicon films can be readily etched in chlorine-containing gases. 

Titanium can be etched in fluorine-, chlorine-, or bromine-containing gases, because all the halides are volatile. Chlorides and bromides have been studied to a great extent since they result in high selectivity over silicon- containing films, and do not promote staining on gold (77). 

In reactive etching of silicon a patterned film is selectively etched by reacting with a gas such as chlorine... 

Further investigation of the nature of these films4 has shown that there is about 2.7% Cl remaining in the completed film. Upon exposing them to a thermal oxidation environment, it was discovered that the interface between the oxide and silicon was etched and film adhesion was lost—the films flaked off. Apparently, the thermal oxidation process released bound chlorine in the oxide which then diffused to the interface where it attacked the silicon. 

These authors found that it was possible to deposit amorphous films whose Ta concentration ranged from 10 to 80 mol % by changing the reactive gas mix. Another feature of the films was that under certain conditions they contained substantial quantities of chlorine and hydrogen. Also, they did not adhere to either silicon or silicon dioxide after annealing (argon atmosphere for 1 hour at 900°C). When the substrates were dry etched in an HCI plasma for 2 minutes, they adhered to the substrate even after annealing. Since this etch removed about 50 A, it appears that the native oxide on the silicon and/or some other surface impurities on both the silicon and silicon dioxide were causing the lack of adhesion. 

Chlorine trifluoride is a promising gas not only as the new cleaning gas but also as the replacement gas for global warming. On the other hand, Ibottoson et al. reported on plasma-less etching of single crystal silicon and some tantalum compounds with chlorine trifluoride [118,119]. The purpose of their studies was to apply chlorine... 

G. A. WOLFF (U. S. Army Signal Research and Development Laboratory) We have studied the etching of silicon using chlorine at elevated temperature as an etchant. We found under certain conditions that a sub-halide layer was formed on the surface inhibiting further reaction. When these samples were placed in water or an ammonia solution, hydrogen was evolved leaving a black residue on the surface which may be silicon. 

Moreover, Fig. 10.2 shows that more a precursor is chlorine-rich, more the growth rate is low. This phenomenon is explained by the etching of silicon by... 

The feed gas to the reactor is composed of molecules that contain the etching species. Fluorine containing molecules such as CF4, CF3H, or SiFs are used to etch silicon. Molecules such as H2 or O2 may also be present in the feed gas to control the reaction pathways and will be subsequently discussed. This feed mixture is termed the recipe for the etching process. To etch aluminum or aluminum silicide, which are used to make the electrical contacts to the active device region, a chlorine containing gas such as BCI3 is used. 

One of the most important aspects of plasma-surface processing is that the plasma itself often strongly modifies the near-surface region. An example of this is shown schematically in Figs. 3a and b, in the case of etching. Figure 3a is a depth profile of an originally crystalline silicon surface that has been exposed to a chlorine plasma. (Chlorine plasma is commonly used to etch silicon and other materials.) The plasma has created various silicon... 

Plasma etchants are available for most of the films commonly used in micromachining. Etching of oxide, nitride, and silicon is usually done with fluorine-containing compounds such as SiF4, CF4, and SF6. Aluminum and other metals can be etched in chlorine plasmas such as SiC l4 and BC13. In certain conditions, better results can be obtained by combining several gases. 

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