Plasma silicon nitrides

It is also interesting to note that the H bound into the plasma silicon nitride film can be driven off, to some extent, by annealing at low temperatures. Data for SiH4 + N2 + He and SiH4 + N2 + Ar depositions are shown in Figure 10.7 Observe that for a film deposited with He at 300°C and then annealed for 10 hours at 300 C, the hydrogen content drops from 19 to 12%. The curves marked NOT are unannealed. Depositions with Ar did not display this behavior. 

After the quality of the plasma silicon nitride films and their dependence on the several system parameters has been evaluated, there still remains the question of whether or not a given process can be commercially viable. Here the issue is the deposition rate and the uniformity of deposition on a wafer and over all wafers in the reactor. The ideal solution is to deposit at a high rate uniformly over many wafers at one time. We cannot simply stack many wafers close together and run a low-pressure process, as in thermal LPCVD, because we have to be sure the plasma discharge is uniform as well. 

Figure 10 Effect of annealing on hydrogen % in plasma silicon nitride films versus deposition temperature (a) He diluent (b) Ar diluent.7 Reprinted by permission of the publisher, The Electrochemical Society, Inc.

W.M., Influence of deposition temperature, gas pressure, gas phase composition, and RF frequency on composition and mechanical stress of plasma silicon nitride layer. J. Electrochem. Soc. 132 893 (1985). 

For comparison values for Si3N4 films prepared by atmospheric-pressure CVD at 900°C from SiH4, NH3, N2 gas mixtures are also listed. Microchemical analysis data have shown that the chemical composition of the plasma silicon nitride films is slightly Si-rich at a Si/N-ratio between 0.8 and 1.0 compared to 0.75 for stoichiometric deposits. As indicated by infrared spectrometry, there are also larger amounts of hydrogen and traces of oxygen in the films. Therefore the true film composition may be represented by SxNyHz [195]. Films deposited at 300°C are thermally stable up to about 400°C. As a consequence of compressive film stress, blis-... 

Hoffman, D. M., et al., Plasma-Enhanced CVD of Silicon Nitride Films from a Metallo-Organic Precursor, J. Mater. Res., 9(12) 3019-3021 (1994)... 

Plasma CVD was first developed in the 1960s for semiconductor applications, notably for the deposition of silicon nitride. The number and variety of applications have expanded greatly ever since and it is now a major process on par with thermal CVD. 

An RF plasma is generated at a frequency of 13.56 MHz. A typical equipment consists ofparallel electrodes as shown inFig. 5.20. It is a cold-wall design which is used extensively forthe deposition of silicon nitride and silicon dioxide for semiconductor applications. 

Reactions (1), (2) and (3), which all use ammonia, have a tendency to deposit silicon nitride with a high ratio of included hydrogen, especially at the lower temperatures and if a plasma is used. This tendency is often detrimental but it can be remedied, at least to some degree, by using nitrogen instead of ammonia ... 

Tsu, D. V., and Lucovsky, G., Silicon Nitride and Silicon Diimide Grown by Remote Plasma Enhanced Chemical Vapor Deposition, J. Vac. Set. Technol. A, 4(3-1 ) 480-485 (May-June 1986)... 

Hussain, T., and Ibberson, V., Synthesis of Ultrafme Silicon Nitride in an RF Plasma Reactor, in Advances in Low-Temperature Plasma Chemistry, Technology, Applications, 2 71-77, (H. Boenig, ed), Technomic, Lancaster (1984)... 

Chemical Vapor Deposition- Deposition of silicon oxide films is accomplished by CVD equipment. Either plasma CVD or ozone oxidation is used. Blanket tungsten films are also deposited by CVD equipment to create contact and via plugs. Polysilicon and silicon nitride films are deposited in hot-wall furnaces. TiN diffusion barrier films are deposited by either sputtering or CVD, the latter giving superior step coverage. 

In the case of H in low-temperature deposited silicon nitride films, ion beam techniques have again been used to calibrate IR absorption. The IR absorption cross sections most often quoted in the literature for Si—H and N—H bonds in plasma-deposited material are those of Lanford and Rand (1978) who used 15N nuclear reaction to calibrate their IR spectrometry. Later measurements in CVD nitride films, using similar techniques, confirmed these cross sections (Peercy et al., 1979). 

The other platform is dielectrics, for example, silicon dioxide, silicon nitride, silicon oxynitride, tantalum pentoxide, and titanium dioxide. They can be deposited by various methods, such as plasma-enhanced chemical vapor deposition, thermal evaporation, electron-beam evaporation, and sputtering. There are a number of dielectrics with refractive indices ranging from 1.45 to 2.4, facilitating diverse waveguide designs to satisfy different specification. Dielectrics have two other... 

The steam reformer is a serpentine channel with a channel width of 1000 fim and depth of 230 fim (Figure 15). Four reformers were fabricated per single 100 mm silicon wafer polished on both sides. In the procedure employed to fabricate the reactors, plasma enhanced chemical vapor deposition (PECVD) was used to deposit silicon nitride, an etch stop for a silicon wet etch later in the process, on both sides of the wafer. Next, the desired pattern was transferred to the back of the wafer using photolithography, and the silicon nitride was plasma etched. Potassium hydroxide was then used to etch the exposed silicon to the desired depth. Copper, approximately 33 nm thick, which was used as the reforming catalyst, was then deposited by sputter deposition. The reactor inlet was made by etching a 1 mm hole into the end... 

This approach allows the deposition of thin films at low temperatures. By comparison, polymer deposition generally requires very high temperatures. For instance, the chemical vapor deposition of silicon nitride requires a temperature of about 900°C, whereas the plasma chemical deposition requires a temperature of only 350°C. 

Experiments like those described above have been performed to evaluate sodium ion barrier properties of Hitachi PIQ and DuPont PI 2540 polyimide films. Also included in the comparison were silicon nitride coatings plasma deposited in both tensile and compressive stress modes. The structure of the samples is illustrated in Figure 9. N-type, (111) oriented silicon substrates were cleaned and oxidized in dry oxygen ambient at 1100°C to form a 1060 A Si02 film. Wafers intended for polyimide characterization were coated with an organic silane film (gamma glycidal amino propyl trimethoxysilane) to promote adhesion of the polyimide to the oxide surface. The polyimide resins were spun onto the wafers at speeds to produce final... 

Table 8.1.5 Processing Conditions for the Synthesis of Silicon Nitride UFPs by an Inductively Coupled RF-Plasma Torch Reactor...

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