A semiconductor non-planar storage capacitor

Abstract: A non-planar storage capacitor comprises a non-planar first capacitor electrode (40), a dielectric layer (45) and a second capacitor electrode (50) formed by a tungsten nitride layer overlying the dielectric layer. Preferably the tungsten nitride layer comprises silicon.

Description: Tungsten nitride has been shown to be an extremely promising material for planar capacitor and gate electrode applications. Tungsten nitride. is stable at high temperatures and prevents dielectric degradation in capacitor applications and acts as a barrier between polycrystalline silicon and tungsten when used as a low resistivity strapping layer in a gate electrode. In one fabrication method Alex Lahav, Karen A. Grim, and Ilan A. Blech, as described in their article, "Measurement of Thermal Expansion Coefficients of W, WSi, WN, and WSiN Thin Film Metallizations," Journal of Applied Physics 67(2), January 15, 1990, page 734, prepare tungsten nitride using reactive sputtering and obtain good film properties. Although sputtering can provide high quality films, surface step coverage is inadequate for many applications. It would be preferred to have an improved step coverage process such as chemical vapor deposition (CVD). Nakajima et al. in an article entitled "Preparation of Tungsten Nitride Film by CVD Method Using WF 6 " appearing in the December 1987 edition of the Journal of Electrochemical Society: SOLID-STATE SCIENCE AND TECHNOLOGY, has demonstrated chemical vapor deposition of tungsten nitride from NH 3 and WF 6 source gases in a conventional hot wall CVD system. Although hot wall CVD systems offer an advantage with respect to wafer throughput, process control and cleanliness are typically not adequate for state-of-the-art applications. Rather, single wafer cold wall deposition systems are preferred. U.S. Patent 5,187,557 relates to a semiconductor device having a capacitor part which is composed of the first electrode including a first titanium nitride film, a dielectric layer and a second electrode including a second titanium nitride film. The titanium nitride film is sandwiched between the dielectric layer and the first and second electrodes. U.S. Patent 5,290,609 relates to a dielectric film of a capacitor. A thin Ta layer is deposited using TA(N(CH 3 ) 2 ) 5 gas and H 2 radicals. The thin Ta layer is then oxidized by O 2 radicals to form a thin Ta 2 O 5 layer. An Si 3 N 4 layer is then formed on the Ta 2 O 5 layer by using SiH 4 and NH 3 gases. Patent Abstracts of Japan, vol. 18, no. 684 (E-1650), 22.12.94 & JP-A-6 275 776 relates to a capacitor with a Ta 2 O 5 film used as a capacitor insulating film. An electrode comprised of tungsten nitride is provided on the Ta 2 O 5 film as an upper electrode. For a CVD process WF 6 and NH 3 offer the advantages of being readily available and providing high deposition rates. However, WF 6 , NH 3 form an adduct at low temperatures (<50°C), and even with a cold wall system there is a minimum acceptable wall temperature to prevent adduct formation. Furthermore, byproducts of the deposition reactions can cause encroachment into silicon or polycrystalline silicon substrates and therefore the process must be modified to reduce encroachment without compromising adhesion or resistivity. Thus, there exists a need for a CVD tungsten nitride process having good adhesion and high deposition rates while providing conformal, low resistivity films with minimal silicon encroachment. Described herein is a method for depositing tungsten nitride comprising silicon using chemical vapor deposition. This method uses a source gas mixture having a silicon based gas for depositing the tungsten nitride to overlie a deposition substrate. The method is useful in the fabrication of a capacitor electrode, a contact plug, and a gate electrode due to the good adhesion, minimal silicon encroachment and low resistivity of the tungsten nitride. The invention is a non-planar storage capacitor as claimed in claim 1 having a tungsten nitride capacitor electrode. Figures 1-3 are cross sectional views of a semiconductor during various fabrication steps. Figure 1 is a cross-sectional view of a portion of a semiconductor substrate having various structures fabricated thereon and having a first capacitor electrode. Figure 2 is the cross-sectional view of figure 1 following the creation of a dielectric layer. Figure 3 is the cross-sectional view of Figure 2 following the creation of a tungsten nitride electrode. In one embodiment the invention is a semiconductor non-planar storage capacitor having a tungsten nitride capacitor electrode comprising silicon formed by a process in which the tungsten nitride is chemically vapor deposited from a source gas comprising a silicon based gas, such as silane. Although the invention is applicable to any number of non-planar capacitors, including trench capacitors and a variety of stacked capacitors, Figures 1-3 depict the process steps for fabricating a stacked capacitor of the invention. Figure 1 is a cross-sectional view of a partially processed semiconductor device 1 having a buried bit line 5, a wordline 10 overlying a field oxide layer 15, and field effect transistors 20. A thin oxide layer 25 has been removed from a contact area 30 of the substrate 35 and a polycrystalline silicon (herein after also "polysilicon" or "poly") layer 40 has been deposited to overly the substrate 35 and contact the contact area 30 of the substrate 35. The poly layer 40 has been doped and patterned with a photo mask (not shown) to create a storage node plate or first electrode of the capacitor of the invention. In Figure 2 a dielectric layer 45, preferably tantalum oxide, is deposited to overly the polycrystalline silicon layer 40. In Figure 3 a tungsten nitride layer 50 is conformally deposited by chemical vapor deposition in a deposition chamber to overlie the dielectric layer 45 thereby forming a second electrode of the storage capacitor. During the chemical vapor deposition a source gas having at least a tungsten source such as tungsten hexafluoride combined with ammonia is combined with carrier gases which may include argon, hydrogen, nitrogen, or other gases. Alternate tungsten sources such as tungsten carbonyl may also be used. The source gas also comprises a silicon based gas such as silane, organic silane, or a compound which is a multiple order of silane, such as di-silane and tri-silane. The source gas is maintained at a pressure conducive to chemical vapor deposition, typically within the range of pressures between 13 Pa and 13 kpa (0.1 and 100Torr) including the end points. The temperature of the deposition substrate is maintained at 300°C, although other temperatures may be used. The temperature of the deposition chamber walls are held at a temperature which minimizes adduct formation, in this embodiment the walls are held at a temperature greater then 25°C although other temperatures lower than the temperature of the deposition substrate will minimize adduct formation. In one embodiment the source gas comprises tungsten hexafluoride, ammonia, argon, and hydrogen. In this case during deposition of the tungsten nitride layer 50 the tungsten hexaflouride, ammonia, argon, and hydrogen have flow rates of 50sccm, 150sccm, 80sccm and 80sccm respectively. Silane being added to the source gas mixture the flow rate of the silane is equal to 4sccm which is 1.098% of the total flow rate of the source gas mixture with the added silane. In the capacitor of the invention the addition of silane to the source gas reduces encroachment into any silicon based materials exposed to the tungsten nitride, improves adhesion of the tungsten nitride to its underlying layer, and reduces the bulk resistivity of the tungsten nitride. For most applications the flow rate of the silane or other silicon based gases should fall within the range of 0.5% to 5% of the total flow rate of the source gas comprising the silicon based gas, although flow rates from .1% to 25% of the total flow rate may be used. It is possible to form the first electrode of the capacitor of the invention using the tungsten nitride when deposited according to the method described above. Although specific embodiments have been described the invention should be read as limited only by the claims.

Claims: A semiconductor non-planar storage capacitor, comprising: a) a non-planar first capacitor electrode; b) a dielectric layer overlying said first capacitor electrode; and c) a tungsten nitride layer overlying said dielectric layer, said tungsten nitride layer forming a second capacitor electrode of the non-planar storage capacitor, said tungsten nitride layer comprising silicon. The non-planar storage capacitor as specified in claim 1, wherein said dielectric layer is tantalum oxide. The non-planar storage capacitor as specified in claim 1, wherein said first capacitor electrode is tungsten nitride. The non-planar storage capacitor as specified in claim 1, wherein the tungsten nitride layer is a conformal film with low resistivity. The non-planar storage capacitor as specified in claim 1, wherein the tungsten nitride layer is a conformal film with minimal silicon encroachment. The non-planar storage capacitor as specified in claim 1, wherein the tungsten nitride layer is a conformal film with good adhesion. The non-planar storage capacitor as specified in claim 1, wherein the tungsten nitride layer is formed by chemical vapor deposition using a gas comprising nitrogen, tungsten and silicon.

Inventors: DOAN TRUNG, MEIKLE SCOTT, DOAN, TRUNG, MEIKLE, SCOTT
Applicants: MICRON TECHNOLOGY INC, MICRON TECHNOLOGY, INC.
Application year: 1995
Main classification: H01L21
IPC codes: H01L21, C23C16