Cyanuric fluoride and related compounds for anisotropic etching

Details Cyanuric fluoride and related compounds for anisotropic etching Cyanuric fluoride and related compounds for anisotropic etching

2001-06-13

2003-01-21

Goudreau, George (Department: 1763)

Etching a substrate: processes

Gas phase etching of substrate

Application of energy to the gaseous etchant or to the...

C216S067000, C216S071000, C438S710000, C438S714000

Reexamination Certificate

active

06508948

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is directed to methods for performing microfabrication of semiconductor based logic, memory and optoelectronic devices and micromechanical systems. In particular, the present invention is directed to microfabrication using anisotropic etching.
Microfabrication techniques are used, for example, to manufacture semiconductor-based logic, memory and optoelectronic devices, and microelectromechanical (MEMS) systems. There has been an ongoing trend toward miniaturization and optimization of these devices such that ever more stringent control is required over their geometries. One method widely applied to achieve these geometries is a process where a lithographic mask is generated on a surface and then features are etched into the surface of the underlying substrate. In order to get a faithful replica of the mask to be etched in the underlying layer, the etching process must have a high degree of anisotropy. That is, the etching rate perpendicular to the surface, as opposed to other directions relative to the surface, must be predominant. Chemical etching is undesirable since it tends to be mostly isotropic (i.e., identical in all directions) because most chemical etch rates are typically independent of direction and solely depend on diffusion.
Anisotropic etching is achieved in practice, e.g., by using reactive ion-assisted plasma etching, where active chemical etchant species (e.g., fluorine atoms) are generated in a plasma reactor along with reactive ions that are directed to strike the etch substrate perpendicular to its surface. In order to achieve anisotropy, a chemical composition is achieved in the plasma that allows the side walls of the feature to be protected from purely chemical etching by the deposition of a protective film. This film must be susceptible to being removed by the reactive ions that will be impinging primarily on the bottom surface of the trench being etched. The exposed substrate at the bottom of the feature is thus subjected to a combination of chemical and ion etching whereas the side walls are essentially untouched.
In order to achieve the desired results, the chemical composition of the plasma must be balanced correctly. It has been observed that better anisotropic etching can be achieved by balancing the formation of fluoro-organic polymeric deposits for side wall protection against the generation of the reactive etchant species that can remove exposed substrate. It has been observed that this balance may be obtained with fluorocarbons having reduced F to C ratios (hereinafter, F:C). For example, C
4
F
8
(F:C=2) is a better anisotropic etch gas than C
2
F
6
(F:C=3). Even lower F:C ratio gases have recently attracted attention for this application (e.g., C
4
F
6
, F:C=1.5 and C
5
F
8
; F:C=1.6). This trend has been described extensively in published literature. For example, see E. Stoffels, et al., “Polymerization in Fluorocarbon Plasmas,”
Purazuma, Kaku Yugo Gakkaishi,
1999, 75, pgs. 800-12. For future applications, plasma sources with even lower F:C ratios are desired.
It is known that when cyanuric fluoride (C
3
N
3
F
3
) and other fluorinated aromatic amines are decomposed in a plasma, there is a substantial tendency to form polymeric deposits. This property was used to advantage in a plasma polymerization process described by Munro, et al. in Munro, et al., “An ESCA Study of the Inductively Coupled RF Plasma Polymerization of 2, 4, 6-Trifluoro-1,3,5-Triazine,”
J. Polym. Sci.: Polym. Chem. Ed.
1984, V. 22, pgs. 2661-66. This polymerization process was being studied in the interest of generating thin films for their own sake and not as a means of enhancing selectivity or profile control in a reactive ion etching application. The polymers deposited by Munro, et al. were composed of fluorine carbon and nitrogen, unlike conventional fluorocarbon based etching gases, which generate only carbon and fluorine-containing deposits.
In the prior art, anisotropic etch gases principally focused on etching silicon oxide from silicon substrates when masked with a patterned and developed polymeric photoresist. These gases generally were comprised of fluorocarbons and hydrofluorocarbons. Enhanced selectivity, and profile control were obtained by using source species having reduced F:C ratios and hence having a greater propensity to polymerize. In some cases, additive gases (e.g. carbon monoxide) are required to improve the etch selectivity, presumably by abstracting active fluorine-containing species formed in the plasma reactor. It is preferable to have a single-source compound for these processes in some cases.
In the prior art, U.S. Pat. No. 6,174,451(Hung et al.) is directed to an oxide etch process using one of three unsaturated 3- and 4-carbon fluorocarbons, specifically, hexafluorobutadiene, pentafluoropropylene, or trifluoropropyne. The unsaturated hydrofluorocarbon, together with argon, is excited into a high-density plasma in a reactor which inductively couples plasma source power into the reactor and RF biases the pedestal a pedestal electrode supporting the wafer being etched.
U.S. Pat. No. 5,843,847 (Pu et al.) is directed to a method for etching a dielectric layer on a substrate with high etching selectivity (i.e. the rate of etching of the dielectric layer to the rate of etching of the overlying resist layer or the underlying silicon, polysilicon, titanium silicide, or titanium nitride layer), low etch rate microloading, and high etch rates. Here, a substrate is placed in a process zone and a plasma is formed from the process gas in the process zone. The process gas comprises (i) fluorocarbon gas for etching the dielectric layer and for forming passivating deposits on the substrate, (ii) carbon-oxygen gas to enhance formation of passivating deposits on the substrate, and (iii) nitrogen containing gas for removing passivating deposits formed on the substrate.
U.S. Pat. No. 5,814,563 (Ding et al.) is also directed to a method for etching a dielectric layer on a substrate with high etching selectivity, low etch rate microloading, and high etch rates. The method here uses fluorohydrocarbon gas, NH
3
-generating gas having a liquefaction temperature from about −60 degrees Celsius to about 20 degrees Celsius, and carbon-oxygen gas. In the method, a substrate having a dielectric layer with resist material thereon is placed in a process zone and a process gas is introduced into the process zone. The substrate is maintained at about +/−50 degrees Celsius of the liquefaction temperature. A plasma is formed from the process gas to etch the dielectric layer on the substrate at an etch rate of greater than 600 nm/minute and an etching selectivity ratio for etching dielectric relative to the underlying polysilicon of substantially ∞:1.
U.S. Pat. No. 5,770,098 (Araki et al.) is directed to an etching process for a semiconductor wafer where the process includes the steps of placing the object in a vacuum processing chamber, introducing an etching gas into the vacuum processing chamber, and applying electrical power to a pair of electrodes within the chamber by a high-frequency electrical power source. A mixed gas of carbon monoxide and a gas which does not contain hydrogen and which contains at least one element from the group IV elements and at least one element from group VII elements is used in the etching gas. At least 86% of an inert gas could be added to the etching gas. Here, the applicants state that this etching gas enables a high etching selectivity and prevents formation of fences.
It is principally desired to provide a method having enhanced properties for reactive ion etching for etching features into a substrate.
It is further desired to provide a method having enhanced properties for reactive ion etching for etching features into a substrate where the etching process has a high degree of anisotropy.
It is further desired to provide a method having enhanced properties for reactive ion etching for etching features into a substrate using halogenate

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