Gas dome dielectric system for ULSI interconnects

Details Gas dome dielectric system for ULSI interconnects Gas dome dielectric system for ULSI interconnects

2002-10-07

2004-08-24

Guerrero, Maria (Department: 2822)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S421000, C438S422000, C438S619000, C438S623000, C438S624000, C438S780000

Reexamination Certificate

active

06780755

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of fabricating electrical conductors for an integrated circuit (IC) having improved electrical properties. The invention effectively reduces the dielectric constant of insulating material between selected IC conductors on the same level (intralevel) or between conductors on superposed levels (interlevel) in VLSI or ULSI circuits, hence dramatically reducing the coupling capacitance between conductor levels. Realization of this method and structure utilizes an enclosed near-unity dielectric constant gas or liquid material, the composition and pressure of which can be selected.
BACKGROUND OF THE INVENTION
There is a need to replace the inorganic/organic insulating material used to isolate metal conductors in ultra large scale integrated circuits (ULSI) in order to reduce the signal RC delay, resulting in a faster (higher frequency) circuit performance. The term ‘RC delay’ stands for ‘resistance-capacitance delay’ and is a function of the type of metal conductor used (resistance component) and the type of insulating material used to isolate the metal conductors (capacitive component). The lower the ‘dielectric constant’, k, of the insulating material, the lower the capacitive component. An ideal gas has a dielectric constant equal to 1.0, whereas most inorganic/organic insulating materials currently used in the semiconductor industry have a dielectric constant of 2.5-3.0 (organic polymers) to 4.3 (inorganic silicon dioxide), or even higher (silicon nitride). Historically, silicon dioxide has been used as the insulating material for on-chip ULSI interconnect purposes. However, with the need to make integrated circuits smaller and faster (resulting in faster computers, etc.), there has been a concerted effort by the semiconductor industry to find a replacement for silicon dioxide. A number of “organic” insulating materials having a lower dielectric constant are being considered, however, most of these materials have reliability problems.
The RC delay associated with interconnect is rapidly becoming the limiting factor in realizing high speed integrated circuits with design rules below 0.25 microns. See
National Technology Roadmap for Semiconductors: Technology Needs
. Published by Semiconductor Industry Assoc., pp 99-110, 1997.
As packing density increases, the cross-sectional area of interconnect lines decreases causing the resistance to length ratio to dramatically increase. The adoption of copper as the conductor of choice can improve the resistance component by almost a factor of two over that of aluminum (from 3.0 to 1.7 micro-ohm-cm resistivity). However, a dramatic reduction in the dielectric constant of the intermetal dielectric material over that of silicon dioxide (k=4.1) is also needed to address the capacitive component for future high speed circuitry.
A reduction in interconnect line capacitance (resulting from a reduction of dielectric constant) can reduce signal propagation delay, reduce power consumption at high frequencies and reduce cross coupling between conductors (cross-talk and noise). Another significant benefit of reducing RC delay is to reduce process complexity (i.e., 12 levels of metal using Al—SiO2 versus 6 levels of metal using Cu-low k at 0.13 microns design rules), and hence improves reliability and yield while reducing cost. A reduction of wire capacitance can also provide an increased degree of design freedom; the designer can use the reduction in capacitance to either improve speed or reduce power. See G. A. Sai-Halasz,
Proc IEEE
, vol 83, no. 1, p 20, 1995. Currently, there is a wide variety of organic and inorganic materials bring investigated as potential candidates for low-k intermetal dielectrics. See D. S. Armbrust, D. Kumar,
Short Course on Dielectrics for ULSI Multilevel Interconnection
Visuals Booklet, DUMIC, Santa Clara, Calif., Feb. 10, 1999. Also, procedures have been proposed to conduct comparative evaluations of these candidates in order to find the optimal material. See T. E. Wade, “Optimum Dielectric Selection Using a Weighted Evaluation Factor”,
DUMIC
, pp 211-218, 1995 and
Semiconductor International
, pp 99-106, vol 38, no. 8, August, 1995. Many of these candidates exhibit severe reliability, manufacturability and/or process integration problems, especially the organic candidates.
Properties required for an acceptable intermetal dielectric material for use in ULSI interconnects include a) low dielectric constant (ideally k=1.0), b) high breakdown field strength (>2 MV/cm), c) low bulk leakage (resistivity>10
15
ohms/cm), d) low surface conductance (surface resistivity>10
15
ohms), e) low stress (compressive or weak tensile>30 Mpa), f) mechanical/chemical/thermal stability, g) no moisture absorption and/or permeability to moisture, h) process compatible (CMP/dual damascene/etc.), i) good thermal properties (high thermal conductivity, low TCE, stable), j) compatibility with environmental, health and safety requirements, etc. The National Semiconductor Roadmap for Semiconductors calls for dielectrics with k=2.5-3.0 for 0.18 micron devices and 2.0-2.5 at 0.15 micron devices. If a reliable unity-k dielectric system could be realized using conventional technological processes, a quantum step towards meeting Roadmap goals could be achieved.
The use of gas dielectrics offers many benefits, including: 1) optimal electrical properties (unity dielectric constant (k=1) for reduced RC delay/cross-talk/power consumption, high breakdown strength, low leakage, high volume and surface resistivity, no polarization effects, low ionic/contamination/migration effects, low mobile ion/charge trapping effects), 2) optimal mechanical properties (no shrinkage, no stress due to thermal intrinsic effects, no problems with adhesion, no defect density issues like pinhole density/particulates/cracks/seams/etch pits/etc., no gap fill problems, no planarization problems), 3) optimal chemical properties (resistant to corrosion, leaching & precipitation, no EHS issues), and 4) optimal design/processing characteristics (scalability, reduced complexity/cost/improved yield, no barriers needed, reduced overall cost-of-ownership, commercially available sub-processes).
To date, liquid dielectric materials have not been used as insulators in the fabrication of integrated circuits. However, current research may well result in liquid (or semi-liquid) dielectric materials having dielectric properties similar to those mentioned above for gases but with superior thermal conduction properties.
The most significant benefits of utilizing gas (and possibly liquid) dielectrics are reduced cost, improved yield and higher speed circuitry. Also, in general the greatest benefit for unity-k dielectrics is where lines are at their minimum pitch.
SUMMARY OF THE INVENTION AND ADVANTAGES
A method of providing an electrically insulating medium in an enclosed envelope which contains multilevel metal conductors of an integrated circuit is disclosed. The method includes the step of providing a base substrate. The base substrate is formed of insulating material. Next, a plurality of discrete multilevel metal conductors are formed on and above the base substrate, and then a plurality of discrete support means are formed to extend upwardly from the base substrate to one or more conductor levels or between conductor levels. A selectively removable material is then deposited on the base substrate and around the support means and the metal conductor.
A dome layer of insulating material is then provided overlying the support means, the conductor levels, and the removable material. Once the dome layer is provided, access opening means are formed in the dome layer to communicate with the removable material. The removable material is then removed through the access opening means. The removable material is removed without interrupting the base substrate, the dome layer, the support means, and the metal conductors. As such, the envelope is defined between the base substrate and the dome layer

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