Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Multiple layers
Reexamination Certificate
1999-04-01
2001-04-17
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Multiple layers
Reexamination Certificate
active
06218314
ABSTRACT:
BACKGROUND OF INVENTION
1) Field of the Invention
This invention relates generally to fabrication of a passivation layer composed of Silicon dioxide and oxynitride for a semiconductor device and more particularly to a process for forming a silicon dioxide-oxynitride continuity film that is part of a has three layers as a passivation film, inter metal dielectric or interlevel dielectric layer.
2) Description of the Prior Art
Once all the steps required to fabricate a working integrated circuit are completed, there still remains the important step of passivating the circuit, this is protecting it form possible contamination during its operating lifetime. Passivation layers are formed over metal lines to protect the metal lines and underlying semiconductor devices from moisture and other contaminants. It is known in the art to use two individually deposited layers for this purpose. One layer, such as silicon nitride and a second layer such as phosphosilicate glass (PSG) as a scavenger to neutralize contaminants already present.
However, current passivation layers formed of silicon nitride create too much stress on the metal lines and cause defects. Therefore, there is a need for a process to form a passivation layer that creates less stress and also has superior contamination and diffusion barrier properties.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 5,616,401 (Kobayashi) shows a oxynitride layer used as a oxidation mask for a field oxide process. U.S. Pat. No. 4,901,133 (Curran et al.) shows a Si rich SiON layer over a poly line.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for fabricating a passivation layer over metal lines that has a low stress and a good diffusion barrier and moisture barrier.
It is an object of the present invention to provide a method for a SOON passivation layer with a first portion near the bottom which has a composition close to silicon dioxide and a portion near the top that has a composition near silicon oxynitride.
It is an object of the present invention to provide a method for a SOON passivation layer with a first portion near the bottom which has a composition close to silicon dioxide and a portion near the top that has a composition near silicon oxynitride that reduces process steps.
To accomplish the above objectives, the present invention provides a method to forms a Silicon Oxide Oxynitride (SOON) passivation layer composed of three layers: {circle around (1)} a bottom silicon oxide layer
22
, {circle around (2)} an oxide/oxynitride transition layer and {circle around (3)} a top silicon oxynitride layer
26
. The SOON passivation film
20
is deposited with a PECVD system. The SOON passivation layer can be used as an interlevel dielectric (ILD) layer, a interlevel dielectric (IDL) or a top passivation layer.
The SOON passivation layer is formed with a first portion near the bottom which has a composition close to silicon dioxide and a portion near the top that has a composition near silicon oxynitride.
The invention's method of fabrication of the silicon oxide-oxynitride passivation film for a semiconductor device includes the following. A metal layer
14
is formed over a dielectric layer
12
over a semiconductor structure
10
.
A silicon oxide-oxynitride (SOON)passivation film
20
is formed composed of {circle around (1)} a silicon oxide layer
22
, {circle around (2)} an oxide/oxynitride transition layer and {circle around (3)} a (top) silicon oxynitride layer
26
.
The oxide/oxynitride transitional layer has compositional ratio between oxygen and nitrogen that varies in the thickness direction thereof is formed on a main surface of the substrate, on which the silicon oxide layer
22
is formed. The transition layer
24
is so controlled in composition that the film has a portion nearest the substrate which has a composition close to that of a silicon oxide film and that the film has a composition closer to that of a silicon oxynitride film towards the top silicon oxynitride layer
26
.
The transition layer preferably has a compositional ratio between nitrogen and oxygen that increases (preferably linearly) from the bottom surface to the top surface of the transition layer.
The substrate
10
is loaded into a plasma enhanced chemical vapor deposition chamber.
The passivation layer is formed by the following three steps.
STEP 1—The first step is performed for a first time period to form the silicon oxide layer
22
. The first step is preferably performed at the following conditions: using a PECVD process and flowing a gas source of silicon and a gas source of oxygen to form the silicon dioxide layer.
STEP 2—The second step is performed for a second time period to form the oxide/oxynitride transition layer
24
; at the following conditions: using a PECVD process and flowing a silicon gas source, an oxygen a gas source and a nitrogen gas source of where the nitrogen gas source flow rate is gradually increased during the second step. Preferably, initially, the nitrogen gas source flow is zero, during the step the ratio of Nitrogen source gas to Oxygen source gas is increased, and, at the end of the second step, the oxygen flow is equal or less than the nitrogen gas source flow.
STEP 3—The third step is performed for a third time period to form the oxynitride layer
26
at the following conditions: using a PECVD process and flowing a silicon gas source and an oxygen a gas source and a nitrogen gas source; so that the oxynitride layer (Si
x
O
y
N
z
) has a molar composition where the x, Y and z values vary with final gas flow ratios. Preferably the oxynitride layer has a composition of about Nitrogen 33% oxygen 33% and Si 33%.
The substrate is then removed from the plasma enhanced chemical vapor deposition (PECVD) reactor.
The invention has the following benefits. The silicon oxide portion near the bottom creates a low stress contact with a metal line. The top oxynitride portion near the top of the SOON passivation layer provides good scratch protection, moisture protection and a good diffusion barrier.
The inventors has found that the invention's 3 layer
22
24
26
provides significant advantages over other multi-layer structures that include a silicon nitride layer, Si-rich oxynitride layer or near silicon nitride layer or portion. These SiN portions create excess stress. The invention's SOON passivation layer
20
reduces stress while provide better barrier protection.
The present invention achieves these benefits in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.
REFERENCES:
patent: 4543707 (1985-10-01), Ito et al.
patent: 4901133 (1990-02-01), Curran et al.
patent: 5616401 (1997-04-01), Kobayashi et al.
patent: 5795833 (1999-08-01), Yu et al.
patent: 5946542 (1999-08-01), Iyer
Ackerman Stephen B.
Hoang Quoc
Nelms David
Saile George O.
Stoffel William J.
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