Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2000-11-16
2004-03-02
Pert, Evan (Department: 2827)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S773000, C257S763000
Reexamination Certificate
active
06700200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to reliable semiconductor via structures, and more particularly, the present invention relates to techniques for converting silicon dioxide layer regions within via hole walls into moisture repellant hydrophobic layer regions.
2. Description of the Related Art
In the fabrication of semiconductor devices, various layers are provided with conductive material, such as metal lines. The metal lines are commonly formed over successive insulating dielectric layers. Accordingly, it is generally necessary to electrically interconnect the metal lines between the dielectric layers. To accomplish this, vias (or via holes) are formed through the dielectric layers to electrically interconnect selected metal lines or features.
Spin on glass material (“SOG material”) is used for some of the dielectric layers. For example, so-called “true” SOG materials, such as that sold under the brand name “LSU 418,” which is available from Allied Signal, Inc. of Sunnyvale, Calif., is used because it has a low k characteristic (e.g., dielectric constant less than 4.0, which is common for silicon dioxide). Many “SOG-like” materials also have a low k characteristic. The SOG-like materials may, for example, be spin coated or result from vapor deposition using methyl silane and hydrogen peroxide chemistry. However, both the true SOG materials and the SOG-like materials oxidize during and after an operation known as ashing. Ashing is commonly performed to remove a photoresist layer that has been spin coated over the SOG material to facilitate patterning operations. Unfortunately, the oxidized SOG materials are known to absorb too much moisture from the atmosphere, in that during later operations (such as, for example, during metal deposition), the absorbed moisture outgasses causing poisoning of the vias. Such poisoning prevents adequate electrical connections from being made, e.g., between the opposite metal layers which are to be interconnected by way of the conductive material in the vias.
Unfortunately, prior art attempts to reduce the amount of the moisture retained by the oxidized SOG materials have not been successful. For example, if thermal outgassing is performed at a high enough temperatures to remove adequate amounts of the moisture (e.g., at about 700 degrees C.) from the oxidized SOG materials, significant problems result. These high outgassing temperatures are generally considered too excessive for the metal layers to withstand without causing damage (e.g., metal layers of aluminum may deform). Also, the SOG material is not stable at the high outgassing temperatures. If lower temperatures are used in an attempt to reduce the moisture retained by the oxidized SOG materials (e.g., at 400 to 450 degrees C. in a PVD chamber), although the metal lines may not be damaged by the temperature, not enough of the moisture is removed. The remaining moisture then outgasses during later attempts to deposit via coating/filling materials such as titanium nitride (TiN) and tungsten (W) metal layers (which are commonly used for the conductive vias), and such outgassing prevents proper continuous deposition of these metal layers in the internal via walls. For example, the outgassing moisture may prevent tungsten from being deposited on the walls of the via, and the TiN will tend to deposit discontinuously (e.g., in separate random groups), rather than in a complete conductive layer.
To facilitate this discussion,
FIG. 1A
shows a semiconductor structure including a substrate
101
supporting a first conductor
102
, such as a metal line, which is to be in contact with a second conductor
103
, such as a conductive layer of titanium nitride shown in FIG.
1
C. Deposited on the substrate
101
is a layer
104
of SOG material, which may include both true SOG materials, materials having a SOG-like characteristic, and other organic low-K dielectric materials. Accordingly, such characteristic includes having a low dielectric constant (K), and oxidizing during photoresist ashing to form a surface layer
106
of silicon dioxide. After deposition of a silicon dioxide layer
107
on the layer
104
of SOG material, a via hole
109
is formed through the silicon dioxide layer
107
and through the SOG material layer
104
to expose the metal
102
as shown in FIG.
1
A.
Between the etching operation and a subsequent deposition operation, a semiconductor structure
111
defined by the substrate
101
and the layers
102
,
104
, and
107
, is exposed to oxygen in the atmosphere. The oxygen thus causes the inner wall surface of the via hole
109
to oxidize and form the surface layer
106
. As described above, the surface layer
106
is very porous, is prone to collect moisture, and upon being heated, releases gaseous moisture.
The effect of the release of the moisture is shown in
FIG. 1C
, which depicts operations intended to deposit a layer
103
of titanium nitride under a layer
114
of tungsten. The purpose of the titanium nitride layer
103
is to electrically interconnect the first conductor
102
to the tungsten layer
114
. However,
FIG. 1C
shows arrows
116
depicting moisture being outgassed from the surface layer
106
during the deposition of the titanium nitride layer
103
. The outgassed moisture prevents the layer
103
of titanium nitride from being continuous, as illustrated by the spaced pieces
103
a
of titanium nitride. It may be understood, then, that the word “layer” in the phrase “layer
103
” denotes the desired form of the titanium nitride, whereas the actual form of the prior art titanium nitride layer is discontinuous as shown in FIG.
1
C. Because the pieces
103
a
are spaced, the desired electrical interconnection from the metal
102
to the tungsten
114
is not achieved.
Moreover, when an attempt is made to deposit the tungsten layer
114
after the titanium nitride pieces
103
a,
the tungsten layer
114
tends to stop short of filling the via, leaving a void
119
shown in
FIGS. 1C and 1D
. The void
119
is filled with neither titanium nitride nor tungsten, such that there is a high likelihood that there will be no electrical conductivity from the metal
102
to the tungsten layer
114
.
In view of the forgoing, there is an unfilled need for a reliable semiconductor via structure, and a method of making reliable via structures to prevent outgassing problems and associated via hole voids.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing improved semiconductor device via structures having an inner hydrophobic wall surface layer to prevent the aforementioned moisture absorption and subsequent outgassing. Such via structures are made using techniques for converting a silicon dioxide inner wall layer into the desirable hydrophobic layer, thus preventing the failure inducing voids in the via structures. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a method of making a via hole in a semiconductor structure is disclosed. The via hole has a surface layer of hydrophobic material, and includes an outer layer of a material having a characteristic of SOG materials. The characteristic is that the outer layer oxidizes during photoresist ashing to form a surface layer of silicon dioxide in the via hole. In the method, an operation is performed after the ashing. The operation includes performing a chemical dehydroxylation operation on the surface layer of silicon dioxide to convert the surface layer of silicon dioxide to the surface layer of hydrophobic material. To achieve this, the semiconductor structure is placed in a closed process chamber, and then, a halogen compound is admitted into the process chamber to facilitate the chemical dehydroxylation operation. In this embodiment, the halogen compound is selected from either NH
4
F, other gaseous combination includi
Cruz Lourdes
Koninklijke Philips Electronics , N.V.
Pert Evan
Zawilski Peter
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