Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Processing feature prior to imaging
Reexamination Certificate
2001-12-31
2004-12-14
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Processing feature prior to imaging
C430S311000, C430S313000, C430S314000, C430S317000, C430S328000, C430S330000, C438S694000
Reexamination Certificate
active
06830877
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method for forming via and contact holes in an insulating material layer situated on a semiconductor substrate and more particularly, relates to a method for forming via and contact holes in an insulating material layer on top of a semiconductor substrate with improved aspect ratios by using deep UV photoresist.
BACKGROUND OF THE INVENTION
In the manufacture of semiconductor devices, metal vias and contacts are formed in via openings and contact holes on semiconducting wafers that have been preprocessed. Semiconductor devices are thus fabricated by connecting the components with metal vias and contacts to form an integrated circuit. In particular, aluminum, aluminum alloys, tungsten and tungsten alloys are frequently used for depositing into via openings and contact holes on semiconducting substrate. The deposition processes can be carried out by a physical vapor deposition (or sputtering) technique or by a chemical vapor deposition technique.
As the dimensions of semiconductor devices are continuously being reduced in a miniaturization effort for matching devices on the sub-half-micron level, via openings and contact holes must also be made smaller. Consequently, the openings and holes to be filled have larger aspect ratios, i.e., the ratios between the depth of the opening or hole and the diameter.
Difficulties have been encountered in depositing a conductive metal into via openings and contact holes that have large aspect ratios by a conventional sputtering process. As the openings or holes become smaller and deeper, the bottom and sides of an opening or hole receive fewer deposited metal particles than the top surface of the device. The end result of such a phenomenon, sometimes called a shadowing effect, is that metal layers formed by the particles hang over the opening forming an overhang. The overhang closes before the opening is completely filled as the deposition process progresses and thus creating a void in the opening or hole.
One technique used to compensate for the shadowing effect of the sputtering process is to taper the sidewalls of the via openings or the contact holes. For instance, during the formation, by a dry etching or reactive ion etching process, the top of the opening is etched more than the bottom of the opening. The sidewalls of the opening therefore may have an angle as high as of 15° with the vertical axis parallel with the depth of the opening. The tapered via opening or contact hole eliminates significantly the under-fill or shadowing effect of the sputtering process, for instance, by aluminum particles. However, the tapered via or contact formed (after filled by aluminum and then etched back) has the drawback of popping out of the via opening or contact hole in a defect known as via delamination. The via delamination becomes a serious problem in a semiconductor device since the device after formation of the via or contact, may be subjected to various thermal cycling processes such as those encountered in various etching, passivation or planarization processes. The expansion or contraction of the metal via or contact caused by the thermal stress during cycling can easily delaminate the via or contact from its opening. When the via delamination defect occurs, the circuit in the semiconductor device fails and the yield of the wafer can be severely affected.
Another difficulty is encountered in forming via holes or contact openings at larger aspect ratios when deep UV photoresist is utilized in the photolithography process. Deep UV photoresist materials have been used in modern IC devices that have feature sizes below 0.4 &mgr;m. The deep UV photoresist material can normally be imaged in the 100~300 nm range, for instance, by using a krypton-fluoride (KrF) laser source at 248 nm wavelength, or an argon fluoride (ArF) laser source at 193 nm, or a fluorine (F
2
) at 157 nm. These laser emissions are of the excimer type which go through transitions from a meta-stable state to an unstable ground state. Photoresist materials have also been developed for exposure at such shorter wavelengths to achieve higher resolution. For instance, such deep UV photoresist includes PMMA, which is sensitive for wavelength at smaller than 250 nm and polybutane sulfone which is sensitive for wavelengths smaller than 200 nm. There are also chemically amplified photoresists which exhibit high photo-speed, excellent resolution and process tolerance. A deep UV photoresist material frequently contains a photo-acid-generator such that hydrogen ions are emitted when the photoresist layer is subjected to UV radiation and heating which accelerates the hydrogen ion generation process. The hydrogen ions generated then combine with the fluorine contained in the oxide forming HF for etching away the oxide layers.
FIG. 1
shows a conventional process for forming a via opening or a contact hole on a semiconductor substrate by using a deep UV photoresist layer. The semiconductor structure
10
is built on a pre-processed semi-conducting substrate
12
with a conducting layer
14
deposited on top. The conducting layer
14
may either be a conductive gate formed of CoSi
x
or TiSi
x
, etc. as a gate structure, or a conductive line such as one formed by Cu. An etch stop layer
16
which is generally formed of SiN, SiON or SiC is deposited on top of the conductive layer
14
as an etch-stop layer. After a thick oxide layer
18
such as an inter-level-dielectric (ILD) layer or an inter-metal-dielectric (IMD) layer and a deep UV photoresist layer
20
are sequentially deposited on top, the deep UV photoresist layer
20
is patterned, the oxide layer
18
is etched by a reactive ion etching (RIE) method to form the via opening or contact opening
30
.
During the RIE process, fluorine contained in the etchant and the carbon contained in the deep UV photoresist material react to form a fluorocarbon-type polymer
22
that will deposit at the bottom of the via opening
30
and thus stopping the via opening formation process. The problem is especially severe when larger aspect ratio holes, i.e., having an aspect ratio of larger than 8, is formed in modern IC devices that uses 0.18 &mgr;m technology. For instance, in the fabrication of a dual damascene device.
In the dual damascene via etch process, an etch stop layer formed of SiN, SiON or SiC is normally used. The etch recipe is divided in two steps of a main etch which stops on the liner or etch stop layer and a liner removal etch for etching through the liner in order to obtain good resistance and leakage performance. The main etch recipe most of the time uses a heavy polymer gas to realize oxide/liner etch selectivity and to stop the etching process on the liner. However, as the via openings and contact holes are getting smaller in the next generation product, i.e., in 0.18 &mgr;m devices, the heavy polymer gas forms a fluorocarbon polymer with the deep UV resist material to coat the bottom of the via openings or the contact holes. The fluorocarbon-based polymeric material coating slows down the hole etching process effectively to produce a hole of smaller aspect ratio. For instance,
FIG. 2
shows a conventional etching process utilizing a deep UV photoresist layer
20
in forming via openings
30
that have a length “L
1
” of about 455 nm. This is about 200 nm smaller than that desired of an ideal via opening.
It is therefore an object of the present invention to provide a method for forming via openings or contact holes that does not have the drawbacks or shortcomings of the conventional method.
It is another object of the present invention to provide a method for forming via openings or contact holes that have improved aspect ratios.
It is a further object of the present invention to provide a method for forming via openings or contact holes by using a deep UV photoresist material that does not produce polymeric coating on the bottom of the via opening or contact hole.
It is another further object of the present invention to provide a method for forming via openings or co
Chen Tsung-Chuan
Hsu Shew-Tsu
Ma Ching-Tien
Barreca Nicole
Huff Mark F.
Taiwan Semiconductor Manufacturing Co. Ltd.
Tung & Associates
LandOfFree
Method for forming via and contact holes with deep UV... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for forming via and contact holes with deep UV..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for forming via and contact holes with deep UV... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3293789