Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2002-05-06
2003-02-11
Chaudhari, Chandra (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S350000, C438S151000, C438S640000
Reexamination Certificate
active
06518596
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of semiconductor device fabrication and in particular the invention provides an improved device structure and method of forming metal contacts in thin film semiconductor devices.
BACKGROUND OF THE INVENTION
A major advantage of thin-film photovoltaic (PV) modules over conventional wafer-based modules is that series interconnection of the individual cells can be accomplished using a deposited metal film. It is known that particular metals make better contact with regions of one dopant type and in particular, aluminium which is commonly used as a metallisation layer makes good contact with n-type material, but can be unreliable when contacting to p-type material unless high temperatures are used.
However, cost is an important factor in thin film device manufacture and additional steps can add significantly to the cost particularly when they include an alignment step. Therefore, processes that avoid alignment steps, or are self aligning, provide significant advantages in low cost device fabrication.
SUMMARY OF THE INVENTION
According to a first aspect, the present invention provides a method of forming p-type and n-type contacts on a thin film semiconductor junction device having an underlying region of a first semiconductor type and an overlying region of a second semiconductor type including the steps of:
a) forming at least one dielectric layer over a free surface of the thin film device;
b) opening a first set of holes in the dielectric layer to expose the upper semiconductor region of the second semiconductor type in the locations where contacts are to be made to the second semiconductor type;
c) forming a first thin metal layer over the at least one dielectric layer and extending into the first set of openings to contact with the second semiconductor type, the first metal layer being formed of a metal selected to make reliable contact with the second semiconductor type;
d) opening a second set of holes through the first metal layer and the dielectric layer to expose a surface of the semiconductor;
e) doping the surface or surfaces of the semiconductor device exposed by the second set of holes in the dielectric layer with a dopant of the same polarity as the underlying region, the further doping extending to the underlying region and isolating the second set of holes from the upper semiconductor region;
f) forming a second thin metal layer over the first metal layer, the second metal layer extending into the openings in the at least one dielectric layer and contacting the surface or surfaces of the semiconductor material exposed by the second set of holes to thereby provide a connection to the underlying semiconductor region; and
g) for each cell in the device, forming an isolation groove through both metal layers to electrically isolate the contacts in the first set of openings from the contacts in the second set of openings.
The doping step, to dope the second set of openings may be either as a direct consequence of opening the second set of holes or as a subsequent process step. However, in the preferred embodiment, the doping of the surfaces of the second set of openings is performed as part of the opening step. Preferably, the opening created by the second opening step extends through the first metal layer, the one or more dielectric layers and through the semiconductor film to expose a supporting surface on which the semiconductor film is formed.
According to a second aspect, the present invention provides a method of forming p-type and n-type contacts on a thin film semiconductor junction device having an underlying region of a first semiconductor type and an overlying region of a second semiconductor type including the steps of:
a) forming at least one dielectric layer over a free surface of the thin film device;
b) opening a first set of holes through the at least one dielectric layer to expose a surface of the semiconductor in the locations where contacts are to be made to the underlying region of the first semiconductor type;
c) doping the surface or surfaces of the semiconductor device exposed by the first set of holes in the at least one dielectric layer with a dopant of the same polarity as the underlying region, the further doping extending to the underlying region and isolating the first set of holes from the upper semiconductor region;
d) forming a first thin metal layer over the at least one dielectric layer and extending into the first set of openings to contact with the first semiconductor type, the first metal layer being formed of a metal selected to make reliable contact with the first semiconductor type;
e) opening a second set of holes through the first metal layer and the at least one dielectric layer to expose the upper semiconductor region of the second semiconductor type in the locations where contacts are to be made to the second semiconductor type;
f) forming a second thin metal layer over the first metal layer, the second metal layer extending into the openings in the at least one dielectric layer and contacting the surface or surfaces of the semiconductor material exposed by the second set of holes to thereby provide a connection to the upper semiconductor region; and
g) for each cell in the device, forming an isolation groove through both metal layers to electrically isolate the contacts in the first set of openings from the contacts in the second set of openings.
The doping step, to dope the first set of openings may be either as a direct consequence of opening the first set of holes or as a subsequent process step. However, in the preferred embodiment, the doping of the surfaces of the first set of openings is performed as part of the opening step. Preferably, the opening created by the first opening step extends through the one or more dielectric layers and through the semiconductor film to expose a supporting surface on which the semiconductor film is formed.
According to a third aspect, the present invention provides a thin film semiconductor device comprising a thin semiconductor film formed on a transparent insulating substrate, the semiconductor film having at least an upper doped region of a first dopant type located adjacent an upper surface of the semiconductor film remote from the substrate, and an underlying doped region of a dopant type of opposite polarity to the first dopant type between the upper doped region and the substrate, at least one dielectric layer extending over the semiconductor film, a first thin layer of a first metal extending over the dielectric layer and a second thin layer of a second metal different to the first metal extending over and in contact with the first metal layer, a first set of openings being provided in the at least one dielectric layer such that the first metal layer contacts the semiconductor region of one dopant type to make electrical connection therewith in the first set of openings, and a second set of openings being provided in the at least one dielectric layer and the first metal layer such that the second metal layer extends into the second set of openings in the at least one dielectric layer and contacts a region of the semiconductor film, of the opposite dopant type, the first metal being selected to make reliable connection with the semiconductor material exposed by the first set of openings and the second metal being selected to make reliable connection with the semiconductor material exposed by the second set of openings.
In the preferred embodiment, the second set of openings extends completely through the semiconductor film to expose a supporting surface on which the semiconductor film is formed. These openings allow direct contact to the underlying semiconductor region. The preferred method of forming these openings also causes the walls of the openings to be simultaneously doped with the same dopant polarity as the underlying region to which contact is being made, thereby isolating the overlying, oppositely doped region from the surfaces of the openings. In a preferred method of forming the openings,
Chaudhari Chandra
Jordan and Hamburg LLP
Pacific Solar Pty Ltd.
LandOfFree
Formation of contacts on thin films does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Formation of contacts on thin films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Formation of contacts on thin films will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3143615