Fabrication method of thin-film semiconductor device

Details Fabrication method of thin-film semiconductor device Fabrication method of thin-film semiconductor device

2001-06-08

2003-08-05

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Formation of semiconductive active region on any substrate

Amorphous semiconductor

C438S486000, C438S151000, C438S166000

Reexamination Certificate

active

06602765

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technology that improves the quality of crystalline semiconductor thin films formed on substrates and minimizes quality variations. In particular, the invention relates to a method for fabricating thin-film semiconductor devices using this technology, in which the performance of thin-film semiconductor devices, wherein a crystalline semiconductor film formed on a substrate is utilized as a semiconductor device channel formation region, is markedly improved, and also the quality of the semiconductor device components can be consistent.
2. Description of Related Art
Conventionally, a fabrication scheme such as that described below has been used when fabricating thin-film semiconductor devices such as polysilicon thin-film transistors (p-Si TFT) at low temperatures of approximately 600° C. or less, wherein general-purpose glass substrates can be used. First, an amorphous silicon layer serving as a semiconductor layer is deposited on the substrate to a thickness of approximately 50 nm by low-pressure chemical vapor deposition (LPCVD). This amorphous layer is then irradiated with a XeCl excimer laser (wavelength: 308 nm) to form a polysilicon film (p-Si film). Since the absorption coefficients of the XeCl excimer laser in the amorphous silicon and polysilicon are high (0.139 nm
−1
and 0.149 nm
−1
respectively), 90% of the laser light incident on the semiconductor film is absorbed at a depth of 15 nm or less from the surface. Next, a silicon oxide layer serving as a gate dielectric layer is formed by chemical vapor deposition (CVD) or by physical vapor deposition (PVD). Gate electrodes are then created using a material such as tantalum to form field effect transistors (MOSFET) consisting of a metal (gate), an oxide layer (gate dielectric layer) and a semiconductor (polysilicon layer). Finally, an interlevel dielectric layer is deposited on top of these layers and, after contact holes are opened, a thin-film of metal interconnects is patterned, completing the thin-film semiconductor device.
However, controlling the energy density of the excimer laser light used in the conventional method of fabricating these thin-film semiconductor devices was difficult, and even slight fluctuations in the energy density caused the semiconductor layer to exhibit significant non-uniformity, even within the same substrate. Moreover, if the irradiation energy density were even slightly higher than the threshold value determined by film thickness and hydrogen content, the semiconductor layer incurred extensive damage, inviting marked deterioration of semiconductor characteristics and product yield. Therefore, the energy density of the laser light had to be set considerably lower than the optimum value to obtain a uniform polycrystalline semiconductor layer. For this reason, obtaining high quality polycrystalline thin films meant that an insufficient energy density could not be avoided. Furthermore, enlarging the grains that comprise the polycrystalline layer was difficult even if the laser was radiated at the optimum energy density; and a large number of defects were left in the layer. Therefore, to consistently fabricate thin-film semiconductor devices such as p-Si TFTs using the conventional fabrication method, the electrical characteristics of the finished thin-film semiconductor devices had to be sacrificed.
Furthermore, in the conventional method of fabricating thin-film semiconductor devices, a problem is also acknowledged in that there is significant non-uniformity in the electrical characteristics of the finished thin-film semiconductor devices. Using conventional excimer laser light irradiation, the largest grain obtainable is approximately 1 &mgr;m. However, it is impossible to control the location of the grains and grain boundaries. Therefore, it is a random probability whether the channel formation region of a thin-film semiconductor device contains a grain boundary. The characteristics of a semiconductor device fluctuate considerably depending on whether the channel formation region contains a grain boundary. This is because if the number of grain boundaries that exist in the channel formation region is large, the electrical characteristics of the semiconductor device are poor, and if the number of grain boundaries that exist in the channel formation region is small, the electrical characteristics of the semiconductor device are comparatively good.
BRIEF SUMMARY OF THE INVENTION
The present invention takes into consideration the abovementioned situation, with the object of providing a method for consistently fabricating extremely high quality thin-film semiconductor devices by controlling the location of grain boundaries in the channel formation region.
Following an overview of the present invention, the fundamental principles of the present invention and its embodiments will be described in detail.
The present invention relates to a method of fabricating a thin-film semiconductor device wherein a semiconductor layer formed on a substrate is used as an active region (semiconductor device active region) of the semiconductor device. The semiconductor device active region designates, in a field effect transistor: a channel formation region, a junction region of the channel formation region and a source region, and a junction region of the channel formation region and a drain region. Alternatively, it designates, in a bipolar transistor: a base region, an emitter and base junction region, and a collector and base junction region. The present invention comprises: a heating system formation process for providing a local heating system on the substrate, which locally heats the semiconductor layer (active semiconductor layer) region that is to serve subsequently as the semiconductor device active region; an active semiconductor layer formation process for forming an active semiconductor layer after this heating system formation process; a crystallization process for melt crystallizing the active semiconductor layer in a condition wherein the active semiconductor layer is locally overheated by the local heating system; and an element separation process for processing the melt crystallized active semiconductor layer into an insular shape to form the semiconductor device active region.
In the present invention, based on the abovementioned construction, when the length of the finished semiconductor device active region is L (&mgr;m), the length L (&mgr;m) of the semiconductor device active region is made to be shorter than the length L
HS
(&mgr;m) of the local heating system (L<L
HS
) in the local heating system formation process or the element separation process. Furthermore, at this time the active semiconductor layer is processed or the local heating system is formed such that the semiconductor device active region is contained within the local heating system in the lengthwise direction. The length L
HS
(&mgr;m) of the local heating system is preferably approximately 7 &mgr;m or less (L
HS
<7 &mgr;m). In respect of the length of the semiconductor active region and the length of the local heating system, ideally the active semiconductor layer or the local heating system is processed such that the length of the semiconductor device active region L (&mgr;m) is approximately half the length L
HS
(&mgr;m) of the local heating system or less (L<L
HS
/2), and the active semiconductor layer is processed such that the semiconductor device active region is completely contained within the local heating system in the lengthwise direction, and does not include the central area in the lengthwise direction of the local heating system.
Furthermore, in the present invention, based on the abovementioned construction, when the width of the finished semiconductor device active region is W (&mgr;m), the width W (&mgr;m) of the semiconductor device active region is made to be shorter than the width W
HS
(&mgr;m) of the local heating system (W<W
HS
) in the heating system formation process or the element

Affiliated with

Also associated with

Rating

Fabrication method of thin-film semiconductor device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Fabrication method of thin-film semiconductor device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fabrication method of thin-film semiconductor device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3087638