Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – By application of corpuscular or electromagnetic radiation
Reexamination Certificate
2002-10-23
2004-09-21
Zarabian, Amir (Department: 2822)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
By application of corpuscular or electromagnetic radiation
C438S513000, C438S914000, C438S923000
Reexamination Certificate
active
06794277
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of doping a semiconductor layer, a method of manufacturing a thin film semiconductor device, and a thin film semiconductor device, and more particularly, a doping method using a crystallized semiconductor layer by excimer laser anneal, a method of manufacturing a thin film semiconductor device such as a thin film transistor, a thin film semiconductor device in which a semiconductor layer made of a material such as polycrystalline silicon is used as a channel.
BACKGROUND OF THE INVENTION
With progress of an advanced information age, the importance of input/output devices is increasing rapidly and the devices are in demand to include advanced and sophisticated features. Furthermore, the spread of personal digital assistant machines is remarkable in recent years, and consequently, the technology of producing TFT on a plastic substrate with more excellent weight saving, flexibility, and nondestructive evaluation rather compared with the conventional glass substrates is desired. In such a situation, research and development of active matrix liquid-crystal-display devices (AM-LCD) using a thin film transistor (TFT) and contact type image sensors (CIS) and the like are actively done.
The thin film transistors, in which a semiconductor film made of silicon is used as a channel, can be classified by a material used in order to construct a carrier-transporting layer (active layer), that is, a semiconductor film made of amorphous silicon (a-Si) and a semiconductor film made of polycrystalline silicon having a crystal phase. Polysilicon (poly-Si) or microcrystal silicon (&mgr;c-Si) is mainly known as the polycrystalline silicon.
Semiconductors made of the polycrystalline silicon such as polysilicon (poly-Si) or microcrystal silicon (&mgr;c-Si) are characterized by the carrier mobility from about 10 to 100 times as high as that of semiconductors made of amorphous silicon, and have very excellent features as a composition material of switching elements. Moreover, the thin film transistors using the polycrystalline silicon for the active layer allow high-speed operation, and therefore are getting most of the attention as the switching elements constituting various logical circuits (for example, a domino logic circuit, a CMOS (Complementary Metal Oxide Semiconductor) transmission gate circuit), multiplexers using these circuits, EPROM (Erasable and Programmable Read Only Memory), EEPROM (Electrically Erasable and Programmable Read Only Memory), CCD (Charge Coupled Device), RAM (Random Access Memory), drive circuits of displays such as a liquid crystal display and an electroluminescent display, and the like in recent years. Moreover, in recent years, remarkable are active matrix type liquid crystal displays employing the thin film transistor (TFT), using such polysilicon for a channel semiconductor film, as the switching element and as a surrounding drive circuit. This is because the constitution of a thin film transistor array, making use of a polysilicon semiconductor film which can be formed at low temperature on a cheap amorphous glass substrate, may allow to implement reflected type panel displays or wide, high-finesse, high-definition, cheap panel displays (for example, a flat type television).
On the other hand, when using poly-Si TFT in switching elements for pixel selection of the liquid crystal display or the like, the OFF state current is high and display quality is low, which is a problem. In MOS transistors using single crystal silicon so far, in a gate reverse bias, a leakage current does not increase, since the channel became in opposite polarity with a source or a drain, a depletion layer is formed and enough pressure-proofing and rectification property can be shown. However, with the poly-Si TFT, a problem arises that a high leakage current occurs since electric current flows through the grain boundary of crystalline particles composing the semiconductor film or through the defect of the particles themselves. Furthermore, since the MOS transistors are not used under very high gate reverse bias, the leakage current has not become a problem. However, in the poly-Si TFT, for example used for the active matrix type liquid crystal displays, the leakage current poses a big problem since it is used under the reverse bias of about 10 V or more. Such a problem is especially important when the poly-Si is used for the thin film transistor for pixel selection of the liquid crystal displays.
In order to reduce the leakage current, it is effective to relax the electric field in the drain edge, and it has been known that LDD (Lightly Doped Drain) structure is effective (General Conference of The Institute of Electronics and Communication Engineers, 2-20, pp. 271, 1978). The structure forms the region which activated the impurities under a low dose such as 1×10
14
/cm
2
or less in the edge part of the drain region, and relaxes the electric field in the edge part of the drain region.
The thin film transistor having the LDD structure is formed, for example, by the following processes so far. First, as shown in
FIGS. 5A
to
5
C, an amorphous silicon containing hydrogen (a-Si:H) film is formed on a glass substrate
101
, and dehydrogenation is performed by the lamp anneal. Then, a polysilicon (poly-Si) semiconductor film
102
is formed by crystallizing the amorphous silicon film using laser irradiation. Then, a gate insulating film
103
and a gate electrode
104
are formed, and heavy doping of impurity ions is performed by using the gate electrode
104
as a mask (FIG.
5
A), where the gate electrode
104
has already been patterned to cover a channel region and an LDD region. Subsequently, the gate electrode
104
is again patterned to cover only the channel region. And light doping of impurity ions is performed by using the re-patterned gate electrode
104
as a mask. Consequently, source drain regions
105
a
and
105
a
are formed to have the LDD structure with low concentration impurities regions
105
b
and
105
b
formed on the sides of the channel region. Then, an interlayer insulating film
106
, contact holes
106
a
, and wiring layers
107
are formed, and the wiring layers
107
are connected to the source drain regions
105
a
and
105
a
through the contact holes
106
a
. More particularly, such processes have been disclosed in Japanese Unexamined Patent Application No. 2000-228526.
When forming the thin film transistor having the LDD structure by such a method, there is a problem of the difference or the variation in lengths of the LDDs on both sides of the channel region (thicknesses of the LDD regions between the channel region and contact regions) due to deviation of the mask during patterning of the gate electrode
104
, and the like. This causes other problems that the properties of the thin film transistor vary and the productivity of the thin film transistor decrease. Moreover, the LDD lengths should not be set to about 2 &mgr;m or less in order to secure a mask alignment margin. For this reason, the resistance of the low concentration impurities regions
105
b
and
105
b
performing as the LDD regions becomes high, and the carrier mobility decreases, which is a problem. Therefore, in a self-alignment type process where the controllability of the LDD lengths is good, it is important to develop a certain process where the controllability is enough at a low dose such as 1×10
14
/cm
2
or less.
By the way, as for the poly-Si TFT, the highest process temperature reaches about 1000° C. in the manufacturing process. Therefore, silica glasses or the like having an excellent heat-resistant property are used as an insulating substrate for the poly-Si TFT manufacturing. That is, it can be difficult in the manufacturing process to use a glass substrate with a comparatively low melting point. However, for a cost reduction of the liquid crystal displays, the use of the glass plate materials with a low melting point is indispensable. Then, in recent years, the development of the so-called low temperature process
Gosain Dharam Pal
Machida Akio
Usui Setsuo
Perkins Pamela E
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
Zarabian Amir
LandOfFree
Method of doping semiconductor layer, method of... 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 of doping semiconductor layer, method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of doping semiconductor layer, method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3218640