JPH04352355A - Manufacture of thin-film transistor - Google Patents

Abstract

PURPOSE:To form thin-film transistors having different channels on the same substrate by reducing the number of mask processes. CONSTITUTION:A first semiconductor layer 2 containing one-conductivity-type impurities and a second semiconductor layer 3 containing opposite-conductivity- type impurities are irradiated partially with a laser beam; they are crystallized; and channel parts 2a containing the one-conductivity-type impurities and channel parts 3a containing the opposite-conductivity-type impurities are formed respectively. Then, a third semiconductor layer containing opposite-conductivity-type impurities and a fourth semiconductor layer containing one-conductivity-type impurities are laminated sequentially. The third and fourth semiconductor layers on the channel parts 3a which are rich in the opposite-conductivity-type impurities are irradiated with a laser beam; a region which is rich in the one- conductivity-type impurities is formed. Thereby, a semiconductor junction part is formed. The channel parts containing the one-conductivity-type impurities form a semiconductor junction part together with the third semiconductor layer containing the opposite-conductivity-type impurities.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film transistor, and more particularly to a method for manufacturing a thin film transistor in which p-channel and n-channel thin film transistors are formed on the same substrate by irradiating laser light.

0002

2. Description of the Related Art Conventionally, there has been a laser beam crystallization method in which an amorphous semiconductor layer is irradiated with laser light to melt and solidify the amorphous semiconductor layer to form a single crystal. Various methods have been proposed for manufacturing three-dimensional ICs by applying this laser beam crystallization method, but when manufacturing three-dimensional ICs, the substrate is always limited to a bulk silicon substrate, and the area is large. In addition, when diffusing impurities into the semiconductor layer, it is done by ion implantation or thermal diffusion, so it may not be possible to diffuse impurity ions uniformly over a wide area, or a substrate that can withstand high temperature heating may not be possible. There are unavoidable technical problems such as having to use .

Therefore, as a method to solve such problems, for example, Japanese Patent Application Laid-Open No. 62-214668 uses an inexpensive glass substrate that can be made into a large area as the substrate 11, as shown in FIG. A SiO2 film 12 or the like is formed on a glass substrate, and boron 12a and phosphorus 12b, which serve as impurities for forming a channel region of a transistor, are partially implanted into a predetermined portion of the SiO2 film 12 using an ion implantation method. By depositing silicon thin films 13 and 19 on the SiO2 film 12 and heating the silicon thin film 13 by irradiating it with laser light, impurities in the SiO2 film 12 are diffused into the silicon thin films 13 and 19, each containing different impurities. It has also been proposed to form channel regions 15 and 19 to form reverse channel type thin film transistors 18 and 23 on the glass substrate 11. In addition, in FIG. 3, 14 and 20 are source/drain regions,
16 and 21 are gate insulating films, and 17 and 22 are gate electrodes.

However, in this conventional method for manufacturing thin film transistors, impurities that form the channel region of the transistor must be implanted into the SiO2 film 12 in advance by ion implantation or the like, and the manufacturing process is complicated and the equipment is large. There is still the problem of having to prepare things.

Furthermore, since impurities for n-type semiconductors and impurities for p-type semiconductors cannot be ion-implanted at the same time, separate mask patterns must be used when forming the n-type channel region and the p-type channel region. However, when forming source and drain regions containing different impurities on channels containing different impurities, two types of mask patterns had to be used, making the mask process complicated. .

The present invention has been devised in view of the problems of the conventional methods, and eliminates the use of complicated processes such as ion implantation and large-scale equipment, and reduces the number of mask processes. It is an object of the present invention to provide a method for manufacturing a thin film transistor in which p-channel and n-channel thin film transistors are formed on the same substrate.

[0007]

[Means for Solving the Problems] According to the present invention, there is provided a step of forming a first semiconductor layer containing an impurity of one conductivity type on a substrate, and partially irradiating the first semiconductor layer with a laser beam. forming a partially crystallized first crystallized region in a first semiconductor layer; and containing an opposite conductivity type impurity in a larger amount than the one conductivity type impurity on the first semiconductor layer. a step of forming a second semiconductor layer to form a second semiconductor layer;
forming a second crystallized region rich in opposite conductivity type impurities by partially irradiating the semiconductor layer with a laser beam to simultaneously heat, melt, and solidify the first and second semiconductor layers; , a first crystallized region and a second crystallized region are formed by removing the first and second semiconductor layers except for the first crystallized region and the second crystallized region. a step of forming an island-like portion, forming a third semiconductor layer containing an opposite conductivity type impurity so as to cover the island-like portion;
forming a semiconductor junction between a crystallized region of and a third semiconductor layer, and containing an impurity of one conductivity type in a larger amount than an impurity of opposite conductivity type in the third semiconductor layer on the third semiconductor layer. a step of forming a fourth semiconductor layer such that the third semiconductor layer and the fourth semiconductor layer are in ohmic contact; and a step of forming a fourth semiconductor layer on the second crystallized region. A step of forming a third crystallized region rich in impurities of one conductivity type by irradiating the layer with laser light and heating it, and forming a semiconductor junction between the second crystallized region and the third crystallized region. A method for manufacturing a thin film transistor is provided, which achieves the above object.

[0008]

[Operation] As described above, by partially irradiating the first semiconductor layer with laser light and crystallizing it, a channel portion containing impurities of one conductivity type is formed, and the first semiconductor layer and the second semiconductor layer are crystallized. By simultaneously irradiating the semiconductor layers with laser light and crystallizing them, a channel portion rich in opposite conductivity type impurities is formed without using a mask. Further, a semiconductor layer containing impurities of opposite conductivity type and a semiconductor layer containing impurities of one conductivity type are sequentially stacked on a channel portion containing impurities of one conductivity type and a channel portion rich in impurities of opposite conductivity type, A semiconductor junction is formed by irradiating the third and fourth semiconductor layers on the channel portion rich in opposite conductivity type impurities with laser light to form a region rich in one conductivity type impurity. Note that a third semiconductor layer containing impurities of another conductivity type is formed on the channel portion containing impurities of one conductivity type, and there is ohmic contact between the third and fourth semiconductor layers. A semiconductor junction is formed as it is without irradiating the laser beam and mixing the third semiconductor layer and the fourth semiconductor. In other words, amorphous silicon or microcrystalline silicon formed by the plasma CVD method contains 10% of semiconductor impurities.
If it contains 15 cm-3 or more, the pn junction does not exhibit rectification properties and exhibits good ohmic characteristics. Therefore, a semiconductor junction can be formed without using ion implantation or thermal diffusion, and the number of mask steps can be reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a process diagram for explaining a method for manufacturing a thin film transistor according to the present invention, and 1 is a substrate made of glass or the like.

A first semiconductor layer 2 is formed on the substrate 1. This first semiconductor layer 2 is made of, for example, amorphous silicon or polycrystalline silicon, and is made of, for example, plasma CVD.
It is formed to a thickness of approximately 500 to 10,000 Å using the D method or the like. This first semiconductor layer 2 has 1015 to 1020 pieces/c
It contains an impurity element for one-conductivity type semiconductor of about 3 m3 (see figure (a)). Note that a silicon oxide film (not shown) or the like may be formed on the substrate 1 if necessary, and the first semiconductor layer 2 may be formed on this silicon oxide film. By forming the silicon oxide film on the substrate 1 in this way, it is possible to prevent the first semiconductor layer 2 from being contaminated by impurities in the substrate 1 when irradiated with laser light, which will be described later. can.

The first semiconductor layer 2 is partially irradiated with a laser beam L1 to crystallize it, thereby forming a first crystallized region 2a. This laser beam L1 is 5×10
A continuous wave argon laser with an output of about 6 W/cm3 and a beam diameter of about 40 μm is preferably used (
(See figure (b)).

Next, a second semiconductor layer 3 containing an opposite conductivity type impurity is formed on the first semiconductor layer 2. This second semiconductor layer 3 is made of, for example, amorphous silicon or polycrystalline silicon, and is formed to a thickness of approximately 500 to 10,000 Å by, for example, plasma CVD. This second
The semiconductor layer 3 contains about 1016 to 1021 impurities/cm 3 , which is higher than the impurity content of the first semiconductor layer 2 (see FIG. 3(c)).

Next, the first semiconductor layer 2 and the second semiconductor layer 3 are partially irradiated with a laser beam L2 to heat and melt, solidify and crystallize, thereby forming a second crystallized region 3a. (see figure (d)). The portion irradiated with the laser beam L2 exhibits an opposite conductivity type. That is, when the semiconductor layer is heated, the impurities in the first and second semiconductor layers are mixed together, and the semiconductor layers exhibit opposite conductivity types with a high content of impurities.

In this manner, the first semiconductor layer 2 is partially single-crystalized to form the first crystallized region 2a containing impurities of one conductivity type, and the first and second semiconductor layers are partially monocrystalized. By crystallizing the second crystallized region 3a rich in impurities of opposite conductivity type, the semiconductor crystallized region 2a exhibiting one conductivity type and the semiconductor crystallized region exhibiting the opposite conductivity type are formed on the same substrate 1. 3a will be formed in large numbers.

The portions of the semiconductor layers 2 and 3 other than the crystallized regions 2a and 3a are removed by etching with a fluoro-nitric acid solution to form a large number of island-like portions made up of the crystallized regions 2a and 3a. Form. That is, the etching selectivity ratio between the amorphous semiconductor film and the crystallized regions 2a and 3a is more than one digit, and the crystallized regions 2a and 3a are difficult to be etched, so the crystallized regions 2a and 3a are Only 3a remains. The remaining regions 2a and 3a become the channel portion of the thin film transistor.

Next, as shown in FIG. 2, a third semiconductor film 4 is formed on the island-shaped portions 2a, 3a of the semiconductor layer. This third semiconductor film 4 is made of, for example, amorphous silicon or microcrystalline silicon, and is formed to have a thickness of approximately 500 to 10,000 Å by, for example, plasma CVD. This third semiconductor film 4 contains 1016 to 1020 pieces/
Contains about cm3 of opposite conductivity type impurities.

A fourth semiconductor layer 5 is formed on the third semiconductor layer 4. This fourth semiconductor layer 5 is also made of, for example, amorphous silicon or microcrystalline silicon, and is formed to a thickness of about 500 to 10,000 Å by, for example, plasma CVD method. This fourth semiconductor layer 5 has a content of 1017 impurities that is higher than that contained in the third semiconductor layer 4.
It contains about 1021 impurities/cm3 of one conductivity type (see figure (a)).

Next, the third and fourth semiconductor layers 4 and 5 on the island portion 3a exhibiting opposite conductivity types are irradiated with laser light L3 and heated. In this case, the third semiconductor layer 4 and the fourth semiconductor layer 5 are heated and harmoniously integrated, and the heated region exhibits one conductivity type. This is because the impurity content in the fourth semiconductor layer 5 is greater than the impurity content in the third semiconductor layer 4 (see FIG. 4B).

The third and fourth semiconductor layers 4 and 5 at the substantially central and peripheral portions of the island-shaped portions 2a and 3a are etched using, for example, a fluoro-nitric acid solution. The portions remaining after etching become the source and drain regions of the thin film transistor.

By forming as described above, the channel portion 2a formed by crystallizing only the first semiconductor layer 2 containing impurities of one conductivity type becomes the third semiconductor layer containing impurities of the opposite conductivity type.
A semiconductor junction can be formed with the semiconductor layer 4 . Note that since good ohmic contact can be obtained between the amorphous semiconductor layer containing impurities of one conductivity type and the amorphous semiconductor layer containing impurities of opposite conductivity type, a fourth semiconductor layer is formed on the third semiconductor layer 4. There is no problem even if there is layer 5. Further, the channel portion 3a rich in opposite conductivity type impurities formed by harmoniously integrating the first and second semiconductor layers is the third and fourth semiconductor layer.
A semiconductor junction can be formed with a semiconductor layer 5a rich in one conductivity type impurity formed by harmoniously integrating the semiconductor layers 4 and 5.

An insulating film made of silicon oxide or silicon nitride, which will serve as a gate insulating film and an interlayer insulating film, is formed on the region having the semiconductor junction thus formed, and the source region and drain region of this insulating film are By removing a portion of the region, depositing aluminum or the like, and etching the portion, a gate electrode, a source electrode, and a drain electrode are formed to complete a thin film transistor.

[0022]

As described above, according to the method for manufacturing a thin film transistor according to the present invention, two semiconductor layers having different types and contents of impurities are partially irradiated with laser light to form a semiconductor junction. Because of this, p-channel and n-channel thin film transistors can be formed on the same substrate without using a large device such as an ion implantation device and with significantly fewer mask steps.

[Brief explanation of drawings]

FIG. 1 is a process diagram for explaining a method for manufacturing a thin film transistor according to the present invention, and is a diagram for explaining a method for manufacturing a channel portion.

FIG. 2 is a diagram for explaining a method of manufacturing a source region and a drain region.

FIG. 3 is a diagram for explaining a conventional thin film transistor manufacturing method.

[Explanation of symbols]

1. Board 2. First semiconductor layer 2a, first crystallized region 3. Second semiconductor layer 3a, second crystallization region 4. Third semiconductor layer 5. Fourth semiconductor layer 5a, third crystallization region

Claims (1)

[Claims] 1. A step of forming a first semiconductor layer containing impurities of one conductivity type on a substrate; a step of forming a first crystallized region that is crystallized according to the method; and a step of forming a second semiconductor layer containing an opposite conductivity type impurity in a larger amount than the one conductivity type impurity on the first semiconductor layer. A second semiconductor layer rich in opposite conductivity type impurities is formed by partially irradiating the first and second semiconductor layers with a laser beam to simultaneously heat and melt the first and second semiconductor layers and solidify them. The first crystallized region and the second crystallized region are formed by forming a crystallized region and removing the first and second semiconductor layers except for the first crystallized region and the second crystallized region. a step of forming an island-like part composed of a crystallized region, and forming a third semiconductor layer containing an opposite conductivity type impurity so as to cover the island-like part; forming a semiconductor junction with a semiconductor layer; and forming a fourth semiconductor layer on the third semiconductor layer containing one conductivity type impurity in a larger amount than the opposite conductivity type impurity in the third semiconductor layer. form,
a step of forming a third semiconductor layer and a fourth semiconductor layer so that they are in ohmic contact; and irradiating the third and fourth semiconductor layers on the second crystallized region with laser light to heat them. A method for manufacturing a thin film transistor, comprising the steps of forming a third crystallized region enriched with impurities of one conductivity type, and forming a semiconductor junction between the second crystallized region and the third crystallized region.