JPH0737808A - Manufacture of polycrystalline semiconductor film - Google Patents

Abstract

PURPOSE:To enhance the crystallizability of a thin polycrystalline silicon film formed by CVD process. CONSTITUTION:A silicon film 2 formed on an insulating substrate 1 is reformed by laser annealing and then a polysilicon film 3 is further formed by a CVD process on this silicon film 2. Through these procedures, a polycrystalline silicon film having excellent crystallizability can be formed even on a thin film.

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 polycrystalline semiconductor film.

[0002]

2. Description of the Related Art A technique for depositing polycrystalline silicon on an insulating substrate such as glass or quartz is a driving circuit in which a high-definition liquid crystal display (hereinafter referred to as TFT-LCD) and a peripheral driving circuit are formed on the same substrate. Currently, research and development are being actively conducted for the purpose of manufacturing an integrated TFT-LCD.

Generally, in a thin film transistor using polycrystalline silicon (hereinafter referred to as a TFT), the thickness of polycrystalline silicon, which is an active layer, is set to 50 nm or less in order to reduce the leak current at the time of OFF.

However, with a polycrystalline silicon film formed by the CVD method, the polycrystalline silicon formed in the initial stage of growth has poor crystallinity, and a polycrystalline silicon film with good crystallinity can be obtained unless the film is thickened. Difficult, so T
There is a problem in that a thin polycrystalline silicon film having a thickness of 50 nm or less having sufficient characteristics cannot be formed as an active layer of FT.

[0005]

In the conventional method for manufacturing a polycrystalline silicon film, the polycrystalline silicon film formed in the initial stage of growth has poor crystallinity, and the TFT must be thickened unless the film is thickened.
However, there is a problem in that it is not possible to obtain a polycrystalline silicon film having good crystallinity enough to have sufficient characteristics as the active layer.

The present invention has been made in view of the above circumstances, and an object thereof is to realize a polycrystalline semiconductor having a thin film thickness of 50 nm or less, which is a polycrystalline semiconductor having sufficient characteristics as an active layer of a TFT. It is to provide a method for manufacturing a semiconductor film.

[0007]

The present invention relates to a method for producing a polycrystalline semiconductor film, which comprises forming a polycrystalline semiconductor film on an insulating substrate by vapor phase epitaxy, wherein a first semiconductor film is vapor-deposited on the insulating substrate. After the growth, the step of heating the first semiconductor film at least at a temperature lower than the melting temperature by a beam annealing method, and the step of vapor-phase growing the second semiconductor film on the first semiconductor film are provided. A method for manufacturing a polycrystalline semiconductor film is provided.

Here, the first semiconductor is not heated until it is melted, but is heated to near the melting temperature and at least the surface of the first semiconductor layer has a low hydrogen content (preferably a hydrogen concentration of 1 × 10 ^15). ˜1 × 10 ¹⁹ atom / cm ³ ).

Particularly, it is preferable that the thickness of the first semiconductor film to be heated by the beam annealing method is 50 to 10 nm or less in order to form the polycrystalline semiconductor laminated film with good crystallinity.

[0010]

When the polycrystalline semiconductor film is formed on the insulating substrate by the vapor deposition method, the crystallinity of the initial growth film in the vicinity of the substrate interface generally deteriorates because the insulating substrate is amorphous.

On the other hand, according to the present invention, since the surface of the semiconductor film is heated by the beam annealing method and then the vapor phase growth film is formed on the surface, the laminated film of these two semiconductor films can be used as a substrate even if it is thin. The surface on the opposite side becomes a polycrystalline film having a good crystallinity or a semiconductor film having a characteristic close to that of a polycrystalline film and having sufficient characteristics to become an active layer of a TFT. This is because the surface state of the first semiconductor film heated by the beam annealing method is modified to have better crystallinity as a base for crystal growth as compared with the surface of the glass substrate or the insulating film.

[0012]

The details of the present invention will be described below with reference to the illustrated embodiments. 1 is a sectional view of a polycrystalline silicon film according to a first embodiment of the present invention. This will be described according to the forming process. First, an amorphous silicon film 2 is formed on the insulating substrate 1 made of a glass substrate by the plasma CVD method to a thickness of about 1 μm.
0 nm is formed. The forming conditions at this time are SiH4: 20
sccm, H2: 80 sccm, 0.5 Torr, substrate temperature 400 ° C
(Fig. 1 (a)).

Next, the amorphous silicon film 2 is modified by irradiating the amorphous silicon film 2 with a laser by a laser annealing method using an excimer laser. The annealing conditions at this time are room temperature, vacuum (1 × 10 −6 Torr or less), irradiation energy: 100 mW / cm ² , irradiation time 14 to 18 n
s. Here, it is not for heating the first semiconductor until melting, but for heating the surface of the first semiconductor to near the melting temperature to modify the surface. The amorphous silicon film 2 is preferably heated to 500 ° C. to the melting point (FIG. 1 (b)).

On the further modified amorphous silicon film 2, SiH4 + SiF4 or SiH is used as a source gas.
By the plasma CVD method using 4 + SiF4 + H2,
A polycrystalline silicon film 3 having a thickness of about 40 nm was formed. The plasma CVD method of the polycrystalline silicon film 3 will be described in more detail. For example, using a parallel plate plasma CVD apparatus,
Substrate temperature: 400 ° C, SiH4: 2s as source gas
ccm, SiF4: 98 sccm, H2: 50 sccm
Was introduced at a pressure of 1 Torr and discharged at an RF power of 200 W to form a polycrystalline silicon film 3. Before forming the polycrystalline silicon film 3, H2 plasma or Si is used.
Interfacial treatment with F4 plasma may be performed (Fig. 1
(C)).

The polycrystalline silicon film formed by such a manufacturing method was evaluated by cross-sectional TEM even though the total film thickness was as thin as about 50 nm.
A clear peak corresponding to Si (220) was observed from the interface of the layers, and it was found that a polycrystalline silicon film with good crystallinity could be formed. For comparison, a 50 nm polycrystalline silicon film formed at one time by the plasma CVD method was evaluated by a cross-sectional TEM. As a result, it was found that only small crystal grains (fine crystal grains) were present, and polycrystalline silicon with good crystallinity was obtained. It was found that the film could not be formed.

FIG. 2 is a sectional view of a polycrystalline silicon TFT according to the second embodiment of the present invention. This will be described below according to the manufacturing process. First, an undercoat layer 4 made of a SiO2 film is formed on an insulating substrate 1 made of a glass substrate, and then an amorphous silicon film 2 and a polycrystalline silicon film 3 having a thickness of 10 nm and 4 respectively are formed by the same method as in the first embodiment.
0 nm is formed (FIG. 2A).

Next, after patterning the silicon films 2 and 3 into islands, the gate insulating film 5 made of a SiO2 film is subjected to EC.
It is formed by the R plasma CVD method (FIG. 2B). Next, after forming the gate electrode 6 made of a refractory metal such as Mo or Ta or doped polycrystalline silicon, and patterning it, a dopant such as P or B is implanted by an ion doping method, and a dopant is added by an excimer laser annealing method. It is activated and the source / drain regions 7 are formed (FIG. 2C).

Finally, the interlayer insulating film 8 made of SiO2 film
After forming a source / drain contact hole, a source / drain electrode 9 made of Al was formed by sputtering and patterned to complete a polycrystalline silicon TFT (FIG. 2D).

The polycrystalline silicon TFT formed by such a manufacturing method had good characteristics such as an ON / OFF ratio of 10 ⁵ or more and a field effect mobility of about 50 cm ² / V · sec. For comparison, a polycrystalline silicon film having a total film thickness of the above-described polycrystalline silicon films 2 and 3 was formed in the same manner as in the second embodiment except that vapor phase growth was continuously performed and excimer laser annealing was performed. As a result of evaluating the TFT, ON /
OFF ratio: 10 ⁵ , field effect mobility: 5 cm ² / V · s
ec, and good characteristics could not be obtained.

The present invention may be variously modified within the scope of the spirit thereof as follows. (1) Although silicon is used for the first and second semiconductor layers, other semiconductors such as C, SiC, and Ge can be similarly formed. (2) The plasma CVD method was used as the vapor phase growth method.
Other methods, for example, ECR plasma CVD method may be used. (3) The beam annealing method uses a laser beam, but other energy beams such as an electron beam may be used. (4) The present invention can be applied to devices other than TFTs, for example, a diode having a PN junction in a polycrystalline semiconductor layer.

[0021]

As described above, according to the method for producing a polycrystalline silicon film of the present invention, a polycrystalline silicon film having a good crystallinity that can be used as an active layer of a TFT can be obtained even with a thin film. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view of a polycrystalline silicon thin film according to a first embodiment of the present invention in process order.

2A to 2D are cross-sectional views in the order of steps of a TFT according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 2 ... Silicon film (amorphous silicon film) 3 ... Polycrystalline silicon film 4 ... Undercoat layer 5 ... Gate insulating film 6 ... Gate electrode 7 ... Source / drain region 8 ... Interlayer insulating film 9 ... Source / drain electrode

Claims (1)

[Claims] 1. A method of manufacturing a polycrystalline semiconductor film, which comprises forming a polycrystalline semiconductor film on an insulating substrate by a vapor phase growth method, comprising: forming a first semiconductor film on the insulating substrate by vapor phase growth;
A step of heating at least the surface of the semiconductor film to a temperature lower than the melting temperature by a beam annealing method to modify it into a low hydrogen layer, and a step of vapor-depositing a second semiconductor film on the first semiconductor film. A method for manufacturing a polycrystalline semiconductor film, comprising: