JPH05299656A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To use a glass substrate as an insulating substrate by oxidizing a semiconductor layer by irradiating it with an oxide plasma due to resonance of an electron cyclotron, and forming a silicon oxide layer on a boundary between a silicon oxide film formed by depositing and the semiconductor layer. CONSTITUTION:Amorphous silicon is deposited on a glass substrate 1 to form a polysilicon film, which is insularly patterned to form a semiconductor layer 2. Then, a silicon oxide film 31 is deposited on the layer 2 by a chemical vapor growing method, then the film 31 is irradiated with oxide plasma due to resonance of an electron cyclotron, a semiconductor part of a boundary between the silicon oxide film and the semiconductor layer is oxydized to form a stoichiometric silicon oxide layer 32. Then, a polysilicon film is formed, patterned to form a gate electrode 4, and with the electrode 4 as a mask a source region 2b and a drain region 2c are formed on the layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, for example, a method of manufacturing a thin film transistor used in a drive circuit of a liquid crystal display or a contact image sensor.

[0002]

2. Description of the Related Art Conventionally, a thin film transistor (TFT) having a thin film laminated structure has been used as a switching element of a drive circuit of an active type liquid crystal display or a matrix drive type contact image sensor. For example, as shown in FIG. 2, the thin film transistor is formed by patterning a semiconductor film deposited on an insulating substrate 11 to form an island-shaped semiconductor layer 12, and on the semiconductor layer 12, the gate insulating film 13 and the island-shaped semiconductor layer 12 are formed. The active layer region 1 is formed by forming the gate electrode 14 and using the semiconductor layer 12 located below the gate electrode 14 as an active layer region 12a which becomes a channel of the transistor, and performing ion implantation using the gate electrode 14 as a mask.
Source region 12b and drain region 1 so as to sandwich 2a
2c to form the source region 12b and the drain region 12
Reference numeral c is a field effect transistor which is connected to the wiring electrodes 17 through a contact hole 16 formed in the gate insulating film 13 and the interlayer insulating film 15. Amorphous silicon (a-Si) or polycrystalline silicon (Poly-Si) is used as the active layer of the thin film transistor, but when a drive circuit is integrated, it is formed of a polycrystalline silicon film having a high operating speed. There is a need.

The gate insulating film 13 is formed by growing a thermal oxide film on the surface of the semiconductor layer 12 by thermal oxidation in an oxygen atmosphere at about 1000.degree. Therefore, since the processing temperature is high, a glass substrate cannot be used as the insulating substrate 11, and an insulating substrate made of fused silica is used, which causes a cost increase of the thin film transistor.

In order to use an inexpensive glass substrate, the strain point temperature is around 600 ° C., so that at least 600
In consideration of heat shrinkage, the manufacturing process must be performed at a lower temperature below ℃ (“OPTRONICS”, 1991, No.
8, P53 ~ P56).

Techniques for forming the gate insulating film 13 at a low temperature include a low pressure CVD method, a normal pressure CVD method, and a plasma CV.
There is a method of depositing the gate insulating film 13 on the semiconductor layer 12 by a chemical vapor deposition method such as the D method.

[0007]

However, when the gate insulating film 13 is deposited by each of the above-mentioned CVD methods, the defect level increases at the interface between the gate insulating film 13 and the semiconductor layer 12, There is a problem that the interface characteristics are deteriorated as compared with the above-mentioned thermal oxide film, and sufficient transistor characteristics cannot be obtained as a thin film transistor. Therefore, a method of performing a heat treatment in a nitrogen atmosphere at about 600 ° C. after forming a gate insulating film by each of the above-mentioned CVD methods, or an active layer in a nitrogen atmosphere at about 600 ° C. before forming a gate insulating film. A method of forming a gate insulating film by the CVD method after slightly oxidizing the surface of a semiconductor layer (polycrystalline silicon film) to be a region has been proposed, but it was not sufficient to improve the transistor characteristics. .. Also, 6
Since the heat treatment process at about 00 ° C. causes the glass substrate to be thermally shrunk, it is not appropriate to perform the above treatment on the thin film transistor formed on the glass substrate.

Further, there has been proposed a method (plasma oxidation method) of oxidizing the surface of a semiconductor layer formed of polycrystalline silicon at a low temperature by RS plasma by glow discharge (for example, J. Elec. Soc. 110 ( 1963) 1240). But,
This method has the drawbacks that (1) the film formation rate is slow, (2) the semiconductor layer is damaged by plasma, and (3) the process control is difficult, and there is a problem in practical use.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of manufacturing a semiconductor device capable of forming a thin film transistor having excellent transistor characteristics on a glass substrate and preventing deterioration of the glass substrate.

[0010]

The method of the present invention is characterized by including the following steps in a method of manufacturing a semiconductor device. As the first step, a semiconductor layer mainly containing silicon is formed on an insulating substrate. As the second step, a silicon oxide film is deposited on the semiconductor layer by chemical vapor deposition. As a third step, a stoichiometric oxidation is performed by irradiating an oxidation plasma by resonance of an electron cyclotron from above the first silicon oxide film to oxidize a semiconductor portion at an interface portion between the silicon oxide film and the semiconductor layer. Form a silicon layer.

[0011]

According to the present invention, the semiconductor layer is oxidized by irradiating the oxidation plasma due to the resonance of the electron cyclotron, and the silicon oxide layer is formed at the interface between the silicon oxide film formed by deposition and the semiconductor layer. The silicon oxide film and the silicon oxide layer can be formed at a low temperature, and even if a glass substrate is used as an insulating substrate, it does not deteriorate. Further, by interposing the silicon oxide layer between the semiconductor layer and the silicon oxide film, the interface characteristics can be improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method of manufacturing a semiconductor device according to the present invention will be described with reference to the drawings. Figure 1 (a)
1F is a cross-sectional explanatory diagram in each step of the method of manufacturing a thin film transistor to which the method of the present invention is applied. Amorphous silicon is deposited on the glass substrate 1 by LPCVD or plasma CVD to a film thickness of 300 to 1000 angstroms, and a solid phase growth method by low temperature annealing at 600 ° C. or lower or KrF excimer laser light (λ = 248n).
m) is irradiated at a density of 300 to 400 mJ / cm ² to form a polysilicon film by a laser crystallization method. Next, the polysilicon film is patterned into an island shape by photolithography and etching to form a semiconductor layer 2 (FIG. 1A).

Then, S at 430 ° C. by the LPCVD method.
An iO ₂ film is deposited, and a silicon oxide film 31 having a film thickness of 1000 angstrom is formed by a chemical vapor deposition method.
After that, the temperature of the glass substrate 1 is set to 500 ° C., and the oxidation plasma is irradiated by the resonance of the electron cyclotron.
That is, O ₂ excited by μ waves in a magnetic field is extracted by a divergent magnetic field, and the glass substrate 1 is irradiated for 2 to 4 hours. The irradiated active oxygen passes through the deposited silicon oxide film 31, acts as an oxidizing species at the interface between the silicon oxide film 31 and the semiconductor layer 2, and the polysilicon in the vicinity of the interface is oxidized. A silicon oxide film is grown, a silicon oxide layer 32 is formed on the silicon oxide film 31 side of the semiconductor layer 2, and a gate oxide film 3 composed of the silicon oxide film 31 and the silicon oxide layer 32 is formed (FIG. 1).
(B)). The irradiation of the oxidative plasma according to the present embodiment is performed by extracting O ₂ excited by μ waves in a magnetic field by a divergent magnetic field, so that the semiconductor layer 2 is not damaged and is most compositionally stable. It is easy to grow the stoichiometric silicon oxide film 32 in the bonded state.

Since the silicon oxide film 31 is formed by the chemical vapor deposition method, the etching rate for the 5% hydrofluoric acid solution is 50 angstroms / sec or more, while the silicon oxide layer is formed. Since the polysilicon film 32 is formed by oxidizing the polysilicon film by the active oxidizing species, it becomes a very dense film and reduces the defect level at the interface between the silicon oxide film 31 and the semiconductor layer 2, and
The etching rate is 20 angstroms / sec or less.

Next, a polysilicon film is formed by the LPCVD method, and the polysilicon film is patterned by the photolithography method to form the gate electrode 4 (FIG. 1).
(C)). Then, the silicon oxide film 31 and the silicon oxide film 32 are patterned using the gate electrode 4 as a mask (FIG. 1D).

Using the gate electrode 4 as a mask, the semiconductor layer 2 is doped with impurities by an ion shower method to form the source region 2b and the drain region 2c in the semiconductor layer 2 facing each other with the gate electrode interposed therebetween, and the substrate temperature 500.
The dopant introduced into the source region 2b and the drain region 2c is activated by performing a heat treatment at 2 ° C. for 2 hours. A portion of the semiconductor layer 2 between the source region 2b and the drain region 2c is an active region 2 that becomes a channel portion of the thin film transistor.
a is formed (FIG. 1E).

In the case of a thin film transistor using a polysilicon film, hydrogen is bonded to a silicon dangling bond (silicon dangling bond) at a grain boundary to inactivate it, and it is electrically neutralized so that trap density is increased. The hydrogenation treatment for reducing is performed in a hydrogen plasma atmosphere at a substrate temperature of 350 ° C. A silicon oxide film is deposited by the PECVD method to form an interlayer insulating film 5. Then, contact holes 6 are formed in the interlayer insulating film 5 located on the source region 2b and the drain region 2c, and a metal film such as aluminum is deposited and patterned to form a wiring electrode 7 (FIG. 1).
(F)).

According to the manufacturing method of the above-described embodiment, the thin film laminating process can be performed at a low temperature of 500 ° C. or less, so that the glass substrate 1 can be prevented from being deteriorated by heat. Further, according to the thin film transistor of the above manufacturing method, the semiconductor layer 2 is oxidized by irradiating the oxidation plasma due to the resonance of the electron cyclotron, and the silicon oxide layer is formed at the interface between the silicon oxide film 31 formed by deposition and the semiconductor layer 2. Since 32 is grown and formed, even when the silicon oxide film 31 is formed by the chemical vapor deposition method, the interfacial characteristics are improved by interposing the silicon oxide layer 32. By reducing the mobility, the transistor characteristics such as mobility and threshold voltage can be improved. Further, the etching rate of the silicon oxide layer 32 is, as described above, 20 angstrom / se.
Since the value is less than or equal to c, the leak current can be reduced by improving the compactness.

The semiconductor layer 2 in the above embodiment is not limited to the polysilicon film and may be formed of an amorphous silicon film or a single crystal silicon film. In addition to the polysilicon film, the gate electrode 4 is formed of a metal film of aluminum (Al), molybdenum (Mo), chromium (Cr), titanium (Ti), or a silicide film of PtSi, TiSi, MoSi, or the like. You may.

Next, the improvement of transistor characteristics will be described by showing specific numerical values. Table 1 shows an evaluation of a MOS capacitor on single crystal silicon. After depositing a silicon oxide film 31 at a temperature of 430 ° C. on an n-type silicon wafer by LPCVD, it is excited by μ waves in a magnetic field. The comparison is made between the fixed charge density Qss (cm ^-2 ) and the interface state Nss (cm ^-2 eV ^-1 ) in the presence or absence of irradiation treatment by the oxidized plasma. As is clear from Table 1, the characteristics of both the fixed charge density Qss and the interface state Nss are improved by the oxide plasma treatment.

[0020]

[Table 1] Presence or absence of oxidative plasma treatment Yes No Fixed charge density Qss (cm ^-2 ) 9.0 x 10 ¹⁰ 3.5 x 10 ¹¹ Interface state Nss (cm ^-2 eV ^-1 ) 7.9 x 10 ¹⁰ 3.0 x 10 ¹¹

Table 2 shows a comparison of the transistor characteristics of the thin film transistor manufactured by the manufacturing method of the above-described embodiment with and without irradiation treatment by the oxidation plasma excited by μ waves in a magnetic field. .. The thin film transistor was formed such that the gate width W / L was 50/10. According to Table 2, the characteristics are improved by subjecting the mobility, the threshold voltage, and the minimum leak current to the oxidizing plasma treatment.

[0022]

[Table 2] Presence or absence of oxidative plasma treatment Yes No Mobility μ (cm ² / VS) 50.6 45.0 Threshold voltage Vth (V) 0.78 2.8 Minimum leakage current Imin (pA) 280 340

[0023]

According to the method of the present invention, the semiconductor layer is oxidized by irradiating the oxidative plasma due to the resonance of the electron cyclotron, and the silicon oxide layer is formed at the interface between the silicon oxide film formed by deposition and the semiconductor layer. Therefore, since the silicon oxide film and the silicon oxide layer can be formed by the low temperature treatment, the glass substrate can be used as the insulating substrate. In addition, since the semiconductor layer is oxidized by irradiation with oxidation plasma due to resonance of an electron cyclotron to form a silicon oxide layer, favorable interface characteristics between the semiconductor layer and the silicon oxide film can be obtained, and a thin film transistor can be formed. The transistor characteristics in the case of manufacturing can be improved.

[Brief description of drawings]

1A to 1F are manufacturing process diagrams showing a method of manufacturing a thin film transistor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional explanatory diagram of a conventional thin film transistor.

[Explanation of symbols]

1 ... Glass substrate, 2 ... Semiconductor layer, 2a ... Active region,
2b ... Source region, 2c ... Drain region, 3 ... Gate insulating film, 31 ... Silicon oxide film, 32 ... Silicon oxide layer, 4 ... Gate electrode, 5 ... Interlayer insulating film, 6 ...
Contact hole, 7 ... Wiring electrode

Claims (1)

[Claims] 1. A first step of forming a semiconductor layer containing silicon as a main component on an insulating substrate, and a second step of depositing a silicon oxide film on the semiconductor layer by chemical vapor deposition. A third step of forming a stoichiometric silicon oxide layer by irradiating an oxidation plasma by resonance of an electron cyclotron from above the silicon oxide film to oxidize a semiconductor portion at an interface portion between the silicon oxide film and the semiconductor layer. A method of manufacturing a semiconductor device, comprising: