JP3008486B2 - Method for manufacturing thin film semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a thin film semiconductor device formed on an insulating material such as a thin film transistor and a three-dimensional LSI device applied to an active matrix liquid crystal display and the like. In detail, the maximum temperature of the manufacturing process
The present invention relates to a method for manufacturing a thin film semiconductor device formed by a low-temperature process of about 600 ° C. or less.

[Conventional technology]

In recent years, with the increase in screen size and resolution of liquid crystal displays, the driving system has shifted from a simple matrix system to an active matrix system, and it is becoming possible to display a large amount of information. The active matrix method enables a liquid crystal display having more than several hundred thousand pixels, and forms a switching transistor for each pixel. As a substrate for various liquid crystal displays, a transparent insulating substrate such as a fused quartz plate or glass that enables a transmission type display is used.

However, in order to increase the size of the display screen and reduce the cost, it is essential to use inexpensive ordinary glass as the insulating substrate. Accordingly, there has been a demand for a technique capable of forming a thin film transistor for operating an active matrix type liquid crystal display on an inexpensive glass substrate with stable performance while maintaining this economic efficiency.

Conventionally, when such a thin film transistor is formed, after forming a channel portion silicon layer and then forming a gate insulating layer, the substrate is formed of oxygen (O ₂ ), laughing gas (N ₂ O), water vapor (H ₂ O). The thermal oxidation method was used in which the gate insulating layer was formed by oxidizing a part of the silicon layer in the channel section by inserting the film in an oxidizing atmosphere containing) and raising the temperature to about 800 ° C to 1100 ° C. . Alternatively, after the silicon layer in the channel is formed, a silicon dioxide film (SiO ₂ film) is formed by a vapor phase growth method such as atmospheric pressure chemical vapor deposition (APCVD) using monosilane (SiH ₄ ), oxygen (O ₂ ) or the like as a source gas. Was deposited to form a gate insulating layer.

[Problems to be solved by the invention]

However, a number of problems have been pointed out in the conventional method described above. First, in the formation of a SiO ₂ film by a thermal oxidation method, a high-temperature heat treatment of at least 800 ° C. or more is involved in the formation, and thus the heat resistance of the thin film layer and the substrate located below the oxide film becomes a problem. For example, when producing a switching transistor for a large-area liquid crystal display, a substrate other than a very expensive fused silica plate cannot withstand such high temperatures. Further, even in a three-dimensional LSI device, the thermal oxidation method is practically unusable because the lower layer transistor deteriorates at high temperatures.

On the other hand, an insulating film deposition method using a gas phase reaction such as the APCVD method can deposit an insulating film at a low temperature of about 750 ° C. or less. This makes it possible to protect the thin film layer below the oxide film and use an inexpensive glass substrate with low heat resistance.
However, the insulating layer formed by vapor phase growth generally has poor film quality, and it is difficult to keep the interface between the channel silicon semiconductor layer and the insulating layer clean. It was difficult to form the device at low temperatures.

Therefore, development of a low-temperature manufacturing method of an SiO ₂ film that can provide the same or better effect as the high-temperature heat treatment has been expected.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an interface and an insulating layer having good semiconductor device characteristics in a low-temperature process in an MIS type thin film semiconductor device having a silicon layer as a channel portion. Is formed.

[Means for solving the problem]

In the method of manufacturing a thin film semiconductor device according to the present invention, a step of forming a first silicon film serving as a channel on a substrate;
Forming a second silicon film having a void on the silicon film, irradiating the second silicon film with oxygen plasma, and irradiating the oxygen plasma with a gate. A step of forming an insulating film and a gate electrode.

(Operation)

The present invention is based on irradiating oxygen plasma to a channel portion silicon layer whose surface layer portion is made of silicon including voids,
This is a material in which the characteristics of the thin film semiconductor device are improved by oxidizing the silicon including the voids, forming one portion of the gate insulating layer at a low temperature, and cleaning the interface between the semiconductor layer and the insulating layer. .

Embodiment 1 Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiment.

1a to 1h are cross-sectional views showing the steps of manufacturing a silicon thin film semiconductor device for forming an MIS field effect transistor.

In this embodiment, 235 mm square quartz glass is used as the insulating substrate 101. However, the type and size of the substrate or the base material are not limited as long as the substrate or the base material can withstand a temperature of 600 ° C. For example, a three-dimensional LSI formed on a silicon wafer can be used as a base substrate. First, a base SiO ₂ film 102 is deposited on an upper surface of a quartz glass substrate 101 that has been subjected to organic cleaning and acid cleaning by an APCVD method. The base SiO ₂ film 102 is formed at a substrate temperature of 300 ° C., a silane flow rate of 120 SCCM, oxygen of 840 SCCM, and nitrogen of about 140 SLM.
Performed under the condition of Å / Sec, the deposited film thickness is 2000 Å. Next, a silicon thin film 103 containing an impurity serving as a donor or an acceptor was deposited by a low pressure chemical vapor deposition (LPCVD) method. (FIG. 1a) In Example 1, phosphorus was selected as an impurity, and phosphine (PH ₃ ) 0.03 SCCM and monosilane (SiH ₄ ) 200 SCCM were used as source gases at a deposition temperature of 600 ° C. and 1500 ° C.
Å Deposited. At this time, the deposition rate was 30 ° / min, and the sheet resistance immediately after film formation was 1951 Ω / □. Next, a resist was formed on the silicon thin film 103, and patterning was performed with a mixed plasma of carbon tetrafluoride (SF ₄ ), oxygen (O ₂ ), nitrogen (N ₂ ), etc., to form source / drain regions 104. . Then, immediately after removing the dirt / natural oxide film on the surface of the region 104, the silicon thin film 105 which will eventually constitute a channel portion and the silicon thin film 106 including a void to be plasma-irradiated will be formed by a low pressure CVD method. Deposited continuously.
(FIG. 1b) The reduced pressure CVD apparatus in this embodiment has a capacity of 184.5
The reaction chamber side walls and ceiling are made of quartz glass.
Outside the reaction chamber made of quartz glass, heaters divided into three zones are installed, and by independently adjusting them, an isothermal region is formed at a desired temperature near the center of the reaction chamber. The substrate was placed horizontally in this isothermal region, and a silicon thin film 105 and a silicon thin film 106 including voids were deposited.

The silicon thin film 105 is made of monosilane (Si
H ₄ ) Deposition was performed using 11.25 SCCM at a deposition temperature of 600 ° C. for 14 minutes and 52 seconds. No diluent gas was used, and the reaction chamber pressure at this time was 7.78.
mTorr. According to preliminary experiments, the deposition rate under these conditions should be 12.105 ° / min, and the silicon thin film 105 should have been deposited at about 180 °. Immediately after depositing the silicon thin film 105 under these conditions, the flow rate of monosilane was reduced to 2.25 SCCM, and then the silicon thin film 106 including voids was deposited at 600 ° C. for 9 minutes 49
Deposited for seconds. No diluent gas was used, and the pressure in the reaction chamber at this time was 1.55 mTorr. According to preliminary experiments, the deposition rate under these conditions was 8.15 ° / min, and the silicon thin film 106 including the voids should have been deposited at about 80 °.

The silicon film including voids shown in Example 1 was confirmed by multi-wavelength dispersion-type polarization ellipsometry (multi-wavelength spectroscopic ellipsometry: MOSS-ES4G by Sopra). The following procedure was used to determine whether the silicon film was a silicon film containing voids. First, it has a crystal plane orientation of <100> and becomes a type semiconductor because it is doped with phosphorus.
A 3.0 Ωcm single crystal silicon wafer was prepared. The substrate is immersed in boiling nitric acid at a temperature of 60% for 5 minutes to remove dirt on the substrate surface, and further immersed in a 5% aqueous hydrofluoric acid solution for 10 seconds to remove a natural oxide film on the substrate surface. AP
A 2000 mm thick SiO ₂ film was deposited by CVD. These deposition conditions exactly match the conditions for depositing the underlying SiO ₂ film 102 of the first embodiment. Then immerse the substrate in boiling nitric acid for 5 minutes,
After immersing in a 1.67% hydrofluoric acid aqueous solution for 15 to 25 seconds,
A silicon film is formed on the SiO _{2 with} a thickness of about 200 ° to 400 °. In this embodiment, the deposition temperature is 600 ° C. by the low pressure CVD method,
A monosilane flow rate of 2.25 SCCM, a deposition time of 42 minutes and 56 seconds, and a reaction chamber pressure of 1.63 mTorr, and a sample deposited to a thickness of 350 mm with a thickness of 350 mm were used.Since the purpose is to check whether the silicon film contains voids, the silicon film Of course, any method may be used. The sample thus obtained is examined by multi-wavelength dispersion-type ellipsometry to confirm the presence or absence of voids. Multi-wavelength spectroscopic ellipsometry uses a rotating polarizer,
Scanning was performed from a wavelength region of 250 nm to 850 nm. The incident light angle is 75.10
It was ゜. The obtained tan Ψ and cos は spectra are obtained from the previously measured void spectra and amorphous
BRUGGEMAN formula (DAGBRUGGEMA) for complex refractive index of silicon spectrum and crystalline silicon spectrum
N, Ann.Phys. (Leipzig) were compared with synthesized composite spectrum according to 24, 636 (1935). At this time, since the volume mixing ratio of each component can be set to an arbitrary ratio, the presence or absence of voids can be determined from the volume mixing ratio that best matches the measured spectrum among those ratios. Deposition temperature 600 by low pressure CVD
In a silicon film deposited at 350 ° C. at a temperature of 125 ° C., a monosilane flow rate of 2.25 SCCM, a deposition time of 42 minutes and 56 seconds, and a reaction chamber pressure of 1.63 mTorr, 49% voids were observed in the silicon film. In addition, deposition temperature 600 ° C, flow rate of monosilane 4.50SC by Yabari low pressure CVD method
CM, deposition time 36 minutes 45 seconds, reaction chamber pressure 3.5 mTorr 310Å
Silicon film deposited to a thickness of 30% in the silicon film
Voids were observed. On the other hand, deposition temperature 600
° C, monosilane flow rate is 6.75 SCCM or more, reaction chamber pressure is 4.
No void was found in the silicon film deposited at 6 mTorr or more. The presence or absence of a void in the silicon film can be determined by the above method.

Next, a resist is formed on the silicon thin film 105 thus formed and the silicon thin film 106 including voids, and is patterned by a mixed plasma of carbon tetrafluoride (CF ₄ ), oxygen (O ₂ ), nitrogen (N ₂ ) and the like. Was done. (FIG. 1c). At this time, the channel portion silicon thin film 107 and the silicon thin film
It was 238 mm when the total film thickness of 08 was measured with a surface roughness meter.

Next, the substrate is washed with boiling 60% concentration nitric acid and further immersed in a 1.67% aqueous hydrofluoric acid solution for 20 seconds to form a silicon thin film 108 on the source / drain region 104 and including voids.
Immediately after the upper silicon oxide film was removed and a clean silicon surface appeared, oxygen plasma 109 was irradiated by an electron cyclotron resonance plasma CVD apparatus (ECR-PECVD apparatus). (FIG. 1d) The outline of the ECR-PECVD apparatus used in the first embodiment is shown in FIG. As the oxygen plasma, a microwave of 2.45 GHz was guided to the reaction chamber 202 through the waveguide 201, and 100 SCCM of oxygen was introduced from the gas introduction tube 203 to establish oxygen plasma. At this time, the pressure in the reaction chamber was 1.80 mTorr, and the microwave output was 2,500 W. An external coil 204 is provided outside the reaction chamber, and a magnetic field of 875 Gauss is applied to the oxygen plasma to satisfy the ECR condition for the electrons in the plasma. The substrate 205 is placed perpendicular to the plasma, and the temperature of the substrate is kept at 300 ° C. by the heater 206.
Under these conditions, oxygen plasma 109 was irradiated for 8 minutes and 20 seconds to oxidize the silicon thin film 108 including the voids, thereby obtaining an SiO ₂ film 110 as one portion of the gate insulating layer. (FIG. 1e) SiO ₂ to be a gate insulating layer continuously without breaking vacuum
A film 111 was deposited on the substrate. (Fig. 1f) This SiO ₂ film has a microwave output of 2,250 W, a silane flow rate of 60 SCCM, and an oxygen flow rate.
Deposition was performed at 100 SCCM at a substrate temperature of 300 ° C. for 18.75 seconds. The pressure in the reaction chamber during deposition was 2.65 mTorr. The multilayer film thus formed is subjected to multi-wavelength dispersion-type ellipsometry (multi-wavelength spectroscopic ellipsometry: Sopra MOSS-ES4G).
And the film thickness of the residual to that channel portion silicon film 112, the thickness of the combined SiO ₂ film of the SiO ₂ film 111 which is deposited by the SiO ₂ film 110 and the ECR-PECVD method was formed by oxidizing a silicon film containing voids The measured values were 174Å and 1432Å, respectively.

Next, chromium was deposited at 1500 ° by a sputtering method, and a gate electrode 113 was formed by patterning. (FIG. 1g) At this time, the sheet resistance was 1.36 Ω / □. Thereafter, a contact hole is formed in the gate insulating film, a source / drain extraction electrode 114 is formed by a sputtering method or the like, and the transistor is completed by performing patterning. (FIG. 1h) In Example 1, aluminum having a film thickness of 8000 ° was used as a source / drain extraction electrode material. At this time, the sheet resistance value of aluminum was 42 mΩ / □.

An example V _gs -I _ds curve characteristics of the thin film transistor was fabricated in this way (TFT) as shown in FIG. 3 3-a. here
I _ds is a source / drain current, V _gs is a gate voltage, and measured at a source / drain voltage V _ds = 4 V and a temperature of 25 ° C. The transistor size was such that the length L of the channel portion was 10 μm and the width W was 100 μm. _{V ds = 4V, V gs =} 10V ON current when turn on the transistor in the I _ds = 7.9μA, off-current is V _ds = 4V which I _ds is minimized, V _gs = at 0V I _ds = 0.38 Pa As a result, a thin film transistor having good transistor characteristics with an on / off ratio of 7 digits or more was obtained. The field effect mobility calculated from the saturation current region of this transistor is 6.
It was 95cm ² / V · Sec. FIG. 3B shows, for comparison,
The characteristics of the conventional TFT were exhibited, except that the silicon thin film including voids was not deposited and oxygen plasma irradiation was not performed, and all the steps were performed in the same manner as in the above process. The on current of this conventional TFT was I _ds = 5.1 μA, the off current I _ds = 0.81 PA, and the field effect mobility was 4.45 cm ² / V · Sec.

From these results, it can be seen that the characteristics of the thin film semiconductor device are improved according to the present invention as compared with the conventional example.

This is an MIS type field effect transistor. The interface between the semiconductor layer and the insulating layer, which greatly affects the transistor characteristics, is formed by a method called oxygen plasma irradiation oxidation of a silicon thin film containing voids. This is the result of obtaining an interface. This is supported by the fact that the embodiment 3-a of the present invention has a steeper rise near the gate voltage 0V than the conventional example 3-b in FIG.

Example 2 A thin film transistor was formed in the same manner as in Example 1 except for the time of irradiating oxygen plasma with an ECR-PECVD apparatus. In Example 2, the oxygen plasma irradiation time for ECR-plasma oxidation of the silicon thin film including the void was 4 minutes and 10 seconds. Except for this, all the steps were carried out under the same conditions as in Example 1. In Example 2, the remaining channel portion silicon film had a thickness of 198 mm.
Si formed by oxidizing a silicon film containing voids
The film thickness of the combined SiO ₂ film of SiO ₂ film deposited by O ₂ film and ECR · PECVD method was there at 1394A. The on current of the TFT thus prepared was I _ds = 7.9 μA, the off current I _ds = 0.36 PA, and the field effect mobility was 7.02 cm ² / V · Sec.

Also in the second embodiment, it can be seen that the characteristics of the thin film semiconductor device are improved according to the present invention.

〔The invention's effect〕

As described above, according to the present invention, in forming a thin-film semiconductor device on a substrate whose surface is an insulating material,
After the channel portion silicon film is deposited, a silicon film including a void is continuously deposited on the channel portion silicon film, and further including the void before forming a gate insulating layer on the silicon film including the void. By irradiating the silicon film with oxygen plasma, it becomes possible to manufacture a thin-film semiconductor device with good transistor characteristics, and to achieve multi-layer LSI and high performance of an active matrix liquid crystal display using thin film transistors. It has a great effect.

[Brief description of the drawings]

1 (a) to 1 (h) are cross-sectional views of an element in each step of manufacturing a silicon thin film semiconductor device according to an embodiment of the present invention. FIG. 2 is a view showing an outline of an electron cyclotron resonance plasma CVD apparatus used for oxygen plasma irradiation and deposition of a SiO ₂ film which is a part of a gate insulating layer in an embodiment of the present invention. FIG. 3 is a view showing the effect of the present invention. 101: insulating substrate 102: base SiO ₂ film 103: silicon thin film containing impurities 104: source / drain region 105: silicon thin film 106: silicon thin film including voids 107: channel silicon thin film 108 …… Silicon thin film containing voids 109 …… Oxygen plasma 110 …… S formed by oxidizing silicon thin film containing voids
iO ₂ film 111 SiO ₂ film deposited by ECR / PECVD method 112 Remaining channel silicon film 113 Gate electrode 114 Source / drain extraction electrode 201 Waveguide 202 Reaction Chamber 203: gas introduction tube 204: external coil 205: substrate 206: heater

Claims (1)

(57) [Claims] A step of forming a first silicon film serving as a channel on a substrate; a step of forming a second silicon film having a gap on the first silicon film; and an oxygen plasma on the second silicon film. And a step of forming a gate insulating film and a gate electrode on the second silicon film after the step of irradiating oxygen gas and the step of irradiating oxygen plasma.