JPS63219123A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To manufacture a thin film transistor having a high field effect mobility on a low-cost glass substrate by forming a polycrystalline silicon film of a high degree of orientation having a particular plane orientation at a low temperature. CONSTITUTION:After heating a substrate 15 to 600 deg.C, a SiH4 gas 26 is introduced into a plasma chamber 12, and a magnetic field satisfying the electron cyclotron resonance condition is generated. A microwave 27 satisfying the resonance condition for this magnetic field is propagated into a microwave guide 17 and introduced into a plasma generating chamber 11 via a microwave introducing window 18. As a result, the gas 26 is decomposed by the interaction of the microwave 27 and the magnetic field, generating a plasma 28 composed of SiH2 ions. At this time, if a d.c. voltage is applied between a holder 14 and the chamber 12, the plasma 28 is deposited on the substrate 15 by the electric field directing to a vacuum chamber 13 and the diverging magnetic field, thereby forming a polycrystalline silicon film. With this, a thin film transistor of a high field effect mobility can be manufactured on a low-cost glass substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a thin film transistor using a polycrystalline silicon film as a semiconductor thin film, a so-called polycrystalline silicon thin film transistor.

[Conventional technology]

In recent years, development of thin film transistors using polycrystalline silicon films as semiconductor thin films has been progressing with the aim of realizing active matrix type flat display panels. In order to realize this flat display panel at low cost, it is necessary to form thin film transistors with high-speed switching characteristics on a low-cost glass substrate.

Therefore, such thin film transistors must be formed at temperatures below 600° C., at which standard glass substrates do not deform, and must have high field-effect mobility.

A conventional method for manufacturing a thin film transistor using a polycrystalline silicon film will be described with reference to a cross-sectional view of a thin film transistor shown in FIG. First, the polycrystalline silicon film 42 is deposited by low pressure CVD.
It is formed on the substrate 41 by a method. Next, the gate insulating film 43 is formed by plasma CVD.

Aluminum is formed by a method such as a low pressure CVD method.

A gate electrode 44 made of a metal film such as molybdenum or a polycrystalline silicon film is formed. Next, impurities such as phosphorus, boron, arsenic, etc. are implanted by ion implantation using the gate electrode 44 as a mask, and then heat treatment is performed to activate the impurities, forming a source region 45° drain on the surface of the polycrystalline silicon film 42. A region 46 is formed. Next, after depositing an interlayer insulating film 47, source regions 45. Contact holes are formed in the interlayer insulating film 47 above the drain region 46, and the source region is formed through these openings.

A source electrode 48 and a drain electrode 49 are formed in contact with the drain region, respectively. Finally, by performing heat treatment at about 400° C. in a gas containing hydrogen, the polycrystalline silicon film 42 is hydrogenated and the contact resistance between the source region 45 and the source electrode 48 is reduced.

The contact resistance between the drain region 46 and the drain electrode 49 is reduced to complete the thin film transistor.

[Problem that the invention seeks to solve]

By the way, in order to improve field effect mobility in the thin film transistor manufactured by the above manufacturing method, it is necessary to use a polycrystalline silicon film with good crystal grain orientation. Furthermore, in order to use a low-cost glass substrate, it is necessary to form a polycrystalline silicon film at a temperature below the strain point of the glass substrate, that is, below 600°C. However, with the conventional method of thermally decomposing hydrogenated silicon gas using the low-pressure CVD method, a polycrystalline silicon film with good crystal grain orientation cannot be formed at a temperature of 600° C. or lower. Therefore, expensive quartz glass must be used as the substrate, and there is a problem in that a thin film transistor with high-speed swinging characteristics cannot be formed on an inexpensive glass substrate.

The present invention has been made to solve the above-mentioned problems, and its purpose is to form a highly oriented polycrystalline silicon film having a specific plane orientation at a low temperature.
An object of the present invention is to provide a method for manufacturing a thin film transistor having high-speed switching characteristics on a low-cost glass substrate.

[Means for solving problems]

That is, the present invention provides a method for manufacturing a thin film transistor comprising a step of forming a polycrystalline silicon film as a semiconductor thin film on a substrate, in which the step of forming the polycrystalline silicon film includes placing the substrate in a vacuum chamber and heating it. a substrate heating step; a plasma generation step of generating plasma by decomposing hydrogenated silicon gas through interaction between microwaves and a magnetic field in a plasma generation chamber adjacent to the vacuum chamber; the plasma reaching the substrate in the film deposition step; the plasma reaching the substrate in the film deposition step; The amount and kinetic energy of the ions therein are selected to form a highly oriented polycrystalline silicon film with a specific plane orientation.

[Effect]

Therefore, in the present invention, by applying voltage to the substrate to form a polycrystalline silicon film, a thin film transistor with high field effect mobility can be obtained at a low heating temperature of the substrate of 600° C. or less.

〔Example〕

Hereinafter, an embodiment of the method for manufacturing a thin film transistor according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of the apparatus used in the present invention,
Here, a case is shown in which a plasma CVD apparatus using electron cyclotron resonance (also referred to as ECR) is used.

In FIG. 1, numeral 11 is a plasma generation chamber containing a plasma chamber 12 by microwave excitation, and numeral 13 is a plasma generation chamber that houses a substrate 15 placed on a substrate holder 14 and is equipped with a heater 16 for heating the substrate 15. It is a vacuum chamber. Further, 1T is a microwave waveguide, 18 is its microwave introduction window, 19 is a gas inlet provided in the plasma chamber 12, 20 is a magnet coil provided outside the plasma chamber 12, and 21 is a microwave introduction window provided in the plasma chamber 12. 22 is an insulator that electrically insulates the plasma chamber 12 and the vacuum chamber 13; 23 is an insulator that electrically insulates the plasma chamber 12 and the substrate holder 14;
This is an external power source for applying a DC voltage between the base plate 15 and the plasma generating chamber 11 to draw out the plasma 28 generated from the plasma generation chamber 11 and depositing it on the substrate 15 with a predetermined kinetic energy. In addition, in FIG. 1, 24 is a shield plate, and 25 is an exhaust port.

First, a method for forming a polycrystalline silicon film will be explained with reference to FIG. First, plasma generation chamber 11. The vacuum chamber 13 is evacuated through the exhaust port 25. Next, the substrate 15 placed on the substrate holder 14 is heated to, for example, 600° C. by the heater 16. Next, as hydrogenated silicon gas, for example, S i H4 gas 26 is introduced into the plasma chamber 12 . Next, a magnetic field that satisfies the electron cyclotron resonance conditions for electromagnetic waves in the microwave region is generated inside the plasma generation chamber 11 by passing a current through the magnet coil 20. Then, a microwave 27 having a frequency that satisfies the electron cyclotron resonance condition with respect to this magnetic field is propagated inside the microwave waveguide 17, and is passed through the microwave introduction window 18 into the plasma generation chamber 1.
1. For example, if the magnetic field strength is 875 Gauss
, the frequency of the microwave 27 is 2.45 GHz. As a result, due to the interaction (ECR) between the microwaves 27 and the magnetic field, the StH<gas 26 is decomposed, and 5
A plasma 28 made of iHz ions or the like is generated. At this time, the substrate holder 14 and the plasma chamber 1 are placed in advance.
2, a DC voltage is applied from an external power supply 23.

Therefore, the plasma 28 is transported onto the substrate 15 by the electric field directed toward the vacuum chamber 13 and the diverging magnetic field, and S
By adhering iH2 ions and the like to the substrate 15, a silicon film, that is, a polycrystalline silicon film is formed.

Regarding the silicon film formed by the above operations,
The results of examining the crystallinity by diffraction are shown in FIG. Here, as an example, the substrate heating temperature is T, = 600°C,
A silicon film (characteristic A1) formed under conditions where the substrate applied voltage is V1 = -400V and the substrate heating temperature is T2 = 500°C.
, only the silicon film (characteristic A2) formed under conditions where the substrate applied voltage is V2--200 V is shown. In addition, FIG. 2 shows that the substrate heating temperature (T3) is 60°C by the low pressure CVD method, which is a conventional method for manufacturing polycrystalline silicon films.
A silicon film formed at 0° C. is also shown as characteristic B. As is clear from Figure 2, in the polycrystalline silicone film formed by the conventional low pressure CVD method, the XD diffraction intensity is weak as shown in characteristic B, and the (111) peak and (220) peak have the same strength. On the other hand, the polycrystalline silicon film according to the present invention has crystal grain orientation (
220) is extremely strong.

Next, a method for manufacturing a thin film transistor formed using a polycrystalline silicon film having the crystal grain orientation shown in FIG. 2 will be explained using the cross-sectional structure of the thin film transistor shown in FIG.

First, about 200 layers of polycrystalline silicon film 32 are deposited on substrate 31. Next, using, for example, a resist, a metal film, etc. as a mask, phosphorus is implanted by ion implantation, and after removing the resist, metal film, etc., heat treatment is performed at about 600° C. to the source region 33. Activate drain region 34.

Next, on the polycrystalline silicon film 32, for example, a silicon nitride film 5IH4 and NH3 are deposited to a thickness of 20 mm by glow discharge decomposition.
A gate insulating film 35 is formed by depositing 0 nm. Next, contact holes are opened in the gate insulating film 35, and a source region 33 and a drain region 34 are connected through each opening.
source electrode 36. in contact with the source electrode 36. The drain electrode 37 is made of aluminum, for example. At the same time, a gate electrode 38 is also formed from the aluminum. Finally, heat treatment is performed at 400° C. for 20 minutes in a gas containing hydrogen, for example, to complete the thin film transistor.

According to the method for manufacturing a thin film transistor according to the above embodiment, a highly oriented polycrystalline silicon film can be formed at low temperature using a plasma CVD method using ECR. can be formed.

As described above, in the thin film transistor according to the present invention, when a silicon film formed at a substrate applied voltage of -400V and a reference heating temperature of 600°C is used, the field effect mobility is 10 cr1.
12/vI! It became I. Therefore, by forming a polycrystalline silicon film by applying a voltage to the substrate, a thin film transistor with high field effect mobility can be manufactured at low temperature.

Furthermore, in conventional methods such as low pressure CVD, the crystal grain size had to be at least 1100 nm or more in order to obtain a field effect mobility of 10 cm2/VB, but according to the present invention, the crystal grain size has to be 14 nm or more. Even if it is small, the same field effect mobility can be obtained. On the other hand, since the surface morphology of a polycrystalline silicon film reflects the crystal grain size, it is necessary to reduce the crystal grain size in order to obtain a smooth film that is easy to process. Therefore, compared to conventional methods such as the reduced pressure C'/D method, the present invention has the advantage that the surface morphology of the polycrystalline silicon film can also be improved.

Note that in the above embodiment, the gate electrode is formed after the step of forming the source region and the drain region.
Isn't it limited to this? The conventional method of ion implantation using the gate electrode as a mask can be similarly carried out, and the present invention is not affected by the order in which T and 1 are formed. Furthermore, although the interlayer insulating film is not deposited in the manufacturing method of the embodiment described above, it goes without saying that the same process can be carried out even if this film is deposited.

〔Effect of the invention〕

As explained above, according to the present invention, a highly oriented polycrystalline silicon film can be formed at a temperature below 600°C, so that the strain point can be reduced to 600°C.
This has the advantage that thin film transistors with high field effect mobility can be manufactured on low-cost glass substrates at temperatures below 00°C.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus used in a method for manufacturing a thin film transistor according to an embodiment of the present invention, and FIG. 2 shows polycrystallinity of a silicon film formed by the apparatus shown in FIG. 1 examined by XD diffraction. A characteristic diagram showing the measurement results, FIG. 3 is a cross-sectional view of a thin film transistor used to explain a method of manufacturing a thin film transistor according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view of a thin film transistor used to explain a method of manufacturing a conventional thin film transistor. FIG. 11... Plasma generation chamber, 12... Plasma chamber, 13... Φ vacuum chamber, 14... Substrate holder, 15... Substrate, 16... Heater, 17
... Microwave waveguide, 18 ... Microwave introduction window, 19 ... Gas inlet, 20 ... Magnet coil, 23 ... External power supply, 26 ... SiH
4,27 fist...φ microwave, 28...plasma,
31...Substrate, 32...Polycrystalline silicon film, 3
3...Φ source region, 34...drain region, 3
5... Gate insulating film, 36... Source electrode, 3
7...Drain electrode, 38... Reference gate electrode.

Claims (2)

[Claims] (1) In a method for manufacturing a thin film transistor comprising a step of forming a polycrystalline silicon film as a semiconductor thin film on a substrate, the step of forming the polycrystalline silicon film includes a substrate heating step of placing and heating the substrate in a vacuum chamber. and decomposing silicon hydride gas by interaction between microwaves and a magnetic field in a plasma generation chamber adjacent to the vacuum chamber,
a plasma generation step of generating plasma; and a film deposition step of applying a voltage between the substrate and the plasma generation chamber to draw out the plasma from the plasma generation chamber and depositing it on the substrate with a predetermined kinetic energy. the amount and kinetic energy of ions in the plasma reaching the substrate in the film deposition step are selected to form a highly oriented polycrystalline silicon film having a specific plane orientation; A method for manufacturing a thin film transistor characterized by: (2) The heating temperature in the substrate heating process is 600°C or less, and the polycrystalline silicon film in the film deposition process has a crystal grain plane orientation (220) with respect to the substrate vertical direction that is higher than other plane orientations. 2. The method of manufacturing a thin film transistor according to claim 1, wherein the thin film transistor is formed by applying an amount of ions and kinetic energy to increase the strength of the thin film transistor.