JP2000332252A - Ion doping method and manufacture of thin-film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve processing capacity of an ion doping device and mobility of a thin-film transistor. SOLUTION: In an ion doping method, by which diborane (B2H6) gas diluted by hydrogen is subjected to plasma decomposition by radio frequency discharge to form ions, and the ions are accelerated and implanted into a substrate without mass separation, the total beam current (μA) which is the product of effective area (cm2) and a beam current density (μA/cm2) of an ion beam is set at 2,000 to 25,000.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion doping method usable for an input / output device such as a liquid crystal display or an image sensor and a method for manufacturing a thin film transistor.

[0002]

2. Description of the Related Art In recent years, in the field of liquid crystal display devices, a technique for fabricating a thin film transistor array with a built-in driving circuit using a thin film transistor on a glass substrate which is inexpensive and easy to have a large area has been actively developed. Has begun.

[0003] An ion doping method is used as a method for producing an SD region (source and drain) and an LDD region of a thin film transistor. This ion doping method is a method of electrically accelerating and implanting ions generated in an ion source without mass separation. Since there is no mass separation mechanism, it is easy to increase the area, and polycrystalline silicon for a liquid crystal display device is used. It is generally used for producing an active matrix substrate. Regarding ion doping equipment, see, for example, “Large-area ion doping technology and its influence on device fabrication”, Semiconductor World, March 1989, p.
111-118.

FIG. 5A is a sectional view showing the structure of the ion doping apparatus used in the first embodiment of the present invention. This ion doping apparatus is composed of four porous electrodes 51 to 54, which are electrodes for acceleration, extraction, suppression, and grounding, respectively. First, the source gas diluted with hydrogen is supplied to the gas introduction pipe 5.
5 and introduced into the plasma chamber 50, the RF power (1
The plasma is decomposed by RF power from 3.56 MHz) 56 to generate an ion beam 57. The generated ion beam is extracted from the plasma chamber 50 at the extraction voltage Vext of the extraction electrode 52, and the acceleration voltage Va of the acceleration electrode 51 is extracted.
It is accelerated by cc and injected into the substrate 58 on the substrate stage 59 without mass separation.

In general, an ion doping apparatus does not have a mass separation mechanism for generated ions, so that various ions generated by plasma decomposition (for example, H _x , PH _x when hydrogen-diluted phosphine (PH ₃ ) is used as a source gas). , P ₂ H
_xx = 1 to 3) are simultaneously injected into the substrate 58. A suppression voltage Vspp is applied to the suppression electrode 53 to suppress X-ray generation due to secondary electrons generated by ion implantation into the substrate. The dose injected into the substrate is calculated by integrating the current of the ion beam measured by a fixed Faraday cup installed around the substrate and using Equation 1.

[0006]

## EQU1 ## Dose (/ cm ² ) = A × Ion beam current density ×
Implantation time [where A is a constant] As described above, the dose is proportional to the ion beam current density and the implantation time. If the dose is constant, doubling the ion beam current density will reduce the implantation time by half. become. Therefore, in order to improve the throughput of the apparatus, a method of increasing the ion beam current density and shortening the implantation time is generally used.

To increase the ion beam current density,
As shown in FIG. 4, high-frequency power is applied as shown in the relationship between the concentration of boron gas (horizontal axis) of ion doping used in forming a P-type thin film transistor and the upper limit dose (vertical axis) that does not cause a decrease in mobility. You just need to increase it. Regarding the relationship between the high frequency power of the ion doping apparatus and the ion beam current density, see, for example, “Ion doping equ
ipment with a largearea ion source for giant-micro
devices "Ion Implantation technology-92p.661-666
It is described in. As described in the above-mentioned reference, generally, when manufacturing an n-channel thin film transistor, phosphine (P) diluted with hydrogen to a concentration of about 5% is used.
H ₃ ) gas is plasma-decomposed to generate an ion beam, and impurities are implanted into the LDD region or the SD region (source and drain regions) of the thin film transistor.

Therefore, the ion beam contains hydrogen ions (H _x ) in addition to the necessary impurities (PH _x and P ₂ H _x ), and the dopant is not included in the total dose.
The ratio of (impurities) is defined as the ion ratio. The ion ratio is expressed by (Equation 2).

[0009]

## EQU2 ## Ion ratio R (%) = Dopant (impurity) dose / total dose × 100 When the total dose to be implanted is large, it is necessary to increase the ion beam current density in order to reduce the throughput. To increase the ion beam current density, the input RF power is increased. However, when the input power to the plasma is increased, the decomposition efficiency of phosphine (PH ₃ ) as a source gas and hydrogen as a diluent gas with respect to the RF power is reduced. Due to the difference, there is a concern that the ion ratio varies depending on the ion beam current density.

FIG. 5B is a reference document, Ion Implantati.
On technology-92, 5% phosphine (PH ₃ ) is used as a source gas, and P ions are implanted into a Si substrate at a constant dose (1E16 ions / cm ² ).
It is an example diagram of a sheet resistance when the activation process is performed,
This is shown in terms of RF power dependence. The sheet resistance (vertical axis) is almost constant even when the RF power (horizontal axis) is changed, that is, the beam current density is changed, and the ratio of P ions to the total beam current is almost constant regardless of the RF power. Conceivable.

On the other hand, in the case of manufacturing a p-channel thin film transistor, diborane (B ₂ H ₆ ) gas diluted with hydrogen to about 5 to 20% is plasma-decomposed to generate an ion beam. However, there is almost no report on the ion beam current density when hydrogen-diluted diborane (B ₂ H ₆ ) gas is used as the source, that is, the ratio of ions to RF power.

FIG. 6 is a sectional view showing each step of an example of a conventional method of manufacturing a thin film transistor. First, a silicon oxide film serving as a buffer layer 12 is formed on a transparent (glass) substrate 11 shown in FIG.
Then, a non-single-crystal silicon (a-Si) film 13 is deposited thereon by plasma CVD at a thickness of 500 °. Next, in order to reduce hydrogen in the a-Si film 13, a heat treatment is performed at 450 ° C. for 90 minutes under a reduced pressure nitrogen atmosphere of 1 Torr.
The a-Si film is polycrystallized by excimer laser annealing to form a poly-Si film 13. As the excimer laser, a XeCl excimer laser having a wavelength of 308 nm is used, and irradiation is performed in a vacuum. The poly-Si film is processed into the shape of a thin film transistor (TFT), and a silicon oxide film serving as the gate insulating film 14 is formed at 1000 Å. After forming the gate insulating film, AlZr (1000A) is formed on Mo-W (1000A).
Are formed to form the gate electrode 15.

As shown in FIG. 6A, after forming the gate electrode material, the gate electrode 15 is formed only on the p-channel thin film transistor, and the n-channel thin film transistor is covered with the gate electrode material. Thereafter, boron ions are implanted by an ion doping method using diborane (B ₂ H ₆ ) gas diluted with hydrogen to 15% as a source gas to form an SD region of a p-channel thin film transistor.

At this time, the boron ion implantation conditions are an acceleration voltage of 60 kV, a current density of 13.9 μA / cm ² , an effective beam meter of 700 mmΦ, a high frequency power of 500 W, and a gas pressure of 40 mP.
The injection was performed at a total dose of 3E15 / cm ² in FIG. Effective ion beam area of 3848 (cm ² ) and beam current density of 13.9
(μA / cm ² ), the total beam current (μA) is 5349
3 μA.

After the boron ion implantation, as shown in FIG. 6B, a gate electrode 15 is formed on the n-channel thin film transistor, and phosphorus ion doping for forming an LDD region of the n-channel thin film transistor is performed. Phosphorus is obtained by decomposing and ionizing phosphine (PH ₃ ) gas diluted with hydrogen to 5% without accelerating voltage of 70 kV and total dose of 1E without mass separation.
Injected at 13 / cm ² . Here, 13a is intrinsic polycrystalline silicon (channel region), and 13b is a low concentration impurity implanted region (LDD region).

Next, as shown in FIG.
After covering the DD region 13b and the entire p-channel thin film transistor with a photoresist mask 30, phosphorus ions are implanted by an ion doping method using a phosphine (PH ₃ ) gas diluted with hydrogen to 5% as a source gas to form an n-channel thin film transistor. High-concentration impurity implanted region (SD region)
13c is formed. The phosphorus ion implantation conditions at this time were an acceleration voltage of 70 kV, a current density of 10.0 μA / cm ² , an effective beam meter of 700 mmΦ, a high frequency power of 250 W, and a gas pressure of 40 m.
The injection is performed with Pa at a total dose of 1E15 / cm ² .

As shown in FIG. 6D, after the phosphorus ions are implanted, the resist mask 30 is removed and the implanted impurities are activated. The activation treatment is performed in a nitrogen atmosphere at 600 ° C. for one hour. After the activation process, an interlayer insulating film 18 made of silicon oxide is formed, a contact hole 19 is opened, and S
D regions (source and drain electrodes) 20 and 21 are formed. Finally, a protective insulating film 23 made of silicon nitride is formed, and heat treatment is performed at 350 ° C. for one hour in a hydrogen atmosphere to hydrogenate crystal defects of the thin film transistor.

[0018]

However, when an impurity is implanted by an ion doping method capable of coping with a large-area substrate, a large amount of hydrogen ions besides the necessary impurity ions because they do not have a mass separation mechanism. Are simultaneously injected. Hydrogen implanted in a state where it is not bonded to impurities to be implanted (H1, H2, H3 ions) among hydrogen ions has a small mass number, so the average flight distance is larger than required impurities, and the thin film transistor The gate electrode used as an implantation mask for the purpose of self-alignment has a small ability to block hydrogen ions, and hydrogen ions are implanted into the channel region of the thin film transistor to form crystal defects. Crystal defects formed in the channel region by the implantation of the hydrogen ions have a problem that the characteristics of the p-type thin film transistor, particularly the mobility, are reduced, and the balance of the characteristics with the n-type thin film transistor is deteriorated. An object of the present invention is to solve such a problem.

[0019]

According to the ion doping method of the present invention, diborane (B ₂ H ₆ ) gas diluted with hydrogen is plasma-decomposed by high-frequency discharge to generate ions, and the ions are accelerated without mass separation. In the ion doping method in which the ion beam is implanted into the substrate, the effective area A (c
m ² ) and the beam current density B (μA / cm ² ), which is a total beam current (μA) of 2,000 to 25,000.

Further, according to the present invention, there is provided a method of manufacturing a p-type top gate thin film transistor using a polycrystalline silicon thin film as an active layer on a light-transmitting substrate. On the other hand, there is a step of ionizing boron and hydrogen at the same time without mass separation, and has an effective area A (cm ² ) of ion beam and a beam current density B (μA
/ Cm ² ) and a total beam current (μA) of 2,000 to 25,000.

In a method of manufacturing a p-type top gate thin film transistor using a polycrystalline silicon thin film as an active layer on a light-transmitting substrate, boron and hydrogen are ionized into the source and drain regions of the p-type thin film transistor. A step of simultaneously implanting without mass separation, wherein a total beam current (μ) is a product of an effective area A (cm ² ) of the ion beam at the time of impurity implantation and a beam current density B (μA / cm ² ).
A) is not less than 2,000 and not more than 25,000, and the total dose of boron and hydrogen is not more than 2E15 / cm ² .

A step of using a hydrogen-diluted diborane gas having a concentration of C (%) to simultaneously ionize boron and hydrogen into the source and drain regions of the p-type thin film transistor without mass separation. The total dose of boron and hydrogen is not more than 2E15 × C / 15 (/ cm ² ).

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 5A shows a structural sectional view of an ion doping apparatus used in an embodiment of the present invention. The configuration of the equipment is as described in the section of the related art. In the first embodiment, the effective area of the ion beam is defined by a region where 3σ <10% of the average current density, and is 700 mmΦ in the first embodiment.

FIG. 1 shows diborane (B ₂₎ diluted with hydrogen to 15%.
FIG. 2 is a diagram showing the total beam amount dependency (a in FIG. 1) of the sheet resistance when activated after H ₆ ) gas is decomposed by high frequency to implant boron into a Si substrate. As the ion doping apparatus, the apparatus shown in FIG. 5A was used, and the total dose including hydrogen was fixed at 1E15 / cm ² , and the average beam current density was adjusted.
(High-frequency power). The vertical axis is the sheet resistance (Ω), and the horizontal axis is the effective area A (cm ² ) of the ion beam.
And the beam current density B (μA / cm ² ). The acceleration voltage is injected at 60 kV. The activation treatment after the injection was performed at 600 ° C. for 1 hour in a nitrogen atmosphere.

The beam current density is set by the high frequency power applied to the plasma. As the beam current density increases, the sheet resistance increases, and the beam current density increases. That is, by increasing the high-frequency power, the boron ion ratio (b in FIG. 1), which is the content of boron in the ion beam, is reduced. In order to obtain the same sheet resistance, the dose needs to be increased, and the throughput is reduced. It indicates that you want to. If the sheet resistance of the source and drain regions of the thin film transistor is 10 kΩ or less, the deterioration of the ON characteristics due to the resistance component is not a problem, and if the total beam current is 25000 (μA) or less, a desired sheet resistance value is obtained. On the other hand, the lower limit of the total beam current is desirably 2000 (μA) or more from the viewpoint of throughput.

FIG. 1 shows that the boron concentration at the time of implantation of a total dose of 1E15 / cm ^{2 was} measured by SIMS (Secondary Ion Mass Spectrosc
Opy) The results measured by the analysis are also shown. Total beam current 11545 μA (this embodiment) and 53493 μA
When compared with (conventional example), the boron dose amounts were 7.7E14 / cm ² and 2.1E14 / cm ² , respectively, and the boron ion ratio to the total dose amount (1E15 / cm ² ) was 77%.
And 21%. As described above, by using the ion doping method according to claim 1, the required impurity concentration (boron in this case) in the ion beam can be made 50% or more. This makes it possible to shorten the implantation time for implanting the required impurity concentration while reducing the actual ion beam current density.
Also, by reducing the average current density at the time of implantation, it is possible to suppress a rise in the substrate temperature at the time of implantation while maintaining the necessary impurity concentration, and use a mask having a low heat resistance such as a photoresist in the doping process. It became possible to use it.

(Embodiment 2) FIG. 2 is a sectional view showing a manufacturing process of a thin film transistor according to Embodiment 2 of the present invention.

First, as shown in FIG. 2A, a buffer layer 12 is formed on a light transmitting (glass) substrate 11 by a plasma CVD method.
Is formed to a thickness of 4000.degree. afterwards,
The non-single-crystal silicon (a-Si) film 1 can be obtained without taking out the light-transmitting substrate 11 on which the silicon oxide thin film is formed into the atmosphere.
3 is deposited at 500 °. Then, at 450 ° C. and 90 ° C. under a reduced pressure nitrogen atmosphere of 1 Torr in order to reduce hydrogen in the a-Si film.
After performing the heat treatment for a minute, the a-Si film is polycrystallized by excimer laser annealing to form a poly-Si film.
As the excimer laser, a Xecl excimer laser having a wavelength of 308 nm was used, and irradiation was performed in a vacuum. The energy density was 350 mJ / cm ² and the average number of irradiation was 16 shots. p
After forming the poly-Si film, it is processed into the shape of a thin film transistor, and a silicon oxide film to be
0 ° is formed. The silicon oxide film was formed by plasma CVD. After forming the gate insulating film, a gate electrode 15 in which AlZr (1000 A) is laminated on Mo-W (1000 A) is formed.

As shown in FIG. 2A, after forming the gate electrode material, the gate electrode 15 is formed only on the p-channel thin film transistor, and the n-channel thin film transistor is covered with the gate electrode material. After removing the photoresist on the gate electrode, diborane diluted with hydrogen to 15%
Boron ions are implanted by an ion doping method using (B ₂ H ₆ ) gas as a source gas to form an SD region of a p-channel thin film transistor.

The boron ion implantation conditions at this time were an acceleration voltage of 60 kV, a current density of 3.0 μA / cm ² , an effective beam meter of 700 mmΦ, a high frequency power of 60 W, a gas pressure of 40 mPa and a total dose of 8E14 / cm ² . Total beam current, which is the product of the effective area 3848 (cm ² ) of the ion beam at the time of boron ion implantation and the beam current density 3.0 (μA / cm ² )
(μA) is 11545 μA.

After the boron ion implantation, as shown in FIG. 2B, a gate electrode 15 is formed on the n-channel thin film transistor, the photoresist on the gate electrode is removed, and a phosphorus ion for forming an LDD region of the n-channel thin film transistor is formed. Perform doping. Phosphorus is phosphine diluted with hydrogen to 5%
Acceleration voltage 70 kV, total dose 1E13 / cm ² without mass separation of the decomposed and ionized (PH ₃ ) gas
Was injected. Here, 13a is an intrinsic polycrystalline silicon (channel region), and 13b is a low concentration impurity implanted region (LDD region).

Next, the n-channel SD area 1 shown in FIG.
After the gate insulating film 14 on 3c is removed by etching and the entire n-channel LDD region 13b and p-channel thin film transistor are covered with a photoresist mask 30,
Phosphorous ion is implanted by an ion doping method using a phosphine (PH ₃ ) gas diluted to
High-concentration impurity implantation region (S
D region) 13c is formed. The boron ion implantation conditions at this time were as follows: an acceleration voltage of 12 kV, a current density of 1.5 μA / cm ² ,
The effective beam meter was injected at a total dose of 5E14 / cm ² at 700 mmΦ, high frequency power of 50 W, gas pressure of 40 mPa.

As shown in FIG. 2D, after phosphorus ion doping, an interlayer insulating film 18 made of silicon oxide is formed, a contact hole 19 is opened, and source and drain electrodes 20 and 21 (SD wiring) are formed. . Thereafter, a protective insulating film 23 made of silicon nitride is formed, and heat treatment is performed at 350 ° C. for one hour in a hydrogen atmosphere to hydrogenate crystal defects of the thin film transistor. After the hydrogenation treatment, a contact hole is opened in the silicon nitride, and a flattening film is formed.
Finally, a display electrode made of ITO is formed, and a thin film transistor array for a liquid crystal display device is completed.

FIG. 3 is a view showing the total dose dependency of the mobility of the p-channel thin film transistor manufactured in the second embodiment. The total beam current (μA), which is the product of the effective area (cm ² ) of the ion beam and the beam current density (μA / cm ² ) during the boron ion doping of the source and the drain of the p-channel thin film transistor, is shown in the conventional example. 53493μ
A is compared with 11545 μA described in the second embodiment. When the boron implantation amount is increased, the mobility of the thin film transistor is reduced, although the sheet resistance of the source / drain region is reduced. This is because hydrogen implanted at the same time as ion doping passes through the gate electrode and is implanted into polycrystalline silicon below the gate electrode to form crystal defects.

Therefore, it is important to increase the boron ion ratio at the time of doping in order to reduce the resistance of the source / drain region while suppressing the decrease in the mobility.
By the way, the effective area of the ion beam shown in the conventional example (cm ² )
Of the beam current density (μA / cm ² ) and the total beam current (μA) of 53493 μA (boron ion ratio 22%) shows a significant decrease in mobility when the total dose is 9E14 / cm ² or more. And the mobility of the thin film transistor and the source
While it is difficult to reduce the sheet resistance of the drain region at the same time, in the second embodiment (ion ratio 77%) using the manufacturing method according to the second aspect of the present invention, a tendency to decrease the mobility is observed. 4. The total dose of 2E15 / cm according to claim 3, wherein the area is
^It has been expanded to a high dose side almost ^two to three times, and the manufacturing margin of the thin film transistor can be more than doubled. In addition, the mobility itself was improved by 25 to 30%.

FIG. 4 shows the upper limit of the dose at which the decrease in the mobility of the p-type thin film transistor manufactured by using the ion doping method according to the first aspect of the present invention is observed, with respect to the gas concentration used in the ion doping. FIG. As shown in FIG. 3, when a gas having a diborane concentration of 15% is used, a decrease in mobility is observed at an injection amount of 2E15 / cm ² or more, but a decrease in mobility is observed as the diborane concentration increases. The amount increases. As shown in FIG. 4 and claim 4, the inclination is (2E15 × gas concentration)
(%) / 15), and when the dose is less than that, it is possible to prevent a decrease in mobility due to hydrogen damage implanted simultaneously with ion doping.

[0038]

As described above, the present invention relates to an ion doping method for forming an SD region of a p-type thin film transistor by using a product of an effective area (cm ² ) of an ion beam and a beam current density (μA / cm ² ). If the total beam current (μA) is 20
When the gas concentration to be used is C in the condition of not less than 00 and not more than 25000 and the total dose including hydrogen is (2E15 ×
By making the gas concentration (%) / 15) or less, a high mobility can be stably obtained in the p-type thin film transistor. As a result, the manufacturing yield of an active matrix array for a liquid crystal display device in which thin film transistors manufactured by using the manufacturing method of the present invention are integrated is greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a total beam current dependency of a p-type Si sheet resistance using an ion doping method according to a first embodiment of the present invention.

FIG. 2 is a process sectional view of a method for manufacturing a thin film transistor according to Embodiment 2 of the present invention.

FIG. 3 is a graph showing the total dose dependency of the mobility of a p-channel thin film transistor in Embodiment 3 of the present invention.

FIG. 4 is a diagram showing a relationship between a boron gas concentration of ion doping used in forming a p-type thin film transistor and an upper limit dose which does not cause a decrease in mobility.

FIG. 5 is a structural cross-sectional view of an ion doping apparatus (a) and an example of an n-type Si sheet resistance formed by an ion doping method (b).

FIG. 6 is a sectional view showing each step of an example of a conventional method for manufacturing a thin film transistor.

[Explanation of symbols]

Reference Signs List 11 Translucent substrate 12 Buffer layer (silicon oxide) 13 Non-single-crystal silicon film 13a Intrinsic polycrystalline silicon (channel region) 13b Low-concentration impurity implantation region (LDD region) 13c High-concentration impurity implantation region (SD region) 14 Gate insulation Film (silicon oxide) 15 Gate electrode 18 Interlayer insulating film (silicon oxide) 19 Contact hole 20, 21 SD wiring (Al / Ti) 23 Protective insulating film (SiN _x ) 30 Photoresist mask

Continued on the front page F-term (reference) 5F110 AA01 AA18 AA19 BB01 BB04 BB10 CC02 DD02 DD13 EE06 EE14 FF02 FF30 GG02 GG13 GG25 GG45 HJ01 HJ02 HJ04 HJ12 HJ18 HJ23 HM15 NN03 NN23 NN09 QQQ19

Claims (4)

[Claims] 1. An ion doping method in which hydrogen-diluted diborane (B ₂ H ₆ ) gas is plasma-decomposed by high-frequency discharge to generate ions, and the ions are accelerated without mass separation and implanted into a substrate. An ion doping method, wherein a total beam current (μA), which is a product of an effective area A (cm ² ) of the ion beam and a beam current density B (μA / cm ² ), is 2,000 to 25,000. 2. A method of manufacturing a p-type top gate thin film transistor using a polycrystalline silicon thin film as an active layer on a light-transmitting substrate, wherein boron and hydrogen are ionized into source and drain regions of the p-type thin film transistor. A step of simultaneously implanting without mass separation, wherein a total beam current (μA) which is a product of an effective area A (cm ² ) of the ion beam at the time of impurity implantation and a beam current density B (μA / cm ² ) is obtained. A method for manufacturing a thin film transistor, wherein the condition is in the range of 2,000 to 25,000. 3. A method for manufacturing a p-type top gate thin film transistor using a polycrystalline silicon thin film as an active layer on a light-transmitting substrate, wherein boron and hydrogen are ionized into source and drain regions of the p-type thin film transistor. A step of simultaneously implanting ions without mass separation, wherein a total beam current (μ) is a product of an effective area A (cm ² ) of the ion beam at the time of the impurity implantation and a beam current density B (μA / cm ² ).
3. The method according to claim 2, wherein A) is 2,000 or more and 25,000 or less, and a total dose of boron and hydrogen is 2E15 / cm ² or less. 4. Diborane (B ₂ ) having a concentration of C (%) diluted with hydrogen
A step of ionizing boron and hydrogen into the source and drain regions of the p-type thin film transistor using H ₆ ) gas and simultaneously implanting them without mass separation, and the total dose of boron and hydrogen is (2E15 × C / 15) (/ cm
² ) The method of manufacturing a thin film transistor according to claim 2, wherein