JPH11154482A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance controllability and stability by a small dose ion doping. SOLUTION: A switching electrode 9 for reducing a beam current density is superimposed on an accelerating electrode 3 for extracting produced ions by a plasma source 8. Finer pores than fine pores provided in the accelerating electrode 3 are provided in the switching electrode 9, the switching electrode 9 is moved in parallel so that the fine pores of both electrodes 3, 9 coincide with each other, and then, the extracted beam current density can be reduced. Since an ion implantation time can be extended without reducing the ion beam density, An implantation amount can be controlled by adjusting the implantation time, and the uniformity and the stability of doping is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor (TFT) used in an active matrix type display device such as a semiconductor device or a liquid crystal display (LCD) or an electroluminescence (EL) display.
in film tansistor).

[0002]

2. Description of the Related Art In recent years, LCDs, organic EL displays,
2. Description of the Related Art Flat panel displays such as plasma displays have been actively developed and put into practical use. Among them, LCDs and organic EL displays are excellent in thinness, low power consumption, and the like, and have been put to practical use in the fields of OA equipment and AV equipment. In particular, an active matrix type LCD in which a TFT is disposed as a switching element for controlling rewriting timing of pixel information in each pixel can display a large screen and a high-definition moving image. It is widely used for monitors such as portable computers, digital still cameras, and video cameras.

A TFT is a field effect transistor (FET) obtained by forming a semiconductor layer in a predetermined shape together with a metal layer on an insulating substrate.
r). In an active matrix type LCD, the TFT is connected to each capacitance for driving the liquid crystal formed between a pair of substrates sandwiching the liquid crystal.

In particular, a TFT using polycrystalline silicon (p-Si) as a semiconductor layer instead of amorphous silicon (a-Si), which has been widely used, has a high operation speed.
Not only the pixel portion but also peripheral driving circuits can be integrally formed on the same substrate, and an LCD with a built-in driving circuit has been manufactured. FIG. 5 shows a sectional view of the TFT. A gate electrode (11) of Cr, Ti, Ta or the like is formed on a transparent substrate (10), and a gate insulating film (12) is formed to cover the gate electrode (11). On the gate insulating film (12), a p-Si film (13) is formed in an island shape so as to pass above the gate electrode (11). In these p-Si films (13), the region immediately above the gate electrode (11) is a non-doped channel region (CH).
Both sides of the channel region (CH) are lightly doped (LD) regions (L) in which impurities such as phosphorus are lightly doped.
D) and further outside are a source region (S) and a drain region (D) doped with the same impurity at a high concentration.

[0005] Above the channel region (CH), an implantation stopper (14) used as a mask for ion implantation when forming the LD region (LD) is left.
An interlayer insulating film (15) is formed covering the p-Si film (13), and a source electrode (16) and a drain electrode (17) are formed on the interlayer insulating film (15). ) Is connected to the source region (S) and the drain region (D) of the p-Si film (13) through a contact hole (CT) opened.

FIG. 6 is a conceptual diagram of an apparatus for doping impurity ions into the above-mentioned source region (S), drain region (D) and LD region (LD). (1) is the outer wall of the device, (2) is the RF electrode, (3) is the accelerating electrode, (4)
Is an extraction electrode, (5) is a suppression electrode, and (6) is a ground electrode. These second electrode (3), extraction electrode (4),
Each of the suppression electrode (5) and the ground electrode (6) has a diameter of about 800 mm, and has 5000 to 6 micropores of about 4 mm in diameter.
000 are provided so that ions can pass therethrough. (7) is a substrate to be processed on which a semiconductor layer to be ion-doped is formed. (8) is a plasma source which is an ion source.

[0007] In the apparatus, phosphine PH3 is supplied as a source gas containing an element to be doped, for example, phosphorus. A high-frequency voltage is applied between the RF electrode (2) and the accelerating electrode (3) to create a state in which plasma is generated.
Here, the source gas is decomposed to generate several types of ions including positive ions to be doped. This ion is generated by the extraction voltage V applied to the extraction electrode (4).
Pulled by ext. The extracted ions are accelerated by the accelerating voltage Vacc and move downward in the drawing. The suppression electrode (5) is given the lowest voltage in the apparatus. After passing through the suppression electrode (5), the ions proceed in a reverse electric field, pass through the ground electrode (6), are extracted as an ion beam, and are processed. The substrate (7) is irradiated. The negative ions are absorbed by the ground electrode (6).

[0008] The ion doping using the apparatus shown in FIG. 6 has the following advantages. First, an ion beam is obtained as an ion current of the same magnitude as the plasma source.
In an apparatus having electrodes having the above dimensions, the current density of the ion beam is about 10 μA / cm 2 and the beam diameter is 500 mm.
The above is obtained, and the uniformity of the beam current can be suppressed to ± 10% or less by optimally setting the acceleration voltage and the extraction voltage. Therefore, a maximum of 500 mm x 500
mm substrate can be processed at a time, and beam line scanning is unnecessary, and the throughput is extremely high.

[0009]

The ion doping method using the apparatus shown in FIG. 6 is extremely useful for doping with a high dose of 10 15 or more, but a low dose of 10 13 or less. Is difficult to control the dose. That is, since the injection speed is extremely high, it is difficult to finely adjust the dose by time management. Therefore, when doping with phosphorus, PH3 is changed to 1% with hydrogen H2.
By sufficiently lowering the concentration of the ion beam using a raw material gas diluted to about
Time control of the dose amount was performed by setting the time to about second.

However, when such a raw material gas having a high dilution ratio is used, the influence of the residue adhering to the electrodes and the inner wall of the apparatus increases, and the instability of the ion beam concentration becomes remarkable as the number of treatments increases. , The dose varies. That is, the fluctuation rate of the ion beam density with respect to the ion beam density increases. As a result, the TF shown in FIG.
In T, when the LD region (LD) is doped,
This causes a problem that the resistance changes and the on-current value fluctuates. Conventionally, by performing cleaning, an equilibrium state with the electrodes and the inner wall of the apparatus has been created in advance to prevent the ion beam density from fluctuating during processing. However, it takes about 5 hours to create such an equilibrium state, and there is a problem in that if it is performed periodically, the throughput is greatly reduced.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and a high-frequency electric field is applied to a raw material containing at least a target impurity to ionize the impurity, and the material is provided outside the high-frequency electric field. An electric field is applied to the impurity ions by one or more first electrodes having a large number of first pores, and an ion beam containing the impurity ions is extracted in a predetermined direction and irradiated to a target substrate. Accordingly, in the method of manufacturing a semiconductor device in which the impurity is injected into the semiconductor layer on the substrate by a predetermined amount, the second electrode having the second electrode having a smaller diameter than the first electrode together with the first electrode. An ion beam that has at least passed through the second micropores and has a current density reduced to a range where the amount to be implanted into the semiconductor layer can be controlled by the implantation time. It is configured to be irradiated.

As described above, by reducing the current density of the ion beam containing the ions of the impurities to be implanted into the semiconductor layer, the implantation time becomes appropriately long without lowering the ion beam concentration. By adjusting, the injection amount can be controlled stably. In particular, the substrate has a structure in which a polycrystalline semiconductor layer is formed on an insulating substrate to form a thin film transistor, and the impurity is implanted at a relatively low concentration into a predetermined region of the polycrystalline semiconductor layer. .

As a result, the resistance of the thin film transistor is controlled, and good device characteristics can be obtained. Further, a high-frequency electric field is applied to a raw material containing at least the target impurity to ionize the impurity, and the impurity is ionized by one or more first electrodes provided outside the high-frequency electric field and having a large number of first pores. A semiconductor device for implanting a predetermined amount of the impurity into a semiconductor layer on the substrate by applying an electric field to the ions and extracting an ion beam containing the ions of the impurity in a predetermined direction and irradiating the ion beam on a target substrate. In the method, together with the first electrode, a second micropore having a smaller diameter than the first micropore, and a second micropore having a diameter similar to that of the first micropore between the second micropores. A second electrode having a large number of third pores is provided, and the second electrode is moved in parallel while being superimposed on the first electrode,
It is possible to select a first state in which the first and second fine holes are matched, and a second state in which the first and third fine holes are matched. The current density of the ion beam passing through the first electrode and the second electrode is switched.

Thus, when the amount to be implanted into the semiconductor layer is large, the beam current density can be increased, and when the amount to be implanted is small, the beam current density can be decreased. Therefore, when implanting a large amount of impurities, the processing time can be shortened by increasing the beam current density, and when implanting a small amount of impurities, the processing time can be reduced by decreasing the beam current density. By controlling, the injection amount can be finely adjusted.

Further, the substrate has a polycrystalline semiconductor layer formed thereon for forming a thin film transistor on an insulating substrate, and the impurity is compared with a predetermined region of the polycrystalline semiconductor layer in the first state. This is a configuration that is injected at a very low concentration. Formation of a low concentration region of a thin film transistor or channel doping for controlling a threshold value is performed with high controllability.

In particular, the substrate has a polycrystalline semiconductor layer formed on an insulating substrate so as to form a thin film transistor, and the impurity is compared with a predetermined region of the polycrystalline semiconductor layer depending on the second state. This is a configuration in which a high concentration is injected. Thus, the source and drain regions, which are high-concentration regions, can be formed using the same device as the low-concentration region, and the device cost is reduced.

Further, a high-frequency electric field is applied to a raw material containing at least the target impurity to ionize the impurity, and an electric field is applied to the impurity ions by a plurality of electrodes provided outside the high-frequency electric field and having a large number of micropores. A method for manufacturing a semiconductor device in which an ion beam containing ions of the impurity is taken out in a predetermined direction and irradiated to a target substrate to implant a predetermined amount of the impurity into a semiconductor layer on the substrate. Among them, at least one electrode has a second micropore having a smaller diameter than the other electrode, and the ion beam that has passed through the second micropore has a current density corresponding to the amount to be injected into the semiconductor layer. Irradiation is performed in a state reduced to a range that can be controlled by the injection time.

As described above, by reducing the current density of the ion beam containing the ions of the impurities to be implanted into the semiconductor layer, the implantation time becomes appropriately long without lowering the ion beam concentration. By adjusting, the injection amount can be controlled stably. In particular, the second
Has a diameter of 0.5 mm or less.

As a result, the current density of the extracted ion beam is sufficiently reduced, so that the implantation amount can be finely adjusted by controlling the implantation time.

[0020]

FIG. 1 shows a conceptual diagram of an apparatus for performing ion doping according to a first embodiment of the present invention. (1) is the outer wall of the device, (2) is the RF electrode,
(3) is an acceleration electrode, (4) is an extraction electrode, (5) is a suppression electrode, and (6) is a ground electrode. (7) a substrate to be processed on which a semiconductor layer to be ion-doped is formed;
(8) is a plasma source which is an ion source. Furthermore,
(9) is a switching electrode of the present invention. As will be described in detail later, the switching electrode (9) is for switching the current density of the extracted ion beam, and is superposed on the accelerating electrode (3).

FIG. 2 is an enlarged view of the acceleration electrode (3) and the switching electrode (9). The accelerating electrode (3) is provided with a first micropore (31) having a relatively large diameter, and the switching electrode (9) is provided with a second micropore (91) having a relatively small diameter. A third microhole (92) having a large target diameter is provided. The diameter of these micropores is, for example, the first micropore (3
1) and the third pore (92) were 4 mm, and the second pore (9
1) is 1 mm or less, for example, 0.5 mm. The switching electrode (9) is movable by a predetermined amount in parallel, and the second fine hole (9) is moved with respect to the first fine hole (31) of the acceleration electrode (3).
The state where 1) matches and the state where the third micro holes (92) match are switched. Therefore, as described later in detail, the current density of the ion beam extracted from the plasma source (8) is limited to the first micropores (31) and the second micropores (9).
In the state where 1) coincides, the dose is small, and the low dose is suitable for low-dose implantation. In the state where the first fine hole (31) and the third fine hole (92) match, the dose is large and the high dose is high. A high dose setting suitable for injection is obtained. FIG. 2 shows a low dose setting.

FIG. 3 is a process sectional view showing a method of manufacturing a TFT using the ion doping method of the present invention. As the substrate to be processed (7), a gate electrode (11), a gate insulating film (12), a p-Si film (13) are formed on a substrate (10).
And the injection stopper (14) is formed.
The substrate (10) is made of non-alkali glass, and the gate electrode (11) is made of Cr, Ti, Ta or the like. The gate insulating film (12) has a silicon oxide film, a silicon nitride film, or a laminated structure of a silicon nitride film and a silicon oxide film. The p-Si film (13) is formed by subjecting a-Si formed by plasma CVD to laser annealing.
It is obtained by polycrystallization. The injection stopper (14) is made of a silicon nitride film, and is patterned by transferring the shape of the gate electrode (11) by photoetching using a backside exposure method.

In this state, doping with N-type conductivity phosphorus is performed at a low dose of 10.sup.13 to form a p-Si film (13) excluding the region covered with the implantation stopper (14).
Is lightly doped (N−). As the source gas, phosphine PH3 of several% by hydrogen dilution is used.
A high-frequency electric field is applied between the RF electrode (2) and the accelerating electrode (3), and the raw material gas is decomposed and ionized by plasma discharge between the electrodes (2, 3) to generate a plasma source (8). . Generated ions are PHx +, P
2Hx +, Hx + (where x = 0, 1, 2, 3) and the like. These ions are extracted by the extraction voltage Vext applied to the extraction electrode (4), accelerated by the acceleration voltage Vacc, and proceed to the suppression electrode (5). The ions passing through the suppression electrode (5) travel in the reverse electric field formed by the suppression voltage Vsup, pass through the ground electrode (6), are extracted as an ion beam, and are irradiated on the substrate (7) to be processed.

In the present embodiment, the acceleration electrode (3)
The second dose (91) of the switching electrode (9) coincides with the first dose (31) of the first electrode (31), and the low dose is set. 0.5 mm. For this reason, the current density of the extracted ion beam is 20 to 60 nA / cm2, which is smaller than the beam current of the apparatus shown in FIG. Therefore, even when doping with a low dose of about 10 13 using low-diluted phosphine PH 3 of several percent, an injection time of about 20 to 60 seconds can be obtained, and the injection amount is changed by changing the injection time. There is room for control, and the dose can be controlled by adjusting the injection time. Further, since the dilution ratio of the source gas is low, the concentration of the ion beam is high, and the fluctuation of the concentration of the ion beam is absorbed. That is, the concentration of the ion beam is high, the influence of the contamination on the electrode and the reactant adhering to the inner wall of the apparatus is relatively small, and the variation in the concentration of the ion beam is suppressed. Therefore, uniform and stable ion doping can be performed over the entire surface.

Although N-type doping has been described here, in the case of P-type doping such as channel doping, diborane B2H6 or the like is used instead of phosphine PH3 as a source gas, and similarly, dose is increased. The amount can be adjusted. FIG. 4 is another process sectional view showing a method for manufacturing a TFT using the ion doping method of the present invention. The substrate to be processed (7) has a gate electrode (11), a gate insulating film (12), a p-
The Si film (13) and the resist (R) have been formed. This step is a step of performing a high dose doping following the step shown in FIG. The resist (R) serves as a doping mask and is formed to have a larger size than the implantation stopper (13).

In this state, the ion doping of phosphorus is
The p-Si film (13) in the region except under the resist (R) is doped at a high concentration (N +) and maintained at a low concentration by the resist (R) by performing the treatment at a high dose of about 15 to the power. The LD region (LD) and the source region (S) and the drain region (D) outside the resist (R) are formed. As the source gas, several% by hydrogen dilution as in the process of FIG.
In this step, the switching electrode (9) has the third micropores (92) as the first electrode of the accelerating electrode (3).
Is set at a high dose corresponding to the fine holes (31).
Therefore, the current density of the extracted ion beam is 10
μA / cm 2 or less, which is as large as that of the conventional apparatus shown in FIG. Therefore, high dose doping can be performed in a sufficiently short time of about 20 seconds.

As described above, the low dose setting and the high dose setting can be easily switched by the switching electrode (9), so that the same ion doping apparatus can be used to finely adjust the dose during low dose doping, and The reduction of the implantation time at the time of high dose doping was achieved. Here, the switching electrode (9) is not limited to the upper side of the accelerating electrode (3) as shown in FIG. 1, but may be configured to be superimposed below the accelerating electrode (3).

Further, the structure of the TFT to which the ion doping method of the present invention is applied is not limited to the bottom gate type in which the gate electrode is below the p-Si film (13) as shown in FIG. A top gate type on a p-Si film of a gate electrode is also possible. In this case, generally, the ion implantation is often performed through the gate insulating film on the p-Si film. However, according to the gist of the present invention, high throughput,
In addition, stable ion implantation can be performed. Further, the semiconductor layer is not limited to p-Si, but may be a-Si,
Further, the dose of other semiconductors can be similarly controlled by doping at a low dose.

Further, as another embodiment of the present invention, the diameter of the first fine hole (31) of the acceleration electrode (3) is reduced to 1 mm.
Hereinafter, an ion doping method and an ion doping apparatus dedicated to doping at a low dose can be obtained by adopting a configuration of preferably about 0.5 mm and omitting the switching electrode (9). In this case, the method is applied only to the step shown in FIG. 3, but the control of the dose is high as described above.

[0030]

As is clear from the above description, a predetermined impurity is doped at a low dose by using an ion doping method which enables a large area to be processed by implanting a large amount of ions into the substrate at one time. In doing so, according to the present invention, by appropriately reducing the current density of the ion beam, the implantation time until reaching a predetermined implantation amount becomes appropriately long, and there is room for controlling the implantation amount by changing the implantation time. By adjusting the injection time, the injection amount can be stably controlled.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an apparatus for realizing an ion doping method according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a main part of an apparatus for realizing an ion doping method according to an embodiment of the present invention.

FIG. 3 is a process cross-sectional view illustrating a method for manufacturing a semiconductor device using an ion doping method according to the embodiment of the present invention;

FIG. 4 is a process cross-sectional view showing the method for manufacturing the semiconductor device using the ion doping method according to the embodiment of the present invention;

FIG. 5 is a conceptual diagram of a conventional ion doping apparatus.

FIG. 6 is a cross-sectional view of a semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer wall 2 RF electrode 3 Acceleration electrode 4 Leader electrode 5 Suppression electrode 6 Ground electrode 7 Substrate to be processed 8 Plasma source 9 Switching electrode 31 First fine hole 91 Second fine hole 92 Third fine hole

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/336 H01L 29/78 616L

Claims (7)

[Claims] 1. A high-frequency electric field is applied to a raw material containing at least a target impurity to ionize the impurity, and one or more first electrodes provided outside the high-frequency electric field and having a large number of first fine holes are provided. A semiconductor in which a predetermined amount of the impurity is implanted into a semiconductor layer on the substrate by applying an electric field to the impurity ions, extracting an ion beam containing the impurity ions in a predetermined direction, and irradiating the ion beam on a target substrate. In the method for manufacturing a device, a second electrode having a second micropore having a smaller diameter than the first micropore is provided together with the first electrode, and at least the second micropore has passed through the second micropore. A method of manufacturing a semiconductor device, wherein an ion beam is irradiated in a state where the current density of the ion beam is reduced to a range that can be controlled by the implantation time. 2. The substrate comprises a polycrystalline semiconductor layer formed on an insulating substrate to form a thin film transistor, and the impurity is implanted at a relatively low concentration into a predetermined region of the polycrystalline semiconductor layer. 2. The method for manufacturing a semiconductor device according to claim 1, wherein: 3. A high-frequency electric field is applied to a raw material containing at least a target impurity to ionize the impurity, and one or more first electrodes provided outside the high-frequency electric field and having a large number of first micropores are provided. A semiconductor in which a predetermined amount of the impurity is implanted into a semiconductor layer on the substrate by applying an electric field to the impurity ions, extracting an ion beam containing the impurity ions in a predetermined direction, and irradiating the ion beam on a target substrate. In the method for manufacturing a device, a second micropore having a smaller diameter than the first micropore together with the first electrode, and the first micropore between the second micropores.
A second electrode having a large number of third micropores having a diameter similar to that of the micropores, and by moving the second electrode in a state of being superimposed on the first electrode in parallel, It is possible to select a first state in which the first and second fine holes are matched, and a second state in which the first and third fine holes are matched. And a current density of an ion beam passing through the first electrode and the second electrode is switched. 4. The substrate according to claim 1, wherein a polycrystalline semiconductor layer is formed on an insulating substrate to form a thin film transistor, and the impurity is compared with a predetermined region of the polycrystalline semiconductor layer according to the first state. 4. The method according to claim 3, wherein the semiconductor device is implanted at a very low concentration. 5. The method according to claim 1, wherein the substrate has a polycrystalline semiconductor layer formed on an insulating substrate to form a thin film transistor, and the impurity is compared with a predetermined region of the polycrystalline semiconductor layer in the second state. 5. The method for manufacturing a semiconductor device according to claim 3, wherein the semiconductor device is implanted at a very high concentration. 6. A high-frequency electric field is applied to a raw material containing at least a target impurity to ionize the impurity, and an electric field is applied to the impurity ions by a plurality of electrodes provided outside the high-frequency electric field and having a large number of micropores. A method for manufacturing a semiconductor device in which an ion beam containing ions of the impurity is taken out in a predetermined direction and irradiated to a target substrate to implant a predetermined amount of the impurity into a semiconductor layer on the substrate. Among them, at least one electrode has a second micropore having a smaller diameter than the other electrode, and the ion beam that has passed through the second micropore has a current density corresponding to the amount to be injected into the semiconductor layer. A method of manufacturing a semiconductor device, characterized in that irradiation is performed in a state reduced to a range controllable by an injection time. 7. The method for manufacturing a semiconductor device according to claim 2, wherein the diameter of the second fine hole is 0.5 mm or less.