JPH05283694A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce a leakage current in the case reverse biased, by forming a channel length longer than a length of the channel length direction of a gate electrode in an insulated-gate type field-effect transistor having at least semiconductor layer, insulating film layer and conductor layer on an insulating substrate. CONSTITUTION:A source region 100, a drain region 101 and a channel region 109 which act as a semiconductor layer are installed on an insulating substrate 105 through a blocking layer 104. A gate insulating film 110 and a gate electrode 111 in which an oxide layer 112 formed by anodizing a material capable of anodization is installed are formed on their regions. Then, a source electrode 102 and a drain electrode 103 are disposed while being brought into contact with the source region 100 and the drain region 101 respectively. By installing the anodized oxide layer 112 in this manner, the distance between both regions 100 and 101 for an ion implantation (that is, channel length 108) is formed longer than a length of the channel length direction of the substantial gate electrode 111 by about twice the thickness of the oxide layer 112, and a leakage current when reverse biased is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to an active matrix type electro-optical device, in particular an active matrix type liquid crystal electro-optical device, and shows a structure of a field effect transistor having clear switching characteristics and a method for manufacturing the same. Is.

[0002]

2. Description of the Related Art A thin film insulating gate type field effect transistor used in a conventional active matrix type liquid crystal electro-optical device has a structure as shown in FIG. Insulating substrate 2
09 with a blocking layer 208 on the source 204,
A gate insulating film 202 and a gate electrode 201 are provided over the semiconductor layer having the drain 205 and the channel region 203. The interlayer insulating film 211 and the source electrode 20 are formed thereon.
6, having a drain electrode 207.

This conventional insulated gate field effect transistor is manufactured by forming a blocking layer on a glass substrate 209 by sputtering with SiO ₂ as a target and then forming a semiconductor layer by plasma CVD. ,
After patterning it, a semiconductor layer to be the source, drain, and channel regions is formed, and then a gate insulating film 202 made of silicon oxide is formed by sputtering.
After that, a low-pressure CVD method is used to form a conductive layer for a gate electrode which is heavily doped with P (phosphorus), and then is patterned to form a gate electrode 201. After that, impurity ions are implanted using the gate electrode as a mask, and the source 20
5 and the drain 204 are produced, and then heat treatment is performed to activate them.

In the insulated gate field effect transistor thus manufactured, the length of the gate electrode 201 in the channel length direction is substantially equal to the channel length 210.

[0005]

The current-voltage characteristic of the insulated gate field effect transistor having such a structure is n.
In the case of channel, as shown in FIG.
However, there is a drawback that the leak current increases as the applied voltage between the source and the drain increases.

When such a leak current increases, when this element is used in an active matrix type liquid crystal electro-optical device, as shown in FIG.
The charge accumulated in the liquid crystal 302 through the leak current 301 was discharged through the leak portion of the element during the non-writing period, and a good contrast could not be obtained.

Therefore, in such a case, as shown in FIG. 5 (B) as a conventional example, it is necessary to install a capacitor 303 for holding charges. However, in order to form these capacitors, an electrode for capacitance by metal wiring is required, which has been a factor of reducing the aperture ratio. In addition, although an example of forming this with a transparent electrode such as ITO to improve the aperture ratio has been reported, it is not welcomed because it requires an extra process.

When only one of the source and the drain of such an insulating gate type field effect transistor is connected to a capacitor element (capacitor) and the transistor is used as a switching element, for example, a known one transistor / cell type element is used. Dynamic random
In an access memory (DRAM) device or an active liquid crystal display device having a circuit as shown in FIG. 5 in each pixel, the voltage of the capacitor element fluctuates due to the presence of parasitic capacitance between the gate electrode and the drain (or source). It was known to do.

The voltage variation ΔV is proportional to the gate voltage V _G and the parasitic capacitance and inversely proportional to the sum of the capacitance of the capacitor element and the parasitic capacitance. Therefore, in order to suppress the voltage variation, a self-alignment method is generally used. It has been attempted to reduce the parasitic capacitance by making a transistor. However, as device design rules shrink,
No matter how the self-alignment method is used, the ratio of parasitic capacitance becomes so large that it cannot be ignored.

Therefore, in order to reduce ΔV, FIG.
As shown in (B), in addition to the original capacitor element,
It has been proposed to connect capacitors in parallel to apparently increase the capacitance of the capacitor element.
Problems such as an increase in capacitor area in a RAM and a decrease in aperture ratio in a liquid crystal display device cannot be ignored. The present invention solves the above problems.

[0011]

As one of the solutions to this problem, the present inventors set the channel length (distance between the source region and the drain region) of the gate electrode in the insulated gate field effect transistor. By forming the offset region in the channel region that is in contact with the source region or the drain region, the offset region where no electric field is applied or very weak is formed by the gate electrode by making the offset voltage longer than the length in the direction. It was found that the characteristics were taken.

The basic configuration of the present invention is shown in FIG. A blocking layer 104 is provided on an insulating substrate 105, and a source region 100 and a drain region 10 are provided as semiconductor layers on the blocking layer 104.
1 and the channel region 109 are provided. Formed on the channel region 109 is a gate insulating film 110, and a gate electrode 111 on which an anodizable material is anodized to form an oxide layer 112 as an insulating layer. The source electrode 102 is in contact with the source region and the drain region,
A drain electrode 103 is provided. In FIG. 1, the interlayer insulator is not particularly provided. However, when the parasitic capacitance between the gate electrode / wiring and the source / drain electrode / wiring becomes a problem, the interlayer insulator is used as usual. May be provided, examples of which are described below in Examples 1-3.

As shown in FIG. 1, a material that can be anodized is selected for the gate electrode portion to be the gate electrode 111 and the oxide layer 112, and the surface portion thereof is anodized to form the oxide layer 112. The distance between the source region 100 and the drain region 101, which is an ion implantation region, that is, the channel length 108 is approximately twice as long as the thickness of the oxide layer 112 than the substantial length of the gate electrode 111 in the channel length direction. Become. Materials for the gate electrode portion are mainly titanium (Ti), aluminum (Al), tantalum (T
a), chromium (Cr), silicon (Si) simple substance, or alloys thereof are suitable.

As a result, no electric field from the gate electrode is applied to the portions 106 and 107 in the channel region 109 facing the oxide layer 112 formed on both sides of the gate electrode via the gate insulating film 110, or the portions of the gate electrode are not formed. It is much weaker than the vertical bottom. Hereinafter, such regions 106 and 107 will be referred to as offset regions especially when they have the same crystallinity and impurity concentration as those of the channel region.

Further, the regions 106 and 107 may be made of an impurity-doped amorphous material. Strictly arguing, the regions 106 and 107 have only to have poorer crystallinity than the source region 100 and the drain region 101 adjacent thereto. For example, if the regions 100 and 101 are made of polycrystalline silicon with large crystal grains, the regions 106 and 107 may be amorphous silicon or so-called semi-amorphous silicon that has slightly better crystallinity than amorphous silicon. Area 100, 1
If 01 is semi-amorphous silicon, region 10
6 and 107 may be amorphous silicon. Of course, it is necessary to take sufficient measures for such amorphous materials to show semiconductor electrical characteristics. For example, hydrogen or halogen may be sufficient for these dangling bonds so that the dangling bonds are reduced as much as possible. Need to be terminated.

By providing such an amorphous region, good TFT characteristics could be exhibited as shown in FIG. 9 (a). FIG. 9B shows a thin film transistor (TFT) having a conventional insulated gate type transistor structure, and as is clear from the figure, a remarkable reverse leakage current was observed by the conventional method. like,
By providing a region that is substantially amorphous,
The properties were improved. That is, providing the impurity region in the amorphous state has the same effect as providing the offset region described above.

The reason why the characteristics are improved by providing such an amorphous region is not yet well understood. One is that the non-crystalline region has a lower ionization rate of the added impurity element than the crystalline region, and therefore has a lower impurity concentration even when the same amount of impurity is added. Since it behaves as if it were, it is considered that a region substantially the same as a so-called low concentration drain (Lightly-Doped-Drain: LDD) was formed. For example,
In the amorphous state, the ionization rate of silicon is 0.1 to 10% at room temperature, which is remarkably smaller than that of a single crystal or polycrystalline semiconductor (almost 100%).

Alternatively, the bandgap in the amorphous state is larger than that in the crystalline state, and this may be the cause. For example, it can be explained from the energy band diagrams as shown in FIGS. 9 (e) and 9 (f). In a normal LDD structure transistor, the energy band diagrams of the source / channel / drain are as shown in FIGS. 9C and 9D. The raised area in the center is the channel region. The stepped portion is the LDD region. As shown in FIG. 9C when no voltage is applied to the gate electrode, when a large negative voltage is applied to the gate electrode,
As shown in FIG. 9D. At this time, although there is a forbidden band between the source and the channel region and between the channel region and the drain, carriers such as electrons and holes cannot move, but the tunnel effect or the trap level in the band gap is hopped. Carrier jumps over the gap. In a normal TFT that does not have the LDD structure, the width of the gap is smaller, so that the current easily flows. This is believed to be a reverse leak. This decrease is particularly remarkable in the TFT. It is presumed that this is because the TFT is an inhomogeneous material such as polycrystal and therefore has many trap levels due to grain boundaries and the like.

On the other hand, increasing the bandgap in the LDD region reduces such reverse leakage. Examples of large LDD band gaps are shown in FIGS. 9 (e) and 9 (f).
Shown in. 9E shows a state in which no voltage is applied to the gate, and FIG. 9F shows a state in which a large negative voltage is applied to the gate. As is clear from (f), the source and channel regions when a negative voltage is applied as compared with (d),
Alternatively, the width of the gap between the channel region and the drain is large. The tunnel effect is significantly affected by the width of the tunnel barrier (in this case the width of the gap), and a small increase in the width of the gap significantly reduces its probability. Also, hopping via localized levels is a complex tunnel effect, so the probability decreases dramatically as the width of the gap increases. For the above reasons, it is considered significant to form an LDD region having a large band gap. The band gap of polycrystalline silicon is 1.1 eV, whereas the band gap of amorphous silicon is 1.5 to 1.8 eV. It is extremely difficult to use a material having such a wide band gap for LDD. Ideal.

In order to manufacture the semiconductor device having the above-described offset region according to the present invention, the gate electrode portion is made of a material that can be anodized after forming the semiconductor layer to be the source, drain and channel regions and the gate insulating film layer 110. Then, impurity ions for making the semiconductor layer p-type or n-type are implanted to form the source region 100 and the drain region 101, and then the surface portion of the gate electrode portion is anodized to oxidize with the gate electrode 111. Layer 1
12 may be formed and a heat treatment process or the like may be performed.

Alternatively, after the semiconductor layer and the gate insulating film layer 110 are formed, a gate electrode portion is formed of a material that can be anodized, and then the surface portion of the gate electrode portion is anodized to form the gate electrode 111 and the oxide layer 112. Form,
After that, a step of performing a heat treatment step may be performed after implanting impurity ions that make the semiconductor layer p-type or n-type to form the source region 100 and the drain region 101.

By taking the steps as described above, an insulated gate field effect transistor having a channel length longer than the length of the gate electrode in the channel length direction can be easily and surely produced without causing performance variations due to mask shift or the like. It becomes possible to manufacture it.

Alternatively, in order to manufacture a semiconductor device of the present invention having an amorphous region, a semiconductor layer to be a source, a drain, a channel region and a gate insulating film layer 110.
After forming the gate electrode portion with a material capable of anodic oxidation, impurity ions for making the semiconductor layer p-type or n-type are implanted to amorphize the semiconductor layer to form the source region 100 and the drain. The region 101 and the amorphous regions 106 and 107 adjacent thereto are formed, and then the surface portion of the gate electrode portion is anodized to form the gate electrode 111 and the oxide layer 112. At this time, the surface of the gate electrode recedes due to oxidation. After that, only the source region 100 and the drain region 101 may be recrystallized in a self-aligned manner by using the gate electrode portion as a mask by, for example, a laser annealing method or a flash lamp annealing method. Here, the reason for being self-aligned is that the impurity region existing therebelow cannot be recrystallized because the gate electrode portion becomes a shadow.

For example, when the ion implantation method is used, the spread of the impurity region due to the secondary scattering of ions is
It can be calculated by the acceleration energy of ions, etc.
Since the recession of the gate electrode is determined by the thickness of the oxide layer, this is also included as a design matter. Therefore, according to the present invention, the positional relationship between the gate electrode and the impurity region can be optimized by a precise design.
That is, the thickness of the oxide layer can be controlled with an accuracy of 10 nm or less, and the secondary scattering at the time of ion implantation can be controlled with the same degree, so that this positional relationship can be manufactured with an accuracy of 10 nm or less. ..

As described above, according to the present invention, precise mask alignment is not newly required, and the present invention hardly lowers the yield. In addition, the characteristics of the transistor obtained by the present invention are greatly improved. Examples will be shown below.

【Example】

Example 1 In this example, a viewfinder for a video camera using a liquid crystal electro-optical device having a diagonal of 1 inch was manufactured and the present invention was carried out.

In this embodiment, a viewfinder is constructed by forming a device using a high mobility TFT (thin film transistor) by the low temperature process having the constitution of the present invention with a constitution of 387 × 128 pixels. FIG. 7 shows the arrangement of the active elements on the substrate of the liquid crystal display device used in this embodiment, and FIG. 6 shows the circuit diagram of this embodiment. A manufacturing process showing the AA ′ cross section and the BB ′ cross section of FIG. 7 is drawn in FIG. 8. AA 'cross section shows NTFT, BB'
The cross section shows PTFT.

In FIG. 8A, an inexpensive glass substrate 4 that can withstand a heat treatment at 700 ° C. or lower, for example, about 600 ° C.
On a silicon oxide film as a blocking layer 401 by using a magnetron RF (radio frequency) sputtering method.
Produce to a thickness of ~ 3000Å. Process condition is oxygen 1
00% atmosphere, film forming temperature 150 ° C., output 400 to 800
W and pressure were 0.5 Pa. The film formation rate using quartz or single crystal silicon for the target was 30 to 100 Å / min.

A silicon film was formed thereon by LPCVD (Low Pressure Vapor Phase) method, sputtering method or plasma CVD method. When forming by the reduced pressure vapor phase method, it is 1 more than the crystallization temperature.
450 to 550 ° C, which is lower than 00 to 200 ° C, for example, 530 ° C
CVD of disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) with
The film was supplied to the apparatus to form a film. The reactor pressure is 30-300
It was Pa. The film forming rate was 50 to 250 Å / min.
Threshold voltage (Vt) between PTFT and NTFT
In order to control the concentration to be substantially the same as that of h), boron may be added during film formation using diborane at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ .

When the sputtering method is used, the back pressure before the sputtering is set to 1 × 10 ^-5 Pa or less, the single crystal silicon is used as the target, and the argon is mixed with hydrogen in an amount of 20 to 80%. For example, argon was 20% and hydrogen was 80%.
The film forming temperature was 150 ° C., the frequency was 13.56 MHz, the sputter output was 400 to 800 W, and the pressure was 0.5 Pa.

When a silicon film is formed by the plasma CVD method, the temperature is, for example, 300 ° C., and monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used. These were introduced into a PCVD apparatus, and high frequency power of 13.56 MHz was applied to form a film.

The coatings formed by these methods are
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. If this oxygen concentration is high, it is difficult to crystallize and the thermal annealing temperature must be high or the thermal annealing time must be long.
If it is too low, the backlight will turn off the light.
The current will increase. Therefore 4 × 10 ¹⁹ to 4 × 10 ²¹
The range was cm ^-3 . Hydrogen is 4 × 10 ²⁰ cm ^-3 and silicon 4
It was 1 atom% when compared as × 10 ²² cm ^-3 .

By the above method, a silicon film in an amorphous state is formed to a thickness of 500 to 5000 Å, for example 1500 Å, and then a heat treatment of medium temperature in a non-oxide atmosphere for 12 to 70 hours at a temperature of 450 to 700 ° C., For example, it was held at a temperature of 600 ° C. under a hydrogen atmosphere. Since the silicon oxide film having an amorphous structure is formed on the surface of the substrate below the silicon film, no specific nuclei are present in this heat treatment and the whole is uniformly annealed by heating. That is, it has an amorphous structure during film formation, and hydrogen is simply mixed therein.

The annealing causes the silicon film to shift from an amorphous structure to a highly ordered state, and a part thereof exhibits a crystalline state. Particularly, in the state after the film formation of silicon, a region having a relatively high order is particularly crystallized and tends to be in a crystalline state. However, since silicon existing between these regions is bonded to each other, the silicon members pull each other. Peak 522 of single crystal silicon as measured by laser Raman spectroscopy
Peaks shifted to lower frequencies than cm ^-1 are observed. The apparent particle size is 50 to 5 when calculated from the half width.
Although it is a microcrystal like 00Å, in reality there are many highly crystalline regions with a cluster structure, and each cluster has a semi-amorphous structure in which silicon is bonded (anchoring) with each other. Could be formed.

As a result, the film exhibits a state in which it can be said that it is substantially free of grain boundaries (hereinafter referred to as GB). Since the carriers can easily move between the clusters through the anchored portions, the carrier mobility becomes higher than that of polycrystalline silicon in which so-called GB is clearly present. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² /
VSec, electron mobility (μe) = 15 to 300 cm ² / V
Sec is obtained.

On the other hand, the film may be polycrystallized by a high temperature anneal of 900 to 1200 ° C. instead of the anneal at a medium temperature as described above, but in that case, the film in the film may be polycrystallized by solid phase growth from the nucleus. Segregation of impurities occurs, oxygen is present in GB,
Although impurities such as carbon and nitrogen increase, the mobility in the crystal is high, but a barrier is created in GB, which hinders the movement of carriers there. As a result 10 cm ² / Vsec
In reality, it is difficult to obtain the above mobility. Therefore, it is necessary to set the concentration of impurities such as oxygen, carbon, and nitrogen to one-several to several tenths of that of semi-amorphous ones. If you do so, 50-100 cm ² / Vse
c was obtained.

The silicon film thus formed was photoetched to form a semiconductor layer 402 for NTFT (channel width 20 μm) and a semiconductor layer 404 for PTFT.

A silicon oxide film 4 serving as a gate insulating film is formed on this.
03 was formed to a thickness of 500 to 2000Å, for example 1000Å. This was performed under the same conditions as the production of the silicon oxide film as the blocking layer. A small amount of fluorine may be added during film formation to immobilize sodium ions.

After that, an aluminum film was formed on the upper side. This is patterned with a photomask and shown in FIG.
(B) was obtained. A gate insulating film 405 for the NTFT and a gate electrode portion 406 were formed, and the length of both of them was 10 μm, that is, the channel length was 10 μm. Similarly, the gate insulating film 407 for the PTFT and the gate electrode portion 4
No. 08 was formed, and the length of both of them in the channel length direction was 7 μm, that is, the channel length was 7 μm. The thickness of both gate electrode portions 406 and 408 was 0.8 μm. In FIG. 8C, boron (B) was added to the source 409 and the drain 410 for the PTFT by an ion implantation method at a dose amount of 1 to 5 × 10 ¹⁵ cm ⁻² . Next, FIG.
As shown in (D), a photoresist 411 was formed using a photomask. As a source 412 and a drain 413 for NTFT, phosphorus (P) was added by an ion implantation method at a dose amount of 1 to 5 × 10 ¹⁵ cm ^-2 .

After that, the gate electrode portion was anodized. L-tartaric acid was diluted with ethylene glycol at a concentration of 5% and the pH was adjusted to 7.0 ± 0.2 with ammonia. The substrate was dipped in the solution, the + side of the constant current source was connected, the platinum electrode was connected to the − side, a voltage was applied in a constant current state of 20 mA, and oxidation was continued until reaching 150 V. Furthermore, at constant voltage at 150V, add 0.1mA
Oxidation was continued until: In this way, the aluminum oxide layer 4 is formed on the surfaces of the gate electrode portions 406 and 408.
14 is formed, and the gate electrode 415 for NTFT and PTF are formed.
A gate electrode 416 for T was obtained. Aluminum oxide layer 4
14 was formed to a thickness of 0.3 μm.

Next, heating anneal was performed again at 600 ° C. for 10 to 50 hours. The source 412 and the drain 413 of the NTFT, the source 409 and the drain 410 of the PTFT were prepared as N ⁺ and P ⁺ by activating impurities. A channel forming region 41 is formed under the gate insulating films 405 and 407.
7, 418 are formed as semi-amorphous semiconductors.

In this manufacturing method, the order of ion implantation of impurities and anodic oxidation around the gate electrode may be exchanged. By forming the insulating layer made of metal oxide around the gate electrode in this manner, the substantial length of the gate electrode is twice the thickness of the insulating film rather than the channel length.
The length was shortened by 6 μm, and the leak current at the time of reverse bias could be reduced by providing the offset region where no electric field is applied.

In this embodiment, the thermal anneal is as shown in FIG.
(E) performed twice. However, the anneal of FIG. 8 (A) may be omitted depending on the desired characteristics, and both may be combined with the anneal of FIG. 8 (E) to reduce the manufacturing time. In FIG. 8E, the interlayer insulator 419 was formed as a silicon oxide film by the above-described sputtering method. The silicon oxide film may be formed by using the LPCVD method, the photo CVD method, or the atmospheric pressure CVD method. The interlayer insulator is 0.2 to 0.6 μm, for example 0.3.
It was formed to a thickness of μm, and then a window 420 for an electrode was formed using a photomask. Further, as shown in FIG. 8 (F), aluminum is formed on the entire surface by a sputtering method, leads 421, 423, and contacts 422 are formed using a photomask, and then the surface is planarized with an organic resin 424 such as a light-transmitting material. Coating polyimide resin,
The re-drilling of electrodes was performed with a photomask.

ITO (indium tin oxide film) was formed by a sputtering method so that the two TFTs have a complementary structure and the output terminal thereof is connected to the electrode of one pixel of the liquid crystal device as a transparent electrode. It was etched with a photomask to form an electrode 425. This IT
O was formed into a film at room temperature to 150 ° C., and was accomplished by oxygen at 200 to 400 ° C. or anneal in the atmosphere. In this way, the NTFT 426, the PTFT 427, and the transparent conductive film electrode 425 were formed on the same glass substrate 401. The electric characteristics of the obtained TFT are PTFT and the mobility is 20.
(Cm ² / Vs), Vth was −5.9 (V), mobility was 40 (cm ² / Vs) in NTFT, and Vth was 5.0 (V).

One substrate for a liquid crystal device was produced according to the method as described above. The arrangement of electrodes and the like of this liquid crystal display device is shown in FIG. NTFT 426 and PTFT 42
7 is provided at the intersection of the first signal line 428 and the second signal line 429. A matrix structure using such C / TFT is provided. The NTFT 426 has a drain 413
Is connected to the second signal line 429 via the lead 421 at the input end of the gate, and the gate 406 is connected to the signal line 428 on which the multilayer wiring is formed. The output end of the source 412 is connected to the pixel electrode 425 via a contact 422.

On the other hand, in the PTFT 427, the input end of the drain 410 is connected to the second signal line 429 via the lead 423, and the gate 408 is connected to the signal line 428 and the source 409.
The output end of is connected to the pixel electrode 425 via the contact 422 as in the NTFT. This embodiment is constructed by repeating such a structure horizontally and vertically.

Next, as a second substrate, ITO (injected) was also formed by sputtering on a substrate in which a silicon oxide film was laminated to 2000 liters on a soda-lime glass by sputtering.
A tin oxide film) was formed. This ITO is room temperature ~ 15
The film was formed at 0 ° C. and was accomplished by oxygen at 200 to 400 ° C. or an anneal in the atmosphere. Further, a color filter was formed on this substrate to obtain a second substrate.

Then, a 6: 4 mixture of an ultraviolet curable acrylic resin and a nematic liquid crystal composition was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. The pitch of the leads on the substrate is 46 μm
Therefore, the connection was made using the COG method. In this embodiment, the gold bumps provided on the IC chip are connected by an epoxy-based silver-palladium resin, and the IC chip and the substrate are embedded and fixed by epoxy modified acrylic resin for the purpose of fixing and sealing. I was there. Then, a polarizing plate was attached to the outside to obtain a transmissive liquid crystal display device.

[Embodiment 2] FIG. 10 shows a sectional view of the present embodiment. First, Corning 7059 glass was used as the substrate 501. Then, the underlying silicon oxide film 502 was formed to a thickness of 100 nm by a sputtering method. Further, the amorphous silicon film 503 is plasma CV
Only 50 nm was formed by the D method. A silicon oxide film 504 was formed thereon with a thickness of 20 nm by the sputtering method for the purpose of protecting the amorphous silicon film. This was annealed at 600 ° C. for 72 hours in a nitrogen atmosphere for recrystallization. Further, this was patterned by a photolithography method and a reactive ion etching (RIE) method to form an island-shaped semiconductor region as shown in FIG. After forming the island-shaped semiconductor region, the protective silicon oxide film 504 was removed. For the removal, wet etching was performed using buffer hydrofluoric acid (a solution in which hydrogen fluoride and ammonium fluoride were mixed). As the buffer hydrofluoric acid, for example, high-purity hydrofluoric acid for semiconductor manufacturing (50
wt%) and the same ammonium fluoride solution (40 wt%) were mixed at a ratio of 1:10 to prepare a solution. The etching rate of this buffer hydrofluoric acid for silicon oxide is 7
0 nm / min, the same for aluminum oxide 60 nm / min
Min, 15 nm / min for aluminum.

Further, a gate oxide film 505 is formed by a sputtering method in an oxygen atmosphere targeting silicon oxide.
Was deposited to a thickness of 115 nm. In this state, phosphorus ions were doped into the gate oxide film 505 by the plasma doping method. This is because gettering of mobile ions such as sodium existing in the gate oxide film is not necessary when the concentration of sodium is low enough not to hinder the operation of the device. In this example, the plasma acceleration voltage was 10 keV and the dose amount was 2 × 10 ¹⁴ cm ⁻² . Then, annealing was performed at 600 ° C. for 24 hours, and an oxide film formed by the impact of plasma doping,
Recovered damage to the silicon film.

Next, an aluminum film was formed by the sputtering method, and this was patterned with a mixed acid (phosphoric acid solution containing 5% nitric acid) to form a gate electrode / wiring 506. The etching rate was 225 nm / min when the etching temperature was 40 ° C.
In this way, the outer shape of the TFT was adjusted. The size of the channel at this time was 8 μm in length and 20 μm in width.

Next, an N-type impurity region (source, drain) 507 was formed in the semiconductor region by the ion implantation method. Phosphorus ions are used as the dopant, the ion energy is 80 keV, and the dose amount is 5 × 10 ¹⁵ cm ^-2.
And As shown in the figure, the doping was performed by through implantation which penetrates the oxide film and implants impurities. The advantage of using such through-in plastic is
This means that the smoothness of the surface of the impurity region is maintained during the subsequent recrystallization process by laser annealing. If not through-implantation, a large number of crystal nuclei are generated on the surface of the impurity region during recrystallization, and unevenness is generated on the surface.
Thus, the structure as shown in FIG. 10 (B) was obtained. As a matter of course, the crystallinity of the portion into which the impurities are implanted is significantly deteriorated by such ion implantation and is substantially in an amorphous state (amorphous state or a polycrystalline state close to it).

Further, electricity is supplied to the wiring 506, and an aluminum oxide film 508 is formed around the gate electrode / wiring (upper surface and side surface) by the anodic oxidation method. Anodic oxidation is performed by adding 3% tartaric acid in ethylene glycol to 5%.
It was carried out using a solution neutralized with ammonia to a pH of 7.0 ± 0.2. First, platinum is immersed in the solution as a cathode, and further the TFT is immersed in the substrate together with the wiring 506.
Was connected to the anode of the power supply. The temperature was kept at 25 ± 2 ° C.

In this state, a current of 0.5 mA / cm ^{2 was} first applied, and when the voltage reached 200 V, the current was supplied while keeping the voltage constant, and the current was reached when the current reached 0.005 mA / cm ^2. Was stopped and the anodization was completed. The thickness of the anodized film thus obtained was about 250 nm. The situation is shown in FIG.

After that, laser annealing was performed.
The laser used is a KrF excimer laser, for example, 3
10 laser pulses with a power density of 50 mJ / cm ²
Shot irradiation. It has been confirmed that the crystallinity of amorphous silicon can be recovered by at least one laser irradiation to withstand the operation of TFT, but the probability of occurrence of defects due to laser power fluctuation is sufficiently reduced. For this purpose, it is desirable that the laser irradiation is performed a sufficient number of times. However, too many laser irradiations reduce productivity, so
It became clear that the 10 times used in this example are the most desirable.

Laser annealing was carried out under atmospheric pressure in order to enhance mass productivity. Since the silicon oxide film has already been formed on the impurity region, there is no particular problem. Even if laser annealing is performed with the impurity region exposed, at the same time as crystallization, oxygen penetrates into the impurity region from the atmosphere and the crystallinity is not good, so a TFT having sufficient characteristics cannot be obtained. It was Therefore, it is necessary to perform laser annealing in vacuum on the exposed impurity regions.

Further, in this example, as shown in FIG. 10D, the laser beam was obliquely incident. For example, in this example, laser light was emitted at an angle of 10 ° with respect to the vertical line of the substrate. The angle is determined according to the design specifications of the device to be manufactured. By doing this,
A region of the impurity region to be crystallized can be made asymmetric by the laser. That is, area 5 in the figure
Reference numerals 09 and 510 are impurity regions that are sufficiently crystallized.
The region 511 is not an impurity region but a region crystallized by laser light. The region 512 is an impurity region but is not crystallized. For example, as shown in FIG.
The impurity region on the right side of 0 (D) may be used.

In this way, the shape of the device was adjusted. After that, as usual, an interlayer insulator is formed by sputter deposition of silicon oxide, an electrode hole is formed by a known photolithography technique, and the surface of the semiconductor region or the gate electrode / wiring is exposed. Then, a metal film was selectively formed to complete the device.

Example 3 TF obtained by the present invention
At T, not only the off current, but also the breakdown voltage between the source / drain and the operating speed change depending on the width of the amorphous semiconductor region and the offset region. Therefore, for example, by optimizing parameters such as the thickness of the anodic oxide film and the ion implantation energy, a TFT can be manufactured according to the purpose. However, these parameters are generally not adjustable for individual TFTs formed on a single substrate. For example, in an actual circuit, it is possible to operate on a single substrate at a low speed
FT and TFT that may have low breakdown voltage but require high speed operation
It may be desired that and are formed simultaneously. Generally, in the present invention, as the width of the offset region or the width of the amorphous impurity semiconductor region is larger, the off current is smaller and the withstand voltage is improved, but there is a drawback that the operation speed is reduced.

The present embodiment shows an example for solving such a problem. This embodiment is shown in FIG. 11 (top view) and FIG. 12 (cross-sectional view). In the present embodiment, Japanese Patent Application No. 3-29633.
The present invention relates to the fabrication of a circuit used in an image display method using a P-channel TFT and an N-channel TFT for driving one pixel (such as a liquid crystal pixel) as described in 1. Here, the N-channel TFT is required to have a high speed, and the breakdown voltage does not matter so much. On the other hand, the operating speed of the P-channel TFT is not so important, but it is required that the off-current is low and that the withstand voltage is good in some cases. Therefore, N channel T
FT has a thin anodic oxide film (20 to 100 nm), and P-channel TFT has a thick anodic oxide film (250 to 400 nm).
Is desired. The manufacturing process will be described below.

Corning 705 as in Example 2
N-type impurity region 602, P-type impurity region 603, gate insulating film 604, gate electrodes / wirings 606 and 607 were formed using substrate 9 as substrate 9. Both the gate electrode and the wiring are connected to the wiring 650. (FIG. 11 (A), FIG.
2 (A))

Furthermore, gate electrodes / wirings 606 and 607
Electricity was applied to the film and aluminum oxide films 613 and 614 were formed around the gate electrodes / wirings 606 and 607 (upper and side surfaces) by anodization. Anodization was performed under the same conditions as in Example 2. However, the maximum voltage is 5
It was set to 0V. Therefore, the thickness of the anodic oxide film produced in this step is about 60 nm. (Fig. 12 (B))

Next, as shown by 651 in FIG. 11B, the gate electrode / wiring 606 was separated from the wiring 650 by laser etching. Then, in this state, anodic oxidation was started again. The conditions were the same as before, but at this time the maximum voltage was raised to 250V. As a result, no current flowed through the wiring 606, and no change occurred. However, since current flows through the wiring 607, an aluminum oxide film having a thickness of about 300 nm was formed around the gate wiring 607. (Fig. 12 (c))

After that, laser annealing was performed.
The conditions were the same as in Example 2. In this case, the width a ₁ of the amorphous region and the offset region of the N-channel TFT (left side of FIG. 12) is so small that it can be ignored.
If the surface of the aluminum wiring is not covered with the anodic oxide film, the laser beam irradiation causes significant damage, so that it is necessary to form the anodic oxide film even if it is thin. On the other hand, P-channel TFT (right side of FIG. 12)
Had an anodized film thickness of 300 nm and an amorphous region of 150 to 200 nm. It is also estimated that the width a _{2 of the} offset region was 100 to 150 nm.
(Figure 12 (D))

As in the case of the second embodiment, the necessary portions of the aluminum wiring are etched by laser irradiation in the atmosphere, and the gate electrode of the P-channel TFT is wired 60.
7 and the wiring 650 was cut. further,
An interlayer insulating film was formed, contact holes were formed, and wirings 624 and 611 were formed. In this way, the circuit was formed.

In the circuit thus manufactured, the N-channel TFT was excellent in high speed although the width of the offset region and the non-crystalline region was small and the off current was slightly large. On the other hand, the P-channel TFT was difficult to operate at high speed, but had a small off-current and was excellent in the ability to retain the charge accumulated in the pixel capacitor.

In this way, different T functions are provided on one substrate.
There are other cases where FTs must be integrated. For example, in a liquid crystal display driver, a high speed TFT is used in a logic circuit such as a shift register and a high breakdown voltage T is used in an output circuit.
FT is required. T according to such conflicting purposes
The method shown in this embodiment is effective for manufacturing FT.

[Embodiment 4] Using the manufacturing method used in Embodiment 1 of the present invention, an active matrix circuit including N-channel TFTs as shown in FIG. 13 was manufactured. That is, the active matrix is the gate line 7
01 and data lines 702, both of which are made of low-resistance aluminum, but have a thickness of 200 to 400 n because they have undergone the anodization process of the present invention.
m aluminum oxide. The width of these lines was 2 μm. The thickness was 0.5 μm. The gate line is provided with a gate electrode 703 of the TFT of each pixel. This is likewise coated with aluminum oxide. A semiconductor layer 704 is formed under the gate electrode, and the N-channel TF of Example 1 is formed.
Similar to T, there is an N-type polycrystalline impurity region doped with phosphorus, and the offset region, which is a feature of the present invention, is designed to have a width of about 200 to 400 nm. The source of this semiconductor layer is the data line 70.
2, while the drain is provided with the display pixel electrode (made of ITO) 70 through the aluminum electrode 705.
Connected to 6.

FIG. 14 shows a circuit diagram of the active matrix device manufactured in this embodiment, an operation of the device of this embodiment, and an operation of a device using a TFT manufactured by a conventional method for comparison. It is a thing. As I mentioned earlier,
In the matrix having such a structure, when charging of the capacitor C _LC is completed and the gate voltage is turned off, the capacitor C _LC is connected to the gate line and the capacitance via the parasitic capacitance C _GD of the gate and the drain. It is known that when they are coupled, the voltage drops by ΔV from the charging voltage. This phenomenon is the same even in the circuit in which the N-channel TFT and the P-channel TFT are connected in parallel as in the first embodiment. For details, refer to Japanese Patent Application No.
-208648.

As shown in FIG. 14, in a circuit consisting of either N-channel or P-channel TFTs, the voltage drop ΔV is represented by ΔV = C _GD · V _G / (C _LC + C _GD ). Here, V _G is the gate voltage ON
It is the fluctuation range from the voltage to the OFF voltage. For example, in a TFT manufactured without using self-alignment, since the parasitic capacitance C _GD is extremely large, ΔV also becomes large, and in order to overcome this, the storage capacitor C _AD is formed in parallel with the pixel capacitor as shown in FIG. However, the capacitance of the pixel capacitor was apparently increased. However, as described above, such measures do not essentially solve the problem and newly cause problems such as a decrease in aperture ratio.

Even if the device is manufactured by the self-alignment method,
This voltage drop becomes a serious problem when the size of the pixel becomes small and the parasitic capacitance of the TFT cannot be ignored compared to the pixel capacitor. For example, in a 3-inch diagonal high-definition panel (for projection), the pixel capacitance is as small as 13 fF. On the other hand, when the TFT is manufactured by adopting the 2 μm rule in the process, the aspect ratio of the wiring is large, and the parasitic capacitance is generated in a three-dimensional geometrical shape even if there is no planar overlap, and the size thereof is several. It also becomes fF. That is, it reaches 10% or more of the capacity of the pixel capacitor.

FIG. 14A shows an example of an active matrix using a conventional TFT. Obviously, ΔV makes it impossible to display as it should be. That is,
In order to operate the TFT at high speed, the gate voltage is required to be higher than the drain voltage. Normally, a voltage about twice the drain voltage is adopted as the gate voltage. Therefore, if the drain voltage is 5V, the gate voltage is 10V or higher. Further, when the gate voltage is made negative in the OFF state for the purpose of perfecting the operation of the TFT, the change in the gate voltage becomes larger. For example, in the case of FIG. 14, the drain voltage is an alternating current of ± 6 V, but the gate voltage is +12 V in the ON state and −4 V in the OFF state. Therefore, V _G = 1 in the above equation.
It becomes 6V. If the parasitic capacitance is 2 fF, FIG.
As shown in, ΔV is 2V, which is 1/3 of the drain charging voltage. Of course, since the electric charges accumulated in the pixels are discharged by the natural discharge, it is actually difficult to ideally perform the display. Then, in order to avoid such a problem, it is necessary to sacrifice the aperture ratio and provide a storage capacitor.

On the other hand, when the present invention is applied, the parasitic capacitance can be significantly reduced. Specifically, it can be 0.1 fF or less. Therefore, ΔV can be almost ignored as shown in FIG. Further, in the present invention, O
Since the FF current is about one digit smaller than that of the TFT manufactured by the conventional method, the spontaneous discharge is much slower, and the display can be ideally performed.

[0074]

As described above, according to the present invention, by providing the insulating film layer of anodic oxidation on the surface of the gate electrode, the channel length becomes longer than the length of the gate electrode in the channel length direction, and both sides of the channel region are formed. It is possible to provide an offset region where no electric field is applied or a very weak electric field is applied by the gate electrode, or an amorphous impurity semiconductor region having a similar effect can be provided by a similar method. Could be reduced. As a result, the charge holding capacity, which was indispensable in the past, is no longer needed, and the aperture ratio, which was around 20% in the past, is reduced to
It is possible to achieve the above or more, and it is possible to obtain a better display quality.

In the present invention, since the offset region or the amorphous impurity region is determined by the thickness of the anodic oxide film of the gate electrode, the width of these regions is 10-100.
It can be controlled very precisely between nm. In addition, the addition of this process did not cause any significant reduction in yield, and there was no factor considered to be the cause of the reduction in yield.

Although the present invention has been mainly described with respect to a silicon-based semiconductor device, it is obvious that the present invention can be applied to a semiconductor device using another material such as germanium, silicon carbide or gallium arsenide.

[Brief description of drawings]

FIG. 1 shows a structure of a semiconductor device according to the present invention.

FIG. 2 shows a structure of a semiconductor device according to a conventional example.

FIG. 3 shows current-voltage characteristics of a conventional semiconductor device.

FIG. 4 shows current-voltage characteristics of the semiconductor device according to the present invention.

FIG. 5 shows a circuit configuration of an active matrix type liquid crystal electro-optical device according to a conventional example.

FIG. 6 is a circuit diagram of an active matrix liquid crystal electro-optical device according to a first exemplary embodiment.

FIG. 7 shows a structure of an active matrix type liquid crystal electro-optical device in Example 1.

FIG. 8 shows a process of manufacturing an active matrix type liquid crystal electro-optical device in Example 1.

FIG. 9 shows a characteristic example of a TFT according to the present invention and its operating principle.

FIG. 10 is a sectional view showing an example of manufacturing steps of a TFT according to the second embodiment.

FIG. 11 shows a top view of an example of a manufacturing process of a TFT according to the third embodiment.

FIG. 12 is a sectional view showing an example of a manufacturing process of a TFT according to the third embodiment.

FIG. 13 shows a structure of an active matrix type liquid crystal electro-optical device in Example 4.

FIG. 14 shows a circuit diagram and an operation of an active matrix electro-optical device according to a fourth embodiment.

[Explanation of symbols]

 105,209 Insulating substrate 104,208 Blocking layer 109,203 Channel region 108,210 Channel length 100,204 Source region 101,205 Drain region 110,202 Gate insulating film 111,201 Gate electrode 112 Oxide layer 211 Interlayer insulating film 102 , 206 source electrode 103, 207 drain electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Takemura, 398 Hase, Atsugi, Kanagawa Prefecture, Semiconducting Energy Laboratory Co., Ltd.

Claims (8)

[Claims] 1. A semiconductor device having an insulating gate field effect transistor having at least a semiconductor layer, an insulating film layer and a conductor layer on an insulating substrate, wherein a channel length is longer than a length of a gate electrode in a channel length direction. . 2. A semiconductor device according to claim 1, wherein the channel length is longer than the length of the gate electrode in the channel length direction by about twice the thickness of the oxide layer formed on the surface of the gate electrode. 3. A method of manufacturing an insulating gate type field effect transistor having at least a semiconductor layer, an insulating film layer and a conductor layer on an insulating substrate, wherein a gate electrode is made of a material which can be anodized after forming the semiconductor layer and the gate insulating film layer. Forming a source or drain region by implanting impurity ions for making the semiconductor layer p-type or n-type after forming the portion, and then performing a heat treatment process after the surface is anodized. A method for manufacturing a semiconductor device, comprising: 4. A metal gate electrode, an anodic oxide layer formed so as to surround the gate electrode, a thin film channel region, and a pair of first impurity regions formed so as to sandwich the channel region. And a second impurity region adjacent to each first impurity region, a thin-film insulating gate type semiconductor device. 5. An insulating gate type semiconductor device according to claim 4, wherein the first impurity region is in an amorphous state. 6. The semiconductor device according to claim 1, wherein the semiconductor device is formed on the insulating substrate, and one of a source and a drain of the semiconductor device is connected to a capacitor element. 7. The semiconductor device according to claim 6, wherein the semiconductor device is used for driving a pixel of a liquid crystal display device. 8. The semiconductor device according to claim 4, wherein the semiconductor device is formed on an insulating substrate, and one of a source and a drain of the semiconductor device is connected to a capacitor element.