JPH0883914A - Polycrystalline semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a polycrystalline semiconductor device in which operating characteristics such as a threshold voltage are accurately controlled to be uniform and its mobility is high and high speed responding characteristics are excellent in the device used as a circuit element for forming a pixel switching element or a driving circuit of, for example, an active matrix type liquid crystal display unit. CONSTITUTION: The hydrogen concentration of an active region in which the current of a channel region 108 of an a-Si:H film 103 flows is formed in lower concentration distribution than the hydrogen concentration in a deeper region than the active region. Thus, the threshold voltage and the operating characteristics of a semiconductor device are accurately controlled to be uniform, and its field effect mobility is high, and the responding characteristics are excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline semiconductor device and its manufacturing method.

[0002]

2. Description of the Related Art In recent years, a laser annealing technique has been developed for producing a polycrystalline semiconductor film having high field effect mobility by crystallizing an amorphous silicon film by irradiating an excimer laser beam to polycrystal silicon. There is. A poly-silicon thin film transistor (Poly-Silicon Thin Film T
It is possible to form a transistor (hereinafter abbreviated as p-SiTFT) on a glass substrate at a low temperature of 450 ° C. or lower.

When such a p-SiTFT is used to form, for example, a drive circuit of an active matrix type liquid crystal display device or a TFT element array of a pixel portion, the individual TFTs are used as the TFTs forming the drive circuit. The operation characteristics are stable, and it is required that the TFT array as a whole has uniform and highly accurate operation characteristics.

However, in the conventional p-Si TFT, it was not possible to form a sufficiently uniform and highly accurate polycrystalline silicon film by the laser annealing method from the viewpoint of its manufacturing method. Therefore, there is a problem in that the operating characteristics of a TFT using a polycrystalline silicon film which has such a large amount of variation and is non-uniform and of low precision are varied and non-uniform. As a result, for example, when the above TFT is used in the pixel section switching element or the driving circuit of the active matrix type liquid crystal display device having several hundreds of thousands of pixels or more, the display image of the liquid crystal display device is a display with uneven display. There was a problem that the quality was extremely low.

By the way, when the amorphous silicon thin film is formed by using a low temperature process of about 450 ° C. which can use a glass substrate, a plasma CVD method is generally used. In the amorphous silicon film formed by this plasma CVD method, generally 1 × 10 ²¹ pieces / cm 2
Includes hydrogen of ³ or more to about 2 × 10 ²¹ (“degree”)
This is because there is some variation in the left column depending on the film forming conditions, etc., but the order of the numerical values is 1 × 10 ²¹ pieces / cm ³ or more as shown in the left column).

When such a hydrogenated amorphous silicon film is irradiated with a laser beam having a high energy density, hydrogen in the film is instantaneously released, and the film in the vicinity of the film is ablated. As a result, the surface and film quality of the hydrogenated amorphous silicon film are roughened, and there is a problem that a TFT cannot be manufactured using this hydrogenated amorphous silicon film.

[0007] Conventionally, such a-containing a large amount of hydrogen
The laser annealing method for the Si: H thin film is as follows: (1) Thermal annealing is performed at 450 ° C. for about 1 hour before laser annealing to desorb hydrogen in the film, and then laser annealing is performed to crystallize.

(2) A method of forming a p-Si film by irradiating a laser beam with a low energy density to release hydrogen, and then irradiating with a high energy density to crystallize the film twice. However, there were two main methods used.

[0009]

[Problems to be Solved by the Invention] However, (1)
The above method has a problem that throughput is poor. Further, in the thermal annealing step, the H concentration is lowered almost uniformly in the depth direction, and as a result, the hydrogen distribution of the obtained p-Si film is also uniform and low, and the energy level of the p-Si film is low. Since it becomes unstable, the T formed using this
We have confirmed that there is a problem that the operating characteristics of the FT element array are non-uniform and low-precision over the entire array.

Further, according to the method (2), since it is possible to suppress the ablation of the film, it is possible to obtain a uniform p-Si film, but at this time the grain size of the p-Si film becomes small. However, there is a problem in that the field effect mobility μ _{FE of} the TFT using this p-Si film is low and the operating characteristics are poor.

As described above, the polycrystalline semiconductor device according to the conventional technique has a large variation in characteristics, is non-uniform, and has low accuracy. For example, when it is formed as a TFT, operating characteristics such as field-effect mobility. There was a problem of low.

The present invention has been made to solve such a problem, and its purpose is to be used as, for example, a pixel element switching element of an active matrix type liquid crystal display device or a circuit element constituting a driving circuit. In the crystalline semiconductor device, the operating characteristics such as the threshold voltage are controlled with high accuracy to be stable and uniform in the entire array, and the field effect mobility is also high, and the high speed response characteristics are excellent. Providing a polycrystalline semiconductor device,
Another object of the present invention is to provide a method for manufacturing a polycrystalline semiconductor layer used in the method.

[0013]

A polycrystalline semiconductor device of the present invention is a polycrystalline semiconductor device having a channel region in which carriers move in a semiconductor layer, wherein an active region in which a current flows in the channel region. A polycrystalline semiconductor, comprising: a polycrystalline semiconductor layer having a hydrogen concentration concentration distribution lower than that of a region deeper than the active region; and a control electrode for controlling carrier movement in the channel region. It is a device.

Further, an insulating substrate, a gate electrode formed on the insulating substrate, an insulating film formed so as to cover the gate electrode, a channel region and a source formed on the insulating film. A polycrystalline semiconductor layer having a drain region and a drain region, wherein the concentration of hydrogen in the active region of the channel region in which a current flows is lower than the concentration of hydrogen in the active layer in a region deeper than the active region. A semiconductor layer, a channel protective layer formed to cover the channel region of the polycrystalline semiconductor layer, and a source electrode and a drain electrode electrically connected to the source region and the drain region of the polycrystalline semiconductor layer, respectively. And a polycrystalline semiconductor device.

In the polycrystalline semiconductor device according to any one of the above, in the channel region of the polycrystalline semiconductor layer, the hydrogen concentration in the active region in which a current from the surface to a depth of 25 nm flows is deeper than that in the active region. A polycrystalline semiconductor device having a concentration distribution lower than the hydrogen concentration of a region.

Further, in the polycrystalline semiconductor device according to any one of the above, the polycrystalline semiconductor layer is a polycrystalline semiconductor layer formed of polycrystalline silicon having a grain size of 50 nm to 2 μm. The hydrogen concentration at the depth of 25 nm from the surface of the channel region in the layer is 5 ×
10 ¹⁸ pieces / cm ^{3 to} 1 × 10 ²⁰ pieces / cm ³ , and the hydrogen concentration in the region deeper than the depth of 25 nm is 1 × 10 ²⁰ pieces / c
The polycrystalline semiconductor device is characterized by having m ^{3 to} 5 × 10 ²¹ pieces / cm ³ .

The manufacturing method of the present invention comprises a step of forming a material film of a semiconductor layer, and a different energy density with respect to the material film of the semiconductor layer with the material film of the semiconductor layer as an object to be annealed, and a low energy density. The energy density difference between the energy beam irradiation at least once and the energy beam irradiation before and / or after the energy beam irradiation is gradually increased from 10 mJ / cm ^{2 to} 50 mJ /
an energy beam such that the cm ² was irradiated a plurality of times, the energy beam annealing hydrogen continuously or stepwise high concentration from the surface of the channel region in the depth direction of the semiconductor layer to form a semiconductor layer to be distributed And a step of manufacturing the polycrystalline semiconductor device.

[0018]

In the polycrystalline semiconductor device of the present invention, the hydrogen concentration in the active region of the polycrystalline semiconductor layer in which the current flows in the channel region is lower than the hydrogen concentration in the region deeper than the active region. In addition, it is possible to control the operating characteristics of the semiconductor device including the threshold voltage with high accuracy to make them uniform, and to make the field-effect mobility thereof high and the high-speed response characteristic excellent.

The present inventors have confirmed by various experiments that the above effects can be obtained by controlling the hydrogen concentration in the polycrystalline semiconductor layer in the depth direction as described above. This is considered to be based on the following theoretical action. That is, the trap level is deeper than the active region in which the drain current flows, measured on the gate electrode side (control electrode) as a surface, that is, a region deeper than 25 nm from the surface, that is, a so-called back channel region. If there is no S
The energy band of the polycrystalline semiconductor layer arranged thereon is bent by the electric charge accumulated inside the iO _x or the like, and the energy level of the polycrystalline semiconductor layer becomes unstable. Then, if the hydrogen concentration on the back channel side is increased, a trap level will be present due to this, and thereby the energy band of the polycrystalline semiconductor layer will be bound (fixed). Therefore, it is possible to suppress the influence of the electric charges from the SiO _x to be extremely small, so that the energy level of the polycrystalline semiconductor layer is stable and a TFT having stable operation characteristics can be realized. That is, for example, a polycrystalline silicon TFT using the above-described polycrystalline semiconductor layer according to the present invention shows the operating characteristics, that is, the threshold voltage (μ _fe , V _th ) and the like when it is formed into an array. It can be extremely uniform and highly accurate throughout the array.

Further, by increasing the hydrogen concentration in the back channel region as described above, in this region,
For example, it is difficult to form crystal grains when the laser annealing according to the present invention is performed. That is, crystallization does not easily occur in the back channel region. Therefore, a region deeper than the active region of the polycrystalline semiconductor layer according to the present invention, that is, 25 n numerically
Since crystal nuclei are less likely to form in a so-called back channel region deeper than the depth of m, a polysilicon film having a large grain size is formed on the surface side, that is, in the active region having a depth of 25 nm from the surface. It is considered to be one.

In the polycrystalline semiconductor layer according to the present invention, a polysilicon film having a large grain size can be formed, so that the operating characteristics such as the field effect mobility μ _{FE of the} p-Si TFT using this can be improved and the uniformity can be improved. It can be formed as anything. That is, it is possible to realize a polycrystalline semiconductor device such as a p-SiTFT which has high operating characteristics such as high-speed operation performance and is uniform and highly reliable.

In the present invention, the hydrogen concentration of the polycrystalline semiconductor layer is controlled by the control electrode (gate electrode, etc.) as described above.
It is preferable to set the depth from the surface on the side facing the substrate to the active region, specifically, the hydrogen concentration in the region up to the depth of 25 nm as described above, to 5 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ^3. .

If the hydrogen concentration in the region up to 25 nm from this surface is too low, dangling bonds are increased and the trap density is increased, and as a result, the operation of a TFT or the like using such a polycrystalline semiconductor layer is increased. The characteristics are low degraded. On the other hand, when the hydrogen concentration is higher than the above numerical range, ablation easily occurs when performing laser annealing, etc., so that a polysilicon film having a large grain size cannot be obtained. As a result, the field-effect mobility is deteriorated due to the small grain size. For example, a TFT using such a polycrystalline semiconductor layer is used.
Has low operating characteristics (especially field-effect mobility). Therefore, it is preferable to set the hydrogen concentration within the above numerical range. However, such a preferable value of the hydrogen concentration is, as a prerequisite, a p-Si semiconductor layer as the polycrystalline semiconductor layer, and its grain size is 50
nm to 2 μm, which is a numerical value when this is used for a TFT.

As a more preferable numerical range of the above hydrogen concentration, the grain size is 150
When a polycrystalline silicon semiconductor layer having a thickness of nm to 2 μm is used for a TFT, the hydrogen concentration in the region from the surface side (that is, the side facing the gate electrode) of the polycrystalline silicon semiconductor layer to the depth of 25 nm is 1 × 10 ¹⁹ to 5 × 10 ¹⁹ / cm
³ and the hydrogen concentration in the deeper region is 1 × 10 ²⁰ / c
It is desirable to set m ³ to 5 × 10 ²¹ / cm ³ .

Then, as a method of manufacturing a polycrystalline semiconductor layer having a hydrogen concentration as described above, an amorphous semiconductor film such as an amorphous silicon film which is a material film for forming a polycrystalline semiconductor such as a polycrystalline silicon layer is used. When the laser beam is annealed to increase the grain size, the energy density input by the laser beam is gradually increased from low energy, and the energy beam annealing is performed at three or more different energy densities. By setting the difference between the energy density of at least one of the plurality of steps of laser annealing and the energy density of the preceding and / or subsequent steps to 50 mJ / cm ² or less,
The present inventors have confirmed that a polycrystalline semiconductor having a large grain size and a uniform size can be formed.

Furthermore, if the hydrogen concentration in the film of the annealed body is large continuously or stepwise in the depth direction from the film surface in the beam irradiation direction, it is possible to prevent ablation of the film due to hydrogen release. Finally, since it can be crystallized at a high energy density, a polycrystalline body having a large grain size can be obtained. Therefore, a TFT with high uniformity and high field effect mobility can be manufactured.

[0027]

Embodiments of the polycrystalline semiconductor device and the method for manufacturing a polycrystalline semiconductor layer according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram for explaining the structure of a polycrystalline semiconductor device of the present invention, following the manufacturing process thereof.

A buffer layer 102 is formed by depositing SiO _x on a substrate 101 using a quartz substrate or a glass substrate (a).

Then, on the buffer layer 102, SiH
_A + Si: H film 103 having a film thickness of 50 nm by plasma CVD at a temperature of 270 ° C. to 350 ° C. in an atmosphere of ₄ + H _2.
To form a film.

Then, the a-Si-H film 103 is irradiated with an excimer laser in a manner to be described later, and multi-step E is performed.
LA (excimer laser annealing) is performed. The p-Si thus formed was crystallized by performing multi-step ELA, and the hydrogen concentration was within the range of 5 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ³ over the depth of 25 nm from the surface. The hydrogen concentration is such that it can be accommodated (b).

In the present embodiment, the thickness of the active region of the TFT is considered to be formed in a region having a depth of 24 nm from its surface in design. This depth is the TFT
It has been confirmed by computer simulations that simulate the structure of the.

Then, the p-Si film whose crystal grain size has grown and turned into p-Si by the multi-step ELA process shown in FIG. 1B is patterned into an island shape by the PEP process, A polycrystalline silicon semiconductor layer 104 is formed. Then, a gate insulating film 105 is formed so as to cover almost the entire surface thereof and the buffer layer 102. This gate insulating film 1
05 is plasma CV using SiO _x , SiN _x, etc.
D, atmospheric pressure CVD, ECR-CVD method or the like is used.
Subsequently, the gate electrode 106 is formed so as to cover the channel region of the p-Si 104 with the gate insulating film 105 interposed therebetween. The material of the gate electrode 106 is Mo-Ta.
PE using a metal such as Mo-W or n ⁺ p-Si
It can be formed in the P step. Then, using the gate electrode 106 as a mask, p of the exposed portion not covered by the gate electrode 106 is self-aligned.
Impurity ions such as P ⁺ or B ⁻ are introduced into the −Si 104, that is, the portions to be the source region and the drain region of the p-Si 104, depending on the n-type or p-type (c). As the charging method, for example, an ion implantation method or a doping method can be used.

Then, in order to activate the impurity ions implanted by the above-mentioned ion implantation method and recover the film damage at that time, almost all the structures built up to the step (c) on the substrate. Thermal annealing or excimer laser annealing is applied to the entire surface. Depending on the energy input in this step, generally, most of the changes in hydrogen concentration and the like in the multi-step ELA step shown in (b) occur in addition to the effective effects such as activation of the impurity ions implanted in the previous step. Therefore, there is no concern that the hydrogen concentration of the polycrystalline semiconductor layer according to the present invention will be adversely affected at this point.

Then, an interlayer insulating film 107 is formed so as to cover almost the entire surface of the gate electrode 106 and the gate insulating film 105. As the interlayer insulating film 107, SiO is used in the present invention.
_x was used. Then, the p-Si layer 10 that penetrates the interlayer insulating film 107 and the gate insulating film 105 and is covered thereunder is formed.
Contact holes 111 and 112 are formed so that the upper surfaces of the source region 109 and the drain region 110 on both sides of the fourth channel region 108 are exposed (d).

Then, the contact holes 111,
A source electrode 113 and a drain electrode 114, which are connected to the source region 109 and the drain region 110 respectively through 112, are formed. The source electrode 113 and the drain electrode 114 can be formed from a metal film of Al, Al-Si, Mo, or the like. As a film forming method, for example, the film can be formed by the sputtering method as in this embodiment (e).

In this way, the main part of FIG.
The polycrystalline semiconductor device according to the present invention having the structure as shown in (e) is completed.

As described above, the hydrogen concentration of the polycrystalline semiconductor layer (p-Si layer 104 in this embodiment) is lower than the hydrogen concentration of the active region where current flows in the channel region, which is deeper than the active region. By forming the concentration distribution, specifically, the hydrogen concentration within the range of 5 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ³ , the semiconductor device including the threshold voltage as shown below is formed. It is possible to control the operating characteristics of (1) with high accuracy to make them uniform, and to have high field-effect mobility and excellent high-speed response characteristics.

Next, a manufacturing method for manufacturing the polycrystalline semiconductor layer which is the main part of the above-described polycrystalline semiconductor device according to the present invention will be described.

As shown in FIG. 2, a buffer layer 202 is formed on an insulating substrate 201 such as alkali-free glass, and then an a-Si-H (hydrogenated amorphous silicon) film 203 is formed. As the buffer layer 202,
In this embodiment, SiO _x which is an insulating film is used. Plasma CV is used for depositing the buffer layer 2 and the a-Si-H film 203.
Method D was used. The a-Si-H film 203 is a source gas Si.
Using H ₄ + H ₂ , deposit at a substrate temperature of 270 ° C.
Form to 50 nm.

A light beam 204 is applied to this film. A laser beam such as an excimer laser or an Ar laser can be preferably used as the light beam 204. Alternatively, needless to say, an electron beam can be preferably used as the energy beam.

For example, Xe is formed on the a-Si-H film 203.
Using a Cl excimer laser (wavelength: 308 nm) beam, the first energy density is 75 mJ / c as shown in FIG.
Irradiation was started from m ² and the laser beam irradiation was repeated for 8 steps while gradually increasing the energy density by 25 mJ / cm ² .

For the XeCl excimer laser, for example, a beam having a beam diameter of 2.5 mm square and an oscillation frequency of 30 Hz is used.
As shown in FIG.
02 (a-Si-H film 203 in this embodiment) is irradiated while being swept (scanned). Beam 4 as shown in FIG.
The irradiation time can be shortened by the method of irradiating 01 back and forth.

On the other hand, according to the method of irradiating the beam 401 by sweeping it in only one direction as shown in FIG.
Since the overlapping direction of 01 is always the same, the object to be annealed 402 can be crystallized more uniformly than in the case of FIG.

Since the sweep speed v is related to the number of times of irradiation with the same energy density per part of the film of the object to be annealed 402, the diffraction intensity in the (1, 1, 1) direction is large from the result of X-ray diffraction. That is, the speed is set to 3 to 7.5 mm / s so that the irradiation is performed 10 to 25 times with high crystallization rate. For example, to get 10 irradiations, the beam
2.5mm ^□ , frequency is 30Hz, sweep speed is 7.5m
Set to m / s.

In the second stage irradiation, as shown in FIG. 3, a laser beam having a ^second energy density of 100 mJ / cm ² is irradiated. Continuously, 3rd energy density 125mJ / cm
² , the energy density of the 4th stage 150mJ / cm ² , ...
..., and the energy density of 250 mJ / cm ² of the eighth, by changing the sequential energy density is irradiated with laser light. Thus, each energy density is always (n + 1th energy density)-(nth energy density) = 25 mJ / cm ² (n = 1, 2, 3, 4, 5, 6, 7) As described above, the irradiation is repeated while changing the energy density at a constant increment of 50 mJ / cm ² or less. By irradiating the energy beam over a plurality of stages while increasing the energy density while keeping the energy density increment at 50 mJ / cm ² or less, the polycrystalline semiconductor layer from the surface of the polycrystalline semiconductor layer which is being formed due to the release of hydrogen is removed. Since the ablation of the heated portion can be suppressed, the crystallization of the polycrystalline semiconductor layer with high energy can be realized.

The hydrogen concentration of the p-Si layer thus obtained is shown in FIG. 12 (a). The hydrogen concentration in the active region in which the current flows in the channel region falls within a concentration distribution lower than the hydrogen concentration in the region deeper than the active region, specifically 5 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ³ , 25n
The hydrogen concentration in the region deeper than m is 1 × 10 ²⁰ / cm ³ or more. The grain size of this p-Si is 800 nm. Using a p-Si layer having such a hydrogen distribution to fabricate 100 TFTs in an array on a 5-inch substrate with W / L = 10 (μm) / 10 (μm), the characteristics are μ _FE =
130 ± 5cm ² / V, threshold voltage Vth = 3 ± 0.5
It became [V], and it was confirmed that the operating characteristics of the semiconductor device can be controlled with high accuracy to be uniform, and the field effect mobility can be high and the high-speed response can be excellent.

On the other hand, for comparison, when thermal annealing was performed at 450 ° C. and then laser annealing was performed at 250 cm ² / V-s to form a p-Si layer, the hydrogen distribution was as shown in FIG. 12 (b).
As described above, the hydrogen concentration became constant in the low concentration region. A TFT was manufactured by using a p-Si layer having such a hydrogen distribution, and its characteristics were confirmed in the same manner as above. Μ _FE = 100 ± 20 cm
² / V, the threshold voltage Vth = 3 ± 2 [V], and the variation is approximately μ _FE in comparison with the semiconductor device according to the present invention.
It was confirmed that it was significantly increased by four times and the threshold voltage Vth was about four times. Thus, in the case of the conventional semiconductor device, when it is formed as a TFT array, the characteristics of the entire array become non-uniform.

However, according to the present invention, a uniform TF having a high μ _FE and an extremely small variation in the characteristics of the entire array is obtained.
A semiconductor device such as a T array can be realized.

In such a semiconductor device of the present invention, a large number of elements are formed in an array over a large area, and highly accurate uniformity of the characteristics of these elements is required, for example, an active matrix type liquid crystal display device. It is suitable for semiconductor devices such as those used in the pixel section switching element and the driving circuit.

(Embodiment 2) In the second embodiment, the case where the present invention is applied to an inverted stagger type TFT will be described with reference to FIG.
Based on.

A gate electrode 1302 is formed on the substrate 1301. The material of the gate electrode 1302 is M
o-Ta or Mo-W is used. Then, a gate insulating film 1303 is formed so as to cover the substrate including it. Then, a first a-Si: H film 1304 is formed thereon.
The film thickness of the first a-Si: H film 1304 is 25 nm,
Deposition is performed at a film forming temperature of 450 ° C. so as to form a film having a low hydrogen concentration.

Then, the first a-Si: H film 1304 is formed.
Then, the laser beam 1305 according to the present invention is irradiated in multiple steps. At this time, the laser beam (ELA) 130 is changed stepwise from low energy to high energy.
Irradiate 5a. As a result, the first a-Si: H film 13
Since No. 04 has a thin film thickness and a low hydrogen concentration, the first p-Si film 1306 thus obtained is a uniformly p-Si film and the hydrogen concentration is low (FIG. 13A).

Subsequently, a second a-Si: H film 1307 is formed by the same method as described above, and this time, a laser beam 1305b is irradiated with an irradiation energy lower than the above to crystallize the film. It becomes p-Si (FIG. 13B). At this time, since the second a-Si: H film 1307 is irradiated with the laser beam 1305b with low power to be crystallized, the second p-Si film 1308 obtained by this has a large amount of hydrogen. . The second p-Si thus formed
The film 1308 and the first p-Si film 1306 have a total of 50 n
An active layer 1309 having a thickness of m is obtained. Therefore, in the active layer 1309, the first p-Si film 1306 has a low concentration of hydrogen, and the first p-Si film 1306 has a region from the surface in contact with the gate electrode where the active region in which current flows exists to a depth of 25 nm The second p-Si film 1308, which is a deep region, has a higher hydrogen concentration than the first p-Si film 1306. At this time, the first a-Si: H + ELA and the second a-
Consistent vacuum processing is performed to prevent contamination of the interface with Si: H + ELA.

Then, the channel etching stopper 13 is formed so as to cover the channel region of the active layer 1309.
Form 10. This channel etching stopper 13
10 is formed using a material such as SiN _x or SiO _x .

Then, each of the source region and the drain region of the active layer 1309 is formed by the impurity ion implantation method or the like.

Then, ohmic contact layers 13 are formed so as to cover the source and drain regions, respectively.
11a and 1311b are formed. In this embodiment, n ⁺ a
-Si film was used as a material.

Then, this ohmic contact layer 131
A source electrode 13 connected to the source region and the drain region of the active layer 1309 via 1a and 1311b, respectively.
12 and the drain electrode 1313 are formed.

As described above, even when the present invention is applied to the inverted stagger type TFT, the hydrogen concentration in the active region can be made lower than the hydrogen concentration in the region deeper than that (the back channel side), and the high electric field effect can be obtained. It is possible to realize mobility and uniform characteristics when a TFT element array is formed.

(Embodiment 3) FIG. 7 shows a second embodiment of the method for producing a polycrystalline semiconductor layer (specifically, a polycrystalline silicon thin film used for a TFT here) according to the present invention.
It is a figure which shows the method of irradiating, changing the energy density of a laser beam.

Similar to the first embodiment shown in FIG. 2,
The buffer layer 202 and the a-Si-H film 20 are formed on the substrate 201.
3 is formed, and the a-Si-H film 203 is irradiated with the light beam 204 from the surface. The flow of such steps is similar to that of the first embodiment.

In the first embodiment, however, the energy density at each stage is (n + 1th energy density)-(nth energy density) = 25 mJ / cm ² (n = 1, 2, 3, 4) 5, 6, 7), the irradiation was repeated by changing the energy density at a constant increment of 25 mJ / cm ² , but in this example, as shown in FIG.
As shown in, the difference in energy density at each stage, that is, the increment of energy density, is (n + 1th energy density) − (nth energy density) = 50 mJ / cm ² (n = 1, 2, 3) Irradiation at a constant increment, that is, at a constant increment of 50 mJ / cm ² which is the maximum value of the increment according to the present invention, the energy density is changed in four steps, and a-Si-H
The film 203 was crystallized.

That is, the energy density of the first laser light irradiation is 75 mJ / cm ² , the energy density of the second laser light irradiation is 125 mJ / cm ² , the third energy density is 175 mJ / cm ² , and the fourth At an energy density of 225 mJ / cm ² . Even with such an irradiation method, the hydrogen distribution similar to that described in the first embodiment was exhibited, and thus it was confirmed that the TFT characteristics were excellent.

FIG. 5 shows the increments of energy density and (1,
1, 1) A graph showing the relationship with the crystallization rate measured by the diffraction intensity. As is clear from the figure, when the energy density increment is larger than 50 mJ / cm ² , the (1, 1, 1) diffraction intensity sharply decreases. From this, it can be seen that in order to obtain a polycrystalline semiconductor layer having a high crystallization rate, the increment of the energy density in the above energy beam irradiation step is preferably 50 mJ / cm ² or less. On the other hand, above that, the crystallization rate is extremely low.

On the other hand, as a comparative example to the above-described manufacturing method according to the present invention, as shown in FIG. 6, the first energy density is irradiated at 75 mJ / cm ² , and then the second energy density is 150 mJ / cm 2. Irradiate with ² . Next, an experiment was performed for the case of irradiation with the third energy density of 250 mJ / cm ² . Here, (n + 1th energy density) −
When (the energy density of n) = is defined as ^{_{ΔE n mJ / cm 2, ΔE}} 1 = 75mJ / cm 2, a ΔE ^₂ = 100mJ / cm _2, the energy density at any stage, ((n + 1) th energy density )-(Nth energy density)> 50 mJ / cm ² . That is, the increment of the energy density at each stage is set to a value larger than that of the present invention, unlike the present invention.

In this way, the increment of energy density is 50 mJ
Irradiation of multi-stage laser light of / cm ² or more caused unevenness on the surface of the formed polycrystalline semiconductor layer, and uniform crystallization could not be performed.

N-channel coplanar TFTs were separately manufactured using the polycrystalline silicon semiconductor layer of the above-mentioned example and the polycrystalline silicon semiconductor layer of the comparative example.
Their operating characteristics and uniformity were evaluated and compared.

As for the characteristics of the TFT using the polycrystalline semiconductor layer formed by the manufacturing method according to the present invention as shown in FIG. 2, the field effect mobility is 130 ± 5 cm ² / Vs, and the threshold voltage Vth is Is 3 ± 0.5 V, and it has been found that a uniform and high field-effect mobility TFT can be realized.

On the other hand, as shown in FIG. 6, the characteristics of the TFT using the polycrystalline semiconductor layer obtained by crystallization by the energy beam irradiation with the energy density increment of 50 mJ / cm ² or more are the field effect mobility. Is 70 ± 15 mJ / cm ² / V ・
s, the threshold voltage Vth was 3 ± 1.5 V, the field effect mobility was low, and the variation was large.

In this way, annealing is performed at different energy densities of at least three steps or more, and irradiation is performed so that the (n + 1) th energy density is higher than the nth energy density, and the energy density is the n + 1th energy. The difference between the density and the nth energy density is 50 mJ / cm ²
By performing a multi-step laser beam annealing as described below to form a polycrystalline semiconductor layer, it is possible to finally crystallize at a high energy density, so that the surface is flat and the grain size is large, and the field effect transfer is achieved. A high-performance and high-performance polycrystalline semiconductor layer can be obtained. The hydrogen distribution of p-Si is as shown in FIG. That is, when a TFT is manufactured using such a polycrystalline semiconductor layer (polycrystalline silicon layer in this example) according to the present invention, a TFT having high field effect mobility and high uniformity can be realized.

Particularly when the increment of the energy density is constant as in this embodiment, the increment is the maximum value of the preferable values.
By setting it to 50 mJ / cm ² , the number of steps of laser beam irradiation can be minimized, and a TFT having high field effect mobility and high uniformity can be manufactured by laser beam annealing for a short time.

(Embodiment 4) Similar to the first embodiment shown in FIG. 2, a buffer layer 202 is formed on a substrate 201, and an a-Si-H film 203 is deposited thereon to a film thickness of 50 nm. This a-Si-H film 203 is formed at 300 [deg.] C. or lower by using the plasma CVD method.

Then, as shown in FIG. 8, the excimer laser beam is first irradiated with the first energy density of 75 mJ / cm ² . Second energy density 100mJ / cm
Irradiate with ² . Also in this case, (n + 1th energy density)-(nth energy density) = ΔE _n mJ / cm ²
When defined as, ΔE ₁ = 25 mJ / cm ² . And then at ΔE ^₂ = 50mJ / cm ₂ as the third energy density 150 mJ / cm ² irradiated with the excimer laser beam,
Subsequently, irradiation is performed at a fourth energy density of 225 mJ / cm ² with ΔE ₃ = 75 mJ / cm ² .

In this way, the energy density increment ΔE _n is not made constant at each step of multiple excimer laser beam irradiation, but the energy density increment is increased within a range of 50 mJ / cm ² in at least one step. 50 mJ / cm ² including steps, and steps before and after
Alternatively, the energy density increment ΔE _n itself may be gradually increased. That is, in the excimer laser beam irradiation method of this embodiment, the energy density increment is 50 mJ / cm.
^The feature is that the increment of the energy density is gradually increased after the step including ² or less.

According to the manufacturing method of the third embodiment, the uniformity of the energy density can be improved in a shorter annealing time than the fixed method of the first and second embodiments. It is possible to obtain a p-SiTFT using a polycrystalline silicon semiconductor layer having a high mobility and good mobility.

Next, attention is paid to hydrogen distribution in the film of the object to be annealed.

A-Si-H film 203 which is an object to be annealed
The optimum film thickness and the energy density for irradiation are determined so that the hydrogen concentration in the film at the n-th step increases continuously or stepwise in the depth direction from the surface in the irradiation direction of the laser beam.

For example, by sequentially performing the irradiation with the energy density as described above, the hydrogen concentration in the film is shown in FIG.
It has a distribution like (c).

FIG. 9A shows the first energy density of 75 m.
The hydrogen concentration in the film after irradiation with J / cm ² is shown in FIG. 9 (b).
The hydrogen concentration in the film after irradiation with the ^second energy density of 100 mJ / cm ² was measured in Fig. 9 (c).
The hydrogen concentration in the film after irradiation with 150 mJ / cm ² is shown.
In this way, laser beam irradiation is repeated on the a-Si-H film 203 which is the object to be annealed so that the hydrogen concentration gradually increases in the film thickness direction. By successively irradiating the laser beam in this way, it is possible to finally irradiate the laser beam with a high energy density of 225 mJ / cm ² , and as a result, a polycrystalline silicon layer having a large grain size of about 800 nm can be formed. Obtainable.

The polycrystalline semiconductor layer (polycrystalline silicon layer in this embodiment) having the above hydrogen concentration distribution is sequentially irradiated with a laser beam, so that the polycrystalline semiconductor layer is irradiated with the laser beam. Since the ablation of the surface due to the release of hydrogen can be suppressed, the surface of the polycrystalline semiconductor layer has high flatness and high crystallinity. The obtained hydrogen concentration distribution of p-Si is shown in FIG.
Since the same thing as (a) is obtained, a TFT with high uniformity and high field effect mobility can be obtained.

On the other hand, the same film thickness of 50 nm a-Si-
When the H film 203 is crystallized, when the laser beam is irradiated by the following conventional method, the a-Si-H film 203 in the portion irradiated with the laser beam is ablated from the surface in the depth direction. Therefore, a good polycrystalline silicon film cannot be obtained.

As shown in FIG. 10 (a), the laser 205 is annealed at a constant energy density of 150 mJ / cm ² as in the prior art (not to mention here, of course, the a-Si-H film 2).
03), the hydrogen concentration in the polycrystalline semiconductor film obtained as a result of the laser annealing has a distribution as shown in FIG.

That is, in the case of the conventional irradiation method of irradiation energy, which is not the optimum irradiation method unlike the present invention, not only hydrogen is released from the film surface but also hydrogen is diffused into the film. Region with a large amount of hydrogen in the film (Fig. 10)
For example, a portion having a depth of 30 to 40 nm) exists.

Therefore, even if a film having such a hydrogen distribution is irradiated with a laser beam in multiple stages while sequentially increasing irradiation energy, hydrogen is released from a portion containing a large amount of hydrogen, and the film is ablated. Therefore, it becomes impossible to obtain a uniform polycrystalline silicon film having good crystallinity.

Therefore, the energy density of the laser beam is adjusted so that the hydrogen concentration in the film to be annealed has the hydrogen concentration distribution according to the present invention, and irradiation is performed, so that the grain size is large and the uniformity is high. A polycrystalline silicon layer can be obtained. As a result, a polycrystalline semiconductor device such as a TFT having high mobility and high uniformity can be realized by using the polycrystalline semiconductor layer according to the present invention such as the polycrystalline silicon layer.

(Embodiment 5) Similar to the first embodiment shown in FIG. 2, a buffer layer 202 is formed on a substrate 201, and an a-Si-H film 203 is deposited thereon to a film thickness of 50 nm. This a-Si-H film 203 is formed at 300 [deg.] C. or lower by using the plasma CVD method.

Then, the a-Si-H film 203 is irradiated with an excimer laser beam 204. As shown in FIG. 11, laser light is irradiated at a first energy density of 75 mJ / cm ² . Next, laser light having a ^second energy density of 150 mJ / cm ² is irradiated with ΔE ₁ = 75 mJ / cm ² . Then, ΔE ₂ = 25 mJ / cm ² and the third energy density is set.
Irradiate at 175 mJ / cm ² and finally ΔE ₃ = 75 mJ /
As cm ² is irradiated with the fourth laser beam energy density 250 mJ / cm ^2. Thus, the a-Si-H film 203
Is crystallized to form p-Si. Here, the energy density at each stage is set to a value at which the film surface does not become rough due to ablation.

As described above, the energy density is increased by 50 mJ / cm ² in at least one step in the energy irradiation of the energy beam, so that the depth of the film surface and its vicinity due to the release of hydrogen up to a depth of 25 nm. It is possible to suppress ablation at the depth of, and to crystallize that portion at a high energy density. Therefore, a polycrystalline silicon layer having good crystallinity can be obtained, and a TFT having high mobility and high uniformity can be realized.

Further, as shown in this example, the energy density increment is not always 50 mJ / cm except for one step.
Since it is not necessary to set it to ² or less, there is an advantage that the number of irradiation steps n can be reduced and the annealing time can be shortened.

In the above embodiment, aS
The case where the technique of the present invention is applied to laser beam annealing for crystallizing an i: H (hydrogenated amorphous silicon) thin film is shown, but needless to say, the application of the present invention is not limited to this. Yes. In addition to this, the present invention can be applied to, for example, light beam annealing at the time of crystallization of an amorphous material such as silicon carbide.

Further, as the energy beam for crystallizing the amorphous semiconductor film in forming such a polycrystalline semiconductor layer, in addition to the excimer laser described above, for example, an Ar laser or a laser other than a laser is used. Needless to say, it is possible to use, for example, an electron beam.

[0092]

As clearly described in the above detailed description, according to the present invention, in the polycrystalline semiconductor device, the operating characteristics such as the threshold value can be controlled with high accuracy and the operating characteristics such as the mobility can be uniform. Thus, it is possible to provide a polycrystalline semiconductor device having high characteristics and excellent high-speed response characteristics.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the structure of a polycrystalline semiconductor device of the present invention, following the manufacturing process thereof.

FIG. 2 is a diagram showing a manufacturing process for manufacturing a polycrystalline semiconductor layer which is a main part of the polycrystalline semiconductor device according to the present invention.

[Figure 3] a diagram showing the irradiation energy density in the case of performing the laser beam irradiation for a first 8 levels with increasing stepwise the energy density by 25 mJ / cm ² to start the irradiation from an energy density of 75 mJ / cm ² is there.

FIG. 4 is a diagram showing a method of irradiating an object to be annealed 402 (a-Si-H film 203 in this embodiment) with a beam 401 while sweeping (scanning).

FIG. 5 is a graph showing the relationship between the increment of energy density and the crystallization rate measured by (1, 1, 1) diffraction intensity.

FIG. 6 is a diagram showing irradiation energy density of a manufacturing method of a comparative example with respect to the manufacturing method of the present invention.

FIG. 7 is a diagram showing a method of irradiating while changing the energy density of the laser beam in the embodiment of the method for producing a polycrystalline semiconductor layer (specifically, a polycrystalline silicon thin film used for a TFT here) according to the present invention. Is.

FIG. 8 is a diagram showing a method of irradiating while changing the energy density of a laser beam in an example of a method of manufacturing a polycrystalline semiconductor layer (specifically, a polycrystalline silicon thin film used for a TFT here) according to the present invention. Is.

FIG. 9 is a diagram showing a hydrogen concentration distribution in a polycrystalline semiconductor layer (film).

FIG. 10: Constant energy density of 150 mJ /
Diagram showing hydrogen concentration in the polycrystalline semiconductor film obtained as a result of the laser annealing when the laser 205 is irradiated with the laser 205 in cm ² (a-Si-H film 203, needless to say here). It is (b).

FIG. 11 is a diagram showing a method of irradiating while changing the energy density of a laser beam in an example of a method for manufacturing a polycrystalline semiconductor layer (specifically, a polycrystalline silicon thin film used for a TFT here) according to the present invention. Is.

FIG. 12 is a polycrystalline semiconductor layer (film) of the present invention and a comparative example.
It is a figure which shows the hydrogen concentration distribution inside.

FIG. 13 is a diagram showing a manufacturing method when the present invention is applied to an inverted stagger type TFT.

[Explanation of symbols]

 101 substrate substrate 102 buffer layer 103 a-Si-H film 104 polycrystalline silicon semiconductor layer 105 gate insulating film 106 gate electrode 107 interlayer insulating film 108 ... Channel region 109 ... Source region 110 ... Drain region 111, 112 ... Contact hole 113 ... Source electrode 114 ... Drain electrode 201 ... Substrate 201 202 ... Buffer layer 202 203 ... a-Si-H film

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/336

Claims (5)

[Claims] 1. A polycrystalline semiconductor device having a channel region in which carriers move in a semiconductor layer, wherein a hydrogen concentration in an active region in which a current flows is higher than a hydrogen concentration in a region deeper than the active region in the channel region. A polycrystalline semiconductor device having a low concentration distribution and a control electrode for controlling carrier movement in the channel region. 2. An insulating substrate, a gate electrode formed on the insulating substrate, an insulating film formed to cover the gate electrode, a channel region and a source formed on the insulating film. A polycrystalline semiconductor layer having a drain region and a drain region, wherein the concentration of hydrogen in the active region of the channel region in which a current flows is lower than the concentration of hydrogen in the active layer in a region deeper than the active region. A semiconductor layer; a channel protection layer formed so as to cover the channel region of the polycrystalline semiconductor layer; and a source electrode and a drain electrode electrically connected to the source region and the drain region of the polycrystalline semiconductor layer, respectively. ,
A polycrystalline semiconductor device comprising: 3. The polycrystalline semiconductor device according to claim 1, wherein the channel region of the polycrystalline semiconductor layer has a hydrogen concentration in an active region in which a current from the surface to a depth of 25 nm flows,
A polycrystalline semiconductor device having a concentration distribution lower than a hydrogen concentration in a region deeper than the active region. 4. The polycrystalline semiconductor device according to claim 1, wherein the polycrystalline semiconductor layer has a grain size of 50 nm to 2 μm.
From a surface of a channel region in the polycrystalline semiconductor layer.
Hydrogen concentration up to 25 nm is 5 × 10 ¹⁸ hydrogen atoms / cm ^{3 to}
1 × 10 ²⁰ pieces / cm ³ and the hydrogen concentration in a region deeper than the depth of 25 nm is 1 × 10 ²⁰ pieces / cm ^{3 to} 5 × 10 ²¹ pieces / cm ³ apparatus. 5. A step of forming a material film of a semiconductor layer, wherein the material film of the semiconductor layer is used as an object to be annealed at different energy densities with respect to the material film of the semiconductor layer, and energy is gradually increased from a low energy density. Energy beam irradiation is performed a plurality of times so that the energy density difference between the energy beam irradiation at least once and the energy beam irradiation before and / or after the energy beam irradiation is 10 mJ / cm ^{2 to} 50 mJ / cm ^2. And an energy beam annealing step of forming a semiconductor layer in which hydrogen is continuously or stepwise distributed in a high concentration from a surface of a channel region of the semiconductor layer in a depth direction thereof. Method for manufacturing polycrystalline semiconductor device.