JPH1187730A - Polycrystalline semiconductor thin film, its formation method, polycrystalline semiconductor tft and tft substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a TFT whose characteristic is higher, by a method wherein the area of stripe-shaped crystal particles is made larger than the area of isotropic crystal particles. SOLUTION: Index arrows on the right side of a microphotograph correspond to an actual size of 50 μm. A direction S indicates a scanning direction in a beam annealing operation. For example, an SiO2 film, a polycrystalline silicon film and an SiNX film as an antireflection coating are laminated respectively on a glass substrate in thicknesses of 200 nm, 130 nm and 50 nm, they are heat-treated, an argon ion laser in a continuous wave oscillation mode is used as a beam light source, and the films are made polycrtalline by a laser annealing operation. That is to say, an HSBA operation is performed. Then, the SiNX film as the antireflection coating is removed by hydrofluoric acid, and the surface of the polycrystalline silicon film is etched by a hydrazine aqueous solution so as to be observed under an optical microscope. Then, about the half or higher of the area of a stripe on the polycrystal silicon film displays a linear look, and a fine isotropic granular region is obserbed in its gap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the manufacture of thin film transistors (TFTs) used as driving elements such as active matrix image display elements. Among them, a polycrystalline semiconductor thin film formed by a high-speed scanning beam annealing method (HSBA) used in a polycrystallization process,
The present invention relates to a method for forming a polycrystalline semiconductor thin film, a polycrystalline semiconductor TFT, and a TFT substrate.

[0002]

2. Description of the Related Art Conventionally, beam annealing has been used to form a polycrystalline semiconductor TFT. However, most of them are melt recrystallization or substantial heat treatment of semiconductor thin films, and in these cases, the thermal phenomenon induced by beam irradiation does not depend much on the scanning speed of the beam spot on the irradiation object. .

First, as a conventional example 1, Japanese Patent Publication No. 3-346
No. 69 can be exemplified as a prior art of melt recrystallization.
Next, as a second conventional example, a technique of performing laser annealing under non-melting conditions has been known. High-speed scanning of the beam spot,
This is a method of obtaining a polycrystalline semiconductor without raising the temperature of the irradiation object almost, and of course, without melting it in a room temperature atmosphere. For example, JP-A-62-104117, JP-A-5-208395, and IEICE Transactions C
-2 Vol. HSBA described in J76-C-2 No. 5 page 259 and JP-A-8-97141.
This invention relates to low-temperature process polycrystalline silicon by argon laser annealing.

[0004]

In the above-mentioned HSBA, that is, an HSBA which scans a beam spot at a high speed on an object to be irradiated and polycrystallizes the non-single-crystal semiconductor thin film without bringing it into a completely molten state, By further setting the optimum irradiation time, a TFT with better uniformity was obtained, and a TFT with high characteristics and good uniformity could be surely formed while maintaining high productivity.

However, with the advancement of technology, the characteristics required for TFTs have become more sophisticated, and higher field-effect mobility has been required. In addition, new issues such as a large screen, high density, integrated integration of peripheral circuits, and improvement in production yield have been required. Further, a TFT display device which has good uniformity and can be manufactured stably at the same time has been required.

[0006]

In order to solve the above-mentioned problems in Japanese Patent Application No. 9-96457, the present inventors have made a first invention as a striped polycrystalline semiconductor formed on an insulating substrate. In the thin film, a field-effect mobility ν _L in the longitudinal direction of the stripe and a field-effect mobility ν _{S in} the width direction of the stripe satisfy a condition of ν _L ≧ 1.5 · ν _S , Further, as a second invention, in a method for forming a polycrystalline semiconductor thin film in which a beam spot is scanned on an amorphous semiconductor thin film to perform polycrystallization, a scanning speed V for inducing spontaneous crystallization of the amorphous semiconductor thin film is used. _A method for forming a polycrystalline semiconductor thin film characterized by scanning at a scanning speed of 90 to 110% of _P has been proposed. Then, the present invention proposed an invention capable of generating anisotropy in the arrangement of crystal grains of the formed polycrystalline semiconductor thin film.

The present invention is a further improved invention of the above-mentioned application. First, the invention of the first group will be described. According to the first aspect of the present invention, in a striped polycrystalline semiconductor thin film formed on an insulating substrate, isotropic crystal grains and streaky crystal grains arranged substantially parallel to the longitudinal direction of the stripes are mixed. In addition, the present invention provides a polycrystalline semiconductor thin film characterized in that the area of streak-like crystal grains is larger than the area of isotropic crystal grains. Here, the area means the ratio of the relative area in a region where substantially the same phase structure of crystals (isotropic crystal grains and streak-like crystal grains) exists from the center of the stripe to the width direction. ing. Both end regions of the stripe are excluded.
Usually, a good phase structure is obtained in a region of about 50 to 80% with respect to the width direction of the stripe, and its state can be confirmed. As the insulating substrate to be used, a general non-alkali LCD glass substrate having a lower softening temperature than a quartz substrate or the like is used.

According to a second aspect of the present invention, there is provided the polycrystalline semiconductor thin film according to the first aspect, wherein the polycrystalline semiconductor thin film contains 1 atm% or more of hydrogen.

According to a third aspect of the present invention, there is provided a polycrystalline semiconductor TF.
3. A polycrystalline semiconductor TFT, wherein the polycrystalline semiconductor thin film according to claim 1 or 2 is used for a channel of T, and a longitudinal direction of the stripe and a direction of the channel are provided substantially in parallel. Substantially parallel means that the main axis direction of the stripe crystal and the current direction of the channel are within 15 °.

According to a fourth aspect of the present invention, there is provided a polycrystalline semiconductor TF.
4. The polycrystalline semiconductor TFT according to claim 3, wherein the source electrode and the drain electrode of T are formed in a comb shape.
It is. In a preferred aspect of the present invention, the gate electrode of the polycrystalline semiconductor TFT has a zigzag shape,
Alternatively, it is bent right and left or formed in a spiral shape.

According to a fifth aspect of the present invention, there is provided a row driving circuit in which a driving element for driving pixels formed in a matrix is provided for each pixel, and a row driving circuit supplies a row signal to a row electrode connected to the driving element. 5. A polycrystalline semiconductor TF according to claim 4, further comprising a column drive circuit for supplying a column signal to a column electrode connected to the element, and a part of the row drive circuit and / or a part of the column drive circuit.
A TFT substrate characterized by using T.

[0012] In a preferred aspect of each of the above inventions,
It is a polycrystalline semiconductor thin film obtained by annealing a 50 to 150 nm-thick amorphous silicon semiconductor containing silicon as a main component.

Next, a second group of the present invention will be described. According to a sixth aspect of the present invention, in the method of forming a polycrystalline semiconductor thin film for performing a polycrystallization by scanning a beam spot on the amorphous semiconductor thin film,
A polycrystalline semiconductor thin film characterized by using an amorphous semiconductor thin film having a crystal nucleus generation density of 0.01 to 0.5 / μm ² when subjected to solid phase growth by heating at 12 ° C. for 12 hours. A method of forming is provided. Preferably, the production density is 0.01 to
0.1 / μm ² .

According to a seventh aspect of the present invention, there is provided a method for forming a polycrystalline semiconductor thin film by scanning a beam spot on the amorphous semiconductor thin film and performing polycrystallization, wherein the film forming temperature of the amorphous semiconductor thin film is 250 ° C. or less. And a method for forming a polycrystalline semiconductor thin film, wherein the dehydrogenation temperature before performing beam annealing is (650 ° C. ± 30 ° C.-film forming temperature). However, the dehydrogenation temperature must be set at 40 for efficient operation.
The temperature is preferably 0 ° C. or higher. Further, the temperature must be lower than the heat-resistant operating temperature of the insulating substrate to be used.
The following is assumed.

[0015] The invention according to claim 8, the scanning speed V _P which induces spontaneous crystallization of the amorphous semiconductor thin film 90 to 110
8. The method according to claim 6, wherein the scanning is performed at a scanning speed of about 0.1%. Then, it is preferable to generate anisotropy in the arrangement of crystal grains of the formed polycrystalline semiconductor thin film.

[0016] The lower side of the area of the scanning speed V _P is 90 to 100
% (<100%), and the upper area is 100 to 1%.
10%. This is basically the same in that a higher field-effect mobility can be obtained than in Conventional Example 2. In the present invention,
It is preferable to select and use a scanning speed from the range of 100 to 110% in terms of productivity and uniformity of the polycrystalline semiconductor thin film.

In a first preferred embodiment, the amorphous semiconductor is an amorphous silicon semiconductor containing silicon as a main component and having a thickness of 50 to 150 nm.
20. A method for forming a polycrystalline semiconductor thin film as described above.

According to a second preferred aspect, the present invention relates to claim 6 or 7.
A polycrystalline semiconductor TFT characterized in that a channel is formed using a polycrystalline semiconductor thin film formed by the method of forming a polycrystalline semiconductor thin film according to the invention described in the first or the preferred embodiment.

According to a third preferred embodiment, a plurality of polycrystalline semiconductor TFTs are provided on an insulating substrate, and at least a part thereof is provided with the polycrystalline semiconductor TFT according to the second preferred embodiment. It is.

According to a fourth preferred mode, a driving element for driving pixels formed in a matrix is provided for each pixel, and a row driving circuit for supplying a row signal to a row electrode connected to the driving element; And a column drive circuit for supplying a column signal to a column electrode connected to the column drive circuit, and the polycrystalline semiconductor TFT of the second preferred embodiment is used for a part of the row drive circuit and / or a part of the column drive circuit. A TFT substrate characterized in that:

According to a fifth preferred aspect, at least one selected from a shift register of a row side drive circuit, an error correction circuit of a row side drive circuit, a current amplification buffer of a row side drive circuit, and an output buffer of a column drive circuit. A TFT substrate using the polycrystalline semiconductor TFT according to the second preferred embodiment.

The polycrystalline semiconductor TFT of the present invention is preferably used particularly in a circuit system which requires high-speed switching and large current driving. In each of the above inventions, the amorphous semiconductor is preferably an amorphous silicon semiconductor containing hydrogen, and the polycrystalline semiconductor thin film is preferably a polycrystalline silicon semiconductor. During mass production by HSBA
This is because polycrystallization can be performed stably.

In each of the above-mentioned inventions, it is more preferable that the thickness of the polycrystalline semiconductor thin film is 80 to 130 nm. This is because a polycrystalline silicon semiconductor thin film can be stably formed, which is preferable for subsequent circuit formation.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 9 shows the correlation between the field-effect mobility of the TFT (vertical axis) and the scanning speed of the beam annealing (horizontal axis). In the region A in the horizontal axis direction, a certain degree of field effect mobility can be stably obtained. In a region where the scanning speed is higher than the region A, the field effect mobility of the polycrystalline semiconductor varies.
For example, a distribution of the field-effect mobility occurs in the width direction of the stripe of the polycrystallized region, and shows a low value as a whole.

On the other hand, was analyzed for the slow G regions of the scanning speed than the A region (including the G ₁ region and the right-side of G ₂ region of the triangular left), characteristics of the field effect mobility as shown in FIG. 9 It was found that anisotropy appeared strongly.
Field effect mobility ν in a direction parallel to the beam scanning direction
It was found that _L shows a value about twice or more of the above-mentioned A region. Using the polycrystalline semiconductor thin film formed in this G region,
In a polycrystalline semiconductor TFT configured to flow a channel current in parallel to the beam scanning direction, a high-speed switching operation can be obtained and a large current drive can be performed.

At this time, it was also found that the field effect mobility of the TFT in the direction perpendicular to the scanning direction of the beam spot, that is, in the width direction of the stripe, was lower than that in the region A. Therefore, the maximum region of the field-effect mobility (for example, when the peak value is V _P = 10.5 m / s,
The scanning speed of the beam annealing is set so as to fall within a G region of about 9.5 to 11.6 m / s) to form stripes of the polycrystalline semiconductor thin film.

Further, a circuit network of a TFT for flowing a channel current in a direction parallel to the beam scanning direction is laid out. As a result, the effective field-effect mobility is dramatically increased as compared with Conventional Example 2, and a high-performance TFT can be obtained.

The scanning speed of the beam showing the maximum value of the field effect mobility is about 10 m / s in absolute value. However, this scanning speed is spontaneous crystallization due to the latent heat of crystallization,
Or, explosive crystallization (explosive crys)
Tallization), which slightly varies depending on the type and physical properties of the amorphous semiconductor thin film.

The progress speed of the spontaneous crystallization (this is the scanning speed V _P that induces the spontaneous crystallization of the amorphous semiconductor thin film)
(Substantially equal to) was determined by changing the scanning speed in HSBA stepwise and analyzing the orientation of crystal grains of the obtained polycrystalline semiconductor thin film by an X-ray diffraction method. Various amorphous semiconductor thin film and HSBA conditions (laser output,
It was possible to know the value of V _P by repeating a sequential experiments beam spot diameter and shape, scanning speed, etc.) for.

Next, physical properties of the polycrystalline semiconductor thin film formed of the HSBA of the present invention will be described. Gradually slowing down the scanning speed from the high speed side, the scanning speed polycrystalline semiconductor thin film begins to show anisotropy is called a separation scanning speed V _X. That is, a polycrystalline semiconductor thin film formed in a region having a scanning speed higher than V _X exhibits random orientation, whereas a polycrystalline semiconductor thin film formed at a scanning speed lower than V _X exhibits anisotropy. V
V _P indicating the peak or maximum region of the field-effect mobility slower position than _X is additionally present. The polycrystalline semiconductor thin film formed at a scan rate of a range including the vicinity V _P indicates the (111) orientation.

It has substantially only the (111) orientation,
This is a polycrystalline semiconductor thin film exhibiting almost a single crystal orientation, showing almost no other orientation. Figure 1 shows the results of this analysis.
0 is shown. The characteristic curve of code PC _13-P indicates that the scanning speed is 13 m.
/ S is a polycrystalline silicon semiconductor thin film formed of HSBA in region A. The characteristic curve PC _10-P is a polycrystalline silicon semiconductor thin film formed of HSBA in the G region at a scanning speed of 10 m / s.

The characteristic curves of these symbols PC _13-P and PC _10-P are obtained by X-ray diffraction of stripes of a polycrystalline silicon semiconductor thin film and show the orientation of crystal grains. The film configuration used in this experiment was such that two SiO ₂ films were formed on AN635 (an alkali-free glass substrate manufactured by Asahi Glass) having a thickness of 1.1 mm.
A polycrystalline silicon semiconductor thin film of 100 nm was formed by HSBA.

In the characteristic curve PC _13-P , three peaks (111), (220) and (311) appear as crystal orientations. On the other hand, a peak of (111) appears in the characteristic curve PC _10-V , but (220) and (31)
The peak of 1) is not observed. Thus, there is a clear difference in the crystal orientation of the polycrystalline silicon semiconductor. Further, it has been found that this tendency is almost universal without depending on the in-plane direction of the polycrystalline silicon semiconductor.

Instead of measuring the orientation by the X-ray diffraction method, the state of the film can be examined by etching the surface of the polycrystalline semiconductor film with an aqueous hydrazine solution and then observing the surface with an optical microscope. Was. That is,
Or scanning speed is faster than V _P, can determine whether slow.

[0035] In other words, you can know the value of V _P of a amorphous silicon semiconductor thin film. When the scanning speed is faster than V _P is the central portion of the polycrystallized stripes have a fine isotropic grains shape (crystal grains 10 in FIG. 11, FIG. 12
11). On the other hand, when the scanning speed is slower than V _P can be observed elongated grain shape in a direction parallel to the scanning direction across stripe (visible streaks 13 crystalline state 2
0). In other words, it was observed that crystal grains were arranged in a streak shape in a direction parallel to the scanning direction, or that a linear texture was formed substantially parallel to the scanning direction.

V _P thus obtained is 10.5 m / s in the case of an amorphous silicon semiconductor thin film formed at 300 ° C. by plasma enhanced CVD (PECVD) and heat-treated at 350 ° C., and 430 ° C. by reduced pressure CVD. Was 11.5 m / s in the case of the amorphous silicon semiconductor thin film formed by the above method. In addition, advanced analysis, V _P · 0.9 for the V _P
High field-effect mobility in the range of the scanning speed of 0 to V _P · 1.10 was found to be expressed.

Further, the highest field-effect mobility can be stably obtained by scanning the beam spot at a scanning speed in consideration of a manufacturing margin or a stability coefficient and a stability margin. Preferably, V _P · 0.93
~ V _P · 1.07. That may be laser annealing in the vicinity V _P to acquire high mobility. If the scanning speed is too slow, the field effect mobility will decrease. This is dependent on the difference between the scanning speed and V _P, presumably because periodicity appears in the crystallinity of the film.

It should be noted, V _P is the scanning speed for approximately maximum or local maximum regions of the characteristic curve shown in FIG. Preferably, V _P · 0.93~V _P · 0.96 or V _P ·,
Using a range of 1.04~V _P · 1.07. Since in the vicinity of V _P is a sharp change of the field-effect mobility, it is preferable to adopt the above range in order to stabilize the dispersion of each production lot of the completed polycrystalline semiconductor TFT.

It has been found that the high-speed side of the upper region is preferable in manufacturing. Although it can be manufactured even at a scanning speed lower than V _P (near the left side of the paper from the peak point in the graph of FIG. 9), in terms of productivity, it is slightly higher than V _P (paper space from the peak point of the graph of FIG. 9). (Near the right side) is preferably used.

In HSBA, the scanning speed at the time of beam annealing is the first parameter in terms of the moving speed of the isothermal surface. Beam diameter in the scanning direction is the second parameter which determines the allowable amount of the difference between the scanning speed and V _P. An appropriate value of the actual beam diameter is in the range of 70 to 150 μm. The difference between the scanning speed and V _P In this range is 10
%, A polycrystalline silicon semiconductor thin film having sufficiently good characteristics can be formed.

In the present invention, the size of the beam spot is defined by a diameter that becomes 1 / e ² , as in the above-described conventional example 2. The hydrogen content of the amorphous silicon semiconductor thin film is a secondary parameter. For stable polycrystallization, 3
In the case of PECVD at a film formation temperature of 00 ° C. or more, 15 at
m% or less, and reduced pressure CVD (or
Called LPCVD. In the case of (2), a value of 2 atm% or less is preferable. This value tends to decrease as the film thickness increases, and to decrease as the scanning speed increases. In order to seal defects inside the polycrystalline semiconductor thin film, it is preferable that the hydrogen content of the amorphous semiconductor thin film is 0.5 atm% or more.

In the step of HSBA used in the present invention, the amorphous silicon semiconductor thin film containing a large amount of hydrogen is annealed,
The hydrogen content is reduced to approximately 15-40%. HFS
The measurement method confirmed that both the reduced pressure CVD and PECVD reduced the content to about 35% of the original content (one sample each).

The laser output is also a secondary parameter, and an appropriate value may be used according to the film condition and the scanning speed. When the output is slightly smaller than the optimum value, the width of the stripe to be polycrystallized becomes small, but the characteristics at the center of the stripe hardly change.

Next, a description will be given with reference to FIG. PEC
VD by 300 ° C. in deposited 350 scans an amorphous silicon semiconductor thin film heat-treated at ° C. speed 10.0 m / s _{(i.e., V P · 0.95), 11.0m} / s (V P · 1.
05), and a laser scanning polycrystalline at _{13.0m / s (V P · 1.24} ), forming a TFT of the scanning direction and the current direction, the width direction of the stripe of polycrystalline silicon semiconductor thin film field effect mobility Shows the results of measuring the distribution of.

The channel width of each TFT is 4 μm. At 10.0 m / s, the field-effect mobility at the center of the stripe is high, but the width of the region exhibiting a high value is relatively narrow, so that the balance between the alignment accuracy, the required field-effect mobility, and its uniformity, In some cases, the condition of 11.0 m / s is more advantageous. Under these conditions, the highest field effect mobility is 10.
0m / s, but with uniformity equivalent to 13m / s
A relatively large field-effect mobility can be obtained. Further, the productivity is improved by the higher scanning speed.

Although the upper limit of the vertical axis in FIG. 16 is 80 cm ² / V · s, there is also an example in which 125 cm ² / V · s is obtained. There is a correlation with the temperature at the time of forming the amorphous silicon semiconductor thin film, and it is considered that a polycrystalline silicon semiconductor thin film of about 200 cm ² / V · s can be formed.

Next, the characteristics of the polycrystalline silicon semiconductor thin film of the present invention will be described. FIG. 18 shows a transmission electron microscope (TEM) photograph of a cross section parallel to the laser scanning direction of a polycrystalline silicon semiconductor thin film formed by scanning a laser beam beam spot at 10 m / s.

The crystal grains are irregular in shape as a whole, and grain boundaries between the crystal grains are not clear. However, it is possible to read a state where, although irregular, the regions having the same contrast (regions having the same azimuth) in the scanning direction are continuous over several μm. This means that crystal grains having a size equal to or less than the film thickness are arranged in the scanning direction with the same orientation. This state of the crystal grains is considered to be the reason for the high mobility in the scanning direction.

FIG. 17 shows the dependence of the activation energy of the on-current of the TFT for flowing a current parallel to the laser scanning direction on the laser annealing scanning speed. It is considered that the activation energy of the on-state current corresponds to the barrier energy at the grain boundary. When the scanning speed is reduced, the activation energy is reduced, and becomes almost zero at 10 m / s. At this scanning speed, the total number of defects at the crystal grain boundaries is extremely small.

Except for the process of forming the polycrystalline silicon semiconductor thin film, the on-current of the polycrystalline silicon semiconductor TFT using the polycrystalline silicon semiconductor thin film formed by solid phase growth by heat treatment at 600 ° C. for 72 hours was exactly the same. The activation energy is 0.06 to 0.07 eV. A polycrystalline silicon semiconductor TFT using a polycrystalline silicon semiconductor thin film formed by irradiating a KrF excimer laser 10 times at 300 mJ is 0.1 μm.
03 to 0.04 eV. According to the method of the present invention, a polycrystalline silicon semiconductor thin film having an extremely small energy barrier at a crystal grain boundary could be obtained.

Next, the content of hydrogen will be described. The polycrystalline silicon semiconductor thin film of the present invention has a characteristic that a relatively large amount of hydrogen atoms are contained in the film. In contrast, J
apan. J. Appl. Phys. Vol. 28p.
As disclosed in 1789-1793, the hydrogen concentration of a polycrystalline silicon semiconductor thin film polycrystalline by excimer laser annealing is 0.2 atm% or less.

Japanese Patent Application Laid-Open No. Hei 4-311038 discloses that as a starting material for performing crystallization by heat treatment,
It is described that an amorphous silicon semiconductor thin film having a hydrogen concentration of 0.08 to 0.8 atm% is appropriate. Further, the hydrogen content in the thickness direction of the polycrystalline silicon semiconductor thin film of the present invention is substantially uniform. The measurement was performed using HFS (Hydr
Oogen Forwarded Scatterin
g) The measurement was performed.

On the other hand, although the polycrystalline silicon semiconductor thin film according to the present invention depends on the forming conditions, in a process using PECVD at a maximum temperature of about 350 ° C., an amorphous silicon semiconductor having a hydrogen concentration of about 10 to 20 atm% is used as a starting material. The hydrogen concentration of the obtained polycrystalline silicon semiconductor thin film using a thin film is preferably at least 1 atm%, and more preferably about 1.6 to 5.0 atm%.

In addition, LPCV using disilane as a source gas
In the process using D at a maximum temperature of about 450 ° C., an amorphous silicon semiconductor thin film having a hydrogen concentration of about 2 atm% was used as a starting material, and the hydrogen concentration of the obtained polycrystalline silicon semiconductor thin film was about 0.5 atm%. It is considered that this relatively large amount of hydrogen atoms sufficiently seals dangling bonds, thereby reducing defects at grain boundaries and contributing to improvement in mobility.

Further, the present inventors have conducted intensive studies on the production of a polycrystalline silicon semiconductor thin film using HSBA. As a result, the optimum dehydrogenation heat treatment temperature range for each film forming temperature of an amorphous silicon semiconductor thin film was found. Turned out to exist. For example, the highest mobility can be obtained when the dehydrogenation heat treatment is performed at 350 ° C. for the film formation at 300 ° C., 400 ° C. for the film formation at 250 ° C., and 450 ° C. for the film formation at 200 ° C. As described above, the optimum heat treatment temperature tends to be higher as the film formation temperature is lower.

Therefore, when the two temperatures are related to each other, the film forming temperature of the amorphous semiconductor thin film is set to 250 ° C. or less, and the dehydrogenation temperature before performing the beam annealing is set to (650 ° C. ± 30 ° C.-film forming temperature). It has been found that a good polycrystalline silicon semiconductor thin film can be formed by performing the method.

When comparing samples subjected to dehydrogenation heat treatment at an appropriate temperature according to the film formation temperature, higher mobility is obtained when the film is formed at a lower temperature. This result agrees with the result of evaluating the nucleation rate of the amorphous silicon film by the solid-phase growth at 600 ° C. for 12 hours in both the deposition temperature dependency and the dehydrogenation temperature dependency.

That is, high mobility can be obtained by polycrystallizing a film which is more amorphous and has a low nucleation rate by HSBA. Here, more amorphous means that the short-range order is more disordered and the density of a portion that easily becomes a crystal nucleus is lower.

[0059] When HSBA by V _P near, in the case of film high mobility can be obtained in the scanning direction area of the line portion in which streak-like crystal grains are included when observed polycrystalline silicon surface, It was confirmed that the area was relatively larger than the area of the uniform portion containing the isotropic crystal grains. Even when scanning faster than V _P, who was HSBA a low nucleation rate amorphous silicon film was relatively high mobility can be obtained than in the case of high nucleation rate amorphous silicon film.

Regarding the crystal nucleus, an optical microscope transmission photograph of the formed polycrystalline silicon film was taken at a magnification of 1000 times. A 5 mm × 5 mm frame (corresponding to an area of 25 μm ² ) is set at random at several places on the photograph, the number of visible crystals contained therein is counted, and the average value of the whole is taken. The generation density of crystal nuclei per area (μm ² ) was obtained.

The linearity is determined by visually discriminating between streak crystal grains and isotropic crystal grains, and by what area ratio exists in the stripe width direction (the direction perpendicular to the longitudinal direction which is the beam irradiation direction). Was counted.

[0062]

Embodiments of the present invention will be described below.
Examples 1, and Examples 4, 5, 7 to 10 are the present invention, and Examples 2, 3, and 6 are comparative examples. 1 to 8
The index arrow shown on the right side of the micrograph of (1) corresponds to the actual size of 50 μm. The direction S in FIGS. 1 to 4 is the scanning direction at the time of beam annealing. 19 to 26 show color micrographs corresponding to FIGS.

Example 1 An SiO ₂ film at 300 ° C., an amorphous silicon film at 250 ° C. on a glass substrate by PECVD,
SiN _X film, respectively as an antireflection film at 350 ° C. 20
0nm, 130nm, 50nm lamination, 400
C., and laser annealing polycrystallization was performed using a continuous oscillation mode argon ion laser as a beam light source. That is, the measurement was performed using the above-mentioned HSBA.

At this time, the beam diameter on the substrate surface is a diameter at which the energy density becomes 13.5% of the maximum value, and the beam diameter in the scanning direction is 100%.
μm, and 140 μm in the vertical direction. Scan speed 1
The amorphous silicon film was polycrystallized at a laser output of 7.0 W at 0 m / s. Since V _{P of the} amorphous silicon film of this example is 10.5 m / s, the scanning speed coefficient K, which is the ratio of scanning speed / V _P , was 95.2%.

After removing the SiN _X film of the antireflection film with 0.5% hydrofluoric acid, the surface of the polycrystalline silicon film was etched with a 64% hydrazine aqueous solution and observed with an optical microscope. And more than half of the area showed a linear appearance, and fine isotropic granular regions were observed in the gaps (FIG. 1). The ratio of the relative area of the linear portion is referred to as a linear ratio. In this example, the linear ratio was about 50%.

In order to evaluate the network structure between the atoms of the amorphous silicon film formed and heat-treated in the same manner as described above, solid-phase growth was performed by heat treatment at 600 ° C. for 12 hours. The density was observed with an optical microscope (FIG. 5). In this example, it was about 0.4 / μm ² .

An n-channel TFT for passing a current in a direction parallel to the beam scanning was formed at the position of the stripe of the polycrystalline silicon film formed of HSBA. The TFT has a self-aligned coplanar structure in which a source and a drain are formed by an ion implantation method. The gate insulating film was formed by plasma CVD. The field effect mobility ν _L of the TFT formed from the polycrystalline silicon semiconductor stripe is 95 cm ² / V ·
s was obtained.

Example 2 An amorphous silicon film was formed at 300 ° C.
A polycrystalline silicon film was formed by HSBA in the same manner as in Example 1 except that a film was formed to a thickness of 20 nm and the heat treatment after the formation of the SiN _x film as the antireflection film was not performed. The linearity of this example is about 30% (FIG. 2), and the field effect mobility v _L is 70 cm ² /
V · s. The result of nucleation in the solid phase growth of the amorphous silicon film used in this example was about 0.8 / μm ² (FIG. 6).

(Example 3) HSBA was performed in the same manner as in Example 1 except that the heat treatment after the formation of the SiN _x film as the antireflection film was not performed.
Thus, a polycrystalline silicon film was formed. The linearity of this example is about 40%, and the field effect mobility ν _L is 50 cm ² / V ·
s (FIG. 3). Further, as a result of nucleation in the solid phase growth of the amorphous silicon film of this example, nucleation was remarkably large, and many portions were mutually bonded, and thus could not be counted (FIG. 7).

(Example 4) An amorphous silicon film was formed at 200 ° C.
A heat treatment is performed at 450 ° C. after the formation of the SiN _x film as the antireflection film at a laser scanning speed of 10.5 m / s.
TF was obtained in the same manner as in Example 1 except that the laser output was changed to 7.2 W.
T was formed. 125 cm ² as the field effect mobility ν _L
/ V · s was obtained. The linearity of the polycrystalline silicon film is about 8
0% (FIG. 4). The result of nucleation in the solid phase growth of the amorphous silicon film used in this example was about 0.07 / μm ²
(FIG. 8).

(Example 5) A TFT was formed in the same manner as in Example 1, except that the laser scanning speed was 12 m / s and the laser output was 8.4 W. Field effect mobility ν _L as 50 cm ² / V ·
s was obtained. At the scanning speed of this example, no linear portion on the surface of the polycrystalline silicon film was observed.

(Example 6) A TFT was formed in the same manner as in Example 2 except that the laser scanning speed was 12 m / s and the laser output was 8.4 W. 40 cm ² / V · as the field effect mobility ν _L
s was obtained. At the scanning speed of this example, no linear portion on the surface of the polycrystalline silicon film was observed. Next, Table 1 summarizes parameters and data of Examples 1 to 6.

[0073]

[Table 1]

(Examples 7 and 8) Using the TFTs of Examples 1 and 4, a row driving circuit and a column driving circuit of a TFT substrate were formed. FIG. 14 shows an example of a plane pattern of the polycrystalline silicon semiconductor TFT 40 used in this example. A source 31, a gate 32, a drain 35, and a silicon island 34 made of a polycrystalline silicon semiconductor were formed. The source 31 and the drain 35 are opposed in a comb shape, the gate 32 is formed in a zigzag or spiral shape, and the current direction of the channel is provided in substantially the same direction as the scanning direction S in HSBA. Utilizing the anisotropy of the field effect mobility of the polycrystalline silicon semiconductor, the higher v _L is used.

Then, it was found that it had a performance capable of supplying a high drain current. It can be used for a driving circuit in a peripheral driving circuit requiring high driving capability. In addition, the switching speed is sufficiently fast, and peripheral circuits can be integrated.

Then, the TFT substrate 10 for the liquid crystal display device
0 was formed. The pixel matrix is 1024 x 128
0, and the row driving circuit 52 and the column driving circuit 51 were integrated on the same glass substrate. FIG. 15 shows a plan view thereof. A part of the shift register 52A of the column driving circuit 51 and the row driving circuit 52 of the TFT substrate 100 and the final buffer 5
The above-mentioned polycrystalline silicon semiconductor TFT was used for 1A.

Further, an alignment film treatment was performed, a counter substrate was provided, the periphery was sealed, empty cells were formed, and liquid crystal was injected into the cells to complete a liquid crystal display device. When the operation test was performed, a good video image was displayed. High-speed operation becomes possible as compared with the prior art, and the operating frequency of the shift register is 8 MHz for the TFT of Example 1 and T
11 MHz was obtained by FT.

(Examples 9 and 10) Using the row drive circuits and column drive circuits of Examples 7 and 8, TFT substrates were prepared. On the same insulating substrate, a display portion (pixel electrode and row electrode, column electrode, and pixel TFT), a row drive circuit, and a column drive circuit were integrated. Since the entire circuit can be built in the same process, the overall manufacturing cost has been reduced,
Further, the production yield was able to be improved.

[0079]

The present invention aims at improving the performance of the conventional polycrystalline semiconductor thin film, finds a method of manufacturing an HSBA which can improve the film quality of the polycrystalline semiconductor thin film, and obtains a TFT with higher characteristics.
Could be obtained.

That is, the amorphous semiconductor thin film is polycrystallized by setting an optimum scanning speed, and furthermore, by combining the physical properties of the polycrystalline semiconductor thin film and the pattern arrangement of the TFTs, compared with the conventional example, Dramatically improved TF
T substrates and active matrix display elements can now be manufactured.

As can be seen from a comparison between Example 1 and Example 2, the field effect mobility of the polycrystalline silicon semiconductor TFT is 7
100 μm because it improved from 0 to 95 cm ² / V · s
The writing time for a pixel having a size of × 300 μm is 0.
It was reduced from 2 μs to 0.15 μs.

Further, the maximum operating frequency of the shift register using such a polycrystalline silicon semiconductor TFT has been improved from the conventional operation performance of 6 MHz to 8 to 11 MHz. As a result, the display density and outer size of a liquid crystal display panel in which a peripheral drive circuit including a row drive circuit and a column drive circuit are integrated on the same substrate under the condition that the pitch is 300 μm and the number of input signals is 40 or less at the maximum. And 1
It can be enlarged from a 5.1 inch size XGA to a 19.1 inch size SXGA (1024 × 1280).

According to the present invention, even if the TFT substrate has a non-monolithic type, that is, a TFT substrate provided with a polycrystalline semiconductor TFT formed on a glass substrate, a peripheral driving circuit that requires high-speed operation and large current driving is combined with the pixel region. Now, it can be integrated further. Also, the driving TF for the pixel portion
T also has a margin of operation margin, and the aperture ratio can be further improved based on the overall optical performance as a display element, for example, a fixed pixel size and a specification of a driving TFT.

In the present invention, a stripe of a polycrystalline semiconductor thin film exhibiting anisotropic field-effect mobility can be obtained, and can be used as an electronic component element used for a display element or the like.

Further, in the present invention, a homogeneous polycrystalline semiconductor thin film which can be used for a TFT for high-speed switching operation can be stably obtained by the field effect mobility.

For example, in the case of employing the block sequential driving method, a TFT substrate capable of displaying a video image even when the writing time to the pixel driving TFT is shortened could be formed. In other words, even if an offset gate structure is used for the pixel driving TFT to provide a certain withstand voltage based on the relationship between the holding ratio and the driving voltage, the polycrystalline semiconductor TFT of the present invention formed from a film with high field-effect mobility can achieve this. did it.

Further, the polycrystalline semiconductor TFT of the present invention could be used even in a circuit system having the strictest operating conditions among the row driving circuits or the column driving circuits. That is, a circuit having a high operating frequency can be integrated and formed on the same substrate by a low-temperature process. With the TFT substrate integrated on the same substrate, the manufacturing cost of the entire production system can be reduced and the size of the TFT substrate can be reduced.

Further, a high-quality and highly-reliable polycrystalline semiconductor thin film can be supplied stably and continuously with high production efficiency. That is, a mass production technology that can be used industrially was established. In addition, it has become possible to integrally produce a low-temperature-formed polycrystalline silicon TFT array substrate in combination with another conventionally known process technology.

Further, according to the present invention, a polycrystalline semiconductor thin film having more uniform characteristics and higher field-effect mobility than the conventional example could be obtained. In particular, the process of polycrystallization using HSBA can achieve high throughput.

Further, according to the present invention, a highly productive HS
Even with BA, a high-performance polycrystalline semiconductor TFT can be stably manufactured, and its reliability has been improved. In particular, it could be applied to small to medium sized TFT-LCDs.
In addition, a large and high-density display element for a workstation can be manufactured. In addition, the present invention can be applied to various applications as long as the effect is not impaired.

[Brief description of the drawings]

FIG. 1 is a micrograph showing a stripe of a polycrystalline silicon thin film of an example (Example 1).

FIG. 2 is a micrograph showing a stripe of a polycrystalline silicon thin film of a comparative example (Example 2).

FIG. 3 is a micrograph showing a stripe of a polycrystalline silicon thin film of a comparative example (Example 3).

FIG. 4 is a micrograph showing a stripe of a polycrystalline silicon thin film of an example (Example 4).

FIG. 5 is a micrograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 1 is thermally grown.

FIG. 6 is a micrograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 2 is thermally grown.

FIG. 7 is a micrograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 3 is thermally grown.

FIG. 8 is a micrograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 4 is thermally grown.

FIG. 9 is a characteristic diagram showing a correlation between a field-effect mobility and a scanning speed in the polycrystalline semiconductor thin film of the present invention.

FIG. 10 is a characteristic diagram showing the orientation of crystal grains of polycrystalline silicon by the HSBA method.

FIG. 11 is a schematic diagram of a polycrystalline stripe surface at a scanning speed (13 m / s).

FIG. 12 is a schematic view of a polycrystalline stripe surface at a scanning speed (11 m / s).

FIG. 13 is a schematic diagram of a polycrystalline stripe surface at a scanning speed (10 m / s).

FIG. 14 is a partially enlarged plan view of a polycrystalline semiconductor TFT of the present invention.

FIG. 15 is a plan view of a TFT substrate of the present invention.

FIG. 16 is a characteristic diagram of the field-effect mobility in the stripe width direction using the change in scanning speed as a parameter.

FIG. 17 is a graph showing a correlation characteristic between a scanning speed and E _act .

FIG. 18 is a TEM photograph of a crystal structure in a cross-sectional direction of a stripe.

FIG. 19 is a color microscope photograph showing a stripe of a polycrystalline silicon thin film of an example (Example 1).

FIG. 20 is a color microscope photograph showing a stripe of a polycrystalline silicon thin film of a comparative example (Example 2).

FIG. 21 is a color microscope photograph showing a stripe of a polycrystalline silicon thin film of a comparative example (Example 3).

FIG. 22 is a color microscope photograph showing a stripe of a polycrystalline silicon thin film of an example (Example 4).

FIG. 23 is a color microscope photograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 1 is thermally grown.

FIG. 24 is a color micrograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 2 is thermally grown.

FIG. 25 is a color micrograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 3 is thermally grown.

FIG. 26 is a color micrograph showing the distribution of crystal nuclei when the amorphous semiconductor used in Example 4 is thermally grown.

[Explanation of symbols]

 1: Field effect mobility when parallel to the scanning direction 2: Field effect mobility when perpendicular to the scanning direction 3: Field effect mobility when exhibiting random orientation

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 29/78 616T 618Z 627E

Claims (8)

[Claims] In a striped polycrystalline semiconductor thin film formed on an insulating substrate, isotropic crystal grains and streaky crystal grains arranged substantially parallel to the longitudinal direction of the stripe exist. A polycrystalline semiconductor thin film having a grain area larger than an isotropic crystal grain area. 2. The polycrystalline semiconductor thin film according to claim 1, wherein the polycrystalline semiconductor thin film contains hydrogen at 1 atm% or more. 3. A channel for a polycrystalline semiconductor TFT.
Or a polycrystalline semiconductor thin film using the polycrystalline semiconductor thin film described in 2, wherein the longitudinal direction of the stripe and the direction of the channel are provided substantially in parallel. 4. The polycrystalline semiconductor TFT according to claim 3, wherein the source electrode and the drain electrode of the polycrystalline semiconductor TFT are formed in a comb shape. 5. A row driving circuit for driving a pixel formed in a matrix, provided for each pixel, for supplying a row signal to a row electrode connected to the driving element, and a column connected to the driving element. A column driving circuit for supplying a column signal to an electrode is provided, and the polycrystalline semiconductor TFT according to claim 4 is used as a part of a row driving circuit and / or a part of a column driving circuit. substrate. 6. A method for forming a polycrystalline semiconductor thin film in which a beam spot is scanned on an amorphous semiconductor thin film to perform polycrystallization, wherein the amorphous semiconductor thin film is heated at 600 ° C. for 12 hours to perform solid phase growth. In this case, the density of crystal nuclei is 0.01 to 0.1.
A method for forming a polycrystalline semiconductor thin film, comprising using an amorphous semiconductor thin film of 5 / μm ² . 7. A method for forming a polycrystalline semiconductor thin film in which a beam spot is scanned on an amorphous semiconductor thin film to perform polycrystallization, wherein a film forming temperature of the amorphous semiconductor thin film is set to 250 ° C. or less.
The dehydrogenation temperature before beam annealing is set to (650 ° C. ± 3
0 ° C.—film formation temperature). 8. The polycrystalline semiconductor thin film according to claim 6 or 7, wherein the scanning in 90-110% of the scanning speed of the scanning speed V _P which induces spontaneous crystallization of the amorphous semiconductor thin film Forming method.