JP2003133560A - Method of manufacturing thin film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely obtain an evaluation result at the time of evaluating the crystal condition of a polysilicon film formed by a low temperature polycrystallization process. SOLUTION: After an amorphous silicon film 6a is formed on a substrate 2, the substrate 2 is cleaned in a cleaning process. In more practical, a pre- process to form a surface oxide layer 6s on the amorphous silicon film 6a with a solution including ozone and a post-process to remove the surface oxide layer 6s with a solution including fluoric acid are performed. Thereafter, an oxide film 6t is formed on the surface of the cleaned amorphous silicon film 6a. Next, a polysilicon film 6 which becomes the channel layer of a thin film transistor is formed by performing a laser annealing process to the amorphous silicon film 6a. In this case, the linearity and/or periodicity of the space structure of the film surface of the polysilicon film 6 is detected and the condition of the polysilicon film 6 is evaluated based on the detection result of the linearity and/or periodicity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor using polysilicon formed by a low temperature polycrystallization process as a channel layer and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a thin film transistor using polysilicon for a channel layer has been put into practical use. When polysilicon is used for the channel layer, the electric field mobility of the thin film transistor becomes very high. Therefore, when it is used as a drive circuit for a liquid crystal display, for example, the display becomes high definition, high speed, small size, and low power consumption. Can be realized.

In addition, a so-called low temperature polycrystalline silicon process, in which amorphous silicon is heat-treated by an excimer laser annealing apparatus to form a polysilicon film, has been put into practical use in recent years. By applying such a low temperature polycrystal process to a manufacturing process of a thin film transistor, heat damage to a glass substrate is reduced, and a heat-resistant large-area and inexpensive glass substrate can be used.

By the way, since the output power of the excimer laser annealing apparatus used in the low temperature polycrystal silicon process is unstable, the grain size of the polysilicon to be formed varies greatly. Therefore, the polysilicon film formed by using the excimer laser annealing apparatus does not always have a good grain size, resulting in poor quality. Therefore, in general, when performing an annealing process using such an excimer laser annealing device, an operation of feeding back the surface state of the polysilicon film generated by energy irradiation to the excimer laser annealing device to set the optimum laser energy density Is done.

For example, the state of a polysilicon film formed by using a low temperature polycrystalline silicon process is objectively and automatically evaluated, and the energy density of a laser irradiated from a laser annealing apparatus is optimized based on the information. A thin film transistor manufacturing system aimed at is disclosed in Japanese Patent Application Laid-Open No. 2001-1964.
No. 30, JP 2001-196592 A, JP 2001-19693 A, etc. are proposed. In these cases, when the polysilicon film is formed by performing excimer laser annealing treatment on the amorphous silicon film, the state of the polysilicon film is determined by performing image processing and evaluating the uneven spatial structure on the surface of the polysilicon film. ,
This is a thin film transistor manufacturing system in which the result is fed back to the setting of the energy density of the excimer laser.

[0006]

By the way, in the process of manufacturing a thin film transistor, impurities deposited on the surface of the amorphous silicon film after the amorphous silicon film is formed are
It is known to affect transistor characteristics and its uniformity. As a countermeasure against this, it is desirable to remove the attached impurities together with the native oxide film on the amorphous silicon by using a solution containing hydrofluoric acid, for example, before performing the laser annealing process on the amorphous silicon film.

However, JP-A-11-354801
As disclosed in Japanese Patent Laid-Open Publication No. 2004-242242, it is known that when a laser annealing process is performed after removing impurities with a solution containing hydrofluoric acid, irregularities on the surface of the polysilicon film are reduced. As a result, it was difficult to perform the above-described crystal evaluation when the laser annealing treatment was performed after the impurities were removed by the solution containing hydrofluoric acid. Therefore, there has been a problem that it is difficult to achieve both the step of removing impurities on amorphous silicon that affects the transistor characteristics and the uniformity thereof and the step of accurately evaluating crystallinity.

[0008]

[Means for Solving the Problems] In order to solve the problems of the prior art, which have been transferred, the following measures have been taken. That is, the present invention provides a film forming step of forming an amorphous silicon film on a substrate, a cleaning step of cleaning the substrate on which the amorphous silicon film is formed, and an amorphous silicon film of the substrate cleaned by the cleaning step. An oxide film forming step of forming an oxide film on the surface of the film, a laser annealing step of forming a polysilicon film to be a channel layer of the thin film transistor by performing a laser annealing process on the amorphous silicon film, A method of manufacturing a thin film transistor, which comprises performing an evaluation step of detecting linearity and / or periodicity of a spatial structure of a film surface and evaluating the state of the polysilicon film based on the detection result of the linearity and / or periodicity. In the cleaning step, the amorphous silicon is used in a solution containing ozone or a gas atmosphere containing ozone. A pretreatment to form a surface oxide layer on the film, characterized by comprising the post-treatment to remove surface oxide layer formed on the amorphous silicon film with a solution containing hydrofluoric acid. Alternatively, the cleaning step is characterized in that the surface of the amorphous silicon film is treated with a solution containing hydrofluoric acid to remove an unnecessary surface oxide layer. Alternatively, the cleaning step is characterized in that the surface of the amorphous silicon film is treated with plasma containing fluorine gas to remove an unnecessary surface oxide layer.

Preferably, in the oxide film forming step, an oxide film is formed on the amorphous silicon film in a solution containing ozone or a gas atmosphere containing ozone. Alternatively, in the oxide film forming step, an oxide film may be formed on the amorphous silicon film in a plasma atmosphere containing oxygen. In the evaluation step, the polysilicon film formed by laser annealing is irradiated with focused ultraviolet light, the reflected light thereof is detected, and the detected reflected light is imaged to obtain the polysilicon film. The surface space structure is evaluated, and the state of the polysilicon film is evaluated based on the evaluation.

According to the present invention, the surface oxide layer containing impurities is removed from the surface of the amorphous silicon film by performing the cleaning step prior to the irradiation of the laser beam. Specifically, pretreatment for forming a surface oxide layer on the amorphous silicon film in a solution containing ozone or a gas atmosphere containing ozone, and removing the surface oxide layer formed on the amorphous silicon film with a solution containing hydrofluoric acid. Perform post-processing. Alternatively, the surface of the amorphous silicon film may be simply treated with a solution containing hydrofluoric acid to remove the unnecessary surface oxide layer. Alternatively, the surface of the amorphous silicon film may be treated with plasma containing fluorine gas to remove the unnecessary surface oxide layer. This subsequent oxide film formation step is performed to form an oxide film again on the surface of the cleaned amorphous silicon film by removing the surface oxide layer. By performing laser annealing through this oxide film, the crystalline state can be evaluated. In this way, by inserting the oxide film formation step between the cleaning step and the laser annealing step, the process of removing impurities on amorphous silicon that affects the transistor characteristics and its uniformity, and the crystallinity are accurately evaluated. It becomes possible to make both processes compatible.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1A to 1C are process diagrams showing a method of manufacturing a thin film transistor according to the present invention. Here, as a typical example, a method for forming thin film polycrystalline silicon for a bottom gate type transistor will be shown. Here, a bottom gate type transistor is taken as an example, but the present invention may be used for a top gate type transistor.

First, in step (1), a gate electrode 3 is formed on an insulating substrate 2 such as glass by, for example, a sputtering method.
A high-melting point metal such as Mo is deposited to a thickness of about 100 nm,
It is processed into a predetermined shape by a lithography technique and dry etching or wet etching. Then, a silicon nitride film 4 and a silicon oxide film 5 to be a gate insulating film are formed on the substrate 2 by a low pressure chemical vapor deposition method (LP-CVD method), a plasma CVD method, a sputtering method or the like to a thickness of about 100 nm. An amorphous silicon film 6a having a relatively small crystal grain is used as an active layer of a thin film transistor (TFT).
Deposit about nm.

In step (2), the surface of the amorphous or relatively small crystal grain silicon film 6a is exposed to, for example, ozone.
Wash with a solution containing about 5 ppm. As a result, the impurities on the silicon film 6a are incorporated into the surface oxide layer 6s on the silicon film 6a formed by ozone cleaning.

In step (3), the surface oxide layer 6s deposited on the silicon film 6a which is amorphous or has a relatively small crystal grain size by ozone is removed by a solution containing, for example, about 1% hydrofluoric acid. The surface of the amorphous silicon film 6a is cleaned. Alternatively, instead of this, the surface of the amorphous silicon film 6a may be treated with plasma containing fluorine gas to remove the unnecessary surface oxide layer 6s. In some cases, step (2) may be omitted, and the surface of the amorphous silicon film 6a may be simply treated with a solution containing hydrofluoric acid to remove unnecessary surface oxide layers such as natural oxide films. Alternatively, the surface of the amorphous silicon film 6a may be simply treated using plasma containing fluorine gas to remove an unnecessary surface oxide layer contaminated with impurities such as a natural oxide film.

In step (4), an oxide film 6t of about 2 nm is formed on the cleaned amorphous or relatively small crystal grain silicon film 6a by exposing the substrate to a solution containing ozone of about 15 ppm, for example. To do. This enables crystal evaluation. In some cases, the oxide film 6t may be formed on the amorphous silicon film 6a in a gas atmosphere containing ozone. Alternatively, the oxide film 6t may be formed on the amorphous silicon film 6a in a plasma atmosphere containing oxygen.

In step (5), the silicon thin film 6a is crystal-grown to a grain size of a predetermined size by excimer laser pulse annealing, and converted into the polysilicon film 6.

In step (6), the polysilicon film 6 formed by laser annealing is irradiated with focused ultraviolet light, the reflective film is detected, and the detected reflected light is CC-reflected.
The surface unevenness 6 of the polysilicon film 6 is picked up by a D camera or the like.
The spatial structure of p is analyzed to determine the crystallinity of the polysilicon film 6. Based on this, the optimum condition of the laser pulse energy density for irradiation in step (5) is calculated and fed back to the irradiation energy density used for the next laser annealing. By forming a thin film transistor using the gate electrode 3, the gate insulating films 4 and 5, and the polycrystalline silicon thin film 6 formed on the glass substrate 2 described above, a thin film poly silicon transistor showing stable characteristics is obtained. can get.

Next, a polysilicon film evaluation apparatus and an evaluation method to which the present invention is applied will be described. A polysilicon film evaluation apparatus to be described below is, for example, a thin film transistor (bottom gate type TFT) having a bottom gate structure.
It is used to inspect the polysilicon film formed during the manufacturing process of FT). As described with reference to FIG. 1, the bottom gate type TFT is a thin film transistor having a structure in which a gate electrode, a gate insulating film, and a polysilicon film (channel layer) are sequentially stacked from the bottom on a glass substrate, for example. is there. That is, the bottom gate type TFT is a TFT having a structure in which the gate electrode is formed between the polysilicon film which becomes the channel layer and the glass substrate. Although an evaluation device for evaluating a bottom gate type TFT will be described here as an example, the present invention is not limited to such a bottom gate type TFT, and a polysilicon film (channel layer) is formed on a glass substrate. After that, it is also possible to apply to a so-called top gate type TFT in which a gate electrode is provided on the upper layer.

Structure of Bottom Gate Type TFT First, a specific configuration example of the bottom gate type TFT will be described with reference to FIG. As shown in FIG. 2, the bottom gate type TFT 1 includes a gate electrode 3, a first gate insulating film 4, a second gate insulating film 5, a polysilicon film 6 and a stopper on a glass substrate 2 having a thickness of 0.7 mm. 7, first interlayer insulating film 8, second interlayer insulating film 9, wiring 10, planarizing film 11,
The transparent conductive film 12 is laminated and configured.

The gate electrode 3 is formed on the glass substrate 2 by 100
A molybdenum (Mo) film having a thickness of up to 200 nm is formed and then patterned by anisotropic etching.

The first gate insulating film 4 has a film thickness of 5 for example.
It is made of 0 nm silicon nitride (SiN _x ). Silicon nitride (SiN _x ) is laminated and formed on the glass substrate 2 on which the gate electrode 3 is formed.

The second gate insulating film 5 has, for example, a film thickness of 2
00nm silicon dioxide (SiO _Two) Consists of this
Silicon dioxide (SiO_Two) Is the first gate insulating film 4
It is formed by being stacked on top.

The polysilicon film 6 has a film thickness of, for example, 30 to 30.
It is made of 80 nm polysilicon (p-Si). The polysilicon film 6 is formed by being laminated on the second gate insulating film 5. The polysilicon film 6 functions as a channel layer of the bottom gate type TFT 1. The polysilicon film 6 is formed, for example, by forming an amorphous silicon (a-Si) film having a thickness of 30 to 80 nm by the LPCVD method or the like and then annealing the amorphous silicon to polycrystallize it. . In the step of polycrystallizing the polysilicon film 6, a laser annealing process using an excimer laser which is an ultraviolet laser is used. This excimer laser annealing process emits a pulsed laser beam whose irradiation surface is linear,
Amorphous silicon is polycrystallized into polysilicon while moving the irradiation region of the pulse beam. The irradiation surface of the laser beam has a length in the longitudinal direction of 20 cm, a length in the short side direction of 400 μm, and a pulse frequency of 300 Hz. The scanning direction of the laser beam at the time of performing the excimer laser annealing treatment is the direction orthogonal to the longitudinal direction of the irradiation surface of the linear laser (that is, the short side direction).

Then, this polysilicon film 6 is polycrystallized by excimer laser annealing, and thereafter, impurities are ion-doped to form source / drain regions. This ion doping is performed on the gate electrode 3
This is performed after the stopper 7 is formed at a position corresponding to the gate electrode 3 so that impurities are not implanted into the upper polysilicon film 6. The stopper 7 is made of, for example, silicon dioxide (SiO ₂ ) having a film thickness of 200 nm,
It is formed by using the mask or the like used when forming the gate electrode 3.

The first interlayer insulating film 8 has a film thickness of, for example, 30.
It is made of 0 nm silicon nitride (SiN _x ), and this silicon nitride (SiN _x ) is laminated and formed on the polysilicon film 6.

The second interlayer insulating film 9 has a film thickness of 15 for example.
It is made of 0 nm silicon dioxide (SiO ₂ ), and this silicon dioxide (SiO ₂ ) is laminated and formed on the first interlayer insulating film 8.

The wiring 10 is the source / source of the polysilicon film 6.
Contact holes for connecting the drain regions are opened at positions corresponding to the source / drain regions of the first interlayer insulating film 8 and the second interlayer insulating film 9, and then aluminum (Al) and titanium (Ti) are formed. Is formed and patterned by etching. This wiring 10
Connects the source / drain regions of each transistor formed on the polysilicon film 6 to form a predetermined circuit pattern on the substrate.

The flattening film 11 is formed of the bottom gate type TF.
A film for flattening the surface of T1 is formed after the wiring 10 is formed and has a film thickness of 2 to 3 μm.

The transparent conductive film 12 is made of, for example, a transparent conductive material such as ITO, and is a conductive line for connecting the wiring 10 to an external element or an external wiring existing outside the bottom gate type TFT 1. This transparent conductive film 12 is
After the contact hole is opened in the flattening film 11, it is formed on the flattening film 11.

In the bottom gate type TFT 1 as described above, since the channel layer is made of polysilicon, the electric field mobility of the channel layer becomes very high. Therefore, when it is used as a drive circuit for a liquid crystal display, for example, it is possible to realize high definition, high speed, downsizing of the display. Further, in the bottom gate type TFT 1 as described above, a so-called low temperature polycrystallization process is used in which the polysilicon film 6 is formed by heat-treating amorphous silicon using excimer laser annealing. Therefore, heat damage to the glass substrate 2 in the polycrystallization process is reduced, and a large-area and inexpensive glass substrate can be used.

Necessity of Inspection of Polysilicon Film By the way, it is said that an important factor for determining the electric field mobility of the polysilicon film 6 is the grain size of polysilicon. The grain size greatly depends on the energy given to the polysilicon film 6 during the excimer laser annealing process. Therefore, the control and stabilization of the energy density of the laser during the excimer laser annealing process greatly affects the characteristics and yield of the completed bottom gate type TFT 1.

However, the excimer laser annealing apparatus used in the excimer laser annealing treatment is
The output variation of the energy density of the emitted laser is relatively large. Therefore, when excimer laser annealing is performed using the excimer laser annealing apparatus, fluctuations in energy given to the polysilicon film 6 with respect to the energy allowable range (manufacturing margin of the polysilicon film 6) at which a good grain size can be obtained. Becomes large and it is difficult to stably manufacture the polysilicon film 6.

Therefore, even when the excimer laser annealing is performed under the same conditions, the grain size of the polysilicon film 6 largely changes, and, for example, when the laser energy becomes too large, the silicon crystal is microcrystallized. In addition, if the laser energy becomes too small, a sufficiently large grain size cannot be obtained, and in each case sufficient electric field mobility cannot be obtained, resulting in a defect.

As described above, in the excimer laser annealing apparatus, the output fluctuation of the energy density of the emitted laser is relatively large. Therefore, it is difficult to control the energy density of the laser so that the grain size of the polysilicon film 6 becomes a good size.

Therefore, in general, when performing an annealing process using such an excimer laser annealing apparatus,
For example, when the polycrystallizing step of the polysilicon film 6 as shown in FIG. 3A is completed, 100% inspection of the crystal state of the polysilicon film 6 formed on the outermost surface thereof,
Alternatively, the product is randomly extracted and the crystal state is inspected to determine whether or not the manufactured product is defective at this stage, or the excimer laser annealing device is used to apply the polysilicon film 6 to the polysilicon film 6. The energy density of the laser is set by feeding back the given energy information.

The polysilicon film evaluation apparatus evaluates the formed polysilicon film 6 at the stage when the polycrystallizing step of the polysilicon film 6 is completed, and the manufactured product is a defective product at this stage. It is used when determining whether or not the value is satisfied, and when setting the laser energy by feeding back information to the excimer laser annealing apparatus.

Evaluation Principle of Polysilicon Film and Evaluation Method (1) First, the evaluation principle of the polysilicon film formed by the above-mentioned excimer laser annealing will be described.

The mobility of the thin film transistor manufactured as described above is greatly affected by the grain size of polysilicon. In order to obtain sufficient mobility, it is desirable that the grain size of polysilicon is large.

The grain size of the polysilicon film largely depends on the energy given by the excimer laser annealing. The grain size of the polysilicon film is shown in FIG.
As shown in (B), when the given energy increases, it increases with it, but when it exceeds a certain predetermined energy (position L in the figure: the energy at this time is the allowable minimum energy L), the grain size is increased. Becomes large enough and then changes little and stabilizes. When the energy is further increased, a certain position (position H in the figure.
The energy at this time is the maximum allowable energy H)
Therefore, the change in grain size becomes large, and polysilicon becomes fine crystal grains at a certain critical point.

Therefore, normally, when excimer laser annealing is performed, the range from the allowable minimum energy L shown in FIG. 3 (B) where the grain size is sufficiently large to the allowable maximum energy H before the fine crystal grains are formed. By controlling the energy density of the laser to be irradiated, a sufficiently large grain size is obtained. By irradiating the amorphous silicon film with laser light that gives energy in such a range, the mobility of the completed thin film transistor can be sufficiently increased.

(2) Next, an image of the film surface of the polysilicon film when the excimer laser annealing is performed with the laser energy density being the optimum value, and the polysilicon film when the energy density is smaller than the optimum value. An image of the film surface is compared with an image of the film surface of the polysilicon film when the energy density is larger than the optimum value. In Figure 4,
The image in each case is shown. FIG. 4A is a diagram showing an image of the film surface of the polysilicon film when the energy density is lower than the optimum value, and FIG. 4B is a film of the polysilicon film when the energy density is the optimum value. It is a figure which shows the image of a surface, and is a figure which shows the image of the film | membrane surface of a polysilicon film when FIG.4 (C) makes an energy density larger than an optimal value. Each image shown in FIG. 4 is an image picked up by a microscope device using ultraviolet light, and details of this microscope device will be described later.

In FIG. 4, the scanning direction of the laser in the excimer laser annealing is the X direction in the figure. In addition,
As described above, the amorphous silicon film is irradiated with the laser beam whose irradiation surface is linear, and the scanning direction is a direction orthogonal to the longitudinal direction of the irradiation surface shape of the laser beam.

Here, comparing the image of FIG. 4 (B) when the energy density during excimer laser annealing is set to the optimum value with the other images shown in FIGS. 4 (A) and 4 (C), , The following features have appeared.

First, the surface image of the polysilicon film when the energy density is set to the optimum value (FIG. 4B) shows the surface image of the polysilicon film in which the energy density is not optimum (FIG. 4A and FIG. The image has linearity as compared with FIG. 4C. Specifically, the image shows linearity in the laser scanning direction (X direction in FIG. 4). That is, the surface of the polysilicon film when the energy density is set to the optimum value is characterized by a regular shape in which linearity appears in its spatial structure.

The surface image of the polysilicon film when the energy density is set to the optimum value (FIG. 4B) shows the surface image of the polysilicon film in which the energy density is not optimum (FIG. 4A and FIG. The image has periodicity as compared with FIG. 4C. Specifically, the image has periodicity in a direction orthogonal to the laser scanning direction (Y direction in FIG. 4). That is, when the energy density is set to the optimum value, the surface of the polysilicon film is characterized by having a regular shape in which the spatial structure has periodicity.

Therefore, in the polysilicon film evaluation apparatus according to the embodiment of the present invention, the state of the polysilicon film is inspected by utilizing the above characteristics. That is, in the polysilicon film evaluation apparatus of the embodiment of the present invention, the surface image of the polysilicon film after the excimer laser annealing is numerically analyzed, and linearity appears in the surface spatial structure of the polysilicon film. Whether the surface spatial structure of the polysilicon film has periodicity, or whether the surface spatial structure of the polysilicon film has linearity and periodicity, the state of the polysilicon film is inspected. To do.

The image of the film surface of the polysilicon film after the excimer laser annealing is performed with the energy density set to a good value is an image showing linearity and periodicity in FIG. 5 (A). As described above, this is considered to be due to the formation of the natural oxide film (SiO ₂ ) on the upper layer of the amorphous silicon film. The thickness of this natural oxide film is 2-3 nm.
It is thought that it has become. Also, this natural oxide film
It is considered that the oxidation stops until the film thickness reaches a certain value and the film thickness does not exceed a certain value.

When the amorphous silicon having the natural oxide film formed thereon is annealed by using an excimer laser, it is considered that the natural oxide film (SiO ₂ ) rises as shown in FIG. 5B. To be If the energy density of the excimer laser annealing is good, the shape of this ridge is such that a plurality of linear convex portions parallel to the scanning direction of the excimer laser are formed, and each straight line has a periodicity at equal intervals. become. Therefore, when a film surface image of the polysilicon film is imaged by a microscope device using ultraviolet light, the influence of the reflected diffracted light by the linear convex portion causes
It is considered that the striped image as shown in (B) can be referred to. Note that, for example, the thickness of the natural oxide film is 2 to 3n.
m, the energy density of the XeCl excimer laser is 30
If it is 0 to 400 mJ / cm ² , the interval between the linear convex portions is about 0.3 μm. This interval is approximately the wavelength of the annealing laser light source.

The shape of this natural oxide film after annealing changes as shown in FIG. 5C due to factors such as the energy density given by excimer laser annealing and the difference in film thickness of the amorphous silicon film. It is considered to be a thing. For example, when the energy density of the excimer laser annealing is not good, it is considered that the linearity and periodicity of the shape of the ridges are broken. Further, even at different locations on the same film surface, linearity and periodicity may not be constant values due to various factors such as a difference in film thickness.

(3) Usually, in the manufacturing process of a thin film transistor, an impurity element removing step using a dilute hydrogen fluoride aqueous solution (dilute HF) is provided. Also in the manufacturing process of the bottom gate type TFT 1 described above, usually, after the amorphous silicon film is formed, the impurities are removed by dilute HF before the laser annealing process.

However, if the substrate is washed with diluted HF after forming the amorphous silicon film, the natural oxide film formed on the amorphous silicon film is dissolved together with the impurities. Therefore, even if laser annealing is performed after that, the surface of the polysilicon film is
The raised shape of the natural oxide film as shown in FIG. 5B is not formed. Therefore, the linearity and periodicity do not appear in the image of the film surface of the polysilicon film, and the state of the polysilicon film cannot be evaluated.

Therefore, in order to make it possible to evaluate the state of the polysilicon film, as shown in FIG. 6, the surface cleaning treatment and the surface oxidation treatment are performed according to the present invention as a pre-step of performing the laser annealing treatment. That is, from the state (state 1) in which the natural oxide film (SiO ₂ ) is formed on the surface of the amorphous silicon film, the diluted HF cleaning is performed to remove impurities. At this time, the surface of the amorphous silicon film may be positively oxidized by immersing the substrate in ozone water prior to the diluted HF cleaning. When the HF cleaning is performed, the amorphous silicon film is in a state in which the natural oxide film (SiO ₂ ) on the surface is dissolved (state 2). A surface oxidation step is provided as the next step. In this surface oxidation step, for example,
The surface of the amorphous silicon film may be oxidized by immersing the substrate in ozone water of about 10 ppm. By providing the surface oxidation step before the laser annealing process, an oxide film can be formed on the amorphous silicon film (state 3). As a result, the laser annealing process causes the oxide film to rise (state 4), and the polysilicon film can be evaluated.

(4) Next, an example of a digitizing method in the case where the captured image of the polysilicon film has linearity, periodicity, linearity and periodicity will be described.

For example, when a picked-up image of a polysilicon film having linearity and periodicity is schematically shown, a large number of straight lines are arranged in parallel as shown in FIG. Is represented as On the other hand, when a captured image of a polysilicon film having neither linearity nor periodicity is schematically shown, irregular short straight lines and the like appear to appear irregularly as shown in FIG. . When numerically evaluating the linearity and periodicity from these images, the images are laid horizontally in a direction perpendicular to the direction in which there is likely to be periodicity The correlation may be expressed as a numerical value and evaluated. For example, if an image having linearity and periodicity is laterally displaced, as shown in FIG.
An image having a high degree of correlation and having a high degree of correlation appears at a certain fixed period, that is, at a certain constant amount of lateral displacement. On the other hand, in an image having neither linearity nor periodicity, as shown in FIG. 8B, even if the images are laterally displaced, an image with a high degree of correlation in which the images overlap each other does not appear at regular intervals. .

By using the concept of digitizing the correlation of the images when the images are laterally shifted as described above, it becomes possible to digitize and evaluate the periodicity of the polysilicon film. One specific method for realizing such a method is to obtain an autocorrelation function of an image, calculate a peak value and a side peak value of the autocorrelation function, and take a ratio of these. Here, the peak value is used to reduce the second minimum value (defocus value) in the y direction from the origin to the origin.
It may be the second or later). The side peak value is the second maximum value (not including the origin) in the y direction from the origin to the 2 in the y direction from the origin.
The value obtained by subtracting the second minimum value, etc. shall be referred to.

In the present invention, it is also possible to evaluate the state of the polysilicon film by evaluating either the linearity or the periodicity.

Further, as another example of the numerical method in the case where the picked-up image of the polysilicon film has linearity, periodicity, linearity and periodicity, for example, a standardized image is linearized. There is a method of adding the values of all pixels in the same direction to obtain the modulation degree. In addition, there is a method of taking the intensity of a certain frequency component by performing a two-dimensional Fourier transform on the standardized image. In addition, an extreme value (a minimum value or a maximum value) in an image (for example, an image that may have linearity in the y direction)
The coordinates in the x direction are extracted, and the coordinates within the range that is vertically long in the y direction (the center in the x direction is the extreme value × the average value of the coordinates, and the length in the x direction is the pitch of the array in the x direction) There is a method of taking dispersion. In addition, the coordinates of the extreme value (minimum value or maximum value) in the image (for example, an image that may have linearity in the y direction) are extracted, and the coordinates in the vertically long range in the y direction (the center in the x direction is the pole There is a method of taking an angle between each point and the points near the top and bottom with respect to the coordinate of (value x coordinate average value, length in x direction is pitch of array in x direction).

Specific Structure of Polysilicon Film Evaluation Device
And Processing Details (1) Next, a specific configuration example of the polysilicon film evaluation apparatus for evaluating the linearity and periodicity of the surface space structure of the polysilicon film as described above will be described.

The polysilicon film evaluation apparatus has a wavelength of 266n.
An image of a bottom-gate TFT manufacturing substrate (a substrate immediately after a polysilicon film is formed by performing excimer laser annealing on an amorphous silicon film) is imaged by a microscope device using an ultraviolet laser of m. This is an apparatus for evaluating the state of the polysilicon film formed from.

FIG. 9 shows a configuration diagram of the present polysilicon film evaluation apparatus.

Polysilicon film evaluation apparatus 20 shown in FIG.
Is a movable stage 21 and an ultraviolet solid state laser light source 22.
, CCD camera 23, optical fiber probe 24,
Polarizing beam splitter 25, objective lens 26, 1 /
The four-wave plate 27, a control computer 28, and an image processing computer 29 are provided.

The movable stage 21 is a stage for supporting the substrate 1 on which a polysilicon film to be inspected is formed. The movable stage 21 has a function of supporting the substrate 1 to be inspected and moving the substrate 1 to a predetermined inspection target position.

Specifically, the movable stage 21 comprises an X stage, a Y stage, a Z stage, a suction plate and the like.

The X stage and the Y stage are stages that move in the horizontal direction. The X stage and the Y stage move the substrate 1 to be inspected in the directions orthogonal to each other so that the substrate 1 to be inspected is moved. It is designed to lead to a predetermined inspection position. The Z stage is a stage that moves in the vertical direction, and is for adjusting the height of the stage. That is, the Z stage moves in the direction of the optical axis of the irradiated ultraviolet laser, in other words, in the direction perpendicular to the plane of the substrate 1. The moving direction of the Z stage is hereinafter referred to as the Z direction. The suction plate is for sucking and fixing the substrate 1 to be inspected.

The ultraviolet solid-state laser light source 22 has a wavelength of 266.
nm ultraviolet laser light source, for example, Nd: YAG
A 4th harmonic all-solid-state laser is used. In addition, as the ultraviolet laser light source, one having a wavelength of about 157 nm has been developed in recent years, and such an ultraviolet laser light source may be used as the light source.

The CCD camera 23 is a camera having a high sensitivity to ultraviolet light, and internally has a CCD as an image pickup element.
An image sensor is provided, and the surface of the substrate 1 is imaged by this CCD image sensor. This CCD camera 23
By cooling the main body, thermal noise, read-out noise, circuit noise, etc. generated in the CCD image sensor or the like are suppressed.

The optical fiber probe 24 is a waveguide for the ultraviolet laser light, and guides the ultraviolet laser emitted from the ultraviolet solid laser light source 22 to the polarization beam splitter 25.

The polarization beam splitter 25 reflects the ultraviolet laser light from the ultraviolet solid-state laser light source 22, irradiates the substrate 1 on the movable stage 21 through the objective lens 26, and at the same time, it is reflected from the substrate 1. The high-sensitivity low-noise camera 3 is irradiated with the reflected light. That is, the polarization beam splitter 25 is used for the ultraviolet solid state laser light source 22.
It is a laser beam separator for separating the optical path of the optical system of the emitted light such as from the optical path of the optical system of the reflected light to the CCD camera 23.

The objective lens 26 is an optical element for magnifying and detecting the reflected light from the substrate 1. The objective lens 26 has, for example, an NA of 0.9 and aberration correction at a wavelength of 266 nm. This objective lens 26 is
It is arranged between the polarization beam splitter 25 and the movable stage 21.

The quarter-wave plate 27 extracts the reflected light component from the ultraviolet laser light. The ultraviolet light circularly polarized by the ¼ wavelength plate 27 is reflected by the substrate 1 and again ¼.
By passing through the wave plate 27, the direction of 90 ° linearly polarized light is rotated. Therefore, the return light is transmitted through the polarization beam splitter 25.

The control computer 28 controls the turning on of the laser light of the ultraviolet solid state laser light source 22, and the movable stage 2.
The control of the moving position of No. 1 and the switching control of the objective lens 26 are performed.

The image processing computer 29 takes in an image of the substrate 1 picked up by the CCD image sensor provided in the CCD camera 23, analyzes the image, and evaluates the state of the polysilicon film formed on the substrate 1. I do.

In the evaluation apparatus 20 having the above-described structure, the ultraviolet laser emitted from the ultraviolet solid-state laser light source 22 is the optical fiber probe 24 and the polarization beam splitter 2.
5, the substrate 1 is irradiated through the objective lens 26 and the quarter-wave plate 27. The light that is linearly polarized is circularly polarized by the quarter-wave plate 27 and is incident on the substrate 1. The phase of the reflected return light changes by 90 °, and when it passes through the ¼ wavelength plate 27 again, the direction of the linearly polarized light rotates by 90 °. Therefore, the reflected return light passes through the polarization beam splitter 25 and enters the CCD camera 23. Then, the CCD camera 23 captures the incident reflected light with a CCD image sensor, and supplies the surface image information of the polysilicon film obtained by the imaging to the image processing computer 29.

Then, the image processing computer 29
However, as described below, the state of the polysilicon film is evaluated based on the information of the captured surface image of the polysilicon film. Then, based on the evaluation result, the setting value of the energy density at the time of excimer laser annealing for forming the polysilicon film is obtained, and whether the polysilicon film formed on the substrate 1 is non-defective or non-defective. Determine whether it is a good product.

(2) Next, the procedure for evaluating the state of the polysilicon film of the image processing computer 29 will be described. The image processing computer 29 obtains a numerical value of the periodicity (hereinafter referred to as an AC value) from the surface image of the polysilicon film by using autocorrelation, and linearity and period of the surface space structure of the polysilicon film. The property is evaluated to evaluate the state of the polysilicon film.

As the evaluation processing procedure, as shown in the flowchart of FIG. 10, first, an image capturing process of the surface of the polysilicon film is performed (step S1). Then, the autocorrelation function is calculated from the captured image (step S
2). Then, a plane perpendicular to the alignment direction including (0, 0) on the image coordinates is cut out (step S3). Subsequently, the peak value and the side peak value of the autocorrelation function on the cut surface are calculated, and the AC value is obtained by taking the ratio of this peak value and the side peak value (step S4).
Subsequently, the polysilicon film is evaluated based on this AC value (step S5).

Here, the autocorrelation function is a function as shown in the following equation.

[Equation 1] The autocorrelation function R (τ) is a function showing the correlation when a certain function f (x) is translated by τ in the x direction.

In this polysilicon film evaluation apparatus 20, the autocorrelation function of the surface image of the polysilicon film is obtained using the following Wiener-Hintin theorem. Note that here, the image information that has been specifically captured is “i”. 1 Two-dimensional Fourier transform of the captured image “i” is performed. : F = fourier (i) 2 Fourier series “f” is squared to generate a power spectrum “ps”. : Ps = | f | ² 3 Inverse Fourier transform of the power spectrum “ps” is performed to obtain 2
Generate a dimensional autocorrelation function "ac". : Ac = inversfourer (ps) 4 The absolute value of the autocorrelation function “ac” is taken to obtain the real number “aca” of the autocorrelation function. : Aca = | ac |

The autocorrelation function "ac" thus generated
When "a" is displayed, the function becomes as shown in FIGS. 11 and 12. FIG. 11 shows an image with high autocorrelation, that is, the autocorrelation function of the surface spatial structure of the polysilicon film having good periodicity and linearity. On the other hand, Fig. 12 shows an image with low autocorrelation, that is, the autocorrelation function of the surface spatial structure of the polysilicon film having poor periodicity and linearity.

From the autocorrelation image calculated by using such Wiener-Hinchin's theorem, the polysilicon film evaluation apparatus 20 further sets the coordinates on the screen perpendicular to the alignment direction (that is, the direction having linearity). A plane including (0,0) is cut out, and a function obtained when the cut out is obtained.
Here, the plane including the coordinates (0, 0) on the screen is cut out in order to standardize the value from the autocorrelation function that changes depending on the experimental parameters such as the illumination light amount and the CCD gain.

The function obtained by cutting out in this way is the autocorrelation function R in the direction perpendicular to the above-mentioned alignment direction.
It is a function corresponding to (τ).

Further, here, the above-mentioned steps S1 to S
Step 3 may be performed as shown in steps S11 to S14 of FIG. 13 below.

Further, the following evaluation may be carried out in place of such an evaluation procedure.

In the evaluation processing procedure, as shown in the flowchart of FIG. 13, first, an image capturing process of the surface of the polysilicon film is performed (step S11). Then, one line of the captured image in the direction (direction with linearity: x direction) perpendicular to the traveling direction of the laser beam (direction with periodicity: y direction) is cut out (step S12). Subsequently, the autocorrelation function is calculated for this one line (step S13). Subsequently, if necessary, these operations are repeated several times to average each line (step S14).

The autocorrelation function in this case is obtained as follows using the Wiener-Hinchin's theorem. Note that here, the image information for one line that has been specifically captured is set to "l". 1 Perform Fourier transform on one line "l" of the captured image. : Fl = fourier (l) 2 Fourier series “fl” is squared to generate a power spectrum “psl”. : Psl = ^| fl | generating a 2 3 power spectrum "psl" inverse Fourier transform to a two-dimensional autocorrelation function "acl". : Acl = inversourier (psl) 4 The absolute value of the autocorrelation function “acl” is taken to obtain the real number “acal” of the autocorrelation function. : Acal = | acl |

The autocorrelation function aca thus generated
When l is represented on the graph, it becomes a function as shown in FIGS. 14 and 15. FIG. 14 shows a function having a high autocorrelation, that is, an autocorrelation function with good periodicity and linearity of the surface space structure of the polysilicon film. On the other hand, FIG.
This is a function having a low autocorrelation, that is, an autocorrelation function with poor periodicity and linearity of the surface space structure of the polysilicon film.

These one-line autocorrelation functions are taken in for all the lines of the image, and each autocorrelation function is averaged. This is the autocorrelation function R (τ) in the direction perpendicular to the alignment direction (that is, the direction having linearity) described above.
Is a function corresponding to.

The polysilicon film evaluation apparatus 20 continues to
The maximum peak value and the side peak value are calculated from the obtained function. Then, the ratio of the maximum peak value to the side peak value is obtained, and this value is taken as the AC value.

Therefore, the AC value has a large difference between the maximum peak value and the side peak value when the image having a high autocorrelation, that is, when the periodicity and linearity of the surface space structure of the polysilicon film are good, the AC value becomes large. The value increases. On the other hand, in the case of an image with low autocorrelation, that is, when the periodicity and linearity of the surface space structure of the polysilicon film are poor, the difference between the maximum peak value and the side peak value becomes small, and the value becomes small.

As described above, in the bottom gate type TFT 1, the surface image of the polysilicon film is captured, the autocorrelation function of the captured image is obtained, and the linearity and periodicity of the surface spatial structure of the polysilicon film are numerically calculated. It has become.

Specifically, A for an example of the captured image
FIG. 16 shows the C value.

In the polysilicon film annealed by the excimer laser as described above, as shown in FIG. 5, a plurality of linear convex portions are formed on the surface of the film, and the linear convex portions are further formed. Since it is arranged periodically, its state can be evaluated by the AC value. That is, since the spatial structure of the surface of the polysilicon film is a reflection type grating, it can be evaluated by the AC value.

(3) Next, the calculation range for obtaining the AC value will be described.

As described above, the AC value is calculated by taking in the surface image of the polysilicon film and performing the two-dimensional Fourier transform on the taken-in image range.

Generally, the larger the calculation range (two-dimensional range of the surface image to be calculated), the more accurate the linearity and periodicity of the surface spatial structure of the polysilicon film will be. However, since the AC value is obtained by performing the two-dimensional Fourier transform as described above, the amount of calculation becomes enormous. Therefore, in order to perform processing at higher speed, it is desirable to make the calculation range smaller.

On the other hand, if the calculation range is too small, the error with the AC value of the entire surface becomes large, and the linearity and periodicity of the polysilicon film cannot be evaluated accurately.

Thus, the calculation range for obtaining the AC value is
It affects accuracy and processing speed. Therefore, in order to obtain the AC value more efficiently and with good reproducibility, the calculation range must be set optimally.

Hereinafter, a surface image of a polysilicon film having a poor periodicity of the surface spatial structure, a surface image of a polysilicon film having a medium periodicity of the spatial structure of the surface, and a polysilicon having a good periodicity of the spatial structure of the surface. The optimum calculation range of the AC value will be described while showing surface images of the film and considering these characteristics. In describing the optimum calculation range, the direction parallel to the laser scanning direction during excimer laser annealing is referred to as the X direction, and the direction orthogonal to the laser scanning direction is referred to as the Y direction.

FIG. 17A shows a surface image of a polysilicon film in which the periodicity of the surface spatial structure is poor as a whole, and FIG. 17B shows a schematic view of this image. If the periodicity of the surface spatial structure is poor, the AC value should be small. However, even if the periodicity is poor as a whole as described above, there is a feature that a portion with good periodicity occurs in the X direction. The portion with the improved periodicity is formed over a certain length in the X direction. Therefore, if the calculation range in the X direction is set to a narrower range than the part where the periodicity is good, only the image of the part where the periodicity is good is cut out and the AC value is calculated. There is a possibility that it will end up. That is, if such a narrow range is set and the calculation is performed, the calculated AC value becomes large even though the image should originally have a small AC value, and an accurate value can be obtained. It may not be possible. Therefore, the calculation range in the X direction is such that, when a surface image of a polysilicon film having a poor periodicity is calculated, even if a portion having a good periodicity is included in the calculation range,
It must be set so that the AC value is sufficiently low. For example, the calculation range of the AC value in the X direction is set to be at least twice as long as the length of the portion where the periodicity is good (the length of L1 in FIG. 2), and the influence of the portion where the periodicity is good is It is better to halve it and get an accurate value.

Subsequently, FIG. 18A shows a surface image of a polysilicon film in which the periodicity of the surface spatial structure is moderate as a whole, and FIG. 18B schematically shows this image. Indicates. When the periodicity of the surface spatial structure is medium, the AC value should be medium. However, such a surface space structure of the polysilicon film having a medium periodicity as a whole is characterized in that portions having a good periodicity and portions having a poor periodicity are alternately repeated.
The portion having the good periodicity and the portion having the poor periodicity are formed over a certain length in the X direction. Therefore, if the calculation range in the X direction is set to a narrower range (or a narrower range than the part with poor periodicity), the part with good periodicity is set. There is a possibility that only the image (or only the image of the portion with poor periodicity) is cut out and the calculation is performed. That is, if such a narrow range is set and calculation is performed, the calculated AC value may become extremely large or may become extremely large, even though the image should originally have a medium AC value. It may become small and it may not be possible to obtain an accurate value.
Therefore, the calculation range for the X direction is set to be equal to or longer than the length of one cycle (the length of L2 in FIG. 3) of the repetition of the portion having the good periodicity and the portion having the poor periodicity with respect to the X direction. It is better to reduce the effect of repetition of the good part and the bad part by half and obtain an accurate value.

FIG. 19 (A) shows a surface image of a polysilicon film in which the periodicity of the surface spatial structure is good as a whole, and FIG. 19 (B) shows a schematic view of this image. If the spatial structure of the surface has good periodicity, the AC value should be large originally. However, even if the periodicity is good as a whole as described above, there is a feature that a portion with poor periodicity occurs in the X direction. The portion where the periodicity is deteriorated is formed over a certain length in the X direction. Therefore, if the calculation range in the X direction is set to be narrower than the part where the periodicity is bad, there is a possibility that only the image of the part where the periodicity is bad is cut out and the calculation is performed. . That is, if such a narrow range is set and the calculation is performed, the calculated AC value becomes small even though the image should originally have a large AC value, and an accurate value can be obtained. It may not be possible. Therefore, the calculation range in the X direction is sufficiently low in AC value even if the calculation range includes a portion where the periodicity is deteriorated when the calculation is performed on the surface image of the polysilicon film having good periodicity. It must be set to be low. For example, the calculation range of the AC value in the X direction is set to be at least twice the length of the portion where the periodicity is bad (the length of L3 in FIG. 4), and the influence of this portion where the periodicity is bad is It is better to halve it and get an accurate value.

If the calculation range for the X direction is set so as to satisfy the above three conditions, an accurate AC value can be obtained. That is, the periodicity of the surface spatial structure is at least twice as large as that of the good periodicity portion of the polysilicon film, and the periodicity of the surface spatial structure of the polysilicon film is medium. It must be at least one cycle of repetition of good and bad periodicity, and the range of the surface spatial structure must be at least twice as wide as that of the good periodicity of the polysilicon film. If you set so that
The C value can be obtained.

On the other hand, in the calculation range for the Y direction, the periodicity is calculated with respect to the array period of a plurality of linear convex portions formed when laser annealing is performed at the optimum energy density. So to find the autocorrelation,
As shown in FIG. 19, the range of two cycles or more is required.

When the calculation range is expanded to increase the accuracy, it is more likely that the calculation range is expanded in the X direction than the calculation range is expanded in the Y direction. This is because, if the calculation range is expanded in the X direction, the effect of the part having good periodicity generated in the polysilicon film having bad periodicity, the part having good periodicity and the part having bad periodicity in the polysilicon film having medium periodicity This is because the influence of the repetition of X in the X direction and the influence of the portion having poor periodicity generated in the polysilicon film having good periodicity are removed. Therefore, when setting the calculation range, it is preferable to set it as a rectangular range in which the length in the X direction is longer than the length in the Y direction.

Further, as described above, the cycle of the array of the plurality of linear convex portions generated when the laser annealing is performed is 0.
Since it is 3 μm, the calculation range in the Y direction is preferably 0.6 μm or more. Further, from experience, in the case of a polysilicon film having a moderate periodicity as a whole, the repetition period of the portion having good periodicity and the portion having poor periodicity in the X direction is 5 μm.
Since it is m, it is desirable that the calculation range in the X direction is 5 μm or more.

(4) Next, the control of the amount of ultraviolet light of the polysilicon film evaluation apparatus 20 for calculating the AC value with good reproducibility will be described.

In the polysilicon film evaluation device 20, the surface of the polysilicon film is irradiated with ultraviolet light, and the reflected light is reflected by the CCD.
And the AC value is calculated from the captured image.

Since the AC value is calculated based on the picked-up image picked up by the CCD, the AC value may change depending on the brightness of the picked-up image. This is because, for example, when the exposure amount to the CCD is insufficient or when the exposure amount is over, the contrast of the captured image itself is reduced and the state of the unevenness cannot be recognized.

FIG. 20 is a graph showing the variation of the AC value with respect to the exposure amount of ultraviolet light to the CCD. Exposure (μJ
/ Cm ² ) is represented by the time (s) for which the shutter of the CCD is open × irradiation light amount (mW / cm ² ). Here, as shown in FIG. 20, when the exposure amount is in a certain range (the range indicated by T ₁ in the figure), the AC value is constant. That is, by controlling the exposure amount within this fixed range, the amount of light incident on the CCD can be controlled so that the AC value can be obtained with good reproducibility.

Therefore, in the polysilicon film evaluation apparatus 20 of the present embodiment, the amount of ultraviolet light emitted from the objective lens is detected by, for example, a photodetector or the like to detect the amount of irradiation light on the polysilicon film. And this irradiation light quantity and CC
The amount of exposure is calculated from the shutter speed of D, and the amount of light incident on the CCD is monitored. Then, while monitoring the incident light amount, for example, the power of the ultraviolet laser, the shutter speed, and the like are feedback-controlled to control the exposure amount so as to be within the above-mentioned fixed range.

Further, FIG. 21 shows a graph showing the variation of the AC value with respect to the brightness of the screen of the captured image. The screen brightness of the captured image is represented by 256 gradations here.
Here, as shown in FIG. 21, when the brightness of the captured image is within a certain range (the range indicated by T ₂ in the figure), the AC value is constant. That is, by controlling the brightness of the captured image to fall within this fixed range, C
The amount of light incident on the CD can be controlled. Thus, the amount of light incident on the CCD can be controlled by detecting the brightness of the captured image instead of detecting the amount of exposure as described above.

Therefore, in the polysilicon film evaluation apparatus 20 of the present embodiment, the brightness of the screen of the picked-up image is set to the CPU
And calculate the incident light amount. Then, while monitoring the incident light amount, for example, the power of the ultraviolet laser, the shutter speed, and the like are feedback-controlled to control the exposure amount so as to be within the above-mentioned fixed range.

(5) Next, the relationship between the AC value obtained as a result of the above-described calculation and the grain size of the polysilicon film and the energy applied to the polysilicon film will be described.

As shown in FIG. 22, the AC value increases proportionally from when the energy given to the polysilicon film by the excimer laser annealing reaches a certain energy E _5, and at the certain energy E _T. That value is the maximum. Then, the AC value reaches a peak value at this maximum energy E _T , then the value decreases proportionally, the decrease ends at a certain energy E _B2 , and the value becomes the minimum value. As described above, the AC value has a peak characteristic for given energy.

When such a peak characteristic of the AC value is superimposed on the characteristic of the change in grain size of the polysilicon film shown in FIG. 3, it becomes as shown in FIG. As shown in FIG. 23, it can be seen that the maximum value of the graph showing the peak characteristics of the AC value falls within the energy range in which the grain size of the polysilicon film is appropriate. In addition, AC
The energy E _{5 at} which the value starts to rise proportionally becomes lower than the allowable minimum energy L which is given to the polysilicon film and the grain size is appropriate. Also, the energy E _B2 when the proportional decrease of the AC value stops and reaches the minimum value
However, the crystal grain size of the polysilicon film becomes higher than the allowable maximum energy H which is the threshold energy for microcrystallization.

Therefore, when evaluating whether or not the grain size of the polysilicon film is good from the AC value having such peak characteristics, the AC value is as shown in FIG.
3 It is only necessary to determine whether or not the value is within the range shown by the thick line.

(6) The AC value having such characteristics is
Evaluate and inspect whether the polysilicon film is a good product
When performing, for example, the AC value of the board to be inspected
Is the minimum allowable energy L or the maximum allowable energy H
AC required when given _LWhichever is higher
Is set as a threshold, and if it is larger than this threshold, it means that the product is a good product.
Inspection is possible by judging.

Further, when the AC value having such characteristics is evaluated and the energy density of the laser emitted from the excimer laser annealing apparatus is optimally set, for example, while changing the energy density of the excimer laser, Laser annealing is performed on a plurality of substrates.
Then, a characteristic diagram of the AC value corresponding to each energy density is drawn, specifically, the characteristic diagram as shown in FIG. 22 is drawn, and the optimum energy density may be obtained from this characteristic diagram.

(7) By the way, as described above, in the bottom gate type TFT, the gate electrode 3 is the polysilicon film 6
Since it is located in the lower layer, the polysilicon film 6 on the gate electrode 3 is more diffused in energy when laser annealing is performed than on the polysilicon film 6 on the glass substrate 2 (source / drain regions). Will be higher. Therefore, even if the energy density given from the excimer laser annealing device is the same, it is given by the polysilicon film 6 on the gate electrode 3 and the polysilicon film 6 on the glass substrate 2 (source / drain regions). The energy will be different, and the grain size will be different on both sides due to the influence.

Generally, when laser annealing is performed by an excimer laser annealing apparatus, the energy density of the polysilicon film located on the gate electrode and the polysilicon film located on the glass substrate (source / drain region) is increased. It cannot be controlled to change, and excimer laser annealing is performed uniformly with the same energy density setting.

Therefore, in the bottom gate type TFT, the characteristic of the AC value with respect to the energy density of the excimer laser is as shown in FIG.
The peak value is different between the drain region) and the gate electrode. Specifically, the AC value of the polysilicon film located on the glass substrate (source / drain region) reaches a peak value at a lower energy density than that of the polysilicon film located on the gate electrode. .

Therefore, when the AC value is evaluated to inspect whether or not the polysilicon film is a good product, and
When the AC value is evaluated and the energy density emitted from the excimer laser annealing apparatus is optimally set, it is necessary to set the values so that the polysilicon films on both sides (on the glass substrate and on the gate electrode) are good. There is.

Next, FIG. 25 shows an example of concrete experimental data of the AC value with respect to the energy density of the excimer laser for the polysilicon film of the bottom gate type TFT. As shown in FIG. 25, the AC value has a characteristic of having different peak values on the gate electrode and the glass substrate.
For example, on the characteristic diagram shown in FIG. 25, it can be seen that it is optimal to set the energy density in excimer laser annealing at 380 mJ.

(8) As described above, the bottom gate type T
When evaluating the polysilicon film formed on the FT, by evaluating the linearity and / or periodicity of the spatial structure on the surface of the polysilicon film, it is possible to easily and non-destructively inspect the polysilicon. It becomes possible to incorporate the inspection process into the manufacturing process. In addition, since the linearity and / or the periodicity are digitized, numerical calculation can be performed without relying on visual inspection or the like. Furthermore, since evaluation is performed by digitizing, automatic inspection is possible, and objective inspection can be performed with high accuracy. In addition, the inspection result can be fed back to the annealing process to increase the yield of the manufactured thin film transistor.

Although a microscope apparatus using an ultraviolet light laser with a wavelength of 266 nm has been applied as an apparatus for imaging the polysilicon film, the linearity and / or periodicity of the surface spatial structure of the polysilicon film has been evaluated. The device that captures the original image for performing is not limited to such a device. For example,
The linearity and / or periodicity of the surface space structure of the polysilicon film may be evaluated based on the image observed by SEM. For example, as shown in FIG. 26, characteristics when an AC value is obtained based on an image captured by a microscope device (DUV) using an ultraviolet laser, and characteristics when an AC value is obtained based on an image captured by SEM Comparing with the characteristics, it can be seen that the SEM provides a more detailed image and thus has a relatively low AC value, but the curves showing the characteristics are almost the same.

Also, an example using an autocorrelation function has been described in detail as a method of digitizing linearity and / or periodicity.
The numerical method is not limited to the example using this autocorrelation function.

In the manufacturing process of the bottom gate type TFT
Next, a specific application example in which the above-described polysilicon film evaluation apparatus 20 is applied to the manufacturing process of the bottom gate type TFT will be described.

First, an AC obtained from a picked-up image of a polysilicon film of a bottom gate type TFT as shown in FIG.
An application example in which the value is evaluated, the evaluation result is fed back to the excimer laser annealing apparatus, and the laser power emitted from the excimer laser annealing apparatus 30 is optimally set (EQC: Equipment Quality).
Control) will be described.

In the excimer laser annealing apparatus, as described above, the fluctuation of the actual output value of the laser power is relatively large with respect to the set value of the laser power. The output laser power exhibits a Gaussian distribution-like characteristic and has variations, and to some extent with respect to a predetermined power setting value. On the other hand, in the case of bottom gate type TFT,
The manufacturing margin of the energy given to the polysilicon film (the energy range which becomes a defective product when the energy outside this range is given) has a relatively large value with respect to the variation.

Therefore, as shown in FIG. 28, the center position of the manufacturing margin of the polysilicon film is the optimum value of the setting value of the laser power, and if the laser power is set to this optimum value, the laser power fluctuates. Even in this case, the energy applied to the polysilicon film falls within the manufacturing margin, and a high yield can be obtained. However, as shown in FIG. 29, when the set value of the laser power is not set to the optimum value of the manufacturing margin, when the laser power changes, the energy given to the polysilicon film may deviate from the manufacturing margin. The yield rate will be low.

Therefore, in this application example, the bottom gate type T
Utilizing the peak characteristic of the AC value of FT, as follows,
Set the laser power of the excimer laser annealing device to the optimum value.

First, in this application example, a plurality of substrates having a polysilicon film formed thereon are manufactured. At this time, the laser power setting of the excimer laser annealing apparatus is changed for each substrate, and the AC value on the gate electrode and the glass substrate for each substrate is obtained.

Then, as shown in FIG. 30 and FIG. 31, A
A peak curve of C value can be drawn on the graph.

When a peak curve of such an AC value is drawn,
It is possible to obtain an allowable range of laser power (manufacturing margin of the polysilicon film) capable of obtaining a good grain size on both the gate electrode and the glass substrate. In particular,
The laser power at the lower limit of the manufacturing margin is the laser power corresponding to the minimum allowable energy (L) of the energy given to the polysilicon film on the gate electrode, specifically, on the gate electrode shown in FIGS. 30 and 31. Laser power (MO (L)) at the left end of the portion drawn by the thick line of AC value of
Becomes The laser power at the upper limit of the manufacturing margin is the laser power corresponding to the maximum allowable energy (H) of the energy given to the polysilicon film on the glass substrate, specifically, the glass power shown in FIGS. 30 and 31. It is the laser power (G (H)) at the right end of the portion drawn by the thick line of the AC value on the substrate.

Then, the intermediate value of the manufacturing margin thus obtained is obtained, and the laser power at this intermediate value is set as the optimum value.

As described above, by obtaining the AC value, obtaining the manufacturing margin, and setting this manufacturing margin as the optimum value, the yield of the bottom gate type TFT can be increased.

[0137]

According to the method for evaluating polysilicon and the thin film transistor manufacturing system and method according to the present invention, an oxide film is formed after cleaning the surface of the amorphous silicon film, and the amorphous silicon film on which the oxide film is formed is subjected to laser annealing. To form a polysilicon film. For this polysilicon film, the linearity and / or periodicity of the spatial structure of the film surface are evaluated. As a result, in the present invention, the linearity and / or periodicity of the spatial structure of the surface of the polysilicon film formed by the low temperature polycrystallization process can be reliably evaluated. That is, according to the method for forming a polycrystalline silicon thin film of the present invention, the amount of impurities mixed in the thin film polysilicon is small, and at the same time, crystallization can be performed with an optimum laser pulse energy, so that a thin film transistor on a large substrate can be obtained. It is possible to obtain good transistor characteristics over the entire surface with a small characteristic variation. As a result, a high-performance system can be simultaneously formed at low cost on an insulating substrate that drives an LCD or an organic EL display.

[Brief description of drawings]

FIG. 1 is a process drawing showing a main part of a method of manufacturing a TFT according to the present invention.

FIG. 2 is a diagram illustrating a schematic cross-sectional configuration of a bottom gate type TFT.

FIG. 3A is a schematic diagram for explaining a cross-sectional structure of a bottom gate type TFT after forming a polysilicon film,
FIG. 6B is a diagram for explaining the relationship between the grain size of the polysilicon film and the energy given by the excimer laser annealing.

FIG. 4 is an image (B) of the film surface of the polysilicon film when excimer laser annealing is performed with the energy density of the output laser being the optimum value, and the film of the polysilicon film when the power is smaller than the optimum value. Surface image (A),
It is a figure for demonstrating the image (C) of the film surface of a polysilicon film at the time of making power larger than an optimal value.

FIG. 5A is a diagram for explaining a cross-sectional structure of a TFT substrate before excimer laser annealing.
(B) is a diagram for explaining a cross-sectional structure of a TFT substrate when excimer laser annealing is performed with a good energy density. (C) is a figure for demonstrating the cross-section of a TFT substrate when excimer laser annealing is performed with an unfavorable energy density.

FIG. 6 is a diagram for explaining a manufacturing process of a TFT in which a surface oxidation step is provided in a step before the excimer laser annealing.

FIG. 7 is a diagram schematically showing a captured image of a polysilicon film having linearity and periodicity.

FIG. 8 is a diagram schematically showing a captured image of a polysilicon film having neither linearity nor periodicity.

FIG. 9 is a configuration diagram of a polysilicon film evaluation apparatus according to an embodiment of the present invention.

FIG. 10 is a flowchart for explaining the evaluation procedure of a polysilicon film.

FIG. 11 is a diagram for explaining an autocorrelation function when the periodicity is high.

FIG. 12 is a diagram for explaining an autocorrelation function when the periodicity is low.

FIG. 13 is a flowchart for explaining another evaluation procedure of the polysilicon film.

FIG. 14 is a diagram for explaining an autocorrelation image when the periodicity is high when evaluated by the other evaluation procedure.

FIG. 15 is a diagram for explaining an autocorrelation image when the periodicity is low when evaluated by the other evaluation procedure.

FIG. 16 is a diagram illustrating characteristics of the obtained AC value for a specific captured image.

FIG. 17 is a diagram showing a surface image of a polysilicon film having a poor spatial structure periodicity on the surface, and a diagram showing a schematic structure thereof.

FIG. 18 is a diagram showing a surface image of a polysilicon film having a medium spatial periodicity of the surface spatial structure, and a diagram showing a schematic configuration thereof.

19A and 19B are a diagram showing a surface image of a polysilicon film having a good spatial periodicity of a surface spatial structure and a diagram showing a schematic structure thereof.

FIG. 20 is a graph showing a change in AC value with respect to an exposure amount of ultraviolet light on a CCD.

FIG. 21 is a graph showing a change in AC value with respect to screen brightness of a captured image.

FIG. 22 is a diagram for explaining characteristics of an autocorrelation value with respect to energy applied to a polysilicon film.

FIG. 23 is a diagram for explaining characteristics of an AC value and a grain size with respect to energy applied to a polysilicon film.

FIG. 24 is a diagram for explaining the characteristics of the AC value with respect to the energy density of the excimer laser in the bottom gate type TFT.

FIG. 25 is a diagram for explaining an example of specific experimental data of AC values with respect to the energy density of an excimer laser for a polysilicon film of a bottom-gate TFT.

FIG. 26 is a microscope device (DUV) using an ultraviolet laser.
The characteristics when the AC value is obtained based on the image captured in
It is a figure for comparing and explaining the characteristic at the time of finding an AC value based on the picture picturized with SEM.

FIG. 27 is a specific application example (EQ in which a polysilicon film evaluation device is applied to a manufacturing process of a bottom gate type TFT).
It is a figure for demonstrating the structure of C).

FIG. 28 is a diagram for explaining the relationship between the manufacturing margin of energy applied to the polysilicon film and the fluctuation of the energy density of the excimer laser (when the energy density is optimally set).

FIG. 29 is a diagram for explaining the relationship between the manufacturing margin of energy applied to the polysilicon film and the fluctuation of the energy density of the excimer laser (when the energy density of the laser is not optimally set).

FIG. 30 shows an example of the relationship between the manufacturing margin of a bottom gate type TFT and the energy density of an excimer laser,
It is a figure for demonstrating the method for calculating | requiring the optimal value of energy density from this example.

FIG. 31 shows another example of the relationship between the manufacturing margin of the bottom gate type TFT and the energy density of the excimer laser, and is a diagram for explaining a method for obtaining the optimum value of the energy density from this other example. is there.

[Explanation of symbols]

1 bottom gate type TFT, 2 glass substrate, 3 gate electrode, 4 first gate insulating film, 5 second gate insulating film, 6 polysilicon film, 6a amorphous silicon film, 6s surface oxide layer, 6t oxide film, 20 Polysilicon film evaluation system, 30 excimer laser annealing system

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuhiro Goda             50 Ogawagami Funaki, Higashiura Town, Chita District, Aichi Prefecture             St. LCD Inc. (72) Inventor Hiroshi Komatsu             50 Ogawagami Funaki, Higashiura Town, Chita District, Aichi Prefecture             St. LCD Inc. F-term (reference) 4M106 AA10 BA05 BA06 CA19 DB04                       DB08 DB12 DB14 DJ20                 5F052 AA02 BA07 BB07 CA07 DA02                       DB02 EA02 EA15 FA19 HA01                       HA03 JA01 JA02                 5F110 AA24 BB01 BB02 CC01 CC03                       CC05 CC08 DD02 EE04 EE44                       FF02 FF03 FF09 FF28 FF30                       FF32 GG02 GG13 GG25 GG47                       HJ12 HL03 HL04 HL11 NN03                       NN04 NN05 NN14 NN15 NN23                       NN24 NN72 PP03 PP05 PP06                       PP31 PP40

Claims (15)

[Claims] 1. A film forming step of forming an amorphous silicon film on a substrate, a cleaning step of cleaning the substrate on which the amorphous silicon film is formed, and an amorphous silicon film of the substrate cleaned by the cleaning step. An oxide film forming step of forming an oxide film on the surface, a laser annealing step of forming a polysilicon film to be a channel layer of a thin film transistor by performing a laser annealing process on the amorphous silicon film, and the formed polysilicon film film The linearity and / or periodicity of the spatial structure of the surface is detected, and an evaluation step of evaluating the state of the polysilicon film based on the detection result of this linearity and / or periodicity is included, and the cleaning step is ozone. Pretreatment for forming a surface oxide layer on the amorphous silicon film in a gas atmosphere containing a solution or ozone containing Method for manufacturing a thin film transistor, characterized in that a solution containing Tsu acid consists postprocessing to remove surface oxide layer formed on the amorphous silicon film. 2. The method of manufacturing a thin film transistor according to claim 1, wherein the oxide film forming step forms an oxide film on the amorphous silicon film in a solution containing ozone or a gas atmosphere containing ozone. 3. The method of manufacturing a thin film transistor according to claim 1, wherein in the oxide film forming step, an oxide film is formed on the amorphous silicon film in a plasma atmosphere containing oxygen. 4. The evaluation step comprises irradiating a polysilicon film formed by laser annealing with condensed ultraviolet light, detecting reflected light thereof, and imaging the detected reflected light, 2. The method of manufacturing a thin film transistor according to claim 1, wherein the surface space structure of the silicon film is evaluated, and the state of the polysilicon film is evaluated based on the surface space structure. 5. A thin film transistor manufactured by the method according to claim 1. 6. A film forming step of forming an amorphous silicon film on a substrate, a cleaning step of cleaning the substrate on which the amorphous silicon film is formed, and an amorphous silicon film of the substrate cleaned by the cleaning step. An oxide film forming step of forming an oxide film on the surface, a laser annealing step of forming a polysilicon film to be a channel layer of a thin film transistor by performing a laser annealing process on the amorphous silicon film, and the formed polysilicon film film An evaluation step of detecting linearity and / or periodicity of the spatial structure of the surface and evaluating the state of the polysilicon film based on the detection result of the linearity and / or periodicity. Thin film characterized by treating the surface of the amorphous silicon film with a solution containing an acid to remove unnecessary surface oxide layer Method of manufacturing a transistor. 7. The method of manufacturing a thin film transistor according to claim 6, wherein in the oxide film forming step, an oxide film is formed on the amorphous silicon film in a solution containing ozone or a gas atmosphere containing ozone. 8. The method of manufacturing a thin film transistor according to claim 6, wherein in the oxide film forming step, an oxide film is formed on the amorphous silicon film in a plasma atmosphere containing oxygen. 9. The evaluation step comprises irradiating a polysilicon film formed by laser annealing with condensed ultraviolet light, detecting reflected light thereof, and imaging the detected reflected light, 7. The method of manufacturing a thin film transistor according to claim 6, wherein the surface spatial structure of the silicon film is evaluated, and the state of the polysilicon film is evaluated based on the evaluation. 10. A thin film transistor manufactured by the method according to claim 6. 11. A film forming step of forming an amorphous silicon film on a substrate, a cleaning step of cleaning the substrate having the amorphous silicon film formed thereon, and an amorphous silicon film of the substrate cleaned by the cleaning step. An oxide film forming step of forming an oxide film on the surface, a laser annealing step of forming a polysilicon film to be a channel layer of a thin film transistor by performing a laser annealing process on the amorphous silicon film, and the above-mentioned polysilicon film formed The linearity and / or periodicity of the spatial structure of the surface is detected, and an evaluation step of evaluating the state of the polysilicon film based on the detection result of the linearity and / or periodicity is provided, and the cleaning step is fluorine. The surface of the amorphous silicon film is treated with plasma containing gas to remove an unnecessary surface oxide layer. Method for manufacturing a thin film transistor, wherein. 12. An oxide film is formed on the amorphous silicon film in a solution containing ozone or a gas atmosphere containing ozone in the oxide film forming step.
1. The method for manufacturing a thin film transistor according to 1. 13. The method of manufacturing a thin film transistor according to claim 11, wherein in the oxide film forming step, an oxide film is formed on the amorphous silicon film in a plasma atmosphere containing oxygen. 14. The evaluation step comprises: irradiating a polysilicon film formed by laser annealing with focused ultraviolet light, detecting reflected light thereof, and imaging the detected reflected light, Evaluate the surface space structure of the silicon film,
The method of manufacturing a thin film transistor according to claim 11, wherein the state of the polysilicon film is evaluated based on this. 15. A thin film transistor manufactured by the method according to claim 11.