JP2002217107A - Method of evaluating polysilicon, thin film transistor manufacturing system, and method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an evaluation result without fail when evaluating a crystal condition of a polysilicon film formed by a low temperature polycrystallizing process. SOLUTION: Linearity or periodicity appear in a spatial structure on a film surface of the polysilicon film, which has been formed according to an energy density applied to amorphous silicon, during the low temperature polycrystallizing process by excimer laser. A surface image of the polysilicon film is photographed by ultraviolet light, and the periodicity of the film surface is digitized (transformed into AC values) from the image utilizing an autocorrelation function. The film condition is evaluated based on the AC value to set an excimer laser power. In the present invention, the surface of the amorphous silicon film is oxidized after the substrate has been cleaned by rare HF and before a laser anneal processing, and a natural oxide film is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating polysilicon formed by a low-temperature polycrystallization process and a system and method for manufacturing a thin film transistor.

[0002]

2. Description of the Related Art In recent years, a thin film transistor using a polysilicon film for a channel layer has been put to practical use. When polysilicon is used for the channel layer, the electric field mobility of the thin film transistor becomes extremely high. For example, when used as a driving circuit for a liquid crystal display, etc., high definition, high speed, small size, etc. of the display are realized. Will be able to

In addition, a so-called low-temperature polycrystallization process for forming a polysilicon film by heat-treating amorphous silicon using an excimer laser annealing apparatus has recently been developed. By applying such a low-temperature polycrystalline 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.

The output power of an excimer laser annealing apparatus used in a low-temperature polycrystalline process is unstable, so that the grain size of polysilicon to be formed fluctuates greatly. Therefore, the polysilicon film formed using the excimer laser annealing device is
The grain size is not always good. For example, there is a problem that a so-called linear defect in which a silicon crystal is microcrystallized, or a so-called writing defect in which a sufficiently large grain size cannot be obtained. there were.

Therefore, in general, when an annealing process is performed by using such an excimer laser annealing apparatus, energy information given to the polysilicon film is fed back to the excimer laser annealing apparatus to obtain an optimum laser energy. Processing for setting the density is performed.

However, in order to evaluate a polysilicon film, conventionally, a surface image is taken using a spectroscopic ellipsometer, a scanning electron microscope, or the like, and the state of the crystal is judged by visually observing the surface image. There was only a method and could not judge objectively without contact.

Accordingly, the present applicant objectively and automatically evaluates the state of a polysilicon film formed using a low-temperature polycrystallization process, and based on the information, determines the energy density of a laser emitted from a laser annealing apparatus. Japanese Patent Application No. 2000-005 proposes a thin film transistor manufacturing system for optimizing
994, Japanese Patent Application No. 2000-005995, Japanese Patent Application 200
No. 0-005996.

The applicant of the present invention has found that when excimer laser annealing is performed on an amorphous silicon film to form a polysilicon film, the spatial structure on the film surface exhibits linearity and periodicity, and the spatial structure varies depending on the energy density given to the amorphous silicon We found that the structure of linearity and periodicity changed. In each of the above-mentioned applications, utilizing such characteristics, a surface image of the polysilicon film is captured with ultraviolet light, and the periodicity of the spatial structure of the surface of the polysilicon film is numerically calculated from the captured image using an autocorrelation function. A thin film transistor manufacturing system has been proposed in which the state of a formed polysilicon film is evaluated based on this numerical value, and the evaluation result is fed back to the setting of the energy density of an excimer laser.

[0009]

Generally, in the manufacturing process of a thin film transistor, dilute hydrogen fluoride (dilute H) is used.
An impurity element removing step by F) is provided. Also in the above-described thin-film transistor manufacturing process, usually, impurities are removed by dilute HF after forming an amorphous silicon film and before performing laser annealing.

However, when laser annealing is performed after such removal of impurity elements by dilute HF, it is difficult to detect a change in the linearity or periodicity of the surface of the polysilicon film. Was.

The present invention has been made in view of such circumstances, and when evaluating a polysilicon film formed by a low-temperature polycrystallization process, a polysilicon film capable of reliably obtaining an evaluation result. An object of the present invention is to provide an evaluation method and a thin film transistor manufacturing system and method.

[0012]

According to the present invention, there is provided a method for evaluating polysilicon, comprising forming an amorphous silicon film on a substrate, and performing laser annealing on the formed amorphous silicon film. A polysilicon evaluation method for evaluating a film, comprising forming an oxide film on the surface of an amorphous silicon film, and performing laser annealing on the amorphous silicon film on which the oxide film has been formed to form a polysilicon film. Irradiating the collected ultraviolet light, detecting the reflected light, imaging the detected reflected light with an imaging unit, and evaluating the linearity and / or periodicity of the surface spatial structure of the polysilicon film. The state of the polysilicon film is evaluated based on the evaluation result of linearity and / or periodicity.

In this polysilicon evaluation method, an oxide film is formed on the surface of an amorphous silicon film, and a laser annealing process is performed on the amorphous silicon film on which the oxide film is formed to form a polysilicon film. The linearity and / or periodicity of the spatial structure on the surface of the silicon film is evaluated.

A thin film transistor manufacturing system according to the present invention includes a film forming apparatus for forming an amorphous silicon film on a substrate, a cleaning apparatus for cleaning the substrate on which the amorphous silicon film is formed, and a cleaning apparatus for cleaning the substrate. An oxide film forming apparatus for forming an oxide film on the surface of the amorphous silicon film of the substrate, a laser annealing apparatus for generating a polysilicon film serving as a channel layer by performing laser annealing on the amorphous silicon film, and An evaluation device that evaluates the linearity and / or periodicity of the spatial structure on the film surface of the polysilicon film, and evaluates the state of the polysilicon film based on the evaluation result of the linearity and / or periodicity. Features.

In this thin film transistor manufacturing system,
An oxide film is formed on the surface of the amorphous silicon film, and a laser annealing process is performed on the amorphous silicon film on which the oxide film is formed to form a polysilicon film. The thin film transistor is manufactured by evaluating the property and / or periodicity.

According to the method of manufacturing a thin film transistor according to the present invention, 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 a cleaning step of cleaning the substrate. An oxide film forming step of forming an oxide film on the surface of the amorphous silicon film of the substrate, a laser annealing step of generating a polysilicon film serving as a channel layer by performing laser annealing on the amorphous silicon film, Evaluating the linearity and / or periodicity of the spatial structure on the film surface of the polysilicon film, and evaluating the state of the polysilicon film based on the evaluation result of the linearity and / or periodicity. Features.

In this thin film transistor manufacturing method, a polysilicon film is formed by forming an oxide film on the surface of an amorphous silicon film and subjecting the amorphous silicon film on which the oxide film has been formed to laser annealing to form a polysilicon film. Linearity of the spatial structure on the membrane surface of the membrane and / or
Alternatively, the periodicity is evaluated, and a thin film transistor is manufactured.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment of the present invention, an apparatus and method for evaluating a polysilicon film to which the present invention is applied will be described.

An apparatus for evaluating a polysilicon film which will be described below as an embodiment of the present invention is, for example, a thin film transistor (bottom gate type TFT) having a bottom gate structure.
Used for inspection of a polysilicon film formed during the manufacturing process. The bottom gate type TFT is a thin film transistor in which, for example, a gate electrode, a gate insulating film, and a polysilicon film (channel layer) are sequentially stacked from a lower layer on a glass substrate. That is, a bottom gate type TFT
Is a TFT having a configuration in which a gate electrode is formed between a polysilicon film serving as a channel layer and a glass substrate. Here, an evaluation apparatus for evaluating a bottom gate type TFT will be described as an example, but 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, the present invention can be applied to a so-called top gate type TFT having a gate electrode provided thereon.

Structure of Bottom Gate TFT First, a specific configuration example of the bottom gate TFT will be described with reference to FIG.

As shown in FIG. 1, a bottom gate type TFT 1 has a gate electrode 3, a first gate insulating film 4, a second gate insulating film 5, a polysilicon film on a glass substrate 2 having a thickness of 0.7 mm. 6, a stopper 7, a first interlayer insulating film 8, a second interlayer insulating film 9, a wiring 10, a planarizing film 11, and a transparent conductive film 12 are laminated.

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

The first gate insulating film 4 has a thickness of, for example, 5
Consists 0nm silicon nitride (SiN _x), silicon nitride (SiN _x) is formed by stacking on the glass substrate 2 to the gate electrode 3 is formed.

The second gate insulating film 5 has a thickness of, for example, 2
00 nm silicon dioxide (SiO ₂), This
Silicon dioxide (SiO₂) Is the first gate insulating film 5
It is formed by being laminated on top.

The polysilicon film 6 has a thickness of, for example, 30 to
It is made of 80 nm polysilicon (p-Si). This polysilicon film 6 is formed by being laminated on the second gate insulating film 5. This polysilicon film 6 functions as a channel layer of the bottom gate TFT 1. The polysilicon film 6 is formed, for example, by forming amorphous silicon (a-Si) of 30 to 80 nm by LPCVD or the like, and then performing an annealing process on the amorphous silicon to be polycrystallized. . In the polycrystallizing step of 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 pulse beam irradiation area. The irradiation surface of the laser beam has, for example, 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 when performing the excimer laser annealing is performed in a direction orthogonal to the longitudinal direction of the irradiation surface of the linear laser (that is, the short side direction).

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

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

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

The wiring 10 is connected to the source /
After a contact hole for connecting the drain region is opened at a position corresponding to the source / drain region of the first interlayer insulating film 8 and the second interlayer insulating film 9, aluminum (Al) and titanium (Ti) Is formed and patterned by etching. This wiring 10
Connects a source / drain region 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.
The film for flattening the surface of T1 is formed after the wiring 10 is formed, and has a 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 external wiring existing outside the bottom gate type TFT 1. This transparent conductive film 12
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 polysilicon is used for the channel layer, the electric field mobility of the channel layer is extremely high. Therefore, for example, when used as a drive circuit for a liquid crystal display or the like, high definition, high speed, and small size of the display can be realized. In the bottom gate type TFT 1 as described above, a so-called low-temperature polycrystallization process of forming a polysilicon film 6 by heat-treating amorphous silicon using excimer laser annealing is used. 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 An important factor that determines the electric field mobility of the polysilicon film 6 is said to be the grain size of the polysilicon. The grain size greatly depends on the energy given to the polysilicon film 6 during the excimer laser annealing. Therefore, the control and stabilization of the energy density of the laser during the excimer laser annealing greatly affects the characteristics and yield of the completed bottom-gate TFT 1.

However, the excimer laser annealing apparatus used in the excimer laser annealing process is:
The output fluctuation of the energy density of the emitted laser is relatively large. For this reason, when excimer laser annealing is performed using an excimer laser annealing apparatus, the fluctuation of the energy applied to the polysilicon film 6 with respect to the allowable range of energy (manufacturing margin of the polysilicon film 6) in which a good grain size can be obtained. And it is difficult to stably manufacture the polysilicon film 6.

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

However, 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, at the stage when the polycrystallizing step of the polysilicon film 6 as shown in FIG. 2 is completed, 100% inspection of the crystal state of the polysilicon film 6 formed on the outermost surface is performed, or The state of the crystal is extracted and inspected to determine whether or not the manufactured product is defective at this stage, and the energy information applied to the polysilicon film 6 to the excimer laser annealing apparatus is determined. Is fed back to set the energy density of the laser.

The polysilicon film evaluation apparatus evaluates the formed polysilicon film 6 at the stage where the polycrystallizing step of the polysilicon film 6 has been completed, and determines that the manufactured product is defective at this stage. It is used to determine whether or not the laser energy is higher than that described above, and to set laser energy by feeding back information to an 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-described 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 excimer laser annealing. As shown in FIG. 3, the grain size of the polysilicon film increases with an increase in the applied energy, but at a certain energy (position L in the figure:
The energy at this time is defined as an allowable minimum energy L. ) Above this, the grain size will be large enough,
After that, the change decreases and stabilizes. As the energy is further increased, from a certain position (position H in the figure; the energy at this time is defined as the maximum allowable energy H),
The change in grain size increases, and the polysilicon becomes microcrystalline at a certain critical point.

Therefore, normally, when excimer laser annealing is performed, the allowable minimum energy L shown in FIG. 3 falls within the range from the allowable minimum energy L at which 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 irradiating laser,
Try to get a sufficiently large grain size. By irradiating the amorphous silicon film with a laser beam giving 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 excimer laser annealing is performed with the laser energy density being the optimum value, and the polysilicon film when the energy density is lower 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 higher than the optimum value. FIG. 4 shows images in each case. FIG. 4A is a diagram showing an image of the film surface of the polysilicon film when the energy density is smaller than the optimum value, and FIG. 4B is the film of the polysilicon film when the energy density is the optimum value. FIG. 4C is a diagram showing an image of the surface, and FIG. 4C is a diagram showing an image of the surface of the polysilicon film when the energy density is larger than the optimum value. Each image shown in FIG. 4 is an image captured by a microscope device using ultraviolet light, and the details of this microscope device will be described later.

In FIG. 4, the laser scanning direction of 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 having a linear irradiation surface, and the scanning direction is orthogonal to the longitudinal direction of the laser beam irradiation surface shape.

Here, the image of FIG. 4B when the energy density at the time of excimer laser annealing is set to the optimum value is compared with the other images shown in FIGS. 4A and 4C. 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) is the surface image of the polysilicon film whose energy density is not optimized (FIGS. 4A and 4B). 4 (C), the image shows linearity. Specifically, the image has linearity in the laser scanning direction (X direction in FIG. 4). That is, when the energy density is set to the optimum value, the surface of the polysilicon film has a feature that the spatial structure has a regular shape in which linearity appears.

The surface image of the polysilicon film when the energy density is set to the optimum value (FIG. 4B) is the surface image of the polysilicon film whose energy density is not optimized (FIGS. 4A and 4B). The image has periodicity as compared to FIG. 4 (C)). Specifically, the image has periodicity in a direction (Y direction in FIG. 4) orthogonal to the laser scanning direction. That is, when the energy density is set to the optimum value, the surface of the polysilicon film has a feature that the space structure has a regular shape in which periodicity appears.

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 features. That is, in the polysilicon film evaluation apparatus according to the embodiment of the present invention, the surface image of the polysilicon film after excimer laser annealing is numerically analyzed, and linearity appears in the surface spatial structure of the polysilicon film. To check the state of the polysilicon film by evaluating whether the surface space structure of the polysilicon film has periodicity, or whether the surface space structure of the polysilicon film has linearity and periodicity. I do.

It should be noted that the image of the surface of the polysilicon film after excimer laser annealing with a good energy density is an image showing linearity and periodicity is shown in FIG. 5A. Thus, it is considered that the influence is that the natural oxide film (SiO ₂ ) is formed on the upper layer of the amorphous silicon film. The thickness of this natural oxide film is 3 to 4 nm.
It is considered that Also, this natural oxide film
It is considered that the oxidation stops at a certain film thickness and does not reach a certain film thickness or more.

When annealing is performed on the amorphous silicon on which the natural oxide film is formed by using an excimer laser, the natural oxide film (SiO ₂ ) is considered to be raised as shown in FIG. 5B. Can be When the energy density of the excimer laser annealing is good, a plurality of linear protrusions parallel to the scanning direction of the excimer laser are formed, and each of the protrusions has periodicity at equal intervals. become. Therefore, when the film surface image of the polysilicon film is imaged by a microscope device using ultraviolet light, a striped image as shown in FIG. 4 can be referred to from the influence of the reflected and diffracted light by the linear convex portion. It is considered something. For example, when the thickness of the natural oxide film is 3 to 4 nm and XeC
lExcimer laser energy density is 300-400mJ
/ Cm ² , the interval between the linear projections is 0.3
It is about μm. This interval is about the wavelength of the laser light source for annealing.

The shape of the natural oxide film after annealing varies as shown in FIG. 5C due to factors such as the energy density given by excimer laser annealing and the difference in the thickness of the amorphous silicon film. It is considered something. For example, when the energy density of the excimer laser annealing is not good, it is considered that the linearity and the periodicity of the shape of the ridge are lost. 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) Here, usually, in the manufacturing process of the thin film transistor, an impurity element removing step using dilute hydrogen fluoride (dilute HF) is provided. Also in the manufacturing process of the above-described bottom gate type TFT 1, impurities are usually removed by dilute HF after forming an amorphous silicon film and before performing laser annealing.

However, if the substrate is washed with dilute HF after the formation of 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
As shown in FIG. 5B, the raised shape of the natural oxide film is not formed. Therefore, 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 be able to evaluate the state of the polysilicon film, as shown in FIG. 6, a surface oxidation treatment is performed as a pre-process for performing the laser annealing treatment. That is, impurities are removed by performing dilute HF cleaning from a state in which a native oxide film (SiO ₂ ) is formed on the surface of the amorphous silicon film (state 1). After the dilute HF cleaning, the amorphous silicon film is in a state in which the natural oxide film (SiO ₂ ) on the surface is dissolved (state 2). As the next step, a surface oxidation step is provided. In this surface oxidation step, for example, a natural oxide film may be formed on the surface of the amorphous silicon film by leaving the substrate in the air for about one day, or the substrate may be immersed in, for example, about 10 ppm of ozone water. May oxidize the surface of the amorphous silicon film. By providing the surface oxidation step before the laser annealing, a natural oxide film can be formed on the amorphous silicon film (state 3). As a result, the natural oxide film is raised by performing the laser annealing. (State 4), and the polysilicon film can be evaluated.

(4) Next, an example of a numerical method when the captured image of the polysilicon film has linearity, periodicity, linearity, and periodicity will be described.

For example, when a captured image of a polysilicon film having linearity and periodicity is schematically represented, 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 represented, as shown in FIG. 8A, an irregular short straight line or the like appears irregularly. . When numerically evaluating the degree of linearity and periodicity from these images and evaluating them, the image is shifted laterally in the direction perpendicular to the direction in which the periodicity will be, and the image when the lateral shift is performed May be expressed as a numerical value and evaluated. For example, when an image having linearity and periodicity is shifted laterally, as shown in FIG.
At a certain period, that is, at every certain amount of lateral shift, an image having a high correlation and a high degree of image overlap appears. On the other hand, in an image having neither linearity nor periodicity, as shown in FIG. 8B, even if the image is shifted sideways, an image having a high degree of overlap and a high correlation does not appear at regular intervals. .

By using the concept of digitizing the correlation of the image when the image is laterally shifted as described above, the periodicity of the polysilicon film can be numerically evaluated. Specifically, as one method of realizing such a method, there is a method of obtaining an autocorrelation function of an image, calculating a peak value and a side peak value of the autocorrelation function, and taking a ratio between these values. Here, the peak value is a second minimum value in the y direction from the origin value from the origin value (used to reduce the defocus value.
). Also, the side peak value is defined as a value between the second maximum value in the y direction from the origin (not including the origin) and the value in the y direction from the origin.
It means the value obtained by subtracting the second minimum value.

According to the present invention, it is possible to evaluate only one of the linearity and the periodicity to determine the state of the polysilicon film.

As another example of a numerical method in the case where the captured image of the polysilicon film has linearity, periodicity, linearity, and periodicity, for example, a standardized image is made uniform in linearity. In a different direction, there is a method of adding the values of all the pixels to obtain the degree of modulation. Further, there is a method of performing a two-dimensional Fourier transform on a standardized image to obtain the intensity of a certain frequency component. In addition, an extreme value (minimum value or maximum value) in an image (for example, an image that will have linearity in the y direction)
The coordinates in the vertical direction in the y direction (the center in the x direction is taken as an extreme value x the average value of the coordinates, and the length in the x direction is set as the pitch of the array in the x direction) There is a technique to take dispersion. Further, the coordinates of an extreme value (minimum value or maximum value) in an image (for example, an image that will have linearity in the y direction) are extracted, and the coordinates are extracted within a vertically elongated range in the y direction (the center in the x direction is defined as With respect to the coordinates of (the length of the x direction is taken as the pitch of the array in the x direction, taking the average of the value x the coordinates), there is a method of taking the angle of each point with the vertically adjacent points.

Specific configuration of polysilicon film evaluation apparatus
And its processing content (1) Next, a specific configuration example of the polysilicon film evaluation apparatus for evaluating the linearity and periodicity of the surface spatial structure of the above-described polysilicon film.

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

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

The polysilicon film evaluation device 20 shown in FIG.
Is a movable stage 21 and an ultraviolet solid laser light source 22
, A CCD camera 23, an optical fiber probe 24,
Polarization beam splitter 25, objective lens 26, 1 /
It comprises a four-wavelength plate 27, a control computer 28, and an image processing computer 29.

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 a function of moving the substrate 1 to a predetermined inspection target position.

More specifically, the movable stage 21 includes an X stage, a Y stage, a Z stage, a suction plate, and the like.

The X stage and the Y stage move in the horizontal direction. The X stage and the Y stage move the substrate 1 to be inspected in directions orthogonal to each other, and move the substrate 1 to be inspected. It leads to a predetermined inspection position. The Z stage is a stage that moves in the vertical direction, and adjusts the height of the stage. That is, the Z stage moves in the direction of the optical axis of the ultraviolet laser to be irradiated, 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 laser light source 22 has a wavelength of 266.
nm laser light source, for example, Nd: YAG
A fourth harmonic all solid state laser is used. In recent years, an ultraviolet laser light source having a wavelength of about 157 nm has been developed, and such an ultraviolet laser light source may be used as the light source.

The CCD camera 23 has a high sensitivity to ultraviolet light.
An image sensor is provided, and the surface of the substrate 1 is imaged by the CCD image sensor. This CCD camera 23
By cooling the main body, thermal noise, readout noise, circuit noise, and the like generated in the CCD image sensor and the like are suppressed.

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

The polarizing 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 via the objective lens 26, and is reflected from the substrate 1 together therewith. The reflected light is transmitted to irradiate the high-sensitivity low-noise camera 3. That is, the polarization beam splitter 25 is used for the ultraviolet solid-state laser light source 22.
This is a laser beam separator for separating the optical path of the optical system of the emitted light such as the optical path of the optical system of the reflected light to the CCD camera 23 from the optical path.

The objective lens 26 is an optical element for expanding and detecting the reflected light from the substrate 1. The objective lens 26 has, for example, an NA of 0.9 and an aberration corrected at a wavelength of 266 nm. This objective lens 26
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 波長 wavelength plate 27 is reflected by the substrate 1 and again １ ／.
By transmitting through the wave plate 27, the direction of 90 ° linearly polarized light is rotated. Therefore, the return light passes through the polarization beam splitter 25.

The control computer 28 controls the lighting of the laser light of the ultraviolet solid-state laser light source 22 and the movable stage 2
1 to control the movement position, control for switching the objective lens 26, and the like.

The image processing computer 29 takes in the image of the substrate 1 taken 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 device 20 having the above-described configuration, the ultraviolet laser emitted from the ultraviolet solid-state laser light source 22 is supplied to the optical fiber probe 24 and the polarization beam splitter 2.
5. The light is applied to the substrate 1 via the objective lens 26 and the 波長 wavelength plate 27. Light that has entered as linearly polarized light becomes circularly polarized by the quarter-wave plate 27 and enters the substrate 1. The phase of the reflected return light changes by 90 °, and when passing through the quarter-wave plate 27 again, the direction of the linearly polarized light is rotated 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 takes an image of 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.

The image processing computer 29
However, as described below, the state of the polysilicon film is evaluated based on the information of the surface image of the taken-in polysilicon film. Then, based on the evaluation result, a set 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 good or bad. Determine whether the product is good.

(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 value obtained by digitizing the periodicity (hereinafter referred to as an AC value) from the surface image of the polysilicon film using the autocorrelation, and obtains the linearity and periodicity of the surface spatial structure of the polysilicon film. The state of the polysilicon film is evaluated by evaluating the properties.

In the evaluation processing procedure, as shown in the flowchart of FIG. 10, first, an image capturing processing of the surface of the polysilicon film is performed (step S1). Subsequently, an autocorrelation function is calculated from the captured image (step S).
2). Subsequently, 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 ratio between the peak value and the side peak value is calculated to obtain the AC value (step S4).
Subsequently, the polysilicon film is evaluated based on the AC value (step S5).

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

[0080]

(Equation 1)

The autocorrelation function R (τ) is calculated by a function f
This is a function indicating the correlation when (x) is translated in the x direction by τ.

In the polysilicon film evaluation apparatus 20, the autocorrelation function of the surface image of the polysilicon film is obtained by using the following Wiener-Hinchin theorem. Here, the specifically captured image information is referred to as “i”. 1. Perform a two-dimensional Fourier transform of the captured image “i”. : F = fourier (i) 2 Generates a power spectrum “ps” by squaring the Fourier series “f”. : Ps = | f | ² 3 Power spectrum “ps” is inverse Fourier transformed to 2
Generate a dimensional autocorrelation function “ac”. : Ac = inverse Fourier (ps) 4 The absolute value of the autocorrelation function “ac” is obtained, and the real number “aca” of the autocorrelation function is obtained. : Aca = | ac |

The autocorrelation function “ac” thus generated
When a ″ is displayed, the function becomes a function as shown in FIGS. 11 and 12. FIG. 11 shows an image having a high autocorrelation, that is, an autocorrelation function having good periodicity and linearity of the surface spatial structure of the polysilicon film. 12 shows an image having a low autocorrelation, that is, an autocorrelation function of the surface space structure of the polysilicon film having poor periodicity and linearity.

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

The function obtained when the clipping is performed is the autocorrelation function R in the direction perpendicular to the above-described alignment direction.
It becomes a function corresponding to (τ).

Here, the above-described steps S1 to S
3 may be performed as shown in steps S11 to S14 in FIG. 13 below.

Further, instead of such an evaluation procedure, the following evaluation may be performed.

In the procedure of this evaluation, as shown in the flowchart of FIG. 13, first, an image capturing process of the surface of the polysilicon film is performed (step S11). Subsequently, one line of the captured image is cut out in a direction (direction having periodicity: y direction) perpendicular to the traveling direction of the laser beam (direction having linearity: x direction) (step S12). Subsequently, an 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 Wiener-Khinchin's theorem. Here, the image information for one line that is specifically captured is set to “l”. 1 Fourier transform is performed on one line “l” of the captured image. : Fl = fourier (l) 2 Generates a power spectrum “psl” by squaring the Fourier series “fl”. : Psl = ^| fl | generating a 2 3 power spectrum "psl" inverse Fourier transform to a two-dimensional autocorrelation function "acl". : Acl = inverses Fourier (psl) 4 The absolute value of the autocorrelation function “acl” is obtained, and the real number “acal” of the autocorrelation function is obtained. : Acal = | acl |

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

The autocorrelation function of one line is obtained for all the lines of the captured image, and each autocorrelation function is averaged. This is the autocorrelation function R (τ) in the direction perpendicular to the above-mentioned alignment direction (that is, the direction having linearity).
Is a function corresponding to.

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

Therefore, in the case of an image having a high autocorrelation, that is, when the periodicity and linearity of the surface spatial structure of the polysilicon film are good, the difference between the maximum peak value and the side peak value becomes large. The value increases. On the other hand, when the image having low autocorrelation, that is, when the periodicity and linearity of the surface spatial 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 determined. Is becoming

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

As shown in FIG. 5, the polysilicon film subjected to the excimer laser annealing has a plurality of linear projections formed on the surface of the polysilicon film. Since they are arranged periodically, the state can be evaluated by the AC value. That is, since the spatial structure on the surface of the polysilicon film is a reflection type grating, it can be evaluated by an AC value.

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

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

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

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

As described above, the calculation range for obtaining the AC value is as follows.
Affects accuracy and processing speed. Therefore, in order to obtain an AC value more efficiently and with good reproducibility, the calculation range must be set optimally.

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

FIG. 17A shows a surface image of a polysilicon film in which the periodicity of the spatial structure on the surface is poor as a whole, and FIG. 17B schematically shows this image. When the periodicity of the spatial structure on the surface is poor, the AC value should originally be small. However, even in the case where the periodicity is poor as a whole, there is a feature that a portion having improved periodicity occurs in the X direction. The portion having 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 of the part having the improved periodicity, only the image of the part having the good periodicity is cut out and the AC value is calculated. May be lost. That is, if the calculation is performed with such a narrow range set, the calculated AC value becomes large even though the image should originally have a small AC value, and an accurate value may be obtained. May not be possible. Accordingly, when the calculation range in the X direction is calculated for the surface image of the polysilicon film having poor periodicity, even if the portion having the improved periodicity is included in the calculation range,
It must be determined 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 the length of the part having the improved periodicity (the length of L1 in FIG. 2), and the influence of the part having the improved periodicity is considered. It is better to halve to get an accurate value.

Next, FIG. 18A shows a surface image of a polysilicon film in which the periodicity of the spatial structure of the surface is medium as a whole, and FIG. 18B schematically shows this image. Is shown. When the periodicity of the spatial structure of the surface is medium, the AC value should originally be a medium value. However, the surface spatial structure of the polysilicon film having a medium periodicity as a whole is characterized in that portions having good periodicity and portions having poor periodicity are alternately repeated.
The portion having the improved periodicity and the portion having the deteriorated periodicity are formed over a certain length in the X direction. For this reason, if the calculation range in the X direction is set to a range narrower than the portion where the periodicity is improved (or a range narrower than the portion where the periodicity is deteriorated), the calculation range of the portion where the periodicity is good is improved. There is a possibility that only the image (or only the image of the portion having poor periodicity) 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 extremely large or extremely, even though the image should originally have a medium AC value. There is a possibility that it becomes smaller or an accurate value cannot be obtained.
Therefore, the calculation range in the X direction is equal to or more than the length of one cycle (length of L2 in FIG. 3) of the repetition of the portion having good periodicity and the portion having poor periodicity in the X direction. The effect of the repetition of the part that is getting better and the part that is getting worse should be halved to get accurate values.

FIG. 19A shows a surface image of a polysilicon film in which the periodicity of the spatial structure of the surface is good as a whole, and FIG. 19B schematically shows this image. If the periodicity of the spatial structure on the surface is good, the AC value should originally be large. However, even when the periodicity is good as a whole as described above, there is a characteristic that a portion having poor periodicity occurs in the X direction. The portion having poor periodicity is formed over a certain length in the X direction. Therefore, if the calculation range in the X direction is set to a range narrower than the portion where the periodicity is deteriorated, there is a possibility that only the image of the portion where the periodicity is poor is cut out and the calculation is performed. . That is, if the calculation is performed with such a narrow range set, the calculated AC value becomes small even though the image should originally have a large AC value, and an accurate value may be obtained. May not be possible. Therefore, when the calculation range in the X direction is calculated with respect to the surface image of the polysilicon film having good periodicity, the AC value is sufficient even if the portion where the periodicity is deteriorated is included in the calculation range. 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 poor (the length of L3 in FIG. 4), and the influence of the portion where the periodicity is bad is considered. It is better to halve to get an accurate value.

If the calculation range in 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 spatial structure on the surface is at least twice as large as that of the portion with good periodicity in the polysilicon film, and the periodicity of the spatial structure on the surface is moderate in the polysilicon film as a whole. The periodicity of the spatial structure on the surface should be at least twice as large as that of the poorly periodic part of the good polysilicon film as a whole. Is set to satisfy
C value can be obtained.

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

When the calculation range is expanded in order to increase the accuracy, it is more likely that the accuracy will be higher when the calculation range is expanded in the X direction than when 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 portion having good periodicity occurring in the polysilicon film having poor periodicity, the portion having good periodicity and the portion having poor periodicity of the polysilicon film having medium periodicity are obtained. This is because the influence of the repetition in the X direction and the influence of the poor periodicity generated in the polysilicon film having good periodicity are removed. Therefore, when the calculation range is set, it is preferable to set the calculation range to a rectangular range in which the length in the X direction is equal to or longer than the length in the Y direction.

Further, as described above, the period of the arrangement of the plurality of linear projections generated when laser annealing is performed is set to 0.1.
Since it is 3 μm, the calculation range in the Y direction is desirably 0.6 μm or more. Further, experience shows that in the case of a polysilicon film having a medium 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
m, the calculation range in the X direction is desirably 5 μm or more.

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

The polysilicon film evaluation device 20 irradiates the surface of the polysilicon film with ultraviolet light, and reflects the reflected light on a CCD.
And an AC value is calculated from the captured image.

Here, since the AC value is calculated based on the captured image captured by the CCD, the value of the AC value may vary depending on the brightness of the captured image. For example, when the exposure amount to the CCD is insufficient or when the exposure amount is excessive, the contrast of the captured image itself decreases, and the state of 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 (time (s) during which the shutter of the CCD is open) × irradiation light amount (mW / cm ² ). Here, as shown in FIG. 20, AC value, when in a certain range exposure (area shown in T _1), has its value constant. That is, by controlling the amount of exposure to be 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, and the amount of light applied to the polysilicon film is detected. And this irradiation light amount and CC
The exposure amount is calculated from the shutter speed of D, and the amount of light incident on the CCD is monitored. Then, while monitoring the amount of incident light, for example, feedback control of the power and shutter speed of the ultraviolet light laser is performed so that the exposure amount falls within the above-mentioned fixed range.

FIG. 21 is a graph showing the variation of the AC value with respect to the brightness of the screen of the captured image. Here, the brightness of the screen of the captured image is represented by 256 gradations.
Here, as shown in FIG. 21, AC value, when in a certain range the brightness of the captured image (area shown in T _2), has its value constant. That is, by controlling the brightness of the captured image to be within this fixed range, the C value is controlled so that the AC value can be obtained with good reproducibility.
The amount of light incident on the CD can be controlled. As described above, 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.

For this reason, in the polysilicon film evaluation apparatus 20 of the present embodiment, the brightness of the screen of the picked-up image is controlled by the CPU.
And monitor the incident light amount. Then, while monitoring the amount of incident light, for example, feedback control of the power and shutter speed of the ultraviolet light laser is performed so that the exposure amount falls within the above-mentioned fixed range.

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

[0118] AC values, as shown in FIG. 22, the energy imparted to the polysilicon film by excimer laser annealing, the value from the time of a certain energy E ₅ increases proportionally, at a certain energy E _T That value is at its maximum. Then, AC value, reached a peak value at the energy E _T made this maximum, then the value is decreased proportionally, completed the decrease in certain energy E _B2, the value becomes the minimum value. As described above, the AC value has a peak characteristic with respect to the applied energy.

FIG. 23 shows a superimposition of the peak characteristic of the AC value on the characteristic of the grain size change of the polysilicon film shown in FIG. As shown in FIG. 23, it can be seen that the maximum value of the graph showing the peak characteristic of the AC value falls within the energy range where the grain size of the polysilicon film is appropriate. In addition, AC
Value the energy E ₅ to start proportionally increase, lower than the allowable minimum energy L the grain size is appropriate given the polysilicon film. Further, the energy _EB2 when the proportional decrease of the AC value stops and reaches the lowest 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 a peak characteristic, the AC value is determined as shown in FIG.
It is only necessary to determine whether the value falls within the range indicated by the bold line in FIG.

(6) The AC value having such characteristics is
Evaluate and inspect whether the polysilicon film is good or not.
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 _LWhichever is higher
Is a good value if it is larger than this threshold.
Inspection is possible by making a judgment.

When the AC value having such characteristics is evaluated and the energy density of the laser emitted from the excimer laser annealing apparatus is set optimally, 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, and more specifically, a characteristic diagram as shown in FIG. 22 is drawn, and an optimum energy density may be obtained from this characteristic diagram.

(7) As described above, in the bottom gate type TFT, the gate electrode 3 is formed of the polysilicon film 6.
, The energy diffusivity when laser annealing is performed is lower than that of the polysilicon film 6 on the gate electrode 3 than the polysilicon film 6 on the glass substrate 2 (on the source / drain regions). Is higher. Therefore, even if the energy density given by 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 (on the source / drain regions). The energies will be different and the grain size will be different for both due to the effect.

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 energy density of the polysilicon film located on the glass substrate (on the source / drain regions) are reduced. It is not possible to control such a change, and excimer laser annealing is performed uniformly at 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 follows.
As shown in FIG. 24, the peak value is different between the position on the glass substrate (on the source / drain region) and the position on the gate electrode. Specifically, the AC value of the polysilicon film located on the glass substrate (on the source / drain regions) reaches a peak value at a lower energy density than the polysilicon film located on the gate electrode. .

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

Next, FIG. 25 shows an example of specific 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 different peak values on the gate electrode and on the glass substrate. For example, it can be seen from the characteristic diagram shown in FIG. 25 that setting the energy density in excimer laser annealing to 380 mJ is optimal.

(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, the polysilicon can be easily inspected nondestructively. The inspection process can be incorporated into the manufacturing process. Further, since the linearity and / or the periodicity are converted into numerical values, numerical calculations can be performed without using a visual inspection or the like. Further, since the evaluation is performed by digitizing, an automatic inspection can be performed, and an 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 transistors.

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

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

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

First, as shown in FIG. 27, the AC obtained from a captured image of the polysilicon film of the bottom gate type TFT is obtained.
An application example (EQC: Equipment Quality Control) in which values are evaluated, the evaluation result is fed back to an excimer laser annealing apparatus, and the laser power emitted from the excimer laser annealing apparatus 30 is optimally set will be described.

In the excimer laser annealing apparatus, the output value of the actual laser power fluctuates relatively greatly with respect to the set value of the laser power as described above. The output laser power exhibits a Gaussian distribution characteristic and varies, and a certain amount of variation occurs with respect to a predetermined power set value. On the other hand, in the case of a bottom gate type TFT,
The production margin of the energy applied to the polysilicon film (the energy range in which a defective product is obtained when energy outside this range is applied) 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 set value of the laser power, and if the laser power is set to this optimum value, the laser power fluctuates. Even so, the energy given 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 fluctuates, the energy given to the polysilicon film may deviate from the manufacturing margin. In many cases, the yield is low.

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

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

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

When a peak curve of such an AC value is drawn,
The allowable range of laser power (manufacturing margin of the polysilicon film) for obtaining a good grain size on both the gate electrode and the glass substrate can be obtained. 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 applied to the polysilicon film on the gate electrode, specifically, the laser power on the gate electrode shown in FIGS. Laser power (MO (L)) at the left end of the portion drawn by the thick line of the 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 applied to the polysilicon film on the glass substrate, specifically, the glass power shown in FIGS. It is the laser power (G (H)) at the right end of the portion of the substrate drawn with the bold line of the AC value.

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

As described above, the AC value is obtained, the manufacturing margin is obtained, and this manufacturing margin is set as an optimum value, whereby the yield of the bottom gate type TFT can be increased.

[0141]

According to the method for evaluating polysilicon and the system and method for manufacturing a thin film transistor according to the present invention, an oxide film is formed on the surface of an amorphous silicon film, and the amorphous silicon film on which the oxide film is formed is laser-annealed. The linearity of the spatial structure on the surface of the polysilicon film and / or the linearity of the polysilicon film on which the film is formed
Or, evaluate the periodicity.

Thus, in the present invention, the linearity and / or periodicity of the spatial structure on the surface of the polysilicon film formed by the low-temperature polycrystallization process can be reliably evaluated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic cross-sectional configuration of a bottom-gate TFT.

FIG. 2 is a diagram for explaining a cross-sectional structure of a bottom-gate TFT after a polysilicon film is formed.

FIG. 3 is a diagram for explaining a relationship between a grain size of a polysilicon film and energy given by excimer laser annealing.

FIG. 4 shows an image of a film surface of a polysilicon film when excimer laser annealing is performed with the energy density of an output laser being an optimum value, and an image of a film surface of the polysilicon film when power is smaller than the optimum value. FIG. 4 is a diagram for explaining an image of the surface of the polysilicon film when the power is larger than the optimum value.

FIG. 5A is a diagram illustrating a cross-sectional structure of a TFT substrate before excimer laser annealing is performed.
(B) is a diagram for explaining a cross-sectional structure of the TFT substrate when excimer laser annealing is performed at a good energy density. (C) is a diagram for explaining a cross-sectional structure of the TFT substrate when excimer laser annealing is performed at an unsatisfactory energy density.

FIG. 6 is a view for explaining a manufacturing process of a TFT provided with a surface oxidation step before 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 no linearity and no 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 illustrating a procedure for evaluating 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 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 in a case where 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 an AC value obtained for a specific captured image.

17A and 17B are a diagram showing a surface image of a polysilicon film having a poor periodicity of the surface spatial structure, and a diagram showing a schematic structure thereof.

18A and 18B are a diagram showing a surface image of a polysilicon film having a medium spatial structure having a medium periodicity, and a diagram showing a schematic configuration thereof.

FIG. 19 is a diagram showing a surface image of a polysilicon film having a good periodicity of a spatial structure on the surface, 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 to a CCD.

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

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

FIG. 23 is a view 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 a characteristic of an AC value with respect to an energy density of an excimer laser in a bottom gate type TFT.

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

FIG. 26 shows a microscope apparatus (DUV) using an ultraviolet laser.
Characteristics when an AC value is obtained based on an image captured in
FIG. 9 is a diagram for comparing and explaining characteristics obtained when an AC value is obtained based on an image captured by an SEM.

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

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

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

FIG. 30 is a diagram illustrating an example of a relationship between a manufacturing margin of a bottom gate type TFT and an energy density of an excimer laser, and illustrating a method for obtaining an optimum value of the energy density from the example.

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

[Explanation of symbols]

Reference Signs List 1 bottom gate type TFT, 2 glass substrate, 3 gate electrode, 4 first gate insulating film, 5 second gate insulating film, 6 polysilicon film, 20 polysilicon film evaluation device, 30 excimer laser annealing device

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koichi Tatsuki 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo F-term in Sony Corporation (reference) 4M106 AA01 AA10 BA07 CA38 DB04 DB30 5F052 AA02 BA07 BB07 DA02 DB02 EA15 JA02 5F110 AA24 BB02 CC08 DD02 EE04 FF02 FF03 FF09 GG02 GG13 GG25 GG47 HJ12 HL03 HL04 HL11 NN02 NN04 NN12 NN14 NN23 NN24 PP03 PP04 PP05 PP31 QQ19

Claims (3)

[Claims] 1. A method for evaluating a polysilicon film, comprising: forming an amorphous silicon film on a substrate; and performing a laser annealing process on the formed amorphous silicon film to evaluate the polysilicon film. An oxide film is formed on the surface of the film, and the amorphous silicon film on which the oxide film has been formed is subjected to laser annealing to form a polysilicon film. Detect
The detected reflected light is imaged by an imaging unit, the linearity and / or periodicity of the surface spatial structure of the polysilicon film is evaluated, and the linearity and / or periodicity of the polysilicon film is evaluated based on the evaluation result. A polysilicon evaluation method characterized by evaluating a state. 2. A thin film transistor manufacturing system for manufacturing a thin film transistor, comprising: a film forming apparatus for forming an amorphous silicon film on a substrate; a cleaning apparatus for cleaning the substrate on which the amorphous silicon film is formed; An oxide film forming apparatus for forming an oxide film on the surface of an amorphous silicon film on a cleaned substrate; a laser annealing apparatus for generating a polysilicon film serving as a channel layer by performing laser annealing on the amorphous silicon film; An evaluation device for evaluating the linearity and / or periodicity of the spatial structure on the film surface of the polysilicon film and evaluating the state of the polysilicon film based on the evaluation result of the linearity and / or periodicity. A thin-film transistor manufacturing system characterized by the above-mentioned. 3. A thin film transistor manufacturing system for manufacturing a thin film transistor, comprising: 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; An oxide film forming step of forming an oxide film on the surface of the amorphous silicon film of the cleaned substrate; a laser annealing step of performing a laser annealing process on the amorphous silicon film to generate a polysilicon film serving as a channel layer; Evaluating the linearity and / or periodicity of the spatial structure on the film surface of the polysilicon film, and evaluating the state of the polysilicon film based on the evaluation result of the linearity and / or periodicity. A method for manufacturing a thin film transistor, comprising: