JP2002184715A - Thin film transistor manufacturing system and object surface evaluating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a processing time by securing the reproducibility of evaluated results when evaluating a polysilicon film formed in a low-temperature polycrystallizing process. SOLUTION: When the low-temperature polycrystallizing process is performed by using an excimer laser, linearity or periodicity appears in the space structure of the surface of the formed polysilicon film in accordance with the energy density given to amorphous silicon. The surface image of the polysilicon film is picked up by irradiating the film with ultraviolet rays and the periodicity of the surface of the film is digitized (AC valued) from the image by utilizing an auto-correlation function. The power of the excimer laser is set by evaluating the state of the film based on the AC value. In calculating the AC value, the picked-up image of the polysilicon film at each moving position is fetched while the film is moved in the axial direction of the irradiating light. The contrast of the image picked up at each position is calculated from the fetched picked-up images and the position where the contrast becomes the maximum is found. Then the AC value is calculated from the image picked up at the position where the contrast becomes the maximum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film transistor manufacturing system and method using a low temperature polycrystallization process,
Also, the present invention relates to an evaluation device and method for evaluating the periodicity of the spatial structure on the surface of an object.

[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 2000-005995, Japanese Patent Application 2000-
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]

However, when an image of the surface of the polysilicon film is picked up by using ultraviolet light, the surface of the film is subjected to reflection and diffraction on the surface of the polysilicon film by using an autocorrelation function. The value obtained by digitizing the periodicity of the spatial structure (AC value) depends on the focal position of the ultraviolet light to be irradiated and the distance between the polysilicon film (the distance in the optical axis direction of the ultraviolet light (hereinafter referred to as the Z direction)). And fluctuate. As described above, according to the distance between the focal position of ultraviolet light and the polysilicon film,
If the value fluctuates, measurement reproducibility cannot be ensured.
Conventionally, the stage supporting the substrate is slightly moved in the Z direction, the above-mentioned AC value is calculated at each movement position, and the AC value having the largest value is extracted, thereby ensuring reproducibility. Was.

However, in order to calculate the AC value, an FFT operation must be performed. When the AC value is obtained for each moving position as in the prior art, the total amount of calculation becomes enormous, and the processing time is reduced. It will be very long.

The present invention has been made in view of the above circumstances, and when evaluating a polysilicon film formed by a low-temperature polycrystallization process, reproducibility of the evaluation result is ensured. An object of the present invention is to provide a thin film transistor manufacturing system and method in which time is reduced.

Another object of the present invention is to provide an evaluation apparatus and method which can ensure the reproducibility of the evaluation result and can evaluate the periodicity of the spatial structure on the surface of the object in a shorter processing time. I do.

[0013]

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, and a channel layer by performing laser annealing on the amorphous silicon film. Laser annealing apparatus for producing a polysilicon film, an optical system for irradiating the polysilicon film with condensed light and detecting the reflected light, and an imaging system for imaging the reflected light detected by the optical system Part, a support part that supports the substrate and moves the irradiation light in the optical axis direction, and controls the support part and controls the periodicity of the surface spatial structure of the polysilicon film based on an image captured by the imaging unit. And an evaluation device having a control unit for evaluation, wherein the evaluation unit controls the support unit to move the polysilicon film in the optical axis direction. Then, the contrast of the captured image of the polysilicon film at each moving position is calculated, the evaluation position of the polysilicon film is determined based on the calculated magnitude of each contrast, and the imaging captured at the evaluation position is determined. The autocorrelation of the image is calculated to evaluate the periodicity of the surface spatial structure of the polysilicon film, and the laser annealing device or the film forming device determines the energy density of the laser or the polysilicon film based on the evaluation of the evaluation device. Is characterized by controlling the film thickness.

In this thin film transistor manufacturing system,
The substrate on which the polysilicon film is formed is moved in the direction of the optical axis of the irradiation light, and a captured image of the polysilicon film at each movement position is captured. The contrast of the captured image at each moving position is calculated from the captured image, and the evaluation position of the polysilicon film is determined based on the calculated magnitude of each contrast. Then, the autocorrelation of the captured image captured at the determined evaluation position is calculated, and the periodicity of the surface spatial structure of the polysilicon film is evaluated.

A method of manufacturing a thin film transistor according to the present invention includes a step of forming a polysilicon film to be a channel layer by annealing an amorphous silicon film with a laser annealing apparatus to manufacture a thin film transistor. A thin film transistor manufacturing method, comprising forming an amorphous silicon film on a substrate, performing a laser annealing process on the amorphous silicon film to form a polysilicon film, and evaluating a spatial structure of the polysilicon film surface. Irradiating the polysilicon film with condensed light to detect reflected light, moving the polysilicon film in the optical axis direction of the irradiating light, imaging the reflected light, and scanning the polysilicon at each movement position. The contrast of the captured image of the film is calculated, and based on the calculated magnitude of each contrast. Determine the evaluation position of the polysilicon film, calculate the autocorrelation of the image captured at the evaluation position, evaluate the periodicity of the surface spatial structure of the polysilicon film, and, based on the evaluation, Or the thickness of the polysilicon film is controlled.

In this method of manufacturing a thin film transistor, the substrate on which the polysilicon film is formed is moved in the optical axis direction of the irradiation light, and captured images of the polysilicon film at each moving position are taken. The contrast of the captured image at each moving position is calculated from the captured image, and the evaluation position of the polysilicon film is determined based on the calculated magnitude of each contrast. Then, the autocorrelation of the captured image captured at the determined evaluation position is calculated, and the periodicity of the surface spatial structure of the polysilicon film is evaluated.

The evaluation apparatus according to the present invention irradiates the inspection object with the condensed light, captures the reflected light, and evaluates the periodicity of the surface spatial structure of the inspection object based on the image. An evaluation device, comprising: an optical system configured to irradiate the object under inspection with condensed light and detecting reflected light thereof; an imaging unit configured to image the reflected light detected by the optical system; A support that supports the object and moves the supported object in the optical axis direction of the irradiation light; and a control of the support and a period of the surface spatial structure of the object based on an image captured by the imaging unit. A control unit for evaluating the property, the control unit controls the support unit to move the object to be inspected in the optical axis direction, and a contrast of a captured image of the object at each moving position. Is calculated, and based on the calculated magnitude of each contrast, Can determine the evaluation position of the inspection object, characterized in that by calculating the autocorrelation of the image captured image at the evaluation positions to evaluate the periodicity of the surface spatial structure of the object to be inspected.

In this evaluation apparatus, the inspection object is moved in the direction of the optical axis of the irradiation light, and captured images of the inspection object at each moving position are taken. The contrast of the captured image at each moving position is calculated from the captured image, and the evaluation position of the inspection object is determined based on the calculated magnitude of each contrast. Then, the autocorrelation of the image captured at the determined evaluation position is calculated, and the periodicity of the surface spatial structure of the inspection object is evaluated.

According to the evaluation method of the present invention, the object to be inspected is irradiated with condensed light, the reflected light is imaged, and the periodicity of the surface spatial structure of the object is evaluated based on the image. In the evaluation method, the inspection object is irradiated with condensed light, the reflected light is detected, the inspection object is moved in the optical axis direction of the irradiation light, and the detected reflected light is imaged. Calculating the contrast of the captured image of the inspection object at each moving position, determining the evaluation position of the inspection object based on the calculated magnitude of each contrast, and autocorrelating the captured image captured at the evaluation position. Is calculated to evaluate the periodicity of the surface spatial structure of the inspection object.

In this evaluation method, the object to be inspected is moved in the optical axis direction of the irradiation light, and captured images of the object to be inspected at each moving position are taken. The contrast of the captured image at each moving position is calculated from the captured image, and the evaluation position of the inspection object is determined based on the calculated magnitude of each contrast. Then, the autocorrelation of the image captured at the determined evaluation position is calculated, and the periodicity of the surface spatial structure of the inspection object is evaluated.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, as an embodiment of the present invention, an apparatus for evaluating a polysilicon film to which the present invention is applied will be described.

The apparatus for evaluating a polysilicon film according to the embodiment of the present invention is used, for example, for inspecting a polysilicon film formed during a manufacturing process of a thin film transistor having a bottom gate structure (bottom gate type TFT). 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, the bottom gate 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 example in which the present invention is applied to an evaluation apparatus for evaluating a bottom-gate TFT will be described. However, the present invention is not limited to such a bottom-gate TFT, and a polysilicon film (channel) may be formed on a glass substrate. After the layer is formed, the present invention can be applied to an evaluation apparatus for evaluating a so-called top gate type TFT in which a gate electrode is provided on the upper layer.

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 this 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 becomes very 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 determining 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 as follows.
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, if 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 annealing 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 according to the embodiment of the present invention 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 At this stage, it is used to determine whether or not the product is defective or to feed back information to an excimer laser annealing apparatus to set laser energy.

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 is in the range from the allowable minimum energy L 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 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 scanning direction of the laser for 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, comparing the image of FIG. 4B when the energy density at the time of excimer laser annealing is set to the optimum value, and 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 polysilicon film surface after excimer laser annealing with a good value of the energy density is an image in which linearity and periodicity appear are 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 an annealing process is performed on the amorphous silicon on which the natural oxide film is formed using an excimer laser, the natural oxide film (SiO ₂ ) is considered to be raised as shown in FIG. 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.

The shape of the natural oxide film after the annealing changes as shown in FIG. 5C due to the energy density given by the excimer laser annealing and the difference in the film 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) 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, an irregular short straight line or the like appears irregularly as shown in FIG. 7A. . 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. 7B, even if the image is shifted sideways, a highly correlated image having many overlapping images 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
A specific configuration example of the processing contents (1) Next, above-described embodiments of the polysilicon film evaluation apparatus of the present invention for evaluating the linearity and periodicity of the surface spatial structure of the polysilicon film Will be described.

The apparatus for evaluating a polysilicon film according to the embodiment of the present invention uses a microscope apparatus using an ultraviolet light laser having a wavelength of 266 nm to manufacture a bottom gate type TFT (polysilicon by performing excimer laser annealing on an amorphous silicon film). This is an apparatus that captures an image of the substrate immediately after the film is formed, and evaluates the state of the formed polysilicon film from the captured image.

FIG. 8 is a configuration diagram of a polysilicon film evaluation apparatus according to an embodiment of the present invention.

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 procedure, as shown in the flowchart of FIG. 9, first, an image capturing process of the surface of the polysilicon film is performed (step S1). Subsequently, an autocorrelation function is calculated from the captured image (step S2).
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). continue,
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 a function indicating a correlation when a certain function f (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, it becomes a function as shown in FIGS. 10 and 11. FIG. 10 shows an image having a high autocorrelation, that is, an autocorrelation function with good periodicity and linearity of the surface spatial structure of the polysilicon film. 11 shows an image having a low autocorrelation, that is, an autocorrelation function of the surface spatial 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 in this manner is the autocorrelation function R in the direction perpendicular to the above-described alignment direction.
It becomes a function corresponding to (τ).

In this case, the above-described steps S1 to S
3 may be performed as shown in the following steps S11 to S14 of FIG.

The following evaluation may be performed instead of such an evaluation procedure.

In the procedure of this evaluation, as shown in the flowchart of FIG. 12, 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. 13 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. 15 shows the C value.

(3) As shown in FIG. 5, the excimer laser-annealed polysilicon film is
Since a plurality of linear projections are formed on the surface of the film and the linear projections are periodically arranged, 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.

FIG. 16 shows the position of the polysilicon film surface,
It shows the AC value with respect to the distance from the focal position of the ultraviolet light laser focused by the objective lens. As shown in FIG. 16, the AC value has a peak characteristic that periodically fluctuates with respect to the position of the polysilicon film in the optical axis direction of the ultraviolet laser (hereinafter, referred to as Z position). That is, when the surface shape of the polysilicon film is imaged, the AC value periodically fluctuates according to the position in the Z direction of the stage supporting the substrate.

Here, assuming that the pattern interval between the plurality of linear projections is d and the wavelength of the ultraviolet light to be irradiated is λ, the variation period T of the AC value with respect to the Z-movement position of the polysilicon film is shown.
Is as follows. T = d ² / λ

For example, if the pattern interval d = 309 nm and the wavelength λ of the ultraviolet light is 266 nm, the variation period T becomes
360 nm.

When the AC value varies depending on the position of the stage supporting the substrate in the Z direction, for example, when comparing the grain sizes of a plurality of substrates or measuring the AC value for one substrate a plurality of times. In such a case, or when it is determined whether the substrate is a good product or a defective product, the reproducibility of the AC value cannot be ensured.

Therefore, in the present embodiment, the AC value having the largest value among the AC values periodically fluctuating with respect to the position in the Z direction of the polysilicon film is extracted as a sample to evaluate the polysilicon film. Is going. For example, the AC value at point X in FIG. 16 (the peak value of the AC value and the largest peak value among the respective maximum peak values) is extracted and evaluated. By extracting the maximum AC value as a sample in this manner, even if the AC value periodically fluctuates with respect to the Z-direction movement position of the polysilicon film,
The reproducibility of the AC value can be ensured.

To extract the maximum AC value, for example, Z
The stage is moved, and the polysilicon film and the objective lens 26 are moved.
Of the polysilicon film (ie, the position of the polysilicon film in the Z direction: the Z position), and the AC at each Z position is changed.
All the values may be calculated, and the maximum AC value may be extracted based on all the calculation results. However, when the AC value is calculated at each Z position, a large amount of FFT operation must be performed, and a huge amount of processing time is consumed.

Here, the present applicant has found that the Z position of the polysilicon film where the contrast calculated from the surface image of the polysilicon film is the maximum coincides with the Z position where the AC value is the maximum. did. Further, the present applicant has found that the peak cycle of the contrast with respect to the position in the Z direction of the polysilicon film coincides with the peak cycle of the AC value with respect to the position in the Z direction of the polysilicon film.

As shown in FIG. 17, the contrast value for each position in the Z direction of the polysilicon film has a peak characteristic with a period of T = d ² / λ, similarly to the AC value. Then, the Z position of the maximum peak value (Y _{1 in} FIG. 17) coincides with the Z position where the AC value is the maximum (X in FIG. 17).

Further, in the case of the AC value, since a plurality of peak values of approximately the same level appear, it is difficult to calculate the maximum peak value from among them. On the other hand, in the case of contrast, the maximum maximum peak (Y _{1 in} FIG. 17)
And the difference between the second largest peak (Y _{2 in} FIG. 17) and the second largest peak is very large. Therefore, extracting the maximum value of the contrast can be performed more easily than extracting the AC value.

The contrast is expressed by, for example, a differential value of the brightness of the edge portion of the image, a modulation degree of the brightness of each pixel, or a standard deviation of each pixel. These calculations can be performed very easily as compared with the calculation of the AC value.

Therefore, in the present invention, the Z position of the polysilicon film is moved by moving the Z stage, and a surface image of the polysilicon film is captured at each Z position to calculate the contrast. Then, an evaluation position where the contrast is maximized is found, and an AC value is calculated at this evaluation position.

By performing the processing in this manner, AC
Processing time can be reduced while ensuring reproducibility of values.

Note that the peak of the contrast may not coincide with the peak of the AC value depending on the characteristics of the optical system for transmitting the ultraviolet laser. For example, 1/4 wavelength plate 2
Even if the rotation angle adjustment of 7 is adjusted to the maximum value of the return light to the photodetector, the peak of the contrast may not coincide with the peak of the AC value. In such a case, for example, for a certain sample, the phase of the contrast with respect to the z position and the phase of the AC value with respect to the z position are measured using the rotation angle of the quarter-wave plate as a parameter, and the two phases match ( In other words, 1 /
Set the rotation angle of the four-wave plate. With the optical system adjusted in this way, the maximum value of the contrast and the maximum value of the AC value are matched for each sample. Also,
For a certain sample, the objective lens may be fixed at the z position where the contrast becomes maximum, and the rotation angle of the 波長 wavelength plate may be adjusted so that the AC value becomes maximum.

Next, the contrast at each Z position, which is performed by the polysilicon film evaluation apparatus 20, is calculated.
The processing procedure for determining the C value calculation position will be described with reference to the flowchart in FIG.

When the process of calculating the AC value is started, the polysilicon film evaluation apparatus 20 first moves the objective lens 26 to perform focusing, and matches the focal position of the focusing laser to the surface of the polysilicon film. (Step S21). As a focusing method, for example,
This is performed using a knife edge method, an image focusing method, a capacitance detection method, or the like.

Subsequently, the Z stage is slightly moved (step S22). This moving amount is, for example, a moving amount that is several times the depth of focus.

Subsequently, an image is captured at the position moved in step S22, and the contrast is calculated from the captured image (step S23). The calculated contrast is stored together with the movement position information at that time.

Subsequently, it is determined whether or not a certain scan range has been moved (step S24). A scan range of R = (period of the surface structure) ² / (wavelength of the measurement light) is sufficient around the Z position at which the contrast becomes the maximum value. However, if the Z position at which the contrast becomes maximum cannot be predicted, it is necessary to scan over this range to find the maximum value.

If it is determined in step S24 that the movement of the predetermined scan range has not been completed, step S22 is performed.
And the process is repeated. If the movement of the scan range has been completed, the process proceeds to step S25.

Subsequently, the maximum value is extracted from each calculated contrast, and the Z stage is moved to the Z position where the maximum value is obtained (step S25).

Subsequently, the image is fetched again at the Z position (or based on the stored image), and the AC value is calculated (step S26).

If there is enough space in the image memory, step S25 can be omitted, and the process can proceed to step S26. When calculating the contrast at each Z position, the image can also be stored, so the AC value may be calculated from the image at Z that gives the maximum contrast in step S26. If the Z position at which the contrast becomes maximum with the objective lens for ultraviolet light can be accurately reproduced only by the autofocus mechanism, the processing of steps S25 to S26 can be omitted. The AC value may be calculated from the image at the Z position adjusted in.

The polysilicon film evaluating apparatus 20 can complete the process in a short time while securing the reproducibility of the AC value by calculating the AC value according to the processing procedure described above.

After calculating this contrast, A
The method of calculating the C value and ensuring the reproducibility of the AC value is not only used, for example, in the evaluation of the polysilicon film,
It can also be used to evaluate the spatial structure of the grating-like material surface. In addition, this method can be used not only when evaluating the spatial structure of a material surface using an apparatus such as a visible light microscope apparatus or an SEM, but also an ultraviolet light microscope apparatus.

Although the calculated contrast has the peak characteristic as described above, the pattern interval of the surface structure of the polysilicon film can be calculated from the peak interval. That is, as described above, the peak interval T
Is determined by T = d ² / λ (d = pattern period, λ = wavelength of irradiation light). Therefore, the pattern interval d of the surface structure of the polysilicon film can be obtained by calculating d = (T × λ) ^1/2 .

(4) 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.

[0122] AC values, as shown in FIG. 19, 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 Its 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. 20 shows the peak characteristics of the AC value superimposed on the characteristics of the change in grain size of the polysilicon film shown in FIG. As shown in FIG. 20, 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 based on the AC value having such a peak characteristic, the AC value is determined as shown in FIG.
It is only necessary to judge whether or not the value falls within the range indicated by the bold line in 0.

(5) An 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. 19 is drawn, and the optimum energy density may be obtained from this characteristic diagram.

(6) 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. 21, 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. 22 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. 22, the AC value has a characteristic of different peak values on the gate electrode and the glass substrate. For example, it can be seen from the characteristic diagram shown in FIG. 22 that setting the energy density in excimer laser annealing to 380 mJ is optimal.

(7) 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 laser having 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 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. 23, 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. 24, the AC obtained from the 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.

As described above, 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. 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. 25, the center position of the manufacturing margin of the polysilicon film becomes 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. 26, 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. 27 and 28, A
A peak curve of the C value can be drawn on the graph.

When such an AC value peak curve 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. 27 and 28. 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. 27 and 28. 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 the manufacturing margin is set as an optimum value, whereby the yield of the bottom gate type TFT can be increased.

[0145]

In the thin film transistor manufacturing system and method according to the present invention, the substrate on which the polysilicon film is formed is moved in the direction of the optical axis of the irradiation light, and the captured image of the polysilicon film at each movement position is captured. The contrast of the captured image at each moving position is calculated from the captured image, and the evaluation position of the polysilicon film is determined based on the calculated magnitude of each contrast. Then, the autocorrelation of the captured image captured at the determined evaluation position is calculated, and the periodicity of the surface spatial structure of the polysilicon film is evaluated.

As a result, in the thin film transistor manufacturing system and method according to the present invention, the crystal state of polysilicon can be easily evaluated nondestructively, and objective evaluation can be performed with high accuracy. . Further, in the present invention, when evaluating a polysilicon film formed by the low-temperature polycrystallization process, the evaluation can be performed in a short processing time while ensuring reproducibility of the evaluation result.

In the evaluation apparatus and method according to the present invention, the object to be inspected is moved in the direction of the optical axis of the irradiation light, and captured images of the object to be inspected at each moving position are taken in. The contrast of the captured image at each moving position is calculated from the captured image, and the evaluation position of the inspection object is determined based on the calculated magnitude of each contrast. Then, the autocorrelation of the image captured at the determined evaluation position is calculated, and the periodicity of the surface spatial structure of the inspection object is evaluated.

As a result, the evaluation apparatus and method according to the present invention can easily and non-destructively evaluate the periodicity of the spatial structure on the material surface, and can perform objective evaluation with high accuracy. Becomes Further, in the present invention, the evaluation can be performed in a short processing time while ensuring the reproducibility of the evaluation result.

[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 diagram schematically illustrating a captured image of a polysilicon film having linearity and periodicity.

FIG. 7 is a view schematically showing a captured image of a polysilicon film having no linearity and no periodicity.

FIG. 8 is a configuration diagram of a polysilicon film evaluation apparatus according to an embodiment of the present invention.

FIG. 9 is a flowchart illustrating a procedure for evaluating a polysilicon film.

FIG. 10 is a diagram for explaining an autocorrelation function when the periodicity is high.

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

FIG. 12 is a flowchart for explaining another evaluation procedure of the polysilicon film.

FIG. 13 is a diagram for explaining an autocorrelation image in a case where periodicity is high when evaluated by the other evaluation procedure.

FIG. 14 is a diagram for explaining an autocorrelation image in a case where periodicity is low when evaluated by another evaluation procedure.

FIG. 15 is a diagram illustrating characteristics of an AC value obtained for a specific captured image.

FIG. 16 is a diagram showing a variation characteristic of an AC value with respect to a distance between a position on a surface of a polysilicon film and a focal position of an ultraviolet light laser focused by an objective lens.

FIG. 17 is a diagram showing a variation characteristic of a contrast and an AC value with respect to a distance between a position of a surface of a polysilicon film and a focal position of an ultraviolet light laser focused by an objective lens.

FIG. 18 is a flowchart illustrating a procedure for evaluating an AC value by a polysilicon film evaluation apparatus.

FIG. 19 is a diagram illustrating characteristics of an autocorrelation value with respect to energy applied to a polysilicon film.

FIG. 20 is a diagram illustrating characteristics of an AC value and a grain size with respect to energy applied to a polysilicon film.

FIG. 21 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. 22 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. 23 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. 24 is a specific application example (EQ) in which a polysilicon film evaluation device is applied to a manufacturing process of a bottom gate TFT.
It is a figure for explaining composition of C).

FIG. 25 is a diagram for explaining a relationship between a manufacturing margin of energy given to a polysilicon film and a change in energy density of an excimer laser (when the energy density is optimally set).

FIG. 26 is a diagram for explaining a relationship between a manufacturing margin of energy given 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. 27 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 explaining a method for obtaining an optimum value of the energy density from the example.

FIG. 28 is a diagram illustrating another example of the relationship between the manufacturing margin of the bottom gate type TFT and the energy density of the excimer laser, and illustrating 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 Nobuhiko Umezu 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo F-term in Sony Corporation (reference) 4M106 AA10 BA05 CA38 CB30 DH01 DH12 DH32 DH38 DH40 DJ04 DJ05 DJ20 5F052 AA02 BB07 DA02 JA02 5F110 AA24 CC07 DD02 EE04 FF02 FF03 FF09 GG02 GG13 GG25 GG47 HK03 HK04 HK07 HK21 HL07 HL14 NN03 NN04 NN14 NN16 NN23 NN24 PP03 PP05 PP06 QQ19

Claims (24)

[Claims] 1. 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; and a polysilicon film serving as a channel layer by subjecting the amorphous silicon film to laser annealing. A laser annealing device for generating, an optical system for irradiating the polysilicon film with condensed light and detecting the reflected light, an imaging unit for imaging the reflected light detected by the optical system, and the substrate And a control unit that supports and moves the irradiation light in the optical axis direction, and a control unit that controls the support unit and evaluates the periodicity of the surface spatial structure of the polysilicon film based on an image captured by the imaging unit. The evaluation device comprises: an evaluation device, wherein the control unit controls the support unit to move the polysilicon film in an optical axis direction. , The contrast of the captured image of the polysilicon film at each movement position was calculated, the evaluation position of the polysilicon film was determined based on the calculated magnitude of each contrast, and the image was captured at the evaluation position. The autocorrelation of the captured image is calculated to evaluate the periodicity of the surface spatial structure of the polysilicon film. The laser annealing device or the film forming device is configured to evaluate the energy density of the laser or the polysilicon based on the evaluation of the evaluation device. A thin-film transistor manufacturing system, wherein the thickness of the film is controlled. 2. The thin film transistor manufacturing system according to claim 1, wherein the control unit of the evaluation device determines an evaluation position of the polysilicon film based on the calculated maximum value of the contrast. 3. An optical system of the evaluation device, wherein a moving position in the optical axis direction of the polysilicon film at which the contrast is maximum, and a moving position in the optical axis direction of the polysilicon film at which the autocorrelation has a maximum value. 2. The thin-film transistor manufacturing system according to claim 1, wherein the adjustment is made so that? 4. The control unit of the evaluation device calculates a differential value of brightness of an edge portion of an image, a modulation degree of brightness of each pixel, or a standard deviation of each pixel as a contrast. The thin film transistor manufacturing system according to claim 1. 5. A thin film transistor manufacturing method for manufacturing a thin film transistor, comprising a polysilicon film forming step of forming a polysilicon film serving as a channel layer by annealing the amorphous silicon film with a laser annealing apparatus. Forming an amorphous silicon film on the substrate, performing a laser annealing process on the amorphous silicon film to form a polysilicon film, evaluating a spatial structure of the surface of the polysilicon film, and collecting the polysilicon film. The reflected light is detected by irradiating the light, and the reflected light is imaged by moving the polysilicon film in the optical axis direction of the irradiated light, and the contrast of the captured image of the polysilicon film at each movement position is calculated. Determines the evaluation position of the polysilicon film based on the calculated magnitude of each contrast Calculating the autocorrelation of the image taken at the evaluation position to evaluate the periodicity of the surface spatial structure of the polysilicon film, and based on the evaluation, determine the energy density of the laser or the film thickness of the polysilicon film. A method for manufacturing a thin film transistor, comprising controlling. 6. The method according to claim 5, wherein the evaluation position of the polysilicon film is determined based on the calculated maximum value of the contrast. 7. The optical system such that the position of movement of the polysilicon film in the direction of the optical axis at which the contrast becomes maximum coincides with the position of movement of the polysilicon film in the direction of the optical axis at which the autocorrelation has a maximum value. 6. The method according to claim 5, wherein the adjustment is performed. 8. The thin film transistor manufacturing method according to claim 5, wherein a differential value of brightness of an edge portion of an image, a modulation degree of brightness of each pixel, or a standard deviation of each pixel is calculated as a contrast. . 9. An evaluation apparatus for irradiating converged light to an object to be inspected, imaging reflected light thereof, and evaluating the periodicity of the surface spatial structure of the object based on the image. An optical system that irradiates the test object with condensed light and detects the reflected light; an imaging unit that captures the reflected light detected by the optical system; and an imaging unit that supports the inspection object and supports the inspection object. A support unit that moves the inspection object in the optical axis direction of the irradiation light, and a control unit that controls the support unit and evaluates periodicity of the surface spatial structure of the inspection object based on an image captured by the imaging unit. The control unit controls the support unit to move the test object in the optical axis direction, calculates a contrast of a captured image of the test object at each moving position, and calculates each calculated contrast. Of the inspection object based on the size of Position determining the evaluation device, characterized in that by calculating the autocorrelation of the image captured image at the evaluation positions to evaluate the periodicity of the surface spatial structure of the object to be inspected. 10. The evaluation apparatus according to claim 9, wherein the control unit determines an evaluation position of the inspection object based on the calculated maximum value of the contrast. 11. The optical system according to claim 1, wherein the moving position of the test object in the optical axis direction at which the contrast is maximum coincides with the moving position of the test object in the optical axis direction at which the autocorrelation has a maximum value. The evaluation device according to claim 9, wherein the evaluation device is adjusted as follows. 12. The evaluation apparatus according to claim 9, wherein the test object is a polysilicon film formed by performing an annealing process on an amorphous silicon film. 13. The evaluation apparatus according to claim 9, wherein the object to be inspected is a polysilicon film formed by performing a laser annealing process on an amorphous silicon film. 14. The apparatus according to claim 9, wherein the control unit calculates a differential value of brightness of an edge portion of the image, a modulation degree of brightness of each pixel, or a standard deviation of each pixel as a contrast. The described evaluation device. 15. The method according to claim 15, wherein the control unit calculates a period of a surface spatial structure of the inspection object based on a contrast peak interval obtained when the inspection object is moved in an optical axis direction. The evaluation apparatus according to claim 9, wherein the evaluation is performed. 16. The control unit measures an interval between adjacent contrast peaks, calculates a square root of a product of a wavelength of irradiation light and the measured interval, and calculates a period of a surface spatial structure of the inspection object. The evaluation device according to claim 15, wherein is calculated. 17. An evaluation method for irradiating converged light to an object to be inspected, imaging the reflected light, and evaluating the periodicity of the surface spatial structure of the object based on the image. The object is irradiated with the condensed light, the reflected light is detected, the object to be inspected is moved in the optical axis direction of the irradiation light, the detected reflected light is imaged, and the object to be inspected at each moving position is captured. Calculating the contrast of the captured image of the object; determining the evaluation position of the inspection object based on the calculated magnitude of each contrast; calculating the autocorrelation of the captured image captured at the evaluation position; An evaluation method characterized by evaluating the periodicity of the surface spatial structure of the object. 18. The evaluation method according to claim 17, wherein the evaluation position of the inspection object is determined based on the calculated maximum value of the contrast. 19. An optical system such that a moving position in the optical axis direction of the test object at which the contrast is maximum coincides with a moving position of the test object in the optical axis direction at which the autocorrelation has a maximum value. 18. The evaluation method according to claim 17, wherein adjustment is performed. 20. The evaluation method according to claim 17, wherein the object to be inspected is a polysilicon film formed by performing an annealing process on an amorphous silicon film. 21. The evaluation method according to claim 17, wherein said object to be inspected is a polysilicon film formed by subjecting an amorphous silicon film to laser annealing. 22. A differential value of brightness of an edge portion of an image,
18. The method according to claim 17, wherein a degree of modulation of brightness of each pixel or a standard deviation of each pixel is calculated as a contrast.
Evaluation method described. 23. The apparatus according to claim 17, wherein a period of a surface spatial structure of the inspection object is calculated based on a contrast peak interval obtained when the inspection object is moved in an optical axis direction. Evaluation method. 24. The control unit measures an interval between adjacent contrast peaks, calculates a square root of a product of a wavelength of irradiation light and the measured interval, and calculates a period of a surface spatial structure of the inspection object. The evaluation method according to claim 23, wherein is calculated.