JPH1056010A - Thin film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film forming method with which a thin film of excellent characteristics can be formed at a low temperature condition. SOLUTION: A film-forming substrate 29 and a monitoring substrate 28 are mounted on a sputtering device 11 to form a film, and an infrared spectroscopic analysis is conducted on the thin film formed on the monitoring substrate 28. A control signal is outputted to an output control means 15 based on the above-mentioned detected value and film forming power is controlled. Also, the temperature inside a chamber 12 is controlled by outputting a control signal to the temperature controlling means 17 of a heater 16. The quality of the SiO2 film, to be formed on a film-forming substrate 13, can be brought into an approriate state by conducting the above-mentioned control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thin film.

[0002]

2. Description of the Related Art Thin film formation is an essential step in various electronic devices, and the film quality required for each thin film differs depending on the structure and function of the electronic device.
When an electronic device is manufactured on the basis of a semiconductor process, there are limitations on the conditions for forming a thin film depending on the configuration of the electronic device.

Conventionally, when such a limitation exists, a driving circuit or a pixel electrode for applying a signal voltage to a gate line and a drain line on a glass substrate or a polymer film substrate in a liquid crystal display device (LCD). A thin film forming step in the case of manufacturing a thin film transistor (TFT) as a switching element connected to the thin film transistor. That is, it is necessary to adopt a low-temperature process in the manufacturing process of the TFT in consideration of the durability of the glass or the polymer material serving as the substrate against heat.

Here, a method of manufacturing a TFT using polysilicon as a semiconductor layer will be briefly described with reference to FIG.
First, a silicon oxide film 2 as a base insulating film is formed on a glass substrate 1. The silicon oxide film 2 is formed by a sputtering method. Next, after depositing an amorphous silicon film on the silicon oxide film 2, this amorphous silicon film is subjected to laser annealing to be converted into a polysilicon film 3, and the polysilicon film 3 is patterned. Thereafter, the silicon oxide film 4 is deposited again by the sputtering method. Then, a gate electrode 5 made of, for example, Al is patterned on the silicon oxide film 4. Further, a silicon nitride film 6 as an interlayer insulating film is deposited on the silicon oxide film 4 and the gate electrode 5 by a plasma CVD method. Thereafter, contact holes 7 are formed in silicon oxide film 4 and silicon nitride film 6.
Are formed to form source / drain electrodes 8. It is known that the ID characteristics of the TFT manufactured in this way depend on the film quality of the polysilicon film 3 as the semiconductor layer and the silicon oxide film 4 as the gate insulating film. In particular, the threshold voltage (Vth) and the flat band voltage (Vfb) depend on the film quality of the gate insulating film and the base insulating film. When a polysilicon TFT is manufactured on a glass substrate as described above, a low-temperature process is required in consideration of the heat resistance of the glass, and a sputtering method capable of forming a thin film at a low temperature is often used.

[0005]

However, in the above-described polysilicon TFT formed by the conventional low-temperature process, as described below, (1) the film quality of the gate insulating film and the like is unstable. The threshold voltage (Vth) fluctuates. (2) Flat band voltage (Vf) in CV characteristics
b) fluctuates. (3) The flat band voltage (Vfb) becomes non-uniform in the plane. (4) A simple method for evaluating the quality of the insulating film has not been established. There was such a problem. As a cause of these problems, since the substrate is made of glass, it is not possible to use a thermal oxide film under high-temperature conditions with stable characteristics, and therefore, it is necessary to use a silicon oxide film formed at a relatively low temperature using a sputtering apparatus. It is thought that there is. For this reason, an insulating film having unstable characteristics due to a delicate change in film forming conditions may be used to form a TFT.
There is a problem that FT is manufactured. In particular, LC
In the case of a TFT used for D, the threshold voltage (Vth)
Variations in the flat band voltage (Vfb) are disadvantageous because they appear as low luminescent spots in pixels. Further, although the standard of the variation of the threshold voltage (Vth) differs depending on the purpose of the device, there is a problem that the threshold voltage (Vth) cannot be used unless it is at least within 1V.

The problem to be solved by the present invention is that a thin film having good characteristics can be surely formed, and in particular, what means should be taken to obtain a thin film having good film quality under low temperature conditions. On the point.

[0007]

According to the first aspect of the present invention,
A step of forming a thin film on a substrate disposed in a film forming apparatus, and irradiating the thin film with measurement light while forming the thin film,
The method is characterized by comprising a step of evaluating the film quality of the thin film, and a step of optimizing film forming conditions according to the evaluation. According to the first aspect of the present invention, it is possible to determine a film forming condition of a thin film formed on a film forming substrate disposed in a film forming apparatus by evaluating a thin film formed on a substrate. It is possible to form a thin film having a good quality.

[0008] The invention according to claim 2 is characterized in that the measuring light is infrared light. The inventors have found that by evaluating the infrared absorption state of a predetermined atomic bond in a thin film by infrared spectroscopy, for example, the quality of a flat band voltage (Vfb) of a TFT can be determined. That is, it has been found that the flat band voltage (Vfb) corresponds to the peak top position by infrared spectroscopy. By evaluating the thin film formed on the substrate using this relationship, it is possible to determine the conditions for forming a thin film having good characteristics, and to continue forming a thin film having good characteristics in the thin film forming process. be able to.

According to a third aspect of the present invention, the thin film is a silicon oxide film. In the invention described in claim 4, the step of evaluating the film quality of the thin film is a step of irradiating the infrared ray to the silicon oxide film and detecting a wave number or a wavelength corresponding to an absorption peak of a Si—O bond. And According to the third and fourth aspects of the present invention, it is possible to form a thin film having good characteristics by evaluating the infrared absorption state of the Si—O bond of the silicon oxide film by conversion infrared spectroscopy. Becomes

According to a fifth aspect of the present invention, the step of optimizing the film forming conditions controls the film forming output power of the film forming apparatus based on the evaluation. The invention according to claim 6 is characterized in that the step of optimizing the film forming conditions controls the film forming temperature in the film forming apparatus based on the evaluation. According to the fifth and sixth aspects of the invention, the quality of a thin film formed on a substrate is controlled based on the detection value of infrared spectroscopy, and the output power of the apparatus and the film formation temperature in the apparatus are controlled. This makes it possible to optimize the quality of the thin film formed on the deposition substrate.

According to a seventh aspect of the present invention, the thin film is an insulating film of a thin film transistor.
According to the seventh aspect of the invention, since the quality of the insulating film of the thin film transistor can be favorably formed, it is possible to manufacture a TFT having no change in the threshold voltage (Vth) or the flat band voltage (Vfb). Becomes

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the method for forming a thin film according to the present invention will be described below based on an embodiment applied to the manufacture of a TFT. First, prior to explaining the method of forming the thin film,
A sputtering apparatus used for forming a thin film will be described with reference to FIG. In the figure, reference numeral 11 denotes a sputtering apparatus as a film forming apparatus, and a substrate holder 13 and a target holder 14 are arranged in a chamber 12 so as to face each other. The substrate holder 13 and the target holder 14 are connected to an output control unit 15. In the chamber 12, a heater 16 is provided. This heater 16 is connected to temperature control means 17. In the above-described chamber 12, light transmitting windows 18 and 19 are formed of a transparent material at positions sandwiching the substrate holder 13 and the target holder 14. Further, the substrate holder 13 and the target holder 14 have light transmission ports 13A, 14A formed at positions corresponding to the light transmission windows 18, 19, respectively. A light source 20 that emits light in the infrared region is disposed outside the chamber 12. Light emitted from the light source 20 is reflected by the reflection plate 21, passes through the light transmission window 19, and transmits the other light. It is set so as to enter the window 18.
In addition, a reflection plate 22 that reflects light emitted from the light transmission window 18 to the outside of the chamber 12 and a spectroscopic analyzer 23 that receives light emitted from the reflection plate 22 are disposed outside the chamber 12. I have. Further, the spectroscopic analyzer 23 includes:
It is connected to the arithmetic processing unit 24. Further, the arithmetic processing unit 24 is connected to a storage means 25 composed of a ROM. The arithmetic processing unit 24 is connected to the output control means 15 and the temperature control means 17 described above. In addition,
In FIG. 1, 26 is a vacuum pump, 27 is a gas introduction path, 28 is a monitor substrate, 29 is a film formation substrate, and 30 is, for example, SiO _2.
Is shown.

Here, the sputtering apparatus 11 described above is used.
Formed under various conditions by using _TwoFourier transformation of the membrane
Si-O bond examined using exchange infrared spectroscopy (FT-IR)
The wave number at the top of the peak indicating_TwoGame membrane
Of the polysilicon TFT used as the gate insulating film
The result of examining the relationship between the voltage and the
You. Si formed using this sputtering apparatus 11
The range of the conditions for forming the O2 film is as follows.

(Deposition conditions) 成膜 Deposition temperature 200 ° C. or less 〇 Deposition power 1.5 kW or less 〇 Atmosphere gas Argon (Ar) and oxygen (O ₂ ) 〇 Monitor substrate Single crystal silicon plate

FIG. 2 is a graph showing the wave number at the top of a peak indicating a Si—O bond obtained by examining a gate insulating film (SiO ₂ ) formed under the above film forming conditions using Fourier transform infrared spectroscopy.
4 is a graph showing a relationship between a flat band voltage (Vfb) of a polysilicon TFT using this SiO ₂ film as a gate insulating film. The spectrum used for evaluation was
The spectrum of the single crystal silicon used for the base is subtracted. From the graph shown in the figure, it can be seen that the flat band voltage and the peak top position by FT-IR correspond. Note that the flat band voltage (Vf
b) means the voltage Vg at the rise of the capacitance with respect to the gate voltage from the CV characteristic, and the threshold voltage (Vth)
Is used in the same sense as By the way, M such as TFT
In the OS transistor, if there is no charge or Na ion generated due to a bond defect in SiO ₂ at the gate insulating film or the electrode interface, the gate voltage is 0 V
At this time, no current flows between the source and the drain, but when a gate voltage is applied even a little, carriers are induced in the semiconductor layer, and the source and the drain become conductive. Although this is an ideal transistor, the ideal threshold voltage (=
0 V). From such a viewpoint, using the graph of FIG. 2, the FT-
By selecting the IR peak top, it is possible to form a thin film with good film quality. Note that factors in the film formation conditions for forming such a thin film exhibiting a peak top include a film formation output and a film formation temperature, but the film formation power is 1.5 kW and the film formation temperature is 100 ° C. In this case, the flat band voltage varies to about −4 V to −7 V despite the same film forming conditions.
By measuring the wave number or wavelength at the peak top of the Si—O bond, the flat band voltage of the thin film transistor can be easily determined before completion.

Meanwhile, in the sputtering apparatus 11 shown in FIG. 1, the value detected by the spectroscopic analyzer 23, that is, the value of the wave number at the peak top in the infrared absorption in the thin film is calculated by the processing unit 24 shown in FIG. Is output as a detection signal. This operation processing device 24
A control signal corresponding to each of the output control means 15 and the temperature control means 17 is output with reference to the detection signal from the spectroscopic analyzer 23 and the data stored in the storage means 25. Therefore, it is possible to control the quality of the thin film formed on the film forming substrate 27 based on the thin film formed on the monitor substrate 28. Here, the optical system provided in the sputtering apparatus 11 and the spectroscopic analyzer 23 constitute a film quality evaluation unit. Infrared spectroscopy, especially Fourier transform infrared spectroscopy, is used for spectroscopic analysis. By using this method, the relationship between the flat band voltage of a TFT and the infrared absorption state of a thin film as a gate insulating film is determined. It can be captured by a continuous correlation as shown in FIG. In addition, other film quality inspection methods, for example, SIM
S, Electron spectroscopy (ESCA), X-ray spectroscopy (EPMA)
The relationship between the flat band voltage of the TFT and the film quality was examined by using the method described above, but a clear correlation could not be obtained.

Next, an embodiment in which the method of forming a thin film of the present invention is applied to a TFT manufacturing process based on the function of the sputtering apparatus 11 will be described with reference to FIG. First, the glass substrate 31 and the monitor substrate 28 are placed on the substrate holder 13 of the sputtering apparatus 11 shown in FIG. Then, the sputtering apparatus 11 is operated to form a base insulating film 32 made of SiO ₂ on the glass substrate 31 to a predetermined thickness as shown in FIG. At this time,
The light from the light source 20 is spectrally measured by the spectroscopic analyzer 23 via the reflection plate 21, the monitor substrate 28, the reflection plate 22, and the like. Based on the measurement result, a detection signal is output from the spectroscopic analyzer 23 to the arithmetic processing device 24, and the arithmetic processing device 2
4 outputs a control signal to the output control means 15 and the temperature control means 17 in consideration of the detection signal and the data of the storage means 25. The output control means 15 receives a control signal from the arithmetic output device 24, controls the power output of the sputtering device 11, and sets film forming conditions for optimizing the film quality of SiO ₂ . At the same time, the temperature controller 17 receives a control signal and performs control for optimizing the temperature of the heater 16. In the present embodiment, the above-described film quality optimization is performed in the step of forming the base insulating film 32. However, when the film quality of the base insulating film 32 has little effect on the operation characteristics of the TFT formed thereon. Evaluation of the film quality and control of the film quality by infrared spectroscopy may be omitted.

Next, the glass substrate 31 is subjected to plasma CVD.
The apparatus is moved into a device (not shown), and an amorphous silicon film is formed on the underlying insulating film 32.
Was subjected to laser annealing of the amorphous silicon film using an excimer laser annealing apparatus (not shown), and FIG.
It is changed to a polysilicon film 33 as shown in FIG.
Thereafter, the polysilicon film 33 is patterned by using a photolithography technique and an etching technique as shown in FIG.

Then, the glass substrate 31 is placed again on the substrate holder 13 of the sputtering apparatus 11 shown in FIG. At this time, the monitor substrate 28 is also placed so as to be located on the light transmission opening 13A of the substrate holder 28. afterwards,
By operating the sputtering apparatus 11, a gate insulating film 34 of SiO ₂ having a predetermined thickness is deposited as shown in FIG. In the glass substrate 31, the base insulating film 3
2 and a gate insulating film 34 are deposited on the polysilicon film 33. On the monitor substrate, only the gate insulating film 34 is deposited. Here, the film quality is evaluated using infrared spectroscopy. That is, the light from the light source 20 is
The light is incident on the spectroscopic analyzer 23 via the monitor substrate 28, the reflection plate 22, and the like, and the light affected by the infrared absorption in the gate insulating film 34 is spectrally measured. Based on the measurement result, a detection signal is output from the spectroscopic analyzer 23 to the arithmetic processing unit 24, and the arithmetic processing unit 24 outputs a control signal in consideration of the detection signal and the data in the storage unit 25.
5 and output to the temperature control means 17. Output control means 15
Sets the film formation conditions for optimizing the film quality of the gate insulating film 34 by inputting a control signal from the arithmetic output device 24 and controlling the power output of the sputtering device 11. At the same time, the temperature controller 17 receives a control signal and performs control for optimizing the temperature of the heater 16.
In the present embodiment, the film quality of the gate insulating film 34 is such that the variation of the flat band voltage (Vfb) and the threshold voltage (Vth) of the TFT is suppressed, and the film quality is fixed at a low voltage. The possible film forming conditions, that is, the film forming output and the film forming temperature are set. Especially,
In this embodiment, the wave number of the FT-IR peak top is ±
It is set to fall within the range of 0.5 / cm. For example, when the output of the apparatus is 1.5 kW and the temperature in the chamber is 10
When the flat band voltage (Vfb) is set to −5 V at 0 ° C., the wave number of the FT-IR peak top is 1061 cm ^−1.
(Wavelength: about 9425 nm). In the present embodiment, the monitor substrate 28 and the glass substrate 31 are simultaneously placed in the sputtering apparatus 11 to form a film. However, first, only the monitor substrate 28 is formed to form a film. After evaluating the conditions, the film formation conditions may be optimized, and then the gate insulating film 34 may be formed on the glass substrate 31.

Next, as shown in FIG. 4B, a gate electrode 35 made of, for example, Al is patterned on the gate insulating film 34, and a silicon nitride film 36 as an interlayer insulating film is entirely formed on the gate electrode 35. The film is formed by a plasma CVD method. Thereafter, a contact hole 37 is opened in the silicon nitride film 36 and the gate insulating film 34 by using a known photolithography technique and an anisotropic etching technique, and the polysilicon film 33 is exposed. Then, by forming the source / drain electrodes 38 using a known technique,
The polysilicon TFT is almost completed.

According to the above embodiment, it is possible to form a high-quality insulating film in which the variation of the flat band voltage is controlled to less than 1 V in a low-temperature process without thermally damaging the glass substrate 31. Therefore, the yield of TFTs and the like can be significantly improved.

Although the embodiment has been described above, the present invention is not limited to this, and various design changes, material changes, and condition changes accompanying the gist of the configuration are possible. For example, in the above embodiment, the present invention is applied to a method for forming a silicon oxide thin film, but it is of course possible to apply the present invention to a method for forming a silicon nitride film.
In this case, by evaluating the infrared absorption state of the Si—N bond by infrared spectroscopy, it is possible to easily control the quality of the thin film to be formed as in the case of silicon oxide. In the above embodiment, the present invention is applied to a transistor having a so-called top gate structure. However, the method for forming a thin film of the present invention may be applied to the manufacture of a transistor having a so-called bottom gate structure. It is possible. Further, in the above embodiment, a sputtering apparatus is used as a film forming apparatus. However, the present invention can be applied to another film forming apparatus such as a CVD apparatus. Further, in the above embodiment, the film forming power and the film forming temperature are used as parameters as the film forming conditions to be controlled. However, these may be controlled simultaneously or only one of them may be controlled. It is also possible to set other parameters as control parameters.

[0023]

As is apparent from the above description, according to the present invention, a thin film having good characteristics can be surely formed. This makes it possible to easily set the film forming apparatus.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a sputtering apparatus used in an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a peak-top wave number detected by infrared spectroscopy and a flat band voltage.

FIGS. 3A to 3C are cross-sectional views illustrating a TFT manufacturing process of the embodiment.

FIGS. 4A and 4B are cross-sectional views showing a TFT manufacturing process of the embodiment.

FIG. 5 is a sectional view showing the structure of a polysilicon TFT.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Sputtering apparatus 12 Chamber 13 Substrate holder 15 Output control means 16 Heater 17 Temperature control means 23 Spectroscopy analyzer 24 Arithmetic processing unit 25 Storage means 34 Gate insulating film

Claims (7)

[Claims] A step of forming a thin film on a substrate disposed in a film forming apparatus; and a step of irradiating measurement light to the thin film during the formation of the thin film to evaluate a film quality of the thin film. And a step of optimizing film forming conditions according to the evaluation. 2. The method according to claim 1, wherein the measuring light is infrared light. 3. The method according to claim 1, wherein the thin film is a silicon oxide film. 4. The step of evaluating the quality of the thin film is a step of irradiating the silicon oxide film with the infrared rays and detecting a wave number or a wavelength corresponding to an absorption peak of a Si—O bond. The method for forming a thin film according to claim 3. 5. The method according to claim 1, wherein in the step of optimizing the film forming conditions, the film forming output power of the film forming apparatus is controlled based on the evaluation. The method for forming a thin film according to the above. 6. The method according to claim 1, wherein in the step of optimizing the film forming conditions, a film forming temperature in the film forming apparatus is controlled based on the evaluation. The method for forming a thin film according to the above. 7. The method for forming a thin film according to claim 1, wherein the thin film is an insulating film of a thin film transistor.