JP6718638B2 - Flexible substrate manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a flexible substrate.

A liquid crystal display (LCD) uses a thin film field effect transistor (TFT). The thin film field effect transistor is formed by using a silicon layer formed on a base material.
In recent years, a liquid crystal display is required to have a flexible structure. Therefore, not only glass but also a flexible resin (plastic) is used as a material of the base material (Japanese Patent Application Laid-Open No. 2013-164603). Gazette).

However, the resin base material has a problem that it is weak against heat when forming a semiconductor layer or when forming a transistor using the semiconductor layer. For example, when crystallizing a silicon layer formed on a base material, an annealing process is performed by an excimer laser. At this time, high-temperature energy of 2000 K, for example, is input to the silicon layer. A resin substrate including an ordinary resin base material cannot withstand the high heat.
In view of the above circumstances, it is an object of the present invention to provide a method for manufacturing a heat-resistant flexible substrate that is easy to use for forming a transistor.

A step of forming a metal layer on the resin substrate by a sputtering method,
Forming a buffer layer including a ZnS—SiO ₂ film, a SiO _x film or a SiN _x film on the metal layer by a sputtering method;
Forming an amorphous silicon layer on the buffer layer by a sputtering method,
A step of subjecting the amorphous silicon layer to laser annealing treatment within a range in which the surface temperature of the amorphous silicon layer is 1600 K or more and does not exceed 2000 K;
Have
In the laser annealing process, an excimer laser is irradiated onto the amorphous silicon layer formed on the flexible substrate at a wavelength of 190 to 400 nm, a pulse width of 15 to 50 ns, and a frequency of 500 to 6 kHz. ..

The flexible substrate includes a metal layer and a heat resistant buffer layer. As a result, even if the excimer laser is irradiated during crystallization of the silicon layer, the heat is diffused by the metal layer and the buffer layer, and the resin base material is not heated above the heat resistant temperature. As a result, damage such as carbonization of the resin base material can be prevented.

It is a schematic sectional drawing which shows schematic structure of the heat resistant flexible substrate which concerns on 1st Embodiment. It is a schematic sectional drawing which shows the example of a semiconductor device. It is a flowchart which shows the flow of the manufacturing process of a flexible substrate. It is a figure which shows the surface temperature of the silicon layer at the time of irradiation of an excimer laser. It is a figure which shows the surface temperature of the base material at the time of excimer laser irradiation. It is a figure which shows each process of the manufacturing process of a semiconductor device. FIG. 7 is a diagram showing each step of the manufacturing process of the semiconductor device, following FIG. 6; FIG. 8 is a diagram illustrating each step of the manufacturing process of the semiconductor device, following FIG. 7. FIG. 9 is a diagram illustrating each step of the manufacturing process of the semiconductor device, following FIG. 8. It is explanatory drawing explaining the work function of titanium and the electron affinity of silicon. FIG. 4 is a prediction diagram of an energy band when titanium and silicon are in contact with each other. It is a schematic sectional drawing which shows schematic structure of the heat resistant flexible substrate which concerns on 2nd Embodiment. It is a figure which shows the surface temperature of the silicon layer at the time of irradiation of an excimer laser. It is a figure which shows the surface temperature of the base material at the time of excimer laser irradiation.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same reference numerals refer to the same components, and the sizes of the respective components are exaggerated in the drawings for clarity and convenience of the description. Further, the embodiment described below is merely an example, and various modifications can be made from such an embodiment.
In addition, what is described as “above” or “above” includes not only those that are directly above in contact, but also those that are above in a non-contact manner and those that are above through other layers. Good.

(First embodiment)

(Schematic structure of substrate)
FIG. 1 is a schematic sectional view showing a schematic configuration of a heat resistant flexible substrate according to the first embodiment.
As shown in FIG. 1, in the flexible substrate 10, a base material 20, a metal layer 30, a buffer layer 40, an insulating layer 50, and a silicon layer 60 are laminated in this order.
The base material 20 is formed of a flexible resin such as polyimide (PI), polycarbonate (PC), polyethylene naphthalate (PEN), polyether sulfone (PES), and cycloolefin polymer (COP). These resins have melting points (glass transition points) or thermal decomposition temperatures of about 200 to 600° C. (these are collectively referred to as heat resistant temperatures).
The material of the base material 20 is not limited to these. As the base material 20, various materials can be adopted as long as they are made of a material having heat resistance of about 100 to 500°C. Further, the base material 20 may be glass instead of the flexible resin as long as it satisfies the above heat resistance.
The metal layer 30 is laminated on the base material 20. The metal layer 30 is formed of a metal such as titanium (Ti), aluminum (Al), chromium (Cr), nickel (Ni), molybdenum (Mo), or an alloy thereof.
Hereinafter, in the first embodiment, the metal layer 30 will be described as the titanium layer 30. However, the metal layer is not limited to the metals shown in the examples, and any metal may be used as long as it has a property of blocking heat or releasing heat (heat dispersion, heat dissipation).
The buffer layer 40 is laminated on the titanium layer 30. The buffer layer 40 is formed to include, for example, a ZnS—SiO ₂ film, a SiO _x film, or a SiN _x film. ZnS-SiO ₂ film, SiO _X film or SiN _X film, because thermal conductivity is low, the buffer layer formed by these, a heat resistant buffer layer.
The insulating layer 50 is stacked on the buffer layer 40. The insulating layer 50 is formed of, for example, a silicon oxide film (SiO _x (mainly SiO ₂ )) or a silicon nitride film (SiN _x ). The insulating layer 50 is formed to enhance the insulating property with respect to the buffer layer 40 and the titanium layer 30. The insulating layer 50 can be omitted.
The silicon layer 60 is stacked on the insulating layer 50. The silicon layer 60 is formed of polysilicon of intrinsic silicon (i-Si). The polysilicon of the silicon layer 60 is formed by crystallizing amorphous silicon laminated on the insulating layer 50 by laser annealing.
The flexible substrate 10 including the above-described structure becomes a semiconductor device such as a TFT by forming the silicon layer 60 (semiconductor layer).

(Structure of semiconductor device)
FIG. 2 is a schematic sectional view showing an example of a semiconductor device.
The semiconductor device 70 shown in FIG. 2 is formed on the flexible substrate 10. The semiconductor device 70 is formed using the silicon layer 60 on the flexible substrate 10.
A source electrode 74 and a drain electrode 75 are formed on the silicon layer 60. The gate electrode 72 is formed between the source electrode 74 and the drain electrode 75 with the insulating layer 80 interposed therebetween. A source wiring 78 and a drain wiring 79 are formed on the source electrode 74 and the drain electrode 75, respectively.
The gate electrode 72, the source electrode 74, and the drain electrode 75 are made of metal or alloy (silicide or the like). The gate electrode 72, the source electrode 74, and the drain electrode 75 may be formed of the same material or different materials. It is preferable to use a metal such as aluminum (Al) or titanium (Ti). By using these metals, each electrode can be formed only by a low temperature process such as a sputtering method or a physical vapor deposition method (PVD). Further, the gate electrode 72, the source wiring 78, and the drain wiring 79 can be formed of the same material.
The insulating layer 80 serves as a gate insulating layer below the gate electrode 72 and serves as an interlayer insulating layer in the other portions, and can be formed by a sputtering method in the same step (a semiconductor device manufacturing process will be described later).

(Flexible substrate manufacturing process)
Next, the process of the method for manufacturing the flexible substrate according to the first embodiment will be described.
FIG. 3 is a flowchart showing the flow of the manufacturing process of the flexible substrate.
First, the base material 20 is prepared (step S101). Subsequently, the titanium layer 30 is deposited on the base material 20 by the sputtering method (step S102). Continuously, the buffer layer 40 is deposited on the titanium layer 30 by the sputtering method (step S103), and the insulating layer 50 is deposited on the buffer layer 40 (step S104). Further, an amorphous silicon layer is deposited on the insulating layer 50 by Xe sputtering (step S105).
Next, an excimer laser (for example, ArF, KrF, XeF, XeCl) is applied to the amorphous silicon layer, for example, a wavelength of 190 to 400 nm, a pulse width of 15 to 50 ns, a frequency of 500 to 6 kHz (preferably 1 kHz), and a fluence (per unit area). in the energy ^{amount) 50mJ / cm 2 ~200mJ / cm} 2, irradiating 10-200 pulses amorphous silicon layer which was formed into a film on a flexible substrate.
As a result, the amorphous silicon layer is crystallized to form the silicon layer 60 made of polysilicon (step S106).
Through the above steps, the flexible substrate 10 as shown in FIG. 1 is formed. Although the excimer laser irradiation is performed in step S106, heat is diffused by the titanium layer 30 and the buffer layer 40, so that the base material 20 is not affected by deformation or the like. This point will be described in detail below.
Further, since the excimer laser preferably contains at least fluorine (F), an embodiment using an excimer laser containing fluorine (for example, ArF, KrF, XeF) will be described below.

(Thermal effect of titanium layer and buffer layer)
The thermal effect of the flexible substrate 10 having the titanium layer 30 and the buffer layer 40 according to the first embodiment will be described.
FIG. 4 is a diagram showing the surface temperature of the silicon layer upon irradiation with the excimer laser, and FIG. 5 is a diagram showing the surface temperature of the substrate upon irradiation with the excimer laser.
A flexible substrate 10 shown in FIG. 1 and a conventional substrate obtained by removing the titanium layer 30 and the buffer layer 40 from the flexible substrate 10 of FIG. 1 were prepared. Then, the irradiation energy of the excimer laser was controlled so that the surface temperature (K) of the silicon layer was 1600 K or higher and reached a maximum of 2000 K (within a range not exceeding 2000 K). The oscillation frequency of the excimer laser was 1 kHz, and the pulse width was 20 to 30 ns.
Then, after the excimer laser irradiation, the surface temperatures of the silicon layer and the substrate were numerically calculated.
4 and 5, the solid line shows the heat resistance result of the flexible substrate 10 of the first embodiment, and the broken line shows the heat resistance result of the conventional substrate without a titanium layer or the like.
As shown in FIG. 4, it was found that there is almost no difference in the transition of the surface temperature of the silicon layer between the flexible substrate 10 of the first embodiment shown by the solid line and the substrate shown by the broken line.
Further, as shown in FIG. 5, in the flexible substrate 10 of the first embodiment shown by the solid line, the surface temperature of the base material did not exceed 500 K (about 227° C.), whereas in the conventional substrate shown by the broken line, The surface temperature of the base material increased to 500 K or more.
It is considered that these results are because the titanium layer 30 absorbs the heat of the silicon layer 60 and diffuses it by inserting the titanium layer 30 into the buffer layer 40.
When the flexible resin substrate 20 is used, the heat resistant temperature is about 100 to 500° C. depending on the material. It has been found that by using the flexible substrate 10 of the first embodiment, crystallization of the silicon layer 60 can be realized while keeping the base material 20 having a heat resistant temperature of about 227° C. or less at the heat resistant temperature. That is, according to the flexible substrate 10 of the first embodiment, by including the titanium layer 30 together with the buffer layer, the base material 20 is protected during crystallization. It can be said that the range of choices of base materials has greatly expanded because even resins with a heat-resistant temperature of about 227°C can be used as base materials. Further, by adjusting the irradiation energy of the excimer laser, even a resin having a heat resistant temperature of about 100° C. can be expected to be applied to a substrate.

(Semiconductor device manufacturing process)
Next, a semiconductor device manufacturing process will be described.
As described above, the semiconductor device according to the first embodiment has the gate electrode 72, the source electrode 74, the drain electrode 75, the source wiring 78, the drain wiring 79, and the drain wiring 79 on the flexible substrate 10 on which the silicon layer 60 is formed. The insulating layer 80 is formed. These can be formed mainly only by a low temperature process such as film formation by a sputtering method or physical vapor deposition (PVD), crystallization/activation by laser annealing, patterning by photolithography and the like. Therefore, in the series of processes described in detail below, the process temperature is 350° C. or lower. In the first embodiment, the chemical vapor deposition method (CVD) is not used because the process temperature is not raised.
6 to 9 are views showing each step of the manufacturing process of the semiconductor device.
As shown in FIG. 6A, the flexible substrate 10 on which the above-mentioned silicon layer 60 is formed is prepared.
As shown in FIG. 6B, a resist layer is formed on the flexible substrate 10 and is patterned by photolithography to form a desired pattern (here, TFT) to form a resist pattern 90. Prebaking and postbaking at the time of forming the resist pattern 90 are preferably about 100 to 120° C. from the viewpoint of low temperature treatment.
As shown in FIG. 6C, the silicon layer 60 is etched using the resist pattern 90, and the silicon layer 60 having a desired pattern is obtained. The etching may be either a wet etching method or a dry etching method.
As shown in FIG. 6D, the resist pattern 90 is removed.
As shown in FIG. 7E, the titanium layer 73 is formed on the silicon layer 60 by the sputtering method.
As shown in FIG. 7F, a resist layer is formed on the titanium layer 73 and is patterned by photolithography so as to have a desired pattern (here, source and drain) to form a resist pattern 92. Pre-baking and post-baking are performed at about 100 to 120°C.
As shown in FIG. 7G, the titanium layer 73 is etched using the resist pattern 92 to obtain the source electrode 74 and the drain electrode 75. The etching may be either a wet etching method or a dry etching method.
As shown in FIG. 7H, the resist pattern 92 is removed. The source electrode 74 and the drain electrode 75 thus formed are Schottky contact type titanium electrodes as the source/drain regions.
As shown in FIG. 8I, the insulating layer 80 (here, SiO ₂ ) is formed by the sputtering method. The insulating layer 80 is formed by oxygen-added argon sputtering at room temperature.
As shown in FIG. 8J, the resist layer formed on the insulating layer 80 is patterned by photolithography to form a resist pattern 94. Pre-baking and post-baking are performed at about 100 to 120°C.
As shown in FIG. 8K, the insulating layer 80 is etched using the resist pattern 94 to form a contact hole. The etching may be either a wet etching method or a dry etching method.
As shown in FIG. 9L, the resist pattern 94 is removed. As a result, the upper portions of the source electrode 74 and the drain electrode 75 are exposed. The etching may be either a wet etching method or a dry etching method.
As shown in FIG. 9M, the aluminum layer 77 is formed by the sputtering method.
As shown in FIG. 9N, the resist layer formed on the aluminum layer 77 is patterned by photolithography to form a resist pattern 96. Pre-baking and post-baking are performed at about 100 to 120°C.
Then, the aluminum layer 77 is etched using the resist pattern 96 to form the gate electrode 72, the source wiring 78, and the drain wiring 79. The etching may be either a wet etching method or a dry etching method. Then, the resist pattern 96 is removed. TFT characteristics can be obtained by performing hydrogen annealing at 200° C. As a result, the semiconductor device 70 shown in FIG. 2 is completed.
As described above, in the first embodiment, the process temperature of 200° C. or lower is achieved in all the steps of forming the semiconductor device.

(Ohmic Schottky contact due to contact between titanium and silicon)
Ohmic Schottky contact due to contact between titanium and silicon in a semiconductor device will be described.
FIG. 10 is an explanatory diagram for explaining the work function of titanium and the electron affinity of silicon. FIG. 11 is a prediction diagram of an energy band when titanium and silicon are in contact with each other.
The work function of titanium is 4.33 [eV] as shown in FIG. The electron affinity of silicon is 4.05 [eV]. When titanium and silicon are brought into contact with each other, as shown in FIG. 11, the electron barrier is lowered at the contact portion, and charge injection from titanium to silicon occurs. As a result, the use of titanium for the source/drain regions facilitates the transfer of electrons from titanium to silicon, and an n-type TFT can be obtained.
By forming a metal (here, titanium) as a source/drain electrode on silicon in this manner, the source/drain regions can be formed by a vacuum vapor deposition method without using an ion implantation method. Therefore, the first embodiment is effective in reducing the cost and simplifying the process as a process for manufacturing a silicon TFT.

(effect)
Next, the effect of the first embodiment will be described.
As described above, in the first embodiment, the flexible substrate 10 includes the titanium layer 30 and the buffer layer 40. Therefore, even if the excimer laser is irradiated during crystallization of the silicon layer 60, the heat is diffused by the titanium layer 30 and the buffer layer 40, and the resin base material 20 is not heated above the heat resistant temperature. Therefore, damage such as carbonization of the base material 20 can be prevented. Particularly, in the first embodiment, since the titanium layer 30 is formed in addition to the buffer layer 40, a higher effect of heat diffusion can be obtained.
In the process of forming a semiconductor device, photolithography technology and sputtering method are used. No CVD is used and no subsequent high temperature annealing step. Therefore, the whole process can be achieved at, for example, 500° C. or lower, or 300° C. or lower, and even 200° C. or lower. Therefore, the base material 20 is not exposed to a high temperature of 500° C. or higher, and damage to the base material 20 can be prevented. Even a resin having a heat-resistant temperature of about 500° C. can be applied as the base material 20, and the range of selection of the resin greatly expands.

(Second embodiment)

(Schematic structure of substrate)
FIG. 12 is a schematic cross-sectional view showing a schematic configuration of the heat resistant flexible substrate according to the second embodiment.
As shown in FIG. 12, in the flexible substrate 10′, the base material 20, the buffer layer 40, the metal layer 30, the insulating layer 50, and the silicon layer 60 are laminated in this order. That is, the insertion position of the metal layer 30 is different from that of the first embodiment. Also in the second embodiment, for the metal layer 30, for example, metals such as titanium (Ti), aluminum (Al), chromium (Cr), nickel (Ni), molybdenum (Mo), and alloys thereof can be used.
Hereinafter, in the second embodiment, the metal layer 30 will be described as the titanium layer 30. However, the metal layer is not limited to the metals shown in the examples, and any metal may be used as long as it has a property of blocking heat or releasing heat (heat dispersion, heat dissipation).
Other configurations and conditions are similar to those of the first embodiment.

(Thermal effect of titanium layer and buffer layer)
The thermal effect of the flexible substrate 10' having the titanium layer 30 according to the second embodiment will be described.
FIG. 13 is a diagram showing the surface temperature of the silicon layer during the excimer laser irradiation, and FIG. 14 is a diagram showing the surface temperature of the base material during the excimer laser irradiation.
A flexible substrate 10′ shown in FIG. 12, a flexible substrate 10 shown in FIG. 1, and a conventional substrate obtained by removing the titanium layer 30 from the flexible substrate 10 shown in FIG. 12 were prepared. Then, the irradiation energy of the excimer laser was controlled so that the surface temperature (K) of the silicon layer was 1600 K or higher and reached a maximum of 2000 K (within a range not exceeding 2000 K). The oscillation frequency of the excimer laser was 1 kHz, and the pulse width was 20 to 30 ns.
Then, after the excimer laser irradiation, the surface temperatures of the silicon layer and the substrate were numerically calculated.
13 and 14, the solid line shows the heat resistance result of the flexible substrate 10 of the first embodiment, the broken line shows the heat resistance result of the conventional substrate without a titanium layer, etc., and the alternate long and short dash line shows the flexibility of the second embodiment. The heat resistance result of the substrate 10' is shown.
As shown in FIG. 13, it was found that with time, the surface temperature of the silicon layer was more likely to decrease in the flexible substrate 10 of the second embodiment shown by the alternate long and short dash line. It is considered that this is because the titanium layer 30 having a high thermal conductivity is closer to the silicon layer 60 than the buffer layer 40, and quickly takes the heat of the silicon layer 60 and diffuses it.
Further, as shown by the alternate long and short dash line in FIG. 14, as for the surface temperature of the base material, in the flexible substrate 10 of the second embodiment, the surface temperature of the base material did not exceed 500 K (about 227° C.). In the conventional substrate indicated by the broken line, the surface temperature of the base material increased to 500 K or more.
It is considered that these results are because the titanium layer 30 absorbs the heat of the silicon layer 60 and diffuses it by inserting the titanium layer 30 into the buffer layer 40.
When the flexible resin base material 20 is used, depending on the material, the heat resistant temperature may be only about 100 to 500°C. By using the flexible substrate 10 ′ of the second embodiment, crystallization of the silicon layer 60 can be realized while keeping the base material 20 at the heat resistant temperature or lower. That is, according to the flexible substrate 10 ′ of the second embodiment, by including the titanium layer 30 together with the buffer layer, the base material 20 is protected during crystallization.
Therefore, also in the second embodiment, the same effect as in the first embodiment can be obtained.

10 flexible substrate 20 base material 30 metal layer 40 buffer layer 50 insulating layer 60 silicon layer 70 semiconductor device 72 gate electrode 73 titanium layer 74 source electrode 75 drain electrode 77 aluminum layer 78 source wiring 79 drain wiring 80 insulating layers 90, 92, 94 , 96 resist pattern

Claims (2)

A step of forming a titanium layer on the resin substrate by a sputtering method,
Forming a buffer layer including a ZnS—SiO ₂ film, a SiO _x film or a SiN _x film on the titanium layer by a sputtering method;
Forming a layer of a silicon oxide film (SiO _x ) or a silicon nitride film (SiN _x ) as an insulating layer on the buffer layer;
Forming an amorphous silicon layer on the silicon oxide film (SiO _x ) or silicon nitride film (SiN _x ) layer by a sputtering method;
A step of subjecting the amorphous silicon layer to a laser annealing treatment in a range in which the surface temperature of the amorphous silicon layer is 1600 K or higher and does not exceed 2000 K;
Have
The laser annealing treatment uses an excimer laser on a flexible substrate with a wavelength of 190 to 400 nm, a pulse width of 15 to 50 ns, a frequency of 500 to 6 kHz, 10 to 200 pulses, and an energy amount per unit area of 50 to 200 mJ/cm ² . Irradiation on the formed amorphous silicon layer,
It is, method of manufacturing a flexible substrate, wherein the surface temperature of the resin substrate in this process does not exceed even once 500K (about 227 ° C.). A step of forming a titanium layer on the resin substrate by a sputtering method,
Forming a buffer layer including a ZnS—SiO ₂ film, a SiO _x film or a SiN _x film on the titanium layer by a sputtering method;
Forming a layer of a silicon oxide film (SiO _x ) or a silicon nitride film (SiN _x ) as an insulating layer on the buffer layer;
Forming an amorphous silicon layer on the silicon oxide film (SiO _x ) or silicon nitride film (SiN _x ) layer by a sputtering method;
A step of subjecting the amorphous silicon layer to a laser annealing treatment in a range in which the surface temperature of the amorphous silicon layer is 1600 K or higher and does not exceed 2000 K;
Have
The laser annealing treatment uses an excimer laser on a flexible substrate at a wavelength of 190 to 400 nm, a pulse width of 15 to 50 ns, a frequency of 1 to 2 kHz, 10 to 200 pulses, and an energy amount per unit area of 50 to 200 mJ/cm ² . Irradiation on the formed amorphous silicon layer,
It is, method of manufacturing a flexible substrate, wherein the surface temperature of the resin substrate in this process does not exceed even once 500K (about 227 ° C.).