JP3376181B2 - Method for preparing thin film of TFE-based polymer - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thin film production method for producing a thin film by irradiating a target of tetrafluoroethylene polymer (TFE polymer) with SR light.

As a method for producing a TFE polymer thin film,
The vacuum deposition method, the ion beam sputtering method, the thin film coating method using plasma, etc. are known. However, in any of the methods, it is difficult to form a thin film having a flat surface while keeping the components in the produced thin film constant.

Recently, TF using laser ablation
The technology for forming E-based polymer thin films has been actively studied (GB Blanchet et al., Applied Physics Letters 62, p1026 (1993) (GB Blanchet).
62 et al. Appl. Phys. Lett. 62, p1026 (1993)) and Y.
Ueno et al., Applied Physics Letters 65, p13
70 (1994) (Y. Ueno et al. Appl. Phys. Lett.
65, p1370 (1994)).

In the laser ablation method, a TFE polymer target is focused and irradiated with laser light to cause ablation to form a TFE polymer thin film on a substrate. Ablation is a phenomenon in which a target material is scattered from a locally generated high-temperature plasma state. An excimer laser is often used as a laser for causing ablation.

When a TFE polymer thin film is produced by the vacuum vapor deposition method, a fibrous structure appears in the film and unevenness occurs on the surface. When it is formed by the ion beam sputtering method, a change in ion beam energy (for example, 400 to 1000e).
V) changes the chemical composition of the TFE polymer thin film. When a method of producing a TFE-based polymer thin film using plasma is used, it is difficult to produce a good quality TFE-based polymer thin film because the chemical composition greatly differs depending on the position of the thin film. In the laser ablation method, the flatness of the thin film is poor and it is difficult to control the crystallinity.
Further, during film formation, Ar or CH ₄ gas (50 to 2
The substrate must be heated to 100-320 ° C. in an atmosphere of 50 mTorr.

In the laser ablation method, a focused beam is used to increase the photon density. From the target irradiated with the laser light, the TFE polymer constituent substance is emitted in a conical shape having the irradiation point as the apex. When such a molecular beam from a point source is received by a planar substrate, the film thickness of the thin film on the substrate is the thickest at the point closest to the point source, and becomes thinner as the distance from the point source increases.

Orbit the substrate to satellite orbit (planetary motion)
It is possible to form a thin film having a relatively uniform thickness on the surface by mechanical movement, but the driving mechanism of the substrate becomes complicated. Further, in order to drive the substrate in a satellite orbit, the size of the reaction chamber for film deposition becomes large. Therefore, there is a limit to making a large-area thin film.

An object of the present invention is to provide a thin film production method capable of growing a TFE polymer thin film on a surface of a large area while controlling flatness or crystallinity.

[0009]

According to one aspect of the present invention, a step of disposing a base member for forming a thin film facing a TFE polymer target, and the target is heated to a temperature higher than room temperature and not higher than 250 ° C. And a step of irradiating the heated target with synchrotron radiation including ultraviolet light having a wavelength of 160 nm to cause ablation of the TFE-based polymer. It Here, the TFE polymer means polytetrafluoroethylene (PTF).
E), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or tetrafluoroethylene-perfluorovinyl ether copolymer (PFA).

[0010]

The TFE polymer material scattered from the target by ablation is deposited on the surface of the underlying substrate to form a thin film of TFE polymer. By heating the target in advance, the film formation rate of the thin film of TFE polymer can be improved, and the flatness and crystallinity can be increased. At this time, it is not necessary to heat the substrate in vacuum.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows a partially cutaway plan view of a thin film forming apparatus according to an embodiment of the present invention. The main configuration of the thin film forming apparatus includes a reaction chamber 10, a gate valve chamber 20, a slit chamber 30, and a synchrotron radiation source (SR light source) chamber 40.

The reaction chamber 10, the gate valve chamber 20, and the slit chamber 30 are connected to the SR light source chamber 40 so as to form a continuous space. SR
The SR light 42 emitted from the electrons that orbit the electron orbit 41 in the light source chamber is introduced into the reaction chamber 10 through the slit chamber 30 and the gate valve chamber 20.

The inside of the SR light source chamber 40 is 10 ⁻⁹ torr.
A high vacuum of r or less is maintained. SR light source chamber 40
Is provided with means for controlling the accumulated current value of electrons circulating in the electron orbit 41, and can control the amount of SR light generated. Further, the SR light source chamber 40 is provided with means for controlling the current value of the electron orbit 41, and the optimum wavelength for causing ablation of the target of interest can be selected. For example, changing the magnetic field can change the electron energy.

The electron orbit 41 has, for example, a circular orbit, and the generated SR light has a flat plate shape. A part of the SR light, for example, a portion having a width of several cm is introduced into the reaction chamber 10 via the slit chamber 30 and the gate valve chamber 20. In the figure, a slit for blocking a part of SR light is arranged in a slit chamber 30 having a flat plate shape in which SR light is parallel to the paper surface. In the present embodiment, a slit provided with a circular through hole having a diameter of 3 mm is arranged. Therefore, the cross section of the SR light that has passed through the slit chamber 30 has a circular shape with a diameter of 3 mm. In addition,
The cross section of SR light gradually increases as it advances,
Keep the slit chamber 30 away from the light source and the reaction chamber 1
Since it is placed close enough to 0, reaction chamber 1
The cross section of the SR light introduced at 0 can be considered as a circular shape having a diameter of about 3 mm.

In the reaction chamber 10, there is arranged a target support means 11 for supporting the PTFE target 12 on the optical path of SR light. PTFE target 12
And the SR light source has a distance of 3 m. When the PTFE target 12 is irradiated with SR light, ablation occurs from the irradiated portion. Therefore, the reaction chamber 10
The degree of vacuum inside is reduced. An exhaust pipe 18 is connected to the reaction chamber 10 in order to maintain a high vacuum.

A base substrate support means 14 for supporting the base substrate 15 is arranged at a position facing the PTFE target 12. When the ablation occurs on the PTFE target surface, the target material scatters, and the base substrate 15
Deposit on the surface of. The distance between the PTFE target 12 and the base substrate 15 is 3 cm. Target support means 11
Heaters 13 and 16 are attached to the base substrate supporting means 14 and the base substrate supporting means 14, respectively, and the PTFE target 12
Also, the base substrate 15 can be heated.

A quartz oscillator type film thickness meter 17 is arranged at a position 10 cm from the SR light irradiation position of the PTFE target 12. The film thickness of the produced PTFE thin film can be constantly observed with the film thickness meter 17.

Reaction chamber 10 and slit chamber 30
A gate valve chamber 20 is disposed between
By closing the gate valve in the gate valve chamber 20, the reaction chamber 10 and the SR light source chamber 40 can be separated in vacuum. By closing the gate valve and leaking inside the reaction chamber 10,
The FE target 12 and the base substrate 15 can be exchanged.

FIG. 2 shows the relationship between the target temperature and the film formation rate when a PTFE thin film is formed using the thin film forming apparatus shown in FIG. The horizontal axis represents the elapsed time from the start of SR light irradiation to the PTFE target 12 in the unit of “second”,
The vertical axis represents the film formation rate in the unit of nm / s. Symbol in the figure ○,
Δ and □ indicate the film forming rates when the temperatures of the PTFE target 12 before SR light irradiation were 200 ° C., 100 ° C., and 25 ° C., respectively. The pressure in the reaction chamber 10 is about 1 × 10 ⁻⁵ torr, and the photon density of SR light on the target surface is 2 × 10 ¹⁵ photons / s · mm ² .
The film forming rate was calculated from the film thickness measured by the film thickness meter 17.

As shown in FIG. 2, the higher the target temperature, the higher the film formation rate. For example, when the target temperature before SR light irradiation is 200 ° C., 100 ° C. and 25 ° C., the film forming rates after 30 seconds from the start of SR light irradiation are about 4.3 nm / s and 1.2 nm / s, respectively. And 0.7 nm / s. The film forming rates when the target temperature is 200 ° C. are about 3.5 times and about 6 times the film forming rates when the target temperature is 100 ° C. and 25 ° C., respectively.

The reason why the film forming rate increases with time is considered as follows. The PTFE target is S
Although heated before R light irradiation, the temperature of the target surface further rises by SR light irradiation. However, PTF
It is below the softening point (250 degreeC) of E. As shown in FIG. 2, when the temperature of the target rises, the film formation rate increases. It is considered that the temperature of the target surface gradually rises as the SR light irradiation time elapses, and the film formation rate gradually increases. As the temperature of the target surface rises gradually and approaches a steady state, the rate of increase of the film formation rate also becomes gentle.

When the target temperature was 100 ° C., the film formation rate hardly increased in the time region 16 seconds after the start of SR light irradiation. It is considered that this is because the target surface temperature is in a substantially steady state after about 16 seconds have passed from the SR light irradiation. On the other hand, when the target temperature is 25 ° C., the film forming rate gradually increases at least 30 seconds after the start of SR light irradiation. This is probably because it takes a long time for the temperature of the target surface to reach a steady state. Further, after a long time has passed from the start of SR light irradiation, the film formation rate when the target temperature is 25 ° C. approaches the film formation rate when the target temperature is 100 ° C. Temperature is 100 ℃
It is thought to rise to some extent.

When the target surface temperature is 200 ° C., the rate of increase in the film formation rate is relatively large in the time range from the start of SR light irradiation up to 12 seconds.
The increase rate is relatively small in the time domain after the lapse of seconds. From this result, the temperature increase rate of the target surface is relatively large during the period from the start of SR light irradiation to 12 seconds,
It is considered that the temperature rise rate decreases after the elapse of seconds.

Incidentally, in the thin film growth, there is a phenomenon that the film forming rate is generally low in the initial stage of growth. The growth nuclei are formed on the surface of the underlayer, and the film formation rate until the growth nuclei grow and the entire surface is covered with the growth layer tends to be slower than the subsequent film formation rate. It is possible that such a phenomenon contributes to the characteristics of FIG.

From the graph of FIG. 2, it can be seen that the deposition rate of the PTFE thin film can be controlled by controlling the temperature of the PTFE target. Further, it is understood that the temperature of the PTFE target should be increased in order to obtain a high film formation rate.

Next, the flatness of the surface of the produced PTFE thin film will be described. Using the thin film production apparatus shown in FIG. 1, a PTFE thin film was produced by setting the substrate temperature to room temperature, 50 ° C. and 100 ° C. without heating the PTFE target. When the surface of the produced PTFE thin film was observed with a scanning electron microscope, a spot pattern having a size of about 0.5 μm was observed on the surface of the produced PTFE thin film at substrate temperatures of 50 ° C. and 100 ° C. This mottled pattern is due to the unevenness formed on the PTFE surface. On the other hand, such a mottled pattern was not observed on the surface of the PTFE thin film prepared at the substrate temperature of room temperature. From this, it is understood that the substrate temperature is preferably about room temperature in order to obtain a PTFE thin film having high surface flatness.

The substrate temperature is set to room temperature and PT before SR light irradiation
When a PTFE thin film was prepared by setting the temperature of the FE target at 200 ° C., a PTFE thin film having higher flatness than that obtained when the PTFE target was not heated could be obtained. By heating the PTFE target, it is possible to obtain a PTFE thin film having high flatness.

Next, the crystallinity of PTFE will be described. PTFE has a property of easily crystallizing, and its crystal structure is a twisted spiral structure close to a hexagonal system. PTFE
Usually constitutes a polycrystalline body composed of single crystal grains having different sizes. The degree of size of each single crystal grain that constitutes a polycrystal is called crystallinity. The larger the single crystal grain, the higher the crystallinity.

FIG. 3A shows an X-ray diffraction pattern of the PTFE target. 3B shows the substrate temperature at room temperature and the target temperature at 200 ° C., FIG. 3C shows the substrate temperature at 50 ° C. and the target temperature at room temperature, and FIG. The X-ray-diffraction pattern of a PTFE thin film when both temperature and target temperature are room temperature is shown.

As shown in FIG. 3A, a sharp peak due to the (100) plane of PTFE appears at a position where 2θ is 18 degrees. In addition, in the range of 2θ of 30 to 45 degrees, PTFE
(110) plane, (200) plane, (201) plane, (10
Small peaks on the 7) plane, the (204) plane, and the (108) plane appear.

When the crystallinity is high, sharp peaks due to the crystal planes within each single crystal grain are observed. When the degree of crystallinity becomes low (the size of single crystal grains becomes small), the stress acting on the interface between the single crystal grains becomes large and strain occurs in the single crystal grains. This distortion causes the crystal plane spacing to deviate from the regular spacing. Therefore, each peak width of the X-ray diffraction pattern becomes wider.

In FIG. 3B, a peak due to the (100) plane is observed at a position where 2θ is 18 degrees. In FIG. 3C, the diffraction intensity is large in a region where 2θ is smaller than 18 degrees, but a peak due to the (100) plane is slightly observed. In FIG. 3D, the sharp peak on the (100) plane disappears, and a broad peak is observed near 2θ of 15 degrees. Further, in all of FIGS. 3B to 3D, a wide peak is observed in a region where 2θ is 35 to 45 degrees.

As shown in FIGS. 3B and 3D, when the substrate temperatures are the same, the higher the target temperature, the higher the crystallinity. However, the melting point of PTFE is about 250 ° C.
Therefore, it is preferable to set the target temperature to 250 ° C. or lower. As shown in FIGS. 3C and 3D, when the target temperatures are the same, the higher the substrate temperature, the higher the crystallinity. Therefore, PTs with various crystallinity can be obtained by changing the substrate temperature and the target temperature.
It can be seen that an FE thin film can be produced.

As described above, the flatness and crystallinity of the PTFE thin film can be controlled by controlling the substrate temperature and the target temperature. For example, crystallinity has a large effect on transparency, gas permeability, and mechanical properties, but has little effect on heat resistance, chemical resistance, non-stickiness, nonflammability, and dielectric properties. Therefore, a PTFE thin film having desired flatness and crystallinity may be produced depending on the application.

For example, the PTFE thin film can be used for surface protection of deliquescent substances, surface protection of electric circuits or IC packages, and the like. It can also be used as a surface-treated film for pots.

Next, the relationship between the light intensity of the SR light with which the target is irradiated and the crystallinity of the produced PTFE thin film will be described. Substrate temperature and target temperature are the same,
The photon density of SR light on the target surface is 1 × 10 ¹⁵
Photon / s · mm ^{2 to} 3 × 10 ¹⁵ Photons / s · mm ²
When a PTFE thin film was produced by changing the film thickness within the range, it was found that the higher the photon density, the higher the film formation rate and the higher the crystallinity. PTFE with good crystallinity
In order to form a thin film, it is preferable that the photon density on the target surface is 1.5 × 10 ¹⁵ photons / s · mm ² or more.

In the above experiment, the SR for irradiating the target
Although the cross section of light is circular with a diameter of 3 mm, the cross section of SR light may be made larger. When the irradiation area becomes large, P
Since the TFE material scatters from a large area, PTFE
The uniformity of the thin film thickness can be improved.

The substrate may be moved in a satellite orbit (planetary motion), for example. By moving the substrate in this manner, it will be possible to further improve the uniformity of the film thickness.

The SR light with which the PTFE target is irradiated preferably contains ultraviolet light having a wavelength of 160 nm.
The single-photon absorption spectrum of PTFE shows a sharp peak near a wavelength of 160 nm. Therefore, ablation can be efficiently generated by irradiating SR light including ultraviolet light having a wavelength of 160 nm.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0042]

As described above, according to the present invention,
The deposition rate of the PTFE thin film can be increased. Also,
A PTFE thin film can be produced while controlling flatness and crystallinity.

[Brief description of drawings]

FIG. 1 is a schematic partially cutaway plan view of a thin film forming apparatus used in an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the film formation rate of a PTFE thin film and the elapsed time from the start of SR light irradiation when the target temperature is changed.

FIG. 3 is a graph showing an X-ray diffraction pattern of a PTFE target and a PTFE thin film.

[Explanation of symbols]

10 Reaction chamber 11 Target support means 12 targets 13, 16 heater 14 Base substrate supporting means 15 Base substrate 17 Film thickness meter 18 Exhaust pipe 20 Gate valve chamber 30 slit chamber 40 SR light source chamber 41 electron orbit 42 SR light

─────────────────────────────────────────────────── --- Continuation of front page (56) References JP-A-6-10119 (JP, A) JP-A-62-41291 (JP, A) JP-A-61-120836 (JP, A) JP-A-60- 8057 (JP, A) JP-A-6-280024 (JP, A) JP-A-6-220615 (JP, A) JP-A-63-19689 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 14/00-14/58 JISST file (JOIS)

Claims (4)

(57) [Claims] 1. A step of disposing a base member for forming a thin film so as to face a TFE polymer target, a step of heating the target to a temperature higher than room temperature and 250 ° C. or lower, and the heated target. And a step of irradiating synchrotron radiation including ultraviolet light having a wavelength of 160 nm to cause ablation of the TFE-based polymer. 2. The method for producing a thin film of a TFE polymer according to claim 1, further comprising the step of heating the thin film forming base member before the step of causing the ablation. 3. A step of disposing a base member for forming a thin film so as to face a TFE polymer target, a step of heating the target, and the heated target containing ultraviolet light having a wavelength of 160 nm, The photon density is 1.
And a step of causing ablation of the TFE polymer by irradiating with synchrotron radiation of 5 × 10 ¹⁵ photons / s · mm ² or more. 4. A step of disposing a base member for thin film formation so as to face a TFE polymer target, a step of heating the target to 200 ° C. or higher and 250 ° C. or lower, and a wavelength of the heated target. And a step of irradiating synchrotron radiation light containing 160 nm ultraviolet light to cause ablation of the TFE-based polymer.