An apparatus and method for preparing poly-p-xylene film

Abstract

The present invention relates to a device and a method for preparing a parylene film. The device includes a support table and a substrate placed on the tabletop of the support table for depositing the parylene film, and further includes a porous flow guide cover buckled above the substrate; a hollow cavity for gas flow is formed between the porous flow guide cover and the tabletop of the support table; by providing the porous flow guide cover, the parylene film can grow densely, effectively solving the problems of rough surface, unevenness, high defect rate, and poor density of the parylene film in the prior art. The method for preparing the parylene film uses the device for chemical vapor deposition. By optimizing the device and the process, the present invention improves the film-forming quality, reduces the defect rate of the parylene film, thereby reducing the self-loss of the flexible metamaterial substrate and effectively improving the performance of the metamaterial.

Description

Technical Field

[0001] The present invention relates to an apparatus and a method for preparing a parylene film. Background Art

[0002] An artificial composite structure or composite material composed of sub-wavelength artificial microstructure units and having special physical properties not possessed by natural materials is called a metamaterial; its physical properties are dominated by its constituent units, so high requirements are imposed on the surface flatness of the artificial microstructure and the substrate. Reducing the diffuse reflection on the surface of the parylene (Parylene-C) film is of great significance for the application research of metamaterials. Metamaterials are one of the current hotspots in scientific research and have great application prospects in radar, stealth technology, electromagnetic wave modulation and sensing, etc.

[0003] Currently, the preparation of parylene (Parylene-C) film mainly uses chemical vapor deposition (CVD). In this method, any substrate is generally used as the base, and the Parylene-C raw material is catalytically cracked in a cracking furnace, and then guided into a deposition chamber through a gas guide hole to deposit a film on the substrate; however, the Parylene-C flexible substrate film prepared by the traditional CVD method has problems such as a high bad point rate and poor quality, which limit its application. Especially in the later lithography process, high requirements are imposed on the surface flatness of the Parylene-C film. How to prepare a high-quality (i.e., high flatness and low bad point rate) Parylene-C film has become the key to realizing high-quality flexible substrate metamaterial devices, which is also a technical problem that needs to be solved urgently by those skilled in the art.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] Aiming at the problems of the flexible low-dielectric-constant parylene (Parylene-C) film for a metamaterial substrate in the prior art, such as rough surface, unevenness, high bad point rate, and poor compactness, an apparatus (chemical vapor deposition apparatus) for preparing a parylene film is proposed; the parylene film prepared by using the apparatus has high flatness, low bad point rate, and good quality.

[0006] Specifically, the apparatus includes a support table and a substrate placed on the tabletop of the support table for depositing a parylene film, and further includes a porous flow guide cover buckled above the substrate; a hollow cavity for gas flow is formed between the porous flow guide cover and the tabletop of the support table.

[0007] The present invention has found that the reason for the above problems in the Parylene-C thin film prepared by the traditional CVD method lies in the non-uniformity of the deposition gas flow on the surface of the substrate in the deposition chamber; the gas state of the Parylene-C raw material coming out of the air guide hole rotates with the gas flow of the rotating table in the deposition chamber, resulting in non-uniformity of the overall gas flow in the deposition chamber. Deposition on the substrate surface will cause vacancy defects on some substrate surfaces, reducing the flatness of the film formation and increasing the defect rate. The non-uniform mass distribution of the Parylene-C thin film leads to an increase in diffuse reflection. During the later preparation of flexible metamaterials, it seriously affects the pattern formed during the lithography of the metamaterials, and further affects the metal structure of the metamaterials.

[0008] The present invention completely covers the substrate with the porous flow guide cover, and a hollow cavity is formed between the porous flow guide cover and the substrate; the gas flow enters the hollow cavity through the porous flow guide cover and is then uniformly deposited on the substrate to form a thin film.

[0009] Preferably, the porous flow guide cover is provided with uniformly distributed air flow holes; the diameter of the air flow holes is 7-9 mm, and the center distance between two adjacent air flow holes is 12-14 mm;

[0010] The present invention has found that it is optimal when the diameter of the air flow holes and the center distance between adjacent air flow holes are within the above ranges. Too small will result in no effect of setting the porous flow guide cover and no influence on the gas flow, and too large will result in non-uniform film thickness.

[0011] In the present invention, when no porous flow guide cover is provided above the substrate, the gas directly enters from the air inlet cylinder, impacts on the inner wall of the chamber and then flows back to the center of the chamber, and thus cannot form a uniform flow field above the substrate, ultimately resulting in the inability to deposit a uniform thin film on the substrate surface; when a porous flow guide cover is provided above the substrate, the gas enters from the air inlet cylinder, impacts on the inner wall of the chamber and then flows back to the center of the chamber, and then enters the hollow cavity through the air flow holes on the porous flow guide cover. At the same time, the porous flow guide cover and the substrate rotate uniformly with the rotating table, and the gas in the hollow cavity is fully mixed again to form a uniform flow field distribution. Therefore, when the gas is deposited on the substrate surface, the gas is uniform and the deposition speed is slow.

[0012] Both the upper surface and the side wall of the porous flow guide cover are provided with uniformly distributed air flow holes, and the diameter of the air flow holes and the center distance between two adjacent air flow holes have a very important influence on the flow field distribution; if the aperture of the air flow holes is too large, a uniformly distributed flow field cannot be effectively formed; if the aperture of the air flow holes is too small, it is not easy to exchange the gas in the hollow cavity with the gas in the chamber; during the deposition process, the gas enters through the air flow holes on the upper surface of the porous flow guide cover and flows out through the air flow holes on the side wall to achieve gas exchange and ensure that a certain amount of Parylene-C is deposited on the substrate surface.

[0013] Preferably, the diameter of the air flow holes is 8 mm; the center distance between two adjacent air flow holes is 13 mm.

[0014] Preferably, the upper and lower bottom surfaces of the porous flow guide cover are parallel to the substrate; the distance from the upper surface of the substrate to the top of the inner wall of the porous flow guide cover is 10-18 mm.

[0015] In the present invention, the side surface of the porous flow guide cover can be perpendicular to the substrate or can form a certain angle.

[0016] Preferably, the porous flow guide cover is a straight cylinder with one end closed;

[0017] Furthermore, the closed side of the straight cylinder is the upper surface, and the open side is the lower surface; the lower surface of the straight cylinder is on the same horizontal plane as the substrate, and the diameter of the lower surface of the straight cylinder is greater than or equal to the diameter of the substrate (preferably greater);

[0018] In the above technical solution, the center of the substrate coincides with the center of the lower surface of the straight cylinder; the upper surface of the straight cylinder, the side surface of the straight cylinder, and the support table form a hollow cavity for gas to flow through, and the substrate is located at the center of the lower surface of the hollow cavity;

[0019] In the above technical solution, uniformly distributed air flow holes are provided on both the upper surface and the side surface of the straight cylinder; the diameter of the air flow holes on the upper surface of the straight cylinder is 7-9 mm (8 mm is particularly ideal), the diameter of the air flow holes on the lower surface of the straight cylinder is 7-9 mm (8 mm is particularly ideal), and the center distance between two adjacent air flow holes is 12-14 mm (13 mm is particularly ideal); the center distance between two adjacent air flow holes at the connection of the upper surface and the side surface of the straight cylinder is not limited.

[0020] Preferably, the height of the porous flow guide cover is 20-22 mm, and the wall thickness is 1.5-2.5 mm.

[0021] Preferably, the bottom area of the open side of the porous flow guide cover is 20%-40% larger than the area of the substrate; or the diameter of the porous flow guide cover is 20%-40% larger than the diameter of the substrate.

[0022] As a preferred embodiment of the present invention, the diameter of the substrate is 100 mm, and the bottom area of the lower surface of the porous flow guide cover is 120-140 mm.

[0023] Preferably, the device further includes: a chamber;

[0024] A support table and a rotating table are provided in the chamber, and the support table, the rotating table, and the lower surface of the chamber are stacked in sequence;

[0025] Wherein, the substrate is disposed on the support table;

[0026] An air inlet cylinder is provided in the chamber; an air inlet and an air outlet are provided on the lower surface of the chamber, the air inlet and the air outlet are oppositely arranged, and the air inlet is connected to the air inlet cylinder; a plurality of round holes with a diameter of 3 mm are provided on the air inlet cylinder; gas enters the air inlet cylinder through the air inlet and then enters the chamber through the round holes;

[0027] In order to ensure that the gas can be relatively uniformly distributed after entering the chamber, the opening direction of the round holes on the air inlet cylinder faces the inner wall of the chamber; thereby ensuring that when the gas enters the chamber through the round holes on the air inlet cylinder, it impacts on the inner wall of the chamber and then flows back to the center of the chamber;

[0028] Preferably, the rotating table rotates when the gas enters the chamber to ensure uniform distribution of the gas in the chamber;

[0029] Preferably, the substrate rotates synchronously with the rotating table, so that the gas is relatively uniformly deposited on the surface of the substrate.

[0030] Preferably, the substrate is a double-polished silicon wafer;

[0031] Preferably, the material of the porous flow guide cover is one of aluminum, stainless steel, gray cast iron, polyethylene material, and glass.

[0032] The present invention disposes the porous flow guide cover above the substrate, which can effectively integrate the uniformity of the air flow on the surface of the substrate and reduce the self-loss of the material; the obtained thin film meets the requirements of the metamaterial for high density and high flatness of the substrate thin film, and promotes the development of the metamaterial and flexible electronic devices.

[0033] The present invention also provides an application of the above device in the preparation of a thin film;

[0034] Preferably, the thin film is a polymer thin film or an organic thin film.

[0035] The present invention also provides a method for preparing a parylene thin film, using the above device for chemical vapor deposition.

[0036] Preferably, the growth evaporation temperature of the chemical vapor deposition is 170-180 °C, the cracking temperature is 680-700 °C, the trachea temperature is 130-140 °C, and the chamber pressure is 17-19 mTorr.

[0037] Through a large number of experimental studies and test experiments, the present invention finds that when the parameters of the chemical vapor deposition are within the above range, the obtained parylene thin film is more uniform, flat, and has a very low defect rate.

[0038] As an optimization of the above technical solution, the growth evaporation temperature of the chemical vapor deposition method is 175 °C, the cracking temperature is 690 °C, the trachea temperature is 135 °C, and the chamber pressure is 18 mTorr.

[0039] As an optimization, the method further includes a step of pre-pumping vacuum: reducing the pressure of the chamber to below 100 mTorr and then venting, repeating 2 to 5 times.

[0040] The step of pre-pumping vacuum is carried out before the start of deposition; it can be carried out once or multiple times.

[0041] The present invention also provides a parylene film prepared by the above method.

[0042] As an optimization, the thickness of the parylene film is 8 to 15 μm.

[0043] The present invention also provides the application of the above parylene film in flexible terahertz band metamaterials;

[0044] Specifically, to ensure the uniformity, no bad points, and smooth surface of the Parylene-C film, controlling the growth rate to 1 μm / h and the thickness to 8 to 15 μm can not only ensure the strength and flexibility of the flexible metamaterial, but also ensure that the transmittance of terahertz waves reaches more than 95%; if the thickness is greater than 15 μm, the growth time is longer and the transmittance of terahertz waves will decrease.

[0045] Advantages of the present invention:

[0046] (1) By setting a porous flow guide cover, the present invention enables the parylene (Parylene-C) film to grow densely, effectively solving the problems of rough surface, unevenness, high bad point rate, and poor density of the parylene film in the prior art;

[0047] (2) Through a large number of experimental studies, the present invention determines the optimal parameters of chemical vapor deposition, effectively reducing the influence of impurities on the parylene film;

[0048] (3) By optimizing the device and process, the present invention improves the film forming quality, reduces the bad point rate of the parylene film, thereby reducing the self-loss of the flexible metamaterial substrate and effectively improving the performance of the metamaterial.

[0049] (4) The parylene film provided by the present invention has high flatness, low bad point rate, and good quality; it has great application value. Description of the Drawings

[0050] Figure 1 It is the preparation flow chart of the parylene film in Embodiment 2 of the present invention;

[0051] Figure 2 Schematic diagram of the porous flow guide cover in Example 1;

[0052] Figure 3 Schematic diagram of the device for preparing poly(p-xylylene) film in Example 1;

[0053] Figure 4 Schematic cross-sectional view of the device for preparing poly(p-xylylene) film in Example 1;

[0054] Figure 5 Test chart of the surface flatness of the Parylene-C film deposited on the first substrate in Example 2;

[0055] Figure 6 Test chart of the surface flatness of the Parylene-C film deposited on the second substrate in Example 2;

[0056] Figure 7 Schematic diagram of the metamaterial prepared by using the Parylene-C film deposited on the first substrate in Example 2;

[0057] Figure 8 Schematic diagram of the metamaterial prepared by using the Parylene-C film deposited on the second substrate in Example 2;

[0058] Figure 9 Test chart of the surface flatness of the Parylene-C film prepared in Comparative Example 1;

[0059] Among them, 1 is a chamber, 2 is an air inlet cylinder, 3 is an air inlet, 4 is an air outlet, 51 is a first substrate, 52 is a second substrate, 6 is a porous flow guide cover, 7 is a support table, and 8 is a rotating table. Detailed implementation manners

[0060] The following examples are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0061] Example 1

[0062] This example provides a device for preparing poly(p-xylylene) film, as shown in Figure 3 and Figure 4 , which includes a support table 7 and a first substrate 51 placed on the tabletop of the support table 7 for depositing poly(p-xylylene) film; it also includes a porous flow guide cover 6 buckled above the first substrate 51; a hollow cavity for gas flow is formed between the porous flow guide cover 6 and the tabletop of the support table 7.

[0063] Preferably, as the above technical solution, the porous flow guide cover 6, as shown in Figure 2As shown, it is a straight cylinder with one end closed; the closed side of the straight cylinder is the upper surface, and the open side is the lower surface; the lower surface of the straight cylinder is on the same horizontal plane as the first substrate 51, and the diameter of the lower surface of the straight cylinder is greater than or equal to the diameter of the first substrate 51;

[0064] In the above technical solution, the center of the first substrate 51 coincides with the center of the lower surface of the straight cylinder; the upper surface of the straight cylinder, the side surface of the straight cylinder, and the support platform form a hollow cavity for gas flow, and the first substrate 51 is located at the center of the lower surface of the hollow cavity;

[0065] As a preference of the above technical solution, uniformly distributed air flow holes are provided on both the upper surface and the side surface of the straight cylinder; the diameter of the air flow holes on the upper surface of the straight cylinder is 8 mm, the diameter of the air flow holes on the lower surface of the straight cylinder is 8 mm, and the center distance between two adjacent air flow holes is 13 mm.

[0066] In this embodiment, the device further includes: a chamber 1;

[0067] A support platform 7 and a rotating platform 8 are provided in the chamber 1, and the support platform 7, the rotating platform 8, and the lower surface of the chamber 1 are stacked in sequence;

[0068] Among them, the first substrate 51 and the second substrate 52 are respectively arranged in the middle layer and the lower layer of the support platform 7;

[0069] An air inlet cylinder 2 is provided in the chamber 1; an air inlet 3 and an air outlet 4 are provided on the lower surface of the chamber 1, the air inlet 3 and the air outlet 4 are oppositely arranged, and the air inlet 3 is connected to the air inlet cylinder 2; a number of round holes with a diameter of 3 mm are provided on the air inlet cylinder 2, and gas enters the air inlet cylinder 2 through the air inlet 3 and then enters the chamber 1 through the round holes;

[0070] In order to ensure that the gas can be relatively evenly distributed after entering the chamber 1, the opening direction of the round holes on the air inlet cylinder 2 faces the inner wall of the chamber 1, so as to ensure that when the gas enters the chamber 1 through the round holes on the air inlet cylinder 2, it impacts on the inner wall of the chamber and then flows back to the center of the chamber;

[0071] In the above technical solution, the rotating platform 8 rotates when the gas enters the chamber 1 to ensure that the gas is evenly distributed in the chamber 1;

[0072] In the above technical solution, the first substrate 51 and the second substrate 52 rotate synchronously with the rotating platform 8, so that the gas is relatively evenly deposited on the surface of the substrate.

[0073] In this embodiment, the first substrate 51 and the second substrate 52 are double-polished silicon wafers, and the porous flow guide cover is made of polyethylene material.

[0074] Example 2

[0075] This example provides a parylene film, which is prepared by using the device of Example 1 and includes the following steps (as Figure 1 shown);

[0076] 1. Preparation before deposition

[0077] (1) Weigh the Parylene-C raw material (powder)

[0078] According to the working state of the device in Example 1, 35 g of Parylene-C raw material is required to prepare a 15-μm Parylene-C film;

[0079] (2) Preparation for starting up

[0080] Turn on the power switch (EMERGENCY STOP) button, press the main control key (MAIN POWER) once, configure the CVD growth evaporation temperature (VAPORIZER) to 175 °C, the cracking temperature (FURNACE) to 690 °C, the trachea temperature (CHAMBER GAUGE) to 135 °C, and set the chamber pressure (VACUUM) to 18 mTorr; vent to above 1000 mTorr and open the chamber;

[0081] (3) Clean the device

[0082] Clean the residual film left in the chamber, rotating table, air inlet, ventilation tube, discharge port, air outlet, cooling tube, etc.; first use a vacuum cleaner to clean the cleaned device again; then wipe the device with detergent; finally wipe it with lint-free paper;

[0083] (4) Install the raw material

[0084] Prepare tin foil, the length and thickness of which should be sufficient to surround the inner wall of the feed port pipe. The tin foil should be close to the inner wall. Evenly spread the Parylene-C raw material weighed in step (1) on the tin foil and close the evaporation chamber door;

[0085] (5) Assemble the equipment

[0086] Install all the equipment and install the porous flow guide cover on the support table. Rotate the rotating table to check whether there is any collision with the ventilation pipe;

[0087] (6) Pre-pump

[0088] Pre-evacuation sucks away the excess release agent and impurities in the cavity. Without turning on the refrigerant, evacuate until the pressure drops below 100 mTorr, then vent to 800 - 900 mTorr and evacuate again. After two pre-evacuation experiments, vent to 1000 mTorr;

[0089] (7) Loading the wafers

[0090] Place the first substrate in the middle layer of the support table, and place the second substrate (control group) in the lower layer of the support table; cover the first substrate with a porous flow guide cover and cover the cavity;

[0091] (8) Re-pre-evacuation

[0092] The pre-evacuation steps are the same as in step (6), and pre-evacuate twice;

[0093] 2. Deposition process

[0094] (1) Evacuation

[0095] Evacuate the pressure in the chamber to below 10 mTorr, turn the pressure knob to the vacuum key (VACUUM), start evacuation, and at the same time turn on the refrigerator;

[0096] (2) Start deposition

[0097] When the pressure in the chamber drops below 10 mTorr, rotate the buttons of the cracking chamber, vacuum tube, and evaporation chamber to the working state key (ENABLE); observe the status of the turntable in the chamber and whether each temperature is rising, and press the switch (PROCESS START), at this time the green light will light up;

[0098] 3. End of deposition

[0099] When the green light flashes, it means that the deposition is completed. When the temperature of the evaporation chamber returns below 30 °C, turn off the instrument; when taking out the first substrate and the second substrate, to prevent impurities from affecting, perform intermittent venting, and vent the pressure to above 1000 mTorr in three time periods.

[0100] In this embodiment, the Parylene-C raw material is heated into a gas state in the evaporation chamber and cracked into free radicals in the cracking chamber; the Parylene-C free radicals enter the intake cylinder through the intake port and enter the chamber through the intake cylinder; the Parylene-C free radicals fill the entire chamber through the air flow in the chamber; the Parylene-C free radical molecules pass through the porous flow guide cover, weakening the air flow disturbance and making the air flow distribution more uniform, so that the free radicals that lose energy at room temperature are evenly re-bonded into polymer molecules on the surface of the first substrate, forming a Parylene-C film with high flatness and low defect points.

[0101] In this embodiment, the Parylene-C film deposited on the first substrate is as Figure 5 shown, with a uniform surface and no particles; the Parylene-C film deposited on the second substrate is as Figure 6 shown, with particles on its surface.

[0102] The metamaterial is prepared using the Parylene-C films deposited on the first substrate and the second substrate of this embodiment; the metamaterial prepared using the Parylene-C film deposited on the first substrate is as Figure 7 shown, with a clean surface and no particles; the metamaterial prepared using the Parylene-C film deposited on the second substrate is as Figure 8 shown, with particles on its surface.

[0103] Comparative Example 1

[0104] This comparative example provides a parylene film, which is only different from that of Example 2 in that the CVD growth evaporation temperature (VAPORIZER) is configured to be 165 °C, the cracking temperature (FURNACE) is 650 °C, the tracheal temperature (CHAMBER GAUGE) is 135 °C, and the chamber pressure (VACUUM) is set to 22 mTorr; the chamber temperature is 25 °C.

[0105] The surface flatness test of the parylene film obtained in this comparative example is as Figure 9 shown, with some bad points on its surface; the main reason is that: the cracking temperature and the growth evaporation temperature are relatively low, resulting in a large number of particles when the Parylene-C powder is vaporized, so bad points appear on the surface of the Parylene-C film deposited on the substrate surface.

[0106] Although the present invention has been described in detail above with general descriptions, specific embodiments and experiments, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. An apparatus for preparing parylene film, comprising a support table and a substrate placed on the tabletop of the support table for depositing parylene film, Characterized in that, It further comprises a porous flow guide cover buckled above the substrate; a hollow cavity for gas flow is formed between the porous flow guide cover and the tabletop of the support table; The porous flow guide cover is provided with uniformly distributed air flow holes; the diameter of the air flow holes is 8 mm, and the center distance between two adjacent air flow holes is 13 mm; The upper and lower bottom surfaces of the porous flow guide cover are parallel to the substrate; the distance from the upper surface of the substrate to the top of the inner wall of the porous flow guide cover is 10 - 18 mm; The porous flow guide cover is a straight cylinder with one end closed; the height of the porous flow guide cover is 20 - 22 mm, and the wall thickness is 1.5 - 2.5 mm; The bottom area of the open side of the porous flow guide cover is 20% - 40% larger than the area of the substrate; or the diameter of the porous flow guide cover is 20% - 40% larger than the diameter of the substrate; The apparatus further comprises: a chamber; A rotating table is arranged in the chamber, and the support table, the rotating table and the lower surface of the chamber are stacked in sequence; An air inlet cylinder is arranged in the chamber; an air inlet and an air outlet are arranged on the lower surface of the chamber, the air inlet and the air outlet are arranged opposite to each other, and the air inlet is connected to the air inlet cylinder; a plurality of round holes with a diameter of 3 mm are arranged on the air inlet cylinder; gas enters the chamber through the air inlet and then through the round holes; The opening direction of the round holes on the air inlet cylinder faces the inner wall of the chamber; The rotating table rotates when gas enters the chamber, and the substrate rotates synchronously with the rotating table.

2. The apparatus according to claim 1, Characterized in that, The substrate is a double-polished silicon wafer; and / or, the material of the porous flow guide cover is one of aluminum, stainless steel, gray cast iron, polyethylene material, glass.

3. Use of the apparatus according to claim 1 or 2 in preparing parylene film.

4. A method for preparing parylene film, Characterized in that, Chemical vapor deposition is carried out by using the apparatus according to claim 1 or 2.

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