阅读说明：本技术 毫米波太赫兹频段极低损耗介质薄膜及表面金属化方法 (Ultra-low loss dielectric film in millimeter wave terahertz frequency band and surface metallization method ) 是由 蔡龙珠 洪伟 蒋之浩 陈晖� 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种毫米波太赫兹频段极低损耗介质薄膜及表面金属化方法。该介质薄膜以柔性环烯烃共聚物薄膜(1)为基底,在柔性环烯烃共聚物薄膜(1)的下面设置作为支撑层的硅片(2),在柔性环烯烃共聚物薄膜(1)的上面设置金属层(3),所述柔性环烯烃共聚物薄膜(1)属于环烯烃共聚物,在毫米波太赫兹频段具有极低的介质损耗,在该介质薄膜表面形成稳定可靠的金属化太赫兹电路结构,实现基于环烯烃共聚物介质薄膜的毫米波太赫兹电路。实现基于环烯烃共聚物新型介质薄膜的毫米波太赫兹电路,对该新型介质薄膜在毫米波太赫兹的应用具有重要的意义。(The invention discloses a millimeter wave terahertz frequency band extremely-low loss dielectric film and a surface metallization method. The medium film takes a flexible cyclic olefin copolymer film (1) as a substrate, a silicon wafer (2) serving as a supporting layer is arranged below the flexible cyclic olefin copolymer film (1), a metal layer (3) is arranged above the flexible cyclic olefin copolymer film (1), the flexible cyclic olefin copolymer film (1) belongs to cyclic olefin copolymer, extremely low medium loss is achieved in a millimeter wave terahertz frequency band, a stable and reliable metallized terahertz circuit structure is formed on the surface of the medium film, and a millimeter wave terahertz circuit based on the cyclic olefin copolymer medium film is achieved. The realization of the millimeter wave terahertz circuit based on the cycloolefin copolymer novel dielectric film has important significance for the application of the novel dielectric film in millimeter wave terahertz.)

1. The medium film is characterized in that a flexible cyclic olefin copolymer film (1) is used as a substrate, a silicon wafer (2) serving as a supporting layer is arranged below the flexible cyclic olefin copolymer film (1), a metal layer (3) is arranged on the flexible cyclic olefin copolymer film (1), the flexible cyclic olefin copolymer film (1) belongs to cyclic olefin copolymer, extremely low medium loss is achieved in a millimeter wave terahertz frequency range, a stable and reliable metallized terahertz circuit structure is formed on the surface of the medium film, and a millimeter wave terahertz circuit based on the cyclic olefin copolymer medium film is achieved.

2. The millimeter wave terahertz frequency band extremely low loss dielectric film according to claim 1, wherein the flexible cyclic olefin copolymer film (1) is a cyclic olefin copolymer composed of norbornene and ethylene, and the cyclic olefin copolymers formed by specific weight doping of the norbornene and the ethylene are different in types, so that the characteristics are different, but the dielectric loss is smaller in the millimeter wave terahertz frequency band.

3. The millimeter wave terahertz frequency band ultra-low loss dielectric film as claimed in claim 1, wherein the surface bonding force between the metal layer (3) and the flexible cyclic olefin copolymer film (1) is related, and when the bonding force is not enough to support the required metal thickness and dimensional accuracy, a layer of metal such as titanium/chromium/platinum needs to be deposited as a bonding transition layer to enhance the bonding force between the metal and the dielectric film.

4. The millimeter-wave terahertz frequency band very low loss dielectric film as claimed in claim 1, wherein the metallized terahertz circuit structure is composed of 200 x 200 identical unit structures, the unit structures are metal coils surrounding square patches, and a cross-shaped resonant cavity is dug inside the metal square patches.

5. The millimeter wave terahertz frequency band extremely low loss dielectric film as claimed in claim 4, wherein the unit circuit size is 120 microns, the groove gap spacing is 8 microns, and a consistent metallization effect is achieved by the metallization method.

6. The surface metallization method of the millimeter wave terahertz frequency band extremely low loss dielectric film according to claim 1, characterized in that: the method comprises the following steps:

s1, fixing a flexible cyclic olefin copolymer film (1) with the thickness of 100 microns on a silicon wafer (2) serving as a supporting layer;

s2, directly depositing a 200-nanometer-thick metal layer (3) film on the surface of the cycloolefin copolymer film (1) by adopting a magnetron sputtering method;

s3, spin-coating a positive photoresist (4) on the thin film of the metal layer (3) by using a spin coater;

s4, after the soft baking process, putting the sample in the step S3 into a photoetching machine, and then irradiating ultraviolet rays on a hollow-out structure mask plate (5) for carving a required metal pattern, wherein the mask plate is aligned with a silicon wafer below, the chemical property of an ultraviolet radiation area (6) can be gradually changed, and the ultraviolet radiation area can be washed away by a developer in the next step;

s5, immersing the sample into a developer solution for developing after baking, dissolving the positive photoresist in the ultraviolet radiation area (6), and keeping the photoresist area which is not irradiated by ultraviolet rays unchanged;

s6, immersing the sample into an etchant, and removing the metal layer (3) film exposed outside, namely uncovered by the photoresist, without affecting the metal layer (3) film below the photoresist;

s7, sequentially putting the sample into an ultrasonic machine of acetone and isopropanol for cleaning, and removing the residual photoresist;

s8, peeling off the silicon wafer (2) of the film sample supporting layer with the metal circuit structure, thereby successfully realizing the first surface circuit structure of the film sample;

and S9, if circuit metallization on the other surface of the dielectric film is required to be realized, the circuit metallization is realized by repeating the previous steps.

Technical Field

The invention relates to a surface metallization method of a novel dielectric film, in particular to a surface metallization method of a novel dielectric film with extremely low loss in a millimeter wave terahertz frequency band.

Background

The development of terahertz sources and terahertz detection technology fields has led to an increasing social demand for terahertz detection devices in imaging and sensing applications. It is well known that the performance of terahertz devices is closely related to the characteristics of the dielectric substrate used. However, studies have shown that oxygen, water and other gases have strong attenuation effects on terahertz signals, which leads to an increase in dielectric loss factor of the dielectric substrate in the terahertz frequency band. Excessive dielectric loss in the terahertz frequency band is considered to be one of the challenges in the development of the terahertz technology.

Therefore, there are now many studies trying to apply various dielectric substrates to device design in the terahertz field, including silicon, silicon dioxide, photoresist (SU-8), Polydimethylsiloxane (PDMS), benzocyclobutene (BCB), polyester synthetic fiber (PET), quartz, and other flexible fabrics. In order to implement the circuits on these substrates, it is necessary to use metals, and to implement the metallization on these dielectric substrates. Because of the different properties of the medium, such as temperature resistance strength and chemical characteristics, how to achieve metallization on the substrate will also be different. Taking an Al2O3 ceramic substrate as an example, common surface metallization methods include a thin film method, a thick film method and a direct copper-clad method, and the three methods have respective advantages and limitations in realizing principles and processes. The thin film method has a disadvantage in that the bonding force between the metal layer and the substrate is unstable, and a transition layer (e.g., Ti) may be required to enhance the bonding force between the metal and the ceramic. After the pattern transfer is completed, the transition layer needs to be etched, so that the complexity of the process is increased, the method needs vacuum conditions, and the production efficiency is low. In the thick film method, the most widely used is the screen printing technology, the process is simple, but the minimum width of the metalized wire which can be realized is larger (about 50 micrometers) due to the limitation of the used conductive paste and the size of the screen. Meanwhile, as the glass binder and the organic solvent are mixed in the slurry, the conductive performance of the manufactured conductive circuit is poor. The direct copper-clad process is a surface metallization technique developed from mainly Al2O3 ceramic substrates. Since the copper foil used is large in thickness, usually 0.1mm or more, it is not easy to obtain a high-precision circuit wiring in the subsequent chemical etching. Meanwhile, oxygen element at a high-temperature reaction interface is difficult to control, and pores may occur between the copper foil and the ceramic, so that the performance of the device is unstable.

At present, a novel dielectric film substrate, namely Cyclic Olefin Copolymer (COC), is found to have extremely low dielectric loss in a millimeter wave terahertz frequency band through research and test. Due to the excellent material characteristics of the cycloolefin copolymer film substrate, the cycloolefin copolymer film substrate has very large application potential in the millimeter wave terahertz field. Because of the special properties of cycloolefin copolymers, they are mainly used in the fields of packaging, optical films, medical devices and lenses. If the application range of the novel dielectric film is expanded to the millimeter wave terahertz field and the preparation of the millimeter wave terahertz circuit based on the cycloolefin copolymer dielectric film is attempted, a method suitable for metallization of the surface of the novel dielectric film needs to be optimized and researched according to the property of the cycloolefin copolymer dielectric film, a stable and reliable metallization circuit structure can be formed on the surface of the novel dielectric film, and the method has important significance for the application of the novel dielectric film in millimeter wave terahertz.

Disclosure of Invention

The technical problem is as follows: the invention provides a millimeter wave terahertz frequency band extremely-low loss dielectric film and a surface metallization method aiming at the defects and the blanks in the prior art, and researches and optimizes a method capable of realizing surface metallization based on the characteristics of a novel dielectric film to finally form a stable and reliable metallization circuit structure.

The technical scheme is as follows: in order to achieve the purpose, the ultra-low loss dielectric film of the millimeter wave terahertz frequency band adopts the following technical scheme:

the medium film takes a flexible cycloolefin copolymer film as a substrate, a silicon wafer used as a supporting layer is arranged below the flexible cycloolefin copolymer film, a metal layer is arranged above the flexible cycloolefin copolymer film, the flexible cycloolefin copolymer film belongs to cycloolefin copolymers, the medium loss is extremely low in a millimeter wave terahertz frequency band, a stable and reliable metallized terahertz circuit structure is formed on the surface of the medium film, and a millimeter wave terahertz circuit based on the cycloolefin copolymer medium film is realized.

The flexible cyclic olefin copolymer film is a cyclic olefin copolymer consisting of norbornene and ethylene, and the cyclic olefin copolymers formed by doping the norbornene and the ethylene with different specific gravities are different, so that the flexible cyclic olefin copolymer film has different characteristics, but has smaller dielectric loss in a millimeter wave terahertz frequency band.

The surface bonding force between the metal layer and the flexible cyclic olefin copolymer film is relevant, and when the bonding force is not enough to support the required metal thickness and dimensional accuracy, a layer of metal such as titanium/chromium/platinum needs to be deposited to serve as an adhesion transition layer so as to enhance the bonding force between the metal and the medium film.

The metallized terahertz circuit structure consists of 200 x 200 identical unit structures, each unit structure is a metal coil surrounding a square patch, and a cross-shaped resonant cavity is dug inside the metal square patch.

The unit circuit size is 120 microns, the groove gap interval is 8 microns, and the metallization effect is achieved through the metallization method.

The surface metallization method of the millimeter wave terahertz frequency band ultra-low loss dielectric film comprises the following steps:

s1, fixing a flexible cyclic olefin copolymer film with the thickness of 100 microns on a silicon chip serving as a supporting layer;

s2, directly depositing a metal layer (3) film with the thickness of 200 nanometers on the surface of the cycloolefin copolymer film by adopting a magnetron sputtering method;

s3, spin-coating a positive photoresist on the metal layer film by using a spin coater;

s4, after the soft baking process, putting the sample in the step S3 into a photoetching machine, irradiating ultraviolet rays on a hollow-out structure mask plate for carving a required metal pattern, wherein the mask plate is aligned with a silicon wafer below, the chemical property of an ultraviolet radiation area can be gradually changed, and the ultraviolet radiation area can be washed away by a developer in the next step;

s5, immersing the sample into a developer solution for developing after baking, dissolving the positive photoresist in the ultraviolet radiation area, and keeping the photoresist area which is not irradiated by the ultraviolet rays unchanged;

s6, immersing the sample into an etchant, and removing the metal layer film exposed outside, namely not covered by the photoresist, wherein the metal layer film below the photoresist is not influenced;

s7, sequentially putting the sample into an ultrasonic machine of acetone and isopropanol for cleaning, and removing the residual photoresist;

s8, peeling off the silicon wafer of the film sample supporting layer with the metal circuit structure, so that the first surface circuit structure of the film sample is successfully realized;

and S9, if circuit metallization on the other surface of the dielectric film is required to be realized, the circuit metallization is realized by repeating the previous steps.

Has the advantages that: the invention discloses a surface metallization method of a dielectric film, in particular to a surface metallization method of a dielectric film with extremely low loss in a millimeter wave terahertz frequency band, which has the following beneficial effects compared with the prior art:

1) the invention provides a surface metallization method of a novel dielectric film, the novel dielectric film has extremely low loss in a millimeter wave terahertz frequency band, a stable and reliable circuit structure is formed on the surface of the novel dielectric film, and the method has important significance for expanding the application range of the novel dielectric film;

2) the novel medium film surface metallization method provided by the invention has generality, starts with the ideas of chemical characteristics (type, chemical resistance, temperature resistance, glass transition temperature and the like), physical characteristics (film thickness, flexibility, surface roughness and the like), and target circuit structure characteristics (metal type, metal thickness, circuit size precision and the like) of a medium film, carries out personalized setting and analysis, and can realize surface circuit metallization;

3) the surface metallization method of the novel dielectric film provided by the invention is simple to operate, low in cost and convenient to integrate, and the formed millimeter wave terahertz circuit has very low loss.

Drawings

FIG. 1 is a flow chart of the metallization of the surface of a novel dielectric film according to an embodiment of the present invention, from step (1) to step (9);

FIG. 2 is a diagram of a flexible terahertz device based on a novel cyclic olefin copolymer film, which is realized in the first embodiment of the present invention;

FIG. 3 is an optical microscope image of a stable terahertz circuit formed by surface metallization in accordance with one embodiment of the present invention;

FIG. 4 is an optical microscope of an easy-to-detach terahertz circuit formed by surface metallization according to a second embodiment of the present invention;

the figure shows that: the flexible cyclic olefin copolymer film comprises a flexible cyclic olefin copolymer film 1, a silicon wafer 2 serving as a supporting layer, a metal layer 3, a positive photoresist 4, a hollow structure mask plate 5 and an ultraviolet radiation area 6.

Detailed Description

The surface metallization method of the millimeter wave terahertz ultralow-loss dielectric film has generality, starts from the ideas of chemical characteristics (type, chemical resistance, temperature resistance, glass transition temperature and the like), physical characteristics (film thickness, flexibility, surface roughness and the like), and target circuit structure characteristics (metal type, metal thickness, circuit size precision and the like) of the dielectric film, performs personalized setting and analysis, and can realize a stable and reliable metallization circuit structure;

the millimeter wave terahertz ultra-low loss dielectric film is a cyclic olefin copolymer composed of norbornene and ethylene, and the cyclic olefin copolymers formed by doping the norbornene and the ethylene in different proportions are different in types, so that the characteristics are different, but the millimeter wave terahertz ultra-low loss dielectric film has smaller dielectric loss in a millimeter wave terahertz frequency band.

The chemical resistance, temperature resistance and glass transition temperature of different types of cycloolefin copolymer medium films are different, and the individual settings of the used metallization methods are also different.

The chemical resistance, temperature resistance and glass transition temperature of the medium film are closely related to the selection and personalized setting of a subsequent metallization method, so that the strength of acid and alkali used in the micro-processing process and the baking temperature are selected to accord with the characteristics of the medium film.

The thickness, flexibility and surface roughness of the dielectric film are related to multiple times of acid-base, acetone and alcohol soaking, photoresist removal, sample peeling and the like in the micro-processing process, and when the film is very thin, the flexibility is good, and the surface is rough and uneven, the dielectric film can be bent through multiple times of operation and rework, so that the metal pattern is disordered and falls off.

The metal type, thickness and size precision required in the medium film metallization process are related to the surface bonding force between metal and the cycloolefin copolymer medium film, and when the bonding force is not enough to support the required metal thickness and size precision, a layer of metal such as titanium/chromium/platinum needs to be deposited to serve as a bonding transition layer so as to enhance the bonding force between the metal and the medium film.

And selecting and individually setting the metallization method to form a stable and reliable metallization circuit structure.

The millimeter wave terahertz frequency band ultra-low loss dielectric film takes a flexible cyclic olefin copolymer film 1 as a substrate, a silicon wafer 2 serving as a supporting layer is arranged below the flexible cyclic olefin copolymer film 1, a metal layer 3 is arranged above the flexible cyclic olefin copolymer film 1, the flexible cyclic olefin copolymer film 1 belongs to cyclic olefin copolymer, the millimeter wave terahertz frequency band ultra-low loss dielectric film has ultra-low dielectric loss, a stable and reliable metallized terahertz circuit structure is formed on the surface of the dielectric film, and the millimeter wave terahertz circuit based on the cyclic olefin copolymer dielectric film is realized.

Or the flexible cyclic olefin copolymer film 1 is a cyclic olefin copolymer composed of norbornene and ethylene, and the cyclic olefin copolymers formed by doping the norbornene and the ethylene with different specific gravities are different in types, so that the characteristics are different, but the dielectric loss is smaller in the millimeter wave terahertz frequency band.

The surface bonding force between the metal layer 3 and the flexible cyclic olefin copolymer film 1 is relevant, and when the bonding force is not enough to support the required metal thickness and dimensional accuracy, a layer of metal such as titanium/chromium/platinum needs to be deposited to serve as a bonding transition layer so as to enhance the bonding force between the metal and the medium film.

The metallized terahertz circuit structure consists of 200 x 200 identical unit structures, each unit structure is a metal coil surrounding a square patch, and a cross-shaped resonant cavity is dug inside the metal square patch.

The unit circuit size is 120 microns, the groove gap interval is 8 microns, and the metallization effect is achieved through the metallization method.

The formation of a stable and reliable metallized circuit structure generally requires several steps, as shown in the flow chart of the novel dielectric thin film surface metallization of fig. 1:

(1) a flexible cycloolefin copolymer film 1 is fixed to a silicon wafer 2 as a support layer.

(2) And depositing a metal layer 3 with a certain thickness on the flexible cyclic olefin copolymer film 1 by a magnetron sputtering method. (3)

A positive photoresist 4 is spin coated on the metal layer 3.

(4) Ultraviolet light is irradiated on the positive photoresist 4 through an exposure operation, a mask plate 5 with a hollow structure is arranged above the positive photoresist 4, wherein an ultraviolet radiation area 6 on the surface of the positive photoresist 4 represents an area which is directly irradiated by the ultraviolet light so as to change chemical properties.

(5) The sample is immersed in a developer solution for development, and the ultraviolet irradiated regions 6 in the positive photoresist 4 are dissolved.

(6) The conductive layer not covered by the positive photoresist 4 is removed with an etchant.

(7) The remaining positive photoresist 4 is removed.

(8) The film sample with the metal circuit structure was peeled from the silicon wafer 2 as a support layer.

(9) Repeating the steps (1) to (8) can obtain the metal circuit pattern on the other side of the flexible cyclic olefin copolymer film 1.

The technical solution of the present invention will be further described with reference to the following embodiments. The technical solutions in the embodiments of the present invention are clearly and completely described by referring to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The first embodiment is as follows: the surface of the novel dielectric film is metallized to form a stable terahertz circuit.

Referring to fig. 1, it is a flow chart of the metallization of the surface of the novel dielectric film of the present invention, and the preparation method includes:

s1, fixing a flexible cyclic olefin copolymer film 1 with the thickness of 100 microns on a silicon wafer 2 serving as a supporting layer.

S2, directly depositing a layer of metal film with the thickness of 200 nanometers on the surface of the flexible cycloolefin copolymer film 1 by adopting a magnetron sputtering method.

And S3, spin-coating the positive photoresist 4 on the gold thin film layer by using a spin coater.

S4, after the soft baking process, putting the sample in the step S3 into a photoetching machine, and then irradiating ultraviolet rays on a specially designed hollow-out structure mask plate 5 (used for carving a required metal pattern), wherein the mask plate is aligned with the silicon chip below. The chemical properties of the uv-irradiated areas 6 change gradually and can be washed away by the developer in the next step.

S5, after baking, the sample is immersed in a developer solution for developing, the positive photoresist in the ultraviolet radiation area 6 is dissolved, and the photoresist area which is not irradiated by the ultraviolet rays is kept unchanged.

S6, the sample is immersed into an etchant to remove the gold thin film layer exposed outside (not covered by the photoresist), and the gold thin film below the photoresist is not affected.

And S7, sequentially putting the sample into an ultrasonic machine of acetone and isopropanol for cleaning, and removing the residual photoresist.

S8, the novel film sample with the metal circuit structure is peeled from the silicon wafer 2 serving as the supporting layer, so that the first-side circuit junction of the film sample is successfully realized.

S9, if circuit metallization on the other side of the novel dielectric film needs to be achieved, the metallization can be achieved by repeating the previous steps.

Further, the realized flexible terahertz device material object based on the novel cyclic olefin copolymer film is shown in fig. 2, the unit structure is a metal coil surrounding a square patch, and a cross-shaped resonant cavity is dug inside the metal square patch.

Further, the optical microscopic image of the stable terahertz circuit formed by surface metallization of the realized flexible terahertz device based on the novel cycloolefin copolymer film is shown in fig. 3, the size of the unit circuit is 120 micrometers, the interval between the grooves and the gaps is 8 micrometers, and the flexible terahertz device has a very consistent metallization effect.

Example two: the terahertz circuit is easy to fall off and is formed by metalizing the surface of a novel dielectric film.

In order to further explain the novel method for metalizing the surface of the cycloolefin copolymer film, personalized setting and analysis can be carried out based on the ideas of the chemical characteristics (type, chemical resistance, temperature resistance, glass transition temperature and the like), the physical characteristics (film thickness, flexibility, surface roughness and the like), and the target circuit structure characteristics (metal type, metal thickness, circuit size precision and the like) of the medium film, so that the metalizing of the surface circuit can be realized. This example provides a case where surface metallization is unsuccessful due to one of the variables.

Referring to fig. 1, a flow chart of the metallization of the surface of the novel dielectric film is shown, except that step S2 is updated, the preparation steps S1 and S3-S9 in the first embodiment are performed.

The updating step S2 is: a layer of metal gold film with the thickness of 300 nanometers is directly deposited on the surface of the flexible cyclic olefin copolymer film 1 by adopting a magnetron sputtering method.

Further, the achieved flexible terahertz device based on the novel cyclic olefin copolymer film has the metallization pattern observed by an optical microscope as shown in fig. 4, which shows an easy-to-fall terahertz circuit diagram. This shows that the metal circuit is easily dropped when a 300 nm thick metal gold film is directly deposited on the novel cycloolefin copolymer film. This demonstrates that the metal thickness in the target circuit structure characteristics is one of the variables for achieving a stable and reliable surface metallization circuit. Unsuccessful surface metallization circuit structures are also readily achieved when other variables of the film chemistry, physical properties, and characteristics of the target circuit structure are outside of suitable ranges. In the specific implementation process, suitable examples and parameters are selected according to the requirements and the properties of the cycloolefin copolymer.

In the above embodiments, the present invention has been described only by way of example, and the principles and embodiments of the present invention have been described by way of specific examples of success and failure, and the above description of the embodiments is only used to help understanding the method of the present invention and its core idea; also, after reading this patent application, those skilled in the art will be able to change the invention in its specific embodiments and application range without departing from the spirit and scope of the invention. In view of the above, the present disclosure should not be construed as limiting the invention.