CN102110599B - The production technology of soluble polyimide - Google Patents

Abstract

The invention discloses a production process of soluble polyimide, which comprises the steps of preparation of polyamic acid solution, cleaning of P-type silicon substrate, oxidation of P-type silicon substrate, vapor deposition of silicon-containing aluminum electrode and the like. Because the present invention does not pass through dianhydride, directly obtains polyimide with diphenyl ether diamine ODA polymerization with pyrophthalic anhydride PMDA, and usually adopts the method for polyimide and other material mixed processing to prepare polyimide composite material Compared with the function of making the polyimide film conductive, the present invention has the characteristics of simple production process, low cost and uniform conductivity, and is compatible with standard CMOS process, and can be used for the protection of aluminum electrodes in integrated circuit production process.

Description

Production process of soluble polyimide

technical field

The invention relates to a production method of an organic polymer material, in particular to a production process of a soluble polyimide.

Background technique

Polyimide (Polyimide, PI) is a good engineering material, because of its outstanding characteristics in performance and synthesis, whether it is used as a structural material or a functional material, it is widely used in aviation, aerospace, microelectronics, nanometers, liquid crystals, etc. , separation membrane and other fields have been widely used. In recent years, the research, development and utilization of polyimide are also very active, and there are many studies on the performance of polyimide, and research is also being carried out from the aspects of solubility and composite materials. In the field of microelectronic devices, polyimide can be used as an insulating layer, buffer layer, protective layer and other functions. The electrode material of electronic devices is generally metal aluminum. Therefore, during long-term use, the aluminum electrodes will be corroded and cause the device Changes in performance. For this reason, some adopt the method of depositing a passivation layer (such as silicon nitride) on the aluminum electrode to protect the aluminum electrode, and some directly use noble metals (such as gold, silver, etc.) as electrodes. Most of the current polyimide conductive films are produced by adding conductive particles or nanomaterials (such as carbon nanotubes, etc.) to the solvent before the polyimide film is formed, and then imidized. Or after the polyimide film is formed into a film, the surface is treated, and the metal is incorporated into the polyimide by chemical methods to form a conductive film on the surface of the film. For the former, due to the use of organic solvents, conductive particles or nanomaterials may cause uneven conductivity on the surface of the polyimide film generated due to uneven distribution, affecting performance; while for the latter, the process is complicated and the cost is relatively high. high.

Contents of the invention

The object of the present invention is to provide a production process of soluble polyimide with high production efficiency, low cost and uniform conductivity.

For realizing the above object, technical solution of the present invention is:

The present invention is a kind of production technique of soluble polyimide, and it comprises the following steps:

(1) Preparation of polyamic acid solution: react polyphthalic anhydride PMDA and diphenyl ether diamine ODA in an aprotic solution (DMF or DMAC) at a temperature of -20°C to room temperature at a ratio of 1:1. During the reaction, pyrophthalic anhydride is added to the solution of diphenyl ether diamine in solid form, and stirring is started at the same time, and the polyamic acid solution generated is clear and transparent;

(2) Cleaning of the P-type silicon substrate: the silicon substrate is cleaned by an industrial standard wet cleaning process (RCA cleaning process), and dried with nitrogen;

(3) Oxidation of P-type silicon substrate: Oxidize the P-type silicon substrate according to the following steps, ① oxidize with dry oxygen and pure oxygen at 1000 ° C for 3 hours, ② oxidize with wet oxygen and pure oxygen at 1000 ° C for 3 hours , ③ Oxidation with dry oxygen and pure oxygen at 1000°C for 3 hours to sequentially grow a silicon dioxide oxide layer with a thickness of 700-900nm;

(4) Evaporation of silicon-containing aluminum electrodes : Evaporate silicon-containing aluminum electrodes on the silicon dioxide oxide layer by vacuum coating, in which the silicon content is 5-7%. The purpose of adding a small amount of silicon to the aluminum electrodes is Enhance the adhesion between the aluminum electrode and the oxide layer on the silicon substrate;

(5) Spin-coat polyamic acid on the aluminum electrode: let the polyamic acid stand at room temperature for 1 hour before coating, so as to avoid defects such as bubbles and holes during the spin-coating process from affecting the quality of the polyimide film. quality; then, spin-coat a polyamic acid film on the evaporated silicon-aluminum electrode at a speed of 7000 rpm.

The pyrphthalic anhydride in step (1) uses freshly sublimed pyrphthalic anhydride to avoid hydrolysis.

In step (1), cooling is added while stirring.

The aprotic solution is DMF or DMAC.

After adopting the above-mentioned scheme, because the present invention does not pass through dianhydride with perphthalic dianhydride PMDA, directly and diphenyl ether diamine ODA polymerization obtains polyimide, and adopts the method for mixing processing of polyimide and other materials to prepare polyimide usually. Compared with the conductive function of polyimide film made of imide composite material, the present invention has the characteristics of simple production process, low cost and uniform conductivity, and is compatible with standard CMOS process, and can be used for aluminum electrodes in integrated circuit production process protection of.

In addition, in the process of developing a capacitive humidity sensor, a silicon-doped metal electrode was used to increase the bonding strength between the electrode and the oxide layer, and a soluble polyimide was used as a moisture-sensitive medium. It was found that on the silicon-aluminum electrode After coating the polyimide film, the polyimide film is as conductive as a pure aluminum electrode. Using this kind of polyimide film as the electrode of the humidity sensor can use a simple process to achieve the purpose of protecting the electrode without adding a passivation layer or using noble metals, which can not only save costs, but also make the sensor more durable. Performance is greatly guaranteed.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is the photomicrograph of polyimide film after imidization;

Fig. 2A is the SEM photograph of the sample section of producing pure aluminum electrode by the present invention;

Fig. 2B is the SEM photograph of the cross-section of the silicon-aluminum electrode sample containing aluminum particles produced by the present invention;

Figure 3 is an interface diagram with island-like particles of different shapes;

Figure 4 is the EDS energy spectrum of the island-shaped particle interface;

Figure 5 shows two different island particle area distribution (MAP) maps.

Detailed ways

The present invention is a kind of production technique of soluble polyimide, and it comprises the following steps:

(1) Preparation of polyamic acid solution: react polyphthalic anhydride PMDA and diphenyl ether diamine ODA in an aprotic solution (DMF or DMAC) at a temperature of -20°C to room temperature at a ratio of 1:1. During the reaction, add pyrophthalic anhydride into the solution of diphenyl ether diamine in solid form, and start stirring at the same time (additional cooling is required if necessary), and the resulting polyamic acid solution is clear and transparent;

(2) Cleaning of P-type silicon substrates: Clean the silicon substrates using an industry standard wet cleaning process (RCA cleaning process), and dry them with nitrogen;

(3) Oxidation of P-type silicon substrate: Oxidize the P-type silicon substrate according to the following steps, ① oxidize with dry oxygen and pure oxygen at 1000 ° C for 3 hours, ② oxidize with wet oxygen and pure oxygen at 1000 ° C for 3 hours , ③ Oxidation with dry oxygen and pure oxygen at a temperature of 1000 ° C for 3 hours, and sequentially grow a silicon dioxide oxide layer with a thickness of 700-900 nm.

(4) Evaporate silicon-containing aluminum electrodes : Evaporate silicon-containing aluminum electrodes on the silicon dioxide oxide layer by vacuum coating, in which the silicon content is 5-7%. The purpose of adding a small amount of silicon to the aluminum electrodes is to Enhances adhesion between aluminum electrodes and oxide layers on silicon substrates. The aluminum electrode thickness is 1.4um.

(5) Spin-coat polyamic acid on the aluminum electrode: let the polyamic acid stand at room temperature for 1 hour before coating, so as to avoid bubbles, holes and other defects during the spin-coating process from affecting the quality of the polyimide film. quality; then, spin-coat a polyamic acid film on the evaporated silicon-aluminum electrode at a speed of 7000 rpm.

In addition, the pyrphthalic anhydride used in the step (1) is freshly sublimed to avoid hydrolysis.

Performance Testing:

Conductivity

After the sample was naturally cooled, the insulation performance of the surface of the polyimide film was tested, and it was found that its conduction state was good. Observing the surface of the polyimide film under a microscope, it is found that there are many black spots on the surface (as shown in Figure 1). The size of the black spots is inconsistent and the distribution is irregular, but the density is uniform in a large area. Tested with the XP-3 step meter, the thickness of the polyimide film is 0.45um, and the black spots on the surface are raised, with a height ranging from 0.15um to 0.38um. The sheet resistance is 0.02Ω/ tested by the four-probe method, and the conduction state is good. On the silicon-aluminum electrode not coated with polyimide film, the sheet resistance of Al film is also 0.02Ω/, so it can be considered that the conductivity of polyimide film is very good.

surface composition

At first, the inventors thought that during the imidization process of polyamic acid, a certain component in polyamic acid interacted with the aluminum electrode, and metallization occurred due to some effect during the imidization process, resulting in The diffusion of aluminum element in the polyimide film leads to the conduction of the polyimide film. For this, use Hitachi S-4800 field emission scanning electron microscope (Field emission scanning electron Microscopy (FE-SEM) was used to observe the microscopic morphology and structure of the sample section, combined with energy dispersive spectroscopy (EDS) to analyze the composition and distribution of elements in the micro-area of the sample.

(1) SEM test

Firstly, cross-sectional scanning was carried out on samples taken from pure aluminum electrodes and silicon-aluminum electrodes, and Fig. 2A and Fig. 2B are SEM photos of the two. When the pure aluminum electrode is used, the polyimide film and the aluminum electrode are very flat; while the silicon-aluminum electrode is used, except that most of the area is as flat as the pure aluminum electrode, there are many islands as shown in Figure 2B particle. Figure 3 is a cross-section of a sample with island-like particles of different shapes.

(2) EDS analysis of PI film

In order to determine the composition of the island-shaped particles, we selected the cross-section containing the island-shaped particles in Figure 2B for EDS analysis. Figure 4 and Table 1 are the EDS spectra of one of the aluminum particles, except for N elements that cannot be measured due to instrumental reasons. The samples outside contain only four elements, C, O, Al, and Si. It can be seen from Figure 4 that the island-shaped particles are mainly composed of aluminum elements. Due to the existence of silicon substrate and SiO2 layer, the measured Si element composition is closer to that of aluminum.

Quantitative results

element source weight ratio% weight error Atomic ratio% atomic error ingredients C K EDS 57.20 +/-4.78 71.18 +/-5.95 C OK EDS 14.18 +/-1.46 13.25 +/-1.37 o K EDS 15.87 +/-0.25 8.79 +/-0.14 al Si K EDS 12.75 +/-0.30 6.79 +/-0.16 Si total 100.00 100.00

Energy dispersive spectrometry (EDS)

Table 1 Quantitative analysis of elements in PI film EDS spectrum

(3) PI film element surface distribution (Mapping)

In order to further determine the composition of the island-shaped particles, the surface distribution test of elements was carried out. Figure 5 shows the MAP diagrams of two different island-shaped particles. It can be seen that the island-shaped particles are substantially entirely composed of aluminum.

Therefore, it can be known from the SEM topography, EDS and MAP images of the sample section coated with polyimide film that the particles protruding from the polyimide film are basically composed of aluminum elements, so that the surface of the film and the silicon-aluminum electrode below Connected to cause the conduction of the polyimide film.

In the process of developing capacitive humidity sensors in the past, in order to increase the bonding strength between the aluminum metal electrode and the silicon substrate, we used the method of evaporating a layer of metal molybdenum on the silicon dioxide substrate and then evaporating the aluminum electrode. In the device, aluminum elements do not form metal particles protruding from the electrode surface on the SiO ₂ substrate, and the polyimide film has good insulation performance. In order to reduce the production process, a small amount of silicon is doped into the aluminum electrode to achieve the same purpose. However, due to the presence of silicon in the electrode material, aluminum particles with a particle size of about 1 μm appear on the electrode surface after evaporation. If the polyimide film coated on it is relatively thin, it may occur that the polyimide cannot completely cover the aluminum particles, so that the polyimide film is conductive.

The stability and dielectric properties of PI make it a coating material that has received great attention in metal protection. In particular, the thermal expansion coefficient of PI is close to that of metal, and it can be used in a wide temperature range for acid, alkali, and high temperature. The metals in the environment play a protective role, which keeps the corrosive species confined to the process of ion mass transfer. Therefore, the method of using conductive polyimide film can play the role of traditional electrodes on the one hand, and protect the electrodes on the other hand, which can reduce the process flow and save costs. It will also have positive effects in the future microelectronics industry. Impact.

Claims (4)

1. a production technology for soluble polyimide, is characterized in that: it comprises the following steps:

(1) preparation of polyamic acid solution: equal benzene dianhydride PMDA and diphenyldiamine ODA is reacted in aprotic solvent in the ratio of 1:1 at the temperature of-20 DEG C ~ room temperature, during reaction, equal benzene dianhydride is joined in the solution of diphenyldiamine in solid form, start to stir, the polyamic acid solution of generation is as clear as crystal simultaneously;

(2) cleaning of P-type silicon substrate: adopt industrial standard wet clean process to clean silicon substrate, dry up with nitrogen;

(3) oxidation of P-type silicon substrate: P-type silicon substrate is oxidized according to following steps, 1. 3 hours are oxidized with dry oxygen pure oxygen at 1000 DEG C of temperature, 2. at 1000 DEG C of temperature, 3 hours are oxidized with wet oxygen pure oxygen, 3. at 1000 DEG C of temperature, 3 hours are oxidized with dry oxygen pure oxygen, order growth silicon dioxide oxide layer, thickness is 700-900nm;

(4) the aluminium electrode that evaporation is siliceous: with the aluminium electrode that method evaporation in silicon dioxide oxide layer of vacuum coating is siliceous, wherein the content of silicon is 5-7%, and the object participating in a small amount of silicon in aluminium electrode strengthens the degree of adhesion on aluminium electrode and silicon substrate between oxide layer;

(5) spin coating polyamic acid on aluminium electrode: first polyamic acid is at room temperature left standstill 1 hour, to avoid the quality occurring the defective effect such as bubble, hole polyimide film in the process of spin coating before overcoating; Then, with the rotating speed of 7000 revs/min spin coating Polyamic Acid Film on the sial electrode that evaporation is good.

2. the production technology of soluble polyimide according to claim 1, is characterized in that: the equal benzene dianhydride in step (1) uses the equal benzene dianhydride just having distilled and obtained to avoid hydrolysis.

3. the production technology of soluble polyimide according to claim 1, is characterized in that: in step (1), the additional cooling when stirring.

4. the production technology of soluble polyimide according to claim 1, is characterized in that: described aprotic solvent is DMF or DMAC.