RU2692373C1 - Method of producing dielectric layer based on polymer coating in microelectronics products - Google Patents

Abstract

FIELD: electronics.

SUBSTANCE: claimed invention relates to the field of microelectronics, namely to methods for production of dielectric layer of interlayer insulation of certain thickness in products of microelectronics based on polymer coating. Method of producing a dielectric layer based on a polymer coating in articles of microelectronics includes the following steps. Preparation of application surface. Coating application. Heat treatment for removal of solvent and volatile reaction products. Coating from polymer solution is applied in two steps. At first step polymer solution is applied by centrifugation. At the second step, it is performed by stage-by-stage ultrasonic spray application. At that, polymer solution of higher concentration and viscosity is used at the first stage than at the second stage.

EFFECT: technical result of claimed invention is formation of thick polymer layer of specified thickness from solution with simultaneous improvement of quality of surface of formed thick polymer layer and uniformity of thick polymer layer over surface area.

6 cl, 9 dwg

Description

The claimed invention relates to the field of microelectronics, and in particular to methods for producing a dielectric layer of interlayer insulation of a certain thickness based on a polymer coating in microelectronics products.

The prior art discloses a method of forming thick polymer layers by applying a solution on a horizontally disposed surface covered with a thin layer of the same material (see SU1556521 publ. 08/20/1988) (1). In this method, the effect of surface tension and gravity on the dose of the solution, under the action of which there is a gradual smoothing of the irregularities of the relief and the spreading of the solution over the surface. For the application of the solution, it is necessary to use an external load, for example, to use centrifugation.

The disadvantage of this method is the impossibility of obtaining with a single application of a uniform thickness of thick polymer layers. The disadvantage of method (1) is also the possibility of incomplete spreading of the solution over the surface as a result of slow centrifugation, or, in the opposite case, with rapid centrifugation, the formation of excess solution on the edge of the plate.

The closest in technical essence is a method of forming thick polymer layers by applying several thin layers of a solution on a horizontal surface (see RU2144472, publ. 01/20/2000) (2). In this method, to obtain a thick-film layer of desired thickness by centrifuging, a layer having a predetermined thickness is applied at one time and then subjected to drying and heat treatment. Then, on the main thin film layer, repeatedly performing the above operation, form a thick film layer consisting of several thin film layers.

The disadvantage of method (2) is the formed interface with the corresponding boundary surfaces of two thin-film layers. Also, the disadvantage of this method is the need for drying and heat treatment after the application of each thin film layer.

The technical result of the claimed method is the formation of a thick polymer layer of a given thickness from a solution with a simultaneous improvement in the surface quality of the formed thick polymer layer and the uniformity of the thick polymer layer over the surface area.

The claimed technical result is achieved by creating a method of obtaining a dielectric layer based on a polymer coating in microelectronic products, including preparing the application surface, applying a thick coating, heat treatment to remove solvent and volatile reaction products, and the coating from the polymer solution is carried out sequentially in two stages: In the first stage, the polymer solution is applied by centrifugation, and in the second, by stepwise ultrasonic (US) application by spice, and first step apply a higher concentration and viscosity of a polymer solution than the second.

The above objectives and advantages of this method will become more apparent when describing with reference to the accompanying images and diagrams, on which:

figure 1 is a polymer layer formed by the combined 2-stage method in the section;

figure 2 - a schematic representation of the movement of the nozzle with a spray cone relative to the substrate (side view), where 1 - spray cone, 2 - nozzle, 3 - direction of movement of the nozzle with spray cone;

figure 3 - a schematic depiction of the trajectory of the nozzle with a spray cone relative to the substrate (top view), where 1 is the substrate rotating at a given speed, 2 is the spray cone, 3 is the nozzle of the ultrasonic spray installation, 4 is the direction of the nozzle movement relative to the substrate, 5 - the direction of rotation of the substrate;

figure 4 is a schematic depicted sequence of technological operations, reflecting the essence of the invention;

figure 5 is a polymer layer (varnish AD-9103 IS TU 6-19-247-84) without a distinguishable interface formed by the combined method described earlier;

figure 6 is a polymer layer (varnish AD-9103 IS TU 6-19-247-84) with a distinct interface formed by layer-by-layer application;

figure 7 - image of the effect of stratification along the boundary of the layers of the polymer;

figure 8 - Image of the surface of the polymer layer formed by the combined method described previously without an intermediate heat treatment, the calculated layer thickness is 100 μm;

figure 9 - Image of spray cone in the process of installation of ultrasonic spray application.

The method of obtaining the dielectric layer (interlayer insulation) of a certain thickness in the products of microelectronics based on polymer coating is as follows. The combined method of obtaining a thick polymer layer is a 2-step process of applying polymer coatings from solutions of different concentrations and viscosities by centrifuging and ultrasonic spray deposition. On the example of varnish AD-9103 IC, for the centrifuging method, the dry residue content in the solution is 12.5-14%, and for the ultrasonic spray application method, the initial solution is diluted (12.5-14% dry) in a ratio of 1: 3 or 1: 4 to obtain acceptable (for the installation of the application) the viscosity of the solution.

The total thickness of the polymer coating layer H _{SL is} calculated by the formula:

, где

where

The thickness of the layer H ₁ obtained by centrifugation:

where v is the viscosity of the solution, b is a coefficient whose value is approximately equal to 2, w is the frequency of rotation, t * is the spreading time (is approximately a few seconds);

The thickness of the layer of H ₂ obtained by the method of ultrasonic spray deposition:

where K is a coefficient (from 0 to 1), characterizes the quantitative characteristic of the total solution volume falling on the substrate, c is the solution concentration in%, V is the solution volume in mm ³ , S is the substrate area in mm ² .

On the prepared stationary substrate installed on the holder in a centrifuge, the initial solution is applied to the center of the dispenser with a viscosity of not more than 52,000 centipoise and a centrifuging method with a rotational speed necessary for complete and uniform distribution over the surface (for polyimides with a dry matter content of 12.5-14 % rotational speed 500-1000 rpm) a coating of thickness H _{1 is} obtained, then an ultrasonic spray application is applied to the substrate rotating at a speed of 1-5 rpm with a leveling layer of polymer with a viscosity of not more than 50 cP and a thickness of 5-10 microns thick and pre-passes soft drying in the light of an IR lamp at a temperature not exceeding 40 ° C. Further growth of the layer of H ₂ , runs cycles of application of 8-12 μm by the ultrasonic spray method of application and soft drying in the light of the IR lamp. When a polymer layer is formed from all materials except photosensitive materials, the substrate is heated and mildly dried in the light of an infrared lamp. The coefficient K, which characterizes the quantitative characteristic of the total volume of the solution falling on the substrate, is due to the formation of a spray cone, which moves in the process of application together with the nozzle from the starting point to the end, located in the region of the edges of the substrate.

Regulation of the area of the base of the spray cone is possible by changing the flow rate of the gas passing through the nozzle. The coefficient K depends on the starting and ending point of the deposition of the material, as well as on the area of the base of the spray cone. The variation of the size of the drop falling on the substrate from the nozzle, and the stability of the spray cone is achieved by varying the power of ultrasound. For the formation of dielectric layers with a thickness of more than 50 microns, application cycles of 25-35 microns are used, followed by convective drying. Full polymerization of the coating is carried out after all application cycles and is the last link in the heat treatment cycle.

An example of the use of the proposed method is the formation of a thick polymer layer based on polyimide on a substrate of silicon or aluminum nitride.

The center of a specially prepared substrate (the method of preparing the surface of the substrate is not specified due to the fact that polymer layers can be deposited on different surfaces, for example, as intermediate dielectric layers or as a dielectric layer directly on the substrate), installed in the centrifuge holder from the metering unit 5 ml of material (lacquer AD-9103 IS TU 6-19-247-84, the dry residue content in the solution is 12.5-14%) and rotates for 1 minute at a speed of 1000 rpm. After the centrifuge is stopped, 1 spray application pass is immediately taken and drying in the light of the IR lamp for 30 minutes. Next is the required number of passes (repetitions) spray application to achieve the required thickness of the polymer layer. In this case, for polyimide with a thickness of more than 50 microns, it is necessary to use an intermediate heat treatment in a heating cabinet with step heating.

Further, the process of forming a layer is described more fully with reference to the accompanying images (figures).

FIG. 1 is applied 2-step method the polymer layer thickness H _slab. The formation of the layer takes place sequentially, namely, on the prepared fixed substrate (functional or technological rigid base) with or without the formed structure, a solution is dispensed in the center, the viscosity of which does not exceed 52,000 cP, then a layer 1 of H ₁ thickness is created by centrifuging. The thickness of the H ₁ layer is calculated using the formula described earlier. Then a layer of stage 2 with a thickness of H ₂ is applied from a solution with a viscosity of not more than 50 cP on a rotating substrate with the formed layer by ultrasonic (US) spray method. The total thickness of the dielectric layer is

.

.

FIG. 2 schematically shows the movement of the nozzle of the installation of ultrasonic spray application (2) with the resulting spray cone (1) relative to the substrate, with a stage 1 layer already formed by centrifugation in the indicated direction (3) when viewed from the side. The nozzle starts and ends the movement and deposition outside the substrate, which has an effect on the values of the coefficient K in the formula for calculating the thickness of the layer 2 stage. The width of the spray cone depends on the flow rate of the gas passing through the nozzle. By increasing the flow rate of the gas passing through the nozzle, the area of the base of the spray cone increases, thereby also affecting the total amount of material falling on the substrate surface and, consequently, affecting the coefficient K. The stability of the spray cone is mainly influenced by the power of the ultrasound source . Depending on the viscosity of the applied material with the wrong power of the ultrasound source in the process, such phenomena as the formation of large droplets or the formation of “foamed” inclusions may occur, leading to defects on the surface and structure of the 2nd stage layer. In order to obtain a quality layer, optimal selection of system characteristics is required; supply pressure — gas flow rate — ultrasound power for the applied material of a certain viscosity.

FIG. 3 schematically shows the movement of the nozzle of the ultrasonic spray application (3) with the formed spray cone (2) relative to the substrate (1) rotating in a certain direction (5) at a speed of 1-10 rpm with a stage 1 already formed by centrifuging, in the indicated direction (4) when viewed from above. The rotational speed of the substrate is chosen such that the distribution of the material over the surface is uniform and there is no accumulation of material on the edge of the plate. Further, the rotation of the substrate is maintained during drying in the light of an infrared (IR) lamp for the required time. It is necessary to take into account that when applying a material on a non-round substrate, the value of the coefficient K will be the lower, the smaller the area of the figure relative to the area of the circumscribed circle for this figure.

FIG. 4 depicts a sequence of basic operations of the technological process, reflecting the essence of the method of forming a thick polymer coating. Depending on the material of the substrate, the material and the state of its surface, the surface is prepared for polymer deposition, as an example, processing a silicon wafer with a formed conductive structure in dimethylformamide and applying an adhesion promoter to the surface before forming a polyimide layer. The time between the operation of surface preparation and the formation of the layer should not exceed 30 minutes, otherwise the operation of surface preparation must be repeated. Next, the dosing and centrifugation from the solution, described for FIG. 1. Then within 1 minute, prior to the beginning of the active exit of the solvent from the formed layer of the 1st stage, a layer is produced by ultrasonic spray coating, described for FIG. 2 and FIG. 3. Obtaining the required thickness of the polymer layer is achieved by changing the number of spray passes. In one pass, a layer of up to 15 microns is formed. Between passes and after the last drying is used in the light of soft infrared lamp heating surface temperature not exceeding 40 ^C. Then heat treatment is carried out with a substrate coated with a thick layer of polymer. It is necessary to take into account the fact that for polyimides, in order to obtain thick layers (more than 50-60 microns thick) with a uniform and smooth surface, it is necessary to perform an intermediate heat treatment without imidization.

FIG. 5 shows an image of a polymer layer (lacquer AD-9103; IC TU 6-19-247-84), obtained using a scanning electron microscope, formed by the combined method described earlier. The image shows that the polymer layer on the silicon substrate has no interface. A polymer layer approximately 29 microns thick is formed by a combined method in two stages, where the first stage is the application by centrifugation at a rotation speed of 1000 rpm for 90 seconds, and the second stage is ultrasonic spray application of the polymer during rotation of 1 rpm and the light of an IR lamp .

FIG. 6 shows an image of a polymer layer (lacquer AD-9103; IC TU 6-19-247-84), obtained using a scanning electron microscope, formed by layering. In this case, the application of the material was carried out layer-by-layer by centrifuging at a rotation speed of 1000 rpm for 1 minute. Between the application, the layer is dried and heat treated. The image shows that there is a clear boundary between the first and the second polymer layer.

FIG. 7 shows the image of the delamination that occurred using a scanning electron microscope. This polymer layer was obtained by the layer deposition method described for FIG. 6. The total thickness of the polymer layer is approximately 72 microns. The image shows that delamination occurs along the boundary between the layers.

FIG. 8 shows the image of the surface of a polymer layer deposited on a silicon substrate. The polymer layer is formed by a combined method, but without an intermediate heat treatment, the need for which was also indicated earlier if the calculated thickness of the polymer layer exceeds 60 microns. In this case, the calculated layer thickness is 100 microns. A polymer layer with a design thickness of 100 μm is formed by a combined method in two stages, where the first stage is the application by centrifugation at a rotation speed of 1000 rpm for 90 seconds, and the second stage is a multi-pass ultrasonic spray application of the polymer during rotation of 1 rpm and IR light -lamps. In the drying process, the solvent from the solution deposited on the surface comes out too quickly, creating the surface of the polymer layer shown in the image.

FIG. 9 shows the image of the spray cone during the operation of the ultrasonic spray installation. In this case, through the nozzle is fed a solution of a polymer based on Varnish AD-9103 IS TU 6-19-247-84.

Claims (15)

1. A method of obtaining a dielectric layer in microelectronics products based on a polymer coating, including preparing the application surface, applying a thick coating, heat treatment to remove solvent and volatile reaction products, characterized in that the coating from the polymer solution is carried out sequentially in two stages: in the first stage the polymer solution is applied by centrifugation, and the second is applied by stepwise ultrasonic spray application, and a greater concentration of polymer solution is used at the first stage tion and viscosity than the second. 2. A method of obtaining a dielectric layer under item 1, characterized in that the time between centrifugation and ultrasonic spray application is not more than 1 minute. 3. A method of obtaining a dielectric layer according to claim 1, characterized in that for centrifuging the viscosity of the polymer solution is not more than 52,000 cP. 4. A method of obtaining a dielectric layer under item 1, characterized in that for ultrasonic spray application, the viscosity of the polymer solution is not more than 50 cP. 5. The method of obtaining the dielectric layer under item 1, characterized in that the total thickness of the layer is determined by the formula:

where v - solution viscosity in P, b is a coefficient whose value is approximately equal to 2, w - rotational speed in rpm, t * - spreading time in min K - coefficient (from 0 to 1), characterizes the quantitative characteristic of the total volume of the solution falling on the substrate, c is the solution concentration in%, V is the volume of solution in mm ³ , S is the area of the substrate in mm ² . 6. A method of obtaining a dielectric layer according to claim 1, characterized in that during the formation of the polymer layer from all materials, except photosensitive ones, the substrate is heated and dried in the light of an infrared lamp.

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