Introduction to the preparation process of silicon nitride ceramic substrate

Traditional silicon-based semiconductors have gradually become unsuitable for the development needs of the semiconductor industry due to their insufficient physical properties. In this context, third-generation semiconductors have emerged. Third generation semiconductor materials have the characteristics of large bandgap width, high breakdown electric field, high thermal conductivity, high electro

 

Traditional silicon-based semiconductors have gradually become unsuitable for the development needs of the semiconductor industry due to their insufficient physical properties. In this context, third-generation semiconductors have emerged. Third generation semiconductor materials have the characteristics of large bandgap width, high breakdown electric field, high thermal conductivity, high electron saturation rate, and strong radiation resistance. In high-frequency, high-voltage, high-temperature and other working scenarios, they have obvious advantages such as easy heat dissipation, small size, low energy consumption, and high power. Silicon carbide has become the most widely used and market share third-generation semiconductor material at present.

Silicon nitride, as a substrate material, has a very obvious reliability. The AMB ceramic liner made of silicon nitride ceramic substrate has a thermal expansion coefficient closer to that of the third-generation semiconductor substrate SiC crystal material, with more stable matching, high thermal conductivity, and high mechanical properties. Silicon nitride ceramic substrate is gradually becoming the preferred substrate material for wide bandgap semiconductor devices. Domestic and foreign enterprises are gradually increasing their investment in silicon nitride substrates.

The overall production process of silicon nitride ceramic substrates includes mixing, ball milling, defoaming, tape casting, stamping, powder coating (powder spraying), glue removal, sintering, powder removal and cleaning, edge grinding, scanning, grinding, ultrasonic cleaning, spin drying, laser cutting, quality inspection and other processes.

1. Mixing, ball milling, defoaming

Mix silicon nitride powder, yttrium oxide powder and other powders with organic additives, and transport the mixed materials to the ball milling process. The ball milling process includes primary ball milling and secondary ball milling:

●The purpose of a ball milling is to mix solid raw materials with liquid materials, and the ball milled product has a larger particle size but can form a slurry.

●The slurry after one ball mill is transported to the secondary ball mill through a closed belt conveyor, and PVB resin (binder to ensure the adhesion of ceramic particles after the slurry dries), polyethylene glycol, and diethyl phthalate (plasticizer to make the substrate flexible for subsequent cutting) are added in proportion to the secondary ball mill. The secondary ball mill further mixes and grinds the slurry.

The slurry after ball milling is transported by a closed belt conveyor to a defoamer for physical removal of bubbles, producing a casting slurry with a certain colloidal viscosity suitable for casting.

Required equipment: mixing grinder, ball mill, defoamer

2. Casting molding

The casting process includes casting and drying processes. Connect the defoaming tank to the feed pipe of the casting machine, pressurize it with nitrogen gas to allow the slurry to enter the casting machine, spread it into a uniform thin film on the film belt, and be transported to the drying channel by the conveyor belt. The slurry is dried by the hot air generated by electric heating at a temperature of about 150-180 ℃. During the drying process, some organic compounds with lower boiling points are evaporated and removed from the slurry

Required equipment: Casting machine

3. Stamping and cutting

Stamping and cutting the cast body to form silicon nitride green sheets.

Required equipment: Stamping machine

4. Powder coating/powder spraying

Apply a layer of boron nitride powder on the surface of the blank using a powder sprayer. Boron nitride powder acts as an isolation ceramic to ensure that the ceramic does not bond to each other during the sintering process.

Required equipment: Powder sprayer

5. Glue dispensing

After powder coating, the green body is sent to a rubber discharging furnace, which performs rubber discharging treatment on the green body at 500-700 ℃, so that the organic additives evaporate and decompose during the rubber discharging process and are removed from the green body.

Required equipment: degreasing furnace/glue removal furnace

6. Sintering

Sintering is a physical and chemical process that involves heating powder materials at high temperatures to produce particle bonding, recrystallization, and other physical and chemical processes, resulting in the densification of block shaped products with certain strength. Place the ceramic body after rubber extrusion in an atmospheric pressure sintering furnace, and use nitrogen protection during the sintering process.  

Required equipment: Sintering furnace

7. Powder removal and cleaning

Remove the boron nitride layer on the surface of the sintered substrate by brushing and ultrasonic cleaning (using pure water cleaning). After sintering, the ceramic substrate may be brushed and dried. There may be a small amount of powder on the surface of the brushed and dried ceramic substrate that has not been completely removed, and a sandblasting machine needs to be used for secondary cleaning.

Required equipment: grinder, dryer, sandblasting machine, ultrasonic cleaning machine

8. Grinding, sweeping, and polishing

By using processes such as edge grinding, scanning, and grinding, the substrate's side and surface are made smoother, improving the accuracy of the product.

The curved surface scanning machine first rinses the substrate surface with abrasive solution, which wets the substrate surface and then uses a brush disc to grind the substrate surface. Curved surface scanning can improve the parallelism of the upper and lower surfaces of the substrate. In subsequent substrate processing, the inductance and capacitance of the substrate can be more strictly controlled, improving the parallelism of the circuit.

Required equipment: Surface scanning machine, edging machine, polishing machine

9. Clean and spin dry

Using ultrasonic cleaning to remove the abrasive solution on the surface of the ceramic substrate, the cleaned ceramic substrate is dried by a spin dryer.

Required equipment: Ultrasonic cleaning, spin dryer

10. Laser cutting

The ceramic substrate is cut into corresponding sizes using a laser cutting machine.

Required equipment: Laser cutting machine

11. Quality inspection and warehousing

Inspect the appearance and internal structural integrity of the product through visual inspection and equipment testing, and sort and store porcelain tiles that meet quality requirements.

Required equipment: Testing equipment