Non-aqueous Gelcasting Process Of Aluminum Nitride And The Research On Temperature Uniformity Of Ceramic Heater

Aluminum nitride ceramic with good thermal conductivity,electrical insulation,low dielectric constant,and thermal expansion coefficient matching silicon is an ideal choice for electronic packaging materials and ceramic heater materials for semiconductor processing and manufacturing equipment.Gel-casting is suitable for preparing complex shape parts for the high strength of green body and avoiding oxygen inhibition.In this paper,a non-aqueous gel-casting method based on nucleophilic addition to prepare special-shaped AlN ceramics was studied.The influence of slurry composition and preparation process on rheological properties of AlN slurry and bending strength of AlN green body was systematically studied,and the AlN ceramics complex shape were fabricated.Moreover,the surface temperature field of AlN ceramic heater was simulated by the finite element simulation software.Different heating models were present and their influences on the surface temperature field uniformity were analyzed.A simple prototype of AlN ceramic heater was made and the surface temperature field was measured.In this paper,the epoxy resin gel system was chosen with ethanol as the solvent,trimethylolpropane trimethylglycidyl ether（TTE）and tetraethylene pentamine（TEPA）as the epoxy resin and hardener respectively.Firstly,the gel kinetics of TTE-TEPA was studied.The results showed that the TTE-TEPA could react at room temperature,and the gel time was shortened with the increase of temperature.Combined with the quantitative analysis by Arrhenius equation,the activation energy of TTE and TEPA reaction was 46.81 k J/mol.The study on the dispersion stability of AlN suspensions showed that TTE played a certain role in dispersion stability.The dispersant triethanolamine（TEAM）had the best stability effect on the AlN suspensions containing TTE,and the optimal addition amount was 1.5 wt%.TEAM act as steric hindrance and electrostatic stabilization in suspension,moving the AlN equipotential point from p H=7 to p H=9.5.Meanwhile TEAM can accelerate the curing process,so the activation energy was reduced to 46.09 k J/mol.The effects of TTE,TEAM and TEPA,solid content and stirring process on the rheological properties of AlN slurry were systematically studied.The rheological behavior of AlN slurry was found to be shear thinning.The viscosity of slurry increases with the increase of solid content,and the viscosity of high solid content slurry of 59 vol%reached688 m Pa s,which can be successfully poured.With the increase of TTE content,dispersant TEAM amount and stirring speed,the viscosity of AlN slurry decreases first and then increases.The AlN slurry with 55 vol%solid loading and low viscosity（252 m Pa?s）was obtained at 1000 rpm stirring speed,in which the dispersant TEAM is 1 wt%,epoxy resin TTE is 15 wt%.Effects of AlN slurry composition,drying and curing process on the morphology and bending strength of AlN green body were studied.It is found that the ethanol environment can effectively solve the problems of hollowing and cracking of green body.With the increase of TTE or solid content,the strength of AlN green body increased first and then decreased.The bending strength reaches the maximum value of 3.2 MPa for the slurry with22 wt%TTE solidified at room temperature.When the content of curing agent was near the theoretical value,the strength of the green body was optimal.The crosslinking curing of TTE and TEPA can occur at room temperature,however,the reaction was incomplete,which caused the lower strength of the 3D network.Therefore,curing temperature was the main factor affecting the bending strength.In this paper,a two-stage curing process was proposed.The first stage is at room temperature.The results showed that the bending strength significantly improved with the increase of the second stage curing temperature.The bending strength of the AlN green body reacheed 35 MPa at the second stage curing temperature of 130℃.Based on the high solid content and low viscosity AlN slurry（55 vol%,268 m Pa?s）,uniform and dense complex shape AlN green body was prepared with two-stage curing process.By optimizing the debinding process,a dense and special-shaped AlN ceramic with density of 3.27 g/cm³ and thermal conductivity of 144 W/（m?K）was prepared by pressureless sintering at 1700℃in N₂ atomosphere.Aiming at AlN ceramic heater,the influence of heating wire shape on the surface temperature field uniformity of ceramic heater was systematically studied by using Comsol finite element simulation software.From the simulation results,the uniformity of the surface temperature field of the square wave,spiral,and circular heating wire models was gradually improved.The simulated results showed that circular ring combined with square wave shape can make ceramic heater have the best temperature uniformity and better tunability.For the optimized model,the surface temperature difference was only 4.96℃and the temperature uniformity was±0.5%when the surface temperature reached 500℃.A simple prototype of AlN ceramic heater was fabricated by the gel-casting process mentioned above and the heating wire was screen printed on the surface of the cermics.The measurement results showed the surface temperature difference was about 10℃and the temperature uniformity reached±1.8%at the maximum surface temperature of 280℃.