Study On Influence Of The Applied Electric Field On Metal-Assisted Chemical Etching

Silicon is the most important material in the semiconductor industry.Metal-assisted chemical etching to fabricate the micro/nano-structures of silicon has been widely used due to its advantages of simple process and low cost.However,with the increasing requirements of microelectronic process,it is difficult for traditional metal assisted chemical etching to achieve the micrometer-scale etching in a short time and to fabricate complex 2D and 3D structures with flat bottoms and vertical sidewalls.Therefore,the thesis attempts to apply the electric field to metal assisted chemical etching to explore the effect of the applied electric field,achieve faster etching and obtain silicon structures with good morphology.In the thesis,colloidal gold was first used as the catalyst.Silicon and the graphite electrode were connected to anode and cathode of the power supply respectively,and p-type(100)silicon was etched under the applied electric field.It is found that the electric field can effectively accelerate the etching process.Depth of the trenches can reach 63.5 ?m with the voltage of 65 V after 17-minute etching,and the bottom of the trenches is very smooth and flat.However,the electric field will bend near the sidewalls of the trenches.Since the movement of colloidal gold is controlled by the electric field,the isotropic etching then happens,making the sidewalls of trenches have the shape of circular arc.Therefore,it is difficult to obtain the trenches with vertical sidewalls by using colloidal gold.Gold film was used as the catalyst later in this project to further explore the influence of the electric field on etching process.The result of the experiment shows that the etching rate is 0.53 ?m/min with the voltage of 5 volts and the etching rate reaches 1.21 ?m/min with the voltage of 20 volts,which has proved that the etching can be effectively accelerated by the applied electric field.Also,the direction of the applied electric field has great influence on the morphology of trenches.When silicon is connected to cathode of the power supply,the trenches with good morphology can be obtained.At the same time,it has been verified that the resistivity of silicon is one of the key factors that determines whether or not trenches can be formed,and only silicon with high resistivity is suitable.Trenches with good morphology and a depth of 36.3 ?m have been obtained with the voltage of 20 volts within 30 min by this method.