Research on EDM Forming Hole of Monocrystalline Silicon and Damaged Layer Removal

Author:Chen Hao Ran

Supervisor:liu zhi dong


Degree Year:2018





Along with the development of science and technology,the demand of the different structure of semiconductor silicon is becoming more and more urgent especially in space line detection,nondestructive testing,cooling channel for high-energy light,etc.For these semiconductors with special structures,it is difficult to machine whether in traditional or nontraditional processing method.When process finished,the removal of metamorphic layer on the cavity surface is still very important which can improve the stability of the workpiece and keep the single crystal structure of the machined surface.Electrical discharge machining(EDM)is a feasible processing method for single crystal silicon which very few domestic and foreign researchers pay attention to.To meet the needs of EDM forming for single crystal silicon and the removal of metamorphic layer on the hole surface of EDMed monocrystalline silicon,the main research work is as follows:1.The EDM forming for single crystal silicon hole processing system was built.The pulse power supply special for semiconductors,servo control system and electrolyte circulation system was developed.The stable EDMed cavity on silicon was achieved.2.The calculation physical model based on energy conversion for EDM forming on silicon was set up and it was used for revealling the materials removal mechanisms in the process of single crystal silicon EDM forming in the microscale and how the material characteristics’effects.And a equivalent circuit model for single crystal silicon EDM forming was established,which provides the theoretical foundation for the continuously machining for silicon by EDM forming.As the bulk resistor and contact resistence exist,it was found that the different position of the into electric will affect machining taper for the discharge energy decreased,the processing method of the variable energy was put forward to decrease machining taper,which will ensure the size precision of the EDM for single crystal silicon.3.The reverse pulse waveform during the process of micro EDM for single crystal silicon was discovered which completes the mechanism of EDM forming for single crystal silicon.The pulse waveform both in the RC and transistor power are compared and using labview and matlab to deal with the waveform data,it was found that the occurrence of reverse pulse can help to improve machining efficiency but increase electrode loss and the workpiece surface roughness.4.A servo control method based on electric current pulse probability detection combine with the periodicly tool rises was raised,a closed-loop control system with online correction of feed speed was designed and constructed,which uses ARM as the main control unit and the electric current pulse probability detection as the core control idea.During the normal machining process,when the sampling probability is less than the set value,the tool electrode will go down in accordance with the set feed speed.At the same time the tool rises in periodicly to promote the interelectrode medium update.When the sampling probability is bigger than the set value,the tool will go up,then the liquid will remove the discharge products to improve the processing environment.5.A processing mode through one-dimensional drive to realize multi-dimensional movement was proposed.Based on three-dimensional printing technology this method can rapidly prepare for bending electrodes fixture,which can realize machining curved holes with different radian.It also avoids using the multi axis NC machine tools,sharply reduces the complex programming and processing cost.The curved blind holes on single crystal silicon were finally successfully machined.6.The detection technology for metamorphic layer thickness of single crystal silicon based on the bragg diffraction principle using back swing curve is proposed.The measurement on metamorphic layer thickness of single crystal silicon after EDM was realized,and the effect of metamorphic layer removal by compound polishing was proved.7.The electrochemical polishing combine with abrasive jet technology based on F~-ionic catalysis effects was put forward.The hole surface of the silicon sample with no metamorphic layer was obtained.An experiment system for metamorphic layer removal was built.The dedicated electrolyte with sodium fluoride as additive was developed.To ensure uniform electric field distribution,through electric field simulation the position of the into electricity was chosen to resolve the electric potential difference caused by the bulk resistor from the into electricity to polishing area in the electrolytic polishing process.The same shape cathode with polishing type hole was designed,the real-time control system on the basis of PID based on virtual instrument was developed to ensure the clearance between electrode bottom and type hole bottom at a right distance,which can improve the electrolyte and abrasive flowing in the clearance between the electrodes and the square hole.At last,the machining surface with no metamorphic layer was got.