ThewholechemicaletchingprocessonaP-typepolycrystallinesiliconsubstratewithresistivity1-2Ω·cmisdescribed.Theformationmechanismofporouspolycrystallinesilicon(PPS)microstructurewasinvestigated.ThosehowtheinitialpitswereformedandanuniformmorphologyofPPSwasobtainedareexplained.Twotypesofetchingmechanismwerecharacterizedasdefectcontrolreactionanddiffusioncontrolreaction.ThemorphologyformedaftertheisotropicacidicsolutionetchingwithdifferentetchingtimeandHF/HNO3concentrationwascomparedwiththeeffectofthesameetchingprocessafteranisotropicalkalineetching.Thestudyshowedthatthethicknessofporouspolycrystallinesiliconlayerwithchemicalacidicetchingentirelydependedontheexistenceofvarioustypesofdefects.