Rippled polysilicon surface capacitor electrode plate for high density DRAM

A method for producing a regular microscopic ripple surface capacitor fabricated on a monocrystalline semiconductor substrate comprising:

• depositing a first polycrystalline silicon layer to form a first capacitor plate on a partially completed device structure over a base insulating layer and a contact opening exposing said substrate;
• forming a layer that can be a selective etching mask for polycrystalline silicon over said first polycrystalline silicon layer;
• forming a resist layer over said layer over said fist layer;
• exposing said resist layer through a mask having a pattern of regular spaced openings in the areas of the planned said capacitor to radiant energy in sufficient quantity through a lens system to under-expose, de-focus an image on said resist layer or a combination of under-expose and de-focus an image on said resist layer to create in said resist layer a ripple image wherein said image does not reach said first polycrystalline silicon layer;
• shifting said mask a fixed distance;
• exposing said resist layer through the said shifted mask to radiant energy in sufficient quantity through a lens system to under-expose, de-focus an image on said resist layer or a combination of under-expose and de-focus an image on said resist layer to create in said resist layer a ripple image wherein said image does not reach said first polycrystalline silicon layer;
• repeating said shifting said mask and exposing said resist steps until a pattern of said regular microscopic ripple has been formed in said resist layer;
• developing said resist layer to leave said pattern of regular microscopic ripple in the surface of the resist layer;
• uniformly and anisotropically etching the said resist layer and said layer over said first layer to create said pattern of regular microscopic ripple mask;
• removing the remaining said resist layer;
• uniformly and anisotropically etching the said regular microscopic ripple into the surface of said first polycrystalline layer;
• removing the remaining said layer over said first layer;
• depositing an insulating layer to form a capacitor dielectric layer over the surface of the said first polycrystalline layer;
• and
• depositing a second polycrystalline silicon layer over said insulating layer to form the second capacitor plate and complete said regular microscopic surface capacitor.