Method of fabricating a grayscale mask using a wafer bonding process

A method of fabricating a grayscale mask, comprising:

• preparing a quartz wafer having a front side and a backside;
• depositing a layer of Si3N4 directly on both sides of the quartz wafer;
• depositing a layer of titanium/TEOS directly on the Si3N4 layer on the backside of the quartz wafer;
• removing the layer of Si3N4 from the front side of the quartz wafer;
• depositing a layer of SRO directly on the front side of the quartz wafer;
• patterning a microlens array on the SRO layer;
• etching the SRO layer to form a microlens array in the SRO layer;
• depositing a layer of titanium;
• patterning and etching the titanium layer;
• depositing a layer of a transparent silicon oxide on the SRO microlens array, wherein a refractive index of the transparent silicon oxide layer is matched to a refractive index of the SRO, so that the reflection at a transparent silicon oxide/SRO interface is minimized;
• CMP to planarize the layer of transparent silicon oxide;
• removing the titanium/TEOS layer from the backside of the quartz wafer;
• bonding the planarized transparent silicon oxide layer to a quartz reticle plate;
• and
• etching to remove Si3N4 from the bonded structure to form a grayscale mask reticle.

A method of fabricating a grayscale mask, comprising:

• preparing a quartz wafer having a front side and a backside;
• depositing a layer of Si3N4 directly on both sides of the quartz wafer;
• depositing a layer of titanium/TEOS directly on the Si3N4 layer on the backside of the quartz wafer;
• removing the layer of Si3N4 from the front side of the quartz wafer;
• depositing a layer of SRO directly on the front side of the quartz wafer;
• patterning a microlens array on the SRO layer;
• etching the SRO layer to form a microlens array in the SRO layer;
• depositing a layer of titanium;
• patterning and etching the titanium layer;
• depositing a layer of a SiOxNy on the SRO microlens array, wherein a refractive index of the SiOxNy layer is matched to a refractive index of the SRO, so that the reflection at a SiOxNy/SRO interface is minimized;
• CMP to planarize the layer of SiOxNy
• removing the titanium/TEOS layer from the backside of the quartz wafer;
• bonding the planarized SiOxNy layer to a quartz reticle plate;
• and
• etching to remove Si3N4 from the bonded structure to form a grayscale mask reticle.