Overlay alignment measurement of wafers

An apparatus to determine the relative position between two layer of a device, wherein a second layer of said two layers is located above a first layer of said two layers, said apparatus comprising:

• a target including a first periodic structure on said first layer said first layer of said device and a second periodic structure that complements said first periodic structure with said second periodic structure on said second layer of said device at a location that is adjacent said first periodic structure;
• a microscopic height variation detector positioned relative to said device to scan said target on said device and produce an electrical signal representative of height variations of said first and second periodic structures in a selected path across said device;
• and
• a computing and control system to provide translation between said microscopic height variation detector and said target on said device in a selected path, and to calculate any offset between said first periodic structure and said second periodic structure of said target from said electrical signals from said microscopic height variation detector.

A method for determining the relative position between two layers of a device in a selected direction wherein a second layer of said two layers is located above a first layer of said two layers, said method comprising the steps of:

• a. placing a first periodic structure of a target on said first layer of said device oriented to facilitate determination of said relative position between said two layers;
• b. placing a second periodic structure of a target, wherein said second periodic structure complements said first periodic structure, at a location that is adjacent said first periodic structure and oriented similarly to the orientation of said first periodic structure in step a. to facilitate determination of said relative position between said two layers;
• c. transversing an atomic sized tip in a first path across said first and second periodic structures of steps a. and b.;
• d. transversing an atomic sized tip in a second path across said first and second periodic structures of steps a. and b.;
• e. detecting vertical deflection of said atomic sized tip in said first path as the transversing of step c. is performed;
• f. detecting vertical deflection of said atomic sized tip in said second path as the transversing of step d. is performed;
• g. generating a first signal proportional to the intensity of the detected deflection in step e.;
• h. generating a second signal proportional to the intensity of the detected deflection in step f.;
• and
• i. calculating any offset between said first periodic structure and said second periodic structure of said target from said signals generated in steps g. and h.

A method for determining the relative position between two layers of a device in a selected direction wherein a second layer of said two layers is located above a first layer of said two layers, said method comprising the steps of:

• a. placing a first periodic structure of a target on said first layer of said device oriented to facilitate determination of said relative position between said two layers;
• b. placing a second periodic structure of a target, wherein said second periodic structure complements said first periodic structure, at a location that is adjacent said first periodic structure and oriented similarly to the orientation of said first periodic structure in step a. to facilitate determination of said relative position between said two layers;
• c. transversing a microscopic height variation detector in a selected path across said first and second periodic structures of steps a. and b. to produce an electrical signal representative of height variations of said first and second periodic structures in said selected path across said first and second periodic structures;
• d. calculating any offset between said first periodic structure and said second periodic structure of said target from variations of said electrical signal generated in step c.