Memory Array Overlay Determination Using Chop Mask Gaps
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Solution Overview
Problem
In the fabrication of memory devices, determining the overlay of features such as contacts and conductive lines becomes challenging as the pitch decreases, causing the contacts to be obstructed or obscured by the conductive lines, making it difficult to accurately assess the offset between these features.
Innovation Solution
The use of a mask material, referred to as a chop mask, to selectively transfer patterns on a wafer, creating a gap between portions of the conductive lines and contacts, allowing for an unobstructed overlay and enabling the determination of the offset between conductive lines and contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pitch of the memory array is decreased to increase memory density, then the memory density is improved, but the contacts become obstructed or obscured by the conductive lines, making overlay determination difficult
Solution Approach 1:
The patent divides the conductive lines into separate portions using gaps, allowing the overlay of contacts relative to conductive lines to be determined without obstruction. The gap segments the conductive line layer, creating a clear view of the contact overlay that would otherwise be hidden.
2Area of moving object
If the contact size is reduced to accommodate smaller pitch, then the memory density is improved, but the overlay of contacts becomes obstructed by conductive lines
Solution Approach 1:
The patent introduces a vertical gap dimension in the conductive line layer, creating a spatial separation that allows overlay measurement in a different dimensional plane. This gap provides a viewing window through which contact overlay can be observed without interference from the conductive lines above.
3Ease of manufacture
If a traditional overlay measurement method is used without gaps, then the process is simpler, but the overlay determination is inaccurate when contacts are obscured
Solution Approach 1:
The gap acts as an intermediary element that enables overlay measurement. By introducing this intermediate spatial separation, the measurement process can accurately determine contact overlay without the direct obstruction that would otherwise prevent precise measurement.
Data Source
AI summary
Methods, apparatuses, and systems related to determining overlay of features of a memory array are described. An example method includes forming a plurality of contacts on a working surface and selectively forming a first portion of a layer of conductive lines and a second portion of the layer of conductive lines in contact with the contacts. The first portion of the layer of conductive lines formed over the working surface is separated from the second portion of the layer of conductive lines formed over the working surface by a gap. The method includes determining an overlay of at least one of the contacts formed over the working surface in the gap relative to one of the conductive lines formed over the working surface.