SEMI International Standards
SEMI New Activity Report Form (SNARF)

Activity Number: 5506
SNARF for: New Standard: Guide for Measuring Flatness and Shape of Low Stiffness Wafers

Originating Global Technical Committee: 3DS-IC
Originating Technical Committee Region: North America
Task Force in which work is to be carried out: 3DS-IC Inspection and Metrology

1. Rationale: The current metrology strategies have evolved from methods used to characterize smaller, lower aspect ratio geometries. Conventionally, three point mounts have been used to measure flatness/warp of wafer along with gravity compensation.

Nowadays, however, the trend goes to use larger in diameter and thinner wafers, for instance in 3DS-IC applications. Larger and thinner wafers are less stiff than conventional ones. Low stiffness leads to a high deflection and sag, which can even exceed the required warp tolerance. In addition, the new applications require a complete depiction of the wafer’s shape, thus interpolation calculation methods based on few data points fail to depict the real free state of the wafer and allow passing failures like local bow.

The industry therefore would benefit from identifying a guide that better reflects the application usage of these wafers. One such approach used in the industry is a similar set up to Sori with a wire mount and a noncontact scanning method that allows depicting a complete picture of the wafer’s shape and dimensional parameters.
This guide will recommend the wafer to be characterized in a position that allows for a free state profile measurement on a semi-continuous flat mounting surface.

This revised SNARF changes the Draft Document from a “Test Method” to a “Guide”

Rate the Estimated Effect on the Industry
2: Major effect on an industry sector - identify the relevant sector

Rate the Estimated Technical Difficulty of the Activity
II: Some Difficulty - Disagreements on known requirements exist but developing consensus is possible

2. Scope:
a: Define the areas to be covered or addressed by this activity or document:
Establish a guide on how to measure wafers with a deflection of more than twice their warp tolerance. This guide can be applied to all materials and geometrical shapes.

b: Expected result of activity
New Standard

3. Projected Timetable for Completion:
a: General Milestones
a. Activity Start: 11/01/2012b. 1st Draft by: 04/01/2013
c. Preballot by: d. Technical Ballot by: 08/26/2014
e. Committee Approval By:11/04/2014

Safety Considerations:
The resulting document is expected NOT to be a Safety Guideline

Intellectual Property Considerations:
a. In complying with the standard or safety guideline to be developed, the use of patented technology or a copyrighted item(s) is NOT required
b. The body of the standard and any appendices or related information sections will NOT include copyrighted material

Comments, Special Circumstances: This guide will look at input of other committees, from HB-LED, PIC, and the silicon wafer committees

SNARF was first revised in October 29, 2012
SNARF was again revised in October 29, 2013 (change from Test Method to Guide)

SNARF was again revised at SEMICON West 2014. Approved via GCS on August 18, 2014.
SNARF title was updated. Previous title: "New Standard: Guide for Measuring Warp, Bow and TTV on Silicon and Glass Wafers Mounted on Wire Grids by Automated Non-Contact Scanning using Laser Scanning Interferometry"

Approval: Activity approved by Committee/GCS on August 18, 2014