SEMI International Standards
SEMI New Activity Report Form (SNARF)

Activity Number: 5409
SNARF for: New Standard: Guide for Metrology for Measuring Thickness, Total Thickness Variation (TTV), Bow, Warp/Sori, and Flatness of Bonded Wafer Stacks

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: Bonded wafer stack (BWS) thickness, total thickness variation (TTV), bow, warp/sori, and flatness metrology is essential before, during, and after the wafer bonding process. These parameters provide meaningful information about the quality of the wafer thinning process (if used), the uniformity of the bonding process, and the amount of bow and warp/sori induced on the wafer stack by the bonding process. The quality of lithography is also dependent on having uniformly flat wafers. Total thickness variation is also critical in bonded wafer manufacturing, since intermittent TSV contact to M2 will occur due to non-planarity. Non-planarity may also affect overlay quality. Subsequently this study can assist producers and users of other wafer bonding processes to develop robust products and conduct meaningful substrate evaluations.

The proposed guideline will provide guidance on key bonded wafer dimensional metrology metrics, along with any limitations and/or issues and needs particular to that technology. The guide will also include applicable ranges for valid measurements where possible.

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:
A number of technologies have been developed to measure bonded wafer stack (BWS) thickness, total thickness variation (TTV), bow, warp/sori, and flatness metrology. Examples include, but are not limited to IR laser profiling, white light confocal microscopy, visible and IR interferometry, opto-acoustic metrology, and capacitance metrology. Each technology has unique strengths and weaknesses—some rely on front-side illumination, others on back-side illumination. Some techniques can measure the thicknesses of individual layers in the bonded wafer stack, and some are capable of measuring surface topography. In this activity, we will provide examples of the capabilities and limitations of these technologies and prepare a guide to the use and suitability of these tools for different applications. Recent studies and reports conducted at SEMATECH will be used as part of this guide.

This guide will cover both temporary and permanent bonded wafer stacks.

b: Expected result of activity
New Standard

3. Projected Timetable for Completion:
a: General Milestones
a. Activity Start: 04/03/2011b. 1st Draft by: 09/01/2012
c. Preballot by: d. Technical Ballot by: 01/01/2013
e. Committee Approval By:04/01/2013

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: None.

Approval: Activity approved by Committee/GCS on April 3, 2012