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SEMI 3D4-0613 - Guide for Metrology for Measuring Thickness, Total Thickness Variation (TTV), Bow, Warp/Sori, and Flatness of Bonded Wafer Stacks

Volume(s): 3D-IC
Language: English
Type: Single Standards Download (.pdf)
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Status
CURRENT - Supported by the technical committee.


Abstract

This Standard was technically approved by the 3DS-IC Global Technical Committee. This edition was approved for publication by the global Audits and Reviews Subcommittee on June 4, 2013. Available at www.semiviews.org and www.semi.org in June 2013.

 

Control of parameters, such as bonded wafer stack (BWS) thickness, total thickness variation (TTV), bow, warp/sori, and flatness metrology, is essential to successful implementation of a 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 deformation induced to the wafer stack by the bonding process. Total thickness variation is also critical in certain bonded wafer manufacturing process steps, since nonplanarity can lead to problems in subsequent processing steps, including lithographic overlay and intermittent electrical contact between metal layers in the bonded wafers. This Guide provides a description of tools that can be used to determine these key parameters before, during, and after the process steps involved in wafer bonding.

 

This Guide provides examples of the capabilities and limitations of various measurement technologies applicable to BWS as well as their suitability for different applications.

 

The Guide describes metrology techniques that are applicable to both temporary and permanently bonded wafer stacks.

 

This Guide is complementary to existing SEMI Test Methods for measuring these parameters on single wafers, in some cases extending existing metrology techniques to a bonded wafer stack and in other cases describing metrology techniques specific to a bonded wafer stack.

 

The Guide focuses on general measurement techniques including IR laser profiling, white light confocal microscopy, visible and IR interferometry, capacitance, and back-pressure 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 additionally capable of measuring surface nanotopography.

 

The metrology examples provided in this Guide originated from industry experts and are believed to be representative of tool performance as of the year 2012. However, as tool and measurement techniques continue to evolve and improve, BWS measurement performance may surpass what is contained in this Guide. The user should investigate metrology suppliers’ current capabilities.

 

The measurements described in this Guide are on bonded wafer stacks with thickness in the range of 50 to 1550 μm.

 

The stacks considered include carrier and device wafers and bonding layers, including cases where there are more than two wafers in a stack. Bonded wafers may be classified as either temporarily bonded (i.e., a device to a carrier wafer) or permanently bonded. Temporary bonding uses a temporary adhesive; permanent bonding could be adhesive, oxide, metal-metal (e.g., Cu-Cu), or hybrid bonding. Two representative two-wafer stacks are depicted in Figures 1 and 2. The first stack (Figure 1) is a bonded pair of 775 µm thick wafers following TSV formation and the bonding operation. The second stack (Figure 2) is a bonded wafer stack with a top wafer thinned to ~50 µm, and bonded on top of a 775 µm wafer using a temporary adhesive.

 


Referenced SEMI Standards

SEMI M23 — Specification for Polished Monocrystalline Indium Phosphide Wafers

SEMI M43 — Guide for Reporting Wafer Nanotopography

SEMI M49 — Guide for Specifying Geometry Measurement Systems for Silicon Wafers for the 130 nm to 16 nm Technology Generations

SEMI M59 — Terminology for Silicon Technology

SEMI M65 — Specifications for Sapphire Substrates to Use for Compound Semiconductor Epitaxial Wafers

SEMI MF533 — Test Method for Thickness and Thickness Variation of Si Wafers

SEMI MF534 — Test Method for Bow of Silicon Wafers

SEMI MF657 — Standard Test Method for Measuring Warp and Total Thickness Variation on Silicon Slices and Wafers by a Noncontact Scanning Method

SEMI MF1390 — Standard Test Method for Measuring Warp on Silicon Wafers by Automated Noncontact Scanning

SEMI MF1451 — Test Method for Measuring Sori on Silicon Wafers by Automated Noncontact Scanning

SEMI MF1530 — Standard test method for Measuring Flatness, Thickness, and Thickness Variation on Silicon Wafers by Automated Noncontact Scanning


Revision History

SEMi 3D4-0613 (first published)


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