A New Carrier Tape for Direct Transfer Bonding (DTB) Process with Ultra-Thin Chips

The article A New Carrier Tape for Direct Transfer Bonding (DTB) Process with Ultra-Thin Chips discusses the development and evaluation of a new carrier tape designed to improve the Direct Transfer Bonding (DTB) process, specifically for ultra-thin chips. DTB is an emerging bonding technology for Chip-on-Wafer (CoW) applications, which avoids the limitations of traditional collet-based bonding by transferring chips through tape.

Key Points:

1. Direct Transfer Bonding (DTB) Technology:
   DTB is a novel bonding technique that allows chips to be transferred onto a wafer using a tape, eliminating issues like chip cracks, contamination, and limited accuracy associated with traditional bonding methods. This process involves several steps, including back grinding, dicing, wafer thinning, and chip transfer, before finally bonding the chips onto the wafer.

2. Carrier Tape Development:
   The carrier tape is crucial in ensuring high bonding accuracy and strength, especially for ultra-thin chips (under 40 µm). The developed tapes are designed with varying adhesive strengths to handle different chip thicknesses effectively. The tape must be strong enough to hold the chips in place but also allow for easy release during the transfer process. The study highlights the importance of selecting the right tape for ultra-thin chips, as conventional tapes used for thicker chips led to bonding failures.

3. Adhesive Strength Evaluation:
   Three different carrier tapes with varying adhesive strengths (Runs 1, 2, and 3) were evaluated using a 180-degree peeling test. Results showed that Run 1, which had the highest adhesive strength, resulted in the failure of chip transfer for all tested chip thicknesses. In contrast, Runs 2 and 3, with lower adhesive strengths, successfully transferred chips at all thicknesses. The initial peak value from the pick-up evaluation was used to assess the adhesive strength, with Run 3 showing the best performance for ultra-thin chips.

4. Pick-up Evaluation:
   The pick-up evaluation involved attaching chips with varying thicknesses (10, 20, 30, 40 µm) to the carrier tapes and testing their transferability using a block-type pick-up tool. The results showed that with lower adhesive strength, chips were more easily peeled off from the tape, improving the transfer rate. The evaluation also identified an "initial peak" in the transfer process, indicating when the chip edge starts to peel off, which was more pronounced with thinner chips.

5. DTB Performance:
   Using the selected Run 3 carrier tape, the DTB performance for 10 µm thick chips was evaluated. The chips were successfully transferred, and the bonding success rate was 97%, with only a few voids observed at the chip-wafer interface. This indicates high bonding quality. Additionally, infrared (IR) imaging revealed the bonding process, showing that the chip's outer edge peeled off before bonding, eliminating chip warping and contributing to reduced defects.

6. Discussion and Future Work:
   The results indicate that reducing the adhesive strength of the tape allows for easier chip edge peeling and improves the bonding process. For ultra-thin chips, this is crucial to prevent warping and defects. Future work will focus on further optimizing the adhesive strength and exploring bonding with chips of different sizes not included in this evaluation.

Conclusion:

The study successfully developed and tested a new carrier tape with optimal adhesive strength for the DTB process with ultra-thin chips. The tape allowed for higher bonding success and reduced defects, offering a promising solution for the direct bonding of ultra-thin chips in semiconductor applications. Future developments aim for a 100% bonding success rate with minimal defects .