Media Perspective | With the support of Shanghai Huali SONOS, the future of eFlash is promising

With the rise of applications such as automotive electronics and the Internet of Things, the market demand for embedded flash memory (eFlash) technology has also risen. However, from the current situation, the design and production of high-end embedded flash memory are mostly in the hands of a few foreign manufacturers, which is contrary to the goal of building independent and controllable Chinese chips.

In view of this, Shanghai Huali, a leading wafer foundry in China, is working with its partners to help upgrade China's embedded flash memory technology. The first batch of concrete results is the high-performance and high-reliability 55nm SONOS embedded flash memory technology for IoT/MCU/smart cards jointly promoted by Huali and Cypress.

From the perspective of embedded storage principles, the current mainstream process is Floating Gate. This traditional silicon process has a long history of application and does not involve changes in materials, so everyone is familiar with it. For this reason, it has been the favorite of embedded storage manufacturers over the years. However, with the increasing requirements for power consumption, performance, cost and reliability, this relatively traditional process has its limitations. For this reason, the industry has explored special process products such as Charge-Trap eFLASH, and Huali's SONOS embedded flash memory technology is a pioneer among them.

According to Shao Hua, director of Huali R&D Department 1, Huali's 55nm SONOS embedded flash memory technology is licensed from Cypress. Based on the 55nm process, these embedded flash memories have achieved important results in terms of high reliability, high competitiveness and high quality, and various technical indicators and product market applications have reached international advanced levels.

This is the world's first mass-produced 55-nanometer SONOS embedded flash memory technology, Shao Hua emphasized. Huali continues to improve, through a series of methods such as process modules, process integration, flash memory device miniaturization, circuit design, mask reduction and yield improvement, to carry out technological innovation in several key aspects such as improving the reliability, product competitiveness and product quality of 55-nanometer embedded flash memory technology products, and has achieved the following leading advantages:

High reliability: Data retention capability far exceeding industry standards

According to reports, the biggest difficulty of 55nm SONOS flash memory devices lies in their reliability, and data retention is the biggest challenge in reliability. In addition to forming flash memory devices, the embedded flash memory process also requires the introduction of a large number of thermal processes such as high-pressure and low-pressure oxygen and annealing. In the 12-inch process, these thermal budgets have an exponentially higher negative impact on the ultra-thin tunnel oxygen layer and storage layer of SONOS flash memory.

Huali has made bold innovations in traditional gate oxide process modules and process integration solutions, and developed the industry's first "ISSG G1 First Solution", which significantly reduced the thermal budget. It not only effectively inhibits the lateral oxidation of the tunnel oxide layer by water vapor, but also significantly inhibits the escape of H from the main deep potential well center in the storage layer; while expanding the programming window, it also significantly improves the data retention capability. The embedded flash memory product can still maintain data for 20 years after extremely harsh 500,000 erases and writes, which is much higher than the industry's standard of 10 years of data retention after 10,000 erases and writes, achieving high-reliability applications and reaching the domestic advanced level.

High quality: ultra-low cost, high yield

Huali's 55nm SONOS embedded flash memory only adds 4 masks to the 55nm logic platform, which has a very strong cost advantage compared with other mass-produced 55nm embedded flash memory technologies in the industry (which require 9 to 12 additional masks). However, the Huali team still further improves quality and reduces costs through a series of technological innovations.

In addition to developing the 3+0 back-end process and CUP (Circuit Under Pad) process structure, we have also achieved an additional 4 mask layer reduction for some customer products through process optimization. In addition, without using redundant circuit design, through wafer edge WEE/EBR/ECP experiments, CMP grinding pressure edge optimization, PH edge defocus optimization, defect edge fixed-point monitoring, etc., the product yield has been greatly improved. It has now reached a stable 97%, reaching the international advanced level in terms of cost and mass production.

Sustainable scaling: down to at least 28nm technology node

In terms of technology node evolution, the storage unit device structure and type of Huali's 55nm embedded flash memory process are advanced and can be sustainably reduced in size. It is expected to be reduced to at least the 28nm technology node, with strong technical sustainability.

Shao Hua told reporters that Huali's 55nm embedded flash memory technology platform completed technical development and started risk mass production in 2016. In 2018, it has achieved verification and mass production of multiple customers and multiple products. The products cover low-power IoT storage chips, touch control chips, high-speed MCUs, embedded FPGAs, smart card chips, security chips, etc.

Shao Hua also said that Huali can now provide a series of services such as customized embedded flash memory IP, design, process, testing and reliability verification to meet the different needs of customers.

Facing the rise of new applications, Huali is ready to go!