Split-Gate Semiconductor Structure With Oxide-Free Source Contacts

The patent segments the etching process into multiple sequential steps with different etching conditions. First, a preliminary etching step removes the silicon oxide layer partially, then a second etching step with modified parameters (such as different chemistry or power settings) completely removes residual oxide in narrow spaces between low-voltage gates. This segmented approach allows the split gate oxide to maintain sufficient thickness for high-voltage device reliability while ensuring complete removal in critical contact regions.

The patent applies preliminary action by performing a first etching step that partially removes the silicon oxide layer before the final etching step. This preliminary etching creates initial openings and reduces the overall oxide thickness, making subsequent complete removal in narrow spaces feasible. The preliminary action prepares the structure for the final precise etching that ensures conductive plug contact without compromising the split gate functionality.

The patent segments the etching process into multiple steps with progressively different parameters. The first etching step uses conditions that remove oxide at a controlled rate, while the second etching step uses more aggressive conditions (such as different chemistry, higher power, or longer duration) specifically targeted at removing residual oxide in narrow spaces. This segmentation allows achieving complete removal without uniformly reducing the split gate oxide thickness that is critical for breakdown voltage characteristics.

The patent applies local quality by making the etching process location-dependent. The multi-step etching approach creates different local outcomes: in regions with split gates, sufficient oxide thickness is maintained for high-voltage operation, while in narrow spaces between low-voltage gates, complete oxide removal is achieved. The etching parameters are optimized to produce different removal depths in different locations, ensuring both contact hole formation and split gate functionality.

The patent segments the single etching process into multiple sequential etching steps, each with optimized parameters for specific objectives. The first etching step forms the initial split gate structure, while the second etching step ensures complete oxide removal in narrow spaces. Although this increases process steps, each step uses standardized etching equipment and chemistry, maintaining relative ease of manufacture while solving the residual oxide blocking problem.

The patent maintains continuity of useful action by performing etching steps in sequence without interrupting the overall manufacturing flow. The multi-step etching process is integrated into the existing fabrication sequence, with each step building upon the previous one. This continuous approach ensures that the split gate structure is formed and refined in a streamlined manner, achieving complete oxide removal while maintaining manufacturing efficiency.