Solid-State Image Sensor Dark Current Reduction via RTA
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Solution Overview
Problem
Existing manufacturing methods for solid-state image sensors face challenges in reducing dark current and maintaining sufficient saturation characteristics at low voltages due to enhanced diffusion of impurity ions at low temperatures, which degrades the charge storage capability and increases voltage requirements, particularly in CMOS sensors.
Innovation Solution
A manufacturing method involving Rapid Thermal Annealing (RTA) at specific temperature ranges (800° C. to 1200° C.) to recover crystal defects and suppress low-temperature enhanced diffusion, forming charge storage and surface regions with precise ion implantation and subsequent RTA treatments, followed by antireflection film formation at lower temperatures to minimize defect recovery time and maintain charge storage efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If CVD is used to form an antireflection film at low temperature (less than 800°C), then the film can be formed successfully, but enhanced diffusion of impurity ions occurs due to crystal defects, causing charge storage capability to degrade
Solution Approach 1:
The patent applies preliminary RTA treatment at high temperature (800-1200°C) before the low-temperature CVD process to recover crystal defects in advance. This preliminary action eliminates the root cause of enhanced diffusion before it can occur during the subsequent antireflection film formation, allowing both low-temperature CVD and precise charge storage region concentration to be achieved
2Reliability
If ion implantation is performed to form a high-concentration charge storage region, then charge storage capability is improved, but saturation characteristics degrade due to increased voltage requirements in CMOS sensors
Solution Approach 1:
The patent changes the temperature parameter by applying RTA treatment at 800-1200°C to recover crystal defects and suppress enhanced diffusion. This parameter change allows the charge storage region to maintain its concentration profile without the need for excessive implantation doses, thereby improving saturation characteristics while preserving charge storage capability
3Manufacturing precision
If RTA is applied at high temperature (800-1200°C) to recover crystal defects, then enhanced diffusion is suppressed, but the process complexity increases
Solution Approach 1:
The patent merges the RTA treatment step with the existing manufacturing flow by positioning it strategically between ion implantation and CVD processes. This combination approach integrates defect recovery and diffusion suppression into a single consolidated heat treatment step, reducing overall process complexity while maintaining precise diffusion control
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces dark current and enhances saturation characteristics at low voltages, improving the performance of CMOS-type solid-state image sensors by stabilizing the charge storage region and suppressing enhanced diffusion, thus achieving better charge storage and transfer efficiency.
Implementation Method 1
heating the semiconductor substrate at a temperature of no less than 800° C. and no more than 1200° C. through RTA (Rapid Thermal Annealing)
Implementation Method 2
forming a charge storage region in a photoelectric converting unit by implanting a semiconductor substrate with ions of an impurity of a first conductivity type
Implementation Method 3
the impurity ions that form the surface region undergo enhanced diffusion due to interaction with the crystal defects within the surface region and the charge storage region
Data Source
AI summary
A manufacturing method for a solid-state image sensor, the method comprises the steps of: forming a charge storage region in a photoelectric converting unit by implanting a semiconductor substrate with ions of an impurity of a first conductivity type, using a first mask; heating the semiconductor substrate at a temperature of no less than 800° C. and no more than 1200° C. through RTA (Rapid Thermal Annealing); forming a surface region of the charge storage region by implanting the semiconductor substrate with ions of an impurity of a second conductivity type, using a second a mask; heating the semiconductor substrate at a temperature of no less than 800° C. and no more than 1200° C. through RTA (Rapid Thermal Annealing); and forming an antireflection film that covers the photoelectric converting unit at a temperature of less than 800° C., after the step of forming the surface region, in this order.