Reliability testing is the “extreme stress test” before mass production of chips, essentially verifying the chip’s survival ability and performance degradation patterns under extreme environments. For the 90-nanometer technology node, issues such as quantum tunneling effects and hot carrier injection are exacerbated due to the reduction in device size, requiring the establishment of a more stringent evaluation system for reliability testing, similar to testing whether a car engine can operate stably in the extreme heat of the desert and the extreme cold of the polar regions.
01
FAB Reliability Assessment Goals and Core Challenges
Lifetime Prediction: Simulate the chip’s 10-year service life to verify whether key parameters (such as the data retention time of memory cells) meet design specifications.
Failure Mechanism Capture: Identify potential failure modes such as gate oxide breakdown (TDDB) and metal electromigration (EM), similar to detecting piston wear patterns in a car engine.
Process Defect Screening: Detect microscopic defects introduced during the manufacturing process (such as etching residues and abnormal interface state density), akin to checking for excessive part tolerance during engine assembly.
02
Key Test Items and Implementation Logic
| Test Type | Physical Mechanism | Test Method | 90 Nanometer Characteristic Challenge |
|---|---|---|---|
| TDDB | The stratospheric oxygen layer gradually forms conductive channels under a high electric field. | Apply a working voltage of 1.5-2 times, monitor the leakage current as it increases over time until breakdown. | The gate oxide thickness is only 1.2-1.5nm, and the quantum tunneling effect is significant. |
| HTOL | High-temperature accelerated aging of devices | Under a continuous operation of 1000 hours at an ambient temperature of 125℃, the failure rate of the monitoring function | Local hotspot temperatures may exceed 150℃, requiring optimization of the heat dissipation design. |
| Data Retention | Charge leakage of floating gate over time | After high-temperature baking (e.g., 250℃/24h), the threshold voltage offset of the storage unit is detected. | The reduction in unit size leads to a decrease in storage charge amount and a narrowing of the fault tolerance window. |
| HCI | Hot carriers collide with the gate oxide interface to produce defects. | Increase the Vds voltage to 1.3 times the operating voltage, monitor the degradation rate of the drive current short. | The channel effect intensifies the carrier kinetic energy, and the interface defect generation rate increases by 30%. |
| EM | The current causes metal atoms to migrate, forming voids/whiskers. | Applying current density > 2MA/cm², evaluating interconnection lifetime through resistance change rate | Copper interconnect structure aspect ratio > 5:1, current crowding effect prominent |
Implementation Process Example – Reliability Verification of a 90nm eFlash Chip:
Initial Screening: CP testing to exclude chips with obvious defects (yield > 85%)
Accelerated Aging: HTOL testing chamber runs continuously for 500 hours (equivalent to 5 years of service life)
Parameter Monitoring: Sampling every 24 hours to check parameters such as storage window, read/write speed, and power consumption
Failure Analysis: FIB/SEM analysis on abnormal chips to locate gate oxide rupture or contact hole voids
Process Optimization: Adjusting the silicon nitride deposition temperature to improve charge retention, resulting in a 40% improvement in the Data Retention specification
03
Data Modeling and Lifetime Prediction
Arrhenius Model: Accelerates chemical reactions by raising temperature to estimate failure time at room temperature.
Formula: AF = exp[(Ea/k)(1/T_use – 1/T_test)]
(Ea = 0.7eV typical value, increasing temperature from 125°C to 150°C can shorten the test time by 3 times)
Weibull Distribution Analysis: Statistical failure time distribution of batch samples to calculate the characteristic lifetime at which 63.2% of devices fail (e.g., TDDB characteristic lifetime should be >10 years)
Case: A 90nm BCD process established a copper interconnect lifetime model using EM test data. After optimizing the via size, electromigration lifetime increased from 3 years to 8 years.
04
Special Scenario Assessment
Automotive Electronics Verification:
- Temperature Cycling Test (-40°C ↔ 150°C, 1000 cycles)
- Vibration Test (20G acceleration for 96 hours)
- Complies with AEC-Q100 Grade 0 standard (maximum operating temperature 150°C)
Memory Device Specific Tests:
- Programming/Erase Endurance Test (after >100,000 cycles, storage window shrinkage <15%)
- Radiation Hardening Verification (α particle soft error rate <1FIT)
05
Failure Analysis and Closed-Loop Improvement
Electrical Localization: Use EMMI (Emission Microscope) to capture abnormal light spots and pinpoint leakage paths.
Physical Dissection: FIB cut the abnormal area and use TEM to observe gate oxide defect density (requirement: <0.1 defects/cm²).
Root Cause Traceback:
- If TDDB failure is concentrated at the chip edges, it may be caused by CMP processes leading to uneven gate oxide thickness.
- If HCI degradation shows a regular distribution, check for ion implantation angle deviations.
Process Iteration: A 90nm logic chip improved HCI lifetime by 2x and reduced interface state density by 50% by introducing fluorine plasma treatment.
06
Mass Production Control Strategy
Inline Monitoring: Add reliability-related parameter testing (e.g., gate current @ Vcc+20%) at key layers (such as after gate oxide growth).
Sampling Rule: Select 3% of each wafer batch for 48-hour HTOL preburn. If failure rate exceeds 0.1%, trigger a full batch re-inspection.
Data Dashboard: Establish SPC control charts for reliability parameters, with automatic alerts for process fluctuations exceeding ±3σ.
Analogous Understanding
Reliability assessment of 90nm chips is like creating a “health record” for the chip:
- Health Checkups (HTOL/TDDB) test organ functions
- Genetic Testing (Failure Analysis) screens for genetic defects
- Exercise Load Tests (EM/HCI) assess endurance limits
- Anti-Aging Research (Lifetime Model) predicts service life
Only chips that pass the full “health checkup” are qualified to serve in harsh industrial or automotive electronics environments.
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