Abstract
High Temperature Reverse Bias (HTRB) reliability failure is found to be caused by huge amount of undesirable hydrogen proton (H+) ions from packaging resin or external environment, while Temperature Humidity Bias (THB) reliability failure is known to be caused by moisture accumulation. A commonly known method of improving HTRB is by increasing phosphorus concentration in the PMD layer to enhance device gettering capability against H+. However, this is usually achieved at the expense of THB reliability as excessive phosphorus on the PMD surface gives rise to moisture accumulation and caused THB failure. In this paper, we performed a series of experiments to uncover two elements in PMD that are responsible to getter H+, which are Phosphorus-Oxygen-Hole-Center (POHC) and dangling bonds. We also discussed 2 possible ways to boost these H+ gettering elements to improve HTRB reliability without the adverse impact on THB reliability: Utilization of Plasma Enhanced Chemical Vapor Deposition (PECVD) Phospho-Tetraethyl-Orthosilicate (PTEOS) in PMD layer to replace the commonly used Atmospheric Pressure Chemical Vapor Deposition (APCVD) or Sub Atmospheric Chemical Vapor Deposition (SACVD) Boro-Phospho-Tetraethyl-Orthosilicate (BPTEOS) and the introduction of Tetraethyl-Orthosilicate (TEOS) capping layer on PMD layer. Both methods have proven to greatly alleviate HTRB and THB reliability marginality problems.
Highlights
One of the common failure modes of High Temperature Reverse Bias (HTRB) is threshold voltage (Vth) drift, which can be caused by a convolution of many factors such as trench corner rounding, trench oxide interface quality, plasma charging, mobile ions, alpha-particles radiated from package [4], molding compound material [5], moisture [6], and so on
Pre-Metal Dielectric (PMD) was the only device protection layer in the opening area between source electrode to gate electrode or gate electrode to edge termination metal. To resolve these two reliability problems, it was imperative that we determined the elements in PMD layer that were responsible to getter H+ and focus on the solution to increase these amount of H+ gettering elements
First experiment was done with the conventional approach by increasing the amount of Phosphorus in PMD BPTEOS which was deposited with the common SACVD technique
Summary
With the widespread commercialization of trench-based power devices such as trench field plate power Metal Oxide Semiconductor Field Effect Transistor (MOSFET), trench super junction MOSFET, trench field-stop Insulated Gate Bipolar Transistor (IGBT) and trench MOS barrier Schottky (TMBS) to minimize on-state power consumption, reliability weaknesses such as High Temperature Reverse Bias (HTRB) and Temperature Humidity Bias (THB) are starting to surface as potential threat to hamper future technology development efforts, especially in the area of device scaling, edge termination design as well as the use of smaller, thinner and greener packages [1,2,3]. To prevent HTRB Vth drift, often, good protective dielectric layers such as post metal passivation or Pre-Metal Dielectric (PMD) or a combination of both are needed These dielectric layers are usually made of BPTEOS film or PTEOS film [7] and they play several roles in the fabrication and operation of the circuit. As shown in Fig., by applying a quick high temperature to dry the failed THB part which was doped with high percentage of Phosphorus, a full Idss recovery was observed This observation reconfirms the theory that Phosphorus being hydrophobic in nature [11], had prevented moisture absorption during THB reliability test and left an abundance of moisture accumulation on PMD surface. We can produce a PMD surface free of Phosphorus that prevents moisture build-up, and improves THB while keeping the PMD bulk with high level of Phosphorus percentage for more H+ gettering sites and better HTRB performance
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