Influence of plasma Etching on GOI/TDDB in plasma Cleaning Machine

Influence of plasma Etching on GOI/TDDB in plasma Cleaning Machine:

Gate Oxide Integrity (GOI) generally refers to the time breakdown (TDDB) test of Gate silicon Oxide capacitance at constant voltage. With the continuous reduction of MOS circuit size, the gate oxide layer becomes thinner and thinner, and the decrease of power supply voltage cannot be synchronized with the gate oxygen thinning, which makes the gate oxide layer need to work under high electric field intensity. The breakdown of gate oxide layer is an important mode affecting the reliability of MOS devices. Usually, the breakdown of the oxide layer is instantaneous under high voltage, but in fact, even if the applied voltage is lower than the critical breakdown electric field, the breakdown will occur after a period of time, which is the breakdown of the oxide layer. A large number of experiments show that this kind of breakdown is closely related to the applied stress and time. In HKMG technology, Gate Dielectric materials by high - k hafnium oxide instead of silicon oxide, GOI was renamed the GDI (Gate Dielectric Integrity).

Actual CMOS device will have various defects in gate oxide, including plasma cleaning machine plasma generated when the oxide layer deposition or follow-up process into the trap charge and movable ions, pinhole, silicon particles, coarse interface, thinning of the local thickness, oxide layer is weak, the physical defects in certain electrical and thermal stress under the action of will lead to the dielectric breakdown, is a major cause of TDDB produce. By improving the plasma equipment process and raw materials of plasma cleaning machine, the influence of random defects can be reduced, so that the oxidation layer breakdown is mainly determined by the properties of materials, at this time the failure is intrinsic failure, is the focus of various plasma cleaning machine plasma equipment research. One is that at constant voltage, a bond at the interface between the dielectric material and the gate or silicon substrate breaks, resulting in a trap, followed by hole and electron capture. After a relatively long period of degradation, electron capture continues until local Joule heat forms a conductive fuse in the dielectric material, resulting in a short circuit between the gate electrode and the silicon substrate, i.e., a short circuit between the cathode and the anode, resulting in the dielectric layer being broken down.

A complete unified model to accurately describe the gate oxide layer breakdown has not been obtained so far, but two empirical models are widely used to describe the TDDB failure mechanism of oxide dielectric layer, one is the E model based on the electric field driving theory, the other is the 1/E model based on the electric current driving theory.

Model E is also known as the thermochemical model. The model holds that TDDB occurs at low field intensity and high temperature because the electric field enhances the thermal fracture of atomic bonds of dielectric materials, and the added electric field makes the polar molecular bonds elongate, thus weakening the bonds and making them more likely to be destroyed in the standard Boltzmann thermal process. The degradation rate increases exponentially with the electric field because the presence of electric field reduces the specific energy of molecular bond fracture. When the local density of the broken bond or seepage point is high enough, a conductive path from anode to cathode will be formed. At this time, failure will occur, and the corresponding time is the failure time. The inverse relationship between the failure time and the degradation rate is, so it decreases with the electric field strength index, which can be expressed in the following form

TF = A0exp (- ϒ Eox) exp (Ea/kBT) (7-10)

Among them, the ϒ electric acceleration factor; Eox refers to the electric field intensity in oxide dielectric layer; Ea is activation energy; KB is Boltzmann constant; A0 is the coefficient related to material and process, and the value of different devices is different. The property of A0 makes TF become a distribution, which is generally weible distribution.

The 1/E model is also known as the anodic cavity injection model. According to the model, under the applied electric field, the electrons injected by Fowler-Nordheim(FN) tunneling effect accelerate from the cathode to the anode, passing through the dielectric layer and causing damage to the dielectric layer. Moreover, when the accelerated electrons arrive at the anode, electron hole pairs are generated in the silicon at the anode interface by collision ionization, and some of the high-energy holes are injected into the valence band of the oxide layer. Under the action of electric field, these holes migrate back to the cathode interface, resulting in degradation of the oxide layer and breakdown. Both electrons and hot holes are the result of FN tunneling effect, and the exponential relationship between the failure time and the reciprocal of the electric field intensity is

F = A0exp (G/Eox) exp (Ea/kBT) (7-11)

Where, G is a temperature-related parameter, and the other parameters are in the same equation (7-10).

For the TDDB failure of the ultra-thin (< 40A)SiO2 dielectric layer, a power-law voltage model can be adopted. This model believes that, because the dielectric layer is very thin, the defect generation is proportional to the hydrogen release caused by the electrons directly tunneling through the gate oxide layer, so the measured defect generation rate is a power function of the voltage applied on the gate oxide layer. Thus, the relationship between failure time and voltage is

TF= B0V-n         (7-12)

When the oxide layer is sufficiently thin, the rate of defect generation is independent of the thickness of the oxide layer, but the critical defect density causing the oxide layer to break down is strongly dependent on the thickness of the oxide layer.

For low-k material TDDB, there is also the corresponding square root E model. The fitting curves of various models for the same set of accelerated TDDB test data were compared. For the data points in the range of high electric field intensity, all the models were well fitted. However, when extrapolated to low electric field intensity, the four models were quite different. Among them, the failure time of model E was short, while that of model 1/E was long, indicating that model E was conservative and model 1/E was radical.

In the plasma cleaning machine plasma equipment CMOS process, related to gate oxide plasma cleaning machine plasma equipment of plasma etching process is a plasma cleaning machine plasma etching equipment source area, plasma cleaning machine plasma etching equipment grid, plasma cleaning machine such as plasma etching equipment side walls, and pseudo grid etching in HKMG technology. These steps have the potential to affect gate oxide TDDB. The literature also reported that the smooth AA upper Angle was of great help to improve the TDDB of the gate oxide layer, which was achieved by introducing an additional top smooth process step after the SiN hard mask etching step of the plasma equipment in the plasma cleaning machine, and the obtained AA Angle presented an ideal arc shape.

In the gate etching of plasma equipment of plasma cleaning machine, if the plasma is not uniform, it will lead to local area electron flow or ion flow from the side of the gate damage gate oxide layer, reduce the quality of gate oxide layer, and then affect the PERFORMANCE of TDDB. Lee et al. found that gate morphology also had an impact on TDDB, and gate morphology with protruding foot was worse in TDDB performance than that of straight gate or concave gate. The reason was that ions would enter the gate oxide layer through the gate protruding foot when injected by plasma cleaning machine and plasma equipment, resulting in oxide layer damage.

Li found such as gate oxide breakdown due to lateral wall size is too small, which is caused by the inhomogeneity of the sidewall etching size, Mahesh such as found in the lateral wall after etching process step to remove the residual polymer, compared with the plasma cleaning machine plasma equipment of H2 / N2 gas plasma, O2 / N2 plasma can greatly improve the TDDB. They believe that the plasma O2/N2 of the plasma cleaning machine has a stronger polymer removal capability, so sufficient process Windows are set aside for subsequent wet cleaning to reduce side wall loss.