Impact of gate-leakage currents on CMOS circuit performance

Al-Co metal gate has been recently proposed both for 25 and 11 nm devices as an alternative for Al-Ti used for 45 nm structures. The polishing dispersions used for Al-Ti gates when tested on Al-Co showed severe pitting and static etch rates upto ∼10 nm/min. The present work describes the development of the required chemistry to reduce the corrosion potential (E corr ) gap between Al and Co and minimize galvanic corrosion. The effect of pH, several oxidizers and additives on the open circuit potentials (E oc ) of Al and Co was investigated and it was discovered that solutions of KMnO 4 and saccharides help reduce the E corr gap in between Al and Co to ∼10 mV. A preliminary corrosion protection mechanism involving the formation of a protective manganese oxide coating on the surface of Al/Co is proposed.Reduction of SiO 2 gate oxide thickness and length has been crucial to the continued scaling down of CMOS devices and obtain performance gain. For example, the 90 nm node had a gate oxide thickness between 8-12 Å. 1,2 In 32 nm devices, a further reduction in the gate oxide thickness is needed but was not possible due to the associated increase in leakage current. 3-6 A combination of high-K dielectric gate film with an appropriate metal gate has effectively solved the problem, as was shown by several authors. [7][8][9] For integrating the metal gate as well as the high-K gate oxide, the gate last or replacement metal gate (RMG) scheme is widely used. 10-13 During this process, the gate is initially fabricated with a dummy material (generally poly-Si), which is later etched off and filled with the appropriate gate metal. 14 Scaling to a gate length (L gate ) of ∼30 nm has been successfully achieved using Al as the gate material. 15 A suitable wetting layer, usually Ti, is needed to flow the Al into and fill the trench vacated by the dummy gate during the RMG process. A typical structure is shown in Fig. 1. However, for L gate < 25 nm, after the poly open CMP, Ti deposited using physical vapor deposition (PVD) is reported 15 to exhibit overhangs at the top of the gate which would retard the flow of Al into the open space. Kwon et al., 16 at IBM, have very recently developed a novel cobalt-aluminum-based metal fill scheme in the replacement metal gate (RMG) process that can be scaled down to 11 nm. Using Co instead of Ti improved the flow of Al into the high aspect ratio trench as well as maintained the desired electrical properties of the gate.One of the challenges of this strategy is that Co and Al in contact with each other in an aqueous medium during a chemical mechanical planarization (CMP) step would form a galvanic couple due to their high (>1V) open circuit potential (E oc ) difference. Galvanic corrosion can occur when two metals with such a large E oc difference contact with each other within the device architecture and are exposed to charge conducting CMP slurries. Al acts as the anode and corrodes faster in the presence of Co as its standard electrode potential (E • = −1.66 V) is low compared to that of Co (...

mentioning

confidence: 86%

Section: Effect Of H 2 O 2 + Different Additives On the E Oc 'S Of Almentioning

confidence: 99%

Role of Potassium Permanganate-Based Solutions in Controlling the Galvanic Corrosion at Al-Co Interface

Lagudu

Chockalingam

Eckonomikos³

et al. 2013

“…In a 32 nm device, 1 the gate oxide thickness should be further reduced, but this is not possible due to an increase in relative leakage current. [2][3][4] The combination of a high-k dielectric gate film and a suitable metal gate effectively solved this problem. [5][6] In the context of materials processing for the 28 nm technology node, a specific application of Al-CMP is found in the "gatelast" integration scheme for high-k/metal gate transistors.…”

mentioning

confidence: 99%

Effect of Glycine and TT-LYK in Alkaline CMP Slurry on Controlling the Galvanic Corrosion at Al-Co Interface

Wang

Sun

Niu

et al. 2019

As the feature size of integrated circuit (IC) shrinks down to 28nm and below, aluminum (Al) is considered to be one of the suitable gate materials, and cobalt (Co) is considered to be one of the suitable barrier materials. During chemical mechanical polishing (CMP) of the Al-Co gate, galvanic corrosion can occur when two kind of metals with a large open circuit potential (Eoc) difference contact with each other within the device architecture and are exposed to charge conducting CMP slurries. Al is severely corroded as an anode in the presence of Co because the standard electrode potential (E = −1.66 V) is lower than that of Co (E = −0.27 V). In this paper, using the advantages of different materials in adsorption and dissolution of different metal, the effect of glycine and TT-LYK (TT) with different concentrations on galvanic corrosion of Al and Co was studied by potentio dynamic and static polarization measurements with impedance monitoring. The potential different between Al and Co electrodes was significantly reduced for selective adsorption characteristics of the complex formed by glycine with Al and Co significantly reduced the potential difference between Al and Co electrodes. The substances formed by TT with Al and Co can be adsorbed on both surfaces well, and the current difference between Al and Co electrodes can be significantly reduced due to the difference in solubility of the reactants. When glycine and TT were used synergistically, the dynamic corrosion potential (Ecorr) difference between Al and Co electrodes was reduced to 10 mV, and the static Ecorr difference was reduced to 17 mV with glycine concentration of 1000 ppm and TT concentration of 100 ppm. The dynamic corrosion current (Icorr) difference was 0.587μA/cm2, and the static Icorr difference was 2.361μA/cm2.

“…1 In 32 nm and less device, the gate oxide thickness should be further reduced, but this is not possible due to an increase in relative leakage current. [2][3][4] The high-k dielectric gate film combined with a suitable metal gate had effectively solved this problem. 5,6 In the context of materials processing for the 28 nm technology node, a specific application of Al-CMP is found in the "gatelast" integration scheme for high-k/metal gate transistors.…”

mentioning

confidence: 99%

Effect of Cystine in Alkaline CMP Slurry on Controlling the Galvanic Corrosion at Al-Co Interface

Wang

Sun

Niu

et al. 2019