Selective Titanium Deposition for CMOS Work Function Control

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Solution Overview

Problem

Existing methods for forming CMOS devices using dual-metal/dual-work function gates face issues with titanium nitride residue generation and damage to the underlying tantalum nitride barrier layer during etching in the NMOS region.

Innovation Solution

A method involving the deposition of a metal nitride barrier layer and a titanium layer on a substrate with selective removal of the titanium layer from the NMOS region using diluted HF or hydrogen peroxide-sulfuric acid, followed by transformation into a titanium nitride work function layer without damaging the barrier layer, and subsequent deposition of N work function metal layers and conductive layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the titanium nitride layer is removed by etching in the NMOS region, then the work function layer can be re-deposited, but titanium nitride residues are generated and the underlying tantalum nitride barrier layer is damaged

Engineering Contradiction:

Improvework function layer re-depositionVSAvoidresidue generation and barrier layer damage

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by depositing the titanium layer selectively only in the PMOS region before the NMOS region, so that when the NMOS region requires work function adjustment, there is no titanium layer to remove, thus avoiding residues and barrier layer damage while still allowing subsequent N-type work function layer deposition

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of the conventional approach of depositing titanium nitride in both regions and then etching it from the NMOS region, the patent inverts the sequence by selectively depositing titanium only in the PMOS region, thereby eliminating the need for etching operations that cause residues and damage

Inventive Principle:

Principle #13The other way round (Inversion)

2Adaptability or versatility

If a dual-metal gate structure is used for PMOS and NMOS, then different work functions are achieved, but the process complexity increases with multiple deposition and etching steps

Engineering Contradiction:

Improvedifferent work functions for PMOS and NMOSVSAvoidmultiple deposition and etching steps

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies local quality by implementing different gate metal configurations in different regions: P-type work function metals (such as titanium nitride) are deposited only in the PMOS region, while the NMOS region receives N-type work function metals (such as titanium aluminum), thereby achieving region-specific work functions without requiring etching of previously deposited layers

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The selective deposition of P-type work function metals is performed as a preliminary action only where needed (PMOS region), allowing subsequent N-type metal deposition in both regions without conflict, thereby simplifying the overall process sequence

Inventive Principle:

Principle #10Preliminary action

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 prevents residue formation and minimizes damage to the underlying barrier layer, ensuring precise work function layer formation for both PMOS and NMOS regions, enhancing the manufacturing process for CMOS devices.

Implementation Method 1

The titanium layer is selectively removed from the second device region by using diluted HF or hydrogen peroxide-sulfuric acid mixture (SPM)

Methodology Applied

Scientific EffectChemical etching:

Implementation Method 2

The titanium layer in the first device region is then transformed into a titanium nitride layer. The titanium nitride layer is a work function layer on the first device region

Methodology Applied

Scientific EffectNitridation: Nitriding

Implementation Method 3

A metal nitride barrier layer is deposited to cover the first device region and the second device region

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Implementation Method 4

A metal nitride barrier layer is deposited to cover the first device region and the second device region

Methodology Applied

Scientific EffectChemical vapor deposition: Chemical Vapour Deposition

Data Source

PatentUS20220367192A1Method of forming a semiconductor device

Publication Date: 2022.11.17 UNITED MICROELECTRONICS CORP

AI summary

A method of forming a semiconductor device is disclosed. A substrate having a first device region and a second device region is provided. A metal nitride barrier layer is formed to cover the first device region and the second device region. A titanium layer is deposited on the metal nitride barrier layer. The titanium layer is selectively removed from the second device region, thereby exposing the metal nitride barrier layer in the second device region. The titanium layer in the first device region is transformed into a titanium nitride layer. The titanium nitride layer is a work function layer on the first device region.