Cap Layer Protects Metal Gate During Contact Plug Formation
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Solution Overview
Problem
Conventional semiconductor manufacturing processes face challenges in maintaining the integrity of metal gates due to exposure to cleaning solutions and etchants during the formation of contact plugs, leading to performance issues such as boron penetration and depletion effects.
Innovation Solution
A method is developed to form semiconductor structures with contact plugs where a cap layer completely covers the gate structure, preventing exposure to cleaning solutions and etchants by forming openings on both sides of the gate structure to create precise positions for the contact plugs, ensuring the gate structure remains intact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple photolithography processes are performed during conventional contact plug formation, then contact plugs can be formed with precise positioning, but the metal gates are exposed to cleaning solutions and etchants which deform or damage them
Solution Approach 1:
A cap layer is introduced as an intermediary protective element between the metal gate and the harmful cleaning solutions/etchants used during photolithography processes. The cap layer completely covers the metal gate structure, allowing multiple photolithography steps to be performed for precise contact plug positioning while the cap layer shields the metal gate from damage. After contact plug formation, the cap layer is removed to expose the intact metal gate for subsequent wiring formation.
2Ease of manufacture
If the gate structure is exposed during contact plug formation processes, then cleaning and etching can be performed, but the metal gate material properties are compromised
Solution Approach 1:
The cap layer is formed in advance before any contact plug formation processes. This preliminary action completely covers the metal gate structure, preventing exposure to cleaning solutions and etchants during subsequent photolithography and etching steps. The cap layer remains in place throughout the contact plug formation process, ensuring metal gate material stability, and is removed only after contact plugs are successfully formed.
3Ease of manufacture
If conventional poly-silicon gate is used, then manufacturing is simpler, but boron penetration and depletion effects occur which reduce device performance
Solution Approach 1:
The gate material is changed from conventional poly-silicon to work function metals (such as tungsten, molybdenum, or their nitrides). This parameter change in material composition eliminates the boron penetration and depletion effects that plague poly-silicon gates, thereby maintaining high gate capacitance and driving force. The cap layer process enables this advanced metal gate structure to be manufactured with the same level of process control as conventional gates.
Data Source
AI summary
A method of forming a semiconductor structure having at least a contact plug includes the following steps. At first, at least a transistor and an inter-layer dielectric (ILD) layer are formed on a substrate, and the transistor includes a gate structure and two source/drain regions. Subsequently, a cap layer is formed on the ILD layer and on the transistor, and a plurality of openings that penetrate through the cap layer and the ILD layer until reaching the source/drain regions are formed. Afterward, a conductive layer is formed to cover the cap layer and fill the openings, and a part of the conductive layer is further removed for forming a plurality of first contact plugs, wherein a top surface of a remaining conductive layer and a top surface of a remaining cap layer are coplanar, and the remaining cap layer totally covers a top surface of the gate structure.