Polysilicon Plug Germanium Doping for Low Contact Resistance
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Solution Overview
Problem
In semiconductor devices, particularly in miniaturized DRAMs, forming a metal silicide layer with sufficient thickness is challenging due to the adverse effects of heat treatment on semiconductor elements, which complicates the formation of ohmic contacts and increases contact resistance.
Innovation Solution
Introducing predetermined impurities, such as germanium, into polycrystalline silicon prior to forming a metal silicide layer allows for the formation of a metal silicide layer with sufficient thickness during a short heating period, reducing contact resistance and enabling a hybrid structure with three layers: polycrystalline silicon, metal silicide, and a conductive film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is performed to form a metal silicide layer on a polysilicon plug, then an ohmic contact can be achieved, but the heat treatment causes adverse effects on semiconductor elements and insufficient silicidation when contact height is reduced
Solution Approach 1:
The patent introduces predetermined impurity (germanium) into the polysilicon plug before forming the metal silicide layer. This preliminary doping action modifies the polysilicon properties in advance, enabling sufficient silicidation to occur during a shortened heat treatment period, thus achieving both adequate contact quality and protection of semiconductor elements from excessive heat exposure
Solution Approach 2:
The patent changes the chemical composition parameter of the polysilicon plug by introducing germanium impurity. This parameter change alters the silicidation kinetics, allowing the metal silicide layer to form with sufficient thickness in a shorter time, thereby resolving the contradiction between achieving ohmic contact and minimizing heat treatment duration
2Length of stationary object
If the contact height is reduced to maintain low device profile, then the thickness of interlayer insulating film becomes thinner, but the heat treatment for silicidation becomes insufficient
Solution Approach 1:
By introducing germanium impurity into the polysilicon plug, the patent changes the material parameters to accelerate silicidation kinetics. This enables the formation of a sufficiently thick metal silicide layer even when the overall contact height is reduced, as the enhanced doping concentration compensates for the reduced thermal diffusion time in shorter contacts
Solution Approach 2:
The preliminary introduction of germanium impurity into the polysilicon plug prepares the material in advance for rapid silicidation. This preliminary action ensures that when the contact height is reduced and heat treatment time is shortened, the silicidation process can still complete adequately within the constrained geometry
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 approach reduces contact resistance by approximately 40% and allows for the refinement of semiconductor devices by ensuring a sufficient metal silicide layer thickness without compromising the integrity of semiconductor elements, enhancing the performance of both memory cell and peripheral circuit regions.
Implementation Method 1
metal, such as titanium, cobalt and nickel, for forming a silicide with silicon are formed as film on the polysilicon plug and the films are heated by lamp annealing to be silicidated
Implementation Method 2
the films are heated by lamp annealing to be silicidated
Implementation Method 3
Generally, a contact between metal and silicon is a Schottky contact
Implementation Method 4
an ohmic contact successfully can be achieved by interposing a metal silicide layer between metal and silicon
Data Source
AI summary
In order to achieve the reduction of contact resistance by forming a metal silicide layer with a sufficient thickness in an interface between a polycrystalline silicon plug and an upper conductive plug, the polycrystalline silicon plug contains germanium, which is ion-implanted before forming the metal silicide layer.