Alkaline Pretreatment for Electroplating Seed Layers
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Solution Overview
Problem
During electroplating of semiconductor wafers, acid-sensitive seed layers, such as nickel-containing layers, are prone to corrosion and void formation due to imbalances in the electrolyte composition, leading to defects in filled recessed features.
Innovation Solution
A pretreatment method involving a pre-wetting liquid with a pH between 7 and 13, typically using a borate or carbonate buffer, is applied to the wafer substrate before electroplating, creating an alkaline environment that protects the seed layer and allows for void-free electrofilling with acidic plating solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an acidic plating solution is used for electroplating, then the electroplating process can proceed effectively, but the nickel-containing seed layer suffers from corrosion and damage
Solution Approach 1:
The patent applies a preliminary alkaline pretreatment step before electroplating. The wafer is contacted with an alkaline solution (pH 7-13) containing a buffer (borate, carbonate, or phosphate) and a wetting agent to modify the seed layer surface and establish a protective alkaline environment. This preliminary action prepares the seed layer to resist subsequent acidic plating solution corrosion while maintaining electroplating effectiveness.
2Device complexity
If electroplating is performed directly without pretreatment, then the process is simple and fast, but voids and defects form in the filled recessed features
Solution Approach 1:
The patent introduces a preliminary alkaline pretreatment step that modifies the seed layer surface and establishes favorable conditions for subsequent electroplating. This pretreatment prevents void formation and defects during the electrofilling process by creating a controlled interface between the seed layer and plating solution, thereby improving fill quality without significantly complicating the overall process.
3Productivity
If the plating solution pH is kept low (acidic), then good electroplating performance is achieved, but acid-sensitive seed layers are damaged
Solution Approach 1:
The patent applies a preliminary alkaline treatment that creates a protective environment for the seed layer before exposure to acidic plating solution. The alkaline solution modifies the seed layer surface properties and establishes a buffer capacity that protects against acid attack during subsequent electroplating, thereby maintaining both electroplating performance and seed layer integrity.
Solution Approach 2:
The patent changes the pH parameter of the plating solution from acidic to alkaline (pH 7-13) during the pretreatment step. This parameter change creates a protective alkaline environment that prevents acid corrosion of the nickel-containing seed layer while still allowing effective electroplating to proceed afterward.
4Reliability
If alkaline pretreatment is applied before electroplating, then seed layer protection is improved, but the process complexity increases
Solution Approach 1:
The patent introduces a single preliminary alkaline pretreatment step that can be integrated into existing electroplating processes. By applying this one-step treatment before electroplating, the seed layer is protected against acid corrosion without requiring multiple complex treatment steps, thus improving reliability while minimizing added process complexity.
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
The method significantly reduces seed layer damage and prevents void formation, enabling effective filling of recessed features without resorting to acid-free electroplating solutions, particularly beneficial for acid-sensitive nickel-containing layers.
Implementation Method 1
contacting the wafer substrate with a pre-wetting liquid, the liquid comprising a buffer and having a pH in a range of between about 7 and about 13 to pre-wet the nickel-containing layer
Implementation Method 2
creating an alkaline environment that protects the seed layer and allows for void-free electrofilling with acidic plating solutions
Implementation Method 3
electrodepositing the metal (e.g., copper) onto the nickel-containing layer using an acidic plating solution, wherein the electrodeposited metal at least partially fills the one or more recessed features
Data Source
AI summary
Prior to electrodeposition, a semiconductor wafer having one or more recessed features, such as through silicon vias (TSVs), is pretreated by contacting the wafer with a pre-wetting liquid comprising a buffer (such as a borate buffer) and having a pH of between about 7 and about 13. This pre-treatment is particularly useful for wafers having acid-sensitive nickel-containing seed layers, such as NiB and NiP. The pre-wetting liquid is preferably degassed prior to contact with the wafer substrate. The pretreatment is preferably performed under subatmospheric pressure to prevent bubble formation within the recessed features. After the wafer is pretreated, a metal, such as copper, is electrodeposited from an acidic electroplating solution to fill the recessed features on the wafer. The described pretreatment minimizes corrosion of seed layer during electroplating and reduces plating defects.