There are many ways to metallize, and today we will introduce the most common metallization process.
1. What is metallization?
Metallization refers to the process of forming a patterned conductive metal film on a wafer.
2. What is the role of metallization? 2.1 Interconnection: Primarily used to interconnect different electronic components, such as transistors, resistors, and capacitors. An IC consists of hundreds of millions or even billions of transistors, which operate in parallel on a silicon wafer. However, if these transistors cannot conduct to each other, they cannot perform their intended functions. These interconnecting metal circuits act like the blood vessels of the IC, ensuring the smooth transmission of electronic signals between different components.
2.2 Acting as a barrier layer
The function of a barrier layer is to prevent electron migration between different metal layers, isolate them from each other, and prevent diffusion or penetration of substances. Additionally, barrier layers are sometimes used as adhesion layers between other material layers, ensuring that newly deposited material adheres firmly to the substrate.
Typical barrier layer materials include titanium, titanium nitride, titanium tungstenide, tantalum, and tantalum nitride. For example, aluminum readily reacts with silicon. When aluminum needs to be wired on silicon, a barrier metal (TiN, TiW) needs to be placed between the two as a barrier.
2.3 Protective function
Metallization acts as a protective layer, tightly wrapping around the surface of a reactive metal to prevent chemicals, moisture, or oxygen from penetrating the chip and thus preventing corrosion. For example, copper exposed to air will gradually form a copper oxide layer. To prevent this, a corrosion-resistant metal, such as palladium, gold, or nickel, can be applied to the copper conductors.
3. What are the methods of metallization?
3.1PVD
Sputtering: Using high-energy ions to bombard a target material, causing the atoms or molecules of the target material to sputter and deposit onto a substrate. Electron beam evaporation: Using a high-energy electron beam to heat a metal, causing it to evaporate and deposit onto a substrate.
3.2 CVD involves reacting gaseous precursors on a wafer to form the desired thin film deposited on the wafer surface. CVD can be used to deposit various metals, such as tungsten, copper, and titanium. The main methods include MOCVD, LPCVD, PECVD, and ALD, with common reaction formulas as follows:
TiCl4 + 2H2 → Ti + 4HCl
WF6+3H2—>W+6HF
3.3 Electroplating
Electroplating involves applying an electric current and utilizing electrochemical principles to deposit metal onto the wafer surface. Common electroplating materials include elemental metals such as Cu, Ni, Au, and Sn, as well as their alloys. For example, Cu is the primary metal for interconnects. Since copper cannot be dry-etched, the interconnect metal filling process must be performed using a double damask process.
3.4 Chemical plating
Metallization in wafer fabrication typically involves depositing metal onto the wafer surface using chemical reactions without applying electricity. Commonly deposited metals include elemental metals such as Ni, Pd, and Au. These are the main methods for metallization in wafer fabrication processes, and the appropriate method can be selected based on design requirements and actual needs.
