Oven - HMDS Pretreatment Vacuum Drying Oven - Wafer Coating and Film Deposition Oven

HMDSPre-treatment Vacuum Dryer

The necessity of pre-treatment systems:

In semiconductor manufacturing processes, photolithography is a crucial step in transferring integrated circuit patterns, and the quality of the coating directly affects the photolithography process. The coating process becomes even more essential, especially when the etched lines are very fine. Any minor flaw in any stage can lead to the failure of photolithography. Most photoresists are hydrophobic in the coating process, while the hydroxyl groups and residual water molecules on the wafer surface are hydrophilic. Directly coating the wafer surface can result in poor adhesion between the photoresist and the wafer, potentially causing localized gaps or bubbles, affecting the coating thickness and uniformity, thereby impacting the photolithography results and development. This is particularly true for positive photoresists, where the developer can easily penetrate the interface between the photoresist and the wafer, leading to issues like smearing and floating resist, which can cause the failure of pattern transfer. Wet etching is also prone to lateral etching. Therefore, introducing a chemical agent HMDS (Hexamethyldisilazane) in the coating process can significantly improve the situation. After applying HMDS to the wafer surface, heating it in an oven allows for a reaction that forms a compound mainly consisting of siloxanes. This is a surfactant that successfully changes the wafer surface from hydrophilic to hydrophobic. Its hydrophobic groups can effectively bond with the photoresist, acting as a coupling agent.

Section II: Product Structure and Performance

2.1Product Structure:

1The equipment housing is made of high-quality cold-rolled steel plates with electrostatic spraying, and the inner shell is constructed from 316L stainless steel material; seamless stainless steel heating tubes are evenly distributed on the outer wall of the inner shell, with no electrical components or flammable explosive devices inside; tempered, bulletproof double-layer glass observation window for easy observation of the items and experiments inside the working chamber.

2The box door features adjustable tightness, with an overall molded silicone door seal ring to ensure the box maintains a high vacuum level.

3．Microcomputer PID temperature control, featuring automatic temperature control, timing, over-temperature alarm, with an LCD display and touch-sensitive buttons for accurate and reliable temperature control.

4The intelligent touch screen control system is paired with a Mitsubishi PLC module, allowing users to modify the program, temperature, vacuum level, and each program duration based on different process conditions.

5．The HMDS gas enclosed automatic suction and addition design ensures excellent sealing performance of the vacuum box, eliminating concerns of HMDS gas leakage.

6Non-dust generating material, suitable for use in a 100-class cleanroom environment.

2.2Product Performance:

1.Due to the HMDS treatment following numerous nitrogen purges, dust interference is eliminated. The system integrates the dehydration baking and HMDS treatment into a single process, conducted within the same container. The wafer first undergoes a dehydration baking at 100°C to 200°C, followed by the HMDS treatment, without being exposed to the atmosphere. This significantly reduces the wafer's absorption of water molecules, resulting in superior processing outcomes.

2.Due to its application as a vapor onto the wafer surface, it boasts a superior uniformity that cannot be matched by liquid coating methods.

3.Liquid coating is a single-chip operation, while this system can process up to 4 trays of wafers at once, offering high efficiency.

4.Applying liquid HMDS to a single wafer requires more solvent than treating four wafers with this system, which has been proven in practice to be more cost-effective in solvent usage.

5. HMDSThis is a toxic chemical substance, inhaling which can cause nausea, vomiting, and irritation to the chest and respiratory tract. Since the entire process is carried out in an enclosed environment, there is no risk of exposure to the liquid or its vapor, making it safer. The exhaust gases are directly pumped to the exhaust gas treatment unit by mechanical pumps, thus ensuring no environmental pollution and contributing to a more eco-friendly and secure operation.

Section 3: HMDS Oven Technical Specifications

IV. Principle of the HMDS Pretreatment System:

HMDSThe pretreatment system, by adjusting parameters such as working temperature, processing time, and holding time during the HMDS pretreatment of the furnace, can uniformly coat a layer of HMDS on the surface of silicon wafers and substrates. This reduces the contact angle of the silicon wafers after HMDS treatment, decreases the amount of photoresist used, and improves the adhesion between the photoresist and the silicon wafer.

V. General Workflow of the HMDS Pretreatment System:

Firstly, determine the working temperature of the furnace. A typical pretreatment program includes: turning on the vacuum pump to evacuate, waiting until the chamber reaches a certain high vacuum, then start to fill with nitrogen, fill to a certain low vacuum, and then repeat the process of evacuating and filling nitrogen. After reaching the set number of nitrogen fills, maintain for a period to allow the wafer to heat up sufficiently and reduce moisture on the wafer surface. Then, start the evacuation process again, fill with HMDS gas, and stop filling HMDS after reaching the set time, entering the holding phase to allow the wafer to fully react with HMDS. After reaching the set holding time, start the evacuation process again, fill with nitrogen, and complete the entire operation. The reaction mechanism between HMDS and the wafer is as follows: first heat to 100℃-200℃To remove moisture from the silicon wafer surface, then HMDS reacts with the surface OH groups, forming siloxanes on the silicon wafer surface. This eliminates hydrogen bonding, converting the polar surface into a non-polar one. The reaction continues until steric hindrance prevents further reaction.

The unboxing temperature can be set by the user to reduce processing time. The normal process takes 50 to 90 minutes (depending on the baking time required for the product), excluding the cooling time (as the cooling time is standard).

Six: Exhaust Emission

Excess HMDS vapor (exhaust) will be extracted by a vacuum pump and discharged into a dedicated waste gas collection pipeline. Special treatment is required in the absence of a dedicated waste gas collection pipeline.