As advanced packaging evolves toward large form factors, high-density interconnects, and high-frequency/high-speed applications, glass substrates—with their excellent dimensional stability, low dielectric loss, and compatibility with TGV (Through-Glass Via) interconnection processes—are transitioning from material validation to process development and engineering verification.

In the TGV glass substrate process, CMP after electroplating filling is not merely about removing the surface copper layer. It must also simultaneously address surface copper overburden removal, via-area local dishing, total thickness variation (TTV), warpage, surface defects, and compatibility with subsequent RDL processes. These metrics are interrelated and directly affect the process window for subsequent lithography, redistribution wiring, and high-density interconnects.

Recently, SiPlus Semiconductor assisted a leading domestic glass substrate manufacturer in conducting a series of process validations for TGV glass substrate CMP. Based on the customer’s sample structure, plating condition, and target requirements, the team performed multiple rounds of parameter and process condition optimizations for CMP and, where specific needs dictated, a double‑side polishing scheme.

TGV Glass Substrate CMP: More Than Just Removing Surface Copper Overburden

After TGV filling, an electroplated copper layer forms on the glass substrate surface. CMP must first accomplish the removal of the surface copper overburden, while simultaneously controlling local dishing in the via areas and the overall surface topography.

For the glass‑copper composite structure, the two materials exhibit different mechanical removal and chemical reaction behaviors. Parameters such as slurry chemistry, delivery method, polishing pressure, rotational speed, pad condition, and processing time must be synergistically matched.

If dishing becomes too large, it may compress the process window for subsequent RDL fabrication, lithography focus, and fine‑line patterning. Therefore, the core of the CMP process is not simply removing the copper layer, but rather establishing a reasonable process balance among copper removal, local topography control, and overall surface shape improvement.

CMP as the Foundation, Double‑Side Polishing for Specific Requirements

In TGV glass substrate processing, CMP typically undertakes the primary tasks of removing the surface copper overburden and planarizing the working surface. By matching slurry chemistry, delivery conditions, pressure, speed, and pad condition, the process can be adjusted for different copper thicknesses, via structures, and incoming material states.

For samples that impose stricter requirements on overall surface shape, TTV, or warpage control, double‑side polishing can be introduced as a supplementary process on top of CMP. Through coordinated machining of both the front and back sides, double‑side polishing serves as an additional solution for specific needs, further improving the overall flatness and warpage performance of the sample.

Multiple Rounds of Process Iteration to Optimize Key Parameter Combinations

For this customer’s samples, the SiPlus team made adjustments in the following key areas:

• Slurry type switching and ratio optimization;

• Upgrading the delivery system with high‑precision peristaltic pumps;

• Fine‑tuning polishing pressure and speed parameters;

• Matching the physical state of the polishing pad with chemical reaction rate and mechanical removal capability;

• Feedback adjustments based on processing results for Cu removal, dishing, and shape evolution.

This debugging was not an isolated adjustment of a single parameter, but rather a coordinated matching of equipment, consumables, materials, and process conditions. After multiple verification rounds, the team established a process condition screening for this type of sample and initially built the parametric correlation among Cu removal, local dishing control, and overall surface shape improvement.

Key Verification Results

Under the specific sample structure, plating condition, and process settings, the following results were achieved in this phased validation:

• After process optimization, the Cu layer on both front and back surfaces of the samples was completely removed;

• Via‑center dishing was reduced from 16–18 μm under the initial process conditions to 0.3–0.6 μm;

• Sample TTV remained at a good level, meeting the process target for this run;

• Sample warpage was reduced from an incoming value of 75.662 μm to 11.508 μm, showing significant overall shape improvement.

The reduction of via‑center dishing from 16–18 μm to 0.3–0.6 μm is an important achievement of this process optimization. This improvement is related to the synergistic adjustment of factors such as pad condition, slurry chemical reactivity, oxidizer proportion, mechanical removal action, delivery stability, and processing time.

From Equipment Capability to Process Adaptability

For glass substrate CMP, the equipment itself provides the foundation for process implementation, but the final processing result depends on the matching among equipment parameters, consumable systems, material states, and process control.

SiPlus’s verification covered equipment parameter adjustment, consumable and delivery condition matching, processing result inspection, and process feedback optimization. The team’s capability extends beyond merely achieving copper removal; it also encompasses integrated control over local topography, overall surface shape, and process windows.

For different sample structures, dimensions, via conditions, plating thicknesses, and target metrics, SiPlus can tailor the process accordingly: using CMP to remove copper overburden and planarize the working surface, or introducing double‑side polishing as a supplementary optimization for specific overall shape and warpage requirements. At the same time, by matching slurry, delivery system, pad, pressure, and speed conditions, the process improves dishing and surface morphology, and continuously adjusts process conditions based on test results, enhancing the adaptability of both equipment and process schemes to various sample types.

This synergy between equipment and process capability is of significant importance for the subsequent introduction of TGV glass substrates into RDL, lithography, and high‑density interconnection processes.

As glass substrates move from material validation to engineering application, it remains necessary to continuously address the processing adaptability and process stability issues arising from different structures, incoming material states, and diverse target specifications. In the future, SiPlus will continue to focus on high‑precision cutting, grinding, and polishing equipment and process applications in the semiconductor and advanced packaging fields, providing precision processing support for the engineering application and volume manufacturing of TGV glass substrates, wafers, and other advanced packaging materials.