Stealth Dicing™ technology

Stealth Dicing technology is a laser dicing technology that uses lasers, with a completely new concept. The range of devices to which this technology applies will be expanding to include MEMS devices and memory devices and others, due to such features as the "completely dry process", "no kerf loss", "no chipping", "high bending strength" and the like.

Technical information of principles, features, and the latest technological trends
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This documents introduces the principles, features, latest technological trend, process, and the environmental contribution of Stealth Dicing technology after sorting out the problems faced by conventional dicing technologies. Please feel free to apply for it.

The video shows the principle and features of Stealth Dicing technology, Stealth Dicing technology dedicated optical system LBA (Laser Beam Adjuster) for Stealth Dicing to realize the throughput improvement, and SDBG (Stealth Dicing Before Grinding) process which is for ultra-thin chip devices less than 50 µm. Please have a look at the video.

Principle

Stealth Dicing technology is a technology that focuses a laser beam of a wavelength that permeates through materials, focus internally and forms a starting point for cracking the wafer (modified layer: Stealth Dicing layer, hereinafter referred to as the "SD layer"), then applies external stress to the wafer, separating it. The process is comprised primarily of two parts, namely the "laser irradiation process" in which the SD layer is formed to crack the wafer interior and the "expansion process" for separating the wafer.

Process 1: Laser irradiation process

A laser beam is focused inside a wafer to form SD layers to separate the wafer. Cracks are also formed from the SD layer, which is formed internally, towards the top and bottom surfaces of the wafer, and these cracks are connected along the line of planned cutting by scanning with the laser beam. Furthermore, to cut thick wafers such as an MEMS device, multiple SD layers are formed in the directions of thickness and cracks are then connected.

The four modes of the SD layer must be used according to the purpose; these are combined to derive optimum processing conditions. Optimum processing conditions exists according to the state of a semiconductor device, such as the thickness of the wafer or the shape of chips, as well as whether any metallic film is present and the like.

Laser irradiation principle

Photograph of SD layer inside a Si wafer

Behavior of SD layer

ST: Stealth
Cracks have not reached the top and bottom surfaces

HC: Half-cut
The crack has reached the top surface

BHC: Bottom side half-cut
The crack has reached the bottom surface

FC: Full-cut
The crack has reached the top and bottom surfaces

Process 2: Expansion process

External force is applied on a wafer in which an SD layer has formed by uniformly tensing the tape in the peripheral direction by tape expansion or the like. This applies tensile stress to the internal crack state of the wafer and extends the cracks to the top and bottom surface, separating the wafer.

Since wafer separation is performed by extending cracks, there is no stress on the device. Furthermore, since there is fundamentally no kerf loss, this can lead to an improvement of chip yield.

Before expansion

After expansion

Expansion (crack extension) principle

1. Tape is extended in a peripheral direction

2. Tensile stress extends internal crack state the wafer

3. Cracks reach the top surface and separate the wafer

Photographs of MEMS devices with a membrane structure cut using Stealth Dicing technology and devices that have protective film and metallic film are shown. This achieves a sharp dicing quality with no chipping on top and bottom surface of the chip. Favorable dicing results with no damage or adhesion of contaminants to the membrane structure at the center of the chip are achieved.

Device photographs

MEMS device with membrane structure

Device with protective and metal films

Features

Differences with conventional technologies

The Stealth Dicing technology resolves problems of blade dicing and ablation dicing with its radical principle.

Blade dicing

A diamond grinding wheel is turned at high speeds to cut wafers with the blade dicing technology, which presents the following types of problems.

○ Stress loads and recontamination due to vibration and cooling water

○ Deterioration of strength due to chipping

○ Fracture and contamination of fragile structure by scattered matter

(Addition of forming process and removal process for protective films)

○ Limitation of chip yield
○ Limitation of processing speed

Ablation dicing

Ablation dicing is a dicing technology that uses a laser. A laser beam is focused on the top surface of a wafer to carve a groove into the wafer to cut it with the ablation dicing technology, which presents the following types of problems.

○ Deterioration of strength due to a thermal effect known as the HAZ (Heat Affected Zone)