Wafer processing flow

FIGURE 3.1 A typical wafer processing flow that shows that CMP is an integral part of the manufacturing process (from Ref. 1). 

The membranes of the microhotplates were released by anisotropic, wet-chemical etching in KOH. In order to fabricate defined Si-islands that serve as heat spreaders of the microhotplate, an electrochemical etch stop (ECE) technique using a 4-electrode configuration was applied [109]. ECE on fully processed CMOS wafers requires, that aU reticles on the wafers are electrically interconnected to provide distributed biasing to the n-well regions and the substrate from two contact pads [1 lOj. The formation of the contact pads and the reticle interconnection requires a special photolithographic process flow in the CMOS process, but no additional non-standard processes. 

Figure 11.3 Process flow from silicon feedstock to wafers for the case of multicrystalline silicon.

A clean silicon surface is critical in the production of smaller and faster logic and memory devices. A typical process flow for advanced integrated circuits consists of 300 to 500 steps, 30% of them being wafer cleaning operations. Trace amounts of impurities such as Na+ ions, metals, and particles are especially detrimental in the reliability of flnished devices. This is the main reason why nonvolatile reactants (alkali, alkaline earth as well as any metal... 

Modifed PTFE can be used in practically all applications, where the conventional polymer is used. In addition to that, new applications are possible because of its improved flow and overall performance. In the chemical process industry, it is used for equipment linings, seals, gaskets, and other parts, where its improved resistance to creep is an asset. In semiconductor manufacturing, modified PTFE is used in fluid handling components and in wafer processing components. Typical applications in electrical and electronic industries are connectors and capacitor films. Other applications are in unlubricated bearings, laboratory equipment, seal rings for hydraulic systems, and antistick components.103... 

An important component in the process flow is a through-wafer via with a nitride liner (and metal fill) that can act as an etch stop for the grinding and polishing wafer-thinning step. This capability allows uniform thinned layers and could provide good wafer-scale planarity for subsequent processing (although characterization of wafer-level planarization has not been reported to date) [41]. Available product information describes the performance and specifications of 3D components [40,42]. 

CMP cost is split between capital cost (cost of CMP tools and slurry delivery tools) and cost of consumables (pads, slurries, and consumable parts). By increasing the run rates (number of wafers processed per hour) of tools, both capital cost and cost of consumables can be decreased. Higher run rates require fewer tools, fewer tools require fewer consumables. Consumable cost can be further cut by extending the lifetime of consumables (if a pad can be made to last twice as long, then the pad cost will be cut in half) or the consumption rate of consumables (slurry flow rate, for example). 

The test wafers had the following process flow. After the deposition of 200 nm of oxide the metal stack with a total thickness of 2200 nm was sputtered. The wafers... 

Unlike W plasma etch back process, the typical W CMP process usually removes the adhesion layer such as Ti/TiN or TiN during the primary polish. As a result, during the over polish step there is some oxide loss. Since the oxide deposition, planarization CMP (oxide CMP), and tungsten CMP steps are subsequent to each other, the oxide thickness profile could become worse further into the process flow. Therefore, the across-wafer non-uniformity of the oxide loss during W CMP process is one of the very important process parameters needs to be optimized. To determine the effect of the process and hardware parameters on the polish rate and the across-wafer uniformity, designed experiments were run and trends were determined using analysis of variance techniques. Table speed, wafer carrier speed, down force, back pressure, blocked hole pattern, and carrier types were examined for their effects on polish rate and across-wafer uniformity. The variable ranges encompassed by the experiments used in this study are summarized in Table I. 

Today, a typical process flow for advanced ICs consists of 300 to 500 steps, 30% of which are wafer cleaning steps." Many process steps during IC fabrication may introduce contamination, which must be cleaned before the next process step. For example, in processes such as steam oxidation, resist etching, and ion implantation, metallic contamination typically introduces a surface concentration of 10 to lO Vcm. The need for wafer cleaning can be separated into three areas (1) preparation of the wafer surfaces for oxidation, diffusion, deposition, and metallization (2) preparation for the application of photoresist and (3) removal of photoresist after the etching process." ... 

The manufacturing processes represent the link between the reliability issues of the microstructure on one hand and those of assembly and packaging on the other. The process flow must take into account, for example, the impact of the applied temperature range, pressure, and media on the sensor structure, which at the time of packaging is already completed. Dicing of sensor structures that include delicate elements, such as freestanding cantilevers or thin membranes, is usually very critical and requires some kind of protection which can be effectively provided by zero-level packaging on the wafer scale. 

A possible fabrication process flow for a single 90-nm technology node microprocessor CMOS inverter, consisting of two transistors— nMOS and pMOS—is presented in this section. Cross-sectional views of the inverter are provided for each major operation, with the operations involving lithographic masking called out with thicker lines, where possible. It must be noted that the illustration is for only a small microscopic area of a microprocessor that is one of hundreds of microprocessors that may populate a given 300-mm wafer at the end of the fabrication process. 

The process flow-sheet does not show the unit processes in preparing the wafer, nor the final assembly and packaging processes. With higher and higher density chips, the assembly and packaging may prove to be a bottleneck. The choice of a particular unit process depends on a variety of factors including experience in using the process and economics. 

Electrical measurement of the dielectric constant is done through the fabrication of metal—oxide—semiconductor capacitor structures, where the ULK serves as the dielectric of the capacitor. A doped Si wafer is used as the substrate, on which the ULK film is deposited. This ULK film is subjected to CMP, say, or any other process whose impact on ULK characteristics needs to be quantified. An aluminum film is deposited on the backside of the Si wafer to form one of the capacitor contacts. Using a shadow mask, aluminum dots of varying diameters are evaporated onto the surface of the ULK film, to form the other terminal of the capacitor. Each aluminum dot is probed to measure its capacitance (at about 100 kHz). Evaporation through a shadow mask allows for the formation of metal contacts without altering the dielectric further— as would be the case if reactive-ion-etch were used to form the contacts. (It should be noted that more complex process flows can be used to eliminate concerns such as dot-size variation, the effect of probe-tip impact on the dielectric being tested, etc.) The results of electrical measurement of the k-value increase post-CMP of the variety... 

Metrology plays a cmcial role in enabling any type of CMP process control, and can be implemented in different ways based on the measurement techniques used, its location in the process flow, and the type and amount of data generated. During the CMP cycle, pad characteristics such as the thickness, the Young s modulus, and viscous properties of the pad tend to be dynamic. Therefore measurement of these properties is very important towards understanding polishing nonuniformity and the maintenance of acceptable WIWNU and wafer-to-wafer nonuniformity. 

Fig. 1 Common process flows for electrochemically etched (porosified) silicon wafers...

Fig. 14. Schematic depicting a flip chip technology utilizing chips with micromachined poljrmer bumps, (a) Process flow for creating micromachined polymer bumps in the wafer state, (b) Die attachment to a chip carrier.

Figure 17.4 Process flow used to fabricate the prototype ultrasonic transducers (a) a silicon (Si) wafer is micromachined to create an array of holes with diameters between 0.75 and 2.00 mm, after which the wafer is then thermally oxidized to grow a 1.5 pm thick S1O2 layer (b) the wafer is then diced into 1 cm wide square die (c) the die is laid flat onto a piece of free-standing F DF film in a jig (the die is now viewed in cross-section through the hole) (d) the die and PVDF film are clamped into the jig against an O-ring forming an air-tight seal, and air pressure is applied to the face of the PVDF film to deflect it into the desired spherical shape (e) finally, conductive epoxy is injected into the hole and a 30 gage wire is potted into the epoxy the air pressure is maintained until the epoxy cures, then the transducer chip is removed from the jig.

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