Corrosion copper

Copper CMP process is a very delicate balance between selective copper removal at the protruded area and targeted copper surface protection at the recessed area. To enhance the removal, an oxidizer and a complexing agent are commonly used in the copper CMP slurry in addition to the mechanical force provided by the abrasive particles and the pad. To protect the copper in the recessed area or avoid isotropic dissolution of copper, a corrosion inhibitor such as benzotriazole (BTA) is usually added to the slurry. BTA is very effective in protecting the copper surface from the corrosive attack. On the 

FIGURE 17.25 Massive galvanic corrosion in the case of experimental copper on Ti barrier. In the picture on the left, some lines have lost all the copper. 

Massive electrochemical attack known as galvanic corrosion [58,59] is the most severe form of copper corrosion. It can completely remove the copper from the structures (Figs. 17.25 and 17.26). It can occur when the wafers are exposed to a corrosive electrolyte for an extended period. It can also occur if the slurry does not contain enough or effective corrosion inhibitor. The source of such a galvanic potential on the patterned copper surface may be due to the fact that some copper structures connected to transistors have a different electrical potential than the rest of the wafer surface. Another possible cause of this type of galvanic potential is related to the barrier material induced metal metal battery effect. Most copper CMP slurries have been developed for Cu structures with Ta or TaN as a barrier material. In some cases, other metals may also be used in addition to the barrier metal. For example, a metal hard mask could contribute to the galvanic corrosion effects. It is also possible that some types of copper are more susceptible to corrosion that others. The grain 

FIGURE 17.26 Corrosion at the surface in an array of small lines (left) on large copper lines (right). 

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Carbonyl sulfide reacts with chlorine forming phosgene (qv) and sulfur dichloride [10545-99-0] and with ammonia forming urea and ammonium sulfide [12135-76-1]. Carbonyl sulfide attacks metals, eg, copper, ia the presence of moisture and is thought to be iavolved ia atmospheric sulfur corrosion (27,28). Its presence ia propane gas at levels above a few ppm may cause the gas to fail the copper-corrosion test. 

The most serious form of galvanic corrosion occurs in cooling systems that contain both copper and steel alloys. It results when dissolved copper plates onto a steel surface and induces rapid galvanic attack of the steel. The amount of dissolved copper required to produce this effect is small and the increased corrosion is difficult to inhibit once it occurs. A copper corrosion inhibitor is needed to prevent copper dissolution. 

Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

In addition to bonding with the metal surface, triazoles bond with copper ions in solution. Thus dissolved copper represents a "demand" for triazole, which must be satisfied before surface filming can occur. Although the surface demand for triazole filming is generally negligible, copper corrosion products can consume a considerable amount of treatment chemical. Excessive chlorination will deactivate the triazoles and significantly increase copper corrosion rates. Due to all of these factors, treatment with triazoles is a complex process. 

Internal surfaces of all tubes were severely attacked (Fig. 4.29). A brown deposit layer consisting of magnetite, iron oxide hydroxide, and silica covered all surfaces. Deposition was thicker and more tenacious along the bottom of tubes. These deposits had a distinct greenish-blue cast caused by copper corrosion products beneath the deposit. Underlying corrosion products were ruby-red cuprous oxide crystals (Fig. 4.29). Areas not covered with deposits suffered only superficial attack, but below deposits wastage was severe. 

Figure 13.64 Red, dezincified gasketed surface of a cast valve throat. Note the partial spalling of the copper corrosion product.

Figure 13.9 Stratified copper corrosion product in plug-type dezincification. Denickelification...

Figure 13.116 Porous copper corrosion products filling an internal surface depression. The edge of one crater seen in Fig. 13.11A is to the right.

Several books contain general summaries of the corrosion behaviour of copper and its alloy and the formation of copper corrosion products and methods for their identification have been described in a number of papers... 

Dissimilar metals in the same system Because of the specific action of many inhibitors towards particular metals, problems arise in systems containing more than one metal. In the majority of cases these problems can be overcome by the choice of a formulation incorporating inhibitors for the protection of each of the metals involved. With this procedure it is necessary not only to maintain an adequate concentration of each of the inhibitors but also to ensure that they are present in the correct proportion. This is because of two effects firstly, failure to inhibit the corrosion of one metal may intensify the attack on the other metal the best example of this is with aluminium and copper in the same system, and failure to inhibit copper corrosion — usually achieved with sodium mercaptobenzothiazole or benzotriazole—can lead to increased corrosion of the aluminium as a result of deposition of copper from copper ions in solution on to the aluminium surface. Secondly, an inhibitor of the corrosion of one metal may actually intensify the corrosion of another metal. Thus, benzoate is usually used to prevent the corrosion of soldered joints by nitrite inhibitor added to protect cast iron in the same system. A benzoate nitrite ratio of greater than 7 1 is necessary in these cases. 

Test method for porosity in gold platings on metal substrates by gas exposures Test method for half-cell potentials of uncoated reinforcing steel in concrete Method for detection of copper corrosion from petroleum products by the copper strip tarnish test... 

D 849 1988 Test method for copper corrosion of industrial aromatic hydrocarbons... 

The periodic development and use of new steel alloys can improve ferrous corrosion resistance however, where economizer units are constructed of copper alloys, under certain conditions serious copper corrosion problems may result. This occurs when FW having a pH over 8.3 also contains small amounts of ammonia and dissolved oxygen (DO). The ammonia may be present, for example, as a result of the overuse or inappropriate application of certain amines. Further damage may occur from the plating-out of the copper-ammonia ion then created as a cathode on boiler tubes. This promotes anodic corrosion of the immediate surrounding anodic areas. 

Today many designers favor the use of particular grades of stainless steel and titanium alloys, but older condensers are often constructed of copper alloys, which may provide a source for copper corrosion, the products of which can be transported back to the boiler. 

Copper corrosion occurring as Transported corrosion debris Resulting from ammoniacal corrosion of steam/CR lines. 

NOTE Where iron and copper corrosion products develop in CR systems, typically the copper is approximately 10% of iron level. 

PMA may require support from a copper corrosion inhibitor under some circumstances because it can adversely affect the corrosion of copper. 

Consequently, when selecting and blending the various raw materials used in all-polymer/all-organic formulations, the questions of thermal and hydrolytic stability and ability to transport or otherwise control colloidal iron oxides (in addition to possible adverse effects such as copper corrosion) become increasingly important at higher boiler temperatures and pressures. 

Ammonia is sometimes used to boost the pH but may be unsuitable where copper alloys are present. Hydrazine and the neutralizing amines produce ammonia as part of their breakdown process, so additional care is required here to minimize copper corrosion. 

The ammonia production is less than in hydrazine, but there may be a perceived of copper and brass corrosion. In fact, any corrosion risk is small, provided that DEHA-treated boiler plants are subjected to the same requirements as hydrazine-treated units, namely, ensuring that all in-leakage of oxygen in the condensate system is fully eliminated. If this objective is achieved, the oxidation of cuprous oxide to cupric oxide tends not occur to any significant degree, and the susceptibility for copper corrosion in the presence of ammonia is equally low. 

Where copper corrosion occurs, the problem usually can be traced back to an excess feed of hydrazine, DEHA, or similar product, coupled with inadequate post-boiler oxygen scavenging. 

Erythorbates are safe products and there are no harmful breakdown products, although when early formulations utilized ammonia as a PH buffer (and neutralizer for part of the carbon dioxide), copper corrosion problems resulted. However, erythorbates are not steam-volatile,and consequently there is no post-boiler oxygen scavenging potential available. Thus, in the event of complete breakdown of the product at high pressure, oxygen-induced, ammonia corrosion of copper may continue unchecked. 

Carbohydrazide itself is of very low volatility, but it decomposes at relatively low temperatures to produce volatile carbon dioxide and ammonia. In theory, the combined corrosive effects of these two materials should be negated in the condensate system, but in practice, this is not always so and both steel and copper corrosion transport problems may develop, primarily as the result of corrosion-enhancement reactions resulting from oxygen in-leakage. It is presumed, therefore, that (similar to hydrazine) some deliberate after-desuperheating line addition of CHZ is necessary if post-boiler section corrosion is to be avoided. 

Where copper corrosion and its subsequent transport is a problem, the FW pH level may be reduced to only 8.7 to 8.8 in order to reduce its aggressiveness toward copper. 

Copper corrosion inhibitor None Benzotri azole/ toyltriazole Benzotriazole/ toyltriazole None Benzotriazole/ toyltriazole Benzotriazole/ toyltriazole... 

At above the critical pressure of 3,203.6 psi, virtually no solids can be tolerated in boiler FW because all of the water is converted to steam, which passes through the turbine. Copper corrosion products tend to be the most troublesome contaminant in supercritical boilers, consequently all efforts must be made to prevent copper and other metallic oxides from entering the boiler. FW quality guidelines include ... 

Where copper corrosion occurs, some small amounts of copper will... 

Although various alkaline citrates and inorganic oxidizing cleaners are sometimes used, the standard procedure, where HC1 is employed, is to add thiourea. This method circumvents the copper corrosion cycle and permits the simultaneous removal of iron and copper deposits. 

Zhang XOG, Stimming U. 1990. Scanning tunnehng microscopy of copper corrosion in aqueous perchloric-acid. Corrosion Sci 30 951-954. 

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