Gravure de plasma seche avec des ions réactive, RIE
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Gravure de plasma avec des ions réactives, RIE

For the formation of integrated circuits it is necessary to structure various layers. This can be done in aquaous solution or wet by a wet etcher or dry by a plasma etcher or dry etcher. Plasma etching of dielectrics, semiconductors and metals is state of the art today. Before etching, a photo resist is deposited on the surface, illuminated through a mask, and developed. The dry etch is then performed so that structured etching is achieved. After the process, the remaining photo resist has to be removed. This is also done in a special plasma etcher, called asher.

For etching, the reactive gas is exited by a high frequent alternating electromagnetic field of 13.56 MHz in a low pressure environment resulting in the formation of reactive ions and radicals. When the ions are accelerated towards the surface of the sample, anisotropic etching is achieved while the reaction of radicals with the sample results in isotropic etching.

For plasma etching in most cases, chlorine or fluorine-chemistry is used for silicon and dielectrics and metals. Oxygen is used for etching polymer materials. For compound semiconductor materials like GaAs or AlGaAs also chlorine chemistry is used frequently. Especially for Indium containing compounds, also methane C H4 is used as etching gas.

Dry etching allows a reproducible, uniform etching of all materials used in silicon and III-V-semiconductor technology.

Polyimide. There are many varieties of polyimide on the market today. They have different curing properties, solids content, etc. However, they are all hydrocarbons, and most etch readily in oxygen plasmas. This reaction is a simple oxidation of the organics forming CO and water. Very important for the removal of polyimide, is insuring that the polyimide does not over heat during the process. If this occurs the polyimide can carbonize, leave a grass like residue, and be virtually impossible to get off. Reducing the ion bombardment solves this problem; running very low power, and/or "floating" the sample in the plasma, and/or using a hybrid reactor can accomplish this.

Silicon Nitride. Silicon nitride typically comprises the final passivation layer of an IC. It etches readily in plasmas that contains a lot of free fluorine (such as SF6/O2 or CF4/O2 plasmas. The SF6 is isotropic by nature. However, in this case, this property is actually advantageous in removing the nitride sidewalls surrounding top metal. During etching SiF4, SF2 and nitrogen are formed.

Silicon Dioxide. There are many types of silicon dioxide in use today. They all etch in the same chemistry using CF4, however the recipes and etch rates vary a little with the type. Typically, highly doped oxides etch faster and oxides with high carbon content etch dirtier. SiF4 and CO are formed during this process. Silicon dioxide etching is intrinsically anisotropic due to the fact that the strong chemical bond between the silicon and oxygen requires ion bombardment to break.

Aluminum (and other metals). Pure aluminum, by itself, etches readily in a Cl2 plasma. However, a native oxide layer covers all aluminum films. Pure Cl2 does not etch this oxide, so BCl3 is added to increase the amount of sputtering and to scavenge the oxygen in the aluminum oxide layer. An important consideration in aluminum etching is moisture contamination. For this reason, as well as safety considerations, a vacuum load-lock is highly recommended for this application.

Silicon. Polysilicon and also mono-crystalline silicon can be etched anisotropically & isotropically in chlorine gas or with fluorine chemistry, and it is also very selective to oxide. During etching volatile Silicon halogenides are formed.

Compound semiconductors. For compound semiconductors like GaAs, AlGaAs in many cases just chlorine Cl2, sometimes mixed with Argon is used. Sometimes BCl3 is added in order to increase anisotropy. Also SiCl4 can be used as an etchant for those materials. Volantile chlorides are formed like GaCl3 or AlCl3 or AsCl3.

Indium compound semiconductors Because Indium halogenides are not very volatile, for those materials methane can be used, forming volatile Trimethylindium. This reaction works also for other III-V-materials. The main problem with alkane plasmas is the formation of polymer depositions on the wafer. This problem can be avoided or minimized by the addition of hydrogen. Also the addition of heavy atoms like Argon can delay the onset of polymers.

Equipment

The machines are available as standard RIE (reactive ion etcher), with ICP (inductive coupled plasma) generator or in triode configuration.

plasma etcher

tic loading. These systems are used for manufacturing silicon and III/V semiconductor devices, MEMS parts, solar cells LEDs, OLEDs and LCDs.

Etching System Etching System Etching System Etching System
Application : Semi & Solar
Substrate : ~ 200 sqmm
Type : RIE or ICP-RIE
Loading : Auto Arm
Application : LED
Substrate : 2" X 32 ea
Type : ICP-RIE
Loading : Auto Arm
Application : LED
Substrate : 2" X 32 ea
Type : ICP-RIE
Loading : Auto Arm
Application : Semi & Solar
Substrate Ordner
Type : ICP-RIE
Loading : Auto Arm

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