DE4209865C2 - Process for improving the effectiveness of aqueous cleaning agents for removing metal-containing residues on semiconductor surfaces - Google Patents

Description

The invention relates to a method for improving the Effectiveness of aqueous cleaning agents for removal metal-containing residues on semiconductor surfaces, esp special silicon wafers.

With the ongoing miniaturization of the structures of electronic components, in which the sub micrometer range is reached, the requirements are the purity of the substrates from which the components are made are particularly increased. This is especially true for the semiconductor wafers made of silicon or gallium arsenide, in the electronic in numerous process steps Structures like transistors and the conductors connecting them tracks are etched. Are back during this process were adsorbed on the surface of the disc, its diameter in the order of the smallest electronic structure ture or above, this leads to serious Malfunctions up to total failure of the circuit ses. The manufacturers of the semiconductor wafers are therefore strives to deliver products that are as free from return as possible are of critical size and it is in the interest the component manufacturer to take precautions that the Disc surfaces remain free of such residues.  

Nevertheless, both the disc and the Component manufacturing repeated process steps necessary, weh disturbing residues are generated. So arise through the mechanical surface treatment by lapping or polishing, or chemical treatment by alka Lisch-oxidative or acidic etching particles made of silicon, Silicon dioxide, metal oxide, metal hydroxide or plastic, which adsorb more strongly on the surface, the smaller you are. Particles adhere particularly firmly, their diameter less than 1 µm (M. R. Kurz, A. Busnaina, F. E. W. Kern Jr., Proc. of Inst. of Environ. Sci, 340-344, 1989). Metallhal However, there are contaminants on semiconductor surfaces to be kept as low as possible because foreign metals reduce the elec tronic conditions in the later component sensitive to disturb. The deposits of metal hydroxides are special difficult to remove because the Si (OH) groups of the etched Excellent adsorption centers for the Represent precipitation (H. Hiratsuka, M. Tanaka, T. Tada, R. Yoshimura, Y. Matsushita, Proc. of 11th Workshop on ULSI Ultra Clean Technology, June 1991 Tokyo, pp. 5-20).

Various cleaning methods have been developed to the residues mentioned and also dust particles from the Indoor air that settles on the pane surfaces have to remove again. Common to all that a liquid detergent on the disc top areas. The most effective cleaning methods will be the removal of residues by an energy support supported. So serve at the Megasonic and at the Ultrasonic cleaning sound waves to particles from the Convey the surface of the pane into the cleaning agent (J.L. Rooney, D.Y.H. Puy, D.C. Grant, Microcontam. 37-40, 98, 99, May 1990). In the so-called "scrubber" method, Wal zensticks creates a strong flowing detergent film, which effectively removes particles adhering to the surface  (W.C. Krusell, D.I. Golland, Proc. Electrochem. Soc. 23-32, 1990).

Have cleaning agents based on organic solvents the disadvantage of being polluting and they pose increased security requirements when handling what is ultimately in the cost of the cleaning process precipitates. Organic cleaning agents therefore play only a subordinate role.

In the case of aqueous cleaning agents, those whose pH value is in the alkaline range have proven particularly useful. A well-known example of this are NH ₄ OH and H ₂ O ₂ containing aqueous solutions which are used in the cleaning process referred to as RCA cleaning (W. Kern, DA Puotinen, RCA Review, vol. 31, p. 187-206 (1970 )).

The removal of metallic contaminants by means of various acids, so u. a. using acetic acid another known cleaning option (O. J. Antilla, M.V. Tilli, J. Elektrochem. Soc., Vol. 138, No. 8th, Aug. 1991, p. 406C, Abstract No. 524).

However, it is disadvantageous that the metal mentioned above residues with conventional aqueous cleaning means are insufficiently removable, and in the case of on set of alkaline detergents new blows arise and adsor on the surface of the pane beers.

The object of the invention was therefore a method to indicate that the effectiveness of aqueous cleaning agents to remove metal-containing residues on semiconductors surfaces, especially silicon wafers improved.

The task is ge by a method of the type mentioned dissolves, which is characterized in that the aqueous Detergent with carbon dioxide and / or before use is charged with oxalic acid.  

Surprisingly, it was found that this measure the effectiveness of the aqueous cleaning agent in Ent distant metal-containing residues on semiconductor surfaces ver almost independent of its chemical composition is improved.

The metering of carbon dioxide and / or oxalic acid, which in the are referred to as auxiliary substances preferably immediately before using the cleaning agent tels. Of course, the metering can also be done early forth and stored the modified cleaning agent become. The improved cleaning effect of the cleaning agent tels is made by adding one of the help substances reached, so that the addition of both only in exceptional cases cases is appropriate. Basically, the cleaning medium with the auxiliary in concentrations up to saturation be acted upon. In connection with energy intra However, it may be necessary to take measures during cleaning be higher, with concentrations below saturation work. Carbon dioxide concentrates are particularly advantageous tions from 10 to 100% of the saturation value, whereby in the Usually during cleaning normal pressure and temperatures of Prevail 10 to 50 ° C. Oxalic acid is preferred in Kon concentrations of 0.1 to 1% (by weight) of the Reini agent added as auxiliary. Sound when used supported cleaning procedures will be the cheapest Concentrations expediently depending on the performed on the basis of preliminary tests.

The purity of the auxiliaries used must be in the Semiconductor industry use the usual requirements there reagents are sufficient. This is expediently coal dioxide through a container filled with the detergent ter until the desired concentration is reached is enough. But it is also possible to clean the windows  perform in a carbon dioxide atmosphere so that the Koh Diffusion into the cleaning agent. in the In the case of oxalic acid as an adjuvant, the addition takes place on best in the form of a concentrated aqueous solution or in powder form.

According to the invention, carbon dioxide and oxalic acid are special suitable auxiliaries to make the effectiveness more watery Detergent to remove residues containing metal To improve semiconductor surfaces, however, it is itself understandably not excluded, with closely related ver bonds, such as formic acid, a similar to achieve a favorable effect.

The metering of the excipient influences the effectiveness of an aqueous cleaning agent almost independent of its chemical composition favorable. Especially before it is partial, pure water according to the invention with a or to apply both of the auxiliaries. For example are the usual after an alkaline-oxidative cleaning Rinse steps with water through the additive additive Lich more effective, since even those adhering firmly to the surface residues containing metal hydroxide are removed. Guess Lich this effect is based on the fact that the auxiliaries both the adsorption capacity of the semiconductor surface as well change the hydration shell of the metal ions and so for the Adsorption and the formation of metal hydroxide precipitates create unfavorable conditions. Surprisingly it was found that water mixed with carbon dioxide is able to use acidic detergents, such as for example dilute hydrochloric acid, with comparable Reini completely to replace the effect. Corrosion problems that are well known in dealing with hydrochloric acid half by using the method according to the invention avoidable without loss of quality. The addition of one or  Both auxiliaries are not only particularly effective of pure water, but also the non-ionic Aqueous cleaning agent containing surfactants with new improve tralem or acidic pH.

The cleaning success is expediently based on a the most important metallic contaminants renal analysis, proven. The is particularly suitable Atomic absorption spectroscopy in connection with a chemi digestion of the oxidic compounds on the Schei surface due to the action of hydrogen fluoride steam at room temperature. The method is under the abbreviation VPD / AAS known to the expert and delivers a reliable Image of the foreign metal content on the surface of the pane.

The following is four examples of performance shown the method of the invention.

example 1

Twice 25 polished silicon wafers (approaches A and B) with a diameter of 150 mm were cleaned system with one from the RCA process under the name SC1- Solution known, ammonia-containing cleaning solution rinsed. The removal of superficially adsorbed, metal-containing residues were removed by a standard Megasonic Facility supported. The treatment lasted 5 minutes a detergent temperature of 50 ° C. Then was the discs in a so-called "quick dump rinser" (QDR) for another 5 minutes with ultrapure water at 25 ° C rinsed and finally dried in a stream of argon. In the opposite batch to batch A was coal in batch B to ultrapure water dioxide has been added until saturation. The final one Analysis (VPD / AAS) of the main contaminants iron, zinc and Copper gave the following result:

Example 2

Twice 25 polished silicon wafers (approaches C and D) with a diameter of 150 mm were in a commercial "Spray Acid Processor" first with an SC1 solution rinsed at 50 ° C. Then the disc was top sprayed with ultrapure water for 3 minutes. The what temperature was 25 ° C. In contrast to approach C er followed the water supply in approach D in a coal di oxide atmosphere. The surface analysis of the final in Argon flow dried slices gave the following contamina values:

Example 3

Twice 25 polished silicon wafers each (approaches E and F) with a diameter of 150 mm, as in Example 1 described, treated with an RC1 solution. While the  Slices from approach E then analogous to the slices of batch A were rinsed with ultrapure water in the QDR in approach F the ultrapure water during the rinsing process in the QDR 0.1% Oxalic acid metered in. The rinsing process with the oxalic acid Detergent took 3 minutes. Then were the slices of batch F for a further 5 minutes with ultrapure water rinsed and dried in a stream of argon. The VPD / AAS analysis the cleaned disc surfaces gave the following con tamination values:

Example 4

Twice 25 polished silicon wafers (approaches G and H) with a diameter of 150 mm were in a commercial Spray Acid processor with SC1 solution for 2 minutes Treated 50 ° C, 3 minutes with carbon dioxide saturated Sprayed ultrapure water and then on a wafer Scrubber cleaned with a surfactant solution and in a stream of argon dried. In contrast to approach G, approach H was the Add surfactant solution carbon dioxide in saturation concentration been settled. The VPD / AAS analysis of the dried slices surfaces resulted in the following contamination values:

The effectiveness of the process according to the invention of water or common aqueous cleaning agents for Removal of metal-containing residues significantly improved. The method according to the invention can be carried out without great effort existing process flows are included. You can also problematic cleaning agents, such as those the basis of hydrochloric acid without loss of quality due to salt acid-free cleaning agents, whose cleaning effect is invented has been increased in accordance with the invention to be replaced.

Claims (5)

1. A method for improving the effectiveness of aqueous cleaning agents for removing metal-containing residues on semiconductor surfaces, in particular silicon wafers, characterized in that the aqueous cleaning agent is acted upon with carbon dioxide and / or with oxalic acid. 2. The method according to claim 1, characterized in that Carbon dioxide in a concentration of 10 to 100% of Saturation concentration at normal pressure and one temperature temperature of 10 to 50 ° C to the aqueous cleaning agent is dosed. 3. The method according to claim 1, characterized in that Oxalic acid in a concentration of 0.1 to 1% (ge based on weight) at a temperature of 10 to 50 ° C aqueous detergent is dosed. 4. The method according to one or more of claims 1 to 3, characterized in that water as a cleaning agent tel is used. 5. The method according to one or more of claims 1 to 3, characterized in that aqueous solutions are not ionic surfactants used as cleaning agents the.