DD147589A1 - POLISHING METHOD FOR SEMICONDUCTOR SURFACES - Google Patents

Abstract

The invention relates to a method of polishing semiconductor surfaces used in the semiconductor processing industry, e.g. in electrical engineering / electronics companies. The use of the invention increases the effectiveness in the chemical-mechanical polishing of semiconductor surfaces, in particular of silicon substrate disks. In the polishing process of the present invention, the disadvantage of scar formation due to a relatively high (OH &exc;!) Concentration of the polishing agent at an elevated working temperature is avoided by the use of a two-component polishing agent which provides the formation of finely divided soft microparticles and high viscosity Ensure suspension. As the first polish component, an abrasive slurry-based slurry is used in a sucrose solution containing a certain amount of alkaline earth metal hydroxide. As the second polishing agent component, an abrasive slurry in an alkali carbonate solution is used. Both polish components are mixed in a certain ratio; it proved expedient to supply the two polishing agent components separately to the polishing device, so that they first mix on the polishing pad.

Description

Title of the invention

Method for polishing semiconductor surfaces

• Field of application of the invention

The invention relates to a method for polishing semiconductor surfaces, which can be applied in microelectronics and semiconductor technology operations.

Ch arakteri sik of the known technical solutions

It is known that crystalline silicon is not attacked by pure acids, while it is relatively easy to dissolve in an alkaline medium.

It is state of the art to use aqueous slurries of such abrasive substances as SiO ₂ , Al ₂ O, SiC, CeO ₂ , Cr ₂ O ₃ or ZrO ₂ as polishing agents for semiconductor materials (eg according to BOGENSCHÜTZ, AF, et al. Feinwerktechnik and Micronic ", 1972, No. 7). The grain size of Abrasiva is then usually below 2, urn.

Sodium hydroxide or potassium hydroxide are often added to the polish slurries as chemically active substances, and organic substances having a strongly basic reaction, such as, for example, are frequently used. As ethylenediamine, used together with or as a substitute for alkali metal hydroxides.

It is also known to use as a polishing tool occupied with a polishing cloth rotating flat disc, wherein the tool and workpiece are pressed together with a certain pressure, move relative to each other and this system per unit time a defined amount of polishing agent is supplied. "....

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In addition, according to an article by MENDEL ("Polishing of Silicon" in "SCP and Solid State Technology" of August 1967), the use of the chemical mechanical polishing of silicon is used, wherein the abrasive used SiO ₂ and by the addition of MaOH a pH Range of 10-11 has been set. The possibility of pH variation is indicated by suitable organic substances

 This polishing method is MENDEL in the patents

1st U.S. Patent No. 3,170,273 dated February 23, 1965 inventor: Walsh, R .0. ; Duke, A.

2. British Patent No. 971,987, issued Mar. 31, 1965.

The known, working in basic environment polishing methods have the disadvantage that you must work with a relatively low (OH ~) concentration, because too high a pH of the suspension generally leads to pitted disc surfaces. On the other hand, lower pH values lead to smaller removal rates, which results in too low a labor productivity when polishing silicon wafers.

Object of the invention

The aim of the invention is to increase the effectiveness in polishing semiconductor surfaces (preferably silicon substrate disks) in the basic medium.

Loan of the essence of the invention

The object of the invention is to increase the effectiveness of the chemical-mechanical polishing on commercial polishing equipment with a polishing agent which does not have the above-mentioned disadvantages. This is achieved according to the invention with a polishing process in which finely divided and so-called "soft" microparticles are formed directly during the polishing process and in which other abrasive particles are added to increase the productivity. The disadvantage of scar formation at elevated (OH ") concentration and / or relatively high average working temperature is the interaction of these" soft "microparticles with abrasive particles of very fine grain size and

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avoided a high viscosity of the suspension. The basic idea behind the preparation of such a polishing agent according to the invention is the use of a sugar or sucrose solution as base liquid for the polishing suspension, since relatively much alkaline earth metal hydroxide (eg Ca (OH) ₂ ) can be dissolved by formation of sucrose in comparison to pure water in the sucrose solution , By filtration or centrifugation, the solution can be cleaned or separated from excess alkaline earth metal hydroxide. ,

By mixing this lime-sugar solution with a finely divided abrasive to obtain the component 1 of the polishing agent according to the invention, while used as component 2 is an alkali metal carbonate solution mixed with abrasives. Mixing components 1 and 2 in proper proportions results in the formation of a relatively high viscosity, n-type polish which is quite unstable to external agents (e.g., heat).

Upon mixing of the components 1 and 2 is essentially the alkaline earth metal hydroxide (eg. 3, the Ca _(0H)?) Reacted by causticizing the alkali carbonates zu.einem finely divided alkaline earth carbonate (eg. As CaCO), according to

Ca (OH) ₂ + K ₂ CO "- * CaCO + 2 KOH.

Components 1 and 2 do not necessarily need to be mixed before use in a polishing machine; it is more convenient to supply them separately to the polishing machine. The chemical removal of silicon in the alkaline medium is carried out in a known manner and is not the subject of the invention.

The high viscosity of the polishing solution according to the invention causes a low mobility of the ions, and thereby favors the chemical degradation of the silicon begins first at the tips of the surface relief of the silicon. The polishing process is about the abrasive grain concentration, the concentration of the alkali carbonate, the polishing speed (i.e., the speed at which the workpiece and tool move against each other), the polishing pressure, the polishing temperature, and the viscosity of the components 1 and 2 in wide ranges controllable or optimizable.

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As abrasives or abrasives may be used SiO least smallest grain size, but other abrasives, such as Al ~ 0 or SiC, are applicable.

Ausführungsbeisρie1

The polishing method according to the invention has been successfully used for polishing both sides of silicon wafers. A polishing machine was used, in which the silicon wafers (with a diameter of, for example, 76 mm) were moved in cages between two polishing wheels covered with polishing cloth. The lower polishing wheel had a speed of

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120 rpm, the circulation number of the cages was 60 rpm, the upper disc was stationary. It was printed with a polishing pressure of 3. 10 Pa and a polishing temperature of 60 ° C worked.

To prepare the component 1, 250 g of cane sugar were dissolved in 1000 g of water and mixed with 50 g of calcium hydroxide. After filtering the lime-sugar solution, 200 g of SiO _{2 were} added to this. The polishing agent component 2 consisted of 750 g of water, 250 g of potassium carbonate and 100 g of SiO ₂ . Both polishing agent components were fed to the machine separately; per hour about 200 ml of component 1 and 200 ml of component 2.

When using the method described, the polishing removal could be almost doubled compared to a suspension prepared from KOH and SiO.

Claims (5)

'- 5 - 2173 - ~> - St * a tr% sf Erf indunq sanspruch A method of polishing semiconductor surfaces, characterized in that a polishing agent is used in which the abrasive or abrasive agent is slurried in one or two solution components, the first particle being an aqueous solution of a sucrose and a Alkaline earth hydroxide and the second component consist of an aqueous alkali carbonate solution. 2. A method for polishing semiconductor surfaces with a polishing agent according to item 1 », characterized in that is preferably used as the abrasive silica having a particle size <0.5, to be slurried in the first and / or second component, wherein about 50 to 300 g of abrasive should be applied to one liter of solution. 3. A method for polishing semiconductor surfaces with a polishing agent according to item 1 and 2, characterized in that as alkaline earth metal base preferably calcium hydroxide Ca (OH) and as a solvent, a cane sugar solution with a sugar content of ^, 40 percent by weight is used, wherein the calcium hydroxide in a larger amount can be set, so that a saturated or supersaturated solution is present. 4. A method of polishing semiconductor surfaces with a polishing agent according to item 1, 2 and 3, characterized in that the two optionally mixed with abrasive solution components are mixed prior to feeding to the polishing device or these are fed separately, so that the mixing directly on the polishing apparatus he follows 5. A method for polishing semiconductor surfaces with a polishing agent according to claim 1,2,3 and 4, characterized in that at an average tool and workpiece temperature of 30 ⁰ C to 90 ⁰ C is polished.