DD300622A7 - Etching agent for anisotropic wet chemical etching of silicon - Google Patents

Abstract

The invention relates to an AEtzmittel for naszchemischen Ettzen of silicon. The invention has for its object to provide an AEtzmittel for anisotropic naszchemischenAtzen of silicon using an alkaline solution, wherein the AEtzmittelangriff rate constant and over the area should be made evenly and a previous successful bath throughput should not lead to any deterioration of AEtzratenreproduzierbarkeit. According to the invention, the object is achieved by adding the alcohol-free aqueous agent for the anisotropic nascent chemical etching of silicon, from an alkali hydroxide solution containing an oxidizing agent whose normal redox potential is 1 V, with only 5 to 50% potassium or sodium hydroxide and 0.1 to 20 * ammonium or potassium peroxodisulfate. Structuring; alkali hydroxide; Silicon; redox potential; ammonium; potassium}

Description

Field of application of the invention

The invention relates to an etchant for anisotropic wet-chemical etching of silicon, in particular .lere of silicon wafers as Strukturierungsteilprozeß in the production of X-ray templates, micromechanical components and sensors whose function is bonded to a deep-etched silicon chip.

Characteristic of the known state of the art

The introduction of structures or windows in silicon wafers is known to take place by means of photolithographic patterning processes utilizing anisotropically acting etchant. Due to necessary etching depths up to the whole wafer thickness, additional etching masks, for example consisting of SiO ₇ are depending on the etchant used - or Si ₃ N ₄ -ScPiCh <s required, which are s'orstrukturiort by a conventional photoetching technique. The etching of the Si wafer takes place in the exposed wafer areas by the use of silicon etchants. As anisotropic, selective silicon etchant for low dopant silicon, ethylenediamine pyrocatechol solutions often still contain organic additives such as ζ. Pyrazine (in catalytic amounts) (see, for example, J. Electrochem, Soc., 126 [1979], 1406-1415), hydrazine solutions (J. Electrochem, Soc., 122: 545-552, 1975), and alkali hydroxide Solutions (Solid State Technol., 19 (19761, 55-58 and Microelectronic Engineering, 3: 221-234, 1985).) Ethylenediamine and hydrazine solutions tend to form pyramidal silicon residues on the etch base during silicon etching, the removal of which is important Moreover, their use at elevated temperature makes their use highly hazardous to health.These disadvantages, in particular the occurrence of pyramids on the etching base, are in accordance with DF-AS 2,245,809 by an alkali metal hydroxide-alcohol mixture with an oxidizing agent additive consisting of hydrogen peroxide or sodium hydroxide. However, it has been shown that these and also pure alkali metal hydroxide solutions in silicon etching increasingly with the Baddu Have poorly reproducible etching rates, which can lead to the complete Ätzstillstand local areas or the entire Siliziumätzfläche. This committee-causing etching state can be recognized on a matt-glossy etching base. An etch rate increase does not recur, so the etch charge must be discarded. These etch rate fluctuations are prevented by additions in accordance with DE-AS 2,245,809, obviously due to bath decomposition. Furthermore, according to this solution, as stated in the patent itself considerable problems in the exact determination of the ratios of the individual bath components to each other depending on the specific Ätzaufgabe, in addition, the choice of a corresponding alcohol (according to the comments in column 3, last paragraph of said patent ) is of importance in order to actually achieve the benefits sought by d 'writing. .

Object of the invention

It is the object of the invention to find an etchant for anisotropic wet-chemical etching using an alkaline solution in which, due to a constant etching rate, a rejection-causing etching state or etching standstill is avoided.

Explanation of the essence of the invention

The invention is based on the principle that even with the multitude of known methods and etchants, simpler solutions are always desirable.

The invention has for its object to provide an etchant for anisotropic wet chemical etching of silicon using an alkaline solution, wherein the etchant attack rate constant and should be uniform over the area and a previous successful bath throughput should not lead to deterioration of Ätzratenreproduzierbarkeit.

It has been found that the omission of the addition of alcohols to aqueous alkaline solutions in the sense of achieving the object of the invention, to achieve this object.

According to the invention the object is achieved in that the alcohol-free aqueous etchant for anisotopic wet chemical

Etching of silicon, from an alkali metal hydroxide solution to which an oxidation agent whose normal redox potential is> 1.4 V is added, consisting of only 5 to 50 mass% of potassium hydroxide and 0.1 to 20 mass%. -% ammonium or

Contains potassium peroxide sulfate. The addition of the individual Ätzbadbestandteile carried out according to the invention such that when using sodium hydroxide ammonium peroxodisulfate in any quantities, potassium peroxodisulfate to the Löslichkeitsgrenze, when using Kaliumhvdroxid the addition of said oxidizing agent until reaching the solubility of the Einzelbadbestandteile follows.

In the etching bath composition according to the invention, silicon is surprisingly etched at a constant etch rate. In the case of a constantly smooth etching base, no etching arrest occurs regardless of the previous bath throughput. The reproducible etching rates are up to 3 pm / min depending on the bath concentration and the bath temperature. For etching through 500 μm thick Si wafers, a high etch rate is desirable for the technology process, but too high etching rates lead to a very rapid increase in defects, so that an etching rate of 1.8 to 2 μm / min for the stated purpose cheapest

 If lower etching depths and, at the same time, finer structures are to be produced, then a lower etch rate, for example, is required. B. from 0.8 to 1 μηι provide that can be easily achieved by a correspondingly lower bath temperature and / or corresponding reduction of the hydroxide concentration.

Thus, there is found an etchant which etches silicon at a reproducible etch rate, so that patterning processes for fabricating X-ray templates, micromechanical devices, and sensors whose function is attached to a deep-etched Si chip are dimensionally feasible with high yield.

embodiment

For a more detailed characterization of the etchant according to the invention, the following exemplary embodiment is intended to serve

 The deep etching silicon substrate is provided with a silicon nitride mask prepared by conventional photolithographic techniques. The deep etching of the silicon substrate is then successful by immersion in the etchant according to the invention. The specified bath components are dissolved in the appropriate amount of water to form 11 etching bath. A bath according to the invention consists of

280 g / l KOH 10 g / l (NH ₄ I ₂ S ₂ Oe (or 12 g potassium peroxodisulfate).

The time and area deep etching of a 525 μπι thick, lightly doped silicon substrate is completed at a bath temperature of 80 ⁰ C after 300 min. This corresponds to an etching rate of 1.8pm / min. The uniformity of the etch progress over the substrate surface does not require any etch time extensions, so that the undercutting of the silicon nitride mask remains below 5 μm. The (111 (faces of the pit walls of the (100) silicon substrate are microscopically smooth

 A further advantageous composition according to the invention is composed of

70 g / l KOH 7 g / l (NH ₄ I ₂ S ₂ O ₈ (or 8.5 g potassium peroxodisulfate).

The etching rate of lightly doped silicon is in this bath, 1.2 mm / RNIN has at 80 ⁰ C. The result of the etching, the same Advantages as in the first case. Another advantageous composition of the etching bath according to the invention consists of

200 g / l NaOH 20 g / l (NH ₄ I ₂ S ₂ O ₈

The etch rate of lightly doped Si (100) at 80 "C is 1.9 mpm.

Claims (2)

1, alcohol-free aqueous etchant for the anisotropic wet-chemical etching of silicon, consisting of an alkali hydroxide solution to which an oxidizing agent is added, characterized in that it contains only 5 to 50% by mass of potassium hydroxide or sodium hydroxide and an oxidizing agent whose normal redox potential is> 1, 4V is included. 2. Anhydrous aqueous etchant for the anisotropic wet chemical etching of silicon, which consists of an alkali metal hydroxide solution to which an oxidizing agent is added, characterized in that it contains only 5 to 50% by mass of potassium or sodium hydroxide and 0.1 to 20 mA. % Ammonium or potassium peroxodisulfate.