JP2024034694A - Silicon etchant - Google Patents

Abstract

To provide a new chemical solution that can wet-etch silicon at high speed when manufacturing a semiconductor device, etc.SOLUTION: An alkaline aqueous solution containing an alkaline compound such as quaternary ammonium hydroxide is a silicon etching agent containing an N-halogenated imide compound, preferably at a concentration of 1 to 500 mmol/L, particularly preferably 20 to 200 mmol/L. As the N-halogenated imide compound, 5- to 7-membered N-brominated cyclic imides such as N-bromosuccinimide, N-bromo-2-methylsuccinimide, and N-bromoglutarate imide are preferred. Further, the alkaline compound is preferably included in a concentration such that the pH is 12.0 or higher, particularly 12.5 or higher.SELECTED DRAWING: None

Description

The present invention relates to a silicon etching chemical solution used in surface processing and etching steps when manufacturing various silicon devices.

Silicon (Si) is applied to various fields because of its excellent mechanical and electrical properties. Utilizing mechanical properties, it is applied to valves, nozzles, printer heads, and semiconductor sensors for detecting various physical quantities such as flow rate, pressure, and acceleration (e.g., diaphragms in semiconductor pressure sensors and cantilevers in semiconductor acceleration sensors), etc. has been done. Further, by utilizing its electrical properties, it is applied to various semiconductor devices such as memory devices and logic devices as a material for parts of metal wiring, gate electrodes, etc.

Processing of silicon in the manufacture of semiconductor devices is mainly performed by etching treatment. Etching methods include dry etching such as RIE (reactive ion etching) and ALE (atomic layer etching), and wet etching using an acidic or alkaline aqueous solution. Although wet etching is often inferior to dry etching in terms of fineness of processing, it is superior to dry etching in terms of productivity because it can process a wide area at the same time and can process multiple wafers at the same time. Among these, wet etching using an alkaline aqueous solution is suitably used in processes where productivity is important, such as when removing an entire unnecessary silicon layer by etching.

Several etching solutions have been proposed that have high productivity, that is, can remove silicon at high speed. For example, an etching chemical solution has been proposed in which an alkali compound, an oxidizing agent, and a hydrofluoric acid compound are contained in water and the pH thereof is adjusted to 10 or more (see Patent Document 1).

Japanese Patent Application Publication No. 2013-135081

Generally, the productivity of wet etching processes is improved by increasing the etching rate. In the production of semiconductor chips, etc., even when wet etching silicon, it is not always possible to apply the same etching agent depending on the structure of the semiconductor chip being manufactured, and the technology is developed so that it can be selected according to the situation. There is a need for enrichment.

Therefore, the object of the present invention is to provide a new alkaline etching solution with a high silicon etching rate due to a new technical configuration.

The present inventors conducted extensive studies to solve the above problems. Then, they discovered that the silicon etching rate can be dramatically increased by incorporating an N-halogenated imide compound into an alkaline aqueous solution, and have completed the present invention.

That is, the present invention is a silicon etching solution containing an alkali compound, an N-halogenated imide compound, and water.

According to the present invention, by containing an N-halogenated imide compound, wet etching of silicon can be performed at a high etching rate. Therefore, even if it is difficult to apply conventional high-speed techniques (etching agents) due to the material to be processed, etc., high-speed etching is possible using the etching agent of the present invention.

(etching solution)
The silicon etching solution of the present invention (hereinafter referred to as "the etching solution of the present invention") is used for etching silicon (crystalline silicon, amorphous silicon) during the manufacture of semiconductor chips. Etching of silicon can be carried out under acid conditions or under alkaline conditions, but the etching solution of the present invention is an alkaline aqueous solution containing an alkaline compound, and is intended for etching under alkaline conditions.

Note that when etching silicon, the higher the alkali concentration (therefore, the higher the alkalinity), the faster the etching rate tends to be. Therefore, the etching solution of the present invention preferably has a pH of 12.0 or higher, preferably 12.5 or higher, particularly preferably 13.0 or higher. On the other hand, the stronger the alkalinity, the higher the risk of leakage, and the components added to make the liquid alkaline tend to be more harmful and are also relatively expensive. From such a viewpoint, the pH may be 14.0 or less, or may be 13.5 or less. Note that this pH refers to a value measured at 24° C. using a glass electrode method.

The etching solution of the present invention contains an alkaline compound to make it alkaline. The alkaline compound is preferably one that does not contain metal as a constituent element, and is preferably ammonia, various primary to tertiary amines, or quaternary ammonium hydroxide. Quaternary ammonium hydroxides are preferred because they can easily be set to .0 or more.

Specific examples of the quaternary ammonium hydroxide include tetramethylammonium hydroxide (TMAH), ethyltrimethylammonium hydroxide (ETMAH), tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and trimethyl. -2-hydroxyethylammonium hydroxide (choline hydroxide), dimethylbis(2-hydroxyethyl)ammonium hydroxide, or methyltris(2-hydroxyethyl)ammonium hydroxide, phenyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide etc. can be mentioned.

The smaller the size, the higher the etching rate. Among the above, quaternary ammonium hydroxide with a total carbon number of 8 or less is preferred, and quaternary ammonium hydroxide (TMAH, ETMAH etc.) are particularly preferred.

In the etching solution of the present invention, these quaternary ammonium hydroxides are usually dissociated in the etching solution and exist as hydroxide ions and quaternary ammonium ions. In other words, the etching solution of the present invention is a liquid containing hydroxide ions to be alkaline and its counter ions (quaternary ammonium ions).

If an alkaline compound such as quaternary ammonium hydroxide is contained, the etching solution will normally be alkaline, and the content may be adjusted as appropriate depending on the desired pH. More specifically, for example, the amount of quaternary ammonium hydroxide required to make the pH of the etching solution 12.5 or higher depends on the types and contents of other components, but is generally 35 mmol/L or higher. be. The higher the amount, the higher the alkalinity, and the content is preferably 50 mmol/L or more, more preferably 100 mmol/L or more, and particularly preferably 150 mmol/L or more. Further, the content may be 1200 mmol/L or less, 1000 mmol/L or less, and in most cases, sufficient performance can be obtained even with 800 mmol/L or less.

The content of alkaline compounds can be calculated from the pH when the content is dilute, but the error becomes large when the content is concentrated. Therefore, it is more accurate to measure the content of counter cations using ion chromatography or the like and calculate from there.

The most important feature of the present invention is that it contains an N-halogenated imide compound. By including the N-halogenated imide compound, the etching rate of silicon is significantly improved compared to the case where it is not included.

As the N-halogenated imide compound, a compound represented by the following general formula (1) can be used.

(In the above formula, X is a halogen atom, and R ₁ and R ₂ are each independently an organic group or are bonded to each other to form a ring structure.)
X in the above formula is a halogen atom such as a chlorine atom, a bromine atom, an iodine atom, etc., and preferably a bromine atom.

In the above formula, when R ₁ and R ₂ are independently organic groups, R ₁ and R ₂ may be the same group or different groups. Further, the organic group may be linear or branched. From the viewpoint of increasing the molar amount per mass, the number of carbon atoms each of R ₁ and R ₂ has is preferably 5 or less, more preferably 3 or less. Further, the total number of carbon atoms in R ₁ and R ₂ is preferably 6 or less, more preferably 4 or less, and particularly preferably 3 or less. Note that the number of carbon atoms in the organic group is the total number of carbon atoms including the branched portion when the organic group is branched.

Specific examples of organic groups that may be R ₁ and R ₂ include methyl group, ethyl group, propyl group, i-propyl group, butyl group, i-butyl group, and t-butyl group.

Further, R ₁ and R ₂ may be bonded to each other to form a ring structure. The number of members of the ring is not limited, but it is preferably a 5- to 7-membered ring (including 3 atoms forming an imide). Further, the ring may have a substituent. When forming a ring, it is preferable that the total number of carbon atoms constituting the ring (excluding the two carbonyl carbons forming the imide) and the carbon atoms of the substituent is 6 or less, and 4 or less is more preferable. Preferably, 3 or less is particularly preferable.

To specifically illustrate the N-halogenated imide compound, examples of the acyclic imide include N-acetyl-N-bromoacetamide, N-acetyl-N-bromopropionamide, N-acetyl-N-bromobutyric acid amide, Examples include N-acetyl-N-bromovaleric acid amide, N-propionyl-N-bromopropionamide, and N-chloro compounds corresponding to these N-bromo compounds.

Further, as the cyclic imide, N-bromosuccinimide, N-bromo-2-methylsuccinimide, N-bromo-2,2-dimethylsuccinimide, N-bromo-2,3-dimethylsuccinimide, N- Succinimides such as bromo-2,2,3,3-tetramethylsuccinimide, N-bromo-2-methyl-2-ethylsuccinimide; N-bromomaleimide, N-bromo-2-methyl Maleic acid imides such as maleic acid imide, N-bromo-2,2-dimethylmaleic acid imide, N-bromo-2,3-dimethylmaleic acid imide; N-bromoglutaric acid imide, N-bromo-2-methyl Glutaric acid imides such as glutaric acid imide; cytaraconic acid imides such as N-bromo citaraconic acid imide; N-bromocyclohexanedicarboxylic acid imide; N-bromophthalic acid imide, etc., and N- corresponding to these N-bromo compounds. Examples include chloro compounds.

As the N-halogenated imide compound, a cyclic imide compound is preferable because a cyclic compound has a smaller space-occupying volume and is less likely to adversely affect etching.

The content of the N-halogenated imide compound in the present invention is not particularly limited as long as it dissolves to form a uniform solution, but is preferably 1 to 500 mmol/L, more preferably 10 to 500 mmol/L. It is 300 mmol/L, particularly preferably 20 to 200 mmol/L.

The etching solution of the present invention contains water as an essential component. Etching will not proceed without water. Although it depends on the types and amounts of other components, in general, the proportion of water is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and 75% by mass. The above is particularly preferable. Further, there is no particular upper limit as long as the other components can be contained in the necessary amounts, but it is usually 99.5% by mass or less, and 99% by mass is sufficient.

Furthermore, if a processing solution such as an etching solution contains metal, it often has an adverse effect on the object to be processed (not limited to the silicon surface to be etched).

Therefore, the etching solution of the present invention preferably does not contain metal. More specifically, inclusion at a concentration above at least the impurity level should be avoided. More preferably, the content of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, and Zn is all 1 ppmw or less, and particularly preferably The content of each of the above metals is 1 ppbw or less. The metals listed here are metals that are expected to affect the quality of chemical solutions used in semiconductor manufacturing.

The silicon etching solution of the present invention may further contain a known component contained in a silicon etching solution made of an alkaline aqueous solution. In this case, even if it is a component that reduces the etching rate of silicon, if it is necessary to incorporate it for some purpose, the etching rate can be improved by incorporating an N-halogenated imide compound as described above. Can be done. Therefore, the effect of lowering the etching rate due to the addition of the other components can be reduced.

On the other hand, when etching silicon in the manufacture of semiconductor chips, it is often desirable not to etch the silicon dioxide portion (surface). Therefore, it is preferable that the etching solution of the present invention does not contain any component that promotes etching of silicon dioxide (SiO ₂ ) under alkaline conditions. A typical example of such a component is fluoride ion. From this viewpoint, the halogen in the N-halogenated imide compound is preferably other than fluorine.

Furthermore, the etching solution of the present invention should be a homogeneous solution in which all the ingredients are dissolved. Further, in order to prevent contamination during etching, the number of particles of 200 nm or more is preferably 100 particles/mL or less, more preferably 50 particles/mL or less, and particularly preferably 10 particles/mL or less. .

(Production method)
The method for producing the etching solution of the present invention is not particularly limited, and the above-mentioned alkali compound and N-halogenated imide compound are mixed with water to a predetermined concentration and uniformly dissolved. Bye.

It is preferable to use quaternary ammonium hydroxide and N-halogenated imide compounds that contain as few metal impurities and insoluble impurities as possible, and if necessary, commercially available products may be recrystallized, column purified, or It can be used after being purified by ion exchange purification, distillation, sublimation, filtration, etc. When employing quaternary ammonium hydroxide as the alkali compound, it is preferable to use a highly purified product, which is manufactured and sold for use in semiconductor manufacturing, depending on the type of quaternary ammonium hydroxide. Note that high-purity quaternary ammonium hydroxide for semiconductor manufacturing is generally sold as a solution such as an aqueous solution. In producing the silicon etching solution of the present invention, this solution may be mixed as is with a required amount of water, an N-halogenated imide compound, or the like.

It is also preferable to use water of high purity with few impurities. The amount of impurities can be evaluated by the electrical resistivity. Specifically, the electrical resistivity of water is preferably 0.1 MΩ·cm or more, more preferably 15 MΩ·cm or more, and particularly preferably 18 MΩ·cm or more. Such water with few impurities can be easily produced and obtained as ultrapure water for semiconductor manufacturing. Furthermore, ultrapure water has significantly less impurities that do not affect (less contribute to) electrical resistivity, making it highly suitable.

Further, as described above, various compounds known as components of chemical solutions for semiconductor manufacturing may be blended as necessary.

Further, the etching solution of the present invention may contain a quaternary ammonium halogen salt such as tetramethylammonium chloride, ethyltrimethylammonium iodide, dodecyltrimethylammonium bromide, and decyltrimethylammonium bromide.

As mentioned above, it is preferable that the etching solution of the present invention does not contain fluoride ions, so even if it is a compound known as a component of a chemical solution for semiconductor manufacturing, ammonium fluoride, tetramethylammonium fluoride, etc. It is preferable not to include fluoride. The same applies to PF ₆ salt, BF ₄ salt, etc.

In producing the etching solution of the present invention, it is also preferable to mix and dissolve each component and then pass it through a filter of several nm to several tens of nm to remove particles. If necessary, the filter passing process may be performed multiple times.

Furthermore, various other known treatments can be performed to obtain necessary physical properties in the production of semiconductor manufacturing chemicals, such as bubbling with an inert gas such as high-purity nitrogen gas to reduce dissolved oxygen.

During mixing and dissolving (and storage), the inner wall of semiconductor manufacturing chemicals is made of or coated with a material that is known to be used as the inner wall of semiconductor manufacturing chemicals, specifically materials such as polyfluoroethylene and high-purity polypropylene, which prevent contaminants from eluting into the etching solution. It is preferable to use containers and equipment that are It is also preferable to clean these containers and devices in advance.

(Applications and usage)
The silicon etching solution of the present invention can be used for etching substrates at each stage of manufacturing silicon wafers or various silicon composite semiconductor devices (silicon devices) including silicon single crystal films, polysilicon films, and amorphous silicon films. can. Note that the silicon single crystal film includes one made by epitaxial growth.

That is, by bringing the silicon etching solution of the present invention into contact with a substrate having a silicon (Si) surface, the Si surface can be etched. On the other hand, the etching solution of the present invention does not etch silicon dioxide (SiO ₂ ) or silicon nitride (SiN), although it depends on the optional components added. Therefore, the object to be processed using the etching agent of the present invention is a substrate having a silicon nitride surface and/or a silicon dioxide surface and a silicon (including silicon single crystal, polysilicon, and amorphous silicon) surface as the processing surface. can be mentioned. Various metal films may also be included. Examples include structures in which silicon and silicon dioxide are alternately laminated, structures in which polysilicon, silicon nitride, and silicon dioxide are patterned on silicon single crystals, and the like.

The substrate processing method using the silicon etching solution of the present invention includes a substrate holding step of holding the substrate in a horizontal position, and a step of holding the substrate in a horizontal position, and rotating the substrate around a vertical axis of rotation passing through the center of the substrate. and a treatment liquid supply step of supplying the etching liquid of the present invention to the main surface.

Another substrate processing method using the silicon etching solution of the present invention includes a substrate holding step of holding a plurality of substrates in an upright position, and a step of immersing the substrates in an upright position in the etching solution of the present invention stored in a processing tank. process.

In a preferred embodiment of the present invention, the silicon etchant is supplied to selectively remove the silicon film when etching silicon wafers, particularly various silicon composite semiconductor devices containing silicon nitride and/or silicon dioxide. Used in the manufacture of silicon devices, which includes an etching process.

The temperature of the silicon etchant during etching using the silicon etchant of the present invention can be adjusted appropriately from a range of 20 to 95°C, taking into account the desired etching rate, the shape and surface condition of the silicon after etching, productivity, etc. Although it may be determined, it is preferably in the range of 35 to 90°C.

When etching using the silicon etching solution of the present invention, etching can be performed while degassing under vacuum or reduced pressure or bubbling with an inert gas. Such an operation can suppress or reduce the rise in dissolved oxygen during etching.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Experimental methods/evaluation methods in Examples and Comparative Examples are as follows.

(abbreviation)
The abbreviations of the compounds used are as follows.

TMAH: Tetramethylammonium hydroxide NBS: N-bromosuccinimide mCPBA: m-chloroperbenzoic acid H ₂ O ₂ : Hydrogen peroxide

(How to adjust etching solution)
After diluting a commercially available TMAH aqueous solution (2730 mmol/L) for semiconductor manufacturing with ultrapure water and mixing it so that the chemical solution is uniform, various additives were added and each example and comparison shown in Table 1 was prepared. The composition of the etching solution according to the example was prepared. The form of each additive used in the preparation is as follows.

<Form of each additive used in preparation>
NBS: Single powder mCPBA: Single powder H ₂ O ₂ aqueous solution: 10300 mmol/L aqueous solution

In both Examples and Comparative Examples, the final concentration of tetramethylammonium hydroxide, which is an alkaline compound, was adjusted and blended to be 260 mmol/L (2.38% by mass).

(Method for measuring pH of etching chemical solution)
Measurements were made at a temperature of 24° C. using a tabletop pH meter F-73 manufactured by Horiba, Ltd. and a pH electrode 9632-10D for strong alkaline samples manufactured by Horiba.

(Evaluation method of etching rate (unit: nm/min))
First, the following three types of Si substrates were prepared in order to determine the etching rate for each crystal plane: Si (100) plane, Si (110) plane, and Si (111) plane.

Substrate A: 2 cm square single crystal silicon substrate (manufactured by SUMTEC Service) whose front and back surfaces are Si (100) mirror surfaces;
Substrate B: 2 cm square single crystal silicon substrate (manufactured by SUMTEC Service) whose front and back surfaces are Si (110) mirror surfaces;
Substrate C: 2 cm square single crystal silicon substrate (manufactured by Enertech) whose front and back surfaces are Si (111) mirror surfaces.

Before each etching treatment, the weight was measured in grams to five decimal places using an electronic balance AUW220D manufactured by Shimadzu Corporation.

Etching treatment was performed by immersing each Si substrate in 100 ml of an etching solution heated to 70° C. for 10 minutes. Thereafter, it was washed with ultrapure water and then dried.

The weight of each substrate after the etching process was measured in the same manner as before the etching process. The etching rate per one side of the substrate was calculated using the following formula (1) using the weight change before and after etching and the density value of 2.329 g/cm ³ of common single crystal silicon. In addition, the unit of "etching rate" in the following formula is "nm/min", the unit of "area of the front and back surfaces of the substrate" is "cm ² ", and "2." is a value indicating the density of single crystal silicon. The unit of ``329'' is ``g/cm ³ '', the unit of ``weight change before and after etching'' is ``g'', and the unit of ``etching time'' is ``min''.

Etching speed = Area of front and back surfaces of substrate x 10/2.329/Weight change before and after etching/Etching time (evaluation)
The following evaluation was given based on how many times the silicon etching rate was compared to the reference example (TMAH aqueous solution).

◎: 1.50 times or more ○: 1.30 times or more, less than 1.50 times △: 0.80 times or more, less than 1.30 times ×: Less than 0.80 times

Then, as an overall evaluation, if both (100) and (110) are ◎, it is "Excellent", if either is ◎, it is "Excellent", and if either is ○, it is "Good". If it was also △, it was classified as "average" (no particular effect), and otherwise it was classified as "impossible."

For reference, the etching rate magnification of the (111) plane is also evaluated as ◎ to × in the same way as above.

Reference Example The etching rate of silicon was evaluated using a 260 mmol/L TMAH aqueous solution. The results are shown in Table 1.

Example 1
The etching rate of silicon was evaluated using an aqueous solution with a TMAH concentration of 260 mmol/L and an NBS concentration of 74 mmol/L. The results are shown in Table 1. In this experimental example, both the (100) plane and the (110) plane were rated ◎, and the overall evaluation was "excellent".

Comparative example 1
An etching solution containing mCPBA instead of NBS was prepared and evaluated. Table 1 shows the concentrations and evaluation results.

Comparative example 2
Instead of NBS, an etching solution containing hydrogen peroxide was prepared and evaluated. Table 1 shows the concentrations and evaluation results.

Claims (5)

A silicon etching solution comprising an alkali compound, an N-halogenated imide compound, and water. The silicon etching solution according to claim 1, wherein the alkali compound is quaternary ammonium hydroxide. The silicon etching solution according to claim 1 or 2, wherein the N-halogenated imide compound is a cyclic imide compound. 4. A method of processing a substrate, comprising: contacting a substrate having a Si surface with the silicon etching solution according to any one of claims 1 to 3, and etching the Si surface. A method for manufacturing a silicon device, comprising the substrate processing method according to claim 4 during the process.