KR20100040598A - Etching solution for silicon wafer - Google Patents

Abstract

PURPOSE: An etching solution for silicon wafer is provided to reduce metal contamination on a silicon wafer and to perform the etching while not degrading the quality of the semiconductor wafer. CONSTITUTION: An alkaline etching solution comprises chemical additives. The alkaline etching solution is NaOH or potassium hydroxide. The chemical additive is a chelating agent. The chelating agent is any one selected from EDTA, NTA, HEDTA, GEDTA, TTHA, HIDA, and DHEG. The chemical additive is added in 0.01 g/L ~ 0.4 g/L based on the alkaline etching solution.

Description

Alkaline etching solution for silicon wafer {ETCHING SOLUTION FOR SILICON WAFER}

The present invention relates to an alkaline etching solution capable of reducing metal contamination of a silicon wafer.

In general, a method of manufacturing a semiconductor wafer includes cutting a single crystal ingot drawn by a single crystal pulling apparatus into a block of a predetermined range, performing an outer diameter grinding, and then cutting a wafer (slicing) on the ingot block to form a thin disc. A slicing step of obtaining a wafer having a shape, a chamfering step of chamfering the outer edge portion of the wafer obtained by the slicing step, a lapping step of wrapping the chamfered wafer to planarize it, and the chamfering step and An etching process for removing the processing defects remaining on the wrapped wafer, a polishing process for polishing the etched wafer surface, and a cleaning process for cleaning the polished wafer and removing the abrasive or foreign matter attached thereto.

Through the machining process such as slicing, chamfering, and lapping during the semiconductor wafer manufacturing process, the semiconductor wafer has a daisy layer, that is, a processing altered layer, on the surface, and the processed altered layer is slipped in the device manufacturing process. It must be removed completely because it causes crystal defects such as dislocations, lowers the mechanical strength of the wafer, and adversely affects the electrical properties, thus requiring the above etching treatment.

By the way, in the etching process in the above etching step, acid etching using an acid etching solution such as mixed acid (using a mixed solution of hydrofluoric acid, nitric acid and acetic acid), alkali such as sodium hydroxide, potassium hydroxide, and alkyl ammonium hydroxide solution, etc. There is alkali etching using an etching solution.

According to the above acid etching, the etching speed is high, but it is difficult to uniformly etch the wafer, thereby deteriorating the flatness of the wafer. Therefore, in recent years, since etching can be performed uniformly even though the etching speed is slow, many alkali etchings (sodium hydroxide solution, potassium hydroxide solution, alkyl ammonium hydroxide solution, etc.) are used that do not deteriorate the flatness of the wafer. .

In alkali etching of said semiconductor wafer, the commercial industrial alkaline solution with high metal impurity concentration is used as it is. It goes without saying that the alkali solution of the industrial grade generally used contains a large amount of metal impurities, but even the alkali solution of the electronic industry grade used for etching semiconductor wafers contains metal impurities of several tens of ppb to several ppm. The situation is.

Examples of the metal impurity contained in the alkaline solution include nickel, chromium, iron, and copper, and nickel, chromium, and iron, which are stainless materials used in the alkaline solution manufacturing process, are particularly high.

1 is a schematic diagram showing a sodium hydroxide production process. As shown in FIG. 1, using an initial sodium chloride solution, oxidation and reduction reactions are performed at the anode and cathode. Chloride ions in the sodium chloride solution are oxidized to chlorine gas, and hydrogen ions are reduced to hydrogen gas. Sodium is prepared. In this process, however, impurities are melted from the nickel electrode constituting the cathode of FIG. 1, and these impurities affect wafer quality.

Conventionally, when the semiconductor wafer was etched using an alkali solution containing these metal impurities, these metal impurities were considered to contaminate only the wafer surface. Therefore, it was judged that metal impurity adhering to the wafer surface was sufficiently removed by pickling afterwards, so that the presence of metal impurity in alkaline etching solution does not have a particularly significant effect on wafer quality. It was.

However, according to recent studies on the alkali etching process, contrary to the above common knowledge in the art, the metal ions of some metal impurities such as copper and nickel in the alkaline etching solution diffuse deeply inside the wafer during alkali etching, It has been clarified that the quality of the wafer is degraded and the characteristics of the semiconductor device formed by the wafer are significantly reduced.

2 shows how impurities contained in the alkaline solution are adsorbed onto the silicon surface. In steps 1 and 2, Ni ^{+ 2} ions react with Si atoms on the silicon surface to be reduced to Ni, and Si is oxidized to SiO ₂ . After Ni is adsorbed on the silicon surface in steps 3 and 4, the reaction is further activated and Ni adsorption is further activated. In addition, the adsorbed Ni is absorbed into the silicon bulk, and the surface of the silicon wafer including the SiO ₂ oxide film is oxidized as a whole by OH- ions of an alkaline solution.

In order to prevent the degradation of wafer quality due to the alkaline etching solution as described above, a high purity alkaline solution should be used. However, in the commercial alkaline solution, the high purity is only an expensive alkaline solution for analytical grade, and the use of this for industrial use was not costly at all.

The present inventors, in order to solve the above problems of the prior art, by adding a chemical additive that can react with the metal impurities present in the alkaline solution, by using a conventional etching solution to lower the reduction potential of the metal impurities, metal When the semiconductor wafer is etched using an alkali solution in which impurities are difficult to adsorb on the silicon surface, the present inventors have found that even if physical impurities are present, wafer quality does not deteriorate and the present invention has been completed.

The present invention provides an alkali solution containing a chemical additive that reacts with metal impurities in an alkali solution, in particular metal ions, to lower the reduction potential, and a semiconductor which makes it possible to perform etching without deteriorating the quality of the semiconductor wafer using the alkali solution. It is an object to provide a method of etching a wafer.

The present invention is characterized in that the alkali solution of the present invention is an alkaline solution containing a chemical additive capable of reacting with metal impurities in the alkaline solution.

The alkali solution used in the present invention is not particularly limited, but a sodium hydroxide solution or a potassium hydroxide solution, which is conventionally widely used as an alkali etching solution for semiconductor wafers, may be mentioned.

In the present invention, the impurity metal ions in the alkaline solution include nickel ions, copper ions, chromium ions, iron ions, and the like. Among them, non-ionized or removed nickel ions and copper ions having a large diffusion rate in silicon crystals, among others. This is important in terms of the quality of semiconductor wafers.

The metal ion concentration in the alkaline solution used for etching the semiconductor wafer of the present invention is preferably limited to 100 ppb or less, more preferably 50 ppb or less, and by such a concentration limitation, the effect of the present invention is more satisfactorily achieved. do.

Chemical additives capable of reacting with metal impurity ions in the alkaline solution include chelating agents that can react with metal impurity ions to form chelating compounds, thereby preventing the diffusion of metal ions. In general, a compound in which two or more multidentate ligands are coordinated is called a chelate, and the ligand is called a chelating agent. Chelating agents include inorganic (polyphosphates) and organic (amino carbonates), but generally refer to the latter organic systems. This is because the inorganic type is rarely used for the purpose of metal ion chelate, and is unstable, and the organic type is particularly used for the purpose. Currently commercially available include EDTA, NTA, HEDTA, GEDTA, TTHA, HIDA, DHEG, and the like.

In the figure below, the structure of Ni ion binding to EDTA in KOH solution is shown structurally. Ni ions in the state combined with the following chelating compound require higher reduction potential than in the state in which only Ni ions are present to be reduced by obtaining electrons from Si atoms on the silicon surface. Therefore, Ni ions become more difficult to adsorb to the silicon surface.

In the present invention, the chelating agent is preferably added in the range of 0.01 g / L to 0.4 g / L with respect to the alkaline etching solution. It is because a metal impurity effect will not be acquired if it is 0.01 g / L or less, and even if it is 0.4 g / L or more, the effect will not become large.

In the case of using the alkaline etching solution containing the chemical additive of the present invention, since the metal impurity has a high reduction potential, it is difficult to reduce the metal impurity, thereby confirming the effect of reducing the contamination of the metal impurity diffused into the wafer.

Next, the Example of this invention is described in detail simultaneously with a comparative example.

<Production of Alkali Etching Liquid>

An aqueous potassium hydroxide solution (concentration 48%, 100 liters, 80 ° C) was prepared. The potassium hydroxide aqueous solution contains 10-50 ppb of Ni.

An alkaline etching solution was prepared by adding and mixing EDTA to 0.1 g / L, 0.2 g / L, and 0.3 g / L in an aqueous sodium hydroxide solution. Hereinafter, in Examples 1, 2, and 3, Metal contamination concentrations were measured.

As a comparative example, the alkaline etching liquid which did not add EDTA to the said potassium hydroxide was used.

<Measurement method of metal contamination concentration inside wafer>

Various high sensitivity methods have been developed for bulk analysis of metal impurity analysis technology of semiconductor wafers.

Dissolve all the wafer pieces in a mixture of hydrofluoric acid and acetic acid (fluoroacetic acid) and remove metal impurities in the solution by atomic absorption spectroscopy (AAS) or inductively coupled plasma-mass spectroscopy (ICP-MS). When quantitative analysis is carried out, and polysilicon is deposited on the surface of the wafer at a high temperature of about 600 to 800 ° C. to about 0.1 to 1 um, metal impurities in the bulk are diffused to the surface and collected thereafter. A method of etching a polysilicon layer with a mixed solution of hydrogen peroxide solution and analyzing the metallic impurities in the solution by AAS or ICP-MS or the like is performed.

Specifically

i) after preparing the silicon wafer,

ii) When the prepared silicon wafer passes silane (SiH4) gas at a constant temperature of 600 to 800 ° C. for a predetermined time, polysilicon is deposited on the wafer surface.

iii) Then, when the wafer is cooled down to room temperature at a rate of about 5 ° C./min, metal impurities in the wafer, particularly copper and nickel, which have good diffusivity, may be formed at the interface between the polysilicon layer and the wafer, or polysilicon. Diffuse into the layer.

iv) The polysilicon layer was completely etched by reacting with a mixture of hydrofluoric acid and nitric acid, and the solution was measured for concentration using ICP-MS.

The nickel concentration measurement results of Examples 1, 2, 3 and Comparative Examples are shown in FIG. 3.

As shown in Fig. 3, when using an alkaline etching solution that does not use EDTA as a chemical additive, the Ni contamination concentration contained in the wafer after etching is 5 x 10 ¹³ atoms / cm ^3, but when EDTA is added, the Ni contamination concentration is added. As about 1 ~ 4 10 ¹² It can be seen that the pollution degree is more than 10 times compared to the comparative example.

1 is a schematic diagram showing a sodium hydroxide manufacturing process.

2 is a schematic diagram showing a process in which impurities contained in an alkaline solution are adsorbed onto a silicon surface.

3 is a graph showing the respective Ni contamination concentrations in Examples and Comparative Examples.

Claims (5)

Alkaline etchant comprising a chemical additive The method of claim 1, The alkali etching solution is an alkali etching solution, characterized in that sodium hydroxide or potassium hydroxide. The method of claim 1, The chemical additive is an alkaline etching solution, characterized in that the chelating agent. The method of claim 3, The chelating agent is an alkaline etching solution, characterized in that any one of EDTA, NTA, HEDTA, GEDTA, TTHA, HIDA, DHEG. The method of claim 3, The chemical additive is an alkali etching solution, characterized in that added in the range of 0.01 g / L to 0.4 g / L with respect to the alkaline etching solution.

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