JPS629634A - Conveying method for silicon wafer - Google Patents

Abstract

PURPOSE:To completely prevent the adverse effects of the contaminated metal contained in a silicon wafer by a method wherein the contaminated metal which can be selectively removed is clearly distinguished by performing a sacrificial oxidization, the contaminated metal is selectively removed, and the other metal which can not be removed by sacrificial oxidation is removed by performing a pretreatment. CONSTITUTION:The surface of silicon is oxidized using oxygen at the temperature of 950 deg.C or above, the metal located on the surface of a wafer and in the vicinity of the surface of the inner layer and having a high tendency of formation of an oxide is oxidized, and said oxide is formed on the wafer surface or in its vicinity. Also, the contaminated metal located on the inner layer is converted to a metal oxide at the above-mentioned temperature by internal oxidation, and the metal is stabilized. Besides, when the contaminated metal is adhered to the back side of the wafer, it is possible that the contaminated metal reaches the surface element region by diffusion when a heat treatment is performed. However, the contaminated metal is turned to a stabilized oxide at the above-mentioned temperature, and the diffusion of the contaminated metal can be prevented. In the oxidized condition wherein an oxide film is adhered as above-mentioned, the wafer surface is in the stably protected state, and the wafer can be conveyed in that state.

Description

Detailed Description of the Invention "Industrial Application Field" This invention protects the surface of a silicon wafer in a silicon semiconductor device manufacturing process, and protects the surface of a metal or silicon inner layer adhering to the surface: r+ Ik +-
I! 1 1 -r ++ 2 Mu Fi
! M iaf eL< Igl f-in
, r↓ Su-h Jgyu Concerning the method of transporting in Taimayo.

"Prior art and its problems" Currently, in the manufacturing process of semiconductor devices such as ICs and LSIs, heavy metal contamination that adversely affects the device characteristics may occur on silicon wafers, especially during transportation, and this can lead to device manufacturing. The yield was decreasing. As a countermeasure against this, conventional methods have been to create a source of agglomeration of contaminant metals by intentionally introducing crystal defects caused by oxides into the silicon wafer, or by introducing defects such as dislocations onto the backside of the wafer for the device. was. However, in all of these methods, the source of aggregation is often too far away from the wafer surface on the element side to cause a contaminating metal aggregation effect, or it is not possible to deal with a large amount of contamination. A new removal method was desired. On the other hand,
Recently, for example, by oxidizing the silicon surface once before applying an oxide film and removing the oxide film,
Sacrificial oxidation methods are used to remove or stabilize contaminated metals.1. h~1- The effect of this alpha oxidation method on the oxide film properties is not clear, and other treatment conditions have not been established, so the contaminant metals cannot be effectively removed or stabilized, and the effectiveness has not improved. The current situation is that there is no such thing.

This invention was made in view of the above circumstances, and it clarifies the effectiveness of target metals in the sacrificial oxidation method and efficiently removes and stabilizes contaminant metals through oxide film formation and pretreatment based on this. The object of the present invention is to provide a method for transporting a silicon wafer with its surface protected by an oxide film.

"Means to solve problems" The present invention was made based on the following findings.

That is, first, Cu is a typical contaminating metal.

Fe, Au, Ni, Co, Mo, Ta 1A (2s
In was deposited onto a silicon wafer by contaminating it as a dilute solution, by vacuum deposition, or by direct contact with a metal piece. Thereafter, this wafer was subjected to oxidation heat treatment at 1000° C. for 1 to 20 hours. Metals attached to the surface of oxidized silicon wafers were identified by high-speed electron diffraction and X-ray diffraction. In addition, the size of the metal oxide was determined by observation using an optical microscope.
The distribution within the wafer was investigated. In addition, elemental and state analyzes of the metals were performed using analytical electron microscopy and micro Auger electron spectroscopy. Furthermore, the depth distribution of metal within the wafer was also investigated using an ion microanalyzer. As a result, some metals easily become oxides through oxidation and remain near the surface and do not diffuse into the wafer, while others easily diffuse into the wafer without oxidizing despite heat treatment in an oxidizing atmosphere. It turns out that there is. Furthermore, it has become clear that the enthalpy of formation of the oxide at room temperature is -100K cal/mo12, which effectively turns into an oxide during oxidation of silicon and makes it difficult for diffusion within the wafer to occur.

The method of the present invention was made based on the above findings, and
Identify the contaminant metals that can be selectively removed by sacrificial oxidation, selectively remove or inactivate the contaminant metals, and remove other metals that cannot be removed or stabilized by sacrificial oxidation by pretreatment. This method reliably prevents the adverse effects of contaminated metals in silicon wafers.

In the method of this invention, contaminant metals that have adhered to or penetrated near the silicon wafer surface cannot be removed or stabilized as oxides even by heat treatment at a temperature range of 950°C or higher, where the formation rate of silicon oxide film is high (oxidation at room temperature The method is characterized in that metals (having an enthalpy of formation of -100 Kcal/mol or more) are removed in advance by acid cleaning, and then an oxide film is formed on the silicon surface by the heat treatment described above, and the silicon wafer is transported in this state.

"Operation" At high temperatures of 950°C or higher, oxygen oxidizes the silicon surface and also oxidizes metals that have a strong tendency to form oxides on the surface and near the surface of the inner layer, forming oxides on or near the wafer surface. do.

Moreover, the contaminant metal in the inner layer becomes a metal oxide through internal oxidation at the above temperature, and is stabilized. Further, although there is a possibility that the metal may reach the front side element region by diffusion, it becomes a stable oxide at the above temperature, and diffusion can be prevented. In such an oxidized state with an oxide film, the surface of the wafer is in a stable and protected state, and can be transported in that state. Therefore, even if the wafer becomes contaminated during transportation, the contamination can be easily removed together with the oxide film by chemical treatment immediately before the wafer is used. Moreover, since the metals that do not become oxides in the oxidation treatment have been previously removed by acid cleaning, the removal or stabilization of the contaminating metals is reliably performed. As for contamination during transportation, since dilute hydrofluoric acid treatment is effective for removing the oxide film, it is sufficient to remove it together with the oxide film immediately before using the wafer after transportation.

Hereinafter, this invention will be explained in more detail with reference to Examples.

"Example" Au, Cu, and N15Pb with significantly different oxide formation tendencies
SCr.

IJ/% Da Ill & n Ta 尤壬th Aff
The l-1 wafer surface was formed by directly contacting the wafer surface with a metal, by immersing the wafer in a solution containing metal ions, and by vacuum evaporation. The wafer to be contaminated had a mirror-polished finish. After the metal was attached to the silicon surface, the wafer was heat-treated at 1100° C. for 1 hour while oxygen gas was flowing.

The silicon oxide film on the surface of the heat-treated wafer was first removed by hydrofluoric acid etching, and then the phase of the metal oxide was identified by X-ray diffraction and electron beam diffraction.

As a result, it was confirmed that metals with a high tendency to form oxides, such as Fe, In, and A12, were converted into oxides.

Further, Au, which has a small tendency to form oxides, existed in a metallic state, and Nt and Cu formed 81 compounds. According to observation using an analytical electron microscope and analysis using an ion microanalyzer, the diffusion of deposited metal in the wafer depth direction shows that metals with a high tendency to form oxides are localized near the surface.
It was confirmed that metals with a small tendency to form oxides, such as Au and CuSNi, were present even in the center of the wafer used, which was 500 μm thick.

The above results are shown in the figure. As is clear from the figure, −1
This shows that the selective removal of metals by oxidation of the present invention is effective for metals having an oxide formation enthalpy of 00K cal/mo12 or more. Furthermore, this result was unexpected from the tendency of the diffusion coefficient in an inert atmosphere, which was used as a measure of the diffusion rate, and shows that the removal method by oxidation of the present invention is significant. Therefore, it is possible to transport the wafer with its surface protected by the oxide film produced by this oxidation, and finally, the contaminated metal can be removed by hydrofluoric acid treatment before use.

"Effects of the Invention" As explained above, according to the method of this invention,
Oxygen oxidizes the silicon surface at higher temperatures, and
Metals with a strong tendency to form oxides on the surface and in the vicinity of the surface of the inner layer are oxidized to form oxides on or near the wafer surface. In addition, the contaminated metal in the inner layer is internally oxidized at the above temperature to become a metal oxide and stabilized. Furthermore, if there is contamination from the back side of the wafer, there is a possibility that metal may diffuse to the front side element region due to heat treatment, but at the above temperature, it becomes a stable oxide and can be prevented from diffusing. In this oxidized state with an oxide film,
The surface of the wafer is in a stable and protected state and can be transported in that state. Therefore, even if the wafer becomes contaminated during transportation, the contamination can be easily removed together with the oxide film by chemical treatment immediately before the wafer is used. Also,
Metals that do not become oxides in the above oxidation treatment are removed in advance by acid cleaning, so that the removal or stabilization of contaminant metals is reliably performed. Furthermore, as for contamination during transportation, dilute hydrofluoric acid treatment is effective for removing the oxide film, so it is removed together with the oxide film immediately before use of the wafer after transportation.

[Brief explanation of the drawing]

The figure shows whether or not metals deposited on the surface of a silicon wafer diffuse and precipitate into the center of a 500 μm thick wafer after an oxidation heat treatment at 1100° C. for 1 hour, and the roughness of these metals.

Claims (1)

[Claims] Contaminant metals that have adhered to or penetrated near the silicon wafer surface cannot be removed or stabilized as oxides even by heat treatment at a temperature range of 950°C or higher. Metals with an oxide formation enthalpy of -100 Kcal/mol or higher at room temperature are pre-oxidized. A method for transporting silicon wafers, which comprises removing them by cleaning, then forming an oxide film on the silicon surface by the heat treatment described above to remove or stabilize the remaining contaminant metals, and transporting the silicon wafer in this state.