JPH01244621A - Method of cleaning surface of silicon single crystal substrate - Google Patents

Abstract

PURPOSE:To obtain a highly pure and defect-free active layer region, by thermally oxidizing the surface of a silicon single crystal substrate and removing the oxide film together with the surface of a silicon layer adjacent thereto. CONSTITUTION:Conditions of thermal oxidation are optimized to produce an oxide film. The surface layer including this oxide film is removed slightly to clean the surface. The conditions of thermal oxidation may be determined, for example, such that oxidation is performed within atmosphere of 900-1200 deg.C for an appropriate period of time selected from 1 to 20hours. The substrate should have an oxygen concentration at least of 10<16>atoms/cm<3> or over and is previously heat treated within atmosphere of 600-800 deg.C. Since Fe captured at the interface between the oxide film and silicon is possibly redistributed into the substrate at a high temperature, the silicon layer may be removed by several mum from the surface simultaneously with removal of the oxide film by means of mixture of hydrofluoric acid and nitric acid solutions. In this manner, Fe in the bulk of the substrate can be removed effectively in combination with the intrinsic getter technique, so that an ideal active layer which is highly pure and free of defects can be obtained on the surface of the substrate.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for cleaning the surface of a silicon single crystal substrate (hereinafter referred to as a substrate) for a semiconductor integrated circuit, and in particular removes metal atomic contamination that does not have a significant intrinsic getter effect. The present invention also relates to a method for obtaining a substrate for semiconductor integrated circuits that has a cleaner surface in addition to the intrinsic getter effect.

(Prior art and its problems) Since a semiconductor element is formed on the surface of a substrate, it must not only be perfect at the time of crystal formation, but also must not be contaminated by various types of contamination.

Currently, substrates are mainly obtained by cutting a silicon single crystal rod perpendicular to its axis using the Czochralski method, mirror-polishing one side of the resulting thin disk, and then cleaning it using a chemical method. .

The surface of the substrate is polished using a method that minimizes disturbance of crystallinity by using chemical etching as much as possible, so that it has very good crystallinity, that is, it removes the dangling bonds of silicon atoms on the surface and eliminates the misfit of the atoms. It was difficult to get a surface without it.

Depending on the classification, dirt attached to the substrate surface may be -
Examples include adsorption of ions such as Na'' and F- to the surface, metals such as Cu, Fe, and Au, and Sin.

Possible causes include polishing of particles and other materials, adhesion of abrasive particles to the surface, fine particle contamination of the surface by various types of dust in the air, and film contamination such as residual caranal stain from various liquids including water used. Various trials and errors have been carried out to clean these surface contaminants, and recently a method that is almost satisfactory is being put into practical use.

Basic cleaning methods combine various chemical and physical actions, and all of them include cleaning with pure water, acids, alkalis, organic solvents, surfactants, dry cleaning, and drying.

Active layer area on the substrate surface, e.g. 10-20t from the surface
Attempts have been made to make the m crystal layer ideally perfect crystal, that is, containing no impurities and no crystal defects. Through the internal formation of minute defects based on dissolved oxygen in single crystals using the Czochralski method,
Impurities and other crystal defects are gettered in the strained region that occurs around these minute defects, and oxygen in the crystal is removed toward the substrate surface by out-diffusion.
This was done through a unique method of fusion. This method has been further improved during the development of semiconductor device manufacturing technology, and is commonly referred to as intrinsic gettering or intrinsic gettering, and is heavily used as one of the 8AQ techniques in semiconductor integrated circuit device technology.

However, if we pay particular attention to the MO8 structure.

Intermediate transition due to change in chemical composition from Si to SiO2 at the oxide-silicon interface, difference in thermal expansion coefficient between Si and Sin, change in impurity element partition between Si and 5in2, oxidation Due to the trapping of impurities within the film, attention must be paid to various impurities within the silicon single crystal, and it has been found to date that this problem cannot be solved using a single crystal substrate alone.

As the oxidation of the substrate progresses, impurities within the substrate are also incorporated into the oxide film as the oxide film grows, and redistribution of impurities occurs near the interface.This redistribution occurs on both sides of the interface between the substrate and the oxide film. The impurity ratio is created so that the chemical potentials match.

In other words, the segregation coefficient is biased to be larger or smaller than 1, ■ the diffusion rate ratio of impurities in the oxide film and the substrate, ■ the movement force of 1 at the interface as oxidation progresses, and the oxidation rate of the substrate and the diffusion of impurities. It is believed that this is caused by factors such as the relative ratio to speed.

For example, B is accumulated in an oxide film in an oxidizing atmosphere, and its concentration decreases on the substrate surface. However, in a 11□ atmosphere, the opposite is true. The concentration of P and Asi increases on the substrate surface. As described above, it is known that the redistribution force of impurities varies depending on the impurity element and the processing atmosphere.

Furthermore, Akira Ohsawa et al.1, J.E.
electrochem.

Soc, Vol. 111. No, 12. P
, 2964 (1984).

Secondary ion mass spec near the oxide film/silicon interface 1-
It has been reported that using a laser scope and chemical etching (JF), copper diffuses into the bulk of silicon and collects at the Fe/Si interface, and Cr is incorporated into the oxide film. It has been found that Fei is accumulated within 100 nm from the surface of the substrate.

As described above, the distribution of various impurities at the oxide film/silicon interface has been reported, but specific measures or optimal processing conditions for removing these impurity elements from the surface of the substrate have not been clarified.

In the present invention, near the oxide film/silicon interface of a thermally oxidized substrate,
By effectively collecting Fe as an impurity element and at the same time utilizing the intrinsic getter effect.

The purpose is to make the active layer region on the surface of a semiconductor integrated circuit substrate highly purified and defect-free.

(Means for Solving the Problems) In order to achieve the above object, the present invention optimizes thermal oxidation conditions, and then slightly removes the surface layer of the substrate, including the oxide film, to clean the surface. provide a method. As the thermal oxidation conditions, an appropriate time within 1 hour to 20 hours is selected in an atmosphere of 900 to 1200°C. At this time, the oxygen concentration of the substrate is at least 1016 atoms/cm3.
Choose the one above.

Further, by performing heat treatment in advance in an atmosphere of 600 to 800°C, high purity and defect-free formation of the substrate surface layer are promoted.

(Function) It is not clear why Fe collects near the interface between the oxide film and silicon, although Fe has a high solubility in silicon and a relatively fast diffusion rate. It was confirmed that Fa was redistributed at the oxide film/silicon interface. Furthermore, as a condition for forming an oxide film, redistribution of Fe does not occur at a low temperature such as 800°C.
It has also been found that at high temperatures such as 1200''C, Fe diffuses into the bulk and the degree of integration near the interface decreases.

From this, it is considered that the reason why Fe gathers at the interface is that the dangling bonds of silicon atoms at the oxide film/silicon interface capture Fe.

However, Fe captured at the interface between the oxide film and silicon,
At high temperatures, redistribution into the substrate is possible, so it is preferable to remove it from the substrate surface together with the oxide film. As for such a removal method, it is best to remove the oxide film using a fluoro-nitric acid mixture and at the same time remove several layers of the silicon layer surface.In this way, Fe in the bulk of the substrate can be effectively removed, and the Fe in the substrate bulk can be effectively removed. If getter technology is used in combination, it is possible to make the active layer on the ideal substrate surface highly purified and defect-free.

Intrinsic gettering has two purposes.
One of these is the out-diffusion of m elements from the substrate surface, and the other is the getter effect of impurities in the surface layer region due to the formation of internal micro defects. For this purpose, substrates are usually used at low temperatures (650-800°C) and high temperatures (over 1000'C).
A two-step heat treatment is performed. Low-temperature annealing forms defect nuclei, and high-temperature annealing generates minute precipitates due to the growth of nuclei. During the high-temperature annealing process, out-diffusion of oxygen from the surface layer simultaneously occurs, so that a defect-free, high-purity active layer (usually a denuded zone: DN) can be formed.

Although there are various theories regarding the composition of the microprecipitates, there is no doubt that the main component is cristobalite containing oxygen. This strain field near the minute precipitate attracts and fixes impurities, and in the intrinsic getter method, promotes high purity of the denuded zone and perfecting of the crystal.

According to experiments conducted by the present inventors, intrinsic gettering is inferior to the interface suction effect, but it is somewhat effective for gettering Fe, and gettering effects have been recognized for other impurities. Therefore, it has been found that it is ideal to use both the formation of an oxide film and the intrinsic getter method at the same time.

It has already been mentioned that oxygen is important in order to obtain the intrinsic getter effect, and for this purpose, oxygen of 10 16 /d or more is required in the substrate.

(Example) How Fe in silicon is redistributed at the interface between an oxide film and silicon was compared by heat treatment in a nitrogen atmosphere and in an oxidizing atmosphere. In addition, the effect of intrinsic gettering on Fe adsorption and the F
The interfacial adsorption effect of e was also investigated. The sample was a p-type CZ method single crystal with a resistivity of 1 oΩ-1 (oxygen concentration Oi
: 20ppma) and FZ method crystal oxygen concentration 0L (0
, 1 ppma) was used.

The heat treatment conditions and amount of oxygen precipitated in this case are shown below.

The surface of the sample was contaminated by immersing it in an aqueous solution of iron dissolved in dilute nitric acid, and the amount of Fe contamination on the surface was 0.5 to IXlX1012.
ato/cm? Met. Assuming that this Fe is uniformly diffused within the crystal, the concentration will be 1 to 2 x 1013atθ
ms, 11 (referred to as the total amount of pollution), the 6 pollution measurement is D
Based on the LTS method.

The results after this heat treatment are shown in FIG.

In heat treatment category A, the Fe impurity concentration is 1 to 3X1012
Atoms/cl corresponds to the solid solubility at 800°C. As described above, heat treatment section A does not show a large gettering effect. In the 0□ atmosphere of heat treatment category B,
Fe impurity 1 diffused inside both FZ and CZ method crystals
The degree of contamination has been significantly reduced to I x 10"atoms/cn? In the N atmosphere, the FZ method crystal has the same amount of contamination as the total contamination, 1.5 x 10"atoms/ad, but in the C
For zg crystal, 8 x 101012ato/- is 1/2
It has become. The difference between FZ and C7 is IG due to O1 precipitation.
However, the gettering effect is small compared to the reduction in contamination caused by the O2 atmosphere. o2 in heat treatment category C
In the atmosphere, both FZ and CZ method crystals are 3 x 1010
The amount increased to 12ato/cx&, and re-release of Fe was confirmed, but the total amount of contamination was 115. FZ in N2 atmosphere
, 07. The total amount of contamination is the same for both method crystals.

In this way, the Fe adsorption effect near the oxide film interface is 1000
It is maximum around ℃, but at low and high temperatures.

The same effect decreases, although for different reasons. Further, it is seen that there is an intrinsic gettering effect on Fe at around 1000°C. However, since it is small compared to the adsorption effect of the interface, it remains an auxiliary effect.

(Effects of the Invention) As described above, in the method of the present invention, Fe element, which causes fJ layer defects and lifetime reduction, can be almost completely removed from a silicon single crystal substrate during the semiconductor device manufacturing process. , it is possible to form an ideal high-purity and defect-free denuded zone on its surface, thereby making it possible to improve the characteristics of semiconductor devices, especially integrated circuits, and to reduce costs by increasing yield.

[Brief explanation of the drawing]

Figure 1 shows Fe impurity 1 degree (a) under various heat treatment conditions.
A graph of 211 test results by DLTS of (toms/rxl) is shown. Patent Applicant Shin-Etsu Semiconductor Co., Ltd. Agent/Patent Attorney Ryo Yamamoto-□11, Ko 1.11

Claims (1)

[Claims] 1) A method for cleaning the surface of a silicon single crystal substrate, which comprises thermally oxidizing the surface of the silicon single crystal substrate and removing the oxide film and the surface of the silicon layer in contact with the oxide film. 2) The surface cleaning method according to claim 1, wherein the thermal oxidation is performed in an atmosphere of 900° C. to 1200° C. for 1 hour to 20 hours. 3) The silicon single crystal substrate according to any one of claims 1 and 2, wherein the oxygen concentration in the silicon single crystal substrate is at least 10^1^6 atoms/cm^3 and is previously heat-treated in an atmosphere of 600 to 800 °C. Surface cleaning method.