JPH0658906B2 - Surface protection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface protection method used in a manufacturing process of electronic devices and the like.

(Prior Art) Conventionally, for example, a natural oxide film is formed on the Si surface, which is
In addition to becoming a protective film on the Si surface, it sometimes becomes an obstacle. That is, it becomes an insulating layer, and it becomes difficult to perform regular crystal growth. Further, when a metal electrode or the like is formed, this insulating layer causes an increase in contact resistance. As a conventional technique for solving this problem, wet etching with hydrofluoric acid, high temperature heat treatment at 800 ° or more, and physical sputtering with Ar ions have been used to remove the natural oxide film.

(Problems to be Solved by the Invention) In the wet etching method, if an oxide film is present in other portions, it is also etched, and the desired process shape cannot be secured. On the other hand, the high temperature heat treatment cannot be used when the distribution of impurities in the semiconductor is redistributed due to the high temperature or when a material that cannot withstand the high temperature is on the same substrate. Physical sputtering by Ar does not prevent damage by physical sputtering.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and form a protective film surface on which a natural oxide film is less likely to occur,
It is an object of the present invention to provide a method capable of removing the protective film at a low temperature and a low damage as needed.

(Means for Solving the Problem) The surface protection method of the present invention is a method of discharging a halocarbon gas or a gas containing the halocarbon gas immediately after the dry etching or dry film formation step and before exposing the sample to the outside air to form a surface protection film. It is characterized in that it is formed, decomposed with Deep UV light on the sample, and further the gas capable of etching the surface protection film is introduced to irradiate the deep UV light to remove the surface protection film, and subsequently the following step is performed in vacuum. .

(Operation) The present invention has solved the problems of the prior art by adopting the above configuration. For example, immediately after plasma etching, reactive sputter etching, film formation process, without exposing the sample to the atmosphere, in a vacuum chamber, CF ₄ , CHF ₃ , C
Gas plasma treatment with a carbon halide such as F ₄ + H ₂ is performed. Then, it is taken out into the open air, and immediately before the next process, for example, in the case of a film forming process, Cl ₂ in the same chamber or a vacuum chamber connected to it in a vacuum,
Photo-etching using F ₂ , Hl, HF, etc. Then, the surface plasma-treated with a gas of a carbon halide for light is extremely hard to be oxidized, and therefore can be easily removed by photoetching. The removed surface has an oxide film or carbon from the atmosphere. A clean surface with no contamination appears, which is very advantageous for the subsequent process.

(Example) An example of the present invention will be described below.

FIG. 1 shows an example in which the method of the present invention is applied to a conventional process in which SiO ₂ etching, resist ashing, and then CVD film formation are performed. First, in Fig. (A), CF ₄
The SiO ₂ 12 was etched with the resist mask 11 using a system gas. Then, the etched surface is a contamination layer (contamination layer, hereinafter abbreviated as a contamination layer) on the Si substrate 13.
14 are formed. This layer contains sputtered substances during etching, particularly oxygen and carbon from the resist, or fluorine and carbon contained in the gas.
The contamination layer 14 was found to be about 150Å by SIMS analysis. Further, as a result of resist ashing in the oxygen plasma shown in (b) of FIG. Then, as it is, to remove this contamination layer 14 by photo-etching, first, a natural oxide film on the contamination layer with an aqueous solution of HF, or on the contamination layer due to oxygen that may have been sputtered into the mask during etching The thin oxide film must be removed.
Then the wet process comes in and the required Si
Up to O ₂ 12 is etched. Therefore, in the present invention, after the resist 11 is ashed by the oxygen plasma of FIG. 1 (a),
CF ₄ is flown into the same chamber and plasma is applied for about 30 seconds to perform surface treatment. Then, the thin oxide film on the contamination layer 14 on the Si substrate 13 is removed, and the processing protection layer 15 shown in FIG. 2 (b) whose surface is replaced with carbon and fluorine is formed. The thickness of this processing protection layer 15 is about 20 to 30 Å, and below that, a contamination layer of about 100 Å remains when the SiO ₂ 12 shown in FIG. Next, in the growth step, this film forming apparatus includes an apparatus capable of irradiating deep UV light while flowing Cl ₂ or F ₂ gas in vacuum, such as an excimer laser apparatus or an Hg lamp. In Figure 1 (c),
When Cl ₂ gas is flown while evacuating and the pressure is 600 mTorr and Deep UV light is irradiated, Cl ₂ gas is decomposed by the Deep UV light and Cl radical is generated. The generated Cl radicals can easily etch the processing protection layer 15 and the contamination layer 14 that is the base thereof. FIG. 2 shows the relationship between the Cl ₂ pressure and the etching rate in this Cl ₂ photoetching. Since the contamination layer is about 150 Å, it is sufficient to select the Cl ₂ pressure which gives an etching rate of about 50 to 70 Å / min for processing in 1 to 2 minutes. FIG. 3 shows the concentration of carbon and fluorine during the etching of the contamination layer during the Cl ₂ photoetching time, which was measured by Auger analysis. It can be seen that the processing protective layer and the contamination layer are removed by etching for about 2 minutes. Carbon concentration drops to almost the same level as carbon pollution caused by carbon dioxide in the air.

Next, based on this principle, the Si surface is easily oxidized, but the treatment protective layer formed by the plasma treatment of the present invention is extremely difficult to be oxidized. An example showing this is shown below.

Table 1 shows the etching rates of Si with Cl ₂ gas and XeF ₂ gas, and similarly with the etching of Cl ₂ or XeF ₂ immediately after etching with Cl ₄ of the plasma-treated sample by changing the gas to CF ₄ without breaking the vacuum. ₂ shows the photoetching rate of ₂ photoetching. That is, while the photo-etching rates of the two types without CF ₄ treatment are about 20Å / min and about 14Å / min,
₄ The photo-etching rate of treated Si is as high as about 100Å / min. That is, the Si surface exposed to halogen atoms such as Cl ₂ and XeF ₂ is very easily oxidized and has a low photoetching rate. On the other hand, like CF ₄ , since it contains carbon even if it contains halogen, its surface is extremely hard to be oxidized. That is, a high etching rate can be obtained by photoetching. Next, in the graph of the result of Auger analysis in Fig. 3, under this condition, the photoetching time is within 2 minutes, that is, while the carbon concentration is high, the oxygen concentration is low, the photoetching time is long, and the carbon concentration is low. When the Si surface begins to appear, the oxygen concentration is increasing. From this also, the layer containing carbon is less likely to be oxidized, and as a result, the contamination layer can be removed without damaging the underlying Si substrate or the like in the photoetching process at low temperature and low damage.

In the above example, Cl ₂ gas was flown while evacuating, and DeepU
Although the V light was irradiated, the treatment protective layer 15 and the contamination layer 14 can be removed even by introducing Cl ₂ gas into the chamber, stopping vacuum evacuation, and setting a Cl ₂ atmosphere to perform Deep UV irradiation.

Further, Cl ₂ gas may be introduced into the chamber to be adsorbed on the sample surface, Cl ₂ gas may be exhausted, and this adsorbed gas may be irradiated with Deep UV. In this case, the etching rate is lowered, but the controllability of the etching rate is improved.

(Effect of the invention) Formation of the surface treatment protective layer of the present invention, and a method of removing it by photoetching as necessary, that is, even when exposed to the outside air, a surface on which a surface oxide film is not formed is obtained. Was given. This effect is due to the above-mentioned Auge of FIG.
It could be confirmed sufficiently from the result of r analysis and the result of photoetching in Table 1.

This method can also be used naturally for a surface protective film before crystal growth, and a sample surface free of carbon and other impurities can be obtained at low temperature and with low damage, so that a natural oxide film of a conventional technique in a semiconductor process or the like can be obtained. The big problem of removal has been completely improved.

[Brief description of drawings]

1 (a) to 1 (c) are schematic cross-sectional views showing an embodiment of the present invention, FIG. 2 is a diagram showing the Cl ₂ pressure dependence of the etching rate of Si, and FIG. It is a figure of the Auger analysis result which shows a mode of removal of impurities, such as carbon which shows an effect. 11 …… Resist mask, 12 …… SiO ₂ 13 …… Si substrate, 14 …… Contour layer 15 …… Process protection layer, 16 …… Deep UV light

Claims (1)

[Claims] 1. A halocarbon gas or a gas containing the halocarbon gas is discharged immediately after the dry etching or dry film formation process and before exposing the sample to the outside air to form a surface protective film,
A surface protection method characterized in that the surface protection film is decomposed by Deep UV light on a sample, and further a gas capable of etching the surface protection film is introduced to irradiate the deep UV light to remove the surface protection film, and subsequently the following step is performed in vacuum. .