JPH0624197B2 - Surface protection method - Google Patents

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, which makes it difficult to perform regular crystal growth, and when forming a metal electrode or the like, the contact resistance increases due to this insulating layer. 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 target 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) In the surface protection method of the present invention, after the dry etching or the dry film formation step, the sample is taken out into the atmosphere and a halocarbon gas or a gas containing it is discharged to form a surface protection film. However, before the next step, a gas capable of etching the surface protective film is introduced to irradiate Deep UV light to remove the surface protective film, and the next step is continuously performed in a vacuum.

(Operation) The present invention has solved the problems of the prior art by adopting the above configuration. For example, after plasma etching, reactive sputter etching, and film forming process, the sample is taken out into the atmosphere, and CF ₄ , CHF ₃ , CF ₄ + H
Gas plasma treatment with a halocarbon gas such as ₂ or a gas containing the same is performed. After that, take it out into the open air,
Immediately before starting the next process, for example, in the film forming step, photoetching using Cl ₂ , F ₂ or the like is performed in the same chamber or a vacuum chamber connected to it in vacuum. Then, the surface plasma-treated with a gas of a carbon halide for light is extremely hard to be oxidized, and thus 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.

FIGS. 1 (a) to 1 (c) show 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 (a)
In the figure, after etching SiO ₂ 12 with a resist mask 11 using CF ₄ type gas, it is taken out into the atmosphere. On the etched surface, a contamination layer (contamination layer, hereinafter abbreviated as a contamination layer) 14 is formed on the Si substrate 13. This layer contains sputtered substances during etching, particularly enzymes from the resist, carbon, or fluorine or carbon contained in the gas. This contamination layer 14 is SIMS
Analysis revealed that it was about 150Å. Further, as shown in (b) in the figure, the resist is ashed in oxygen plasma and remains unremoved.
Next, in order to remove the contamination layer 14 by photoetching as it is, first, a natural oxide film on the contamination layer with an aqueous solution of HF, or on the contamination layer due to an enzyme which is considered to have been sputtered into the mask during etching The thin oxide film must be removed. Then, a wet process is performed and necessary SiO ₂ 12 is also etched. Therefore, in the present invention, after the resist 11 is ashed by the enzyme plasma shown in FIG. 1 (a), it is taken out in the same chamber or in another chamber, CF ₄ is flown, and plasma is raised for about 30 seconds to perform surface treatment. Then, the thin oxide film on the contamination layer 14 on the Si substrate 13 was removed, and the surface was replaced with carbon and fluorine. The treatment protection layer 15 shown in FIG.
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,
Turning to the growth process, this film forming apparatus, Cl ₂ in vacuo
Alternatively, there is a device capable of irradiating Deep UV light while flowing F ₂ gas, such as an excimer laser device or a Hg lamp. Fig. 1 (c)
At, the Cl ₂ gas was flowed while evacuating, and the pressure was increased.
When the deep UV light is irradiated at 600 mTorr, Cl ₂ gas is released.
It is decomposed by DeepUV light and Cl radicals are generated. The generated Cl radicals can easily etch the processing protective layer 15 and the contamination layer 14 which is the base thereof.
FIG. 2 shows the relationship between the Cl ₂ pressure and the etching rate in this Cl ₂ photoetching. About 150Å
Since it is a contamination layer of a certain degree, it is sufficient to select a 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 concentrations of carbon and fluorine during the etching of the contamination layer during the Cl ₂ photoetching time, which were measured by Auger analysis. It can be seen that the protective layer and the contamination layer are removed by etching for about 2 minutes. Carbon concentrations fall to about the same level of carbon pollution from 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 rate of Si with Cl ₂ gas and XeF ₂ gas, and also with Cl _{2 of} the sample plasma-treated by changing the gas to CF ₄ immediately after etching with Cl ₂ or XeF ₂ without breaking the vacuum. _It shows the photo-etching rate of _two photo-etching. That is, the photo-etching rates of the two types without CF ₄ treatment are about 20Å / min and about 14Å / min, while the photo-etching rate of Si treated with CF ₄ is about 100Å
It is as big as / min. That is, the surface of Si exposed to halogen atoms such as Cl ₂ and XeF ₂ is very likely to be oxidized,
Light etching rate is low. On the other hand, like CF ₄ , since it contains carbon even if it contains halogen, its surface is extremely difficult to be oxidized. That is, a large etching rate can be obtained by photoetching. Next, A in Fig. 3
In the graph of the results of the uger analysis, under the condition that the photo etching time is within 2 minutes, that is, when the carbon concentration is high, the oxygen concentration is low, the photo etching time is long, the carbon concentration is low, and 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-mentioned embodiment, Cl ₂ gas is flown while evacuating and the De
Although it was irradiated with epUV light, Cl ₂ gas was introduced into the chamber at once, vacuum exhaust was stopped, and a Cl ₂ atmosphere was created.
The treatment protective layer 15 and the contamination layer 14 can be removed even by irradiation with.

Further, Cl ₂ gas may be introduced into the chamber to be adsorbed on the sample surface, the Cl ₂ gas may be exhausted, and the 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.

(Effects of the Invention) A method of forming the surface treatment protective layer of the present invention and removing it by photoetching as necessary, that is, a surface on which a surface oxide film is not formed even when exposed to the outside air is obtained. Was given. This effect is explained by the Aug.
er analysis results and the photo-etching results in Table 1 were fully confirmed.

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 view showing the Cl ₂ pressure dependence of the etching rate of Si, and FIG. 3 is a view showing the present invention. 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 …… contamination layer 15 …… processing protection layer, 16 …… Deep UV light

Claims (1)

[Claims] 1. After the dry etching or dry film forming step, the sample is taken out into the atmosphere and a halocarbon gas or a gas containing the same is discharged to form a surface protective film, and the above-mentioned surface is formed before the next step. A method for surface protection, which comprises introducing a gas capable of etching a protective film, irradiating it with light to remove the surface protective film, and subsequently performing the following steps in vacuum.