JPH04213824A - Plasma polymerized film and method of removing heavy metal contamination - Google Patents

Abstract

PURPOSE:To remove without damage the plasma polymerized film and heavy metal contamination generated on Si surface by conducting reactive ion etching. CONSTITUTION:The silicon substrate 5, on which reactive ion etching has been finished, is put in a treatment chamber 7, and then the silicon oxide film is removed by etching. These processes are repeated two or more times.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing heavy metal contamination and a plasma polymerized film formed on a silicon surface after reactive ion etching in the manufacturing process of semiconductor devices.

0002

2. Description of the Related Art In the manufacturing process of semiconductor devices, oxygen plasma etching or oxygen R
A removal method using IE is often used. In these removal methods, highly reactive oxygen atoms generated by plasma react with the plasma polymerized film to generate volatile oxides such as carbon dioxide (CO2), and then the Si surface is further cleaned. wet chemical cleaning methods, such as sulfuric acid (H2 SO4)/hydrogen peroxide (H2 O
2) solution, H2SO4/nitric acid (HNO3) solution,
Alternatively, treatment with hydrofluoric acid or the like is performed. These treatments are described, for example, in the article "Young et al., Journal of the Electrochemical Society, 12
Volume 2, No. 5, Page 675, 1975” (M.G.
Yang. etc. Al, Journal of th
e Blectrochcmical Society
, Vol. 122, No. 5, 675 (1975
)), “Mew et al., Journal of Applied Physics, Vol. 59, No. 8, p. 2958, 1986.”
(X. C. Mu. et. al. Jural
of Applied Physics, Vol.
59, No. 8, 2967 (1986)), Gampino et al., Journal of the Electrochemical Society, Vol. 137, No. 3, p. 976, 19
'90' (J.P. Gambino.et.al,
Journal of theElectroche
mical Society, Vol. 137. No
．． 3, 976 (1990)) etc.

On the other hand, a method using ultraviolet light has been proposed as a method for removing organic substances on the Si surface or organic coatings such as resist. In this method, active oxygen atoms generated by irradiation with ultraviolet light in an oxygen or air atmosphere combine with carbon on the Si surface or with carbon, which is one of the main constituent elements of the resist material. ,
By forming a volatile oxide such as CO2 and removing carbon, the above-mentioned organic substances, resist, etc. are removed. Regarding these techniques, for example, the document "Journal of Vacuum Science and Technology A, Volume A3, No. 3, Page 1027, 1985" (Journal of Vacuum Science
nce & Technology A. Vol. A3
．． No. 3, 1027 (1985)), “Journal of the Electrochemical Society, 13
4, No. 8, p. 2052, 1987” (Journ
al of the electrochemical
Society. Vol. 134, No. 8, 2
052 (1987)), “Journal of the Electrochemical Society, Vol. 136, No. 5, 1
474 pages, 1989” (Journal of th
e Electrochemical Society
．． Vol. 136, No. 5,1474 (1989))
It is described in etc. Furthermore, an invention related to an organic film removal device applying the above-mentioned technology has been proposed (Japanese Patent Application Laid-open No. 1911/1999).

0004

[Problems to be Solved by the Invention] In removing the plasma polymerized film formed on the Si surface after RIE, the above-mentioned oxygen plasma etching or method using oxygen RIE removes charged particles (ions, etc.) generated in the plasma.
electrons), and neutral particles bombard every surface of the processing chamber walls. For this reason, when there are contaminants such as heavy metals on the walls of the processing chamber, or when the walls of the processing chamber are made of a metal material such as stainless steel, the surface may be sputtered due to collision with the particles, resulting in heavy metals and other contaminants. contaminants adhere to the Si surface. In addition, like the inner wall of the processing chamber, the Si surface is also affected by the particles, so the S
There are problems such as defects occurring near the i-surface and contaminants such as heavy metals attached to the Si surface by RIE entering the inside of the Si substrate. In the method using ultraviolet light, there is no impact from charged particles or neutral particles, so heavy metal contamination as described above can be reduced. R.I.E.
No study has been conducted as a method for removing the plasma-polymerized film, heavy metal contamination, or damaged layer caused by plasma irradiation that occurs later.

The purpose of the present invention was proposed in order to improve the above-mentioned drawbacks, and the purpose of the present invention was to eliminate the plasma polymerized film, heavy metal contamination, and plasma irradiation damage layer near the Si surface that are generated on the Si surface after RIE. It is an object of the present invention to provide a method for removing a plasma polymerized film without causing heavy metal contamination or damage during removal.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a plasma polymerized film 1 as shown in FIG.
By irradiating the Si substrate 4 with attached ultraviolet light in a processing chamber with an air or oxygen atmosphere,
The plasma polymerized film is oxidized by ultraviolet light and ozone generated by the ultraviolet light, and the plasma polymerized film on the Si surface is removed. Next, silicon oxide film (SiO2) on Si
Soak in hydrofluoric acid, etc. to remove. After this, ultraviolet light irradiation or wet organic substance removal is performed again in the atmosphere. At this time, SiO2 is formed on the Si surface, so this SiO2 is removed using hydrofluoric acid or the like. The present invention is characterized in that the method described above removes the plasma polymerized film without heavy metal contamination and damage, and also removes the heavy metal contamination 2 on the Si surface and the damaged layer 3 near the Si surface caused by RIE. shall be.

[0007]

[Operation] When irradiated with ultraviolet light in air or an oxygen atmosphere, oxygen molecules are excited and active oxygen atoms and ozone are generated. Furthermore, this ozone is also excited by ultraviolet light to produce oxygen atoms. These oxygen atoms act as a strong oxidizing agent, oxidize the plasma polymerized film on the Si surface, generate volatile oxides such as carbon dioxide (CO2), and remove the plasma polymerized film. In addition, active oxygen atoms combine with Si, resulting in SiO2
form. By removing this SiO2 using hydrofluoric acid or the like, heavy metal contamination on the Si surface can be removed together with SiO2. However, when a damaged layer exists near the Si surface due to, for example, RIE, the oxygen atoms generated by the above-mentioned ultraviolet light irradiation cannot sufficiently oxidize this damaged layer, and oxidation stops. Therefore, the Si surface from which the plasma polymerized film has been removed by the above method is irradiated with ultraviolet light again, or a chemical solution is used to remove the Si surface.
i Oxidize the surface. As a result, the damaged layer near the Si surface is oxidized. SiO2 thus formed
The damaged layer can be removed by removing it using hydrofluoric acid or the like.

[0008]

[Example] Next, an example of the present invention will be described. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention. FIG. 2 shows a schematic diagram of the device of the invention. The wafer 5 is placed on a wafer susceptor 8 in a processing chamber 7 in which an ultraviolet light source 6 is installed, and air or oxygen is introduced into the processing chamber 7 through a gas inlet 9. Thereafter, the wafer 5 is processed using ultraviolet light generated from the ultraviolet light source 6. Gas introduced through the gas inlet 9 and volatile gas generated by ultraviolet light irradiation are exhausted through the gas exhaust port 10. It is considered that it is more effective to make the distance between the wafer 5 and the ultraviolet light source 6 as close as possible. This is because ozone generated by ultraviolet light irradiation has a wide absorption band centered around a wavelength of 260 nm. In this embodiment, a low-pressure mercury lamp was used as the ultraviolet light source 6. In addition, the power density of ultraviolet light is 50m at a distance of 30mm from the ultraviolet light.
It was V/cm2.

In this example, RIE was performed on single crystal silicon using a mixed gas of fluorocarbon 14 (CF4) and hydrogen (H2) as an etching gas, and a plasma polymerized film was formed on the Si surface. Using. After the sample was placed on the wafer susceptor 8, it was irradiated with ultraviolet light in the air. The irradiation time of ultraviolet light was 20 minutes.

[0010] The sample irradiated with ultraviolet light showed hydrophilicity. This result suggests that ultraviolet light irradiation caused the removal of the plasma polymerized film by desorption of C and the formation of SiO2 near the surface.

[0011] Next, the sample was immersed in dilute hydrofluoric acid to remove SiO2, but the sample still showed hydrophilicity. It can be seen from this that no clean Si surface is exposed. This result was the same even if the irradiation time of ultraviolet light was increased. FIG. 3 shows the relationship between the ultraviolet light irradiation time and the SiO2 film thickness measured with an ellipsometer. It can be seen that when the irradiation time is 20 minutes or more, the film thickness is saturated and oxidation is not progressing.

Carbon (C) near the surface of this sample,
Oxygen (O) and silicon (Si) were investigated by Auger electron spectroscopy (AES). 4 and 5 show the AES results of the sample immediately after RIE and after the diluted hydrofluoric acid treatment described above. In the sample mentioned above, compared to immediately after RIE, C
It can be seen that the plasma polymerized film was removed by desorption of C. However, the same amount of C as Si was detected near the surface, and it is considered that a compound of Si and C is formed on the Si surface. The reason why the growth of SiO2 was stopped and C could not be removed sufficiently with one UV light irradiation is that the damage layer created near the Si surface by RIE caused the diffusion of active oxygen atoms. This is thought to be due to the inhibition of

Therefore, this sample was again irradiated with ultraviolet light for 10
After that, the sample was immersed in diluted hydrofluoric acid. As a result, the sample showed hydrophobicity, and after the second UV light irradiation,
It is considered that the desorption of C and the oxidation of the Si surface further progressed, and the subsequent diluted hydrofluoric acid treatment exposed the clean Si surface. FIG. 6 shows the results of examining this sample by AES. After the first UV light irradiation, compared to the AES results of the sample treated with diluted hydrofluoric acid (Figure 5), C was further reduced, and it was confirmed that SiO2 on the surface was also removed. Ta. From these results, it was found that the plasma polymerized film on the surface could be removed by the method described above and that a clean Si surface could be obtained.

As one of the general methods for removing the plasma polymerized film formed after RIE, after performing oxygen RIE,
A commonly used method is to clean the surface with a H2 SO4 /H2 O2 solution and then remove oxides with diluted hydrofluoric acid or buffered hydrofluoric acid. Therefore,
For comparison, AES analysis was performed on a sample from which the plasma polymerized film was removed by this conventional method. The results are shown in FIG. Comparison with FIG. 6 shows that the removal method according to this example using ultraviolet light irradiation has a large effect on reducing C.

The amount of heavy metal contamination on the Si surface was investigated using a total internal reflection fluorescent X-ray spectrometer (TXRF). As a result, as shown in FIG. 8, heavy metal contamination generated on the Si surface by RIE was reduced to about 1/3 using the conventional method, whereas iron (Fe) was reduced to about 1/3 using the removal method of the present invention. In this case, Fe was reduced to about 1/5. This involves the removal of SiO2 formed on the Si surface by ultraviolet light irradiation, and the
This is because the heavy metal contamination that existed on the i surface was also removed.
It has been found that the method for removing plasma polymerized films according to the present invention is an extremely effective method for reducing heavy metal contamination.

Next, as a second embodiment, a case will be described in which a surface cleaning treatment using a chemical solution is performed instead of the second ultraviolet light irradiation in the first embodiment. As a sample, a wafer manufactured under the same conditions as in the first example was used. This sample was subjected to ultraviolet irradiation for 20 minutes in air, as in the first example, and then immersed in diluted hydrofluoric acid to remove SiO2 on the sample surface. Next, the sample was treated with H2S, which is commonly used as a wet method for removing organic matter.
Organic matter was removed by immersion in O4 /H2 O2 solution for 5 minutes. After treatment with the chemical solution, the sample showed hydrophilicity. This indicates that SiO2 is formed on the surface. Therefore, after sufficient water washing, the sample was immersed in diluted hydrofluoric acid to remove SiO2 from the sample surface. The sample after this treatment showed hydrophobicity. Further, as a result of examining this sample by AES, it was found that C was decreased and the plasma polymerized film on the surface was removed. In addition, the amount of heavy metal contamination on the Si surface investigated by TXRF was almost the same as in the conventional method using oxygen RIE. However, the removal method according to the present invention is considered to be superior in that it causes less damage to the Si substrate, and is more effective as a process with less damage than the conventional method.

[0017]

As explained above, the plasma polymerized film removal method of the present invention oxidizes the plasma polymerized film formed on the Si surface after RIE with ultraviolet light irradiation and ozone generated thereby, and removes the Si substrate. By removing the plasma polymerized film on the Si surface with low contamination and damage, and removing SiO2 formed on the Si surface using hydrofluoric acid, the Si surface damaged by RIE and heavy metals on the Si surface can be removed. This removes contamination and exposes a clean Si surface. Therefore, when the present invention is applied as a post-processing process when a contact hole on a shallow junction of a semiconductor device is processed by RIE, damage to the shallow junction can be reduced compared to, for example, a conventional method using oxygen RIE. In addition, a clean Si surface with less heavy metal contamination can be obtained. Therefore, a high-performance semiconductor device with low junction leakage current and low contact resistance can be manufactured.

[Brief explanation of the drawing]

FIG. 1 shows the structure of the Si surface after RIE.

FIG. 2 shows a schematic structural diagram showing an example of a removal device for carrying out the present invention.

FIG. 3 shows the relationship between the irradiation time of ultraviolet light and the oxide film thickness measured with an ellipsometer.

FIG. 4 shows the results of AES analysis in the depth direction immediately after RIE.

FIG. 5 shows the results of AES analysis in the depth direction after ultraviolet light irradiation and diluted hydrofluoric acid treatment.

FIG. 6 shows the results of AES analysis in the depth direction after repeating ultraviolet light irradiation and diluted hydrofluoric acid treatment twice.

FIG. 7 shows the analysis results of a sample processed by a conventional method.

FIG. 8 shows the relationship between various treatment methods including the present invention and the amount of heavy metal contamination investigated by TXRF.

[Explanation of symbols]

1 Plasma polymerized membrane 2 Heavy metal pollution 3 Damage layer 4 Si 5 Wafer 6 Ultraviolet light source 7 Processing room 8 Wafer susceptor 9 Gas inlet 10 Gas outlet.

Claims (2)

[Claims] 1. A silicon substrate etched by reactive ion etching is loaded into a processing chamber equipped with an ultraviolet light irradiation device, and the silicon surface is etched by ultraviolet light irradiation in air or an oxygen atmosphere. After oxidizing the surface, this silicon oxide film is etched. By repeating these steps two or more times, a plasma polymerized film formed on the silicon surface due to reactive ion etching, heavy metal contamination on the silicon surface, and A method of removing damaged layers near the surface by plasma irradiation. 2. Filling the processing chamber with a silicon substrate etched by reactive ion etching,
The silicon surface is oxidized by irradiation with ultraviolet light in air or an oxygen atmosphere, then this silicon oxide film is etched, and the silicon surface is further oxidized again with a chemical solution to oxidize the silicon surface. A method of etching the oxide film to remove a plasma polymerized film formed on the silicon surface by reactive ion etching, heavy metal contamination on the silicon surface, and damaged layers near the surface due to plasma irradiation.