JPH02102528A - Ashing process - Google Patents

Abstract

PURPOSE:To enable degenerated resist to be reduced into ashes within a short time by a method wherein a mixed gas comprising oxygen, ozone and carbon fluoride gas is fed to produce plasma to reduce a resist into ashes. CONSTITUTION:A mixed gas comprising oxygen containing high concentration ozone, carbon fluoride gas such as tetrafluorometane(CF4), trifluoromethane(CHF3), hexafluoroethane(C2F6), etc., used as an etching gas in the manufacture of a semiconductor device is made plasmatic. Consequently, even if arsenic, phosphorus, boron, etc., are ion-implanted in the manufacturing process, sufficient ashing rate can be shown without increasing the high-frequency power for producing plasma. Through these procedures, a resist can be reduced into ashes within a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for removing a resist in a dry state, and particularly to an ashing method by ashing the resist.

(Prior art) When manufacturing semiconductor devices such as IC1LSI, various treatments are applied to a silicon substrate on which a resist with a circuit pattern is formed using photo processing techniques, X-ray irradiation, electron beam irradiation, etc. After that, an ashing process is performed to remove the resist.

The resist is removed by a wet process in which it is immersed in an oxidizing liquid such as sulfuric acid containing hydrogen peroxide, or by a dry process using oxygen plasma, ultraviolet rays, ozone, or the like. Wet processing using a liquid requires a lot of effort to dispose of waste liquid, and there are also problems in that impurities contained in the liquid have an adverse effect on semiconductor devices, so dry processing is increasingly used.

In the method using oxygen plasma, which is the mainstay of dry processing, the ashing performance improves by increasing the output of the high frequency wave that generates the plasma, but as the degree of integration of semiconductors increases, damage to semiconductor devices due to ions and electrons generated by the plasma increases. has become a problem, and ashing methods using ozone or ultraviolet light are considered promising as ashing methods that do not cause damage to semiconductor devices.

(Problems to be Solved by the Invention) In the manufacturing process of semiconductor devices, there are several resist removal steps, so shortening the processing time in the resist ashing step is an effective way to increase the productivity of semiconductor devices. has important significance.

Therefore, a method of ashing the resist at high speed is required. However, in the ashing method using oxygen plasma, which is the mainstay of dry processing, although the resist ashing speed increases by increasing the high-frequency power used to generate the plasma, harmful ions and electrons are generated as the plasma is generated. Particularly in semiconductor devices that have become more highly integrated and miniaturized, problems such as damage to the electrical characteristics of the semiconductor, such as breakdown of an insulating film and charge-up, have become a problem.

In order to prevent such negative effects on semiconductor devices due to plasma, the high frequency power for plasma generation is lowered to 100 to 200 W and a mixed gas containing ozone is supplied into the plasma generation chamber.
A method has been proposed to obtain a processing speed equivalent to that obtained by applying high frequency power of 00 to 700 W. (Tokuko 53
-24302). However, with this method, it is possible to simply remove thermally hardened resist in a relatively short time, but the ashing speed of resist that has been subjected to various treatments in the semiconductor manufacturing process is slow. becomes smaller. Especially in the semiconductor manufacturing process, arsenic,
When ions such as phosphorus or boron are implanted, the implanted ions and the polymeric compound of the resist appear to undergo a chemical reaction that transforms the resist into a substance that has extremely high resistance to oxidation, resulting in a very slow removal rate. becomes smaller.

For example, “Monthly Sem1conductor World
dj Vol. 7 No. 5 Pages 49 to 50 (19
(May 1988 issue) describes the resist residue after ion implantation, stating that ion-implanted resists exhibit large resistance to oxygen plasma, and phosphorus-implanted resists do not have ion-implanted resists. Residue in case of resist is 4
It has been revealed that there are 2,496 residues compared to 99 in inch wafers, and that 8,474 residues remain in wafers in which arsenic ions have been implanted.

In order to deal with such problems, it has been considered essential to wet-process the resist using a strong acid, since dry processing using oxygen plasma alone cannot deal with the resist after ion implantation. In addition, the resist ashing method, which uses ozone to act on the heated resist to ash the resist, is attracting attention as a dry resist ashing method that has less impact on semiconductor devices. Although there is very little adverse effect on the characteristics of the semiconductor device such as ashing, the removal rate becomes extremely low if ions are implanted more than in the case of ashing using oxygen plasma.

(Means for Solving the Problems) Therefore, the present inventors focused on a reactive gas added to the processing gas supplied into the processing apparatus using oxygen plasma, and found that even if the high frequency energy for turning into plasma is small, It has been found that a high ashing rate can be obtained and that this method is particularly effective in ashing the resist after ion implantation.

In other words, oxygen containing a high concentration of ozone and tetrafluoromethane (CF4), which is used as an etching gas in the manufacture of semiconductor devices, are present in the processing chamber where the resist is removed.
, ) is a mixture of fluorinated carbon gases such as refluoromethane (CHF3) and hexafluoroethane (CaFs), and despite the low output of high-frequency power used to generate plasma, it achieves an extremely high ashing rate. This is a method of ashing the resulting resist, and even if the resist has been ion-implanted with arsenic, phosphorous, boron, etc., a sufficient removal rate can be obtained without increasing the output of high-frequency power introduced into the processing chamber.

(Function) Oxygen containing high concentrations of ozone and fluorinated carbon gases such as tetrafluoromethane (CF4), refluoromethane (CHFs), and hexafluoroethane (C2F11), which are used as etching gases in the manufacture of semiconductor devices. By turning a mixed gas into plasma, even when ions such as arsenic, phosphorus, and boron are implanted during the manufacturing process, a sufficient ashing rate can be obtained without increasing the high-frequency power for plasma generation. This greatly contributes to the mass production of devices.

(Example) An apparatus for carrying out the method of the present invention will be described below based on the attached drawings.

A semiconductor device 4 from which a resist 3 is to be removed is placed on a sample stage 2 in a processing chamber 1 . An electrode 5 for generating plasma is installed inside the processing chamber, and an external high frequency power source 6 is connected to the processing chamber.
13.56MH2 high frequency power is supplied from Further, a supply pipe 7 for supplying gas into the processing chamber, a pressure control valve 8, and an exhaust system 9 for processing gas such as ozone are attached. The supply pipes include a pipe from the ozone generator 10 and a pipe from the fluorinated carbon gas storage tank 11, each connected to a flow control valve 12.
It is attached via 13. Plasma generation is not limited to such a radio frequency current; a 2.45 GHz microwave current can also be used. The plasma that excites the processing gas may be generated directly within the processing chamber, or may be generated in a separate chamber and introduced into the processing chamber. Further, the ashing method of the present invention can be applied to either a pattern-type device or a batch-type device.

Example 1 As the processing gas supplied into the processing chamber (1) only oxygen,
(2) Oxygen containing ozone at a concentration of 80 OOPPPM, (3) Gas containing oxygen with tetrafluoromethane added, (4) Gas containing ozone and tetrafluoromethane at a concentration of 80,000 PPM (7) Gas containing ozone and tetrafluoromethane are supplied at a flow rate of 3 cc/min each, and the inside of the processing chamber is 0.35 t.
The pressure was reduced to or. There are 13 electrodes installed in the processing chamber.
．． A high frequency power of 56M11Z was supplied.

The high frequency power supplied was 70W.

The resist to be ashed contains 8.0x1016 arsenic.
A material implanted with CI-2 ions was used. Table 1 shows the ashing speed when using each gas. When a mixed gas of oxygen, ozone, and fluorinated carbon is used as the processing gas, the etching selectivity between the resist and silicon oxide is 1000, which does not have any adverse effect on the semiconductor device being manufactured.

Table 1 Example 2 When we investigated the relationship between the amount of tetrafluoromethane added to ozone-containing oxygen and the ashing rate, we found that for resists without ion implantation, the ashing rate increased with the amount of tetrafluoroethane added. However, in a resist with arsenic ion implantation, the amount added is 10%.
The ashing speed increases until then, but after that the ashing speed decreases.

(Effects of the Invention) As detailed above, the method of the present invention achieves low output by using fluorinated carbon gas as an oxygen gas containing ozone gas as a processing gas, despite the low output of high-frequency power for plasma generation. Ashing using oxygen plasma using output high-frequency power has the effect that even resist that has been altered due to chemical reaction with the implanted ions due to ion implantation, which takes a long time to ash, can be ashed in a short time.

[Brief explanation of the drawing]

FIG. 1 shows an ashing device for carrying out the ashing method of the present invention. 1...Processing chamber 2...φφ sample stage 3...Resist 4...Semiconductor device 5...Fist/plasma generation electrode 6/III/High frequency power source 711...Supply pipes 8/9・ ・Pressure control valve・Exhaust system・Ozone generator・Fluorinated carbon gas storage tank・Flow control valveFist flow control valve

Claims (3)

[Claims] (1) An ashing method characterized by supplying a mixed gas of oxygen, ozone, and fluorinated carbon gas to generate plasma and ashing the resist. (2) The ashing method according to claim 1, wherein the fluorinated carbon gas is tetrafluoromethane, trifluoromethane, or hexafluoroethane. (3) The ashing method according to claim 1 or 2, wherein the resist is a resist after ion implantation.