JP2839615B2 - Cleaning solution for semiconductor substrate and method for manufacturing semiconductor device - Google Patents

Description

Description of the Invention [Object of the Invention] (Industrial application field) The present invention relates to a cleaning solution for semiconductor substrates and a method for producing the same, and more particularly to a method for removing metal contamination.

(Prior Art) Various cleaning liquids have been developed as cleaning liquids for semiconductor wafers depending on purposes. As a cleaning liquid for the purpose of removing metal contamination, a cleaning liquid such as an HCl-H ₂ O ₂ system is used. The basic cleaning principle of this cleaning liquid is to ionize and dissolve metals in an acidic liquid by utilizing the function of an oxidizing agent. The higher the temperature of the cleaning liquid, the greater the effect of ionization and the easier it is to dissolve the metal, and thus the higher the cleaning effect. However, a metal having a low standard free energy of formation of an oxide, for example, Al, is taken in the vicinity of the surface of the silicon oxide film and forms a stable oxide. Oxide thus taken into the oxide film does not easily ionize even in an acidic solution, and Cu, Fe, Ni
However, there is a problem that the cleaning effect is low as compared with metals having a high standard free energy of formation.

(Problems to be Solved by the Invention) In the conventional cleaning method, there is a problem that the standard free energy of formation is low and the cleaning power is low with respect to the metal taken in near the silicon oxide film surface. The present invention provides a cleaning solution and a cleaning method for efficiently ionizing and cleaning any metal, particularly a metal having a low standard free energy of formation, which is taken in an oxide film.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, a first invention is directed to an etching solution for etching a silicon oxide film on a semiconductor substrate, and an etching solution for etching the silicon oxide film. Provided is a cleaning solution for a semiconductor substrate including a nonmetallic oxidizing agent having a higher oxidation reaction rate than an etching rate and a strong acid for ionizing a metal.

According to a second aspect of the present invention, there is provided an etching solution for etching a silicon oxide film on a semiconductor substrate, a nonmetallic oxidizing agent having an oxidation reaction rate higher than an etching rate of the etching solution for the silicon oxide film, and ionizing a metal. An object of the present invention is to provide a method for manufacturing a semiconductor device, which includes a step of cleaning a semiconductor substrate using a cleaning solution containing a strong acid.

(Action) In the cleaning liquid configured as described above, basically, the principle of cleaning is to ionize a metal with a strong acid. At that time, an oxidizing agent is used to efficiently ionize even a metal having a small ionization tendency. Further, the surface of the silicon oxide film is etched with an etchant to expose the metal existing near the surface of the silicon oxide film to the surface. Then, the metal exposed on the surface is ionized by the strong acid. Incidentally, the oxidizing agent in the present invention,
It is important to have a role of always forming an oxide film on the surface of the silicon film as well as assisting in ionizing a metal having a low ionization tendency. That is, since a nonmetallic oxidizing agent having an oxidation reaction rate higher than the etching rate of the etching solution with respect to the silicon oxide film is used, the silicon oxide film always exists on the wafer surface after cleaning. The reason that the silicon oxide film should be present on the wafer surface is to prevent metals such as Cu from adsorbing on the wafer surface. These metals, which are likely to form silicide, adsorb to the wafer when the wafer is exposed, so the oxidation rate is made faster than the etching rate, so that a silicon oxide film is always present and this adsorption is prevented. is there.

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

In this example, the weight ratio of the etching solution was 0.025.
% Hydrofluoric acid and 0.8 ppm or more as a nonmetallic oxidizing agent
A cleaning solution containing ozone in a concentration range of 25.0 ppm or less and hydrochloric acid or sulfuric acid of PH2 or less, which is safe as a strong acid, is used.

The limit at which a metal can be ionized depends on the concentration of the acid and the oxidizing power of the cleaning solution, and varies depending on the metal. In particular, a strong oxidizing power is required for ionizing a metal having a low ionization tendency. In order to ionize all metals, mainly Fe, Ni, Al, Cu, Ag, Mg, Mn, Pb, Zn, Co, Mo, Ti, etc., detected at semiconductor product manufacturing sites, the acid concentration must be less than PH2 It is possible with a strong acid. Although hydrofluoric acid is used as an etching solution, the concentration of hydrofluoric acid needs to be a concentration capable of etching the outermost surface layer of SiO ₂ .

The interatomic distance of SiO ₂ is 1.6 ° between Si and O, and 2.6 between O and O.
Å. From this, it is necessary to etch at least 2.6 mm. Since the etching of a silicon oxide film with hydrofluoric acid has a large temperature dependence, it is necessary to make the temperature uniform within the wafer surface or within the batch. Therefore, it is most preferable to perform the treatment at around normal temperature. FIG. 1 shows the result of examining the dependence of the etching time on the amount of etching of the SiO ₂ film at 22 ° C. From this figure, weight ratio
With a 0.025% hydrofluoric acid solution, it is saturated at an etching amount of 2.5 mm. From this result, it is necessary that hydrofluoric acid has a concentration of 0.025% or more by weight.

The use of ozone as the oxidizing agent requires that hydrofluoric acid be used at around room temperature, so that it has sufficient oxidizing power around room temperature, is non-metallic, and does not adversely affect the wafer. Because they are satisfied. Incidentally, the wafer surface after cleaning is required to be in a state where a silicon oxide film is present. The reason for this is to prevent the metal which easily forms silicide from adsorbing to the wafer surface as described above. Therefore, ozone as an oxidizing agent not only ionizes metal impurities but also oxidizes silicon of the wafer, so it is necessary to oxidize at a faster rate than etching with hydrofluoric acid. Due to the above mentioned hydrofluoric acid etching rate, 2.5Å
As shown in FIG. 2, an ozone concentration of 0.8 ppm is required to oxidize the wafer. Also, ozone is 3 ℃ at 0 ℃ ・ 1atm.
Since it can be dissolved in pure water up to 8.5 ppm, it is almost 25 ppm at 22 ° C, and the effective range of ozone concentration is 0.8 ppm to 25 ppm. Therefore, if the ozone concentration is in this range, the metal detected at the manufacturing site can be sufficiently ionized under a strong acid of PH2 or less. As a method for adding ozone, ozone water dissolved in pure water may be used to mix with hydrofluoric acid and an acid, or ozone gas may be directly dissolved in hydrofluoric acid and an acid. Further, the cleaning may be performed while bubbling gaseous ozone without dissolving ozone before cleaning. In this case, it is sufficient that the ozone gas sufficiently contacts the entire wafer. As described above, the upper limit of the hydrofluoric acid concentration is restricted by the ozone concentration, but it is necessary to set the concentration at which the etching of the silicon oxide film is rate-determining.

FIG. 3 is a comparison diagram of cleaning results between the present invention and the conventional technology. In the present invention, the concentration of hydrochloric acid is 5 wt%, and the concentration of hydrofluoric acid is 0.0
Ozone gas was dissolved in a mixed solution of 25 wt%, and the wafer was washed at 22 ° C. for 10 minutes using a washing solution having a concentration of 2 ppm. Further, as a conventional technique, a wafer is washed at 80 ° C. for 10 minutes using a mixed solution having a concentration of hydrochloric acid of 5 wt% and a concentration of hydrogen peroxide of 4.8 wt%. Thus, in the present invention, it was confirmed that metals such as Al, which were conventionally difficult to clean, can be effectively removed.

[Effects of the Invention] As described above, according to the present invention, it is possible to efficiently ionize and clean a metal having a low standard free energy of formation and taken in the vicinity of the surface of a silicon oxide film. Become.

[Brief description of the drawings]

FIG. 1 is a diagram showing an etching rate of a silicon oxide film when a hydrofluoric acid solution having a weight ratio of 0.025% and 0.05% is used,
FIG. 2 is a diagram showing the oxidation rate of silicon with 0.8 ppm and 1.5 ppm of ozone water, and FIG. 3 is a comparison diagram of the cleaning effect between the present invention and the prior art.

Claims (2)

(57) [Claims] An etching solution for etching a silicon oxide film on a semiconductor substrate, a non-metallic oxidizing agent having an oxidation reaction rate higher than an etching rate of the etching solution for the silicon oxide film, and a strong acid for ionizing metal. A cleaning solution for a semiconductor substrate, comprising: 2. An etching solution for etching a silicon oxide film on a semiconductor substrate, a nonmetallic oxidizing agent having an oxidation reaction rate higher than an etching rate of the etching solution with respect to the silicon oxide film, and a strong acid for ionizing a metal. Cleaning a semiconductor substrate using a cleaning solution having the following.