JP3185732B2 - Substrate surface metal contamination removal method - Google Patents

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 metal impurities present on the surface of a semiconductor substrate covered with an SiO ₂ film of a semiconductor device.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, it is known that metal impurities adhering to the surface of a semiconductor substrate adversely affect the electrical characteristics of the device. In order to remove the contamination due to the metal impurities and to prevent the contamination to others, various cleaning steps are introduced at important points in the manufacturing process. As a cleaning chemical in the cleaning step, for example, a mixed solution of ammonia (NH ₄ OH) and hydrogen peroxide (H ₂ O ₂ ) (SC-1 or APM, hereinafter APM), HC
I · H ₂ O ₂ mixture (SC-2 or HPM, hereinafter HPM
To), nitric acid _{(H 2 SO 4) · H} 2 O 2 mixture (hereinafter SPM
And a diluted HF solution (hereinafter referred to as DHF).

[0003] Among these cleaning chemicals, HPM and SPM are particularly effective for metal impurities, and cleaning with these removes metal contaminants by dissolving them. For this reason, no effect is obtained for elements that are difficult to melt in the cleaning solution or that do not melt at all, for example, Pt, Ir, Ru, and the like. Cleaning with DHF in the cleaning liquid removes metal impurities and particles adhering to the surface by etching the entire SiO ₂ film such as a natural oxide film or a thermal oxide film on the surface of the Si substrate. However, in the cleaning method using DHF, the SiO ₂ film on the surface is etched to expose the bare Si surface. The bare Si surface is in an extremely active state, and is in a state where contaminants are easily adsorbed. Therefore, according to this cleaning means, metals and particles once released into the DHF solution are likely to be re-adsorbed, and are likely to be contaminated from the atmosphere after cleaning, the carrier, or the device in the next step.

As a countermeasure for this, Japanese Patent Laid- Open Publication No. Hei 8-3178
1 discloses a means for adding H ₂ O ₂ to a dilute HF aqueous solution and forming a thin SiO ₂ film together with the etching of the SiO ₂ film as shown in FIG.

[0005]

However, according to the means disclosed in Japanese Patent Application Laid-Open No. 8-31781, the SiO ₂ film to be formed is very thin and is formed simultaneously with the etching reaction by HF. Is in an active state, and the re-adsorption of metal contaminants cannot be completely suppressed. Moreover, the oxidation of the Si substrate
Since O ₂ is formed, the re-adsorbed metal contaminants are taken into the SiO ₂ film. Further, Japanese Unexamined Patent Publication No.
The method disclosed in No. 31781 utilizes the oxidation of the Si substrate that appears after etching the entire oxide film on the surface, and therefore can be used only in the initial stage of device formation. After the capacity formation process,
This method cannot be used after forming the interlayer insulating film. In view of the above problems, an object of the present invention relates to a method for removing metal impurities present on the surface of a semiconductor substrate covered with a SiO ₂ film, and particularly to Pt, Ir, and Ru that hardly melt with a conventionally used cleaning liquid. And other metal contamination.

[0006]

In order to achieve the above object, the present invention provides a method for removing metal contaminants adhering to the surface of a semiconductor substrate covered with a SiO ₂ film.
F) or ammonium fluoride (NH ₄ F), and etching the SiO ₂ film with a cleaning solution containing nitric acid (HNO ₃ ) and / or hydrochloric acid (HCl).

According to the first aspect of the present invention, an upper layer of a metal electrode, a metal wiring and a capacitor is formed of a silicon oxide film (SiO
₂ ) is a method for removing metal contaminants attached to the surface of the semiconductor substrate covered with ( ₂ film), comprising hydrofluoric acid (HF) or ammonium fluoride (NH ₄ F), and nitric acid (HNO ₃ ) and hydrochloric acid (HCl). etching the SiO ₂ film with a washing solution containing both or either one, characterized in that the thin film from the previous etching the SiO ₂ film. The invention according to claim 2 is a method for removing metal contaminants adhering to the surface of a semiconductor substrate in which an upper layer of a metal electrode, a metal wiring, or a capacitor is covered with a SiO ₂ film, comprising hydrofluoric acid (HF) or The etching is performed by using a cleaning solution containing ammonium fluoride (NH ₄ F) and / or nitric acid (HNO ₃ ) and / or hydrochloric acid (HCl) under the condition that a part of the SiO ₂ film is left.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1A shows SiO 2
₂ shows a state in which a metal contaminant 13 adheres to the surface of the Si substrate 11 covered with the _second film 12. Next, FIG.
As shown in (b), the substrate contaminated with the metal is immersed in a cleaning liquid 14 containing HF or NH ₄ F, and the SiO ₂ film 12 is etched to such an extent that the Si substrate surface 11 is not exposed. Thereafter, as shown in FIG. 1 (c), the chemical solution attached to the substrate is washed away with pure water, and dried using a spin drier or the like. As described above, the metal contaminants 13 that adhere to the surface of the SiO ₂ film 12 and are not easily dissolved in the cleaning solution are:
By partially etching the SiO ₂ film 12,
It is removed together with the SiO ₂ film 12. Further, the metal contaminants 13 removed and released into the solution are not re-adsorbed by the SiO ₂ film 12 remaining on the substrate surface.

In one embodiment of the present invention,
Although the method of removing metal contamination on the substrate surface of the Si substrate 11 covered with the SiO ₂ film 12 has been described, the present invention is not limited to this. According to the method for removing metal contamination on the surface of the substrate, the SiO ₂ film 12 remains and prevents erosion or the like of the lower layer of the SiO ₂ film by the cleaning liquid, so that the lower layer of the SiO ₂ film 12 is not damaged. Therefore, even when a metal electrode, a metal wiring, a capacitance portion, and the like have already been formed below the SiO ₂ film, the method of removing the metal contaminants is effective.

When HNO ₃ and / or HCl are added to the cleaning solution 14 containing HF or NH ₄ F, not only are the particles released into the cleaning solution but also the ionic solution. Since the ratio of metal contaminants eluted therein increases, the effect of removing metal contaminants is further obtained.

[0011]

(Embodiment 1) Next, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 (a) shows the S covered with the SiO ₂ film 12.
This shows a state where the metal contaminant 13 is attached to the surface of the i-substrate 11. Next, as shown in FIG. 1B, the metal-contaminated substrate was immersed in a cleaning solution 14 containing HF for 5 minutes, and the SiO ₂ film was coated on the substrate ₂ so that the surface of the Si substrate was not exposed.
Etching is performed leaving 00 nm. Then, FIG.
The chemical solution attached to the substrate is washed away with pure water as described above, and dried using a spin drier or the like. According to the above procedure, when the substrate having Pt adhered to the metal adhesion amount of 1 × 10 ¹² cm ⁻² was processed, the metal adhesion amount was 1 × 10 ⁸ cm.
^-Reduced to ² units.

For comparison, the SiO _{2 on the} surface of the Si substrate 11 was
When the entire film 12 is etched, SPM is used as a cleaning liquid.
When the method described in Japanese Patent Application Laid-Open No. 8-31781 was used, the same processing was performed on the same substrate as described above. When the entire SiO ₂ film 12 was etched, the metal adhesion amount was 3 to 5 × 10 ⁹ cm ⁻² . This was due to the re-adsorption of the metal released into the cleaning solution, which reduced the removal effect. When SPM is used as a cleaning liquid,
The metal adhesion amount was 6 to 8 × 10 ¹⁰ cm ⁻² . SPM
In the case of cleaning, since etching of the SiO ₂ film and dissolution of the metal do not occur, the metal adhering to the surface with a small force is released, and a sufficient effect of removing metal contamination cannot be obtained. Also in the method disclosed in JP-A-8-31781, 1-4 × 10 ⁹ cm ⁻² remained on the surface. In the above method, etching and generation of the SiO ₂ film occur simultaneously, and since the surface is in an active state, re-adsorption of metal occurs.
A sufficient removal effect cannot be obtained.

[0013] In the first embodiment of the present invention has been described substrate contaminated with Pt, the substrate surface metal decontamination method of the present invention, SiO ₂ film 12 deposited contaminating metals
To remove contaminant metals by etching
It is effective for all metals that are not easily dissolved by conventional cleaning liquids such as Ir and Ru. Further, in the first embodiment of the present invention, the processing with one substrate is taken as an example.
The number of sheets to be processed is not limited, and a large number of sheets may be processed simultaneously.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIG. One of the nonvolatile semiconductor memory devices includes a ferroelectric material such as PZT.
(Pb (Zr, Ti) O ₃ : leadzirconat
ferroelectric RAM (ra
ndaccess memory). Pt, Ir, or the like is used for the capacitance electrode of this device, and a large amount of metal contamination occurs in the capacitance formation step. In the second embodiment of the present invention, in such a semiconductor device, metal contamination attached to the substrate was removed. FIG. 2 (a), (b)
1 shows a device structure when performing cleaning for removing metal contamination. FIG. 2 (a) shows a MOS formed already.
An SiO ₂ film 42 is formed on the formation region 23 such as a transistor.
Are formed, and ferroelectric capacitors 24 to 26 are formed thereon. Here, an SiO ₂ film is formed on the back surface and the peripheral portion of the substrate. However, this SiO ₂ film is formed at the time of forming the transistor and need not be formed. However, if necessary,
It may be newly formed.

In forming the ferroelectric capacitor, a large amount of metal contamination occurs, particularly when forming the capacitor electrode by the sputtering method or when forming the capacitor pattern. FIG. 2B shows a structure in which the upper part of the ferroelectric film capacitor is covered with the SiO ₂ film 27.
In this structure, cleaning for removing metal contamination attached to the substrate is performed. This SiO ₂ film 27 is usually used for separating a wiring material from a lower region thereof. If the SiO ₂ film 27 is formed by adding only the film thickness to be etched in the next cleaning step, it is particularly necessary to increase the number of newly added steps. Not be. However, there is no problem if a new SiO ₂ film is formed after the next cleaning process.

When Pt was used for the capacitance electrode, the amount of Pt contamination on the substrate surface was 5 × 10 ¹² cm ⁻² . When cleaning was performed with a cleaning liquid containing HF in the same manner as in the first example, the metal adhesion amount was 2-3 × 10 ⁹ cm ⁻² . Also, HF
When washing was performed by adding HCl and HNO ₃ to the washing solution containing, the metal adhesion amount was 0.8 to 1 × 10 ⁹ cm ⁻² . As a comparison, cleaning with SPM was performed on the same device. In the cleaning by SPM, the amount of deposited metal after the cleaning is 2 to 5 × 10 ¹¹ cm ⁻² , and a sufficient cleaning effect cannot be obtained by this method. Further, Japanese Patent Application Laid-Open No. 8-31
The method disclosed in No. 781 cannot be applied to this structure because the ferroelectric substance is eluted by the solution because the capacitance portion is exposed.

[0017]

As described above, according to the method for removing metal contamination on the substrate surface of the present invention, in the method for removing the metal adhered to the surface of the Si substrate covered with the SiO ₂ film, the underlying Si substrate or the underlying device is removed. By etching the SiO ₂ film on the substrate surface to such an extent that the region is not exposed, the metal can be removed together with the SiO ₂ film and the re-adsorption of the metal from the cleaning solution can be prevented. It has the effect of removing. In particular, there is an advantage that even if the contaminant metal on the surface is Pt, Ir, or Ru, which is hardly melted by the cleaning liquid, it can be sufficiently removed. Further, as in the second embodiment, in the process of forming a semiconductor device such as a ferroelectric RAM, metal contamination can be sufficiently removed, so that an apparatus used in a subsequent process can be shared with another semiconductor device. In addition, it is possible to reduce costs such as the production line equipment.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional example.

[Explanation of symbols]

11, 21, 31 Si substrate 12, 22, 27, 32 SiO ₂ film 13, 33 Metal contaminant 14, 34 Cleaning solution 15, 35 Cleaning tank 16, 36 Pure water 17, 37 Cleaning tank 2 24 Capacity Lower electrode 25 Capacity Upper electrode 26 Ferroelectric film

Continuation of the front page (56) References JP-A-7-240394 (JP, A) JP-A-4-45531 (JP, A) JP-A-3-218629 (JP, A) JP-A-5-102123 (JP) JP-A-8-45882 (JP, A) JP-A-7-22518 (JP, A) JP-A-8-340086 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H01L 21/304-21/308

Claims (2)

(57) [Claims] 1. A method for removing metal contaminants adhering to a surface of a semiconductor substrate in which an upper layer of a metal electrode, a metal wiring, or a capacitor is covered with a silicon oxide film (SiO ₂ film), comprising: ammonium fluoride and _(NH 4 F)
And etching the SiO ₂ film with a cleaning solution containing nitric acid (HNO ₃ ) and / or hydrochloric acid (HCl), and making the SiO ₂ film thinner than before etching. Pollution removal method. 2. The method according to claim 1, wherein the upper layer of the metal electrode, the metal wiring, and the capacitor is S.
This is a method for removing metal contaminants attached to the surface of a semiconductor substrate covered with an iO ₂ film, wherein hydrofluoric acid (HF) or ammonium fluoride (NH ₄ F) is used.
A method of removing metal contamination on a surface of a substrate, comprising etching with a cleaning solution containing nitric acid (HNO ₃ ) and / or hydrochloric acid (HCl) under conditions that leave a part of the SiO ₂ film.