JP2002502125A - How to insulate organic substances from substrates - Google Patents

Abstract

  (57) [Summary] A plasma comprising a gas or gas mixture of any of the following groups: a) sulfur trioxide alone, 2) sulfur trioxide and one auxiliary gas, and 3) sulfur trioxide and at least two auxiliary gases. To ashing the organic film from the substrate. As the auxiliary gas, any of steam, ozone, hydrogen, nitrogen, nitrogen oxide, or a halide such as tetrafluoromethane, chlorine, nitrogen trifluoride, hexafluoroethane, or methyltrifluoride can be used.

Description

Background 1 of the Detailed Description of the Invention] invention. FIELD OF THE INVENTION The present invention relates generally to the removal of organic materials present on various substrates, and more particularly, to the manufacture of semiconductors, flat panel displays, read / write heads, and other related devices during manufacturing. The present invention relates to an organic film temporarily formed on a substrate layer and an ashing method for removing an organic substance. 2. 2. Description of Related Art In a semiconductor device manufacturing process, removal of a photoresist film is an important operation. It has been known for some time to use an incineration method using a gas having a particularly high oxygen content to remove an organic film such as a resist or polyimide. Advances in plasma tools and related processing techniques over the past decade have managed to keep pace with the difficult face of the emergence of new types of very large scale integrated circuit (VLSI) and very large scale integrated circuit (ULSI) devices. I have responded without. However, as feature sizes continue to decrease and film thicknesses continue to decrease in these devices, there are new manufacturing challenges for each type of integrated circuit (IC).

As the size of integrated circuits continues to shrink significantly, the incineration method always faces two problems: That is, a) the resist is removed at a higher speed without leaving any residue, and b) the degree of damage to the substrate layer under the resist film is reduced. These generally conflicting objectives have been met by altering either the physical conditions of the plasma medium or the chemical conditions of the ashing process. For example, higher processing rates can be achieved either by creating a high density plasma environment or by using or generating species in the plasma environment that react more efficiently with resist.

Substrate damage is likewise caused by both physical and chemical conditions of the plasma. For example, the effects of charging and ion bombardment are directly related to the physical properties of the plasma. The high-energy ions transfer small amounts of heavy metal (eg, iron, copper, and lead) and alkali metal (eg, sodium and potassium) atoms that are generally present as impurities in the resist film to the substrate layer under the resist. Can be. Heavy metal contamination, and especially the subsequent infiltration and migration of the heavy metal into other substrate layers (eg, silicon), can adversely affect minority carrier lifetime, thereby impairing device performance. The effect of such a Bombard process is
As the end of the ashing process is approached, the thickness of the resist film becomes thinner, especially as the thickness of the photosensitive substrate becomes thinner.

The plasma chemistry can also damage the substrate and cause etching or other detrimental effects to the underlying layers of the resist. For example, if a halogenated gas mixture such as oxygen (O ₂ ) and tetrafluoromethane (CF ₄ ) is used to increase the rate of plasma ashing, etching of silicon oxide (SiO ₂ ) due to fluorine (F) Happens. Similarly, spin-on-glass (
Moisture is formed in the surface of the SOG) film, resulting in an increase in the dielectric constant or a related indirect via-poisoning phenomenon.

While the downstream type incineration process is the most widely used processing method, the above considerations, although varying in degree depending on the application, for example, barrel type,
This applies to all conventional dry etching plasma devices, such as downstream type or parallel electrode type structures. In order to increase the processing speed and minimize the problem of ion damage, it is conceivable to employ a technique for increasing the plasma density and lowering the ion energy. A new type of advanced plasma source separates the control of plasma density from the control of ion energy in the plasma by techniques such as electron cyclotron resonance (ECR) or inductively coupled plasma (ICP) with microwave or radio frequency power. To achieve the stated objectives.
Such and other types of plasma technology and tools are known and many are the subject of U.S. patents.

Regardless of the nature and mode of the plasma employed, the rate and perfection of the ashing in conventional ashing tools is created in the plasma with the resist and substrate layer, as well as unwanted etching or damage to the substrate layer. It is greatly affected by chemical reactions with ionic neutral and radical species. In a typical downstream or other conventional incinerator, the nature of the plasma gas mixture is a major determinant of the incineration rate, and the incineration rate is also sensitive to "ashing temperature". The nature of the plasma gas mixture also affects the ash activation energy, which is a measure of how the ash rate is affected by the ash temperature.

Activation energy is obtained from the slope of the Arrhenius plot, which is a linear representation of the ash rate as a function of the reverse ash temperature. Therefore, the activation energy is small (
The smaller the slope of the Arrhenius plot) means that the incineration rate is less affected by the incineration temperature and the incineration process is more stable and uniform. It also means that the lower the activation energy, the lower the incineration temperature can be without significantly impairing the incineration rate. This is especially true for the fabrication of very large scale integrated circuit (VLSI) and very large scale integrated circuit (ULSI) devices where low processing temperatures are required but acceptable levels of ashing rates are acceptable and practical (ie, 0.5 μm (Levels greater than / min) should be maintained.

Ashing rates and activation energies for a series of gas mixtures consisting of one or more of oxygen, hydrogen, nitrogen, water vapor and halide gases are thoroughly discussed in U.S. Pat. No. 4,961,820. In this patent, activation energy does not change when nitrogen is added to oxygen plasma (0.52 eV with respect to oxygen).
The incineration rate is only marginally improved (0.1-0.2 μm / min at 160 ° C.). However, the addition of 5 to 10 percent hydrogen or steam to oxygen reduced activation energy to about 0.4 eV, but only improved the ash rate as did the addition of nitrogen. Nitrogen and 5-10
When both percent hydrogen or steam were added, the incineration rate was (1
At 60 ° C.) there was a synergistic effect of increasing to a more realistic level of 0.5 μm / min.

When a halide (eg, tetrafluoromethane) was added to the oxygen plasma, the greatest improvements were found in activation energy (down to 0.1 eV) and ashing rate (levels greater than 1.5 μm / min). However, in this case, tetrafluoromethane also results in etching a substrate layer such as silicon oxide, polysilicon and aluminum by a fluorine reaction. Inclusion of water vapor in the reaction gas mixture can reduce the damage caused by tetrafluoromethane, but it has been reported that this may be due to the suppression of halogen activity as a result of the reaction of water and tetrafluoromethane. .

As noted above, research is continuing on satisfactory reactive gases that provide adequately fast ashing rates without detrimentally affecting the substrate layer underlying the resist film. In addition, very large scale integrated circuits (VLSI) and very large scale integrated circuits (UL
SI) Lower ashing temperatures and ashing process stability (lower activation energies) are key requirements for obtaining a satisfactory reaction gas mixture, as equipment manufacturing constraints are becoming more stringent. It is getting.

The inventor has successfully used anhydrous sulfur trioxide (SO ₃ ) for non-plasma resist removal applications at temperatures substantially below 200 ° C. Experiments have shown that exposing the resist-coated substrate surface to sulfur trioxide can keep the polysilicon and metal substrate surfaces intact without harmful effects.
Silicon and metal surfaces exposed to sulfur trioxide are also protected by the inactivating effect of sulfur trioxide. Therefore, sulfur trioxide, alone or in a reaction gas mixture, appears to be a suitable material candidate for plasma ashing applications. In particular, sulfur trioxide promotes the formation of oxygen radicals in the presence of oxygen plasma, so that a remarkable improvement in the ashing reaction rate can be expected.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved process for ashing organic materials, including photoresist residues, from substrates by including sulfur trioxide gas as part of the reaction gas mixture. It is to be. This object is achieved by employing one of the three groups of gas mixtures in the ashing process. These three
The types of mixtures are as follows: (1) Group 1 gases consist solely of sulfur trioxide gas, and (2) Group 2 gases consist of sulfur trioxide and water vapor, ozone, hydrogen, nitrogen, nitrogen oxides, Or one of halides such as tetrafluoromethane (CF ₄ ), chlorine (Cl ₂ ), nitrogen trifluoride (NF ₃ ), hexafluoroethane (C ₂ F ₆ ), and methyltrifluoride (CHF ₃ ). (3) The gas of group 3 consists of a mixture of sulfur trioxide and at least two of the above-mentioned auxiliary gases.

As is known in the art, if some of these auxiliary gases are added to the main reactive ashing gas in the appropriate amount and at the appropriate time of processing, these auxiliary gases will have favorable ashing process characteristics and organic membranes. Promotes removal action. Such favorable properties and effects are: a) faster ashing rate, b) lower activation energy, and c) no substrate etching during the organic removal process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Organic photoresist stripping and plasma ashing using one of the three groups of gases described above can be performed using conventional downflow, barrel, downstream, direct, or other types. Using plasma ashing tools known in the art. The present invention relates to the nature of the gas used in the incineration process and can be applied to any conventional incineration tool. Downflow type, barrel type, direct type,
Downstream or other types of plasma ashing tools are known in the art and do not constitute the present invention.

The basic concept of the present invention is to reduce the activation energy or increase the incineration rate if the sulfur trioxide gas is used in appropriate amounts and process conditions and, if necessary,
Includes process-hardened photoresist by lowering the operating temperature of the ashing process or using it in gaseous form as a reactive gas mixture with some type of auxiliary gas needed to improve the effectiveness or efficiency of the ashing process All kinds of organic coatings,
The films, layers and residues are ashed or reacted with them to remove substantially from the substrate surface, clean or strip. In all embodiments of the present invention, sulfur trioxide is supplied to a source container, from which sulfur trioxide gas is supplied in large quantities to the processing chamber at the appropriate time during the ashing process. In the source container, the sulfur trioxide may be a mixture of a solid, liquid or gas with a solid material in the form of alpha, beta, gamma or mixtures thereof.

Specifically, the following coating, film, layer, and residue organic substances can be removed by the treatment of the present invention. That is, polymerized or non-polymerized photoresists, photoresist residues, photosensitive and non-photosensitive organic compounds, paints, resins, multilayer organic polymers, organometallic composites, sidewall polymers (si
dewall polymer), and organic spin-on-glass. Examples of the photoresist include a positive optical photoresist, a negative optical photoresist, an electron beam photoresist, an X-ray photoresist, and an ion beam photoresist.

Such coatings, films, layers and residues have been formed on various substrates. Examples of substrates include, but are not limited to, the following: a) silicon, polysilicon, germanium, group 3-5 substances,
And a semiconductor wafer and device composed of Group 2-4 materials, b) oxides, c)
Nitrides, d) oxynitrides, e) inorganic dielectrics, f) metals and alloys, g) ceramic devices, h) photomasks, i) liquid crystal and flat panel displays, j) printed circuit boards, k) magnetic writing / A read head, and l) a thin film head.

The ashing process of the present invention can be performed in a temperature range from room temperature (about 20 ° C) to 350 ° C. However, the ashing process of the present invention is preferably performed at a temperature as low as possible while maintaining an etching rate as high as possible. Thus, more preferably, the ashing process of the present invention is performed at a temperature below about 200 ° C. 1. First Embodiment One embodiment provides a plasma ashing process using any of the conventional downflow, barrel, direct, downstream and other ashing tools known in the art. Is what you do. In the first embodiment, the plasma is generated using the group 1 gas. In particular, the reaction gas consists only of sulfur trioxide. Sulfur trioxide is supplied to the plasma generation chamber and first evacuated and evacuated to a suitable vacuum. The flow rate of the sulfur trioxide gas during the process is controlled by the control device. Plasma is generated by the reaction gas by supplying microwave power to the plasma generation chamber. The activated species generated as a plasma flow into the processing chamber and come into contact with the organic film on the substrate surface by any one of the methods disclosed in the prior art. The organic film reacts with the plasma, and as a result,
The organic film is removed or chemically altered so that it can be removed in a subsequent washing or cleaning step during processing. Processing constraints such as flow rate, microwave power, etc. are similar to those conventionally employed in the art, as described in US Pat. Nos. 4,669,689 and 4,961,820. . 2. Second Embodiment Another embodiment of the present invention provides a plasma ashing process using any of the conventional downflow, barrel, direct, downstream or other types of ashing tools. Is what you do. In this second embodiment, a plasma is generated using Group 2 gases. In particular, the reaction gas consists of sulfur trioxide and one type of auxiliary gas. Sulfur trioxide and an auxiliary gas are supplied to the plasma generation chamber and first evacuated and evacuated to a suitable vacuum. The concentration of sulfur trioxide in the Group 2 reaction gas is about 1-95 volume percent. The remainder consists of the auxiliary gas (99-5 volume percent).

During processing, the flow rate of each gas is controlled by the control device. By supplying microwave power to the plasma generation chamber, plasma is generated by the reaction gas. Activated species generated as plasma are discharged into the processing chamber,
Contacting the organic film on the substrate surface by any one of the methods disclosed in the prior art. The organic film reacts with the plasma, and as a result, the organic film is removed,
Or, it may be chemically altered so that it can be removed in a subsequent washing or cleaning step during processing. As described above, the processing restrictions such as the flow rate and the microwave power are the same as those conventionally adopted in this field.

The auxiliary gas is water vapor, ozone, hydrogen, nitrogen, nitrogen oxide, or tetrafluoromethane (CF ₄ ), chlorine (Cl ₂ ), nitrogen trifluoride (NF ₃ ), hexafluoroethane (C ₂ F ₆ ), Any gas selected from the group consisting of halides such as methyltrifluoride (CHF ₃ ) may be included. Examples of nitrogen oxides include nitrous oxide (N ₂ O), nitric oxide (NO), nitric oxide (NO ₃ ), and nitrogen dioxide (NO ₂ ). 3. Third Embodiment Still another embodiment of the present invention is a conventional downflow type, barrel type, direct type,
The plasma ashing process is performed using any of the downstream type and other types of ashing tools. In this third embodiment, a plasma is generated using Group 3 gases. In particular, the reaction gas consists of sulfur trioxide and at least two auxiliary gases. Sulfur trioxide and auxiliary gas are supplied to the plasma generation chamber, and are first evacuated and evacuated to a suitable vacuum. The concentration of sulfur trioxide in the Group 3 reaction gas is about 1 to 95 volume percent. The remainder consists of the auxiliary gas (99-5 volume percent).

The flow rate of the processing gas is controlled by the control device. When microwave power is supplied to the plasma generation chamber, plasma is generated by the reaction gas. The activated species generated as a plasma are exhausted into the processing chamber and contact the organic film on the substrate surface by one of the methods disclosed in the prior art. The reaction between the organic film and the plasma results in the organic film being removed or chemically altered so that it can be removed in a subsequent cleaning or cleaning step during processing. As described above, processing restrictions such as flow rate and microwave power are the same as those conventionally employed in this field.

 The auxiliary gas includes at least two of the auxiliary gases described above.

In each of the above embodiments, the organic film, including the resist layer, was substantially completely removed, with little or no damage to the underlayer.

The processing for removing organic substances from the substrate surface by using the plasma ashing processing using a reaction gas containing sulfur trioxide has been described above. It will be apparent to those skilled in the art that various changes and modifications can be made to the obvious properties, and such changes and modifications are considered to be within the scope of the following claims.

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Claims (13)

[Claims] 1. A method for removing an organic substance from a substrate surface, comprising: a) sulfur trioxide and at least one selected from the group consisting of water vapor, ozone, hydrogen, nitrogen, nitrogen oxides and halides. Generating a plasma from a reaction gas comprising 5 to 99 volume percent of an auxiliary gas; and b) applying the plasma to the surface of the substrate containing the organic material, but sufficient to incinerate the organic material. Impacting the substrate for a time that is not sufficient to damage the substrate surface. 2. The method of claim 1 wherein said reaction gas consists essentially of sulfur trioxide. 3. The method of claim 2, wherein the reactant gas consists essentially of sulfur trioxide and one of the auxiliary gases, wherein the concentration of the sulfur trioxide is about 1 to 95 volume percent. The method of claim 1. 4. The method of claim 1, wherein said reacting gas consists essentially of sulfur trioxide and at least two of said auxiliary gases, said sulfur trioxide having a concentration of about 1 to 95 volume percent. Item 7. The method according to Item 1. 5. The method according to claim 1, wherein the nitrogen oxides are nitrous oxide (N ₂ O), nitric oxide (N ₂ O)
NO), nitrogen trioxide _(NO 3), and a method according to claim 1, characterized in that it is selected from the group consisting of nitrogen dioxide (NO _2). 6. The halide is tetrafluoromethane (CF ₄ ), chlorine (Cl ₂ ), nitrogen trifluoride (NF ₃ ), hexafluoroethane (C ₂ F ₆ ),
And The method of claim 1, wherein a is selected from the group consisting of methyl trifluoride (CHF _3). 7. The method according to claim 1, wherein the organic substance is a polymerized or non-polymerized photoresist, a photoresist residue, a photosensitive or non-photosensitive organic compound, a paint, a resin, a multilayer organic polymer, an organometallic compound, or a sidewall. The method of claim 1, comprising a material selected from the group consisting of a sidewall polymer and an organic spin-on-glass. 8. The method of claim 1, wherein the photoresist is selected from the group consisting of a positive optical photoresist, a negative optical photoresist, an electron beam photoresist, an X-ray photoresist, and an ion beam photoresist. Item 7. The method according to Item 7. 9. The method according to claim 1, wherein the substrate comprises: a) silicon, polysilicon, germanium,
A semiconductor wafer and apparatus composed of a group 3-5 substance and a group 2-4 substance, b
A) oxides, c) nitrides, d) oxynitrides, e) inorganic dielectrics, f) metals and alloys,
g) ceramic devices, h) photomasks, i) liquid crystal and flat panel displays, j) printed circuit boards, k) magnetic write / read heads, and l)
The method of claim 1, wherein the method is selected from the group consisting of thin film heads. 10. The method of claim 9, wherein said metal and alloy are selected from the group consisting of aluminum and aluminum-silicon-copper alloy. 11. The method of claim 1, wherein said plasma ashing step is performed at a temperature in a range from room temperature to 350 ° C. 12. The method according to claim 1, wherein said temperature is lower than 200 ° C.
The method of claim 1. 13. The method of claim 1, wherein said step is performed in a downflow, barrel, downstream, or direct incinerator.