JP2003257952A - Insulation film etchant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide on the market an etchant which is capable of etching a silicon nitride film or a High-k insulation film by nearly the same process as with hot phosphoric acid (hot aqueous solution of phosphoric acid) while effectively suppressing the surface roughness of Si. <P>SOLUTION: The insulation film etchant is made by adding at least one kind selected from a water-soluble polymer and an interfacial active agent as an addition agent to an aqueous solution of phosphoric acid. For the water- soluble polymer, polyvinyl pyrolidone is preferably used, while for the interfacial active agent, a cationic interfacial active agent or an interfacial active agent having a fluoroalkyl group as a hydrophobic section is preferably used. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a phosphoric acid aqueous solution used for etching an insulating film, and more particularly to a wet etching technique in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In forming a large-scale integrated circuit (ULSI), in recent years, circuits have been miniaturized and high voltages have been required for the purpose of speeding up transistors and reducing power consumption.
-k Introducing new materials such as gate insulating film.

At present, a silicon nitride film is used as a mask material when forming an element isolation structure. When etching this, a phosphoric acid aqueous solution heated to about 160 ° C., a so-called “hot phosphoric acid” is used. It is used. However, in this process, since the silicon portion exposed at the time of etching the silicon nitride film is corroded and roughened, that is, a so-called Si surface roughening occurs, the influence of the Si surface roughening increases with the miniaturization of the circuit, and the device yield and reliability Has been regarded as a problem that can significantly reduce

On the other hand, in recent years, with the miniaturization of circuits, the gate insulating film has become extremely thin, but the gate leakage current generated at that time cannot be ignored. Therefore, currently, as it is of SiO ₂ alternate with the gate insulating film, SiO ₂
There is an increasing number of cases in which a gate insulating film is formed using a so-called “High-k material” such as Al ₂ O ₃ , ZrO ₂ , and HfO ₂ having a higher dielectric constant. Since the capacitance of the insulating film is proportional to the dielectric constant and inversely proportional to the film thickness, the use of High-k material makes it possible to increase the physical film thickness without changing the electrical effective film thickness as compared with the case of using SiO ₂ . As a result, the leak current can be reduced. Such a High-k insulating film is difficult to etch, and can be etched only with an HF diluting solution or the above hot phosphoric acid. However, if a HF diluting solution is used during this etching, the SiO _{2 in the} non-etching area will be
However, when hot phosphoric acid is used, the Si surface becomes rough, which is a problem.

[0005]

As described above,
In the ULSI manufacturing process, hot phosphoric acid, which has been used as an etching agent for a silicon nitride film, has a problem due to miniaturization and introduction of new materials for higher performance. There are two major problems, the first is the problem of Si surface roughness, which is a problem at the same time as the accuracy of etching of silicon nitride film is improved due to the miniaturization, and the second is the high-quality material as a new material. Etching of the k insulating film and roughening of the Si surface at that time. That is, since the Si surface is severely roughened with respect to the silicon nitride film etching and the High-k gate insulating film etching at the time of circuit miniaturization, the hot phosphoric acid process which is a conventional technique cannot be applied.

Therefore, hot phosphoric acid improved so that the silicon nitride film and the high-k material can be etched and the surface roughness of Si can be prevented is earnestly desired by the market. Therefore, in the present invention, the above two problems can be carried out in almost the same process as hot phosphoric acid, and an etching agent which can etch a silicon nitride film or a high-k insulating film while effectively suppressing the surface roughness of Si is put on the market. The purpose is to provide.

[0007]

This object is achieved by any of the following constitutions (1) to (12). (1) An insulating film etching agent containing, in an aqueous phosphoric acid solution, at least one compound selected from a water-soluble polymer and a surfactant as an additive. (2) The insulating film etching agent according to (1) above, wherein the water-soluble polymer is a polyvinyl polymer. (3) The insulating film etching agent according to (2), wherein the polyvinyl polymer is polyvinylpyrrolidone. (4) The insulating film etching agent according to (3) above, wherein the polyvinylpyrrolidone has a weight average molecular weight of 5000 or more. (5) The insulating film etching agent according to (1) above, wherein the surfactant is a cationic surfactant. (6) The insulating film etching agent according to (1) above, wherein the surfactant has a fluorinated alkyl group as a hydrophobic portion. (7) The insulating film etching agent according to any one of (1) to (6) above, wherein the concentration of the additive is 1% by mass or less. (8) The insulating film etching agent according to any one of (1) to (7) above, wherein the concentration of the additive is 0.005% by mass or more. (9) The insulating film etching agent according to any one of (1) to (8), wherein the phosphoric acid aqueous solution has a concentration of 40 to 90% by mass. (10) The insulating film etching agent according to any one of (1) to (9), which is used for etching silicon nitride. (11) The insulating film etching agent according to any one of (1) to (9), which is used for etching a metal oxide having a higher dielectric constant than SiO ₂ . (12) The insulating film etching agent according to the above (11), wherein the metal oxide is Al ₂ O ₃ , ZrO ₂ or HfO ₂ .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the property of the surface of Si is utilized in order to prevent the surface of Si from being roughened by a phosphoric acid aqueous solution. When Si is present at the Si-H end, the surface keeps hydrophobic. Therefore, by adding a small amount of a surfactant or water-soluble polymer having a hydrophobic portion to a highly hydrophilic solvent such as phosphoric acid, the molecules having these hydrophobic portions can be added to the Si surface, which is a hydrophobic surface. It can be adsorbed selectively. By utilizing this fact, the attack of phosphoric acid molecules on Si can be prevented by the adsorbed molecules, while the above molecules having a hydrophobic part are relatively hard to adsorb and Si nitride film or High- The k film can be etched as usual.

The properties required for these molecules having a hydrophobic part are that they are stably dispersed in a high-concentration phosphoric acid aqueous solution,
That is, it does not decompose for a long time at a high temperature of ℃ and under strong acid conditions. However, general surfactants and water-soluble polymers undergo decomposition such as carbonization under such conditions and cannot exist stably. Therefore, as a compound capable of stably maintaining a dissolved state under such conditions, there are 3 types of polyvinyl-based water-soluble polymers, cationic surfactants, fluorinated alkyl groups, and surfactants having a perfluoroalkyl group.
The seed was extracted.

First, since the main chain of the vinyl-based water-soluble polymer is composed of CC bonds which are covalent bonds,
The main chain is stable without splitting even under high temperature and strong acid conditions, and a side chain having a stable functional group such as a pyrrolidone skeleton and having a hydrophilic functional group is also required. Further, those having a reactive functional group such as polyvinyl alcohol or polyacrylic acid in the side chain or those having an aromatic ring susceptible to decomposition are not preferable. From the above,
As the vinyl-based water-soluble polymer, polyvinylpyrrolidone, water-soluble polyacrylamide derivative, polyvinylmaleimide and the like are preferable.

When polyvinylpyrrolidone is added to the phosphoric acid aqueous solution, the influence of the weight average molecular weight of polyvinylpyrrolidone on the etching rate and the surface roughness of Si is small. However, if the weight average molecular weight is too small, the stability under high temperature and strong acid conditions is lowered and the effect of the present invention is impaired. Therefore, the weight average molecular weight of polyvinylpyrrolidone is 5
It is preferably 000 or more. On the other hand, when the weight average molecular weight is too large, the viscosity becomes high and it becomes difficult to handle, and the solubility in the phosphoric acid aqueous solution decreases. Therefore, the weight average molecular weight of polyvinylpyrrolidone is preferably 10 million or less.

Next, in the cationic surfactant, the cationic group forms a salt with phosphoric acid, so that the water-soluble functional group is relatively stabilized. Furthermore, if the hydrophobic portion is aliphatic, the whole is stable and can be used. Examples of such compounds include quaternary ammonium-based trimethyllauryl ammonium chloride and tetrabutyl ammonium chloride.

Finally, a surfactant having a perfluoroalkyl group as a hydrophobic portion is considered to be stable from the viewpoint of acid resistance of perfluoroalkyl at high temperatures.
Examples include perfluoroalkyl sulfonic acid and perfluoroalkyl quaternary ammonium. The number of carbon atoms of the perfluoroalkyl group in the surfactant having a perfluoroalkyl group as the hydrophobic portion is not particularly limited, but is generally about 3 to 12.

In the present invention, two or more kinds of additives may be used in combination.

The etching agent of the present invention is used in a large-scale integrated circuit (LSI) formed on a Si wafer or a liquid crystal thin film transistor (TFT) formed on a glass substrate.
For the removal process after using the silicon nitride film as a mask during pattern formation such as for element isolation, and for the process of removing the unnecessary gate insulation film after forming the gate electrode on the High-k gate insulation film. Applied. Specifically, a silicon nitride film is formed on a Si substrate by CVD, patterned by photolithography and dry etching, and then partially oxidized using the remaining silicon nitride film as a mask, so-called "LOCOS" ( local oxidation of sil
icon) structure or dry etching of the substrate Si at the time of forming the element isolation structure to form a groove for filling SiO ₂ for forming a so-called “STI” (shallow trench isolation) structure. After that, the etching agent of the present invention is used in the step of removing the unnecessary silicon nitride film. The etching agent of the present invention can also be applied to a step of removing an unnecessary portion of the high-k film after forming a gate electrode by forming a high-k material on a Si substrate.

In this specification, High-k material means S
A metal oxide having a dielectric constant higher than that of iO ₂ , such as A
l ₂ O ₃ , ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , TiO ₂ , La ₂
O ₃ can be mentioned, and among these, Al ₂ O ₃ , ZrO ₂ , and HfO ₂ are particularly effective in the present invention. These High-k materials are used for the gate insulating film.

The apparatus for using the etching agent of the present invention may be any of a spray type single-wafer apparatus, a dip type bath apparatus, a spray type batch apparatus and the like, but a dip type bath apparatus is most preferable because high temperature is used. .

In the etching agent of the present invention, the phosphoric acid concentration is preferably 40 to 90% by mass, more preferably 60.
~ 85% by weight, the additive concentration is preferably 1% by weight
Below, it is more preferably 0.005 to 1% by mass, and further preferably 0.01 to 0.2% by mass. A decrease in phosphoric acid concentration causes boiling of the etching agent and a decrease in etching rate, and an increase in phosphoric acid concentration also causes a decrease in etching rate.
An increase in the additive concentration causes problems in handling due to an increase in viscosity and a decrease in the etching rate.
Can also cause the surface roughness of.

The phosphoric acid used in the etching agent of the present invention is orthophosphoric acid (H ₃ PO ₄ ).

The conditions for the etching treatment may be appropriately set so that the etching target can be sufficiently etched and damages other than the etching target can be prevented. Generally, a silicon nitride film or a high-k film is used. In either case, it is preferable that the liquid temperature of the etching agent is 100 to 160 ° C. and the treatment time is about 1 to 30 minutes.

Although it is possible to rinse with water directly after the treatment with the etching agent, it is preferable to rinse for 15 minutes or more in order to prevent the additive from remaining on the substrate. When an apparatus having a circulation type filter line is used, the etching agent of the present invention can be repeatedly used, in which case a stable etching rate can be obtained by keeping the water content in the etching agent constant. It becomes possible to obtain.

[0022]

EXAMPLES Examples will be shown below to describe specific embodiments of the invention.

Example 1 (Stability of Additive at High Temperature) An etching agent was prepared by mixing 1 g of a 5% aqueous solution of the additive shown in Table 1 with 100 g of an electronic grade 85% aqueous phosphoric acid solution. did. Next, these etching agents were heated in an oil bath set at 160 ° C. in advance and left as they were for 5 hours. Table 1 shows the properties of the etching agent after standing.

[0024]

[Table 1]

As shown in Table 1, polyvinylpyrrolidone which is a polyvinyl-based water-soluble polymer, trimethyllauryl ammonium chloride which is a cationic surfactant, and perfluoroalkyl in which a perfluoroalkyl group is a hydrophobic portion. Only the system to which any one of the three types of sulfonic acid is added is stable and remains colorless and transparent,
It is considered that the addition system of other components deteriorated due to coloration or precipitation of insoluble matter.

Example 2 (Effect of Suppression of Si Surface Roughness) Similar to Example 1, various additives were added to 85% phosphoric acid aqueous solution to prepare an etching agent. In addition, a (100) P-conduction type silicon chip in which the natural oxide film was removed by performing HF treatment was prepared. Next, the chips were immersed in an etching agent heated to 150 ° C., each chip was taken out after 1.5 hours, and the surface condition was observed with a scanning electron microscope (SEM). The results are shown in Table 2.

[0027]

[Table 2]

It can be seen from Table 2 that the surface roughness of Si can be suppressed by adding a water-soluble polymer or a surfactant to the phosphoric acid aqueous solution. Further, when polyvinylpyrrolidone, trimethyllauryl ammonium chloride or perfluoroalkyl sulfonic acid is used as the additive, the silicon chip keeps a flat state, while those with other additives are treated with silicone. The part was oxidized and a watermark was generated.

Considering together with the results in Table 1, polyvinylpyrrolidone, trimethyllauryl ammonium chloride and perfluoroalkyl sulfonic acid do not deteriorate even under high temperature and strong acid conditions, so that the effect of preventing Si surface roughness is sufficiently realized. it is conceivable that.

Example 3 (Etching of Silicon Nitride Film) A chip in which a silicon nitride film was laminated on a silicon substrate to a thickness of about 100 nm was prepared, and an additive was added to an 85% phosphoric acid aqueous solution in the same manner as in Example 2. The chip was immersed in the etching agent (150 ° C.) for 10 minutes. The film thickness of the silicon nitride film before and after the treatment was measured by a reflectance spectroscopic measurement method, and the film thickness (etching) amount of the obtained silicon nitride film is shown in Table 3.

[0031]

[Table 3]

Polyvinylpyrrolidone (weight average molecular weight =
(3 million) is added in an amount of 0.05% by mass, the etching amount is the same as that of the phosphoric acid aqueous solution without additives, but when the concentration is 0.5% by mass, the etching amount is halved, and a large amount of addition is required. It can be seen that the addition of the agent hinders etching. Further, when the three components of polyvinylpyrrolidone, trimethyllauryl ammonium chloride and perfluoroalkyl sulfonic acid were compared, it was observed that the etching amount of the two components other than polyvinylpyrrolidone slightly decreased. The influence of the molecular weight of polyvinylpyrrolidone was small.

Example 4 (Etching of High-k Material) Al ₂ O ₃ or HfO ₂ was laminated on a (100) P-conduction type silicon wafer by a CVD method to a thickness of about 5 nm,
This was cut into a square having a plane size of 2 cm × 2 cm to produce a chip. This chip was immersed in an etching agent (150 ° C.) obtained by adding an additive to a phosphoric acid aqueous solution for 5 minutes as in Example 3, and then taken out. Then, after allowing the etching agent to cool, the concentrations of Al and Hf eluted in the etching agent were quantified with an inductively coupled plasma mass spectrometer (ICP-MS) to calculate the amount of film slip (etching), The chip after the treatment was observed by SEM, and it was examined from the reflection state of the secondary electron beam whether these films were present on the surface and whether the silicon surface was rough. The results are summarized in Table 4.

[0034]

[Table 4]

In Table 4, the SEM observation result shows "flat.
"Same as BareSi" means that the reflection degree of the secondary electron beam on the chip surface is the same as that on the Si surface, and
This means that the chip surface was flat and not rough. From Table 4, when the chips were treated for 5 minutes at 150 ° C. with an aqueous phosphoric acid solution containing polyvinylpyrrolidone (weight average molecular weight = 3,000,000) at a concentration of 0.05% by mass,
It is considered that the -k material was completely etched away and the Si surface was exposed. Moreover, it can be seen that the exposed Si surface was flat without roughness.

Example 5 Polyvinylpyrrolidone having a weight average molecular weight of 200,000 was added to 0.0% in 85% phosphoric acid aqueous solution of electronic grade.
An etching agent added with 01% by mass to 0.07% by mass was prepared, and the state of the surface of the silicon chip after treatment at 125 ° C. for 3 hours and the amount of reduction of the silicon nitride film in the treatment time of 10 to 30 minutes were measured. It was measured. The results are shown in Table 5. In addition, Table 5 shows the etching rate of the silicon nitride film obtained from the film reduction amount.

[0037]

[Table 5]

As shown in Table 5, the additive concentration is 0.005
It was found that the effect was obtained even in the case of mass%, and that the roughness did not occur on the surface of the silicon chip at the addition concentration of 0.01 mass% or more. On the other hand, the etching rate calculated from the film reduction amount of the silicon nitride film is as shown in Table 5 below.
It was found that there was almost no change between the added amount of 0.005% by mass and 0.07% by mass.

[0039]

EFFECTS OF THE INVENTION By using the etching agent of the present invention, S is partially exposed during etching of the silicon nitride film or during etching of the high-k insulating film that is difficult to etch.
Since the surface roughness (corrosion) of the i substrate can be prevented, a high yield can be achieved even when the circuit is miniaturized.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeru Kamon             353, Nishi-Kano, Sekijuku-cho, Higashi-Katsushika-gun, Chiba Prefecture             Ein Polymers Co., Ltd. Sekijuku Factory (72) Inventor Norio Kaneko             353, Nishi-Kano, Sekijuku-cho, Higashi-Katsushika-gun, Chiba Prefecture             Ein Polymers Co., Ltd. Sekijuku Factory (72) Inventor Takashi Yada             3-3-7 Fushimi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Kishimoto Sangyo Co., Ltd. (72) Inventor Kota Niwa             4-11-2 Nihonbashihonmachi, Chuo-ku, Tokyo             Kishimoto Sangyo Co., Ltd. F-term (reference) 5F043 AA35 AA37 BB23 BB25 GG10

Claims (12)

[Claims] 1. An insulating film etching agent containing, in an aqueous phosphoric acid solution, at least one compound selected from a water-soluble polymer and a surfactant as an additive. 2. The insulating film etching agent according to claim 1, wherein the water-soluble polymer is a polyvinyl polymer. 3. The insulating film etching agent according to claim 2, wherein the polyvinyl polymer is polyvinylpyrrolidone. 4. The insulating film etching agent according to claim 3, wherein the polyvinylpyrrolidone has a weight average molecular weight of 5,000 or more. 5. The insulating film etching agent according to claim 1, wherein the surfactant is a cationic surfactant. 6. The insulating film etching agent according to claim 1, wherein the surfactant has a fluorinated alkyl group as a hydrophobic portion. 7. The insulating film etching agent according to claim 1, wherein the concentration of the additive is 1% by mass or less. 8. The insulating film etching agent according to claim 1, wherein the concentration of the additive is 0.005% by mass or more. 9. The insulating film etching agent according to claim 1, wherein the phosphoric acid aqueous solution has a concentration of 40 to 90 mass%. 10. The insulating film etching agent according to claim 1, which is used for etching silicon nitride. 11. The insulating film etching agent according to claim 1, which is used for etching a metal oxide having a dielectric constant higher than that of SiO ₂ . 12. The metal oxide is Al ₂ O ₃ , ZrO ₂
Alternatively, the insulating film etching agent according to claim 11, which is HfO ₂ .