FILM FORMING METHOD

Examples of a film forming method include placing a substrate on a susceptor arranged in a chamber, and introducing a hydrogen-containing gas and a nitrogen gas into the chamber, and applying radio frequency power to an electrode above the susceptor to generate plasma, and form a nitride film on the substrate, wherein a flow rate of the hydrogen-containing gas is equal to 1% or less of a flow rate of the nitrogen gas.

TECHNICAL FIELD

Examples are described which relate to a film forming method.

BACKGROUND

A device structure having a high aspect ratio is required in connection with increase of the density of LSIs. Such a structure is mechanically weak, and may be deformed by the stress of a thin film to be formed later. For a three-dimensional device structure having a high aspect ratio, there is a case where film formation of a SiN film using halogenated silane as a precursor is performed. In this case, in order to enhance a step coating effect of the SiN film, it is considered that the pressure in a chamber is set to a comparatively high pressure of 20 Torr to 30 Torr.

Under the above condition, it is impossible to control the stress of the SiN film. Particularly, when only N2is used as a reactant, the compressive stress of the SiN film reaches several hundred megapascals. When a SiN film having a high compressive stress is formed on a substrate having a fine three-dimensional structure, the structure is deformed. Furthermore, when a SiN film having a high compressive stress is formed in a device for improving characteristics by stress control, it causes deterioration of device characteristics.

SUMMARY

Some examples described herein may address the above-described problems. Some examples described herein may provide a film forming method capable of controlling the stress of a nitride film.

In some examples, a film forming method includes placing a substrate on a susceptor arranged in a chamber, and introducing a hydrogen-containing gas and a nitrogen gas into the chamber, and applying radio frequency power to an electrode above the susceptor to generate plasma, and form a nitride film on the substrate, wherein a flow rate of the hydrogen-containing gas is equal to 1% or less of a flow rate of the nitrogen gas.

DETAILED DESCRIPTION

A film forming method according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding constituent elements are represented by the same reference signs, and duplicative descriptions thereof may be omitted.

FIG. 1is a diagram showing a configuration example of a substrate processing apparatus10. A susceptor14is arranged in a chamber12. A parallel plate structure is provided by the susceptor14and an RF electrode16arranged on the susceptor14. Various kinds of gases are provided onto a substrate18through openings provided in the RF electrode16. The susceptor14and the RF electrode16are provided as a parallel plate, so that capacitively coupled plasma (CCP) can be generated. Plasma processing is applied to the substrate18placed on the susceptor14. The substrate18is, for example, a Si wafer. The plasma processing includes film formation processing.

As gas sources, a material gas source22, a carrier gas source32, and a reaction gas source40are prepared. The material gas source22is in a liquid state, and the vapor thereof is provided into the chamber12by using a carrier gas from the carrier gas source32. The carrier gas is, for example, N2or Ar. The material gas is, for example, a precursor of the SiN film. That is, the liquid material gas source22can be used as a Si precursor for forming the SiN film.

Si Precursors

In some embodiments, the Si precursor for depositing SiN thin film comprises a silyl halide. In some embodiments, the Si precursor comprises iodine. In certain embodiments, the Si precursor is H2SiI2.

Examples of silicon precursors for depositing SiN are provided in U.S. patent application Ser. No. 14/167,904, filed Jan. 29, 2014, entitled “Si PRECURSORS FOR DEPOSITION OF SiN AT LOW TEMPERATURES,” which is incorporated herein by reference in its entirety.

In some embodiments, the Si-precursor comprises iodine and one or more ligands such as one or more organic ligands. In some embodiment, the Si-precursor may comprise iodine and one or more alkyl groups, such as a methyl group, ethyl group, propyl group, and/or hydrogen. In some embodiments, the Si-precursor comprises iodine and one or more other halides, such as bromine or chlorine.

The material of a hydrogen-containing gas can be stored as the Si precursor in the material gas source22. Any material of the above-described Si precursors may be used as the hydrogen-containing gas, but halogenated silane such as H2SiI2may be used, for example. For example, an Nitrogen precursor such as N2is stored in the reaction gas source40.

N Precursors

As discussed above, the second reactant for depositing silicon nitride according to the present disclosure may comprise a nitrogen precursor, which may comprise a reactive species. Suitable plasma compositions of a PEALD process include nitrogen plasma, radicals of nitrogen, or atomic nitrogen in one form or another. In some embodiments, hydrogen plasma, radicals of hydrogen, or atomic hydrogen in one form or another are also provided. And in some embodiments, a plasma may also contain noble gases, such as He, Ne, Ar, Kr and Xe, preferably Ar or He, in plasma form, as radicals, or in atomic form. In some embodiments, the second reactant does not comprise any species from a noble gas, such as Ar. Thus, in some embodiments plasma is not generated in a gas comprising a noble gas.

Whether or not gas is supplied from the material gas source22, the carrier gas source32, and the reaction gas source40and also the gas flow rates thereof are adjusted by valves V1, Va, and V3, respectively. An exhaust pipe20is connected to the chamber12. A valve21and a pump23are fitted to the exhaust pipe20. For example, the pressure in the chamber12can be determined by adjusting the opening degree of the valve21and the pumping ability of the pump23.

FIG. 2is a diagram showing an example of a film forming method. In this film forming method, the nitride film is formed on the substrate by a PEALD method. Specifically, Feed, Purge 1, RF, and Purge 2 are repeated at plural times in this order.

In the step of Feed, after the substrate18is placed on the susceptor14, a precursor, for example, as a Si precursor, is provided in the chamber12. Specifically, the vapor of the material gas source22may be provided into the chamber12together with the gas of the carrier gas source32. As a result, the Si precursor is provided onto the substrate18. In all the steps of Feed, Purge 1, RIF, and Purge 2, the reactant gas from the reaction gas source40may be provided into the chamber12, and the carrier gas from the carrier gas source32may be provided into the chamber12.

In the step of Purge 1, purge is performed to exhaust unnecessary materials. In this step, for example, a surplus Si precursor is exhausted.

In the step of RF, radio frequency power (RF power) is applied to the RF electrode16to generate plasma and form the SiN film on the substrate18. Plasma may include N radicals, H radicals, NH radicals, and NH2radicals. The time for which the radio frequency power is applied to the RF electrode16is set to, for example, 3.3 seconds.

In the step of Purge 2, purge is performed to exhaust unnecessary materials. In a series of processing, nitrogen gas as the reaction gas can be made to flow continuously. By repeating this series of processing at plural times, the SiN film is formed on the substrate18. The film thickness of the SiN film is set to, for example, 2 nm or less. In order to form the SiN film of about 2 nm, the above series of processing is performed, for example, at about 100 to 200 cycles.

As shown at the bottom stage ofFIG. 2, a hydrogen-containing gas is always supplied into the chamber during formation of the nitride film. In this example, the material gas from the material gas source22is provided in all the steps of Feed, Purge 1, RF, and Purge 2, thereby providing the hydrogen-containing gas. That is, in this example, the hydrogen-containing gas is the vapor of the material gas source22. In the step of Feed, the supply amount of the gas from the material gas source22can be increased, and in subsequent steps thereto, the supply amount of the gas can be reduced. The hydrogen-containing gas is supplied to control the stress of the nitride film.

Various kinds of gases containing hydrogen can be adopted as the hydrogen-containing gas. For example, DCS (dichlorosilane), ammonia, H2, CHx, BHxor the like can be used as the hydrogen-containing gas. In case where the hydrogen-containing gas differs from the material gas, the hydrogen-containing gas is supplied into the chamber from a system different from that of the material gas source22.

For example, there is considered a case where the internal pressure of the chamber12is set to 2000 Pa, the HRF power to be applied to the RF electrode16is set to 660 W, the distance between the electrodes of the parallel plate is set to 12 mm, and the step of RF is performed without introducing any hydrogen-containing gas. That is, in the step of RF, the reactant gas and the carrier gas are provided into the chamber. In this case, the compressive stress of the nitride film reaches several hundred megapascals. On the other hand, when hydrogen-containing gas such as H2gas is introduced in the step of RF under the same film forming condition, a tensile stress can be generated in the nitride film. This is considered to be because H atoms which are temporarily captured into a thin film during film formation are desorbed, so that the thin film tries to shrink.

FIG. 3is a diagram showing the relationship between the flow rate of the H2gas to be introduced into the chamber in the step of RF and the stress of the fanned nitride film. H2gas corresponds to the hydrogen-containing gas.FIG. 3shows data when the pressure in the chamber is set to 1000 Pa, 2000 Pa, 3000 Pa, When the pressure in the chamber is set to 2000 Pa, the HRF power is set to 550 W or 600 W and the flow rate of the hydrogen-containing gas is changed within the range from 5 to 20 sccm, the nitride film becomes a film having a tensile stress of 125 to 680 MPa. The reason why the tensile stress of the nitride film increases as the amount of hydrogen-containing gas is increased is considered to be that the amount of H atoms captured into the film increases as the amount of hydrogen-containing gas is increased, and the shrinking amount of the film increases accordingly. In this example, by changing the flow rate of the hydrogen-containing gas from 0 sccm to 20 sccm, the stress of the nitride film can be changed. When the flow rate of the hydrogen-containing gas is equal to 0 sccm, the proportion occupied by the hydrogen-containing gas among the gases supplied into the chamber is equal to 0%. When the flow rate of the hydrogen-containing gas is equal to 20 sccm, the proportion occupied by the hydrogen-containing gas among the gases supplied into the chamber is equal to, for example, 0.14%.

When the flow rate of the hydrogen-containing gas is set to 20 sccm or more, the stress of the nitride film becomes constant, and even when the flow rate is further increased, the stress hardly changes. This is considered to be because the stress control effect caused by the H atoms captured in the film is saturated when the supply amount of the hydrogen-containing gas exceeds a certain flow rate.

The flow rate of the hydrogen-containing gas at which the saturation of the stress control effect appears depends on the pressure in the chamber. For example,FIG. 3shows that under the pressure of 1000 Pa in the chamber, the stress of the film increases even when the supply amount of the hydrogen-containing gas is increased beyond 20 sccm. On the other hand, under the pressure of 3000 Pa in the chamber, it is possible to control the stress of the film by adjusting the flow rate of the hydrogen-containing gas in the range from about 0 to 10 sccm, but when the flow rate of the hydrogen-containing gas exceeds 10 sccm, the stress does not change even by further increasing the flow amount of the hydrogen-containing gas.

FIG. 4is a graph showing the relationship between the flow rate of the H2gas to be introduced into the chamber in the step of RF and the stress of the formed nitride film.FIG. 4shows the stress when the flow rate of the hydrogen-containing gas is changed in the range from 0 to 500 sccm. Under the pressure of 1000 Pa in the chamber, when the flow rate of the hydrogen-containing gas is equal to 10 sccm or less, it is possible to adjust the stress of the nitride film by adjusting the flow rate of the hydrogen-containing gas. On the other hand, when the flow rate of the hydrogen-containing gas exceeds 100 sccm, the stress adjustment effect of the nitride film by the adjustment of the flow rate of the hydrogen-containing gas is saturated.

As described above, the tensile stress of the SiN film can be controlled by changing the flow rate of the hydrogen-containing gas. When the pressure in the chamber is set to, for example, 2000 Pa or more, the coating effect of the substrate by the nitride film can be enhanced.

FIG. 5is a diagram showing the stress of a nitride film formed by a film forming method according to another example. In this example, 0.07% of the total flow rate is set to be occupied by H2gas which is the hydrogen-containing gas. In this example, it is shown that the stress of the nitride film can be made a compressive stress by adjusting the RF power to be applied to the RF electrode. When the nitride film has a compressive stress, the value of the stress inFIG. 5is a negative value. For example, a compressive stress is generated in the nitride film by introducing 10 cc of H2gas as the hydrogen-containig gas, setting the pressure in the chamber to 1000 Pa, and adjusting the HRF power. The compressive stress can be generated by applying electric power of 350 W or more. When the RF power is changed from 350 W to 500 W, the stress of the nitride film changes from −158.1 MPa to −864.8 MPa. From this result, it is apparent that the compressive stress of the SiN film can be controlled by changing the HRF power under a condition that a small amount of H2is added.

From the results described above, it is possible to generate a compressive stress, for example, by using halogenated silane which is the film forming material as the hydrogen-containing gas and setting the pressure in the chamber to 1000 Pa during film formation, and a tensile stress can be generated by making the pressure in the chamber ranging from more than 1000 Pa to not more than 2000 Pa.

In the step of RF inFIG. 2, H2can be supplied as the hydrogen-containing gas in addition to N2as the reactant gas. At this time, the flow rate of H2may be set to 1% or less of the flow rate of N2. The stress control can be performed by introducing the hydrogen-containing gas and the nitrogen gas into the chamber and applying radio frequency power to the RF electrode16on the susceptor14to generate plasma and form the nitride film on the substrate18. In particular, the flow rate of the hydrogen-containing gas is set to 1% or less of the flow rate of the nitrogen gas, thereby enhancing stress controllability. For example,FIG. 3shows that when the flow rate of the hydrogen-containing gas is small, it is easier to control the stress of the nitride film by adjusting the flow rate of the hydrogen-containing gas. As described above, it is possible to generate the compressive stress as well as the tensile stress in the nitride film to be formed.

FIG. 6is a diagram showing a nitride film formed while providing a hydrogen-containing gas. A convex portion50ais formed on a substrate50, so that there is an uneven pattern on the surface of the substrate. This uneven pattern is covered with a nitride film52. When the surface of the substrate50has an uneven pattern and the uneven pattern is covered with the nitride film, it is desired to prevent the substrate50from being deformed by the stress of the nitride film52, For example, by reducing the stress of the nitride film according to the foregoing method, deformation of the substrate50can be suppressed. Further, in each of the foregoing examples, formation of the nitride film with the pressure in the chamber set to 1000 Pa or more contributes to the enhancement of the coating effect by the nitride film.