Patent Application
20230386793
The present invention relates to an etching method and an etching apparatus.
With prevalence of mobile devices such as a smartphone and advance of a cloud technology, high integration of semiconductor devices has been promoted around the world, and there is a strong demand for an accompanying highly difficult semiconductor processing technology. For example, with regard to a memory semiconductor, the limits of planar circuit miniaturization in a NAND flash memory are beginning to appear and, in view of this, mass production has been applied to a memory using a three-dimensional multi-layer technology. Meanwhile, with regard to a logic semiconductor, a fin type FET (Field Effect Transistor) having a three-dimensional structure is becoming mainstream and, as a technology that goes beyond that, a GAA (Gate All Around) type semiconductor technology has been actively developed.
As such three-dimensional implementation and miniaturization of an element structure is simultaneously and concurrently pursued, in a device fabrication process, there have been demands for high-precision processing dimensional precision, a high selectivity of a material to be etched to another material, a high etching rate that implements a high throughput, high-precision isotropic etching, and the like. Particularly for the isotropic etching, a wet etching technique using a chemical liquid such as etching of silicon dioxide using a hydrofluoric acid or etching of silicon nitride using a hot phosphoric acid has been used widely. Meanwhile, with increasing miniaturization of devices, a pattern collapse due to a surface tension of the chemical liquid has presented a problem, and a dry etching technique less suffering from such a problem is in strong demand.
The silicon nitride is a material widely used for spacers or the like in semiconductor devices. As a conventional dry etching technique for a nitride not using a chemical liquid, an ALE (Atomic Layer Etching) method for titanium nitride using a fluorocarbon plasma and infrared irradiation is disclosed in Patent Literature 1. Meanwhile, an etching method that uses vibrational excitation of hydrogen fluoride (referred to as HF) to be able to ensure a high selectivity of silicon nitride to silicon dioxide is disclosed in each of Nonpatent Literatures 1 and 2.
The technology in each of Nonpatent Literatures 1 and 2 applies the vibrationally excited HF to the silicon nitride to reduce activation energy for bond breaking between nitrogen and silicon and thereby etch the silicon nitride. For the silicon dioxide, the vibration energy of oxygen and hydrogen is substantially equal to the vibration energy of fluorine and hydrogen, and accordingly resonance occurs and the activation energy does not decrease. In addition, since activation energy for disassociation is also low, adsorption of the HF scarcely occurs and, consequently, the silicon nitride is etched selectively to the silicon dioxide. Therefore, the technology may become an extremely important technology not only in trimming of the silicon nitride or the like, but also in a step of selectively etching the silicon nitride in a multilayer film including the silicon nitride and the silicon dioxide or the like.
In Nonpatent Literatures 1 and 2, the vibrationally excited HF is supplied to the silicon nitride by using a plasma of a NF3/N2/O2/H2 gas mixture. However, in general, a lifetime of the vibrationally excited HF is only about a microsecond or shorter, and a hydrogen plasma consumes generated fluoride ions and fluoride radicals under a scavenger effect. As a result, it is difficult for the technology described above to supply a sufficient amount of the vibrationally excited HF to a substrate region. In addition, from a viewpoint of processability, a higher density and a large number of stacked layers in a device cause a supply rate-controlled state where a sufficient etchant cannot be supplied to details such as a bottom portion of a hole, and consequently it becomes difficult to implement uniform etching irrespective of location.
An object of the present invention is to provide an etching method and an etching apparatus that allow etching processing of a silicon nitride film to be performed at a high etching rate, while maintaining high processing dimension controllability at an atomic layer level, high uniformity in a pattern depth direction, and high selectivity to silicon dioxide.
To solve the problem described above, an etching method according to a representative aspect of the present invention is implemented by including: a first step of supplying an etchant containing hydrogen to a sample having a surface at which a silicon nitride is exposed to form a first modified layer in which the hydrogen is bonded to the silicon nitride; a second step of supplying an etchant containing fluorine to the sample to form, over the first modified layer, a second modified layer in which the hydrogen and the fluorine are bonded to the silicon nitride; and a third step of irradiating the first modified layer and the second modified layer with an infrared ray.
An etching method according to another representative aspect of the present invention is implemented by including: a fourth step of supplying an etchant containing a hydrogen fluoride to a sample having a surface at which a silicon nitride is exposed to form a first modified layer in which hydrogen is bonded to the silicon nitride and a second modified layer in which the hydrogen and fluorine are bonded to the silicon nitride; and a fifth step of irradiating the first modified layer and the second modified layer with an infrared ray.
According to the present invention, it is possible to provide an etching method and an etching apparatus that allow etching processing of a silicon nitride film to be performed at a high etching rate, while maintaining high processing dimension controllability at an atomic layer level, high uniformity in a pattern depth direction, and high selectivity to silicon dioxide. Problems, configurations, and effects other than those described above will be made apparent by the following description of an embodiment.
The present inventors have attempted to etch silicon nitride by using various gases. As a result, the present inventors have found that a supply of an etchant containing hydrogen to the silicon nitride results in formation of a modified layer containing hydrogen in a surface thereof, a supply of an etchant containing fluorine to the silicon nitride results in formation of a modified layer containing hydrogen and fluorine in an uppermost surface, an amount of generation of the modified layers has self-saturation, and the modified layers are removed by infrared irradiation.
The present invention has been achieved on the basis of such new findings. According to the present invention, the modified layers are formed by supplying hydrogen and fluorine in the etchants to the surface of the silicon nitride, and the surface modified layers are irradiated with an infrared ray to be removed. By repeating the formation and the removal, it is possible to etch an intended amount of the silicon nitride.
In addition, with an etching technique of the present invention, instead of supplying vibrationally excited HF to over the silicon nitride, the modified layers containing hydrogen and fluorine are formed in advance, and then the modified layer are irradiated with the infrared ray to generate the vibrationally excited HF. Therefore, it is possible to efficiently supply a sufficient amount of the vibrationally excited HF to the silicon nitride. An energy for the vibrational excitation of the HF mentioned herein corresponds to an about 2.4 μm wavelength range and, accordingly, it is possible to cause the vibrational excitation by irradiation with the infrared ray including the wavelength range mentioned above. A characteristic feature of the present invention is that, immediately below the modified layer containing hydrogen and fluorine, the modified layer containing only hydrogen is placed.
In general, the vibrationally excited HF is generated on the basis of a chemical formula H2+F→HF*+H (where HF* represents the vibrationally excited HF), and therefore it is required to supply excessive hydrogen to fluorine. This is because a reaction factor is larger than that of a matching reaction given by F2+H→HF*+F. Accordingly, by placing the modified layer containing only hydrogen, it is possible to more efficiently generate the vibrationally excited HF.
In addition, according to the etching technique of the present invention, processing having self-saturation is performed, and accordingly uniformity of an etching amount in each of a wafer in-plane direction and a pattern depth direction increases. Moreover, since the etching amount is determined by a depth of the modified layers and the number of times cycle processing was repeated, it is possible to precisely control the etching amount.
The following will describe embodiments of the present invention in detail with reference to the drawings. Note that, throughout all the drawings for illustrating the embodiments, parts having the same functions are given the same reference sings, and a repeated description thereof is omitted. Note that, for improved clarity of illustration of a configuration, even a plan view may be hatched.
Using
An infrared ray to be applied to a wafer (sample) on the wafer stage 102 is required to vibrationally excite HF and etch silicon nitride as will be described later, and accordingly a light source capable of supplying a sufficient amount of the ray to vibrationally excite the HF to the wafer stage needs to be disposed to output the ray. In addition, since heating of the wafer contributes to removal of a by-product resulting from etching, such as ammonium silicate, ammonium, or silicon fluoride, it is desirable to have a heating mechanism. It is also possible to cause the infrared lamp 103 to function as a heating mechanism that heats the wafer placed on the wafer stage 102.
The gas supply unit 106 has an ability to selectively supply a gas containing hydrogen, a gas containing fluorine, and a gas containing both the hydrogen and the fluorine such as the HF. Examples of the gas (etchant) containing hydrogen include H2, HCl, HF, H2O, NH3, CH4, and the like. Examples of the gas (etchant) containing fluorine include SF6, CF4, CHF3, CH2F2, CH3F, C2F6, C4F9, NF3, and the like. It is desirable that the gas supply unit 106 also has an ability to supply a reducing gas, such as BCl3, and an ability to supply an inert gas capable of dilution, such as argon or nitrogen.
In the processing chamber 101, a gas dispersion plate 108 that disperses the gas introduced from the gas introduction unit 105 can be disposed. Alternatively, it may also be possible to dispose, between the plasma source 104 and the wafer stage 102, a shield plate 109 that controls respective amounts and distributions of the introduced gas and ions and radicals each generated from the plasma source 104. It may also be possible to further provide an adjustment mechanism that adjusts a pressure in the processing chamber 101 or a distance between the plasma source 104 and the wafer stage 102 so as to prevent the ions from being supplied to the wafer. To cool a wafer (semiconductor substrate) to be placed on an upper surface thereof, the wafer stage 102 preferably includes a mechanism that supplies a helium gas to a back surface of the wafer and a cooling mechanism that cools the wafer stage 102, such as a chiller.
Next, a description will be given of a specific example of silicon nitride etching. A schematic diagram illustrated in
First, in Step S101, a wafer having a surface at which silicon nitride is exposed is placed on the wafer stage 102. In Step S102 (first step), an etchant containing hydrogen is supplied from the gas supply unit 106 into the processing chamber 101 via the gas introduction unit 105 and applied to the silicon nitride of the wafer to form a modified layer (first modified layer) L101 in which hydrogen is bonded to the silicon nitride at the surface thereof. In Step S103 (second step), an etchant containing fluorine is applied to the silicon nitride via the gas introduction unit 105 to form a modified layer (second modified layer) L102 in which hydrogen and fluorine are bonded to the silicon nitride at an outermost surface thereof.
In Step S103, when the etchant contains hydrogen, fluorine is consumed under a scavenger effect and it becomes difficult to supply a sufficient amount of the fluorine to the silicon nitride, and therefore it is desirable that the etchant contains no hydrogen. In the present embodiment, radicals are supplied as the etchant but, even when a form in which the etchant is supplied is a gas or ions, the effect remains unchanged. When ions or radicals are used as the etchant, the ions or radicals are generated from the plasma source 104.
In Step S104 (third step), the modified layer L101 and the modified layer L102 that have been formed are irradiated with an infrared ray from the infrared lamp 103. This promotes vibrational excitation of the HF to cause etching of the silicon nitride film.
In
From the results in
In
According to the present embodiment, through Steps S102 and S103, the modified layer L102 containing hydrogen and fluorine is formed at the outermost surface of the sample, and the modified layer L101 containing only hydrogen is formed immediately below the modified layer L102. It will be understood that, by irradiating a structure of the modified layers with an infrared ray in Step S104, the silicon nitride layer is etched.
As is obvious from the foregoing, the etching method according to the present embodiment has a high selectivity to the silicon dioxide film. Therefore, providing an additional step for removing an initial oxide film such as a natural oxide film between Steps S101 and S102 and introducing a reducing etchant such as BCl3 is also effective in increasing the etching rate. In addition, since the silicon nitride film contains nitrogen and nitrogen is more likely to move than silicon, it can be considered that introducing an etchant containing nitrogen, such as N2 or NF3, from which self-complexity can be expected, is effective in reducing roughness or the like.
Next, a description will be given of the etching of the silicon nitride in an actual device structure. The etching of the silicon nitride, particularly highly selective isotropic etching to be performed on the silicon dioxide film, is expected to be applied to a step of removing dummy word lines or the like.
Using
A schematic diagram illustrated in
In Step S105, a wafer having a surface at which the silicon nitride is exposed is placed on the wafer stage 102. In Step S106, an etchant containing HF is applied from the gas introduction unit 105 to the silicon nitride. Since a hydrogen atom has an atomic radius smaller than that of a fluorine atom, and consequently reaches a deeper portion in a sample, in the same manner as in the first embodiment, a modified layer L104 (first modified layer) containing hydrogen and fluorine is formed in an outermost surface, and a modified layer L103 (second modified layer) containing hydrogen is formed immediately below the modified layer L104.
In the present embodiment, radicals are supplied as the etchant but, even when a form in which the etchant is supplied is a gas or ions, the effect remains unchanged. When ions or radicals are used as the etchant, the ions or radicals are generated from the plasma source 104.
In Step S107, an infrared ray is applied from the infrared lamp 103 to the modified layer L103 and the modified layer L104 that have been formed to promote vibrational excitation of HF. As a result, a silicon nitride film is etched.
In
From the results in
From the foregoing results, it will be understood that, to etch the silicon nitride film, Steps S106 and S107 are required. It will also be understood that, even when infrared irradiation is performed simultaneously with the application of the plasma of the HF gas, the silicon nitride film is etched and therefore, to etch the silicon nitride, the infrared irradiation may be performed simultaneously with the supply of the etchant.
The etching method that simultaneously performs the infrared irradiation described above is applicable not only to the cycle etching described heretofore, but also to continuous etching. Meanwhile, when an umbrella made of an alumina base material that does not transmit an infrared ray is placed on the silicon nitride film to provide a state where the infrared ray is not directly applied only to the sample, the silicon nitride film is not etched (see
From the foregoing result, it will be understood that the infrared irradiation is required to drive the vibrational excitation of HF and, for appropriate driving, infrared irradiation of a given intensity or higher is required. Therefore, adjustment of the distance between the wafer stage 102 and the infrared lamp 103 or of a luminous intensity of the infrared lamp 103 is important.
Next, a description will be given of etching of silicon nitride in a real device structure. The etching of the silicon nitride, particularly atomic-layer-level etching that allows precise control of an etching amount, is also applicable to a trimming step of planarizing sidewall portions of the device.
According to the present invention, by forming the modified layer containing hydrogen and the modified layer containing hydrogen and fluorine on the silicon nitride film and then performing the infrared irradiation, it is possible to supply a sufficient amount of vibrationally excited HF to the silicon nitride film. As a result, it is possible to provide a technology that allows etching processing of the silicon nitride film to be performed at a high etching rate, while maintaining high processing dimension controllability at an atomic layer level, high uniformity in a pattern depth direction, and high selectivity to silicon dioxide.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/006253 | 2/19/2021 | WO |
