PROCEDURES FOR SHARE SEPARATION

Abstract

A method for depositing a silicon layer is provided in which the stresses of the layer can be adjusted while maintaining its optical properties. A silicon target (3) and a substrate (Sw) are arranged in a vacuum chamber (1) to form a layer on the substrate. A sputtering gas is introduced into the vacuum chamber (1) in a vacuum atmosphere. The target is charged with electrical energy to form a silicon layer (Sf) on the surface of the substrate by sputtering. The silicon layer deposition is carried out in two independent steps: a first step to deposit a first silicon layer (Sf1) with a columnar structure, and a second step to deposit a second silicon layer (Sf2) with a columnar structure and a higher layer density than the first silicon layer.

Description

TECHNICAL AREA

[0001] This invention relates to a layer deposition method and in particular to a layer deposition method for forming a silicon layer which can be used as a hard mask and the like. BACKGROUND

[0002] Among the steps for manufacturing semiconductor devices is a step for forming a hard mask that limits the etching area during the dry etching of an insulating layer (e.g., a silicon oxide layer) formed on the surface of a substrate from a silicon wafer. The purpose of this hard mask formation step is to restrict the etching area during the dry etching of the electrical insulating layer. In one instance, a silicon layer is used as the hard mask (see, e.g., Patent Specification 1). Assuming that this type of silicon layer has a layer density with high etch resistance, the silicon layer is required to have a predetermined range of layer stresses to prevent deformation of the etched shape during dry etching.

[0003] When structuring is performed on a resist layer deposited onto a silicon layer using an exposure apparatus, it is sometimes necessary to align the resist with pre-existing wiring patterns. This type of positioning (alignment) is typically achieved using laser beams to detect alignment marks formed at predetermined locations on the substrate. Furthermore, due to the recent trend towards finer wiring patterns, laser beams with smaller spot diameters have been employed to enable more precise positioning. In this context, it is also essential that the aforementioned silicon layer possesses optical properties that fall within a range of predefined refractive index (n-value) and extinction coefficient (k-value) at predetermined layer thicknesses.

[0004] When depositing the aforementioned silicon layer, the use of a sputtering system is considered, particularly when productivity is a factor. In this case, the silicon layer is deposited to a predetermined thickness by introducing a noble gas into a vacuum chamber suitable for holding a silicon target and the object to be deposited (i.e., an object on which a layer is to be deposited or formed) in a vacuum atmosphere. The target is then charged with negative potential DC or AC electrical energy, thus sputtering the target and depositing the silicon layer to a predetermined thickness. Adjustments to the sputtering conditions at this stage, such as...Given parameters such as the partial pressure of the sputtering gas at the time of layer deposition; the electrical power with which the target is charged; the bias power for the substrate; and similar factors, it is generally known that the layer stresses or the optical properties can be independently adjusted to predetermined ranges. However, it was not possible, for example, to adjust the layer stresses while maintaining the optical properties. DOCUMENTS ON THE STATE OF TECHNICAL PATENT DOCUMENTS

[0005] Patent document 1: Japanese patent no. 6952866 REVELATION OF THE INVENTIONAL TASKS TO BE SOLVED BY THE INVENTION

[0006] In view of the above points, the objective of the present invention is to provide a method for depositing a silicon layer in which adjustments to the layer stresses are possible while maintaining the optical properties of the silicon layer. MEANS OF SOLVING THE TASKS

[0007] As a result of intensive efforts and studies, the inventors of the present invention have arrived at the following conclusions: When depositing a (single) silicon layer with a predetermined thickness by sputtering a silicon target, the desired optical properties (in particular the refractive index and the extinction coefficient) cannot be maintained, even when the sputtering conditions are adjusted, such as the partial pressure of the sputtering gas at the time of layer deposition, the electrical power applied to the target, the bias power for the substrate, and the like, in order to keep the layer stresses within a predetermined range. The inventors' findings also include the following points: For example, if a refractive index (n-value) range of 4 to 5 and an extinction coefficient (k-value) range of 0.3 to 0.6 are required, e.g.,Regarding the optical properties required for the aforementioned positional adjustment, the inventors discovered that the required optical properties are more easily achieved when the silicon layer is grown as a columnar layer and when the layer density is adjusted by changing the sputtering conditions. Thus, the sputtering conditions under which the optical properties could be maintained within specified ranges were first determined, without considering the layer stresses. The silicon layer to be deposited under these sputtering conditions was defined as the main silicon layer. A columnar layer with a lower density than that of the main silicon layer was then formed as the base layer of the main silicon layer under sputtering conditions that resulted in a difference in layer density.The inventors determined that the layer stresses can be adjusted depending on the density difference in the layer density while maintaining the optical properties.

[0008] To solve the aforementioned problems, this invention is a method for depositing a silicon layer, comprising: arranging a silicon target and a substrate in a vacuum chamber; introducing a sputtering gas into the vacuum chamber in a vacuum atmosphere; and charging the target with electrical energy to deposit the silicon layer onto a surface of the substrate by sputtering. In the aforementioned method, the deposition of the silicon layer is carried out in two independent steps, comprising: a first step of depositing a first silicon layer with a columnar structure; and a second step of depositing a second silicon layer with a columnar structure having a higher layer density than the layer density of the first silicon layer.

[0009] It has been confirmed that, while maintaining optical properties, the layer stresses can be adjusted using the aforementioned method, depending on the density difference between the first and second silicon layers. Furthermore, during the layer deposition process, silicon layers are also deposited on components such as protective plates and the like, located within the vacuum chamber. At this point, the second silicon layer, which has a high layer density, is applied to the surface layer. Therefore, the number of particles suspended in the vacuum chamber as a result of detachment from the surface layer of the aforementioned components can decrease with each subsequent silicon layer deposition. Consequently, the number of particles that can be deposited on an object after layer deposition can be minimized as much as possible.Furthermore, the following points were confirmed: Layer deposition can be carried out with a good layer distribution in the plane of the substrate, and layer deposition can also be carried out without a difference in the layer thickness distribution between the objects for layer deposition when layer deposition has been repeatedly carried out on a large number of objects for layer deposition.

[0010] In the present invention, assuming that a partial pressure of the sputtering gas in the vacuum chamber is defined as a reference partial pressure in the first step, the partial pressure of the sputtering gas in the second step can be made lower than the reference partial pressure. In this process, the layer density of the first silicon layer and the second silicon layer can advantageously be varied by varying the partial pressure of the sputtering gas in the first and second steps. It is advantageously possible to continuously deposit the first silicon layer and the second silicon layer within a single vacuum chamber by adding the difference in layer density. In this case, the ratio of the partial pressure in the first step to that in the second step can be adjusted in a range of 0.1 to 0.7.If the ratio of the partial pressures is less than 0.1, a thin layer with high density, a refractive index (n-value) that is too high, and an extinction coefficient (k-value) that is too high is obtained. Conversely, if the ratio of the partial pressures is greater than 0.7, the thin layer consists of a thin layer with lower density, a refractive index (n-value) that is too low, and an extinction coefficient (k-value) that is too low.

[0011] Furthermore, in the present invention, the ratio of the thickness of the first silicon layer to the thickness of the silicon layer can be adjusted to a range of 0.3 to 0.8. Thus, without varying the optical properties at a given layer thickness, the layer stresses can be advantageously adjusted.

[0012] If bias power is applied to the object during the sputtering process, the bias power can be adjusted from 20 W to 100 W in both the first and second steps. This allows for precise adjustment of the layer density of the first and second silicon layers, enabling the layer voltages to be set over a wide range. However, if the bias power is below 20 W, the controllability (tracking) of the power supply becomes poor, leading to unstable conditions for layer deposition. Conversely, if the bias power exceeds 100 W, excessively dense thin layers with excessively high refractive indices (n-values) and extinction coefficients (k-values) are formed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic view showing the arrangement of a sputtering device as a layer deposition device for depositing a silicon layer according to this embodiment. Fig. 2(a) and Fig. 2(b) are diagrams to illustrate the deposition processes of silicon layers. Fig. Figure 3 is a SEM image of a silicon layer deposited under specified conditions. Fig. 4(a), Fig. 4(b) and Fig. 4(c) are diagrams showing the results of experiments at the time of deposition of the silicon layers according to the method according to these embodiments. Fig. Figure 5 is a diagram showing the results of experiments at the time of deposition of the silicon layers according to the method according to these embodiments. MODES FOR IMPLEMENTING THE INVENTION

[0013] The following example, with reference to the accompanying drawings, explains how the object to be coated is a silicon oxide layer of a predetermined thickness on one side of a silicon wafer (hereinafter referred to as "substrate Sw") and the silicon target has a predetermined purity. Argon is used as the sputtering gas to form a silicon layer on the surface of substrate Sw by sputtering. Based on the above example, an embodiment of a method according to the invention for depositing a silicon layer is now described. In the following descriptions, terms indicating direction, such as "top" and "bottom," are to be understood as referring to Fig. 1 based.

[0014] With reference to Fig. Figure 1, reference numeral SM, shows a magnetron-type sputtering device capable of performing the layer deposition process according to an embodiment of the present invention. The sputtering device SM is equipped with a grounded vacuum chamber 1. A vacuum pump 12 is connected to the vacuum chamber 1 via an exhaust pipe 11, allowing the interior of the vacuum chamber 1 to be evacuated to a predetermined pressure (level of vacuum). A gas line 13 is connected to a side wall of the vacuum chamber 1. A mass flow controller 14 is inserted into the gas line 13 and is connected to a gas source (not shown) for argon gas. In this arrangement, the argon gas, the flow rate of which is controlled by the mass flow controller 14, can be introduced into the vacuum chamber 1.

[0015] The vacuum chamber 1 is equipped internally with a table 2. The table 2 has: a base 21, which is arranged on the inside of the bottom surface of the vacuum chamber 1 via an electrical insulator 21a; and a clamping plate 22, which is made, for example, of aluminum nitride or boron nitride and is arranged on the base 21. An electrode 22a for use in an electrostatic clamping device is installed in the clamping plate 22. By charging the electrode 22a with electric current from a power source (not shown) for the electrostatic clamping device, a substrate Sw, which is mounted with an upward-facing layer support surface, can be electrostatically drawn (held). At this point, the substrate Sw is in an electrically suspended state.Although not described in detail here, particularly in connection with the illustration, the clamping plate 22 is equipped with a heating and cooling mechanism so that the substrate Sw can be set to a predetermined temperature during layer deposition.

[0016] Furthermore, the vacuum chamber 1 is equipped with a cathode unit Uc. The cathode unit Uc has a target 3 and a magnet unit 4, which is arranged above the target 3 to generate a magnetic stray field in a space between the target 3 and the substrate Sw. A support plate 31 is glued (or attached) to the side of the target 3 opposite the sputtering surface 3a. In this way, the target 3 and the substrate Sw are positioned coaxially with each other in the vacuum chamber 1 by attaching a peripheral part of the support plate 31 to an upper wall of the vacuum chamber 1 via an electrical insulating material 32. An output of the sputtering power supply Ps is connected to the target 3, so that direct current with, for example, a negative electrical potential can be applied in pulses.The vacuum chamber 1 is lined internally with protective plates 5 made of stainless steel or aluminum, which enclose the space between the substrate Sw and the target 3 to prevent the sputtered particles from adhering to the inner walls of the vacuum chamber 1. The protective plates 5 consist of: upper protective plates 51, which are suspended from the upper wall of the vacuum chamber 1; and lower protective plates 52, which are movable in a vertical direction by means of a lifting mechanism Du, equipped with a cylinder, a motor, and the like.

[0017] The vacuum chamber 1 is internally equipped with cylindrical block bodies 6, each having a frustoconical outline and arranged around the table 2. The block bodies 6 are made of metal such as aluminum and copper and are mounted by electrical insulators 61 located on the inner surface of the bottom of the vacuum chamber 1. Regarding the installation of the block bodies 6, the upper part of each block body 6 is either flush with the upper surface (layer storage surface) of the substrate Sw, which is held by the stage 2, or positioned below the upper surface. Thus, it is arranged such that at least part of the outer cylindrical surface faces directly into the plasma atmosphere that forms in the vacuum chamber 1. The configuration of the block body 6 need not be limited to the above, nor need it completely enclose the perimeter of the table 2.For example, a plurality of plate elements, each having an arc-shaped outline, can be arranged along the same circumference, thus forming the block body 6. An output 71 from the DC power supply 7 is also connected to the block body 6. At the time of layer deposition, a positive potential is applied by the DC power supply 7 in a suitable manner to act as the anode. Furthermore, an output 81 of the AC power supply 8 is connected to the table 2, so that a bias voltage of a predetermined range can be applied to the substrate Sw at the time of layer deposition. A method for depositing layers of this embodiment is described below, in which a silicon layer is deposited on the substrate Sw using the sputtering device SM mentioned above, up to a predetermined layer thickness.

[0018] The substrate Sw is mounted on the table 2 with the layer surface facing upwards, and after the substrate Sw has been electrostatically aspirated, the interior of the vacuum chamber 1 is evacuated. Once the interior of the vacuum chamber 1 has reached a predetermined pressure, a predetermined flow rate of argon gas is introduced into the vacuum chamber 1 by the mass flow controller 14, maintaining a specific effective evacuation rate. The target 3 is then pulsed with direct current at a negative electrical potential from the sputtering power supply Ps. The argon gas flow rate is set at this point to a range of 100 sccm to 1000 sccm (the partial pressure of the argon gas in the vacuum chamber 1 is 0.3 Pa to 8.0 Pa). The electrical power to be applied is set to a range of 1.0 kW to 5.0 kW.If the argon gas flow rate is below 100 sccm, a thin, high-density layer forms with an excessively high refractive index (n-value) and extinction coefficient (k-value). Conversely, if the argon gas flow rate exceeds 1000 sccm, the sputtering rate is too slow, resulting in poor productivity. Furthermore, if the electrical power input is less than 1.0 kW, the sputtering rate is reached too late, leading to poor productivity. However, if the electrical power input exceeds 5.0 kW, a high-density layer forms with an excessively high refractive index (n-value) and extinction coefficient (k-value).

[0019] During the layer deposition by sputtering of the target 3, it can alternatively be configured such that: a positive electrical potential (e.g., in a range of 0 V to 100 V, preferably 30 V) is applied to the block body 6 by the DC power supply 7; and a bias power (in a range of 20 W to 100 W) is applied to the substrate Sw by the AC power supply 8. If the bias power is below 20 W, the controllability of the power supply (trackability property) may be poor, leading to unstable conditions for layer deposition. Conversely, if the bias power exceeds 100 W, the thin film achieves a high density, resulting in excessively high refractive index (n-value) and extinction coefficient (k-value). Consequently, a plasma atmosphere forms in the space between the substrate Sw and the target 3.The ions of the argon gas in the plasma sputter the target 3, and the sputtered particles are sprayed off the target 3 according to the prescribed cosine law. As in . Fig. As shown in Figure 2(a), a silicon layer with a columnar structure and relatively low layer density (hereinafter referred to as the "first silicon layer Sf1") is deposited (first step). In this case, the layer thickness of the first silicon layer Sf1 is determined based on a standard for the layer thickness of the silicon layer to be deposited from now on. Based on this layer thickness and the sputtering rate, which depends on the electrical power supplied to target 3, the sputtering time for the deposition of the first silicon layer Sf1 is determined.

[0020] Subsequently, once the preset sputtering time has elapsed, the mass flow controller 14 is switched to a state in which the target 3 is charged with electrical energy while the argon gas flow rate is varied. At this point, the argon gas flow rate is set to a range of 20 sccm to 80 sccm (the partial pressure of the argon gas in the vacuum chamber 1 is then 0.08 Pa to 0.2 Pa). In other words, the ratio between the partial pressure of the second stage and the partial pressure of the first stage is set to a value between 0.1 and 0.7. If the ratio of the partial pressures is less than 0.1, the thin film will have a high density with an excessively high refractive index (n-value) and an excessively high extinction coefficient (k-value).Conversely, if the ratio of the partial pressure is higher than 0.7, the thin film has a low density, resulting in a refractive index (n-value) and an extinction coefficient (k-value) that are too low. Accordingly, as in . Fig. As shown in Figure 2(b), a silicon layer (hereinafter referred to as "second silicon layer Sf2") is formed (laminated) which also exhibits a columnar structure, but has a higher layer density and a "closer-grained" silicon layer than that of the first silicon layer Sf1 (second step). The sputtering time is adjusted to achieve the layer thickness of silicon layer Sf1. It has been confirmed that if the ratio of the layer thickness of the first silicon layer Sf1 to that of silicon layer Sf1 is set to a range of 0.3 to 0.8, the layer stresses can be varied without altering the optical properties at a given layer thickness. It has also been confirmed that if the ratio of the layer thickness of the first silicon layer Sf1 to that of silicon layer Sf1 is set to a range of 0.3 to 0.7, the optical properties can be further refined at a predetermined layer thickness.

[0021] According to the embodiments described above, it has been confirmed that the layer stresses can be adjusted, while maintaining the optical properties, depending on the density difference between the first silicon layer Sf1 and the second silicon layer Sf2, which are grown in the column structure. Furthermore, during the deposition of silicon layer Sf1, silicon layers are also deposited on the inner surfaces of the deposition protection plates. At this point, the second silicon layer Sf2 has been deposited with a high layer density on a portion of the surface layer. When the deposition of silicon layer Sf1 is repeated, the number of particles that are peeled off from the surface layer of the deposition protection plates and suspended in vacuum chamber 1 is reduced.Consequently, the number of particles that can be deposited on the substrate Sw after the layer is deposition is reduced as much as possible. Furthermore, it has been confirmed that layer deposition can be carried out with a uniform layer thickness distribution on the inner plane of the substrate Sw, and that layer deposition can be performed with little or no difference in the layer thickness distribution between substrates Sw when the layer deposition is repeatedly carried out on a large number of substrates Sw.

[0022] To confirm the effects mentioned above, the following experiment was conducted using the sputtering device SM mentioned above. In this experiment, the substrate Sw was fabricated by depositing a 100 nm thick silicon oxide layer onto the surface of a silicon wafer, with the aim of depositing a 50 nm thick silicon layer on the surface of the silicon oxide layer. As a preliminary test, the electrical power to be pulsed onto the target 3 was set to a frequency range of 150 kHz and from 1 kW to 10 kW, and the argon gas flow rate was set to a range of 20 sccm to 1000 sccm (the partial pressure of the argon gas in the vacuum chamber was in the range of 0.08 to 8 Pa at this time). Under the conditions mentioned above, silicon layers with a thickness of 25 nm were deposited onto a variety of substrates Sw.It was confirmed that under these sputtering conditions, the refractive index (n-value) was in the range of 4 to 5 and the extinction coefficient (k-value) in the range of 0.3 to 0.6. Although not explained in detail, SEM images of the silicon layers after deposition confirmed that the silicon layers, whose refractive indices and extinction coefficients both fall within the aforementioned ranges, grew in the column structure and that the layer densities varied with the argon gas flow rates.

[0023] Subsequently, the electrical power with which the target 3 was to be pulsed was set to a frequency of 150 kHz and 4 kW; the flow rate of the argon gas was appropriately varied in a range of 30 sccm to 300 sccm; as a base layer, the first silicon layer Sf1 was deposited on a variety of substrates Sw with a layer thickness of 25 nm; subsequently, the second silicon layer Sf2 with a layer thickness of 25 nm was deposited on the surface of the first silicon layer Sf1.The sputtering conditions at the time of deposition of the second silicon layer Sf2 were set under the sputtering conditions confirmed in the aforementioned earlier experiments, such that the electrical power to which target 3 was to be subjected was a frequency of 150 kHz and 4 kW, and the argon gas flow rate was set to 70 sccm (hereinafter referred to as "Sputtering Conditions 1"). The experiments confirmed that the layer stresses (MPa) decreased when the argon gas flow rate was below 100 sccm and that the layer stresses varied depending on the argon gas flow rate. At this time, it was confirmed that the refractive index and the extinction coefficient were maintained within the aforementioned ranges.

[0024] Fig. Figure 3 shows an SEM image where the sputtering conditions at the time of deposition of the first silicon layer Sf1 were set such that the electrical power applied to the target 3 in pulses was at a frequency of 150 kHz and 4 kW, and the argon gas flow rate was also set to 240 sccm (hereinafter referred to as "sputtering conditions 2"). The SEM image shows the first silicon layer Sf1 and the second silicon layer Sf2, which were continuously deposited under sputtering conditions 1 and 2, each with a layer thickness of 25 nm. It can be seen from the SEM image above that the layer density of the first silicon layer Sf1 and the second silicon layer Sf2 grew in the columnar structure and that the layer density of the first silicon layer Sf1 is lower than that of the second silicon layer Sf2.Incidentally, it was confirmed that a similar trend was observed when the electrical power used to charge Target 3 was varied while the argon gas flow rate was kept constant.

[0025] Experiments were then conducted by varying the sputtering time when the first silicon layer Sf1 and the second silicon layer Sf2 were deposited under sputtering conditions 1, 2, so that the ratio of the layer thickness of the first silicon layer Sf1 to the layer thickness (50 nm) of the entire silicon layer Sf was varied. According to the experiments, as shown in Fig. 4(a) and Fig. As shown in Figure 4(b), it was confirmed that in a range of layer thicknesses from 10% to 80%, the refractive index (n-value) remained within a range of 4 to 5 and the extinction coefficient (k-value) remained within a range of 0.3 to 0.6; in other words, it can be confirmed that the specified optical properties were maintained. As further shown in Fig. As shown in Figure 4(c), it was confirmed that the layer stresses can be varied by varying the layer thickness. In particular, it was confirmed that a low layer stress of ±200 MPa can be maintained for a layer thickness ratio in the range of 30% to 80%. Subsequently, during the continuous deposition of the first silicon layer Sf1 and the second silicon layer Sf2, each with a layer thickness of 25 nm, under sputtering conditions 1, 2, the bias power from the AC power supply 8 was applied to the substrate Sw by varying it in the range of 40 W to 100 W. According to the arrangement mentioned above, as shown in Figure 4(c), it can be observed that the layer stresses can be varied by varying the layer thickness. Fig. Figure 5 shows that the layer stresses varied depending on the preload power, while maintaining the specified optical properties.

[0026] The embodiments of the present invention have been described so far, but as long as the technical concept of the present invention is not deviated from, various modifications are possible. Silicon layers were described in the embodiments mentioned above, but it should be noted that this invention is also applicable to a laminated layer in which the layer stresses can be adjusted while maintaining the optical properties (e.g., a layer with silicon as its main component, containing nitrogen and oxygen) by having the layer have a columnar structure with a difference in layer density (e.g., a layer with silicon as its main component, containing nitrogen and oxygen). Furthermore, an example was described in the embodiments mentioned above in which the first and second steps were carried out continuously in the same vacuum chamber 1.However, the present invention is not limited to this, but such steps can also be carried out in separate vacuum chambers. DESCRIPTION OF REFERENCE MARKS SM Sputtering System Sw Substrate (object for layer deposition) Sf silicon layer Sf1 first silicon layer Sf2 second silicon layer 1 vacuum chamber 14 Mass flow controllers (for adjusting the partial pressure of the sputtering gas) 3 silicon targets PS Sputtering power supply QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 6952866

[0005]

Claims

[1] Method for depositing a silicon layer, comprising: Arranging a silicon target and an object for layer deposition in a vacuum chamber; introducing a sputtering gas into the vacuum chamber in a vacuum atmosphere; charging the target with electrical energy to deposit the silicon layer onto a surface of the object for layer deposition by sputtering; wherein the deposition of the silicon layer is carried out in two independent steps, comprising: a first step of deposition of a first silicon layer with a columnar structure; and a second step of deposition of a second silicon layer with a columnar structure with a higher layer density than the layer density of the first silicon layer. [2] Method for depositing a silicon layer according to claim 1, characterized in that a partial pressure of the sputtering gas in the vacuum chamber is defined as a reference partial pressure in the first step, and then the partial pressure of the sputtering gas is made lower than the reference partial pressure in the second step. [3] Method for depositing a silicon layer according to claim 1, wherein the ratio of the layer thickness of the first silicon layer to the silicon layer is adjusted to a range of 0.3 to 0.

8. [4] Method for depositing a layer according to any one of claims 1 to 3, wherein, while the layer is deposited on the surface of the object for layer deposition by sputtering, a pre-voltage power is supplied to the object for layer deposition, wherein the pre-voltage power is set to a range of 20 W to 100 W in the first step and in the second step.

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