Deposition of thick layers of silicon dioxide

Abstract

To deposit thick SiO2 layers at a high deposition rate with acceptable wafer warpage within a required thermal budget.SOLUTION: A method includes the steps of: disposing a substrate in a chamber; performing a first deposition step by PECVD to deposit an intermediate layer on the substrate, the intermediate layer including silicon nitride; and performing a second deposition step by PECVD to deposit at least one silicon dioxide layer on the intermediate layer. The first deposition step includes a step of introducing into the chamber a first gas mixture including silane, nitrogen gas, and either hydrogen gas or ammonia gas, and sustaining plasma from the first gas mixture in the chamber. The second deposition step includes a step of introducing into the chamber a second gas mixture including tetraethyl orthosilicate, and sustaining plasma from the second gas mixture in the chamber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the deposition of thick layers of silicon dioxide. [Background technology]

[0002] Thin dielectric layers are widely used in the fabrication of semiconductor devices, MEMS devices, optical and electro-optical devices or structures. Whether CVD, PECVD, HDP-CVD, PEALD or ALD is used, stresses will be induced in the thin dielectric layers during the deposition process. This stress may be due to external factors such as differences in the thermal expansion coefficient of the thin dielectric layer and the underlying substrate, or due to internal factors such as defects in the microstructure of the thin dielectric layer. Compressive or tensile stresses that may be induced in the thin dielectric layers can result in unwanted wafer distortions that can cause problems in subsequent process steps or failure of the thin dielectric layer itself in the form of cracks or delamination. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 9,472,610 [Patent Document 2] US Patent No. 2012 / 015113 Summary of the Invention [Problem to be solved by the invention]

[0004] The thicker the coating, the more difficult the stress control becomes. For applications requiring thick layers of SiO2 greater than 10 μm thick, traditional PECVD processes tend to be the preferred technology for high deposition rates. These traditional processes often require low deposition rates or multiple stress balancing layers to minimize wafer distortion and achieve a crack-free layer. This results in a complex deposition process and a low overall deposition rate. For example, US 9472610 discloses that it is not possible to deposit silicon dioxide layers greater than 20 microns thick at temperatures below 280° C. without cracking due to stress buildup in the layers, and therefore silicon dioxide is deposited in alternating tensile and compressive stress layers. US 2012 / 015113 discloses the formation of multiple layers of thermal SACVD and PECVD SiO2 with a total layer thickness of up to 3.5 microns. The deposition rate, layer density, and stress are all affected by the deposition temperature, so the thermal budget that the wafer can tolerate is another constraint when considering the deposition process. In many MEMS and 3D packaging applications, there are strict low temperature constraints that limit the deposition temperature to below about 300° C. to prevent damage or warping of the devices.

[0005] Therefore, there is a need for a method to deposit thick SiO2 layers at high deposition rates that can tolerate wafer bow within the required thermal budget. [Means for solving the problem]

[0006] SUMMARY OF THE PRESENT EMBODIMENT The present invention, in at least some embodiments, addresses the problems and needs described above. According to a first aspect of the present invention, there is provided a method for depositing silicon dioxide on a substrate by plasma enhanced chemical vapor deposition (PECVD), the method comprising the steps of placing the substrate in a chamber, performing a first deposition step by PECVD to deposit an intermediate layer comprising silicon nitride on the substrate, and performing a second deposition step by PECVD to deposit at least one silicon dioxide layer on the intermediate layer, the first deposition step comprising introducing a first gas mixture comprising silane, nitrogen gas, and either hydrogen gas or ammonia gas into the chamber at about 1000 rpm to deposit the intermediate layer on the substrate. The method includes maintaining a plasma from the first gas mixture in the chamber at a temperature between about 220°C and about 300°C, and the second deposition step includes introducing a second gas mixture including tetraethylorthosilicate into the chamber and maintaining a plasma from the second gas mixture in the chamber at a temperature between about 220°C and about 300°C to deposit at least one silicon dioxide layer on the intermediate layer, the intermediate layer having a total compressive stress between -400 MPa and -100 MPa, each of the at least one silicon dioxide layer having a total neutral stress between -50 MPa and +50 MPa, and the at least one silicon dioxide layer having a total thickness of at least 10 μm.

[0007] The present invention allows for the deposition of TEOS-based silicon dioxide layers having a total thickness of at least 10 μm on silicon wafers at high deposition rates of up to 1.5 μm / min and at temperatures within a low thermal budget without cracking. Without wishing to be bound by theory or speculation, it is believed that the silicon nitride (SiN)-containing intermediate layer improves adhesion of the tetraethylorthosilicate (TEOS)-based silicon dioxide (SiO2) layer to the substrate, particularly if the substrate comprises or is formed from silicon (Si), and the compressive stress of the intermediate layer reduces the net stress of the intermediate layer / SiO2 stack when the neutral stress SiO2 layer is deposited on the intermediate layer. The net compressive stress increases the crack threshold of the TEOS-based SiO2 layer. Notably, the inclusion of the intermediate layer reduces the density of the TEOS-based SiO2 layer, which allows a thicker SiO2 layer to be deposited before the crack threshold of the SiO2 is reached. This effect has also been shown to occur regardless of whether the intermediate layer is deposited from a plasma formed from an ammonia-containing or ammonia-free gas mixture.

[0008] The first gas mixture may be substantially free of ammonia. The first gas mixture may consist of or consist essentially of silane, nitrogen gas, and hydrogen gas. Alternatively, the first gas mixture may consist of or consist essentially of silane, nitrogen gas, and ammonia gas. The second gas mixture may further comprise oxygen gas. The second gas mixture may further comprise hydrogen gas. The second gas mixture may further comprise helium gas. The second gas mixture may consist of or consist essentially of tetraethylorthosilicate, helium gas, hydrogen gas, and oxygen gas.

[0009] During the first deposition step, silane, nitrogen gas, hydrogen gas, and ammonia can be introduced into the chamber at associated flow rates in sccm. During the second deposition step, tetraethylorthosilicate, helium gas, hydrogen gas, and oxygen gas can be introduced into the chamber at associated flow rates in sccm. During the second deposition step, helium gas can be introduced into the chamber through two or more gas inlets. Preferably, a helium gas flow rate from a first gas inlet of the two or more gas inlets can be higher than a helium gas flow rate from a second gas inlet of the two or more gas inlets. Preferably, the first gas inlet also functions as a gas inlet for introducing tetraethylorthosilicate into the chamber. By having at least two separate sources of helium gas into the chamber, the helium gas introduced into the chamber through a first gas inlet can function as a carrier gas for the tetraethylorthosilicate introduced into the chamber through the first gas inlet, and the helium gas introduced into the chamber through a second gas inlet can function to stabilize the plasma to maintain reproducible operation.

[0010] Silane may be introduced into the chamber during the first deposition step at a flow rate in the range of about 50 sccm to about 400 sccm, optionally about 90 sccm to about 350 sccm, optionally about 180 to about 330 sccm, or optionally at a flow rate of about 325 sccm.

[0011] Nitrogen gas may be introduced into the chamber during the first deposition step at a flow rate in the range of about 2000 sccm to about 8000 sccm, optionally about 2500 sccm to about 7000 sccm, optionally about 2600 sccm to about 6500 sccm, or optionally at a flow rate of about 6000 sccm.

[0012] If present in the first deposition step, hydrogen gas may be introduced into the chamber at a flow rate in the range of about 250 to about 750 sccm, optionally about 400 sccm to about 600 sccm, or optionally at a flow rate of about 500 sccm.

[0013] If present in the first deposition step, ammonia gas may be introduced into the chamber at a flow rate in the range of about 25 sccm to about 500 sccm, optionally at a flow rate of about 35 sccm to about 475 sccm, or optionally at a flow rate of about 450 sccm.

[0014] Tetraethylorthosilicate may be introduced into the chamber during the second deposition step at a flow rate in the range of about 1 sccm to about 10 sccm, optionally about 3 sccm to about 7 sccm, or optionally at a flow rate of about 5 sccm.

[0015] If present in the second deposition step, oxygen gas can be introduced into the chamber during the second deposition step at a flow rate in the range of about 1.0 slpm to about 10 slpm, optionally about 4.0 slpm to about 8.0 slpm, or optionally at a flow rate of about 6.5 slpm.

[0016] If present in the second deposition step, hydrogen gas can be introduced into the chamber during the second deposition step at a flow rate in the range of about 0.25 to about 2.0 slpm, optionally about 0.75 slpm to about 1.5 slpm, or optionally at a flow rate of about 1.0 slpm.

[0017] If present in the second deposition step, the total flow rate of helium gas may be introduced into the chamber in the second deposition step at a flow rate ranging from about 1000 sccm to about 2000 sccm, optionally from about 1200 sccm to about 1650 sccm, or optionally about 1450 sccm. The flow rate of helium gas introduced into the chamber in the second deposition step through a first gas inlet of the at least two gas inlets may range from about 600 sccm to about 1900 sccm, optionally from about 800 sccm to about 1650 sccm, or optionally about 1250 sccm. The flow rate of helium gas introduced into the chamber in the second deposition step through a second gas inlet of the at least two gas inlets may range from about 50 sccm to about 500 sccm, optionally from about 100 sccm to about 300 sccm, or optionally about 200 sccm.

[0018] During the first deposition step, the process temperature may be less than about 280° C. The process temperature may be greater than about 225° C. During the first deposition step, the process temperature may be about 250° C. During the second deposition step, the process temperature may be less than about 280° C. The process temperature may be greater than about 225° C. During the second deposition step, the process temperature may be about 250° C. By maintaining the substrate at these temperatures, the substrate can be kept within low thermal budget constraints, making the method suitable for depositing silicon nitride and silicon dioxide layers on temperature sensitive substrates. For example, the method may be used to deposit silicon nitride and silicon dioxide layers on temperature sensitive substrates including device layers and / or interconnects, which may include copper layers embedded in a dielectric or die attached to the substrate.

[0019] During the first deposition step, the plasma is maintained in the chamber, the chamber may have a pressure in the range of about 1 Torr to about 3 Torr, or optionally a pressure of about 2 Torr. During the second deposition step, the chamber may have a pressure in the range of about 3 Torr to about 5 Torr, or optionally a pressure of about 4 Torr.

[0020] The steps of the first aspect of the present invention may be carried out in a capacitively coupled PECVD reactor.

[0021] The plasma is maintained in the first deposition step using a high frequency RF power in the range of about 500 W to about 1500 W, optionally about 540 W to about 1320 W, or optionally about 700 W to about 1000 W. The high frequency RF power in the first deposition step may have a frequency in the range of about 10 MHz to about 15 MHz, preferably a frequency of 13.56 MHz.

[0022] The plasma in the second deposition step may be maintained using high frequency RF power. Preferably, the plasma may be maintained using high frequency and low frequency RF power.

[0023] The high frequency RF power in the second deposition step may have a frequency in the range of about 10 MHz to about 15 MHz, preferably around 13.56 MHz. The high frequency RF power in the second deposition step may have a power in the range of about 1500 W to about 3000 W, optionally about 1750 W to about 2300 W, or optionally about 1950 W.

[0024] The low frequency RF power in the second deposition step may have a frequency in the range of 100 kHz to about 500 kHz, optionally about 200 kHz to about 450 kHz, optionally about 300 kHz to about 400 kHz, or optionally a frequency of about 375 kHz. The low frequency RF power in the second deposition step may have a power in the range of about 200 W to about 600 W, optionally about 400 W to about 550 W, or optionally about 350 W.

[0025] The total compressive stress of the intermediate layer may be at least -100 MPa, optionally at least -200 MPa, optionally at least -250 MPa, or optionally at least -300 MPa. The thickness of the intermediate layer may be at least 0.05 μm, optionally at least 0.25 μm, or optionally at least 0.5 μm. The total neutral stress of each of the at least one silicon dioxide layer may be between -30 MPa and +30 MPa. The total stress of the at least one silicon dioxide layer may be between -50 MPa and +50 MPa, optionally between -30 MPa and +30 MPa. The total thickness of the silicon dioxide layers may be at least 20 μm, optionally at least 30 μm, or optionally at least 40 μm. The thickness of each of the at least one silicon dioxide layer may be at least 1 μm, optionally at least 2 μm, or optionally at least 5 μm. At least one silicon dioxide layer may be deposited onto the intermediate layer at a deposition rate of at least 1.0 μm / min, optionally at least 1.25 μm / min, or optionally at least 1.5 μm / min.

[0026] The at least one silicon dioxide layer may consist of or consist essentially of a single silicon dioxide layer. Alternatively, the at least one silicon dioxide layer may comprise two or more silicon dioxide layers. The two or more silicon dioxide layers may be deposited in the same chamber. The second deposition step may be performed directly after the first deposition step without breaking the vacuum conditions in the chamber. Alternatively, the substrate may be removed from the chamber between the first and second deposition steps. The substrate may be transferred to another chamber between the first and second deposition steps. Alternatively, the first and second deposition steps may be performed in the same chamber. The inventors have found that by removing the substrate from the chamber after the first deposition step, the vacuum conditions may be broken without significantly changing the processing performance of the intermediate layer and the silicon dioxide stack. Thus, the substrate may be processed in the same chamber or in a different chamber with the same performance, improving processing efficiency and processing flexibility.

[0027] The substrate may be a semiconductor substrate. The substrate may be a silicon-containing substrate. The semiconductor substrate may be silicon.

[0028] According to a second aspect of the present invention there is provided a substrate having at least one silicon dioxide layer deposited thereon using a method according to the first aspect, wherein each of the at least one silicon dioxide layer has a total neutral stress of between -50 MPa and +50 MPa and the at least one silicon dioxide layer has a total thickness of at least 10 μm.

[0029] The substrate may be a semiconductor substrate. The substrate may be a silicon-containing substrate. The substrate may be silicon. The substrate may include a plurality of dies. The substrate may include features such as one or more device layers and / or interconnects or dies mounted thereon. The features may be temperature sensitive. The features may include a copper layer, for example a copper layer embedded in a dielectric material. The total neutral stress of each of the at least one silicon dioxide layer may be between -30 MPa and +30 MPa. The total stress of the at least one silicon dioxide layer may be between -50 MPa and +50 MPa, optionally between -30 MPa and +30 MPa. The total thickness of the at least one silicon dioxide layer may be at least 20 μm, optionally at least 30 μm, or optionally at least 40 μm. The thickness of each of the at least one silicon dioxide layer may be at least 1 μm, optionally at least 2 μm, or optionally at least 5 μm.

[0030] According to a third aspect of the present invention there is provided a plasma enhanced chemical vapour deposition apparatus for depositing silicon dioxide on a substrate by plasma enhanced chemical vapour deposition using a method according to the first aspect of the present invention comprising a chamber, a substrate support disposed within the chamber for supporting a substrate, at least one gas inlet for introducing a gas or gas mixture into the chamber at a flow rate, plasma generating means for maintaining a plasma in the chamber, high frequency power supply means configured to supply high frequency RF power to the at least one gas inlet, low frequency power supply means configured to supply low frequency RF power to at least one of the substrate support and the at least one gas inlet, and a controller configured to switch between a first set of process conditions and a second set of process conditions, the first set of process conditions being configured to perform a first deposition step of depositing an intermediate layer on the substrate, the intermediate layer comprising silicon nitride, the second set of process conditions being configured to perform a first deposition step of depositing at least one silicon nitride on the intermediate layer. a controller configured to perform a second deposition step of depositing at least one silicon dioxide layer on the intermediate layer, the first set of process conditions being configured to perform the first deposition step by introducing a first gas mixture including silane, nitrogen gas, and hydrogen gas or ammonia gas into the chamber through the at least one gas inlet and maintaining a plasma from the first gas mixture in the chamber using the plasma generating means at a temperature between about 220° C. and about 300° C. to deposit the intermediate layer on the substrate, the second set of process conditions being configured to perform the second deposition step by introducing a second gas mixture including tetraethylorthosilicate into the chamber through the at least one gas inlet and maintaining a plasma from the second gas mixture in the chamber using the plasma generating means at a temperature between about 220° C. and about 300° C. to deposit at least one silicon dioxide layer on the intermediate layer.

[0031] The second gas mixture may further include oxygen gas. The second gas mixture may further include hydrogen gas. The second gas mixture may further include helium gas. The at least one gas inlet may include two or more gas inlets. Preferably, a first gas inlet of the two or more gas inlets is configured to introduce helium gas and tetraethylorthosilicate into the chamber, and a second gas inlet of the two or more gas inlets is configured to introduce helium gas into the chamber. The low frequency power supply means may be configured to supply low frequency RF power to the at least one gas inlet.

[0032] Although the invention has been described above, the invention extends to any inventive combination of the features disclosed above or in the following description, drawings, or claims. For example, a feature disclosed in relation to one aspect of the invention may be combined with a feature disclosed in relation to any other aspect of the invention.

[0033] For the avoidance of doubt, whenever reference is made in this specification to "comprising" or "including" and similar terms, it is to be understood that the invention also includes more restrictive terms such as "consisting of" and "consisting essentially of."

[0034] For the avoidance of doubt, it is to be understood that stress measurements having negative values ​​indicate compressive stress, while stress measurements having positive values ​​indicate tensile stress.

[0035] For the avoidance of doubt, silicon nitride or SiN deposited by PECVD in the temperature range of interest is understood to be an amorphous film that contains or consists of silicon, nitrogen and hydrogen, and in some embodiments is referred to as α-SiN:H or α-Si 1-x N x :H yThe percentages of Si, N, and H can vary depending on the deposition parameters. However, for convenience and brevity, these films will be referred to herein as silicon nitride or SiN. These films have excellent dielectric properties. PECVD silicon dioxide or SiO2 films deposited from TEOS precursors are also amorphous dielectric films containing hydrogen atoms and potentially trace amounts of carbon. PECVD TEOS-based oxides deposited in the temperature range of interest are not stoichiometric SiO2, but are amorphous films that contain or consist of silicon, oxygen, and hydrogen, and in some embodiments are α-SiO:H or α-Si 1-x O x :H y However, for convenience and brevity, these PECVD TEOS-based oxides will be referred to herein as silicon dioxide or SiO2. [Brief description of the drawings]

[0036] Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 13 is a graph showing FTIR spectra of PECVD SiN layers from N2 / H2 precursors subjected to both neutral and compressive stress. [Diagram 2] 13 is a graph showing FTIR spectra of PECVD SiN layers from NH3 precursor under both neutral and compressive stress. [Diagram 3] 1 shows FTIR spectra of SiN layers from neutral stress NH3 precursor, SiN layers from neutral stress N2 / H2 precursor, and PECVD SiO2 layers from TEOS precursor deposited on silicon substrate. [Figure 4] 1 shows SEM images of a 40 μm trench formed on a silicon substrate coated with a silicon dioxide layer, A) without an intermediate layer according to the invention, and B) with an intermediate layer according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Suitable equipment for depositing the intermediate layer and silicon dioxide layer according to the exemplary method (and comparative examples) of the present invention includes the SPTS Delta™ fxP parallel plate PECVD system available from SPTS Technologies Limited, Newport, South Wales, UK. All exemplary embodiments and comparative examples described below were carried out using this equipment. However, the results are generally expected to be obtained with capacitively coupled PECVD equipment. Stress measurements were performed on a Tenor Flx™ 3300-R system.

[0038] In the exemplary methods below, the intermediate layer is formed of silicon nitride (SiN), however, it is anticipated that intermediate layers that include one or more other components in addition to SiN will also exhibit the advantages described below.

[0039] The PECVD apparatus of the present invention includes a chamber, a substrate support disposed within the chamber for supporting a substrate, at least one gas inlet for introducing a gas or gas mixture into the chamber at a flow rate, a plasma generating means for maintaining a plasma within the chamber, a high frequency power supply configured to supply high frequency RF power to the at least one gas inlet, a low frequency power supply configured to supply low frequency RF power to at least one of the substrate support and the at least one gas inlet, and a controller configured to switch between a first set of process conditions and a second set of process conditions, the first set of process conditions configured to perform a first deposition step of depositing an intermediate layer on the substrate, the intermediate layer comprising silicon nitride, and the second set of process conditions configured to perform a second deposition step of depositing at least one silicon dioxide layer on the intermediate layer. A first set of process conditions is configured to perform the first deposition step by introducing a first gas mixture including silane, nitrogen gas, and either hydrogen gas or ammonia gas into the chamber through the at least one gas inlet and maintaining a plasma from the first gas mixture in the chamber using the plasma generating means at a temperature between about 220° C. and about 300° C. to deposit the intermediate layer on the substrate. A second set of process conditions is configured to perform a second deposition step by introducing a second gas mixture including tetraethylorthosilicate, helium gas, hydrogen gas, and oxygen gas into the chamber through the at least one gas inlet and maintaining a plasma from the second gas mixture in the chamber using the plasma generating means at a temperature between about 220° C. and about 300° C. to deposit at least one silicon dioxide layer on the intermediate layer.

[0040] The at least one gas inlet may include two or more gas inlets, preferably a first gas inlet of the two or more gas inlets configured to introduce helium gas and tetraethylorthosilicate into the chamber and a second gas inlet of the two or more gas inlets configured to introduce helium gas into the chamber.

[0041] Two RF power sources operating at 13.56 MHz and 375 kHz are coupled to a gas distribution plate, also known as a "showerhead", located towards the top of the chamber. The substrate is placed on a substrate support below the gas distribution plate and coaxially with the substrate support. The substrate support is resistively heated and a cooling mechanism allows control of the substrate support and, in turn, the substrate temperature. Once the appropriate RF and process gas pressures are reached, a plasma is generated between the gas distribution plate and the substrate support / substrate. The chamber is evacuated by a pumping system and attached to a transfer module operating under vacuum.

[0042] The substrate is preferably a semiconductor substrate, and is most preferably formed of silicon. In the embodiments described herein, the substrate is in the form of a silicon wafer having a diameter of 300 mm and a typical thickness of about 775 μm. However, other substrate materials, substrate shapes, diameters and thicknesses may be used with the method and apparatus of the present invention. It will be understood that the deposition conditions required to practice the present invention, including gas flow rates, chamber pressure and power received by the substrate and / or gas inlets, may vary in a manner known in the art depending on the substrate material and shape. In the embodiments described herein, a silicon wafer has a trench formed in its upper surface, the trench being about 40 μm deep, and the method of the present invention was used to fill the trench with a deposited silicon dioxide layer. However, the silicon dioxide layer may be deposited on other features of such a substrate as well, including vias, bare silicon surfaces or dies attached to the substrate surface.

[0043] The inventors have found that by coating a substrate, particularly one that contains or consists of silicon, with an intermediate layer containing SiN, it is possible to substantially increase the thickness of the neutral / low stress TEOS-based SiO2 layer that can be deposited before cracking or delamination occurs. In the absence of an intermediate layer containing SiN, the maximum thickness of SiO2 that can be deposited without cracking or delamination is 20 μm, and is a stack of layers with alternating tensile and compressive stresses or deposited at a very low deposition rate. However, when using an intermediate layer containing SiN deposited by PECVD, a SiO2 layer thickness of more than 30 μm was obtained with a neutral stress (+22 MPa) intermediate layer, and a SiO2 layer thickness of more than 40 μm was obtained with a compressive stress (-200 MPa) intermediate layer at a deposition rate of up to 1.5 μm / min. The increase in the crack threshold thickness was observed for intermediate layers with thicknesses of 0.05 μm to 0.5 μm, but the effect is expected to extend to thicker intermediate layers.

[0044] A comparison of a substrate processed in a conventional manner and a substrate processed according to an embodiment of the method of the present invention is shown in FIG. 4. FIG. 4 shows two SEM images of a cross section of a 40 μm deep trench in a silicon deposition of a TEOS-based SiO2 layer with a neutral stress of about 40 μm. In the image labeled "A", there is no intermediate layer between the SiO2 layer and the substrate, whereas in the image labeled "B", a total stress N2 / H2-based compressive SiN layer of about -200 MPa was deposited first, followed by a single neutral stress TEOS-based SiO2 layer. Severe cracks are observed in image A, for example, both in the center of the right side wall of the trench and near the top surface of the SiO2 layer. In contrast, image B shows no evidence of cracks other than cleavage damage during the preparation of the sample. EXAMPLES

[0045] Exemplary embodiments of the present invention include introducing silane (SiH4), nitrogen gas (N2), and hydrogen gas (H2) or ammonia gas (NH3) into a PECVD chamber in a first deposition step. A plasma is maintained in the chamber to cause a PECVD process to deposit an intermediate layer comprising silicon nitride (SiN) on the substrate. Preferably, the intermediate layer consists or consists essentially of SiN.

[0046] In a second deposition step after the first deposition step, a gas mixture including tetraethylorthosilicate (TEOS), oxygen gas (O2), H2, and helium gas (He) is introduced into a PECVD chamber containing the substrate, which may be the same or different from the chamber used in the first deposition step, and a plasma is maintained in the chamber, allowing a PECVD process to occur to deposit at least one silicon dioxide (SiO2) layer on the intermediate layer.

[0047] It may be advantageous to avoid the use of ammonia in the first deposition step to produce the intermediate layer. Therefore, the inventors investigated the properties of the intermediate layer with and without the use of ammonia in the first deposition step. The process conditions used for the deposition of the NH3-free and NH3-based SiN layers are given in Table 1. The depositions were carried out at 250 °C in both cases.

[0048] [Table 1]

[0049] Figure 1 shows the FTIR spectrum of two SiN layers on a Si substrate produced without ammonia in the gas mixture SiH4 / N2 / H2. The contribution of the substrate has been subtracted. The spectrum shows a peak at about 3340 cm -1 NH stretching, about 2130cm -1 Si-H stretching, approximately 1170 cm -1 NH bending at 850 cm -1The spectrum shows an absorption peak associated with the Si-N stretching at ∼2130 cm compared to neutral SiN by normalizing the spectrum to the Si-N peak. -1 It can be seen that the area of ​​the Si-H stretching peak decreases slightly and the wavenumber increases at , and that the Si-N stretching peak shows a tendency to increase in wavenumber as it approaches the NH bending mode of compressed SiN.

[0050] Figure 2 shows the FTIR spectra of NH3-based PECVD SiN layers under neutral and compressive stress conditions, where the gas mixture is SiH4 / NH3 / N2. The spectra are similar to those in Figure 1, but the NH bending peak is more pronounced for the NH3-based SiN.

[0051] Figure 3 shows the FTIR absorption spectrum of 1 μm of TEOS-based SiO2 on silicon and a N2 / H2-based SiN layer deposited on a silicon substrate (after subtracting the contributions of the substrate and SiN). -1 The SiO peak gradually broadens around the center of the SiN layer. Similar results are observed for NH3-based SiN layers. The change in width of the SiO peak is shown in Table 2 below as the full width at half maximum (FWHM) of the SiO peak for silicon and the four SiN variants.

[0052] [Table 2]

[0053] As can be seen from Table 2, the width of the peak increases with the introduction of the neutral SiN layer and broadens slightly further when the layer is compressed. A wider peak indicates a less dense layer, and therefore a thicker layer can be deposited before the SiO2 cracks.

[0054] The refractive index of the intermediate layer was investigated and is shown in Table 3 below. For both N2 / H2 and NH3 based SiN depositions, the refractive index of the SiO2 layer decreased as the compressive stress of the SiN layer increased, with the refractive index change being more pronounced for the SiN layer formed from N2 / H2. The total stress of the intermediate layer with and without a SiO2 layer on top of the intermediate layer is also shown in Table 4 below. The total stress for the neutral stress SiO2 layer without the intermediate layer present was -7 MPa.

[0055] [Table 3]

[0056] [Table 4]

[0057] The N2 / H2-based layers exhibit a higher refractive index, indicative of a higher Si content in the N2 / H2 layers when compared to their NH3-based counterparts. The net stress of the SiN / SiO2 stack is less compressive than would be expected from the stress values ​​of the individual layers, suggesting that the intermediate layer modifies the properties of the SiO2 layer. In both cases, the stress is tunable via modification of processing conditions.

[0058] Neutral stress SiO2 layers were deposited at approximately 250°C using TEOS / O2 / H2 / He chemistry, supporting deposition rates up to 1.5 μm / min. Processing details can be found in Table 5 below.

[0059] [Table 5]

[0060] A He flow rate of 1250 sccm serves as a carrier gas for the TEOS, while 200 sccm is fed directly to the gas distribution plate in a separate line to stabilize the plasma and maintain reproducible operation. By adjusting the power of the high and low frequency sources, the total stress of the SiO2 layer can be effectively controlled. For example, a high frequency source of 2300 W and a low frequency source of 550 W can be used to put the layer in compression, while a high frequency source of 1500 W can be used to put the layer in tension. The measured stress values ​​and refractive index of the layer are shown in Table 6 below.

[0061] [Table 6]

[0062] Without being bound by any theory or speculation, the 1183 cm -1 The SiN in the interlayer appears to significantly affect the structure of the SiO2, as measured by the broadening of the Si-O FTIR peak at 1183 cm. The structural changes of TEOS appear to be relatively independent of the source of the SiN in the interlayer, as determined by the refractive index and FTIR spectrum of the SiO2 layer. Without being bound by any theory or speculation, it is speculated that the presence of SiN in the interlayer improves the adhesion of the TEOS-based SiO2 onto the substrate, especially when the substrate is formed of or contains Si. The compressive stress of the interlayer is speculated to reduce the net stress of the interlayer / SiO2 stack when a neutral stress SiO2 layer is deposited on the interlayer. The net compressive stress increases the crack threshold of the TEOS-based SiO2 layer, increasing the thickness of the SiO2 layer that can be deposited before cracking or delamination occurs. Surprisingly, the SiN in the interlayer exhibits a peak at 1183 cm -1 The increase in the TEOS-based SiO2 layer structure affects the structure of the upper SiO2 layer as measured by the broadening of the Si-O FTIR peak at 1000 nm. This broadening of the peak indicates a decrease in the density of the TEOS-based SiO2 layer. The structural change of the TEOS-based SiO2 layer appears to be relatively independent of the refractive index and the source of the SiN component in the intermediate layer as determined by FTIR.

[0063] It should be noted that the neutral stress TEOS-based SiO2 can be deposited as a single layer or can be deposited in stages to form multiple SiO2 layers, each with neutral stress, so that the cracking performance is not altered. Preferably, if multiple SiO2 layers are present, the total stress of at least one SiO2 layer is between -50 MPa and +50 MPa, optionally between -30 MPa and +30 MPa, to ensure that the total stress throughout the SiO2 deposition is neutral. By providing multiple SiO2 layers, the chamber can be periodically cleaned during the second deposition step to prevent contamination of the SiO2 layer(s). Multiple SiO2 layers can be deposited in a single wafer chamber or cluster tool or a multi-station PECVD tool if necessary. The intermediate layer and the TEOS-based SiO2 can be deposited in the same or different chambers, in either case the cracking performance is not altered. Following deposition of the intermediate layer, the process can continue under vacuum or a vacuum pause can be performed before starting the deposition of the TEOS-based SiO2. The choice of chamber and deposition sequence is highly dependent on the tool configuration. [Explanation of symbols]

[0064] A,B SEM images of the trench.

Claims

1. A method for depositing silicon dioxide on a substrate by plasma-enhanced chemical vapor deposition (PECVD), The steps include placing the substrate inside the chamber, A first deposition step is performed by PECVD to deposit an intermediate layer containing silicon nitride onto the substrate, The process includes a second deposition step performed by PECVD to deposit at least one silicon dioxide layer on the intermediate layer, The first deposition step includes introducing a first gas mixture comprising silane, nitrogen gas, and hydrogen gas or ammonia gas into the chamber and maintaining a plasma from the first gas mixture in the chamber at a temperature of about 220°C to about 300°C in order to deposit the intermediate layer on the substrate, The second deposition step includes introducing a second gas mixture containing tetraethyl orthosilicate into the chamber and maintaining a plasma from the second gas mixture in the chamber at a temperature of about 220°C to about 300°C to deposit the at least one silicon dioxide layer on the intermediate layer, A method wherein the intermediate layer has a total compressive stress of -400 MPa to -100 MPa, each of the at least one silicon dioxide layers has a total neutral stress of -50 MPa to +50 MPa, and the total thickness of the at least one silicon dioxide layer is at least 10 μm.

2. The method according to claim 1, wherein the second gas mixture further contains oxygen gas.

3. The method according to claim 1 or 2, wherein the second gas mixture further contains hydrogen gas.

4. The method according to claim 1, wherein the second gas mixture further contains helium gas.

5. The method according to claim 4, wherein during the execution of the second deposition step, the helium gas is introduced into the chamber through two or more gas inlets.

6. The method according to claim 1, wherein silane is introduced into the chamber at a flow rate of about 50 sccm to about 400 sccm during the execution of the first deposition step.

7. The method according to claim 1, wherein nitrogen gas is introduced into the chamber at a flow rate of about 2,000 sccm to about 8,000 sccm during the execution of the first deposition step.

8. The method according to claim 1, wherein in the first deposition step, hydrogen gas is introduced into the chamber at a flow rate of about 250 to about 750 sccm.

9. The method according to claim 1, wherein in the first deposition step, ammonia gas is introduced into the chamber at a flow rate of about 25 sccm to about 500 sccm.

10. The method according to claim 1, wherein tetraethyl orthosilicate is introduced into the chamber at a flow rate of about 1 sccm to about 10 sccm during the execution of the second deposition step.

11. The method according to claim 2, wherein oxygen gas is introduced into the chamber at a flow rate of about 1.0 slpm to about 10 slpm during the execution of the second deposition step.

12. The method according to claim 3, wherein hydrogen gas is introduced into the chamber at a flow rate of about 0.25 slpm to about 2.0 slpm during the execution of the second deposition step.

13. The method according to claim 4, wherein the total flow rate of helium gas introduced into the chamber in the second deposition step is in the range of about 1,000 sccm to about 2,000 sccm.

14. The method according to claim 13, wherein in the second deposition step, the flow rate of helium gas introduced into the chamber through the first gas inlet of the at least two gas inlets is in the range of about 600 sccm to about 1900 sccm, and / or in the second deposition step, the flow rate of helium gas introduced into the chamber through the second gas inlet of the at least two gas inlets is in the range of about 50 sccm to about 500 sccm.

15. The method according to claim 1, wherein during the execution of the first deposition step and / or the second deposition step, the processing temperature is less than about 280°C and / or greater than about 225°C.

16. The method according to claim 1, wherein the plasma in the first deposition step is sustained using high-frequency RF power having a frequency in the range of 10 MHz to about 15 MHz, and the high-frequency RF power has a power in the range of about 500 W to about 1500 W.

17. The method according to claim 1, wherein the plasma in the second deposition step is sustained using high-frequency RF power having a frequency in the range of 10 MHz to about 15 MHz and low-frequency RF power having a frequency in the range of 100 kHz to about 500 kHz.

18. The method according to claim 17, wherein the high-frequency RF power in the second deposition step has a power of about 1500W to about 3000W.

19. The method according to claim 17 or claim 18, wherein the low-frequency RF power in the second deposition step has a power of about 200 W to about 600 W.

20. The method according to claim 1, wherein the total compressive stress of the intermediate layer is at least -100 MPa.

21. The method according to claim 1, wherein the thickness of the intermediate layer is at least 0.05 μm.

22. The method according to claim 1, wherein the total neutral stress of each of the at least one silicon dioxide layers is between -30 MPa and +30 MPa.

23. The method according to claim 1, wherein the substrate is silicon.

24. The method according to claim 1, wherein the substrate is removed from the chamber between the first deposition step and the second deposition step.

25. A substrate having at least one silicon dioxide layer deposited thereon using the method of claim 1, wherein each of the at least one silicon dioxide layer has a total neutral stress in the range of -50 MPa and +50 MPa, and the total thickness of the at least one silicon dioxide layer is at least 10 μm.

26. The substrate according to claim 25, wherein the total thickness of the at least one silicon dioxide layer is at least 20 μm.

27. A plasma-enhanced chemical vapor deposition apparatus for depositing silicon dioxide on a substrate by plasma-enhanced chemical vapor deposition using the method described in claim 1, Chamber and, A substrate support portion is arranged within the chamber to support the substrate, A gas inlet for introducing a gas or gas mixture into the chamber at a certain flow rate, and a plasma generating means for maintaining a plasma within the chamber. A high-frequency power supply means configured to supply high-frequency RF power to at least one of the gas inlets, A low-frequency power supply means configured to supply low-frequency RF power to at least one of the substrate support portion and the at least one of the gas inlet, The system includes a controller configured to switch between a first set of processing conditions and a second set of processing conditions, wherein the first set of processing conditions is configured to perform a first deposition step of depositing an intermediate layer on the substrate, the intermediate layer comprising silicon nitride, and the second set of processing conditions is configured to perform a second deposition step of depositing at least one silicon dioxide layer on the intermediate layer. The first set of processing conditions is configured to perform the first deposition step by introducing a first gas mixture containing silane, nitrogen gas, and either hydrogen gas or ammonia gas into the chamber through at least one gas inlet, and maintaining a plasma from the first gas mixture in the chamber at a temperature of about 220°C to about 300°C using the plasma generating means to deposit the intermediate layer on the substrate. A plasma-enhanced chemical vapor deposition apparatus, wherein the second set of processing conditions is configured to perform a second deposition step of depositing at least one silicon dioxide layer on the intermediate layer by introducing a second gas mixture containing tetraethyl orthosilicate, helium gas, hydrogen gas, and oxygen gas into the chamber through the at least one gas inlet, and maintaining the plasma from the second gas mixture at a temperature of about 220°C to about 300°C in the chamber using the plasma generating means.

Images