WO2005013348A2

WO2005013348A2 - Formation of ultra-thin oxide and oxynitride layers by self-limiting interfacial oxidation

Info

Publication number: WO2005013348A2
Application number: PCT/US2004/024595
Authority: WO
Inventors: David L. O'meara; Cory Wajda; Anthony Dip; Michael Toeller; Toshihara Furukawa; Kristen Scheer; Alessandro Callegari; Fred Buehrer; Sufi Zafar; Evgeni Gousev; Anthony Chou; Paul Higgins
Original assignee: Tokyo Electron Ltd; International Business Machines Corp
Current assignee: Tokyo Electron Ltd; International Business Machines Corp
Priority date: 2003-07-31
Filing date: 2004-07-30
Publication date: 2005-02-10
Anticipated expiration: 2006-01-31
Also published as: JP4933256B2; JP2007500946A; WO2005013348A3

Abstract

Ultra-thin oxide and oxynitride layers are formed utilizing low pressure processing to achieve self-limiting oxidation of substrates and provide ultra-thin oxide and oxynitride. The substrates to be processed can contain an initial dielectric layer such as an oxide layer, an oxynitride layer, a nitride layer, a high-k layer, or alternatively can lack an initial dielectric layer. The processing can be carried out using a batch type process chamber or, alternatively, using a single-wafer process chamber. One embodiment of the invention provides self-limiting oxidation of Si-substrates that results in Si02 layers with a thickness of about 15Å, where the thickness of the Si02 layers varies less than about 1 Åover the substrates.

Description

FORMATION OF ULTRA-THIN OXIDE AND OXYNITRIDE LAYERS BY SELF-LIMITING INTERFACIAL OXIDATION

[0001] This PCT application is based on and relies for priority on United States Non-provisional Patent Applications numbered 10/630,969 and 10/630,970, both filed on July 31 , 2003, the entire contents of both of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to semiconductor processing, and more particularly, to a method for forming uniform ultra-thin oxide and oxynitride layers.

BACKGROUND OF THE INVENTION

[0003] Thin oxide (e.g., SiO₂) and oxynitride (e.g., SiO_xN_y) layers are often us€sd as dielectric layers at the Si surface of an integrated circuit. This is in part because of excellent electrical properties of the oxide and oxynitride layers, including high electron mobility and low electron trap densities. Semiconductor transistor technology currently requires oxide and oxynitride gate dielectric layers for conventional gate dielectric applications that are less than about 10-15 angstrom (A) thick, or as thin as 5-7 A for use as interface layers with high-dielectric constant materials (also referred to herein as high-k materials).

[0004] A native oxide layer that is typically a few angstrom thick, forms easily on clean Si surfaces, even at room temperature and atmospheric pressure. An oxide layer with a desired thickness that is larger than the native oxide thickness, can be grown through the native oxide layer, but usually the thickness uniformity and quality of the oxide layer is poor across the entire Si substrate.

[0005] Alternatively, the native oxide (or the chemical oxide) can be removed from Si surface prior to growing a new oxide layer. The native oxide layer can, for example, be removed using liquid baths containing dilute hydrofluoric acid (HF) or by using HF gas phase etching. A new oxide layer can then be re-grown on the clean Si surface by conventional thermal oxidation, but the initial oxidation can proceed quickly and result in poor thickness uniformity and inadequate electrical properties. For ultra-thin (<2θA) oxide layers used in transistor technologies, the leakage current is dominated by the tunneling current.

[0006] Si-oxynitride layers are viewed as one of the most promising alternate materials to replace the SiO₂ gate oxide, while still being compatible with the Si technology. Thin oxynitride layers are usually formed either by thermal processing methods or by plasma-based methods. Nitridation of ultra-thin oxide layers, that results in the formation of oxynitride layers, has been shown to alleviate various limitations encountered with oxide layers. The improvements include increased resistance to boron penetration, lower tunneling leakage current and interface-state generation, and less threshold voltage shift under constant current conditions. The improved dielectric properties that are observed for oxynitride layers are attributed to the fact that the nitrogen atoms at the surface of the SiO₂/Si act as a barrier to boron penetration and can reduce strain at the Siθ₂/Si interface.

SUMMARY OF THE INVENTION

[0007] A method is provided for forming ultra-thin oxide layers for gate dielectric applications, and other applications, such as dielectric interface layers underneath high-k materials. The method utilizes low processing pressure (and/or low partial pressure of an oxygen-containing gas) to achieve self-limiting oxidation of substrates that results in ultra-thin oxide layers. [0008] In one embodiment of the invention, the substrates to be processed can be clean and lack an initial dielectric layer. Self-limiting oxidation of the substrates results in formation of ultra-thin oxide layers on the substrate. [0009] In another embodiment of the invention, the substrates to be processed can contain an initial dielectric layer comprising at least one of an oxide layer, an oxynitride layer, a nitride layer, and a high-k layer. The initial dielectric layer is used to control the growth of ultra-thin oxide layers that are formed between the initial dielectric layer and the substrate in a self-limiting oxidation of the substrates.

[0010] A method is provided for forming ultra-thin oxynitride layers for gate dielectric applications, and other applications, such as dielectric interface layers underneath high-k materials. The method utilizes low partial pressure of a nitrogen-containing oxidizing gas and optionally an oxygen-containing gas, to achieve self-limiting oxidation of substrates that results in ultra-thin oxynitride layers.

[0011] In one embodiment of the invention, a substrate to be processed can be clean and lack an initial dielectric layer. Self-limiting oxidation of the substrate results in formation of an ultra-thin oxynitride layer on the substrate. [0012] In an alternate embodiment of the invention, the substrate to be processed can contain an initial dielectric layer comprising at least one of an oxide layer, an oxynitride layer, and a nitride layer. The initial dielectric layer is used to control the growth of an ultra-thin oxynitride layer in a self-limiting oxidation of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the accompanying drawings:

[0014] FIG. 1 A schematically shows a cross-sectional view of a gate electrode microstructure;

[0015] FIG. 1 B schematically shows a cross-sectional view of an alternate gate electrode microstructure;

[0016] FIG. 2A schematically shows a cross-sectional view of a clean substrate;

[0017] FIG. 2B schematically shows a cross-sectional view of an oxide layer grown by a self-limiting process according to an embodiment of the present invention;

[0018] FIG. 3 shows a flowchart for forming an oxide layer according to an embodiment of the invention;

[0019] FIG. 4A schematically shows a cross-sectional view of a dielectric layer overlying a substrate; [0020] FIG. 4B schematically shows a cross-sectional view of an oxide layer grown by a self-limiting process according to another embodiment of the invention;

[0021] FIG. 5A schematically shows a cross-sectional view of an oxide layer overlying a substrate;

[0022] FIG. 5B schematically shows a cross-sectional view of an oxide layer grown by a self-limiting process according to another embodiment of the invention;

[0023] FIG. 6 shows a flowchart for forming an oxide layer according to an another embodiment of the invention;

[0024] FIG. 7 schematically shows a cross-sectional view of an oxynitride layer grown by a self-limiting process according to an embodiment of the present invention;

[0025] FIG. 8 shows a flowchart for forming an oxynitride layer according to an embodiment of the invention;

[0026] FIG. 9A schematically shows a cross-sectional view of an oxide layer overlying a substrate;

[0027] FIG. 9B schematically shows a cross-sectional view of an oxynitride layer grown by a self-limiting process according to an alternate embodiment of the invention;

[0028] FIG. 10A schematically shows a cross-sectional view of a dielectric layer overlying a substrate;

[0029] FIG. 10B schematically shows a cross-sectional view of an oxynitride layer grown by a self-limiting process according to an alternate embodiment of the invention;

[0030] FIG. 11 shows a flowchart for forming an oxynitride layer according to an alternate embodiment of the invention;

[0031] FIG. 12A shows oxide thickness versus oxidation time for oxide layers grown by a self-limiting process according to another embodiment of the present invention;

[0032] FIG. 12B shows oxide uniformity versus oxidation time for oxide layers grown by a self-limiting process according to another embodiment of the present invention; and [0033] FIG. 13 shows a simplified block diagram of a processing system for forming oxide and oxynitride layers.

DETAILED DESCRIPTION OF THE INVENTION [0034] A method is provided for forming ultra-thin oxide and oxynitride dielectric layers. These dielectric layers find use in semiconductor microstructures, for example, as gate dielectrics and as dielectric interface layers located between high-k materials and the underlying substrates. The method is capable of achieving ultra-thin layers, which can be of the order of a few angstroms.

[0035] FIG. 1 A schematically shows a cross-sectional view of a gate electrode microstructure. The gate electrode microstructure 10, which can be a part of an integrated circuit, comprises a substrate 100, a dielectric layer 102, and an electrode layer 106. The substrate 100 can, for example, be a Si substrate that is single-crystal Si or polycrystalline-Si (poly-Si). A Si substrate can include numerous active devices and/or isolation regions (not shown). The Si substrate 100 can be of n- or p-type, depending on the type of device being formed, and can, for example, consist of any diameter substrate, such as a substrate with a diameter greater than about 195 mm, e.g., a 200 mm substrate, a 300 mm substrate, or an even larger substrate. [0036] The dielectric layer 102 overlying the substrate 100 can, for example, be an ultra-thin (less than about 2θA) oxide layer. It should be noted that the term "oxide" includes oxidized materials containing oxygen that are typically used in semiconductor applications. Such materials include, for example, Si, that forms a Si0₂ dielectric layer upon oxidation. An oxide layer can be formed by thermal oxidation of the substrate in the presence of a process gas that includes an oxygen-containing gas, e.g., 0₂, 0₃, H₂0, and H₂0₂. As would be appreciated by those skilled in the art, thermal oxidation may take place in other gaseous environments and, therefore, is not limited to the gases listed. Moreover, it is contemplated that the gases listed may not be used in a pure form but may be mixed with other gases without departing from the scope of the present invention.

[0037] Alternatively, the dielectric layer 102 can further contain at least one of an oxynitride layer, a nitride layer, and a high-k layer. Dielectric materials featuring a dielectric constant greater than that of Si0₂ (k~3.9) are commonly referred to as high-k materials. In addition, high-k materials may refer to dielectric materials that are deposited onto substrates rather than grown on the surface of the substrate (e.g., Siθ2, SiO_xN_y). The high-k layer can, for example, be selected from one of Hf0₂₎ ZrO₂,Ta₂O5, Ti0₂, Al₂0₃, and HfSiO. In addition to the traditional doped poly-Si, the electrode layer 106 can, for example, comprise at least one of W, Al, TaN, TaSiN, HfN, HfSiN, TiN, TiSiN, Re, Ru, and SiGe. As would be appreciated by those skilled in the art, other materials may be employed, in various combinations, without departing from the scope and spirit of the invention.

[0038] The term "oxynitride" includes oxidized materials containing oxygen and nitrogen. Such materials include, for example, Si-oxynitride, that forms SiO_xNy in an oxidation process that includes nitrogen-incorporation. An oxynitride layer is commonly formed using a process gas comprising a nitrogen-containing oxidizing gas containing at least one of NO, N₂O, and NH₃. For example, high quality SiO_xN_y layers can be formed using rapid thermal nitrous oxide (RTNO) treatment of Si surfaces. Alternatively, oxynitride layers can be formed using plasma nitridation methods, including remote plasma nitridation (RPN) of oxide layers.

[0039] Nitrogen content (concentration) and nitrogen distribution within an oxynitride layer can influence the device performance. Oxynitride layers can have an isotropic distribution of nitrogen and oxygen atoms, or alternatively, the atom distribution can be anisotropic. Nitrogen incorporation into oxide layers is used to increase the dielectric constant of the oxide layers, to control Si surface oxidation, and to act as a barrier layer to prevent diffusion of atoms through the different layers. Increasing the dielectric constant can reduce the leakage current that is observed when compared to an oxide layer having the same capacitance.

[0040] In current semiconductor devices, one function of oxide gate dielectric layers is to "gate" the electrons, by controlling the flow of electricity across the transistor. With the introduction of high-k materials, these layers will likely still be required at the channel and/or gate electrode to preserve interface-state characteristics. This includes forming an interface with good electrical properties, preventing uncontrolled Si surface oxidation, reducing reactions between different layers, and acting as a barrier layer to prevent diffusion of atoms to the different layers (e.g., dopant penetration from the gate electrode 106 into the substrate 100). In practice, good device performance depends on controlling the thickness of the dielectric layer 102, such that it remains thin, thereby avoiding increasing the equivalent oxide thickness (EOT) of the gate electrode structure.

[0041] FIG. 1 B schematically shows a cross-sectional view of an alternate gate electrode microstructure. The gate electrode microstructure 20 in FIG. 1B differs from the gate electrode microstructure in FIG. 1A by the inclusion of a relatively thick high-k layer 104 between the electrode layer 106 and the dielectric layer 102. The high-k layer 104 in the gate electrode structure 20 can be physically thicker than the dielectric layer 102, while attaining the necessary capacitance

[0042] FIG. 2A schematically shows a cross-sectional view of a clean substrate 100. A clean substrate 100 is a substrate that does not have an oxide layer. To create the clean substrate 100, a "dirty" substrate can be cleaned, for example, by placing it in a liquid bath containing dilute hydrofluoric acid (HF) or, alternatively, exposing it to HF gas phase etching. The dilute HF liquid solution can be a H₂0:HF (e.g., 50:1) mixture. Following the HF cleaning process, the substrate can be rinsed in de-ionized (D.I.) water prior to the oxidation process. As would be appreciated by those skilled in the art, cleaning of the substrate is not limited solely to the use of a HF bath or HF gas phase etching. Substrates may be processed in many different ways to create the clean substrate 100.

[0043] Once the clean substrate 100 is created, a new ultra-thin oxide layer can be grown on the clean surface by a self-limiting process, where the oxide growth rate (and the resulting final oxide layer thickness) can be carefully controlled by selecting the appropriate process conditions, such as the partial pressure of the oxygen-containing gas in the process gas and in the process chamber, and the substrate temperature.

[0044] FIG. 2B schematically shows a cross-sectional view of an oxide layer grown by a self-limiting process according to an embodiment of the present invention. The oxide layer 102B has a thickness D₂B that is uniform over the whole substrate 100. [0045] Suitable process conditions that enable self-limiting growth of an oxide and an oxynitride layer with a desired thickness and thickness uniformity can be determined by direct experimentation and/or design of experiments (DOE). For example, adjustable process parameters can comprise time, temperature (e.g., substrate temperature), process pressure, and composition of the process gas. Throughout the discussion of the invention, reference will be made to the generation of an oxide layer and an oxynitride layer. Both are encompassed by the invention. Reference to one shall include reference to the other, unless otherwise indicated or otherwise contrary to common sense or the knowledge of those of ordinary skill in the art.

[0046] FIG. 3 shows a flowchart for forming an oxide layer according to an embodiment of the invention. At 200, the process is started. At 202, a substrate is positioned in a process chamber, and the chamber is evacuated, if necessary. Following process chamber evacuation, organic contamination was effectively removed from the substrates at a process chamber temperature of about 300° C in an ambient containing about 1 % oxygen. In addition, several pump/purge cycles were performed using an inert gas. At 204, a process gas including an oxygen-containing gas is flowed into the process chamber. The partial pressure of the oxygen-containing gas can be less than about 50 Torr. Alternatively, the partial pressure of the oxygen containing gas can be less than about 40 Torr. The substrate temperature can be between about 500° C and about 1000° C, for example, about 700° C. The process chamber pressure can be lower than atmospheric pressure. In fact, the process chamber pressure can be lower than about 50 Torr. The thickness uniformity of the oxide layer can vary less than about 1 A over the substrate. At 206, an oxide layer with uniform thickness is formed on the substrate in a self-limiting oxidation process. The thickness of the oxide layer can be less than about 15A. In fact, it can be less than about 10 A. The substrate is processed for a time period that enables formation of the desired oxide layer, and the process ends at 208. Each of the process stages 200, 202, 204, 206, 208 are not intended to encompass only one processing step. To the contrary, as indicated above, each stage may encompass one or more processing steps or operations.

[0047] FIG. 4A schematically shows a cross-sectional view of a dielectric layer 102C overlying a substrate 100. The initial dielectric layer 102C can, for example, comprise at least one of an oxide layer (e.g., Si0₂), a nitride layer (e.g., SiN), an oxynitride layer (e.g., SiO_xN_y), or a high-k layer, that can be deposited onto the Si substrate 100. Typically, the dielectric layer 102C is a few angstroms thick.

[0048] FIG. 4B schematically shows a cross-sectional view of an oxide layer 102D grown by a self-limiting process process according to an alternate embodiment of the invention. The initial dielectric layer 102C in FIG. 4A is used to control the growth of the oxide layer 102D at the Si interface, where the thickness of the oxide layer 102D is controlled by a self-limiting oxidation of the Si substrate 100 through the dielectric layer 102C. As would be appreciated by those skilled in the art, the initial dielectric layer 102C itself can be formed by a self-limiting oxidation process.

[0049] FIG. 5A schematically shows a cross-sectional view of an oxide layer 102E overlying a substrate 100. The initial oxide layer 102E has a thickness D₂E and can, for example, consist of an ultra-thin native oxide layer that is typically a few angstroms thick, and forms easily on surfaces of various clean substrates (e.g., Si), even at room temperature and atmospheric pressure. Alternatively, the ultra-thin oxide layer 102E can be a chemically deposited oxide layer. The initial oxide layer 102E can provide a starting oxide layer for growing a thicker oxide layer.

[0050] FIG. 5B schematically shows a cross-sectional view of an oxide layer 102F grown by a self-limiting process in accordance with an alternate embodiment of the invention. The thickness D₂E of the oxide layer 102E in FIG. 5A is less than the thickness D₂F of the oxide layer 102F. Importantly, due to the self-limiting growth mechanism of the oxide layer 102F, it is not necessary for the initial oxide layer 102E to have good thickness uniformity, in order to grow an oxide layer 102F with good thickness uniformity. [0051] FIG. 6 shows a flowchart for forming an oxide layer according to an alternate embodiment of the invention. At step 210, the process is started. At step 212, a substrate containing an initial dielectric layer is positioned in a process chamber and the chamber is evacuated. At step 214, a process gas comprising an oxygen-containing gas is flowed into the process chamber. At step 216, an oxide layer with uniform thickness is formed between the initial dielectric layer and the substrate in a self-limiting oxidation of the substrate. The substrate is processed for a time period that enables formation of the desired oxide layer, and the process ends at step 218. The process parameters can be as described above. Similar results were observed. [0052] FIGs. 7-11 will now be relied upon for purposes of discussing, among other things, the creation of a thin oxynitride layer on a silicon substrate 100. One starting point for creating a thin oxynitride layer on a substrate 100 is to begin with a clean substrate 100, like the clean substrate 100 illustrated in FIG. 2A. The creation of a clean substrate 100 is discussed above and, therefore, will not be repeated here.

[0053] FIG. 7 schematically shows a cross-sectional view of an oxynitride layer grown by a self-limiting process according to an embodiment of the present invention. The oxynitride layer 102G has a well-controlled thickness D₂G that is uniform over the whole surface of the substrate 100. The ultra-thin oxynitride layer can be grown on the clean substrate 100 by a self-limiting process, where the oxynitride growth rate (and the resulting final oxynitride layer thickness) is carefully controlled by selecting the process conditions, particularly the partial pressures of a nitrogen-containing oxidizing gas in the process gas and in the process chamber, and the substrate temperature. [0054] In the self-limiting process, the process gas can comprise a nitrogen- containing oxidizing gas containing at least one of NO, N₂0, and NH₃. In addition, the process gas can also contain an oxygen-containing gas (e.g., at least one of O₂, O₃, H₂O, and H2O2.). Following the formation of an oxynitride layer, the oxynitride layer can be post-annealed using a process gas comprising N₂O or 0₂, for example. Alternatively, the oxynitride layer can be post-treated in a plasma nitridation process using a process gas comprising at least one of N₂, NO, N O, and NH₃. As would be appreciated by those skilled in the art, other nitrogen-containing gases may be employed without departing from the scope of the invention. Moreover, other processes may be employed to form the oxynitride layer, anneal the layer, or otherwise treat the layer in a desirable manner, without departing from the scope of the invention. [0055] Suitable process conditions that enable self-limiting growth of an oxynitride layer with a desired thickness and thickness uniformity, can be determined by direct experimentation and/or design of experiments (DOE). For example, adjustable process parameters can comprise time, temperature (e.g., substrate temperature), process pressure, and composition of the process gas, among other parameters.

[0056] FIG. 8 shows a flowchart for forming an oxynitride layer according to an embodiment of the invention. At 800, the process is started. At 802, a substrate is positioned in a process chamber and the chamber is evacuated. At 804, a process gas comprising a nitrogen-containing oxidizing gas (e.g., NO N₂0, or NH₃), and optionally an oxygen-containing gas (e.g., 0₂, O , H₂0, and H₂O₂), is introduced into the process chamber. At 806, an oxynitride layer is formed on the substrate in a self-limiting oxidation process. The substrate is processed for a time period that enables formation of the desired oxynitride layer, and the process ends at 808. As would be appreciated by those skilled in the art, each of the steps or stages in the flowchart of FIG. 8 may encompass one or more separate steps and/or operations. Accordingly, the recitation of only five steps in 800, 802, 804, 806, 808 should not be understood to be limited solely to five steps or stages. Moreover, each representative step or stage 800, 802, 804, 806, 808 should not be understood to be limited to only a single process.

[0057] FIG. 9A schematically shows a cross-sectional view of an oxide layer 102H overlying a substrate 100. The initial oxide layer 102H has a thickness D_2H and can, for example, be an ultra-thin native oxide layer that is typically a few angstroms thick, and forms easily on surfaces of various clean substrates (e.g., Si), even at room temperature and atmospheric pressure. Alternatively, the initial oxide layer 102H can be a chemically deposited oxide layer formed by a self-limiting oxidation process. The initial oxide layer 102H can provide a starting growth layer for growing a thicker oxynitride layer with good thickness control and thickness uniformity.

[0058] FIG. 9B schematically shows a cross-sectional view of an oxynitride layer grown by a self-limiting process according to an alternate embodiment of the invention. The thickness D2_H of the oxide layer 102H in FIG. 9A is less than the thickness D₂₁ of the oxynitride layer 102I. Importantly, due to the self- limiting growth mechanism of the oxynitride layer 1021, it is not necessary for the initial oxide layer 102H to have good thickness uniformity, in order to grow an oxynitride layer 1021 with good thickness uniformity. [0059] FIG. 10A schematically shows a cross-sectional view of a dielectric layer 102J overlying a substrate 100. The initial dielectric layer 102J can, for example, be an oxynitride layer or a nitride layer that is a few angstroms thick (U₂j). FIG. 10B schematically shows a cross-sectional view of an oxynitride layer 102K grown by a self-limiting process according to another embodiment of the invention. The initial oxynitride or nitride layer 102J in FIG. 10A is used to control the growth of an oxynitride layer 102K at the Si interface, where the thickness D₂κ of the oxynitride layer 102K is controlled by a self-limiting reaction of the substrate100 through the dielectric layer 102J. The resulting oxynitride layer 102K contains oxidized material from the reaction of the oxidizing species with the substrate 100 and with the dielectric layer 102J. The initial dielectric layer 102J, itself, can be formed in a self-limiting oxidation process.

[0060] FIG. 11 shows a flowchart for forming an oxynitride layer according to an alternate embodiment of the invention. At 1110, the process is started. At 1112, a substrate containing an initial dielectric layer is positioned in a process chamber and the chamber is evacuated. The initial dielectric layer can comprise at least one of an oxide layer, an oxynitride layer, or a nitride layer. A nitride layer can, for example, comprise a SiN_x layer, formed using deposition of a SiN_x material or nitridation of a Si layer. At 1114, a process gas comprising a nitrogen-containing oxidizing gas and optionally an oxygen- containing gas, is introduced into the process chamber. At 1116, an oxynitride layer is formed in self-limiting oxidation of the substrate. The substrate is processed for a time period that enables formation of the desired oxynitride layer, and the process ends at 1118. [0061] FIG. 12A shows oxide thickness versus oxidation time for oxide layers grown by a self-limiting process according to another embodiment of the present invention. Analogous to the oxide layer 102E overlying a substrate 100 shown in FIG. 5A, the starting 200mm Si substrates (wafers) in FIG. 12A, contained chemical oxide layers that were about 10 A thick. Self- limiting oxidation of the Si substrates containing the chemical oxide layers was carried out for 3 to 80 min under low-pressure conditions. The oxidation process utilized a process gas containing an about 3:1 N₂:O₂ gas mixture, a process chamber pressure of about 8 Torr, and a substrate temperature of about 700°C. Typical gas flows were about 3 slm N₂ and about 1 slm 0₂ in a batch type process chamber for a batch size of 100 wafers. [0062] The oxidation curves in FIG. 12A show the average oxide thickness measured at 9 points (lower curve) and 49 points (upper curve) on the substrates using ellipsometry and a refraction index of 1.46. It is evident from FIG. 12A that the oxide growth saturates at an oxide thickness of about 15 A for these processing conditions. At each measured oxidation time (3, 10, 45, 80 min.), the oxide layer thickness varied by less than about 1 A for all 49 measurement points.

[0063] FIG. 12B shows oxide uniformity versus oxidation time for oxide layers grown by a self-limiting process according to another embodiment of the present invention. The oxide thickness uniformity for the 9 point and 49 point measurements is shown as %3-sigma values, and the overall trend shows improved oxide thickness uniformity over the whole Si substrate as the oxide layers grow thicker. Electrical measurements obtained for ultra-thin oxide layers (~15A) shown in FIGs. 12A and 12B, showed good electrical properties when used as interface layers underneath high-k layers in gate electrode microstructures (see FIG.1 B).

[0064] The basic mechanism in a dry oxidation process is the diffusion of an oxidizing species through an existing oxide layer and the reaction of the oxidizing species with the substrate at the oxide/substrate interface. In a self- limiting oxidation process, the rate of oxidation decreases as the thickness of the oxide layer increases. This is likely due to hindered diffusion of the oxidizing species through the existing oxide layer to the oxide/substrate interface. In order to achieve properties of self-limiting oxidation, the oxidation ambient forms an oxidation barrier on the substrate. [0065] In mathematical terms, Fick's Law (J=-DχdC/dx) describes the dependence of mass flux (J) through a layer, on the ratio of change in concentration (dC) to the change in layer thickness (dx), with a material constant diffusivity (D). The partial pressure of the oxidizing ambient is used to control the concentration gradient component, which in turn determines the final thickness of the layer given a fixed mass flux, which is at the limit of the oxidation potential (self-limited oxidation). In order to achieve properties of self-limiting oxidation, it is important that the oxidation ambient forms an oxidation barrier on the substrate. In FIG. 12A, only about 0.5 A of additional oxide growth is observed during the last 30 min. of the 80 min. self-limited process, and the self-limiting process leads to a more uniform oxide layer thickness.

[0066] In the self-limiting oxidation process, shown in FIGs. 12A and 12B, it is observed that in substrate regions that contain a relatively thin oxide layer, an oxide layer grows faster than in regions where the oxide layer is thinner. This leads to formation of oxide layers where the thickness of the oxide layer is more uniform over the whole substrate, whether the initial oxide layer is uniform or not. It is believed that the slow oxide growth rate that is observed in FIGs. 12A and 12B permits long oxidation/anneal times, and improves the electrical quality of the resulting oxide layer, by removing bulk and interface traps, when a saturated, fully oxidized, stable oxide layer is formed. [0067] In a self-limiting oxidation process, the oxide growth rate (and the resulting final oxide layer thickness) can be reduced/increased by decreasing/increasing the oxygen partial pressure in the process gas and in the process chamber. In addition, the oxide growth rate can be reduced/increased by lowering/increasing the substrate temperature. [0068] In a self-limiting oxidation process for forming oxynitride layers, the oxynitride growth rate (and the resulting final oxynitride layer thickness) can be reduced/increased by decreasing/increasing the partial pressure of the nitrogen-containing oxidizing gas in the process chamber. A low partial pressure of the nitrogen-containing oxidizing gas allows controlled growth of thin oxynitride layers. The partial pressure of the nitrogen-containing oxidizing gas can, for example, be less than about 10 Torr. In an alternate embodiment, the partial pressure of the nitrogen-containing oxidizing gas can be less than about 5 Torr. In addition, the growth rate of the oxynitride layer can be reduced/increased by lowering/increasing the substrate temperature. The pressure of the processing chamber can be less than atmospheric pressure. Alternatively, the process chamber pressure can be less than about 50 Torr.

[0069] The oxidation data shown in FIGs. 12A and 12B, illustrates that it is possible to reproducibly grow oxide layers that are about 15 A thick, with excellent uniformity, from substrates containing oxide layers that are a few angstroms thick. The ability to start with substrates that contain an initial oxide layer (e.g., a chemical or native oxide), can remove the need to strip the initial oxide layer, prior to growing a new oxide layer or an oxynitride layer on a clean substrate, as long as the initial oxide thickness is less than the desired final oxide or oxynitride thickness.

[0070] Semiconductor transistor technology currently requires oxide and oxynitride layers that are less than about 10-15 A thick for conventional gate dielectric applications (FIG. 1 A), or as thin as about 5-7 A for use as dielectric interface layers with high-k materials (FIG. 1 B). Formation of ultra-thin oxide layers that are thinner (<1θA) than an initial oxide layer, can require removal of at least a portion of the initial oxide layer prior to growing the thinner oxide layers.

[0071] In the aforementioned process example described in FIGs. 12A and 12B, the process gas comprised O₂ gas and N inert gas. Alternatively, the inert gas can comprise at least one of Ar, He, Ne, Kr, Xe. The addition of an inert gas to the process chemistry is, for example, to dilute the process gas or adjust the process gas partial pressure(s). The parameter space for the oxidation process can, for example, utilize a chamber pressure less than about 50 Torr, a process gas flow rate less than about 2000 seem, an inert gas flow rate less than about 1000 seem, and a substrate temperature from about 500° C to about 1000° C. The substrate temperature can be held constant during the oxidation process or, alternatively, the substrate temperature can be ramped during the process.

[0072] In a self-limiting oxidation process for forming oxynitride layers, the oxynitride growth rate (and the resulting final oxynitride layer thickness) can be reduced/increased by decreasing/increasing the partial pressure of the nitrogen-containing oxidizing gas in the process chamber. A low partial pressure of the nitrogen-containing oxidizing gas allows controlled growth of thin oxynitride layers. The partial pressure of the nitrogen-containing oxidizing gas can, for example, be less than about 10 Torr. In an alternate embodiment, the partial pressure of the nitrogen-containing oxidizing gas can be less than about 5 Torr. In addition, the growth rate of the oxynitride layer can be reduced/increased by lowering/increasing the substrate temperature. The pressure of the processing chamber can be less than atmospheric pressure. Alternatively, the process chamber pressure can be less than about 50 Torr.

[0073] In the aforementioned process example described in FIGs. 12A and 12B, the process gas comprised O₂ gas and N₂ inert gas. In a self-limiting process to grow oxynitride layers the nitrogen-containing oxidizing gas in process gas can, for example, comprise at least one of NO, N₂O, and NH₃. In addition, the process gas can further contain an oxygen-containing gas (e.g., at least one of O₂, O₃, H₂O, and H₂O₂). Furthermore, the process gas can contain an inert gas. The inert gas can comprise at least one of Ar, He, Ne, Kr, Xe, and N₂. The addition of an inert gas to the process chemistry is, for example, to dilute the process gas or adjust the process gas partial pressure(s).

[0074] The parameter space for the oxidation process for forming oxynitride layers can, for example, utilize a process gas flow rate less than about 2000 seem, an inert gas flow rate less than about 1000 seem, and a substrate temperature from about 500° C to about 1000° C. For example, the substrate temperature can be about 700° C. A partial pressure of a nitrogen-containing oxidizing gas can, for example, be less than about 10 Torr. In an alternate embodiment, the partial pressure of a nitrogen-containing oxidizing gas can be less than about 5 Torr. The substrate temperature can be held constant during the oxidation process or, alternatively, the substrate temperature can be ramped during the process. The chamber pressure can be below atmospheric pressure. Alternatively, the chamber pressure can be less than 50 Torr.

[0075] A processing system for forming ultra-thin oxide and oxynitride layers can comprise a batch type process chamber capable of processing multiple substrates (wafers) simultaneously. Alternatively, the processing system can comprise a single wafer process chamber. The process chamber can process any diameter substrates, such as substrates with a diameter greater than about 195 mm, such as 200 mm substrates, 300 mm substrates, or even larger substrates. A batch type process chamber can provide an advantage over single wafer process chambers by allowing long processing times for self-limiting processes

[0076] FIG. 13 shows a simplified block diagram for a processing system for forming oxide and oxynitride layers. The batch type processing system 300 comprises a process chamber 302, a gas injection system 304, a pumping system 306, a process monitoring system 308, and a controller 310. The gas injection system 304 is used to introduce a process gas for purging, cleaning, and processing one or more substrates 314. Multiple substrates 314 can be loaded into the process chamber 302 and processed using substrate holder 312. A self-limiting oxidation process that is carried out in a batch type processing system, can allow for a large number of tightly stacked substrates to be processed using substrate holder 312, thereby resulting in high wafer throughput.

[0077] When carrying out a self-limiting process, it can be advantageous to load the wafers to be processed into the process chamber 302 at a temperature below which wafer oxidation occurs. A typical process according to the invention comprised loading the wafers to be processed into a batch type process chamber that was at a temperature of about 300° C and comprised an ambient atmosphere containing about 1 % oxygen. These process conditions were effective in removing organic contamination from the substrates 314. In addition, several pump/purge cycles were performed using an inert gas.

[0078] Next, the process chamber temperature and process chamber pressure were adjusted to the desired values in an inert ambient to avoid substrate oxidation under non-equilibrium conditions. When the process temperature was reached, the substrates 314 were exposed to a process gas for a time period that resulted in formation of the desired oxide or oxynitride layer. At the end of the oxidation process, the process chamber 302 was evacuated and purged with an inert gas, and the substrates removed from the process chamber 302.

[0079] The process can be controlled by a controller 310 capable of generating control voltages sufficient to communicate and activate inputs of the processing system 300 as well as monitor outputs from the processing system 300. Moreover, the controller 310 can be coupled to and exchange information with the process chamber 302, the gas injection system 304, the process monitoring system 308, and a vacuum pumping system 306. For example, a program stored in the memory of the controller 310 can be utilized to control the aforementioned components of the processing system 300 according to a stored process recipe. One example of the controller 310 is a DELL PRECISION WORKSTATION 610™ , available from Dell Corporation, Dallas, Texas.

[0080] Real-time process monitoring can be carried out using the process monitoring system 308 during processing. For example, mass spectroscopy (MS) can provide qualitative and quantitative analysis of the gaseous chemical species in the process environment. Process parameters that can be monitored using MS include gas flows, gas pressure, ratios of gaseous species, and gas purities. These parameters can be correlated with prior process results and various physical properties of the oxide or oxynitride layers.

[0081] It should be understood that various modifications and variations of the present invention may be employed in practicing the invention. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

CLAIMS:

1. A method of forming a semiconductor microstructure, the method comprising: positioning a substrate in a process chamber; flowing a process gas comprising an oxygen-containing gas in the process chamber; and forming an oxide layer on the substrate, the layer being formed in a self-limiting oxidation process, wherein a partial pressure of the oxygen- containing gas in the process chamber is less than about 50 Torr.

2. The method according to claim 1 , wherein the thickness of the oxide layer is less than about 15A.

3. The method according to claim 1 , wherein the thickness of the oxide layer is less than about 10A.

4. The method according to claim 1 , wherein the thickness uniformity of the oxide layer varies less than about 1 A over the substrate.

5. The method according to claim 1 , wherein the substrate diameter is greater than about 195 mm.

6. The method according to claim 1 , wherein the partial pressure of the oxygen-containing gas is less than about 40 Torr.

7. The method according to claim 1 , wherein the oxygen-containing gas comprises 0₂.

8. The method according to claim 7, wherein the process gas further comprises N2.

9. The method according to claim 8, wherein a N₂:0₂ flow ratio is about 3:1.

10. The method according to claim 1 , wherein the process gas further comprises an inert gas.

11. The method according to claim 10, wherein the inert gas comprises at least one of Ar, He, Ne, Kr, Xe, and N₂.

12. The method according to claim 1 , further comprising: exposing the substrate to a temperature between about 500°C and - 1000°C.

13. The method according to claim 12, wherein the temperature is about 700°C.

14.The method according to claim 1 , wherein the substrate comprises Si and the oxide layer comprises SiO₂.

15. The method according to claim 1 , wherein-a pressure within the process chamber is less than atmospheric pressure.

16. The method according to claim 15, wherein the pressure is less than about 50 Torr.

17. A method of forming a semiconductor microstructure, the method comprising: positioning a substrate containing an initial dielectric layer in a process chamber; flowing a process gas comprising an oxygen-containing gas in the process chamber; and forming an oxide layer with high thickness uniformity, the oxide layer being formed between the initial dielectric layer and the substrate in a self- limiting oxidation process, wherein a partial pressure of the oxygen-containing gas in the process chamber is less than about 50 Torr.

18. The method according to claim 17, wherein the initial dielectric layer comprises at least one of an initial oxide layer, an initial oxynitride layer, an initial nitride layer, and an initial high-k layer.

19. The method according to claim 18, wherein the initial oxide layer comprises Si0₂.

20. The method according to claim 18, wherein the initial oxynitride layer comprises SiO_xN_y.

21. The method according to claim 18, wherein the initial nitride layer comprises silicon nitride.

22. The method according to claim 18, wherein the initial high-k layer comprises at least one of HfO₂, ZrO₂ , Ta₂O₅, TiO₂, Al₂0₃, and HfSiO.

23. The method according to claim 17, wherein pressure within the process chamber is less than about 40 Torr.

24. The method according to claim 17, wherein the oxygen-containing gas comprises O₂.

25. The method according to claim 24, wherein the process gas further comprises N₂.

26. The method according to claim 17, wherein the process gas further comprises an inert gas.

27. The method according to claim 26, wherein the inert gas comprises at least one of Ar, He, Ne, Kr, Xe, and N₂.

28. The method according to claim 17, further comprising: exposing the substrate to a temperature between about 500° C and 1000° C.

29. The method according to claim 28, wherein the temperature is about 700°C.

30. The method according to claim 17, wherein a pressure within the process chamber is less than atmospheric pressure.

31. The method according to claim 17, wherein a pressure within the process chamber is less than about 50 Torr.

32. A microstructure, comprising: a substrate; and an oxide layer, the oxide layer being formed in a self-limiting oxidation process in a process chamber, wherein a partial pressure of an oxygen- containing gas in process chamber is less than about 50 Torr.

33. The microstructure according to claim 32, wherein a thickness of the oxide layer is less than about 15 A.

34. The microstructure according to claim 32, wherein a thickness of the oxide layer is less than about 10 A.

35. The microstructure according to claim 32, wherein the microstructure further comprises: a high-k layer on the oxide layer, and an electrode layer on the high-k layer.

36. The microstructure according to claim 35, wherein the high-k layer comprises at least one of Hfθ2, Zr0₂ , Ta₂O₅, TiO₂, AI O₃, and HfSiO.

37. The microstructure according to claim 35, wherein the electrode layer comprises at least one of W, Al, TaN, TaSiN, HfN, HfSiN, TiN, TiSiN, Re, Ru, and SiGe.

38. A microstructure comprising: a substrate; an initial dielectric layer; and an oxide layer, the oxide layer being formed between the initial dielectric layer and the substrate in a self-limiting oxidation process, wherein a partial pressure of an oxygen-containing gas is less than about 50 Torr.

39. The microstructure according to claim 38, wherein a thickness of the oxide layer is less than about 15 A.

40. The microstructure according to claim 38, wherein a thickness of the initial dielectric layer is less than about 10 A.

41. The microstructure according to claim 38, wherein the initial dielectric layer comprises at least one of an initial oxide layer, an initial oxynitride layer, an initial nitride layer, and an initial high-k layer.

42. The microstructure according to claim 38, wherein the initial nitride layer comprises silicon nitride.

43. The microstructure according to claim 38, wherein the initial dielectric layer is formed in a self-limiting oxidation process.

44. The microstructure according to claim 38, the microstructure further comprising: a high-k layer on the initial dielectric layer; and an electrode layer on the high-k layer.

45. The microstructure according to claim 44, wherein the high-k layer comprises at least one of HfO₂, ZrO₂ , Ta₂0₅, TiO₂, AI₂O₃, and HfSiO.

46. The microstructure according to claim 45, wherein the electrode layer comprises at least one of W, Al, TaN, TaSiN, HfN, HfSiN, TiN, TiSiN, Re, Ru, and SiGe.

47. A processing system comprising: a process chamber; a gas injection system configured to introduce a process gas in the process chamber, wherein the process gas comprises an oxygen-containing gas; a substrate holder, the substrate holder exposing a substrate to the process gas in the process chamber, wherein an oxide layer is formed on the substrate in a self-limiting process, wherein the partial pressure of an oxygen- containing gas in the process chamber is less than about 50 Torr; and a controller that controls the processing system.

48. The processing system according to claim 47, wherein the process chamber comprises a batch type process chamber.

49. The processing system according to claim 47, wherein the process chamber comprises a single wafer process chamber.

50. The processing system according to claim 47, further comprising a process monitoring system and a pumping system.

51.The processing system according to claim 47, wherein the substrate comprises Si and the oxide layer comprises Si0₂.

52. The processing system according to claim 47, wherein the substrate further comprises an initial dielectric layer.

53. The processing system according to claim 52, wherein the oxide layer is formed between the initial dielectric layer and the substrate.

54. The processing chamber according to claim 47, wherein the substrate holder is adapted to hold substrates having a diameter greater than about 195 mm.

55. A method of forming a semiconductor microstructure, the method comprising: positioning a substrate in a process chamber; flowing a process gas comprising a nitrogen-containing oxidizing gas in the process chamber; and forming an oxynitride layer on the substrate, the oxynitride layer being formed in a self-limiting oxidation process, wherein a partial pressure of the nitrogen-containing oxidizing gas in the process chamber is less than about 10 Torr.

56. The method according to claim 55, wherein the thickness of the oxynitride layer is less than about 15 A.

57. The method according to claim 55, wherein the thickness of the oxynitride layer is less than about 10 A.

58. The method according to claim 55, wherein the thickness uniformity of the oxynitride layer varies less than about 1 A over the substrate.

59. The method according to claim 55, wherein the substrate diameter can be greater than about 195 mm.

60. The method according to claim 55, wherein the partial pressure of the nitrogen-containing oxidizing gas in the process chamber is less than about 5 Torr.

61. The method according to claim 55, wherein the nitrogen-containing oxidizing gas comprises at least one of NO, N₂0, and NH₃.

62. The method according to claim 55, wherein the process gas further comprises an oxygen-containing gas.

63. The method according to claim 62, wherein the oxygen-containing gas comprises at least one of O2, O₃, H2O, and H2O2.

64.The method according to claim 55, wherein the process gas further comprises an inert gas.

65. The method according to claim 64, wherein the inert gas comprises at least one of Ar, He, Ne, Kr, Xe, and N₂.

66. The method according to claim 54, further comprising: exposing the substrate to a temperature between about 500° C and 1000° C.

67. The method according to claim 66, wherein the temperature is about 700° C.

68. The method according to claim 55, wherein the substrate comprises Si and the oxynitride layer comprises SiO_xN_y.

69. The method according to claim 55, further comprising: exposing the oxynitride layer to a plasma nitridation process.

70. The method according to claim 69, wherein the plasma nitridation process utilizes a process gas comprising at least one of N₂, NO, N₂O, and NH₃.

71.The method according to claim 55, further comprising: post-annealing the oxynitride layer using a process gas comprising at least one of N₂O and 0₂.

72. The method according to claim 55, wherein the substrate contains an initial dielectric layer.

73. The method according to claim 72, wherein the initial dielectric layer is formed in a self-limiting oxidation process.

74. The method according to claim 72, wherein the initial dielectric layer comprises at least one of an oxide layer, an oxynitride layer, and a nitride layer.

75. The method according to claim 74, wherein the oxide layer comprises SiO₂, the oxynitride layer comprises SiO_xN_y, and the nitride layer comprises SiN_x.

76. The method according to claim 55, wherein a pressure in the processing chamber is below atmospheric pressure.

77. The method according to claim 76, wherein the pressure is less than about 50 Torr.

78. A microstructure, comprising: a substrate; and an oxynitride layer on the substrate, the oxynitride layer being formed in a self-limiting oxidation process in a process chamber, wherein a partial pressure of a nitrogen-containing oxidizing gas in the process chamber is less than about 10 Torr.

79. The microstructure according to claim 78, wherein a thickness of the oxynitride layer is less than about 15 A.

80. The microstructure according to claim 78, wherein a thickness of the oxynitride layer is less than about 10 A.

81. The microstructure according to claim 78, further comprising: a high-k layer deposited on the oxynitride layer; and an electrode layer on the high-k layer.

82. The microstructure according to claim 81 , wherein the high-k layer comprises at least one of HfO₂, Zr0₂ , Ta₂O₅, Ti0₂, Al₂0₃, and HfSiO.

83. The microstructure according to claim 81 , wherein the electrode layer comprises at least one of W, Al, TaN, TaSiN, HfN, HfSiN, TiN, TiSiN, Re, Ru, and SiGe.

84. A processing system, comprising: a process chamber; a gas injection system configured to introduce a process gas in the process chamber, wherein the process gas comprises a nitrogen-containing oxidizing gas; a substrate holder, the substrate holder exposes a substrate to the process gas in the process chamber, wherein an oxynitride layer is formed on the substrate in a self-limiting process, wherein a partial pressure of a nitrogen-containing oxidizing gas in the process chamber is less than about 10 Torr; and a controller that controls the processing system.

85. The processing system according to claim 84, wherein process chamber comprises a batch type process chamber.

86. The processing system according to claim 84, wherein process chamber comprises a single wafer process chamber.

87. The processing system according to claim 84, further comprising a process monitoring system and a pumping system.

88. The processing system according to claim 84, wherein the substrate comprises Si and the oxynitride layer comprises SiO_xN_y.

89. The processing system according to claim 84, wherein the partial pressure of the nitrogen-containing oxidizing gas in the process chamber is less than about 5 Torr.

90. The processing system according to claim 84, wherein the nitrogen- containing oxidizing gas comprises at least one of NO, N₂0, and NH₃.

91. The processing system according to claim 84, wherein the process gas further comprises an oxygen-containing gas.

92. The processing system according to claim 91 , wherein the oxygen- containing gas comprises at least one of 0₂, O₃, H₂O, and H₂O₂.

93. The processing system according to claim 84, wherein the process gas further comprises an inert gas.

94. The processing system according to claim 93, wherein the inert gas comprises at least one of Ar, He, Ne, Kr, Xe, and N₂.

95. The processing system according to claim 84, wherein the substrate is exposed to a temperature between about 500° C and 1000° C.

96. The processing system according to claim 84, wherein the substrate is exposed to a temperature about 700° C.

97. The processing system according to claim 84, wherein a pressure in the processing chamber is below atmospheric pressure.

98. The processing system according to claim 97, wherein the pressure is less than about 50 Torr.