SYSTEMS, DEVICES AND METHODS RELATED TO REACTIVE EVAPORATION OF REFRACTORY MATERIALS

Abstract

Systems, devices and methods related to reactive evaporation of refractory materials. In some embodiments, a method for performing reactive evaporation can include positioning a volume of refractory material such as tantalum within an evaporation chamber and forming a vacuum environment therein. The method can further include providing a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles. The method can further include introducing a flow of reactive gas such as nitrogen into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material. The flow of reactive gas can be selected such that a layer such as tantalum nitride formed on a substrate by deposition of the evaporated particles includes a range of a desirable property.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Application Nos. 61/897,802 filed Oct. 30, 2013, entitled SYSTEMS, DEVICES AND METHODS RELATED TO REACTIVE EVAPORATION OF REFRACTORY MATERIALS, and 61/897,814 filed Oct. 30, 2013, entitled REFRACTORY METAL BARRIER IN SEMICONDUCTOR DEVICES, the disclosure of each of which is hereby expressly incorporated by reference herein in its entirety.

BACKGROUND

1. Field

The present disclosure generally relates to reactive evaporation of refractory materials.

2. Description of the Related Art

In some semiconductor fabrication processes, formation of a layer on a substrate such as a wafer can be achieved by an evaporation process. In situations where thermal evaporation may not be suitable, techniques such as electron-beam (also referred to as e-beam) evaporation can be utilized.

Electron-beam evaporation is a deposition process where source material is heated by a beam of electrons to yield evaporated atoms or particles that are deposited on exposed surfaces. E-beam evaporation can be preferable over thermal evaporation when, for example, higher density depositions are desired. Further, under ideal operating conditions, electron-beam only heats the source material and not the holder such as a crucible or a hearth. Since the holder is not heated as in thermal evaporation, contamination from the holder is typically lowered.

SUMMARY

According to some implementations, the present disclosure relates to a method for performing reactive evaporation. The method includes positioning a volume of refractory material to be evaporated within an evaporation chamber, and forming a vacuum environment within the evaporation chamber. The method further includes providing a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles. The method further includes introducing a flow of reactive gas into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material. The flow of reactive gas is selected such that a layer formed on a substrate by deposition of the evaporated particles includes a range of a desirable property.

In some embodiments, the refractory material can include tantalum (Ta), and the reactive gas can include nitrogen gas (N2). The layer can include tantalum nitride (TaN). The tantalum nitride can have a composition expressed as TaN_x, with the quantity x having a value in a range between 0 and 0.5.

In some embodiments, the desirable property can include a mechanical property. The selected flow of reactive gas can be in a range having a lower flow limit and an upper flow limit. The lower flow limit of the range can be selected to correspond to be at or higher than a first flow rate that yields a first stress level associated with the layer. The first stress level can include a stress level associated with transition between tensile stress and compressive stress associated with the layer. The first stress level can have a value of approximately zero.

In some embodiments, the lower flow limit of the range can be selected such that the layer provides a compressive stress to the substrate. The lower limit and the upper limit of the range can be selected such that the compressive stress has a magnitude less than a selected value. The lower limit of the range can be selected such that the compressive stress varies sufficiently slowly as a function of the flow to be substantially reproducible.

In some embodiments, the desirable property can include an electrical property. The electrical property can include a sheet resistance associated with the layer. The sheet resistance can increase as a function of the flow of the reactive gas. The upper limit of the range can be selected such that the sheet resistance associated with the layer is less than a selected sheet resistance value.

In some embodiments, the method can further include forming one or more additional layers over the layer formed with the flow of reactive gas. Each of the one or more additional layers can be formed by electron-beam evaporation, such that all of the layers can be formed utilizing one photolithography and one deposition type.

In some implementations, the present disclosure relates to a reactive evaporation system that includes an evaporation chamber configured to hold a volume of refractory material to be evaporated. The system further includes a vacuum system in communication with the evaporation chamber, with the vacuum system being configured to provide a vacuum environment within the evaporation chamber. The system further includes an electron-beam system configured to provide a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles. The system further includes a gas supply system in communication with the evaporation chamber. The gas supply system is configured to provide a flow of reactive gas into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material. The flow of reactive gas is selected such that a layer formed on a substrate by deposition of the evaporated particles includes a range of a desirable property.

According to some implementations, the present disclosure relates to a method for forming a metalized stack on a semiconductor substrate. The method includes mounting the semiconductor substrate within an evaporation chamber, and positioning a volume of refractory material to be evaporated within the evaporation chamber. The method further includes forming a vacuum environment within the evaporation chamber. The method further includes depositing a refractory material barrier layer on the semiconductor substrate. The depositing includes providing a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles. The depositing further includes introducing a flow of reactive gas into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material. The flow of reactive gas is selected such that the refractory material barrier layer includes a range of a desirable property.

In some embodiments, the method can further include forming one or more additional layers over the refractory material barrier layer. The one or more additional layers can include a second layer formed over the refractory material barrier layer. The second layer can be configured as a diffusion barrier, an adhesion layer, or a layer having a desired electrical property. The second layer can include a titanium (Ti) layer.

In some embodiments, the one or more additional layers can further include a conductive metal layer formed over the second layer. The conductive metal layer can include a gold (Au) layer.

In some embodiments, the one or more additional layers can further include a passivation layer formed over the conductive metal layer. The passivation layer can include a titanium (Ti) layer. In some embodiments, each of the refractory material barrier layer, the adhesion layer, the conductive metal layer, and the passivation layer can be formed by electron-beam evaporation utilizing one photolithography and one deposition type.

In some embodiments, the metalized stack can include a gate structure of a transistor. The transistor can include a pseudomorphic high electron mobility transistor (pHEMT).

For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the inventions have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an electron-beam (e-beam) evaporator that can be utilized to implement one or more features as described herein.

FIG. 2 shows a more specific example of the evaporator of FIG. 1.

FIG. 3 shows a more specific example of the evaporator of FIG. 2.

FIG. 4 shows a process that can be implemented to form a layer of refractory material having one or more desirable properties on a substrate such as a semiconductor wafer.

FIG. 5 shows an example of how mechanical stress associated with a layer of deposited refractory material can change as a function of flow rate of a reactive gas such as nitrogen.

FIG. 6 shows an example of how sheet resistance associated with a layer of deposited refractory material can change as a function of flow rate of a reactive gas such as nitrogen.

FIG. 7 shows a more generalized example of how flow rate or concentration of reactive gas can be selected to yield desirable mechanical and/or electrical properties associated with a deposited layer.

FIG. 8 shows a more generalized example of how an operating condition can be selected to yield desirable first and/or second properties associated with a deposited layer.

FIG. 9 shows an example focused ion beam (FIB) image of a metal stack that includes a refractory material layer formed utilizing a technique having one or more features as described herein.

FIG. 10 schematically depicts a stack configuration that can be implemented utilizing one or more features of the present disclosure to generate a metal stack such as the example of FIG. 9.

FIG. 11 shows an example of the sheet resistance performance can be maintained over different fabrication runs.

FIG. 12 shows an example of standard deviation for the example sheet resistance performance being maintained of the different fabrication runs.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and do not necessarily affect the scope or meaning of the claimed invention.

In some semiconductor fabrication processes, formation of a refractory-material layer on a substrate such as a wafer can be desirable. Examples of such a refractory-material layer are described herein in greater detail.

In some implementations, such a layer can be formed by an evaporation process; and in situations where thermal evaporation may not be suitable, techniques such as electron-beam (also referred to as e-beam) evaporation can be utilized. Electron-beam evaporation is a deposition process where source material is heated by a beam of electrons to yield evaporated atoms or particles that are deposited on exposed surfaces. E-beam evaporation can be preferable over thermal evaporation when, for example, higher density depositions are desired, which can be achieved by a relatively large amount of energy delivered to the source material by electrons. Further, under ideal operating conditions, electron-beam only heats the source material and not the holder such as a crucible or a hearth. Since the holder is not heated as in thermal evaporation, contamination from the holder is typically lowered.

In some situations, refractory materials can fragment during e-beam evaporation, thereby resulting in changes in properties. Such materials can be deposited on the substrate by, for example, reactive evaporation, where reactive gas can be introduced to evaporants resulting from e-beam heating of the source material. Under selected conditions, such evaporants can react with the reactive gas to form a layer on the substrate, and such a layer can have desirable properties. Non-limiting examples of such reactive gas and desirable properties are described herein in greater detail.

FIG. 1 schematically depicts an e-beam evaporator 100 that can be utilized to implement evaporation techniques having one or more features as described herein. The e-beam evaporator 100 is depicted as having a volume of source material 106 held in a holder such as a crucible 108 (also referred to herein as a hearth). A beam of electrons 104 is shown to be directed to a surface (e.g., upper surface) of the source material so as to yield source particles 112 evaporating from a heated region 110. Such source particles 112 (also referred to herein as evaporants) can be directed to any available directions from the heated region 110; and can travel in a line-of-sight manner. Thus, in the example of FIG. 1, parts (e.g., semiconductor wafers) 114a-114c on which a film of the source material is to be formed can be positioned appropriately to receive such source particles 112.

Because of the foregoing nature of the evaporants, an emitter 102 of electron-beam is typically positioned so that evaporants generally do not reach and undesirably coat the emitter 102. For example, the emitter 102 is shown to be positioned below the source material holder 108 so as to be out of the line-of-sight travel of the evaporants 112.

To deliver the electron-beam 104 from the emitter 102 to the upper surface of the source material 106, magnetic field (B, depicted as an arrow 116) can be provided to bend the trajectories of the electrons. In the example of FIG. 1, a constant static magnetic field is depicted as going into the plane of illustration. Accordingly, an electron travelling within the plane with a speed of v experiences a magnetic force with a magnitude of evB and a direction that is perpendicular to the direction of travel. The resulting motion of the electron generally defines, for example, about 270 degrees of a circular path, thereby allowing electrons from the “hidden” emitter 102 to be delivered to the upper surface of the source materials 106 in a curved manner.

FIG. 1 further shows that in some embodiments, the e-beam evaporator 100 can include or be in communication with a vacuum component 124 configured to provide a desirable vacuum or reduced pressure within the evaporator 100. Examples of such a vacuum component are described herein in greater detail.

FIG. 1 further shows that in some embodiments, the e-beam evaporator 100 can include or be in communication with a gas supply 122 configured to provide a desirable flow of reactive gas into the evaporator 100. Examples of such a gas supply are described herein in greater detail.

FIG. 1 further shows that in some embodiments, the e-beam evaporator 100 can include or be in communication with a controller 120 configured to control or facilitate control of one or more features associated with the operation of the evaporator 100. Examples of such control features are described herein in greater detail.

FIG. 2 shows an example evaporator 100 that can be a more specific example of the evaporator of FIG. 1. In some embodiments, such an evaporator can be configured to implement reactive evaporation having one or more features as described herein. In the example evaporator 100 of FIG. 2, delivery of an electron-beam 104 from an emitter 102 to a volume of source material 106 being held by a holder 108 can be implemented as described herein. Incidence of electrons on the source material 106 results in a heated region, from which evaporants 112 are emitted. Such evaporants are depicted as travelling in their respective lines of sight to thereby be deposited on exposed surfaces of substrates such as semiconductor wafers 134. As described herein, some or all of such evaporants can react with reactive gas to yield one or more desired properties for the deposited layer on the wafers 134.

In the example evaporator 100 shown in FIG. 2, the wafers 134 can be held in desired locations and orientations in a wafer-holder 132 to receive the reacted evaporants 112. In the example shown, the wafer-holder 132 can be configured to rotate by a rotating mechanism 136 that couples the wafer-holder 132 to a dome assembly 138. Such a rotation of the wafer-holder 132 can yield a more uniform deposition of evaporants among the various wafers 134.

In the example shown in FIG. 2, the dome assembly 138, a side wall 140, and a floor 144 can form a chamber 130 that includes an internal volume 142. Such a volume can be provided with an appropriate level of vacuum or reduced pressure to facilitate the evaporation process. Such a vacuum or reduced pressure can be provided and/or facilitated by a vacuum component 124 that is in communication with the chamber 130.

In the example shown in FIG. 2, reactive gas can be introduced into the chamber 130 by a gas supply component 122 to facilitate one or more features of the reactive evaporation process as described herein. Examples of such a reactive gas and how the gas can be provided to the chamber 130 are described herein in greater detail.

As described herein, some or all of the foregoing techniques for performing reactive evaporation can be controlled and/or facilitated by a controller 120. In some embodiments, such a controller can include a processor and a memory for storing, for example, data, executable instructions, etc. Such a memory can be a computer readable medium (CRM), including a non-transitory CRM.

In some embodiments, some or all portions of the controller 120 can be located with the evaporator 100, remotely located from the evaporator 100, or any combination thereof. It will be understood that components of the controller 120 itself may be located generally together, in communication from remote locations, or any combination thereof.

FIG. 3 shows and example reactive evaporation configuration 100 that can be a more specific example of the evaporator 100 of FIG. 2. In FIG. 3, source material 106 can include tantalum (Ta) held by a hearth 108, and reactive gas can include nitrogen gas (N₂). Evaporation of tantalum by electrons from an electron emitter 102 can react with the nitrogen gas within an evacuated volume 142 of a chamber 130 so as to allow formation of a tantalum nitride (TaN) layer on each of a plurality of wafers 134 being held by a rotatable dome 132. Although described in the context of tantalum as a refractory material and nitrogen as a reactive gas, it will be understood that other refractory materials and/or reactive gases can also be utilized.

In the example of FIG. 3, the reactive evaporation configuration 100 can include a shutter 180 and a monitor such as a crystal monitor 150 to facilitate automated monitoring and/or control (e.g., by a control system 120) of thickness of a deposited layer on each of the wafers 134 held by the rotating dome 132. Examples of how such crystal monitor 150 and shutter 180 can be implemented, as well as additional details concerning the rotatable wafer-holding dome 132, are described in U.S. Pat. No. 8,022,448 titled “APPARATUS AND METHODS FOR EVAPORATION INCLUDING TEST WAFER HOLDER,” which is expressly incorporated by reference in its entirely.

In the example of FIG. 3, a desired vacuum or reduced pressure for the volume 142 of the chamber 130 can be provided or facilitated by a vacuum interface assembly 170. Such an assembly can be configured to provide, for example, a vacuum formation path (e.g., arrow 172) between the volume 142 and a vacuum pump (not shown). In some embodiments, the level of vacuum can be monitored by the control system 120 utilizing, for example, a pressure gauge 174 that measures the pressure associated with the evacuated volume 142. The control system 120 can be configured to, for example, operate the vacuum interface assembly 170 and/or the vacuum pump so as to decrease, increase, or maintain the pressure associated with the evacuated volume 142.

In the example of FIG. 3, a desired flow rate of the nitrogen gas can be provided to the volume 142 of the chamber by, for example, a mass flow controller (MFC) 164. The MFC 164 is shown to be implemented along a gas path 162 between a source (not shown) and a gas inlet 160. The gas inlet 160 can be positioned within the volume 142.

In some embodiments, the level of flow rate of nitrogen gas introduced into the evacuated volume can be monitored and/or controlled by the control system 120 utilizing, for example, the MFC 164. The control system 120 can be configured to, for example, allow flow, stop flow, increase flow rate, decrease flow rate, time the duration of flow, etc. Such a control functionality can be utilized to obtain deposited TaN layers having one or more desirable properties as described herein.

FIG. 4 shows a process 200 that can be implemented to perform evaporation to yield a deposition layer having one or more advantageous features as described herein. In block 202, one or more substrates such as semiconductor wafers can be positioned in a chamber to form a layer of refractory material by evaporation deposition. In block 204, vacuum or reduced pressure can be provided in the chamber to facilitate the evaporation deposition. In block 206, reactive gas can be provided to the chamber at a selected flow rate. In block 208, refractory material can be evaporated from a source with energetic electrons. In block 210, evaporation of the refractory material can be performed for a selected duration to form a desired layer that includes the refractory material on the substrate.

FIGS. 5 and 6 show examples of properties of layers that can result from the foregoing reactive evaporation process. FIG. 5 shows an example where measured stress values resulting from 250 angstrom (A) thick TaN films are plotted for different nitrogen gas flow rates in standard cubic centimeters per minute (sccm). FIG. 6 shows an example where measured sheet resistance values resulting from the 250 angstrom thick TaN films are plotted for the different nitrogen gas flow rates. Table 1 lists the values of the data points plotted in FIGS. 5 and 6.

TABLE 1
Film	N2		Sheet		Deposition
thickness	flow rate	Stress	resistance		rate
(Å)	(sccm)	(MPa)	Rs (Ω/sq)	Sigma	(Å/s)
250	0	767.8	81.13	1.886	0.5
250	5	601.8	140.38	2.623	0.5
250	5	578.6	147.94	2.68	0.5
250	10	158.2	139.26	2.622	0.5
250	12	455.5	96.212	2.139	0.5
250	15	−87.1	157.78	2.644	0.5
250	15	−176.3	146.75	2.858	0.5
250	20	−182.4	176.16	3.261	0.5
250	60	−111.2	364.89	4.426	0.5
250	100	−526.9	960	1.356	1

In the example shown in FIG. 5, stress data points having positive values can be considered to be tensile stresses on the substrate provided by the respective deposited films (e.g., 250 Å thick films having TaN). Stress data points having negative values can be considered to be compressive stresses on the substrate provided by the respective deposited films (e.g., 250 Å thick films having TaN). One can see that for flow rates of N₂ between 0 and about 14 sccm, tensile stress results from the example 250 Å thick TaN film. At about 14 sccm and higher values of N₂ flow rate, compressive stress results from the example 250 Å thick TaN film.

In the example stress curve in FIG. 5, suppose that it is desirable to obtain a deposited TaN layer having a selected thickness (e.g., 250 Å) that results in a stress magnitude being less than some selected threshold value (e.g., about 200 MPa). Within the tensile stress region resulting from relatively low N₂ flow rate values, one can see that the stress magnitudes either exceed the threshold value or fluctuate too rapidly. One can also see that there is a relatively rapid change in stress in a relatively small range of N₂ flow rate, as tensile stress transitions to a zero-stress level and then to compressive stress.

In the compressive stress region, however, there is a relatively large range of N₂ flow rate (e.g., about 14 to 70 sccm) where the stress magnitude remains below the example 200 MPa threshold value. Further, the compressive stress level is shown to change relatively smoothly within such a flow rate range, as well as beyond the range. As shown in FIG. 5, the stress level between about 15 to 22 sccm is relatively flat at a value of about 180 MPa. As described herein, at least some portion of such a range of N₂ flow rate can also yield a desired electrical property such as sheet resistance.

FIG. 6 shows a plot of measured sheet resistance values resulting from the example 250 angstrom thick TaN films deposited using different nitrogen gas flow rates. One can see that the sheet resistance Rs (in units of Ω/sq) generally increases as the N₂ flow rate increases.

In the example sheet resistance curve in FIG. 6, suppose that it is desirable to obtain a deposited TaN layer having a selected thickness (e.g., 250 Å) that results in a sheet resistance Rs being less than some selected threshold value (e.g., Rs value corresponding to N₂ flow rate of about 22 sccm). Such below-threshold sheet resistance can be obtained by utilizing N₂ flow rate that is less than 22 sccm. When the foregoing N₂ flow rate range (e.g., about 22 sccm or lower) that yields a desirable electrical property such as sheet resistance is considered along with the example N₂ flow rate range (e.g., about 15 sccm or higher) that yields a desirable mechanical property such as stress level, one can see that an example N₂ flow rate range of about 15 to 22 sccm can yield desirable results for both properties.

In the example results described in reference to FIGS. 5 and 6, the N₂ flow rate is measured by the mass flow controller (MFC) 164 described in reference to FIG. 3. For a particular evaporator device, such a flow rate can yield a corresponding concentration of nitrogen at a desired location within the evaporator device. For a different evaporator device, however, the same flow rate can yield a different concentration at a similar desired location within that evaporator device. Accordingly, it will be understood that various concepts described in reference to the examples of FIGS. 5 and 6 can be implemented in a more generalized manner.

For example, FIG. 7 shows a configuration 300 where a distribution 310 of a mechanical property and a distribution 320 of an electrical property are plotted as functions of reactive gas flow rate or concentration. Such a concentration can be, for example, a concentration at a desired location within an evaporator chamber. Such a desired location can be, for example, at or near where wafers are located. At such a location, the reactive gas concentration can be substantially uniform and generally representative of the reactive gas concentration within the evaporator chamber.

In the example of FIG. 7, the mechanical property (e.g., stress level) can have a desired value (e.g., zero stress level). Relative to such a desired value, a desired range 312 can be specified; and such a desired range can include a selected upper limit that has a value greater than the desired value by an amount ΔP1. Similarly, the desired range 312 can include a selected lower limit that has a value less than the desired value by an amount ΔP2. The values of ΔP1 and ΔP2 may or may not be the same. In some situations, the desired range 312 can also be defined by an upper limit alone, or by a lower limit alone.

In the example of FIG. 7, the electrical property (e.g., sheet resistance) can have a desired range 322 that includes, for example, values less than or equal to a selected limit. In some situations, the desired range 322 can also be defined by a lower limit, or by upper and lower limits.

Based on the foregoing example desired range 312 for the mechanical property, one can see that a range of values for the reactive gas flow rate or values for concentration of the reactive gas in the evaporator chamber can be from a lower limit 314 (where the curve 310 is at the selected upper limit) to an upper limit 318 (where the curve 310 is at the selected lower limit). In the context of the stress level example described in reference to FIG. 5, the stress level may change too rapidly near such a lower limit 314, or even near another lower limit 316 (where the curve 310 is at the desired value). Accordingly, a lower limit 317 can be selected to yield a range where the mechanical property does not vary rapidly. In the example shown in FIG. 7, such a lower limit yields a range of horizontal axis values between limits 317 and 318.

Based on the foregoing example desired range 322 for the electrical property, one can see that a range of values for the reactive gas flow rate or values for concentration of the reactive gas in the evaporator chamber can include values that are less than or equal to an upper limit 324. Thus, when such a range of values (flow rate or concentration) based on the electrical property is combined with ranges of values (flow rate or concentration) based on the mechanical property, a range of values (flow rate or concentration) can be obtained to satisfy both of the desired mechanical and electrical properties. Such a range of values can have a lower limit of 330, 332 or 334 corresponding to the lower limits 314, 316 or 317 associated with the mechanical property curve 310, and an upper limit 334 corresponding to the upper limit 324 associated with the electrical property curve 320.

The example of FIG. 7 is described in the context of obtaining a range associated with a reactive gas to satisfy desired ranges of a mechanical property and an electrical property. FIG. 8 shows a more generalized configuration 350 where one or more features of the present disclosure can be implemented in a reactive evaporation process to obtain one or more ranges associated with an operating condition to satisfy desired range(s) associated with one or more properties associated with a deposited refractory-material layer such as a TaN layer.

In the example of FIG. 8, a first property (e.g., mechanical property such as stress level) can have a desired range 362; and a first property curve 360 can be within such a desired range (362) at one or more ranges of the operating condition (e.g., flow rate or concentration). Similarly, a second property (e.g., electrical property such as sheet resistance) can have a desired range 372; and a second property curve 370 can be within such a desired range (372) at one or more ranges of the operating condition.

For the first property, one or more ranges of the operating condition that satisfy the range 362 are depicted as ranges 364a to 364b, 364c to 364d, 364e to 364f, 364g to 364h, and 364i to 364j. For the second property, one or more ranges of the operating condition that satisfy the range 372 are depicted as a range 374a to 374b. Accordingly, one or more ranges of the operating condition that satisfy both of the ranges 362 and 372 of the first and second properties are depicted as 380 (384a to 384b) and 382 (384c to 384d).

FIG. 9 shows a focused ion beam (FIB) image of an example metal stack that includes a refractory material layer formed utilizing a reactive evaporation technique having one or more features as described herein. The example metal stack can include a TaN layer (e.g., 150 Å) formed over a substrate. In the example, the substrate is shown to include a layer of silicon nitride (SiN) (e.g., 1,500 Å) formed over a semiconductor material such as gallium arsenide (GaAs). It will be understood that one or more features of the present disclosure can also be implemented on other types of semiconductor materials.

The example metal stack in FIG. 9 can further include a titanium (Ti) layer (e.g., 700 Å) formed over the TaN layer. The titanium (Ti) layer is typically easier to form by evaporation. Thus, the TaN layer underneath the Ti layer can be relatively thin and provide one or more functionalities as described herein; and the Ti layer can provide functionalities such as diffusion barrier (e.g., when the metal structure is being used as a FET gate), Schottky barrier (e.g., when the metal structure is being used as a Schottky diode anode), adhesion, and/or desired electrical properties. The example metal stack can further include a gold (Au) layer (e.g., 500 Å) formed over the Ti layer. It will be understood that the thickness values are approximate, and can vary depending on particular designs.

FIG. 10 shows that in some embodiments, the example stack of FIG. 9 can further include a second Ti layer (e.g., thickness d4) formed over the Au layer. As described in reference to FIG. 9, various layers can have their thicknesses adjusted for different designs. More particularly, the TaN layer is depicted as having a thickness of d1, the first Ti layer is depicted as having a thickness of d2, the Au layer is depicted as having a thickness of d3, and the second Ti layer is depicted as having a thickness of d4.

In some embodiments, TaN layers formed utilizing one or more features as described herein can include relative content of tantalum and nitrogen that can be expressed as a formula TaN_x, where the quantity x can be in a range of 0.0 to 0.5. It will be understood that other ratios can also be utilized.

FIGS. 11 and 12 show example plots of sheet resistance values and relative variation values resulting from formation of a gate layer structure over different runs (e.g., over time and/or using different evaporator units), demonstrating that relatively consistent performance results can be expected utilizing one or more features of the reactive evaporation techniques described herein. To form the example gate layer structure, a chamber pressure of approximately 1.3×10⁻⁶ mbar was provided. A N₂ flow rate of approximately 20 sccm was provided for approximately 240 seconds during a ramp or soak portion, before the shutter (e.g., 180 in FIG. 3) was opened or any TaN was deposited on the wafers, to provide sufficient nitrogen stabilization and uniformity throughout the chamber. A TaN layer was formed by continuing the N₂ flow rate of approximately 20 sccm and opening the shutter to yield a TaN deposition rate of approximately 0.5 Å/s. At such a deposition rate, reactive evaporation for approximately 300 seconds yielded a TaN layer having a thickness of approximately 150 Å.

A Ti layer was formed over the TaN layer utilizing an electron-beam evaporation deposition process. A deposition rate of approximately 2.0 Å/s was utilized; and the overall thickness of the Ti layer was approximately 250 Å.

A Au layer was formed over the Ti layer utilizing an electron-beam evaporation deposition process. A deposition rate of approximately 10.0 Å/s was utilized; and the overall thickness of the Au layer was approximately 4,500 Å.

Another Ti layer was formed over the Au layer utilizing an electron-beam evaporation deposition process. A deposition rate of approximately 1.0 10.0 Å/s was utilized; and the overall thickness of the Ti layer was approximately 30 Å.

Table 2 lists the average sheet resistance (Rs) values and the relative variation (stdev) values for the six different gate layer fabrication runs plotted in FIGS. 11 and 12. The Rs values were measured for gate layers on wafers without being patterned into gate structures. For such measurements, an average of about 49 data points were measured across a given wafer with about 5 mm edge exclusion. One can see that the average sheet resistance (Rs) values associated with the six runs are fairly consistent and reproducible in a range of about 0.0625 to 0.0655 of Ω/sq. One can also see that the standard deviation of the Rs values associate with the six runs are also fairly consistent and reproducible in a range of about 1.0 to 1.3%.

TABLE 2
Run	Rs (Ω/sq)	Stdev (%)
1	0.0640	1.157
2	0.0627	1.026
3	0.0625	1.004
4	0.0636	1.047
5	0.0646	1.157
6	0.0654	1.293

As described herein by way of examples, the formation of TaN layer can be advantageously implemented by a reactive evaporation technique, where reactive gas such as nitrogen can be provided through a gas supply system to a standard evaporation system. As also described herein, optimum or desired deposition conditions can be determined based on finding, for example, a N₂ gas flow rate (or corresponding nitrogen pressure inside the chamber) in a range where a property such as film stress level is at a desired range and also relatively insensitive to small changes in the flow rate. Under such deposition conditions, the composition of the film can be controlled easily, and the resulting film can provide excellent barrier properties. As also described herein, electrical resistance of such a film in the vertical direction can be very low (e.g., due to low thickness).

From a fabrication perspective, the ability to form a refractory-material layer such as a TaN layer utilizing electron evaporation as described herein can allow implementation of a one-step (e.g., one photolithography and one deposition type) process for fabricating layered structures such as gate or interconnect structures. For example, and as described herein in reference to FIGS. 9-12, each layer of the example TaN—Ti—Au—Ti stack can be formed utilizing an electron evaporation process utilizing each layer's respective source material. With the TaN layer, reactive gas can be provides as described herein; and introduction and removal of such gas to and from the evacuated chamber can be implemented relatively easily without breaking vacuum of the chamber.

As described herein, sheet resistance of a TaN_x film can be adjusted by, for example, flow rate of a reactive gas such as nitrogen. Accordingly, a device having such a TaN_x film can be implemented as a thin-film resistor (TFR).

In some embodiments, a TaN_x layer formed as described herein can be implemented on, for example, III-V semiconductors such as gallium arsenide (GaAs) substrates. In the context of the TFR, evaporation method allows use of a lift-off technique to define the resistor, essentially eliminating various problems associated with dielectric assisted lift-off (DAL) technique typically utilized in sputter deposition. In addition, the TaN resistor can be formed directly on, for example, silicon nitride, so as to make the TFR less susceptible to leakage through the GaAs substrate.

Tantalum is a refractory metal with a very high melting point which is generally a challenge to evaporate. However, as described herein, systems, devices and method for depositing TaN_x layers with electron beam evaporation with nitrogen incorporation can yield a stable TaN_x film having some of all desired properties of a sputtered TaN layer.

It is noted that in an evaporated TaN_x film, the amount of nitrogen incorporated into the film can be dependent not only on the N₂ flow, but also on the level of background oxygen and carbon within the chamber and/or the source. Such an effect of oxygen in the film can be addressed or minimized by, for example, controlling the presence of oxygen (e.g., by maintaining low level of oxygen in the film).

The foregoing example of the evaporated TaN TFR is one of a number of devices for which one or more features of the present disclosure can be utilized to fabricate such devices. Other non-limiting examples related to TaN layers can be found in U.S. patent application Ser. No. ______ [Attorney Docket 75900-50059US], titled “REFRACTORY METAL BARRIER IN SEMICONDUCTOR DEVICES,” filed on even date herewith, which is expressly incorporated by reference in its entirely, and which is to be considered part of the specification of the present application.

The present disclosure describes various features, no single one of which is solely responsible for the benefits described herein. It will be understood that various features described herein may be combined, modified, or omitted, as would be apparent to one of ordinary skill. Other combinations and sub-combinations than those specifically described herein will be apparent to one of ordinary skill, and are intended to form a part of this disclosure. Various methods are described herein in connection with various flowchart steps and/or phases. It will be understood that in many cases, certain steps and/or phases may be combined together such that multiple steps and/or phases shown in the flowcharts can be performed as a single step and/or phase. Also, certain steps and/or phases can be broken into additional sub-components to be performed separately. In some instances, the order of the steps and/or phases can be rearranged and certain steps and/or phases may be omitted entirely. Also, the methods described herein are to be understood to be open-ended, such that additional steps and/or phases to those shown and described herein can also be performed.

Some aspects of the systems and methods described herein can advantageously be implemented using, for example, computer software, hardware, firmware, or any combination of computer software, hardware, and firmware. Computer software can comprise computer executable code stored in a computer readable medium (e.g., non-transitory computer readable medium) that, when executed, performs the functions described herein. In some embodiments, computer-executable code is executed by one or more general purpose computer processors. A skilled artisan will appreciate, in light of this disclosure, that any feature or function that can be implemented using software to be executed on a general purpose computer can also be implemented using a different combination of hardware, software, or firmware. For example, such a module can be implemented completely in hardware using a combination of integrated circuits. Alternatively or additionally, such a feature or function can be implemented completely or partially using specialized computers designed to perform the particular functions described herein rather than by general purpose computers.

Multiple distributed computing devices can be substituted for any one computing device described herein. In such distributed embodiments, the functions of the one computing device are distributed (e.g., over a network) such that some functions are performed on each of the distributed computing devices.

Some embodiments may be described with reference to equations, algorithms, and/or flowchart illustrations. These methods may be implemented using computer program instructions executable on one or more computers. These methods may also be implemented as computer program products either separately, or as a component of an apparatus or system. In this regard, each equation, algorithm, block, or step of a flowchart, and combinations thereof, may be implemented by hardware, firmware, and/or software including one or more computer program instructions embodied in computer-readable program code logic. As will be appreciated, any such computer program instructions may be loaded onto one or more computers, including without limitation a general purpose computer or special purpose computer, or other programmable processing apparatus to produce a machine, such that the computer program instructions which execute on the computer(s) or other programmable processing device(s) implement the functions specified in the equations, algorithms, and/or flowcharts. It will also be understood that each equation, algorithm, and/or block in flowchart illustrations, and combinations thereof, may be implemented by special purpose hardware-based computer systems which perform the specified functions or steps, or combinations of special purpose hardware and computer-readable program code logic means.

Furthermore, computer program instructions, such as embodied in computer-readable program code logic, may also be stored in a computer readable memory (e.g., a non-transitory computer readable medium) that can direct one or more computers or other programmable processing devices to function in a particular manner, such that the instructions stored in the computer-readable memory implement the function(s) specified in the block(s) of the flowchart(s). The computer program instructions may also be loaded onto one or more computers or other programmable computing devices to cause a series of operational steps to be performed on the one or more computers or other programmable computing devices to produce a computer-implemented process such that the instructions which execute on the computer or other programmable processing apparatus provide steps for implementing the functions specified in the equation(s), algorithm(s), and/or block(s) of the flowchart(s).

Some or all of the methods and tasks described herein may be performed and fully automated by a computer system. The computer system may, in some cases, include multiple distinct computers or computing devices (e.g., physical servers, workstations, storage arrays, etc.) that communicate and interoperate over a network to perform the described functions. Each such computing device typically includes a processor (or multiple processors) that executes program instructions or modules stored in a memory or other non-transitory computer-readable storage medium or device. The various functions disclosed herein may be embodied in such program instructions, although some or all of the disclosed functions may alternatively be implemented in application-specific circuitry (e.g., ASICs or FPGAs) of the computer system. Where the computer system includes multiple computing devices, these devices may, but need not, be co-located. The results of the disclosed methods and tasks may be persistently stored by transforming physical storage devices, such as solid state memory chips and/or magnetic disks, into a different state.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

The disclosure is not intended to be limited to the implementations shown herein. Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. The teachings of the invention provided herein can be applied to other methods and systems, and are not limited to the methods and systems described above, and elements and acts of the various embodiments described above can be combined to provide further embodiments. Accordingly, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.

Claims

1. A method for performing reactive evaporation, the method comprising:

positioning a volume of refractory material to be evaporated within an evaporation chamber;

forming a vacuum environment within the evaporation chamber;

providing a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles; and

introducing a flow of reactive gas into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material, the flow of reactive gas selected such that a layer formed on a substrate by deposition of the evaporated particles includes a range of a desirable property.

2. The method of claim 1 wherein the refractory material includes tantalum (Ta).

3. The method of claim 2 wherein the reactive gas includes nitrogen gas (N2).

4. The method of claim 3 wherein the layer includes tantalum nitride (TaN).

5. The method of claim 4 wherein the tantalum nitride has a composition expressed as TaNx, the quantity x having a value in a range between 0 and 0.5.

6. The method of claim 1 wherein the desirable property includes a mechanical property.

7. The method of claim 6 wherein the selected flow of reactive gas is in a range having a lower flow limit and an upper flow limit.

8. The method of claim 7 wherein the lower flow limit of the range is selected to correspond to be at or higher than a first flow rate that yields a first stress level associated with the layer.

9. The method of claim 8 wherein the first stress level includes a stress level associated with transition between tensile stress and compressive stress associated with the layer.

10. The method of claim 9 wherein the first stress level has a value of approximately zero.

11. The method of claim 9 wherein the lower flow limit of the range is selected such that the layer provides a compressive stress to the substrate.

12. The method of claim 11 wherein the lower limit and the upper limit of the range are selected such that the compressive stress has a magnitude less than a selected value.

13. The method of claim 11 wherein the lower limit of the range is selected such that the compressive stress varies sufficiently slowly as a function of the flow to be substantially reproducible.

14. The method of claim 13 wherein the desirable property further includes an electrical property.

15. The method of claim 14 wherein the electrical property includes a sheet resistance associated with the layer, the sheet resistance increasing as a function of the flow of the reactive gas.

16. The method of claim 15 wherein the upper limit of the range is selected such that the sheet resistance associated with the layer is less than a selected sheet resistance value.

17. The method of claim 1 further comprising forming one or more additional layers over the layer formed with the flow of reactive gas.

18. The method of claim 17 wherein each of the one or more additional layers is formed by electron-beam evaporation, such that all of the layers are formed utilizing one photolithography and one deposition type.

19. A reactive evaporation system comprising:

an evaporation chamber configured to hold a volume of refractory material to be evaporated;

a vacuum system in communication with the evaporation chamber, the vacuum system configured to provide a vacuum environment within the evaporation chamber;

an electron-beam system configured to provide a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles; and

a gas supply system in communication with the evaporation chamber, the gas supply system configured to provide a flow of reactive gas into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material, the flow of reactive gas selected such that a layer formed on a substrate by deposition of the evaporated particles includes a range of a desirable property.

20. A method for forming a metalized stack on a semiconductor substrate, the method comprising:

mounting the semiconductor substrate within an evaporation chamber;

positioning a volume of refractory material to be evaporated within the evaporation chamber;

forming a vacuum environment within the evaporation chamber; and

depositing a refractory material barrier layer on the semiconductor substrate, the depositing including providing a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles, the depositing further including introducing a flow of reactive gas into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material, the flow of reactive gas selected such that the refractory material barrier layer includes a range of a desirable property.

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