Method of controlling solid phase diffusion of boron dopants to form ultra-shallow doping regions

Abstract

A method is provided for forming an ultra-shallow boron doping region in a semiconductor device. The method includes depositing a diffusion filter layer on a substrate, the diffusion filter containing a boron nitride layer, a boron oxynitride layer, a silicon nitride layer, or a silicon oxynitride layer, and depositing a boron dopant layer on the diffusion filter layer, the boron dopant layer containing boron oxide, boron oxynitride, or a combination thereof, with the proviso that the diffusion filter layer and the boron dopant layer do not contain the same material. The method further includes heat-treating the substrate to form the ultra-shallow boron dopant region in the substrate by controlled diffusion of boron from the boron dopant layer through the diffusion filter layer and into the substrate.

Claims

1. A method of forming an ultra-shallow boron doping region in a semiconductor device, the method comprising: depositing a diffusion filter layer on a substrate, the diffusion filter layer containing a boron nitride layer, a boron oxynitride layer, a silicon nitride layer, or a silicon oxynitride layer; depositing a boron dopant layer on the diffusion filter layer, the boron dopant layer containing boron oxide, boron oxynitride, or a combination thereof, with the proviso that the diffusion filter layer and the boron dopant layer do not contain the same material; and heat-treating the substrate to form the ultra-shallow boron dopant region in the substrate by controlled diffusion of boron from the boron dopant layer through the diffusion filter layer and into the substrate, wherein the diffusion filter layer, the boron dopant layer, or both the diffusion filter layer and the boron dopant layer, are deposited by atomic layer deposition (ALD) using alternating gaseous exposures of a boron amide precursor and a reactant gas.

2. The method of claim 1, further comprising prior to the heat-treating, depositing a cap layer on the boron dopant layer.

3. The method of claim 2, wherein the cap layer contains a boron nitride layer.

4. The method of claim 1, further comprising removing the diffusion filter layer and the boron dopant layer from the substrate.

5. The method of claim 1, wherein the heat-treating is performed in an inert atmosphere.

6. The method of claim 1, wherein the substrate contains a raised feature or a recessed feature, and the diffusion filter layer and the boron dopant layer are conformally deposited on the raised feature or in the recessed feature.

7. The method of claim 1, wherein the boron dopant layer contains boron oxide and the reactant gas includes H.sub.2O, O.sub.2, or O.sub.3, or a combination of two or more thereof.

8. The method of claim 1, wherein the boron dopant layer contains boron oxynitride and the reactant gas includes a) H.sub.2O, O.sub.2, or O.sub.3, and NH.sub.3, or b) NO, NO.sub.2, or N.sub.2O, and optionally one or more of H.sub.2O, O.sub.2, O.sub.3, and NH.sub.3.

9. The method of claim 1, wherein the diffusion filter layer is deposited using alternating gaseous exposures of the boron amide precursor and the reactant gas containing NH.sub.3.

10. The method of claim 1, wherein the diffusion filter layer and the boron dopant layer are deposited in the same process chamber, and wherein the substrate is maintained at the same substrate temperature during deposition of the diffusion filter layer and the boron dopant layer.

11. A method of forming an ultra-shallow boron doping region in a semiconductor device, the method comprising: depositing a diffusion filter layer on a substrate, the diffusion filter layer containing a boron nitride layer, a boron oxynitride layer, a silicon nitride layer, or a silicon oxynitride layer; depositing a boron dopant layer on the diffusion filter layer, the boron dopant layer containing boron oxide, boron oxynitride, or a combination thereof, with the proviso that the diffusion filter layer and the boron dopant layer do not contain the same material; and heat-treating the substrate to form the ultra-shallow boron dopant region in the substrate by controlled diffusion of boron from the boron dopant layer through the diffusion filter layer and into the substrate, wherein the diffusion filter layer, the boron dopant layer, or both the diffusion filter layer and the boron dopant layer, are deposited by atomic layer deposition (ALD) using alternating gaseous exposures of an organoboron precursor and a reactant gas.

12. The method of claim 11, wherein the boron dopant layer contains boron oxide and the reactant gas includes H.sub.2O, O.sub.2, or O.sub.3, or a combination of two or more thereof.

13. The method of claim 11, wherein the boron dopant layer contains boron oxynitride and the reactant gas includes a) H.sub.2O, O.sub.2, or O.sub.3, and NH.sub.3, or b) NO, NO.sub.2, or N.sub.2O, and optionally one or more of H.sub.2O, O.sub.2, O.sub.3, and NH.sub.3.

14. The method of claim 11, wherein the diffusion filter layer is deposited using alternating gaseous exposures of the organoboron precursor and the reactant gas containing NH.sub.3.

15. The method of claim 11, further comprising prior to the heat-treating, depositing a cap layer on the boron dopant layer.

16. The method of claim 11, further comprising removing the diffusion filter layer and the boron dopant layer from the substrate.

17. The method of claim 11, wherein the heat-treating is performed in an inert atmosphere.

18. The method of claim 11, wherein the substrate contains a raised feature or a recessed feature, and the diffusion filter layer and the boron dopant layer are conformally deposited on the raised feature or in the recessed feature.

19. A method of forming an ultra-shallow boron doping region in a semiconductor device, the method comprising: depositing a diffusion filter layer on a substrate, the diffusion filter layer containing a boron nitride layer; depositing a boron dopant layer on the diffusion filter layer, the boron dopant layer containing boron oxide or boron oxynitride; depositing a cap layer on the boron dopant layer; heat-treating the substrate in an inert atmosphere to form the ultra-shallow boron dopant region in the substrate by controlled diffusion of boron from the boron dopant layer through the diffusion filter layer and into the substrate; and removing the diffusion filter layer and the boron dopant layer from the substrate.

20. The method of claim 15, wherein the cap layer contains a boron nitride layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIGS. 1A-1C show schematic cross-sectional views of a process flow for forming an ultra-shallow boron dopant region in a substrate according to an embodiment of the invention;

(3) FIG. 2 show a schematic cross-sectional view of a film structure for forming an ultra-shallow boron dopant region in a substrate according to another embodiment of the invention;

(4) FIGS. 3A-3C show schematic cross-sectional views of a process flow for forming an ultra-shallow boron dopant region in a substrate according to yet another embodiment of the invention;

(5) FIG. 4 show a schematic cross-sectional view of a film structure for forming an ultra-shallow boron dopant region in a substrate according to another embodiment of the invention;

(6) FIG. 5 shows a boron dopant depth profile for an as-deposited and a heat-treated (annealed) film structure containing Al.sub.2O.sub.3/B.sub.2O.sub.3/Si layers;

(7) FIG. 6 shows a boron dopant depth profile for an as-deposited and a heat-treated (annealed) film structure containing SiN/BN/Si layers;

(8) FIG. 7 shows normalized Rs results for heat-treated B.sub.2O.sub.3 and BN layers on Si substrates;

(9) FIG. 8 shows Rs results for heat-treated B.sub.2O.sub.3 layers on Si substrates;

(10) FIGS. 9-11 compare boron dopant depth profiles for heat-treated (annealed) samples containing B.sub.2O.sub.3/Si layers to a depth profile for a Si substrate; and

(11) FIG. 12 shows boron solid solubility as a function of temperature.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

(12) Methods for forming ultra-shallow boron dopant regions in semiconductor devices by solid phase diffusion from a boron dopant layer through a diffusion filter layer into a substrate layer are disclosed in various embodiments. The boron dopant regions can include, for example, ultra-shallow source-drain extensions for planar transistors, FinFETs, or tri-gate FETs. Other applications of ultra-shallow boron dopant region formation can include channel doping in replacement gate process flows, and for FinFET, or extremely thin silicon on insulator (ET-SOI) devices. Devices with extremely thin alternative semiconductor channels may also be doped using the disclosed method, for instance germanium on insulator devices (GeOI) or Ge FinFETs, and III-V channel devices such as GaAs, InGaAs, or InGaSb FinFETs. In addition, devices formed in amorphous Si or polycrystalline Si layers, such as EDRAM devices may utilize the disclosed method to adjust the Si doping level.

(13) One skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Furthermore, it is understood that the various embodiments shown in the drawings are illustrative representations and are not necessarily drawn to scale.

(14) Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not denote that they are present in every embodiment. Thus, the appearances of the phrase in one embodiment in various places throughout this specification are not necessarily referring to the same embodiment of the invention.

(15) Previous work on boron doping by solid state diffusion includes the use of a B.sub.2O.sub.3 dopant layer as a source of boron dopants, where the B.sub.2O.sub.3 dopant layer is in direct contact with the substrate and boron atoms diffuse directly into the substrate from the B.sub.2O.sub.3 dopant layer during a heat-treating. The thickness, boron content, and boron depth profile of the resulting boron dopant region in the substrate is a function of the thickness of the B.sub.2O.sub.3 dopant layer and the heat-treating conditions, including substrate temperature and duration of the heat-treating. However, new methods are needed to better control the properties of the boron dopant region.

(16) Embodiments of the invention provide a novel new approach to control the properties of the boron-doped region, including the junction depth. According to one embodiment, an inert and thermally stable diffusion filter layer containing boron nitride (BN) is positioned between the substrate and the boron dopant layer. According to other embodiments, the diffusion filter layer can contain a boron oxynitride layer, a silicon nitride layer, or a silicon oxynitride layer. The diffusion filter layer can act as a blocking layer to impede boron diffusion and control the properties of the boron doping region, including the thickness, boron content, and boron depth profile. In one example, the diffusion filter layer may be used to achieve less than boron saturation concentration in the boron doping region. For example, a thickness of the diffusion filter layer can be used to control the properties of the boron doping region. In one example, the diffusion filter layer can include a BN layer deposited by atomic layer deposition (ALD) and a B.sub.2O.sub.3 dopant layer can also be deposited by ALD. The use of ALD provides a method of manufacturing a boron-doped semiconductor device with excellent control over the thickness of the BN layer, the boron dopant layer, and the properties of the boron doping region.

(17) According to one embodiment, a method is provided for forming an ultra-shallow boron doping region in a semiconductor device. The method includes depositing a diffusion filter layer on a substrate, the diffusion filter layer containing a boron nitride layer, a boron oxynitride layer, a silicon nitride layer, or a silicon oxynitride layer, and depositing a boron dopant layer on the diffusion filter layer, where the boron dopant layer contains boron oxide, boron oxynitride, or a combination thereof, with the proviso that the diffusion filter layer and the boron dopant layer do not contain the same material. The method further includes heat-treating the substrate to form the ultra-shallow boron dopant region in the substrate by controlled diffusion of boron from the boron dopant layer through the diffusion filter layer and into the substrate.

(18) A significant drawback to using a pure B.sub.2O.sub.3 dopant layer is the extreme air instability of B.sub.2O.sub.3. This is due to its high reactivity with moisture in the ambient which results in boric acid formation that has a high vapor pressure. The inventors have realized that a cap layer may be formed on the B.sub.2O.sub.3 dopant layer to protect the B.sub.2O.sub.3 dopant layer from the moisture. According to one embodiment, the cap layer can contain or consist of BN. The use of the cap layer allows for heat-treating a substrate containing the B.sub.2O.sub.3 dopant layer in non-clustered thermal processing system.

(19) According to one embodiment, the boron dopant layer can contain boron oxynitride (BNO). In some examples, a composition of the boron oxynitride can range from nitrogen-doped boron oxide with B and O as the major elements to an oxygen-doped boron nitride with B and N as the major elements. Increasing the nitrogen-content and reducing the oxygen-content in the BNO allows for further controlling the properties of the boron doping region since the presence of nitrogen increases the thermal stability of BNO relative to B.sub.2O.sub.3. In one embodiment, a cap layer may be formed on the BNO layer to protect the BNO layer from moisture.

(20) FIGS. 1A-1C show schematic cross-sectional views of a process flow for forming an ultra-shallow dopant region in a substrate according to an embodiment of the invention. FIG. 1A shows a schematic cross-sectional view of substrate 100, a diffusion filter layer 102 on the substrate 100, and a boron dopant layer 104 on the diffusion filter layer 102. The substrate 100 can be of any size, for example a 200 mm substrate, a 300 mm substrate, or an even larger substrate. According to one embodiment, the substrate 100 can contain Si, for example crystalline Si, polycrystalline Si, or amorphous Si. In one example, the substrate 100 can be a tensile-strained Si layer. According to another embodiment, the substrate 100 may contain Ge or Si.sub.xGe.sub.1-x compounds, where x is the atomic fraction of Si, 1-x is the atomic fraction of Ge, and 0<x<1. Exemplary Si.sub.xGe.sub.1-x compounds include Si.sub.0.1Ge.sub.0.9, Si.sub.0.2Ge.sub.0.8, Si.sub.0.3Ge.sub.0.7, Si.sub.0.4Ge.sub.0.6, Si.sub.0.5Ge.sub.0.5, Si.sub.0.6Ge.sub.0.4, Si.sub.0.7Ge.sub.0.3, Si.sub.0.8Ge.sub.0.2, and Si.sub.0.9Ge.sub.0.1. In one example, the substrate 100 can be a compressive-strained Ge layer or a tensile-strained Si.sub.xGe.sub.1-x (x>0.5) deposited on a relaxed Si.sub.0.5Ge.sub.0.5 buffer layer. According to some embodiments, the substrate 100 can include a silicon-on-insulator (SOI). In some embodiments the substrate 100 can include a compound semiconductor, e.g., GaAs.

(21) The diffusion filter layer 102 and the boron dopant layer 104 may be deposited by atomic layer deposition (ALD). In one example, a B.sub.2O.sub.3 dopant layer 104 may be deposited by ALD by a) providing a substrate in a process chamber configured for performing an ALD process, b) exposing the substrate to a vapor phase boron amide or an organoborane precursor, c) purging/evacuating the process chamber, d) exposing the substrate to a reactant gas containing H.sub.2O, O.sub.2, or O.sub.3, a combination thereof, e) purging/evacuating the process chamber, and f) repeating steps b)-e) any number of times until the B.sub.2O.sub.3 dopant layer has a desired thickness. In another example, a BNO dopant layer 104 or a BNO diffusion filter layer 102 may be deposited by ALD using in step d) a reactant gas containing 1) H.sub.2O, O.sub.2, or O.sub.3, and NH.sub.3, or 2) NO, NO.sub.2, or N.sub.2O, and optionally one or more of H.sub.2O, O.sub.2, O.sub.3, and NH.sub.3. In one example, a BN diffusion filter layer 102 may be deposited by ALD using a reactant gas containing NH.sub.3 in step d).

(22) According to embodiments of the invention, the boron amide may be include a boron compound of the form L.sub.nB(NR.sup.1R.sup.2).sub.3 where L is a neutral Lewis base, n is 0 or 1, and each of R.sup.1 and R.sup.2 may be selected from alkyls, aryls, fluoroalkyls, fluoroaryls, alkoxyalkyls, and aminoalkyls. Examples of boron amides include B(NMe.sub.2).sub.3, (Me.sub.3)B(NMe.sub.2).sub.3, and B[N(CF.sub.3).sub.2].sub.3. According to embodiments of the invention, the organoborane may include a boron compound of the form L.sub.nBR.sup.1R.sup.2R.sup.3 where L is a neutral Lewis base, n is 0 or 1, and each of R.sup.1, R.sup.2 and R.sup.3 may be selected from alkyls, aryls, fluoroalkyls, fluoroaryls, alkoxyalkyls, and aminoalkyls. Examples of boron amides include BMe.sub.3, (Me.sub.3N)BMe.sub.3, B(CF.sub.3).sub.3, and (Me.sub.3N)B(C.sub.6F.sub.3).

(23) According to some embodiments, a diffusion filter layer 102 containing a silicon nitride layer or a silicon oxynitride layer may be deposited or grown on the substrate 100 using methods well known to those skilled in the art.

(24) In some examples, a thickness of each of the diffusion filter layer 102 and the boron dopant layer 104 can be 10 nanometers (nm), or less, or 4 nm or less, for example between 1 nm and 4 nm, between 2 nm and 4 nm, or between 3 nm and 4 nm. However, other thicknesses may be used.

(25) The film structure in FIG. 1A may be heat-treated (annealed) to diffuse boron from the boron dopant layer 104 through the diffusion filter layer 102 and into the substrate 100. This is schematically shown in FIG. 1B where boron diffusion is represented by arrows 108. The heat-treating forms an ultra-shallow boron dopant region 106 in the substrate 100 underneath the diffusion filter layer 102. The heat-treating can include heating the substrate 100 in an inert atmosphere (e.g., argon (Ar) or nitrogen (N.sub.2)) to a temperature between 100 C. and 1000 C. for between 10 seconds and 10 minutes. Some heat-treating examples include substrate temperatures between 100 C. and 500 C., between 200 C. and 500 C., between 300 C. and 500 C., and between 400 C. and 500 C. Other examples include substrate temperatures between 500 C. and 1000 C., between 600 C. and 1000 C., between 700 C. and 1000 C., between 800 C. and 1000 C., and between 900 C. and 1000 C. Still other examples include a substrate temperature greater than 800 C., a substrate temperature of 900 C., or greater than 900 C. In some examples, the heat-treating may include rapid thermal annealing (RTA), a spike anneal, or a laser spike anneal.

(26) In some examples, a thickness of the ultra-shallow boron dopant region 106 can be between 1 nm and 10 nm or between 2 nm and 5 nm. However, those skilled in the art will readily realize that the lower boundary of the ultra-shallow boron dopant region 106 in the substrate 100 may not be abrupt but rather characterized by gradual decrease in dopant concentration.

(27) Following the heat-treating and formation of the ultra-shallow boron dopant region 106, the boron dopant layer 104 and the diffusion filter layer 102 may be removed using a dry etching process or a wet etching process. The resulting structure is depicted in FIG. 1C. According to one embodiment, the structure depicted in FIG. 1C may be heat-treated a second time at a higher temperature to activate the boron dopants in the boron dopant region 106.

(28) According to another embodiment, as depicted in FIG. 2, a cap layer 105 may be deposited on the boron dopant layer 104 prior to the heat-treating. Following deposition of the cap layer 105, the film structure in FIG. 2 may be heat-treated as described in reference to FIGS. 1B-1C to form an ultra-shallow boron dopant region 106 in the substrate 100. In one example, the cap layer 105 can contain or consist of BN. In another example, the cap layer 105 may be an oxide layer, a nitride layer, or oxynitride layer, and can include Si and/or one or more of the high-k dielectric materials. The cap layer 105 may be deposited by chemical vapor deposition (CVD), or ALD, for example. In some examples, a thickness of the cap layer 105 can be between 1 nm and 100 nm, between 2 nm and 50 nm, or between 2 nm and 20 nm.

(29) FIGS. 3A-3C show schematic cross-sectional views of a process flow for forming an ultra-shallow boron dopant region in a substrate according to yet another embodiment of the invention. The process flow is similar to the process flow in FIGS. 1A-1C but, as depicted in FIG. 3A, further includes forming a patterned diffusion filter layer 112 on the substrate 100, and a patterned boron dopant layer 114 on the patterned diffusion filter layer 112. For example, conventional photolithographic patterning and etching methods may be used to form the patterned diffusion filter layer 112 and the patterned boron dopant layer 114.

(30) The film structure in FIG. 3A may be heat-treated (annealed) to diffuse boron from the patterned boron dopant layer 114 through the patterned diffusion filter layer 112 and into the substrate 100. This is schematically shown in FIG. 3B where boron diffusion is represented by arrows 118. The heat-treating forms an ultra-shallow boron dopant region 116 in the substrate 100 underneath the patterned diffusion filter layer 112.

(31) Following the heat-treating and formation of the ultra-shallow boron dopant region 116, the patterned boron dopant layer 114 and the patterned diffusion filter layer 112 may be removed using a dry etching process or a wet etching process. The resulting structure is depicted in FIG. 3C.

(32) According to another embodiment, as depicted in FIG. 4, a patterned cap layer 115 may be formed on the patterned boron dopant layer 114 prior to the heat-treating. Following formation of the patterned cap layer 115, the film structure in FIG. 4 may be heat-treated as described in reference to FIGS. 1B-1C to form an ultra-shallow boron dopant region 116 in the substrate 100.

(33) According to another embodiment, the patterned cap layer 115 in FIG. 4 may be replaced by a blanked (not patterned) cap layer that is deposited on the patterned boron dopant layer 114 and on the substrate 100 adjacent the patterned diffusion filter layer 112.

(34) According to another embodiment, the patterned diffusion filter layer 112 in FIG. 3A may be replaced by a blanked diffusion filter layer.

(35) According to one embodiment of the invention, two or more of diffusion filter layer, the boron dopant layer, and the cap layer may be deposited in a single process chamber. This prevents exposure of these layers to ambient moisture and other oxidizing gases in air. In one example, ALD of these layers may be achieved during sequential processing in the process chamber where a boron nitride layer is deposited using alternating gaseous exposures of a boron amide or an organoboron precursor and a first reactant gas (e.g., NH.sub.3), thereafter a boron oxide layer is deposited using alternating gaseous exposures of a boron amide or an organoboron precursor and a second reactant gas (e.g., H.sub.2O, O.sub.2, or O.sub.3, or a combination of two or more thereof), and thereafter a boron nitride cap layer is deposited using alternating gaseous exposures of a boron amide or an organoboron precursor and a third reactant gas (e.g., NH.sub.3 for a boron nitride layer). In one example, the boron oxide layer may be replaced by a boron oxynitride layer that is deposited using alternating gaseous exposures of a boron amide or an organoboron precursor and a fourth reactant gas (e.g., a) H.sub.2O, O.sub.2, or O.sub.3, and NH.sub.3, or b) NO, NO.sub.2, or N.sub.2O, and optionally one or more of H.sub.2O, O.sub.2, O.sub.3, and NH.sub.3. According to one embodiment, the diffusion filter layer and the boron dopant layer may be deposited in the same process chamber, where the substrate is maintained at the same substrate temperature during deposition of the diffusion filter layer and the boron dopant layer

(36) FIG. 5 shows a boron dopant depth profile for an as-deposited and a heat-treated (annealed) film structure containing Al.sub.2O.sub.3/B.sub.2O.sub.3/Si layers. The depth profile plot was obtained using backside SIMS and further shows depth profiles for Si and Al. The B.sub.2O.sub.3 and Al.sub.2O.sub.3 layers were deposited by ALD in the same process chamber, where the B.sub.2O.sub.3layers were deposited using 60 ALD cycles. The film structure was heat-treated (annealed) at 1000 C. for 30 seconds in a N.sub.2 atmosphere.

(37) FIG. 6 shows a boron dopant depth profile for an as-deposited and a heat-treated (annealed) film structure containing SiN/BN/Si layers. The depth profile plot was obtained using backside SIMS and further shows depth profiles for Si and SiN. The BN and SiN layers were deposited by ALD, where the BN layers were deposited using 40 ALD cycles. The film structure was heat-treated (annealed) at 1000 C. for 30 seconds in a N.sub.2 atmosphere.

(38) The SIMS depth profiles in FIGS. 5 and 6 demonstrate that boron diffuses very easily from a B.sub.2O.sub.3 layer into a Si substrate during a heat-treating at 1000 C. but, for comparison, BN is a very inert and stable material in contact with Si. This can be explained, at least in part, that BN is more refractory than B.sub.2O.sub.3 and the melting point for BN is 2966 C. but only 450 C. for B.sub.2O.sub.3. Embodiments of the invention utilize this property to use BN as a diffusion filter layer to impede and control the boron diffusion from a boron dopant layer through the diffusion filter layer and into a Si substrate. Thus, the boron diffusion may be controlled by tailoring the thickness of the diffusion filter layer.

(39) FIG. 7 shows normalized Rs results for heat-treated B.sub.2O.sub.3 and BN layers on Si substrates. The film structures contained cap layer/B.sub.2O.sub.3/Si and cap layer/BN/Si that were heat-treated at 1000 C. for 30 seconds in a N.sub.2 atmosphere. The normalized sheet resistance (Rs) results show that boron diffuses very easily from a B.sub.2O.sub.3 layer into a Si substrate during a heat-treatment at 1000 C. In contrast, BN is a very inert and stable material in contact with Si.

(40) FIG. 8 shows Rs results for heat-treated B.sub.2O.sub.3 layers on Si substrates. The B.sub.2O.sub.3 layers were deposited using 30, 40, and 60 ALD cycles, and thereafter, heat-treated at 900 C. or 1000 C. for 30 seconds in a N.sub.2 atmosphere. The B.sub.2O.sub.3 layer deposition and the heat-treating were performed in a clustered wafer processing tool without exposure to air. The Rs results show that boron diffusion into the Si substrate increases with increased heat-treating temperature and increased B.sub.2O.sub.3 layer thickness.

(41) FIGS. 9-11 compare boron dopant depth profiles for heat-treated (annealed) samples containing B.sub.2O.sub.3/Si layers to a depth profile for a Si substrate. The B.sub.2O.sub.3 layers were deposited using 60 ALD cycles and then heat-treated at 900 C. (FIGS. 10) and 1000 C. (FIG. 11) and the depth profiles compared to a Si substrate (FIG. 9). The SIMS results show that the boron diffuses deeper into the Si substrate with increasing heat-treating temperature. The boron concentration near the B.sub.2O.sub.3/Si interface is about 1E+20 atoms/cm.sup.3, which is near the boron solid solubility shown in FIG. 12 (adapted from Vick and Whittle, J. Electrochem. Soc. 116, 1142 (1969)).

(42) A plurality of embodiments for forming ultra-shallow boron dopant region in a substrate by solid phase diffusion of boron from a boron dopant layer through a diffusion filter layer into the substrate have been disclosed in various embodiments. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. This description and the claims following include terms that are used for descriptive purposes only and are not to be construed as limiting. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teaching. Persons skilled in the art will recognize various equivalent combinations and substitutions for various components shown in the Figures. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.