_refis not robust against the etching 34—rather, the etching 34 attacks the undoped dielectric material 46_refand removes a portion thereof. Hence, dummy fins 50_refremaining after the etch step 34 applied to the undoped dielectric material 46_refdo not retain their shape and size (i.e. critical dimension, CD) after the etch 34, but rather the critical dimension shrinks.

With reference to FIG. 6, and without being limited to any particular theory of operation, it is believed that the improved robustness of the deposited doped dielectric material 46 that is doped with lithium, beryllium, or boron is due to the lithium, beryllium, or boron dopant incorporating as an interstitial dopant in the doped dielectric material 46, and that the interstitial lithium, beryllium, or boron dopant atoms block ingress of oxygen atoms into the doped dielectric material 46. This is shown diagrammatically in FIG. 6, where the top diagram shows the reference undoped dielectric material 46_refand the bottom diagram shows the doped dielectric material 46. Oxygen atoms can ingress into the reference undoped dielectric material 46_refinterstitially, and produce oxidation of the reference undoped dielectric material 46_ref. The oxidized reference undoped dielectric material 46_refthen is more susceptible to damage during the etch step 34. In FIG. 6, top diagram, this is shown by indicating atoms of the undoped dielectric material 46_refand ingress of oxygen atoms (indicated in FIG. 6 by the label “O”) into the dielectric material 46_ref.

By contrast, in the doped dielectric material 46, the lithium, beryllium, or boron interstitial dopant tends to react with oxygen near the surface of the material 46. FIG. 6, bottom diagram shows an example for boron dopant, where boron dopant atoms at or near the surface are shown in FIG. 6, bottom diagram, indicated by the label “B”. The boron atoms react with oxygen to form a surface layer of B₂O₃which blocks further ingress of oxygen into the doped dielectric material 46, thus forming a protective surface layer rich in B₂O₃. Similar formation of B₂O₃is expected at or near an interface with another material if oxygen would otherwise move from that other material into the doped dielectric material 46.

With brief reference back to FIG. 3, a further benefit of the lithium, beryllium, or boron doping is that the surface layer rich in B₂O₃(or lithium oxide or beryllium oxide, in the case of lithium or beryllium doping, respectively) forms an additional amount of thickness (and/or density) that serves as a sacrificial etch layer during the etch step 34. This is shown in FIG. 2 as an additional thickness d_swellfor the deposited doped dielectric material 46, compared with the reference undoped dielectric material 46_ref. While this is directly observable at the upper surface, it is expected that additional density will accumulate at the sides where the deposited doped dielectric material 46 is in contact with the conformal sacrificial layer 42 as well.

Yet a further benefit of the lithium, beryllium, or boron doping is believed to be improved temperature stability. This is because Si—B—C—N compounds typically have higher specific strength-temperature characteristic than Si—C—N compounds.

With reference to FIG. 7, these beneficial effects were demonstrated experimentally as follows. As indicated at the bottom of FIG. 7, samples were prepared by: (A) starting with a silicon wafer; (B) deposit a SiCN dielectric layer; (C) perform boron implantation to dope with boron (except for the “DMY fin only” sample); and (D) perform etching in accord with the etch step 34 of FIG. 1. Transmission electron microscopy (TEM) was used to measure the SiCN thickness before and after the etch step (D). The plot of FIG. 7 shows the results for four samples: DMY fin only (here the B implantation step (C) was skipped); and B-doped-1, B-doped-2, and B-doped-3 samples with successively increasing B concentration (in the range 10¹³-10¹⁸atoms/cm³). In the plot of FIG. 7, the lefthand bar for each sample is the TEM-measured thickness before the etch step (D), and the righthand bar is the TEM-measured thickness after the etch step (D). The thickness scale is shown on the left of the plot (range 315-345 nanometers). The difference in height between the lefthand bar (thickness before etch) and the righthand bar (thickness after etch) is the etch loss, which is also indicated in the plot by points connected by a line. The etch loss scale is shown on the right of the plot (range −2.0 to 16 nanometers).

As can be seen in FIG. 7, there is about 13 nanometers of etch loss for the DMY fin only sample which received no boron doping. The B-doped-1, B-doped-2, and B-doped-3 samples show decreasing etch loss with increasing boron concentration, with the highest boron concentration B-doped-3 sample showing no etch loss at all (actually a thickness gain after etching is shown, but this “increase” is under 1 nanometer and is believed to be within the margin of error of the TEM thickness measurement). This demonstrates that the boron doping protects against etch loss.

As can be further seen in FIG. 7, the before-etch thickness increases with increasing boron concentration, from around 323 nanometers for the undoped sample (DMY fin only) to about 340 nanometers for the B-doped-3 sample. This is believed to reflect the swell thickness increase d_swellindicated in FIG. 2.

FIG. 7 presents results for boron doping. However, it is expected that similar benefits will be attainable with lithium doping or with beryllium doping. This is because lithium, beryllium, and boron are similarly sized atoms (atomic number Z being Z=3, Z=4, and Z=5 for lithium, beryllium, and boron respectively) so that lithium and beryllium should also be interstitial dopants in Si_1-x-yC_xN_y. Additionally, while boron reacts with oxygen to form B₂O₃, lithium similarly reacts with oxygen to form Li₂O and beryllium similarly reacts with oxygen to form BeO. Hence, lithium or beryllium dopant atoms at or near the surface of the dielectric material or at or near an interface with another material are expected to react with oxygen form a protective surface oxide that prevents further ingress of oxygen into the deposited doped dielectric material 46. The protective Li₂O or BeO is also expected to provide surface swell. Hence, the experimental results for boron doping presented in FIG. 7 are expected to also be achievable with lithium or beryllium doping.

As a nonlimiting illustrative quantitative example, the 3D conductive channels