DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention now will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. Like reference numerals refer to like elements throughout.

[0024] Embodiments of the present invention will now be described in detail below with reference to FIGS. 4 through 15 , which illustrate various embodiments of the present invention, and various processes of fabricating embodiments of the present invention. In embodiments of the present invention, an integrated circuit device is provided that includes a conductive plug in a trench isolation structure that is electrically connected to the substrate through a trench floor that is at least partially devoid of an insulating layer. In other embodiments of the present invention, the trench floor may be completely or substantially devoid of an insulating layer. Thus, if a substrate is lightly doped with P-type impurities, the conductive plug and the substrate may form an ohmic contact. Therefore, a voltage applied to the substrate may be directly applied to the conductive plug in the trench making it is possible to achieve tight device isolation between the active regions having a source/drain region that is doped with n-type impurities. Thus, the present invention may reduce the occurrence of the inverse narrow width effect.

[0025] Referring to FIG. 4, a gate line is formed on an active region 13 in a cell area of a dynamic random access memory (DRAM) in accordance with the present invention. As illustrated in FIG. 5 , integrated circuit devices according to embodiments of the present invention will be described in further detail. As seen in both the cross section of the cell area and the peripheral circuit area of FIG. 5, a substrate 10 is provided having a face 40 . A trench is provided in the face 40 of the substrate 10 , which has a trench sidewall 45 and a trench floor 48 . Although embodiments of the present invention are described herein as having a single trench sidewall, such as in a circular or elliptical shaped trench, the present invention should not be limited to this configuration. For example, embodiments of the present invention may have two or more sidewalls, such as in a polygonal trench.

[0026] A first insulating layer 20 is provided on the trench sidewall 45 that exposes at least part of the trench floor 48 . The first insulating layer 20 may be a single layer of, for example, SiON. If the first insulating layer 20 includes a layer of SiON it may have a thickness of from about 10 Å to about 100 Å. Alternatively, the insulating layer 20 may include multiple layers of, for example, silicon oxide and silicon nitride. It will be understood that the first insulating layer 20 may include other materials that may perform the functions of the first insulating layer and should not be limited to the materials described above.

[0027] A conductive plug 31 is provided in the trench on the trench floor 48 . The conductive plug 31 has a plug top 50 opposite the trench floor 48 that is electrically connected to the substrate 10 at the trench floor 48 . The plug top 50 is recessed beneath the face 40 of the substrate 10 as illustrated in FIG. 5 . The conductive plug 31 may include, for example, polysilicon or metals having high work-function. If the conductive plug 31 includes polysilicon, the polysilicon may be heavily doped with p-type impurities. The conductive plug 31 may have a thickness of about 3000 Å.

[0028] A second insulating layer is provided on the top of the conductive plug. The second insulating layer may include, for example, a silicon nitride layer 33 . The silicon nitride layer 33 may have a thickness from about 10 Å to about 500 Å. The second insulating layer may further include a layer of silicon oxide 35 . As illustrated in FIG. 5 , the second insulating layer is on the plug top 50 and may extend onto the trench sidewall 45 between the plug top 50 and the face 40 of the substrate 10 . Alternatively, the second insulating layer may include a conformal insulating layer on the plug top 50 that is recessed beneath the face 40 of the substrate 10 and also extends onto the trench sidewall 45 between the plug top 50 and the face 40 of the substrate 10 . A chemical vapor deposition (CVD) silicon oxide layer may optionally be provided on the surface of the integrated circuit device (not shown).

[0029] Integrated circuit devices according to embodiments of the present invention may provide an advantage over conventional integrated circuit devices, for example, the integrated circuit of FIG. 3 . In particular, some embodiments of the present invention provide a conductive plug in a trench isolation structure that is electrically connected to the substrate through a trench floor that is at least partially devoid of an insulating layer. Alternatively, the trench floor may be completely or substantially devoid of an insulating layer. Thus, if a substrate is lightly doped with P-type impurities, the conductive plug and the substrate may form an ohmic contact. Therefore, a voltage applied to the substrate may be directly applied to the conductive plug in the trench. As a result, the conductive plug may have the same potential as the sidewall of the trench. Accordingly, it is possible to decrease the possibility of an inversion channel being formed at the upper sidewall of the trench, even though a subthreshold voltage may be applied to the gate. This may improve the inverse narrow width effect. In addition, the p-type impurities in the conductive plug may be diffused into the floor of the trench in a subsequent thermal process, thereby increasing the doping concentration of the substrate under the trench. Thus, it may be possible to achieve tight device isolation between the active regions 13 having a source/drain region (not shown) that is doped with n-type impurities.

[0030] Now referring to FIGS. 6A and 7A , aspects of conventional integrated circuits will be described. As illustrated in FIG. 6A, a voltage of a conventional integrated circuit is typically higher in both ends of a channel than in a middle of the channel. Furthermore, as illustrated in FIG. 7A, a hole concentration of a conventional device is higher in the middle than in the sides of the channel. In contrast, as illustrated in FIGS. 6B and 7B , a voltage of an integrated circuit according to embodiments of the present invention is higher in both ends of the channel than in the middle of the channel and a hole density of a device according to embodiments of the present invention is higher in both sides of the channel than in the middle of the channel.

[0031] In a memory device, current flows through a channel when one voltage is applied to a transistor drain through a bitline and another voltage is applied to a gate electrode. In a conventional transistor as shown in FIGS. 6A and 7A , current starts to flow at both ends of the channel before a voltage is sufficiently applied to a gate electrode. In contrast, according to embodiments of the present invention as shown in FIGS. 6B and 7B , a negative voltage may be applied to the inside of the trench. Thus, current may not flow at both ends of the channel before an operational voltage is sufficiently applied to the gate electrode. As a result, the inverse narrow width effect may be reduced. According to embodiments of the present invention, the insulating layer formed on the sidewall of the trench serves as a gate insulating layer of the lateral gate. Thus, an electric field which is transferred from an adjacent element through a device isolation layer in the prior art trench may be shielded from the device isolation layer in the present invention.

[0032] Now referring to FIG. 8, a chart that illustrates the difference between drain currents which flow at a given voltage applied to the gate electrode in the prior art (represented by triangular dots) and embodiments of the present invention (represented by black dots) will be described. As illustrated, according to embodiments of the present invention a drain current does not flow when the gate voltage is low. Furthermore, as illustrated in FIG. 9 , according to embodiments of the present invention, the narrower the channel width, the higher the threshold voltage. In contrast, in a conventional integrated circuit, the narrower the channel width, the lower the threshold voltage. The results exhibited by embodiments of the present invention are similar to the results of the LOCOS technique discussed above, i.e. the narrow width effect. The narrow width effect may be a tolerable matter in high-integration semiconductor devices because adjusting the polysilicon doping concentration in order to reduce the number of problems that affect the reliability of the integrated circuit easily controls it.

[0033] FIGS. 10 through 15 illustrate the fabrication of integrated circuits according to embodiments of the present invention. As seen in FIG. 10, a trench is formed in the face 40 of a silicon substrate 10 . A pad oxide layer 15 is formed on the substrate 10 and a silicon nitride layer 17 is formed on the pad oxide layer 15 . The silicon nitride layer 17 is relatively thicker than the pad oxide layer 15 . For example, the pad oxide layer 15 may have a thickness of about 10 Å to about 500 Å and the silicon nitride layer 17 may have a thickness of about 1,500 Å. An optional mask, i.e. a silicon oxide layer, and an anti-reflective layer for a photolithographic process may be formed on the silicon nitride layer 17 .

[0034] The trench may be formed in the face 40 of the substrate 10 . For example, the silicon nitride layer 17 and the pad oxide layer 15 may be patterned to form a mask using conventional photolithographic and etching processes known to those having skill in the art. The mask may be formed to expose a trench area in which a shallow trench isolation layer is formed. Using the mask, the substrate 10 may be etched through the mask a distance of thousands of angstroms, for example, 2500 Å, to form a trench. The trench in the face 40 of the substrate 10 has a trench sidewall 45 and a trench floor 48 .

[0035] Now referring to FIG. 11 , the trench sidewall 45 is annealed. This annealing process may cure the crystalline defects caused during the etching process. A first insulating layer 20 is formed on the trench sidewall 45 . Conventionally, the first insulating layer includes a thermal oxide layer formed by annealing and a silicon nitride layer formed on the thermal oxide layer. Alternatively, the first insulating layer may be formed of a single SiON layer to simplify the fabrication process. If a single SiON layer is utilized, the trench formed in the face 40 of the substrate 10 may be annealed at a temperature of about 850° C. in nitrogen ambient, forming an SiON layer on the exposed surface of the substrate 10 having a thickness of about 10 Å to about 100 Å. The first insulating layer 20 may be removed from at least part of the trench floor 48 , but the first insulating layer may remain on the trench sidewall 45 . The first insulating layer may be removed using an anisotropic etch.

[0036] Now referring to FIG. 12, a conductive plug 31 is formed in the trench on the trench floor 48 . The conductive plug 31 has a plug top 50 opposite the trench floor 48 . The conductive plug is electrically connected to the substrate 10 at the trench floor 48 through the portion of the trench floor 48 where the first insulating layer 20 has been removed. The plug top 50 is recessed beneath the face 40 of the substrate 10 . The conductive material may be formed on the entire surface of the device in FIG. 11 to a thickness of about 3,000 Å and then etched so that the conductive plug is recessed beneath the surface of the substrate 10 . In order to recess the conductive plug 31 , a full isotropic etch may be used using an etchant that has an etching selectivity with respect to the conductive plug 31 . If, for example, the conductive plug 31 is made of polysilicon, it may be doped with impurities by using an ambient containing an impurity gas. Alternatively, the entire surface of the substrate 10 may be doped with impurities after forming the conductive plug 31 . Thus, for example, boron ions may be implanted with 30 keV and dose of 1×10 ¹⁵ ions/cm ² .

[0037] The impurity concentration of the surface layer of the active region may be changed little because it is covered by the etching mask. However, a concentration of, for example, p-type impurities may be increased around the trench floor due to the fact that the conductive plug 31 is electrically connected to the substrate 10 without an insulating layer therebetween. This aspect of the present invention can lead to a tight device isolation between the n-type transistors due to the p-n junction made at the boundary between the source/drain region and impurity enhanced substrate around the trench floor. Such an effect may be regarded as similar to the conventional narrow width effect discussed above with respect to the LOCOS technique.

[0038] Now referring to FIG. 13, a second insulating layer may be formed on the surface of the structure in FIG. 12 . The second insulating layer may include a silicon nitride layer 33 . The silicon nitride layer 33 is formed on the top of the conductive plug and may have a thickness of about 10 Å to about 500 Å. The second insulating layer is formed on the top of the conductive plug and may extend onto the trench sidewall 45 . If the conductive plug 31 is formed of a polysilicon layer, the polysilicon layer may be heated and nitrified in a nitrogen-contained gas. The second insulating layer, for example, a silicon nitride layer 33 , may be formed on the top of the conductive plug 31 , and may serve as an oxygen barrier for preventing re-oxidation of the conductive plug 31 in a high temperature process of oxygen ambient.

[0039] Now referring to FIG. 14, a chemical vapor deposition (CVD) silicon oxide layer 35 may be formed on the structure of FIG. 13 , and planarized by way of a chemical mechanical polishing (CMP). As a result, a second insulating layer of a shallow trench isolation layer is completed. Thus, the second insulating layer may include both a silicon nitride layer 33 and a silicon oxide layer 35 . Now referring to FIG. 15 , identical to FIG. 5 , the mask layers such as silicon nitride layer 17 and silicon oxide layer 15 may be removed. Since mask layers include silicon nitride, the mask layers may be removed by means of a phosphate-contained etchant.

[0040] As discussed above, embodiments of the present invention can provide integrated circuit devices having a trench isolation structure that includes a conductive plug in the trench isolation structure that is electrically connected to the substrate through a trench floor that is at least partially devoid of an insulating layer. Thus, if a substrate is lightly doped with p-type impurities, the conductive plug and the substrate may form an ohmic contact. Therefore, a voltage applied to the substrate may be directly applied to the conductive plug in the trench making it is possible to achieve tight device isolation between the active regions having a source/drain region that is doped with n-type impurities. Accordingly, embodiments of the present invention may reduce the occurrence of the inverse narrow width effect.

[0041] In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.