TW201405779A - Semiconductor device and method of fabricating the same - Google Patents

Abstract

A semiconductor device includes a semiconductor substrate, two floating gates, a control gate and a first dielectric layer. The two floating gates are disposed on the substrate, the control gate partially overlaps each of the floating gates, and a part of the control gate is disposed between the two floating gates. Furthermore, the first dielectric layer disposed between the floating gates and the control gate has a fixed thickness.

Description

Semiconductor device and method of fabricating the same

The present invention relates to a semiconductor device and a method of fabricating the same, and more particularly to a semiconductor device having a high gate coupling ratio (GCR) and a method of fabricating the same.

Flash memory is a non-volatile memory that retains the information stored in memory in the absence of an external power supply. In recent years, flash memory has been widely used in mobile phones, digital cameras, and video players because of its rewritable and rewritable advantages. ), an electronic product such as a personal digital assistant (PDA) or a system on a chip (SOC) under development.

However, due to the trend toward miniaturization of electronic products, the size of the flash memory cell is reduced, resulting in a decrease in the gate coupling ratio (GCR). Therefore, how to improve the gate coupling value to improve the electrical performance of the flash memory cell is a problem that the related art desires to improve.

It is an object of the present invention to provide a semiconductor device having a high gate coupling value and a method of fabricating the same to improve the performance of the semiconductor device.

A preferred embodiment of the present invention provides a semiconductor device comprising: a semiconductor substrate, two floating gates, a control gate, and a first dielectric layer. The two floating gates are disposed on the semiconductor substrate, wherein the control gate partially overlaps the floating gates, and the partial control gates are located between the two floating gates. In addition, the first dielectric layer is disposed between the two floating gates and the control gate, and the first dielectric layer has a fixed thickness.

Another preferred embodiment of the present invention provides a method of fabricating a semiconductor device comprising the following steps. First, a gate dielectric layer and a first gate layer are sequentially formed on a semiconductor substrate, and the gate dielectric layer is located between the first gate layer and the semiconductor substrate. Next, at least one opening is formed in the first gate layer. Then, a dielectric layer is formed on the semiconductor substrate in a comprehensive manner, and the dielectric layer covers the first gate layer. Subsequently, a second gate layer is formed to fill the opening and overlap the first gate layer.

The present invention provides a T-shaped control gate so that the control gate can simultaneously overlap the top surface and a side surface of the two floating gates, compared with the structure in which the control gate overlaps only the top surface of a floating gate. The structural design of the control gate of the present invention can increase the overlap area between the floating gate and the control gate to increase the gate coupling value, thereby reducing the operating voltage of the semiconductor device and improving the performance of the semiconductor device. In addition, a first dielectric layer is integrally disposed between each of the floating gates and the control gate, and the first dielectric layer has a fixed thickness, so that each of the floating gates and the control gates can be The pitch is a fixed value, which in turn results in a stable capacitance value.

The present invention will be further understood by those of ordinary skill in the art to which the present invention pertains. .

Please refer to Figure 1. FIG. 1 is a cross-sectional view showing a semiconductor device according to an embodiment of the present invention. As shown in FIG. 1, the semiconductor device 10, taking a flash memory cell as an example, includes a semiconductor substrate 12, a gate stack 14 disposed on the semiconductor substrate 12, and a select gate 20 setting. On the side of the gate stack 14, wherein the gate stack 14 includes a floating gate 16 and a control gate 18. The semiconductor substrate 12 can comprise, for example, a substrate comprised of germanium, gallium arsenide, a blanket insulating (SOI) layer, an epitaxial layer, a germanium layer, or other semiconductor substrate material. The floating gate 16, the control gate 18, and the selection gate 20 are typically constructed of polysilicon. Dielectric layers 22/24/26, such as oxide layers, may be disposed between the gates to electrically insulate each other. The semiconductor device 10 further includes a source/drain doping region 28/30 disposed in the semiconductor substrate 12 on both sides of the gate stack 14, and a channel region 32 defined in the source/drain doping region 28/30. In the semiconductor substrate 12 between. In addition, the dielectric layer 22 between the floating gate 16 and the semiconductor substrate 12 is a tunneling oxide layer through which the hot electrons tunneling into and out of the floating layer. The gate 16 functions to access the data of the semiconductor device 10.

In general, the gate coupling ratio (GCR) is one of the important indicators for determining the performance of a flash memory cell. The higher the gate coupling value is, the flash memory. The lower the operating voltage required for the unit to perform a write or erase operation, the better the performance. The gate coupling value can be defined as: GCR=C1/(C1+C2)

The capacitance between the floating gate 16 and the control gate 18 is C1, and the capacitance between the floating gate 16 and the channel region 32 in the semiconductor substrate 12 is C2. It can be seen from the above relationship that the method of increasing the GCR can increase C1 and/or reduce C2. For example, since the capacitance is proportional to the overlapping area of the formed capacitance, the floating gate 16 and the control gate can be increased by The overlap area between 18s increases C1 and increases the gate coupling value.

In order to increase the gate coupling value, the present invention provides a semiconductor device. Please refer to FIG. 2 and FIG. FIG. 2 is a schematic view showing the layout of a semiconductor device according to a preferred embodiment of the present invention. Figure 3 is a cross-sectional view of the semiconductor device of the preferred embodiment of the present invention taken along line A-A' of Figure 2; 2 is a top view, in order to clearly express the relative relationship of the main elements, the elements partially labeled in FIG. 3 are not shown in FIG. 2.

As shown in FIGS. 2 and 3, the semiconductor device 100 includes a flash memory cell 104, a gate dielectric layer 104, at least two floating gates 106, and a first dielectric layer. 108 and a control gate 110 are sequentially disposed on a semiconductor substrate 102. The semiconductor substrate 102 can comprise, for example, a substrate comprised of germanium, gallium arsenide, a germanium-on-insulator (SOI) layer, an epitaxial layer, a germanium layer, or other semiconductor substrate material. The gate dielectric layer 104 and the first dielectric layer 108 may be composed of a dielectric material, including germanium. An oxide, oxynitride or a high-k dielectric layer having a dielectric constant greater than 4, wherein a gate dielectric layer 104 is disposed between each of the floating gates 106 and the semiconductor substrate 102 to serve as a tunneling oxide layer The hot electrons are tunneled into and out of the floating gate 106 via the gate dielectric layer 104 to achieve the data access function of the semiconductor device 100; and the first dielectric layer 108 is disposed on the two floating gates 106 and the control gate. Between the poles 110, it may be a single layer structure or a multilayer structure composed of, for example, an oxide-nitride-oxide (ONO) laminate, which can serve as an oxide layer between the gates to provide electrical insulation. . The floating gate 106 and the control gate 110 may each be composed of a conductive material, including a polysilicon, a metal halide or a metal material having a specific work function, wherein the floating gate 106 can be used to store hot electrons, and the gate 110 is controlled. A function that can be used to control data access of the semiconductor device 100.

It should be noted that the control gate 110 is a T-shaped control gate, and the control gate 110 partially overlaps the two floating gates 106 and is located between the two floating gates 106, that is, the control gate. The pole 110 can simultaneously overlap a portion of the top surface of each of the floating gates 106, the opposite side S1/S2 of the two floating gates 106, and the semiconductor substrate 102 between the two floating gates 106. Therefore, in the semiconductor device 100, the control gate 110 overlaps not only the top surface of the two floating gates 106 in the first direction D1 (the top surface of the floating gate 16 overlaps the control gate 18). Similarly, the control gate 110 may also overlap the opposite side S1/S2 of the two floating gates 106 in the second direction D2 to increase the overlapping area of the floating gate 106 and the control gate 110 to increase the gate coupling value. .

In addition, in the semiconductor device 100, each of the floating gates 106 and the control gate 110 Only the first dielectric layer 108 is disposed between the first dielectric layer 108 and the first dielectric layer 108 is disposed on each of the floating gates 106 and the semiconductor substrate 102. In more detail, the first dielectric layer 108 contacts a top surface of each floating gate 106, one side S1/S2 of each floating gate 106, a bottom surface of the control gate 110, and an overlapping two floating gates 106. The semiconductor substrate 102 is between, and the side surfaces S1/S2 of the floating gates 106 that the first dielectric layer 108 contacts are facing each other. In other embodiments, the first dielectric layer 108 disposed between the control gate 110 and the two floating gates 106 may also directly contact the semiconductor substrate 102. In addition, in the embodiment, the surfaces of the first dielectric layer 108 and the contact floating gate 106 are parallel to each other, and the first dielectric layer 108 has a fixed thickness, so that the floating gates 106 and the control can be controlled. One of the gates 110 has a fixed pitch.

The semiconductor device 100 further includes two selective gates 112 disposed on one side of each of the floating gates 106 and the control gates 110. The select gate 112 is composed of a conductive material and may include polysilicon, metal germanide or a metal material having a specific work function for assisting in controlling the data access function of the semiconductor device 100. The select gate 20 of the semiconductor device 10 has an arcuate surface. In this embodiment, each of the select gates 112 of the semiconductor device 100 has a flat top surface parallel to a top surface of each of the floating gates 106 and A top surface of the gate 110 is controlled and has an inverted L shape to partially overlap the corresponding floating gates 106, that is, each of the selection gates 112 can overlap the corresponding floating gates 106. The corner A1/A2 and part of the top surface. When the semiconductor device 100, for example, the flash memory cell performs the erase operation, part of the hot electrons stored in the floating gate 106 can be released through the selection gate 112 through the corners A1/A2, which helps to reduce The operating voltage and processing time required for the erase operation of the semiconductor device 100 are performed.

In addition, the second dielectric layers 114 are respectively disposed between the selection gates 112 and the floating gates 106 and between the selection gates 112 and the control gates 110, and serve as an oxide layer between the gates to provide electricity. The insulating effect, wherein the gate dielectric layer 104, the first dielectric layer 108, and each of the second dielectric layers 114 collectively surround the corresponding floating gates 106.

Also, a first doped region 116 and two second doped regions 118 can be used as the source/drain doping region of the semiconductor device 100, wherein the first doped region 116 is disposed between the two floating gates 106. In the semiconductor substrate 102, that is, the control gate 110 will overlap the first doping region 116; and the second second doping regions 118 are respectively disposed on the floating gate 106 relative to the first doping region 116. In the semiconductor substrate 102 on the other side, that is, the two second doping regions 118 are respectively disposed in the semiconductor substrate 102 on both sides of the two floating gates 106. In this embodiment, the first doping region 116 can be electrically connected to a source line (SL), and the second doping regions 118 can be electrically connected to a bit line, respectively. BL). In addition, the two sidewalls 120 of the dielectric material may be respectively disposed on the semiconductor substrate 102 between the selection gate 112 and each of the second doping regions 118, and may be used to adjust the first doping region 116 and the second doping. The pitch of the regions 118, i.e., the length of the electron channel, also prevents signals applied to the select gate 112 and the second doped region 118 from interfering with each other.

Please refer to Table 1, and please refer to Figure 3 together. Table 1 shows a reference table of operating conditions of a semiconductor device according to a preferred embodiment of the present invention. As shown in Table 1, when the semiconductor device 100 is in different operating states including programming, erasing, or reading, different signals are respectively applied to each terminal including selection. Gate 112. The second doped region 118 electrically connected to the one bit line BL, the first doping region 116 electrically connected to the source line SL or the control gate 110 to complete the corresponding operation. For example, when the semiconductor device 100 is selected for a programming operation, a first positive potential, such as +8 volts (V), is applied to the control gate 110 to capacitively couple the first positive potential to the floating gate 110. The gate 106 is further provided. Further, a second positive potential such as +2.5 V is applied to the selection gate 112, and a third positive potential such as +4.5 V is applied to the source line SL, that is, to the first doping. A region 116, and a current such as +1 milliamperes (μA) are applied to the bit line BL, that is, to the second doping region 118 to be common to the first doping region 116 and the second doping region 118. The hot electrons are formed in the channel region, and by controlling the potential difference formed between the gate 110 and the channel region, an electric field across the gate dielectric layer 104 is formed so that the hot electrons can pass over the gate dielectric layer 104 to enter the floating region. In the gate 106, the write operation is completed. When the semiconductor device 100 is not performing a write operation together with other semiconductor devices (not shown), that is, when the semiconductor device 100 is not selected for a write operation, a same voltage Vcc can be applied to the control gate 110 and the bit. The source line BL, and the selection gate 112 and the source line SL can be grounded to maintain a potential of 0V.

The present invention also provides a method of fabricating a semiconductor device to form the above-described semiconductor device. Please refer to FIGS. 4 to 14. 4 to 14 are schematic views showing a method of fabricating a semiconductor device in accordance with a preferred embodiment of the present invention. As shown in FIG. 4, first, a gate dielectric layer 202 and a first gate layer 204 are sequentially formed on a semiconductor substrate 200. The semiconductor substrate 200 may include, for example, germanium, gallium arsenide, and germanium. A substrate composed of an insulating (SOI) layer, an epitaxial layer, a germanium layer, or other semiconductor substrate material. The gate dielectric layer 202 is composed of a dielectric material, including tantalum oxide, nitrogen oxide or a high dielectric constant dielectric layer having a dielectric constant greater than 4, which can be subjected to a thermal oxidation process or a chemical vapor deposition. , CVD) or atomic layer deposition (ALD) deposition processes are formed. In this embodiment, the gate dielectric layer 202 is composed of cerium oxide formed by a thermal oxidation process. The first gate layer 204 may be composed of a conductive material, including polycrystalline germanium, metal germanide or a metal material having a specific work function, for example, a low pressure chemical vapor deposition (LPCVD) process or a plasma enhanced chemical gas. Polycrystalline germanium formed by deposition processes such as plasma-enhanced CVD (PECVD) processes, and in-situ doped polysilicon in the deposition process as required.

In addition, to define an active region formed by the first gate layer 204 and the gate dielectric layer 202, as shown in FIG. 5, before the gate dielectric layer 202 and the first gate layer 204 are formed, A plurality of shallow trench isolation (STI) 206 protruding from the surface of the semiconductor substrate 200 may be formed first, wherein the cross-sectional direction D3 of FIG. 4 and the cross-sectional direction D4 of FIG. 5 are perpendicular to each other. Then, the gate dielectric layer 202 and the first gate layer 204 are sequentially formed on the semiconductor substrate 200 as described above, and then a planarization process removal portion such as chemical mechanical polishing (CMP) is performed. The first gate layer 204 defines a plurality of active regions that are predetermined to form a semiconductor device. That is, a portion of the shallow trench isolation 206 protruding from the semiconductor substrate 200 can define the first gate layer 204 and the gate dielectric layer 202. The mask. Shallow trench isolation 206 typically comprises a dielectric material, such as tantalum oxide, and the method of forming shallow trench isolation 206 is well known to those skilled in the art and will not be described herein, and shallow trench isolation 206 The shape, position and order of formation are not limited to this.

Subsequently, as shown in FIG. 6, at least one opening 208 is formed in the first gate layer 204, wherein the opening 208 exposes a portion of the gate dielectric layer 202 and the semiconductor substrate 200 is not exposed. After the opening 208 is formed, an ion implantation process is performed to form a first doped region 210 in the semiconductor substrate 200 under the gate dielectric layer 202 exposed by the opening 208 as a source of a subsequently formed semiconductor device/ Bungee doped area. In this embodiment, the first doping region 210 is electrically connected to a source line (SL). The method of forming the opening 208 includes forming a patterned mask (not shown) on the first gate layer 204, and performing an etching process, such as an anisotropic etching process, or performing a wet etching process. The etchant preferably has a selectivity to the material of the first gate layer 204 and the material of the gate dielectric layer 202 to remove portions of the first gate layer 204 to expose the gate dielectric layer 202.

Next, as shown in FIG. 7 and FIG. 8 , a first dielectric layer 212 is first formed on the semiconductor substrate 200 , wherein the first dielectric layer 212 covers the first gate layer 204 and the opening 208 is exposed. The gate dielectric layer 202, and the exposed shallow trench isolation 206. The first dielectric layer 212 is a single layer structure or a multilayer structure composed of a dielectric material, for example, formed by a thermal oxidation process, a thermal nitridation process, a plasma enhanced chemical vapor deposition process, or a low pressure chemical vapor deposition process. An oxide-nitride-oxide (ONO) stack. Next, a second gate layer 214 is formed to fill the opening 208 and overlap the first gate layer 204. The second gate layer 214 may include a conductive material such as polysilicon, metal germanide or a metal material having a specific work function, for example, A polycrystalline germanium formed by a deposition process such as a low pressure chemical vapor deposition process or a plasma enhanced chemical vapor deposition process. Then, a mask layer 216 is formed on the second gate layer 214. The mask layer 216 is a single layer structure or a multilayer structure composed of an oxidation resistant material, for example, a tantalum nitride layer formed by a chemical vapor deposition process. , or a composite layer composed of cerium oxide and cerium oxide.

As shown in FIG. 9, the mask layer 216, the second gate layer 214, and the first dielectric layer 212 are patterned to form a control gate 218, and the patterning method thereof may include the following steps. First, the patterned mask layer 216 ′ is formed by a lithography process, and the mask layer 216 ′ is used as a mask to perform an etching process, for example, an anisotropic etching process to remove a portion of the second gate. Layer 214 and a portion of the first dielectric layer 212; or additionally forming a patterned mask (not shown) for performing an etching process to remove a portion of the patterned mask layer 216, a portion of the second gate layer 214, and portions A dielectric layer 212 causes the remaining second gate layer 214 to form a control gate 218. In addition, a portion of the first dielectric layer 212' may be selectively retained, For example, the bottom oxide layer in the ONO stack is on the first gate layer 204 to avoid damage to the surface of the first gate layer 204 when the control gate 218 is processed.

Then, as shown in FIG. 10, a portion of the first gate layer 204 is removed to form two floating gates 220A/220B, the method of which may include the following steps. First, the two sacrificial sidewalls 222A/222B are formed around the control gate 218. The sacrificial sidewalls 222A/222B may be a single layer or a multi-layer structure, or may include a liner or the like. In addition, the sacrificial sidewalls 222A The material of /222B may include high temperature oxide (HTO), tantalum nitride, hafnium oxide or tantalum nitride (HCD-SiN) formed using hexachlorodisilane (Si ₂ Cl ₆ ), but not This is limited to this. The method of forming the sacrificial sidewalls 222A/222B is a conventional technique and will not be described herein. Next, the control gate 218 and the sacrificial sidewalls 222A/222B are used as masks to remove portions of the first gate layer 204 to form two floating gates 220A/220B, and the control gate 218 partially overlaps the two floating gates. The poles 220A/220B, in more detail, the control gate 218 may partially overlap the top surface of each of the floating gates 220A/220B and the opposite inner side S3/S4 of the two floating gates 220A/220B. In addition, the opposite outer sides S5/S6 of the two floating gates 220A/220B are etched by using the sacrificial sidewalls 222A/222B as a mask to define, that is, etched in a self-aligned manner.

Next, as shown in FIG. 11, the sacrificial sidewalls 222A/222B are removed to expose the top surface of the floating gates 220A/220B covered by the original sacrificial sidewalls 222A/222B, including the floating gates 220A/220B. A corner A3/A4. Wherein, the top surface area of the floating gate 220A/220B covered by the sacrificial sidewall 222A/222B is positively correlated with self-alignment The bottom area of the sacrificial sidewalls 222A/222B is formed. Accordingly, a gate stack structure 224 including a gate dielectric layer 202, two floating gates 220A/220B, a first dielectric layer 212, and a control gate 218 is formed. In addition, doped regions 226 may be selectively formed in the semiconductor substrate 200 on both sides of the gate stack structure 224 prior to forming subsequent select gates to adjust the electrical performance of the subsequently formed select gates.

As shown in FIG. 12, the second dielectric layer 228A/228B composed of the high temperature yttrium oxide formed by the thermal oxidation process is then further formed by the deposition process to form the third gate layer 230 to cover the patterned mask layer. 216', the second dielectric layer 228A/228B, and the two sides of the gate stack structure 224. The third gate layer 230 may include polysilicon, metal germanide, or a metal material having a specific work function, such as a polysilicon formed by a deposition process. Subsequently, as shown in FIG. 13, a portion of the third gate layer 230 is removed to form two select gates 232A/232B disposed on opposite sides of the gate stack structure 224, respectively. The method of forming the selection gates 232A/232B includes the following steps. First, the third gate layer 230 is subjected to a planarization process such as etching back until the patterned mask layer 216' is exposed to define the height of the selected gate 232A/232B formed and the selection gates 232A/232B respectively. There is a flat top surface; a lithography and etching process is then performed to complete the select gates 232A/232B and define the size and width of the select gates 232A/232B. Accordingly, each of the selection gates 232A/232B has a flat top surface and an inverted L-shaped structure, and partially overlaps the corresponding floating gates 220A/220B, respectively, and the overlapping portions are the sacrificial sidewalls. The area covered by the sub-222A/222B.

In this embodiment, the second dielectric layer 228A/228B is a polysilicon layer inter-layer oxidation. An inter-poly oxide (IPO) is disposed between the third gate layer 230 and each of the floating gates 220A/220B and between the third gate layer 230 and the control gate 218 to provide an electrical insulating effect. And the second dielectric layer 228A/228B does not cover the top surface of the control gate 218. Thus, the gate dielectric layer 202, the first dielectric layer 212, and the second dielectric layers 228A/228B can collectively surround the corresponding floating gates 220A/220B.

In this embodiment, the control gate 218, the floating gate 220A/220B, and the selection gate 232A/232B are all formed by using polysilicon, so it is necessary to shield and protect the patterned mask layer 216'. The patterning process of the control gate 218 of FIG. 9 , the process of forming the sidewall spacers 222A/222B and the patterned floating gate 220A/220B of FIG. 10, and the etching process of the third gate layer 230 of FIG. 13 And the patterning process of selecting gate 232A/232B. Therefore, after the above process is completed, the patterned mask layer 216' can be selectively removed.

After removing the patterned mask layer 216', as shown in FIG. 14, after the two sidewall spacers 234A/234B are formed outside the respective selection gates 232A/232B, an ion implantation process is performed to form two second dopings. Regions 236A/236B are in semiconductor substrate 200 on either side of gate stack structure 224. In this embodiment, the second and second doping regions 236A/236B can serve as source/drain doping regions and are electrically connected to a bit line (BL), respectively. So far, the semiconductor device 238 of the present invention has been completed.

The selection of the gate and the second dielectric layer of the present invention is not limited to the above embodiment. In other embodiments, the gate and the second dielectric layer may also be fabricated by other methods. The method forms structures of different shapes. Other preferred embodiments of the present invention will be described in the following, and in order to facilitate the comparison of the various embodiments and the simplification of the description, the same elements are denoted by the same symbols in the following embodiments, and mainly for each implementation. The differences between the examples are explained, and the repeated parts are not described again.

Please refer to Figures 15 to 19. 15 to 19 are schematic views showing a method of fabricating a semiconductor device according to another preferred embodiment of the present invention. First, the method of fabricating the semiconductor device described above is performed to form a stacked structure as shown in FIGS. 7 and 8, and then, as shown in FIG. 15, the patterned mask layer 216, the second gate layer 214, and the first A dielectric layer 212, a first gate layer 204, and a gate dielectric layer 202 to form a patterned mask layer 310, a control gate 308, and two floating gates 306, and control the side S7 of the gate 308 The opposite outer sides S9/S10 of S8 and the two floating gates 306 are aligned with each other. The patterning method can include the following steps. First, the patterned mask layer 310 is formed by a lithography process, and the mask layer 310 is used as a mask to perform an etching process, for example, an anisotropic etching process to partially remove the second gate layer 214. (forming control gate 308), first dielectric layer 212, first gate layer 204 (forming two floating gates 306), and gate dielectric layer 202; or additionally forming a patterned mask (not shown) The etching process is performed to partially remove the mask layer 216, the second gate layer 214, the first dielectric layer 212, the first gate layer 204, and the gate dielectric layer 202. In addition, the control gate 308, the first dielectric layer 212, the two floating gates 306, and the gate dielectric layer 202 covered by the patterned mask layer 310 may be collectively defined as a gate stack structure 311.

Subsequently, two sidewalls 312 are formed on the sidewalls of the gate stack structure 311. The sidewall spacers 312 may be a single layer or a multilayer structure, or may include a liner or the like. Further, the material of the sidewall spacers 312 may include high temperature yttrium oxide. (high temperature oxide, HTO), tantalum nitride, hafnium oxide or tantalum nitride (HCD-SiN) formed using hexachlorodisilane (Si ₂ Cl ₆ ), but not limited thereto. In the present embodiment, the sidewall spacers 312 are preferably a planar stacked structure composed of a plurality of materials having different etching rates for the same etching solution, such as a liner-tantalum nitride-yttria. The method of forming the sidewall spacers 312 is a conventional technique and will not be described herein.

Next, as shown in FIG. 16, doped regions 313 are selectively formed in the semiconductor substrate 200 on both sides of the gate stack structure 311 to adjust the electrical performance of the subsequently formed select gates. Then, an etching step is performed to remove a portion of the sidewall spacer 312 and a native oxide (not shown) on the surface of the semiconductor substrate 200 to expose the semiconductor substrate 200 on both sides of the remaining sidewall sub-312'. Wherein, the remaining sidewall spacers 312' may be a structure including a liner-tantalum nitride.

Next, as shown in FIG. 17, a dielectric layer 314 is formed, for example, by forming a yttrium oxide layer on the bare semiconductor substrate 200 through a thermal oxidation process, and forming a third gate layer 316 to cover the patterned mask through the deposition process. A cap layer 310, remaining sidewalls 312', and a dielectric layer 314. The third gate layer 316 may comprise polysilicon, metal telluride or a metal material having a specific work function, such as polysilicon formed using a deposition process.

Thereafter, as shown in FIG. 18, a portion of the third gate layer 316 and a portion of the dielectric layer 314 are removed to form two gates 302 that are respectively disposed on the gate stack structure 311. Side, in addition, the remaining dielectric layer 314' and the remaining sidewalls 312' may be used together as the second dielectric layer 304. The method for forming the selection gate 302 includes a planarization process such as etching back and a lithography and etching process as described above to determine the height and width of the selection gate 302, respectively, and details are not described herein. It should be noted that since the remaining dielectric layer 314' and the remaining sidewalls 312' are formed through different processes, the thickness of the second dielectric layer 304 is not in principle a fixed value. That is, the thickness of the vertical portion of the second dielectric layer 304 (consisting of the remaining sidewalls 312') is substantially not equal to the horizontal portion of the second dielectric layer 304 (by the remaining dielectric layer 314' The thickness of the composition).

Subsequently, as shown in FIG. 19, the patterned mask layer 310 is removed, and two sidewall spacers 318 are formed on the outer sides of the respective selection gates 302, and then an ion implantation process is performed to form the second second doping regions 320. On both sides of the gate stack structure 311, the second doping region 320 can serve as a source/drain doping region and are electrically connected to a bit line (BL), respectively. Thus far, the semiconductor device 300 of the present invention has been completed.

Please continue to refer to Figure 19. Compared with the semiconductor device 100 shown in FIG. 3 , the material and the relative position of the selection gate 302 of the semiconductor device 300 (the side disposed on each of the floating gate 306 and the control gate 308 ) are the same as the semiconductor device 100 . The selection gate 112 is similar. The difference is that, in this embodiment, the sides of the control gate 308 are aligned with the opposite outer sides of the two floating gates 306, and the selection gates 302 have a strip-shaped cross section and are not partially overlapped and floated. The gate 306, in addition, the thickness of the second dielectric layer 304 is not a fixed value, such as the pitch of each of the select gates 302 and the corresponding floating gates 306 or the control gates 308 and T-shaped control gates 308. Spacing will be associated with each select gate 302 The pitch of the semiconductor substrate 102 is different, that is, the thickness of the second dielectric layer 304 in the second direction D2 is different from the thickness of the second dielectric layer 304 in the first direction D1.

Please refer to Table 2. Table 2 lists the operating condition reference table of the semiconductor device in the selected state according to another preferred embodiment of the present invention. As shown in Table 2, when the semiconductor device 300 is selected and in different operating states including writing, erasing or reading, different signals are respectively applied to the respective terminals including the selection gate 302 and the electrical connection. a second doped region 320 to a single line, a first doped region 210 electrically connected to the source line, a control gate 308, or an electrical connection to an end of the semiconductor substrate 200 to perform a corresponding operation . It should be noted that in the present embodiment, the pitch of the selection gate 302 and the semiconductor substrate 200 of the semiconductor device 300 as shown in FIG. 19 (the thickness of the second dielectric layer 304 in the first direction D1) is substantially The upper side is smaller than the pitch of the selection gate 112 of the semiconductor device 100 and the semiconductor substrate 102 as shown in FIG. 3 (the thickness of the second dielectric layer 114 in the first direction D1), thereby contributing to the reduction of the semiconductor device 300, for example. : The operating voltage required for the flash memory unit to perform a read operation. In addition, when the semiconductor device 300 is selected for the erase operation, an electric field across the gate dielectric layer 202 can be formed by controlling the potential difference between the gate 308 and the semiconductor substrate 200, and through the Fullerhan The Fowler-Nordheim tunneling (FN tunneling) mechanism allows hot electrons stored in the floating gate 306 to be released from the semiconductor substrate 200 across the gate dielectric layer 202 to complete the erase operation.

In summary, the present invention allows the control gate to simultaneously overlap the top surface and the side surface of the two floating gates by a T-shaped control gate, and only overlaps the top of the floating gate with the control gate. Compared with the structure of the surface, the structure design of the control gate of the present invention can increase the overlapping area between the floating gate and the control gate to increase the gate coupling value, thereby reducing the operating voltage of the semiconductor device and improving the performance of the semiconductor device. . In addition, a first dielectric layer is integrally disposed between each of the floating gates and the control gate, and the first dielectric layer has a fixed thickness, so that each of the floating gates and the control gates can be The pitch is a fixed value, which in turn results in a stable capacitance value.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

10,100,238,300‧‧‧ semiconductor devices

12,102,200‧‧‧Semiconductor substrate

14‧‧‧gate stacking

16,106,220A,220B,306‧‧‧Floating gate

18,110,218,308‧‧‧Control gate

20,112,232A,232B,302‧‧‧Select gate

22,24,26,314,314'‧‧‧ dielectric layer

28, 30‧‧‧ source/drain doping

32‧‧‧Channel area

104,202‧‧‧ gate dielectric layer

108,212,212'‧‧‧First dielectric layer

114,228A, 228B, 304‧‧‧Second dielectric layer

116,210‧‧‧First doped area

118,236A, 236B, 320‧‧‧Second doped area

120,234A, 234B, 312, 312', 318‧‧‧ Sidewall

204‧‧‧First gate layer

206‧‧‧Shallow trench isolation

208‧‧‧ openings

214‧‧‧second gate layer

216‧‧‧ mask layer

216', 310‧‧‧ patterned mask layer

222A, 222B‧‧‧ Sacrifice side wall

224,311‧‧‧ gate stack structure

226,313‧‧‧Doped area

230, 316‧‧‧ third gate layer

A1, A2, A3, A4‧‧‧ corner

BL‧‧‧ bit line

C1, C2‧‧‧ capacitor

D1‧‧‧ first direction

D2‧‧‧ second direction

D3, D4‧‧‧ section direction

S1, S2‧‧‧ side

S3, S4‧‧‧ inside

S5, S6, S9, S10‧‧‧ outside

S7, S8‧‧‧ side

SL‧‧‧ source line

FIG. 1 is a cross-sectional view showing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a schematic view showing the layout of a semiconductor device according to a preferred embodiment of the present invention.

Figure 3 is a cross-sectional view of the semiconductor device of the preferred embodiment of the present invention taken along line A-A' of Figure 2;

4 to 14 are schematic views showing a method of fabricating a semiconductor device in accordance with a preferred embodiment of the present invention.

15 to 19 are schematic views showing a method of fabricating a semiconductor device according to another preferred embodiment of the present invention.

100‧‧‧Semiconductor device

102‧‧‧Semiconductor substrate

104‧‧‧ gate dielectric layer

106‧‧‧Floating gate

108‧‧‧First dielectric layer

110‧‧‧Control gate

112‧‧‧Select gate

114‧‧‧Second dielectric layer

116‧‧‧First doped area

118‧‧‧Second doped area

120‧‧‧ Sidewall

A1, A2‧‧‧ corner

BL‧‧‧ bit line

D1‧‧‧ first direction

D2‧‧‧ second direction

S1, S2‧‧‧ side

SL‧‧‧ source line

Claims (20)

A semiconductor device comprising: two floating gates disposed on a semiconductor substrate; a control gate partially overlapping the floating gates, and a portion of the control gates being located on the floating Between the gates; and a first dielectric layer disposed between the floating gate and the control gate, and the first dielectric layer has a fixed thickness. The semiconductor device of claim 1, wherein only the first dielectric layer is between the floating gate and the control gate, such that a distance between each of the floating gate and the control gate is fixed. value. The semiconductor device of claim 1, wherein the control gate is a T-shaped control gate. The semiconductor device of claim 1, wherein the first dielectric layer contacts a top surface of each of the floating gates, a side of each of the floating gates, and the semiconductor between the floating gates Substrate. The semiconductor device of claim 4, wherein the side faces of each of the floating gates in contact with the first dielectric layer face each other. The semiconductor device according to claim 1, wherein the control gate is disposed on the floating gate The first dielectric layer between the gates is in direct contact with the semiconductor substrate. The semiconductor device of claim 1, further comprising: a first doped region disposed in the semiconductor substrate between the floating gates, wherein the control gate overlaps the first doped region; The second doped regions are respectively disposed in the semiconductor substrate of each of the floating gates opposite to the other side of the first doped region. The semiconductor device of claim 1, further comprising: a gate dielectric layer respectively disposed between each of the floating gates and the semiconductor substrate; and two selection gates respectively disposed on the floating gates and the gate Controlling one side of the gate; and two second dielectric layers are respectively disposed between each of the selection gates and each of the floating gates and between the selection gates and the control gates, wherein the gates are The electrical layer, the first dielectric layer, and each of the second dielectric layers collectively surround each of the corresponding floating gates. The semiconductor device of claim 8, wherein each of the selection gates comprises an inverted L shape and partially overlaps each of the corresponding floating gates. The semiconductor device of claim 8 wherein each of the select gates has a flat top surface. The semiconductor device of claim 10, wherein the top surface of each of the selection gates is flat A top surface of each of the floating gates and a top surface of the control gate are disposed. The semiconductor device of claim 8, wherein each of the select gates comprises a strip profile and the floating gates are not partially overlapped. The semiconductor device of claim 8, wherein a thickness of each of the second dielectric layers is a non-fixed value. The semiconductor device of claim 8, wherein a distance between each of the selection gates and a corresponding one of the floating gates or a distance between each of the selection gates and the control gate is substantially different from each of the selection gates The distance between the pole and the semiconductor substrate. A method of fabricating a semiconductor device includes: sequentially forming a gate dielectric layer and a first gate layer on a semiconductor substrate, and the gate dielectric layer is located on the first gate layer and the semiconductor substrate Forming at least one opening in the first gate layer; forming a first dielectric layer on the semiconductor substrate in a comprehensive manner, and the first dielectric layer covers the first gate layer; and forming a second A gate layer fills the opening and overlaps the first gate layer. A method of fabricating a semiconductor device according to claim 15, wherein the opening exposes a portion of the gate dielectric layer and the semiconductor substrate is not exposed. The method of fabricating a semiconductor device of claim 15 further comprising forming a first doped region in the semiconductor substrate below the exposed gate dielectric layer of the opening. The method of fabricating a semiconductor device according to claim 15, further comprising: removing a portion of the second gate layer and a portion of the first gate layer to form a gate stack structure; forming two select gates respectively disposed on the gate device Two sides of the gate stack structure; and two second doped regions are formed in the semiconductor substrate on both sides of the gate stack structure. The method of fabricating a semiconductor device of claim 18, wherein the method of forming the gate stack structure further comprises: removing a portion of the second gate layer to form a control gate; forming two sacrificial sidewalls surrounding the Controlling the periphery of the gate; and using the control gate and the sacrificial sidewall as a mask to remove a portion of the first gate layer to form two floating gates, and the control gate partially overlaps the floating Gate. The method of fabricating a semiconductor device of claim 18, wherein the method of forming the gate stack structure further comprises: removing a portion of the second gate layer with the same mask to form a control gate and removing portions The first gate layer forms two floating gates, and the side edges of the control gate and the opposite outer sides of the floating gates are aligned with each other.