TWI886793B - Transistor structure - Google Patents

Abstract

A transistor structure includes a gate, a spacer, a channel region, a first concave, and a first conductive region. The gate is above a silicon surface. The spacer is above the silicon surface and at least covers a sidewall of the gate. The channel region is under the silicon surface. The first conductive region is at least partially formed in the first concave, wherein a conductive region of a neighborhood transistor structure next to the transistor structure is at least partially formed in the first concave.

Description

Transistor structure

The present invention relates to a transistor structure, in particular to a transistor structure with low leakage current.

In the prior art, the most commonly used transistor is a metal-oxide-semiconductor field-effect transistor (MOSFET) formed in a planar silicon wafer, wherein the transistor has a gate formed on a silicon surface, and the gate is separated from the silicon surface by a dielectric material. In addition, the drain and source of the transistor are formed in a substrate under the silicon surface. As the size of the transistor is increasingly miniaturized, the transistor can be implemented using a fin structure transistor (e.g., a fin field effect transistor (FinFET), a tri-gate FET, or a double-gate transistor, etc.) so that the size of the transistor can continue to be miniaturized from 22 nanometers to 7 nanometers, or continue to be miniaturized to a size smaller than 7 nanometers. However, most technologies of the fin structure transistor emphasize the current driving capability of the transistor by generating a high ON current to demonstrate the high performance of the transistor, rather than emphasizing the ability of the transistor to have a low leakage current to demonstrate the low OFF current of the transistor. However, for deep nano-silicon technology, the use of the fin structure transistor as a low leakage current and low power consumption device is becoming increasingly important, especially when the fin structure transistor is used as a switching device in memory circuits (such as static random access memories (SRAMs), dynamic random access memories (DRAMs), portable integrated circuits (ICs) or wearable integrated circuits, etc.).

For example, the most commonly used memory cell for DRAM has an access transistor and a storage capacitor. When the prior art uses a planar transistor or a fin structure transistor as the access transistor, the access transistor suffers from a high leakage current problem (e.g., more than 1 picoampere per memory cell) when in the OFF state. The high leakage current problem causes the signal stored in the DRAM to leak out quickly, resulting in the DRAM requiring a very short refresh time to restore the stored signal (otherwise the stored signal will be lost), so the high leakage current problem is unacceptable. In addition, when the access transistor is in the off state, there are many known sources of leakage current, such as (a) gate-to-channel leakage, (b) gate-induced drain leakage (GIDL), (c) drain-induced barrier lowering (DIBL) leakage, (d) sub-threshold channel leakage, and (e) source/drain sidewall or region leakage caused by p-n junctions in silicon materials. In order to make the off current of each device meet the level close to femto-ampere, the parameters of the transistor size in each device must be relaxed to an unacceptable level, which violates the transistor scaling theory, where the transistor scaling theory requires the transistor size to be reduced to reduce the size of the memory cell in order to achieve the economy of Moore’s Law. In an exaggerated example, for a 10-nanometer process technology, the gate length needs to be greater than 100 nanometers to reduce the off current to meet the requirement of 1 femto-ampere per memory cell, which is very impractical. Therefore, how to provide transistors with low leakage current is an important issue for designers of dynamic random access memory.

An embodiment of the present invention discloses a transistor structure. The transistor structure includes a gate, a spacer, a channel region, and a first conductive region. The gate is located above a silicon surface. The spacer covers a side wall of the gate. At least a portion of the channel region is located below the gate and the spacer. The first conductive region is formed between the spacer and a side insulating layer, wherein a portion of a side wall of the first conductive region is covered by the side insulating layer.

In another embodiment of the present invention, the first conductive region is partially formed in a first groove, and the side insulating layer is partially formed in the first groove. A bottom insulating layer is formed in the first groove, and the first conductive region is located on the bottom insulating layer. The first conductive region includes a first upper portion, a second upper portion, and a lower portion, the first upper portion and the second upper portion contact the spacer layer, and the lower portion contacts the channel region and is located on the bottom insulating layer. In addition, the transistor structure further includes a contact region. The contact region is at least partially formed in the first groove, wherein the second upper portion of the first conductive region contacts the contact region, and the side insulating layer separates the first upper portion and the lower portion of the first conductive region from the contact region. In addition, in another embodiment of the present invention, the first conductive region includes silicon, silicon carbide, or silicon germanium.

In another embodiment of the present invention, the transistor structure further includes a second conductive region, another side insulating layer, and another contact region. The second conductive region is partially formed in a second groove. The other side insulating layer is partially formed in the second groove. The other contact region is partially formed in the second groove, wherein the second conductive region includes a first upper portion, a second upper portion, and a lower portion, the lower portion of the second conductive region contacts the channel region, the second upper portion of the second conductive region contacts the other contact region, and the other side insulating layer separates the first upper portion and the lower portion of the second conductive region from the other contact region.

In another embodiment of the present invention, the transistor structure further includes another spacer layer. The other spacer layer covers the other sidewall of the gate, wherein the length of the channel region is not less than the sum of the length of the gate, the length of the spacer layer, and the length of the other spacer layer. In addition, the spacer layer and the other spacer layer are regenerated spacers. In addition, in another embodiment of the present invention, the transistor structure further includes a lightly doped drain region located below the spacer layer.

Another embodiment of the present invention discloses a transistor structure. The transistor structure includes a gate, a spacer, a channel region, a first conductive region, and a second conductive region. The gate is located above a silicon surface. The spacer is located above the silicon surface and covers a side wall of the gate. At least a portion of the channel region is located below the gate and the spacer. The transistor structure is an asymmetric transistor structure.

In another embodiment of the present invention, a first doping concentration distribution of the first conductive region along a first extension direction is different from a second doping concentration distribution of the second conductive region along a second extension direction. The structure between the gate and the first conductive region is different from the structure between the gate and the second conductive region. A lightly doped drain region is formed between the gate and the first conductive region. In another embodiment of the present invention, the first conductive region includes a first lower portion below the silicon surface, the second conductive region includes a second lower portion below the silicon surface, and the thickness of the first lower portion is different from the thickness of the second lower portion. The width of one end of the channel region adjacent to the first conductive region is different from the width of the other end of the channel region adjacent to the second conductive region. The material of the first conductive region is different from the material of the second conductive region.

Another embodiment of the present invention discloses a transistor structure. The transistor structure includes a gate, a spacer, a channel region, a first conductive region, and a second conductive region. The gate is located above a silicon surface. The spacer is located above the silicon surface and covers a side wall of the gate. The spacer is located above the silicon surface and covers a side wall of the gate. At least a portion of the channel region is located below the gate and the spacer. The first conductive region is electrically coupled to one end of the channel region and the second conductive region is electrically coupled to the other end of the channel region. The turn-on current of the transistor structure depends on at least one of the parameters of the first conductive region, the parameters of the channel region, the asymmetric parameters of the transistor structure, and the presence of a second insulating layer covering the sidewalls of the first conductive region.

In another embodiment of the present invention, the off current of the transistor structure depends on at least one of the parameters of the first conductive region, the parameters of the channel region, the asymmetric parameters of the transistor structure, and the first insulating layer present under the first conductive region.

The present invention discloses a transistor structure. The transistor structure includes a gate, a spacer, a channel region, a first conductive region, and a second conductive region, wherein the spacer separates the first conductive region and the second conductive region from the gate, and the spacer separates the first conductive region and the second conductive region from the gate. In addition, the first conductive region is formed on the side wall of a first groove, and the second conductive region is formed on the side wall of a second groove, wherein a portion of the side wall of each of the first conductive region and the second conductive region is covered by an insulating layer, and another additional insulating layer can be selectively formed on the bottom surface of the first groove, and the same is true for the bottom surface of the second groove. Therefore, compared with the fin structure transistor provided by the prior art, the transistor structure provided by the present invention can reduce leakage current and adjust the turn-on/turn-off current of the transistor through the parameters of the transistor.

100, 1600, 1601, 1602, 1603: Transistor structure

101: Gate

103: Spacer layer

1031: Part 1

1032: Part 2

105: Channel area

107: First conductive area

1071, 1091: Lower part

1072, 1092: The first upper part

1073, 1093: The second upper part

109: Second conductive area

110: Shallow trench insulation structure

111: Dielectric layer

112: Base

113: Silicon surface

115: Covering structure

117: First groove

119, 127: First insulating layer

121, 129: Second insulation layer

123, 131: Contact area

125: Second groove

133: Conductive area

135: Lightly doped drain region

1231, 1311: Isolation materials

200-218: Steps

301: First dielectric layer

303: Polycrystalline silicon layer

305: First oxide layer

307: First nitride layer

401: Thin oxide layer

403: Second nitride layer

405: Second oxide layer

501: Partial

1003: Second dielectric layer

1303: Gap

1304: Insulation layer

G: Gate structure

S0-S3: Source

D0-D3: Drain

Figure 1A is a schematic diagram of a transistor structure disclosed in the first embodiment of the present invention.

Figure 1B is a schematic diagram of a transistor structure disclosed in another embodiment of the present invention.

Figure 2 is a flow chart of a method for manufacturing a transistor structure disclosed in the second embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating the formation of a first dielectric layer, a polysilicon layer, a first oxide layer, and a first nitride layer on a silicon surface.

Figure 4 is a schematic diagram illustrating the formation of a dielectric layer, a gate, and a covering structure.

Figure 5 is a schematic diagram illustrating the formation of a spacer layer next to a dielectric layer, a gate, and a capping structure.

FIG. 6A is a schematic diagram illustrating the use of a spacer layer as a mask for anisotropic etching technology to form a first groove and a second groove.

FIG. 6B is a schematic diagram illustrating etching back the spacer layer to expose a portion of the silicon surface according to another embodiment of the present invention.

Figure 7 is a schematic diagram illustrating the formation of a first insulating layer in the first groove and the second groove.

Figure 8 is a schematic diagram illustrating etching back the first insulating layer.

FIG. 9 is a schematic diagram illustrating the formation of a first conductive region and a second conductive region on a first insulating layer.

Figure 10A is a schematic diagram illustrating the removal of the spacer layer according to another embodiment of the present invention.

FIG. 10B is a schematic diagram illustrating forming a second dielectric layer on a spacer layer, a cover structure, a first conductive region, and a second conductive region according to another embodiment of the present invention.

Figure 11 is a schematic diagram illustrating the formation and etching back of the second insulating layer.

Figure 12A is a schematic diagram illustrating the final structure of the transistor structure.

FIG. 12B is a schematic diagram illustrating the final structure of the transistor structure according to the embodiment shown in FIG. 6B.

FIG. 13 is a schematic diagram illustrating another embodiment of the present invention in which the first conductive region and the second conductive region are completely formed in the first groove and the second groove, respectively.

FIG. 14 is a schematic diagram illustrating the removal of the second oxide layer of the spacer layer according to another embodiment of the present invention.

Figure 15 is a schematic diagram illustrating the regeneration of the third oxide layer according to another embodiment of the present invention.

Figure 16 is a schematic diagram illustrating four embodiments of transistor structures according to another embodiment of the present invention.

Figure 17 is a schematic diagram of a transistor structure disclosed in another embodiment of the present invention.

Please refer to FIG. 1A. FIG. 1A is a schematic diagram of a transistor structure 100 disclosed in a first embodiment of the present invention. As shown in FIG. 1A, the transistor structure 100 includes a gate 101, a spacer 103, a channel region 105, a first conductive region 107, and a second conductive region 109. In addition, a shallow trench isolation (STI) structure 110 is formed next to the transistor structure 100, wherein the structure of the shallow trench isolation structure 110 is well known to those skilled in the art in the field of the present invention and will not be described in detail here. The gate 101 is formed on a dielectric layer 111, wherein the dielectric layer 111 is formed on a silicon surface 113 of a substrate 112. In addition, a capping structure 115 may be formed on the gate 101. The spacer 103 is formed on the silicon surface 113 and includes a first portion 1031 and a second portion 1032, wherein the first portion 1031 covers the left sidewall of the gate 101, and the second portion 1032 covers the right sidewall of the gate 101. In addition, in an embodiment of the present invention, the spacer 103 has a three-layer structure, wherein the three-layer structure is a thin oxide layer, a nitride layer, and an oxide layer. However, the present invention is not limited to the spacer 103 having the three-layer structure. That is, the spacer layer 103 may be a single-layer or multi-layer dielectric layer, and the multi-layer dielectric layer may include nitride, oxide, oxynitride, or other dielectric materials. The channel region 105 is formed below the gate 101 and the spacer layer 103, and the channel region 105 is aligned with the spacer layer 103. Because of the spacer layer 103, the length of the channel region 105 is greater than the length of the gate 101. However, in another embodiment of the present invention, the channel region 105 is not completely located under the gate 101 and the spacer layer 103. That is, at least a portion of the channel region 105 is located under the gate 101 and the spacer layer 103. In addition, the length of the channel region 105 can be adjusted according to the length of the spacer layer 103 and the length of the gate 101. In addition, a doping region can be formed in the channel region 105. In addition, in another embodiment of the present invention, a lightly doped region can be formed between the gate 101 and the first conductive region 107 and/or between the gate 101 and the second conductive region 109.

The first conductive region 107 is formed and contacts the sidewall of a first groove 117, and the first conductive region 107 includes a lower portion 1071 and an upper portion (including a first upper portion 1072 and a second upper portion 1073), wherein the lower portion 1071 is coupled to the channel region 105, and the first upper portion 1072 and the second upper portion 1073 are coupled to the first portion 1031 of the spacer layer 103. In addition, the top surface of the second upper portion 1073 can be higher or lower than the top of the gate 101, and as shown in FIG. 1A, the thickness of the lower portion 1071 (e.g., the distance from the top to the bottom of the lower portion 1071, wherein the top of the lower portion 1071 is aligned with the silicon surface 113) is greater than the thickness of the channel region 105 (e.g., the distance from the top to the bottom of the channel region 105). In addition, in another embodiment of the present invention, the height of the first conductive region 107 is greater than the length of the gate 101 along the silicon surface 113, or greater than the sum of the length of the gate 101 along the silicon surface 113 and the length of the spacer 103 along the silicon surface 113. In addition, the first conductive region 107 may include a material containing silicon such as silicon (Si), silicon carbide (SiC), or silicon germanium (SiGe).

A first insulating layer 119 is formed in the first groove 117 and covers the bottom surface of the first groove 117, wherein the first insulating layer 119 is formed below the lower portion 1071. A second insulating layer 121 is formed beside the first conductive region 107 and covers the sidewalls of the lower portion 1071 and the sidewalls of the first upper portion 1072. In addition, the material of the first insulating layer 119 and/or the material of the second insulating layer 121 may be oxide, nitride, or other insulating materials. In one embodiment of the present invention, the first insulating layer 119 and/or the second insulating layer 121 may be formed by thermal oxidation. In addition, in another embodiment of the present invention, the first insulating layer 119 and the second insulating layer 121 are formed by atomic layer deposition (ALD) or chemical vapor deposition (CVD).

In addition, a conductive region 133 is also partially formed in the first groove 117, wherein the conductive region 133 is contained in an adjacent transistor structure next to the transistor structure 100, and the conductive region 133 can be separated or electrically isolated from the first conductive region 107 by the second insulating layer 121 or other separation methods. In another embodiment of the present invention, the conductive region 133 and the first conductive region 107 are formed and connected together, thereby forming a "collar"-shaped conductive region in the first groove 117, and the adjacent transistor structure next to the transistor structure 100 can be a dummy structure or other transistor.

In addition, the first conductive region 107 is coupled to a contact region 123 through the second upper portion 1073, wherein the contact region 123 is used for future interconnection of the transistor structure 100. Due to the second insulating layer 121, the second insulating layer 121 separates the lower portion 1071 and the first upper portion 1072 of the first conductive region 107 from the contact region 123. In addition, the contact region 123 may include heavily doped polysilicon or a material including metal. In this case, the conductive region 133 is physically separated from the first conductive region 107, and the conductive region 133 is electrically coupled to the first conductive region 107 through the contact region 123.

The first conductive region 107 has a first doping concentration distribution along a first extension direction of the first conductive region 107, wherein the first extension direction extends upward from the lower portion 1071 to the second upper portion 1073. That is, the first extension direction is parallel to (or substantially parallel to) the normal direction of the silicon surface 113. In particular, the first doping concentration distribution includes the doping concentration of the lower portion 1071, the doping concentration of the first upper portion 1072, and the doping concentration of the second upper portion 1073. In one embodiment of the present invention, the doping concentration of the first upper portion 1072 and/or the doping concentration of the second upper portion 1073 is higher than the doping concentration of the lower portion 1071. However, the present invention is not limited to the doping concentration of the first upper portion 1072 and/or the doping concentration of the second upper portion 1073 being higher than the doping concentration of the lower portion 1071, that is, the first doping concentration distribution may be other doping concentration distributions, such as a combination of light doping, normal doping, and heavy doping in any order.

In addition, the resistance of the first conductive region 107 can be controlled by adjusting the first doping concentration distribution of the first conductive region 107. That is, for example, when the turn-on current of the transistor structure 100 flows from the first conductive region 107 to the channel region 105, the value of the turn-on current also depends on the first doping concentration distribution of the first conductive region 107. In addition, the voltage drop of the first conductive region 107 can be reduced or changed by controlling the resistance of the first conductive region 107. In addition, as shown in FIG. 1A, the length of the channel region 105 is greater than the length of the gate 101, and the first insulating layer 119 also reduces the contact area between the first conductive region 107 and the substrate 112. Based on the above reasons, the leakage current of the transistor structure 100 can be reduced. In addition, in another embodiment of the present invention, the resistance of the first conductive region 107 can be controlled by the height, width, or length of the first conductive region 107. In addition, in another embodiment of the present invention, when the leakage current of the transistor structure 100 is not a key factor for the operation purpose of the transistor structure 100, the first insulating layer 119 can be omitted.

Similar to the first conductive region 107, the second conductive region 109 of the transistor structure 100 is formed and contacts a sidewall of a second groove 125, and the second conductive region 109 includes a lower portion 1091 and an upper portion (including a first upper portion 1092 and a second upper portion 1093), wherein the second conductive region 109 has a second doping concentration distribution along a second extension direction of the second conductive region 109, and the second extension direction extends upward from the lower portion 1091 to the second upper portion 1093. In addition, the first doping concentration distribution of the first conductive region 107 and the second doping concentration distribution of the second conductive region 109 are symmetrical. However, in another embodiment of the present invention, the first doping concentration distribution and the second doping concentration distribution can be intentionally made asymmetric.

In addition, a first insulating layer 127 is formed under the second conductive region 109, a second insulating layer 129 is formed beside the second conductive region 109, and the second conductive region 109 is coupled to a contact region 131. The structures and features of the second conductive region 109, the first insulating layer 127, the second insulating layer 129, and the contact region 131 can refer to the above description of the structures and features of the first conductive region 107, the first insulating layer 119, the second insulating layer 121, and the contact region 123, and will not be repeated here.

Please refer to FIG. 1B. The embodiment of FIG. 1B is similar to the embodiment of FIG. 1A, but the difference between the embodiment of FIG. 1B and the embodiment of FIG. 1A is that the conductive region 133 of the adjacent transistor structure is physically and electrically isolated from the first conductive region 107 by the second insulating layer 121 and an isolation material 1231. In addition, the top of the first conductive region 107 and the top of the conductive region 133 can be aligned with the top of the spacer layer 103, so the first conductive region 107 (or the conductive region 133) can be electrically coupled to other wires independently. Similarly, another conductive region of another adjacent transistor structure is physically and electrically isolated from the second conductive region 109 by the second insulating layer 129 and another isolation material 1311, so the second conductive region 109 can also be electrically coupled to another wire independently.

Please refer to FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6A, FIG. 6B, FIG. 7, FIG. 8, FIG. 9, FIG. 10A, FIG. 10B, and FIG. 11. FIG. 2 is a flow chart of a method for manufacturing a transistor structure 100 disclosed in a second embodiment of the present invention. The manufacturing method of FIG. 2 will be explained using FIG. 3, FIG. 4, FIG. 5, FIG. 6A, FIG. 6B, FIG. 7, FIG. 8, FIG. 9, FIG. 10A, FIG. 10B, and FIG. 11, wherein FIG. 3, FIG. 4, FIG. 5, FIG. 6A, FIG. 6B, FIG. 7, FIG. 8, FIG. 9, FIG. 10A, FIG. 10B, and FIG. 11 also illustrate the transistor structure 100. The adjacent transistor structure (or adjacent pseudo structure), but in order to simplify Figures 3, 4, 5, 6A, 6B, 7, 8, 9, 10A, 10B, and 11, its structure is not marked in Figures 3, 4, 5, 6A, 6B, 7, 8, 9, 10A, 10B, and 11. The detailed steps of the manufacturing method are as follows: Step 200: Start; Step 201: Form a first dielectric layer 301, a polysilicon layer 303, a first oxide layer 305, and a first nitride layer 307 on a silicon surface 113; Step 202: Form a dielectric layer 111, a gate 101, and a capping structure 115 by etching a region outside a gate pattern; Step 204: Form a spacer layer 103 next to the dielectric layer 111, the gate 101, and the capping structure 115; Step 206: Use the spacer layer 103 as an anisotropic etching technique (anisotropic etching) technique) to form the first groove 117 and the second groove 125; step 208: forming the first insulating layer 119 and 127 in the first groove 117 and the second groove 125 respectively; step 210: etching back the first insulating layer 119 and 127; step 212: forming the first conductive region 107 and the second conductive region 109 on the first insulating layer 119 and 127 respectively; step 214: forming and etching back the second insulating layer 121 and 129; step 216: forming the contact region 123 and 131 respectively by filling the first groove 117 and the second groove 125; step 218: ending.

First, using the process steps known to those skilled in the art, a shallow trench insulation structure 110 (as shown in FIG. 1A ) can be formed in the substrate 112, wherein the top of the shallow trench insulation structure 110 is about 25 to 30 nanometers below the silicon surface 113, and the bottom surface of the shallow trench insulation structure 110 can penetrate about 300 to 1000 nanometers into the substrate 112. In addition, as shown in FIG. 3 , in step 201, a first dielectric layer 301 is formed on the silicon surface 113, wherein the first dielectric layer 301 can be a thermally grown oxide, an oxide and a composite insulating material, or other high-k materials. Next, a polysilicon layer 303 (including doped polysilicon, polysilicon plus silicide material, metal, or other gate materials) is deposited on the first dielectric layer 301, and a first oxide layer 305 and a first nitride layer 307 are sequentially deposited on the polysilicon layer 303.

In step 202, as shown in FIG. 4, a gate pattern corresponding to the dielectric layer 111, the gate 101, and the capping structure 115 is defined by a lithography masking step, and an area outside the gate pattern is etched using the anisotropic etching technique, wherein the dielectric layer 111 includes a first dielectric layer 301, the gate 101 includes a polysilicon layer 303, and the capping structure 115 includes a first oxide layer 305 and a first nitride layer 307.

In step 204, a thin oxide layer 401, a second nitride layer 403, and a second oxide layer 405 are sequentially formed, wherein the thin oxide layer 401 is coupled to the dielectric layer 111, the gate 101, and the capping structure 115, the second nitride layer 403 is coupled to the thin oxide layer 401, and the second oxide layer 405 is coupled to the second nitride layer 403. Then, as shown in FIG. 5, the spacer layer 103 (including the first portion 1031 and the second portion 1032) is formed using the anisotropic etching technology. In addition, the spacer layer 103 is not limited to a three-layer structure, that is, the spacer layer 103 may include a two-layer structure or other multi-layer structures.

In step 206, as shown in FIG. 6A, the spacer layer 103 is used as a mask to form the first groove 117 and the second groove 125 by etching technology (such as the anisotropic etching technology), and the sidewalls of the first groove 117 and the second groove 125 are aligned with the spacer layer 103, wherein the depth of each groove in the first groove 117 and the second groove 125 can be 10 nanometers, or between 10 nanometers and 30 nanometers. In addition, in another embodiment of the present invention, a portion of the second oxide layer 405 and the second nitride layer 403 may be etched again to expose a portion 501 of the silicon surface 113 (as shown in FIG. 6B), wherein the portion 501 is located at the top of the sidewalls of the first groove 117 and the second groove 125, resulting in the sidewalls of the first groove 117 and the second groove 125 not being aligned with the spacer layer 103. In the subsequent steps of the manufacturing method, FIGS. 7-9, 10A, 10B, 11, and 12A are described based on the structure of FIG. 6A, and FIG. 12B is described based on the structure of FIG. 6B.

In step 208, as shown in FIG. 7, a first insulating layer 119 is formed in the first groove 117 and covers the sidewalls and bottom of the first groove 117. Similarly, a first insulating layer 127 is formed in the second groove 125 and covers the sidewalls and bottom of the second groove 125. In addition, the first insulating layers 119 and 127 can be thermally grown oxides, deposited oxides, deposited composite insulating materials, or other high dielectric constant materials.

In step 210, as shown in FIG. 8, portions of the first insulating layers 119 and 127 are etched back so that the tops of the first insulating layers 119 and 127 are lower than the silicon surface 113, so that the sidewalls of the channel region 105 are exposed.

In step 212, as shown in FIG. 9, the first conductive region 107 is formed and contacts the sidewall of the first groove 117, and is disposed on the first insulating layer 119. Similarly, the second conductive region 109 is formed and contacts the sidewall of the second groove 125, and is disposed on the first insulating layer 127. In one embodiment of the present invention, the first conductive region 107 and the second conductive region 109 are formed by a deposition method (e.g., the atomic layer deposition method or the chemical vapor deposition method). However, in another embodiment of the present invention, the first conductive region 107 and the second conductive region 109 are grown by a selective epitaxial growth method (SEG). In particular, the selective epitaxial growth method can use the left sidewall of the channel region 105 as a silicon-growth seeding to grow a single-crystalline silicon layer on the sidewall of the first groove 117 as the lower portion 1071 of the first conductive region 107, and then continue to grow the remaining first conductive region 107 (e.g., the first upper portion 1072 and the second upper portion 1073) based on the lower portion 1071. During the selective epitaxial growth method, the first doping concentration distribution of the first conductive region 107 can be controlled. Similarly, the selective epitaxial growth method can use the right side wall of the channel region 105 as the silicon growth seed to partially grow the single crystal silicon layer on the side wall of the second groove 125 as the second conductive region 109.

In addition, each of the lower portion 1071, the first upper portion 1072, and the second upper portion 1073 can be deposited (or grown) by a different mechanism (e.g., using a different doping concentration or using other non-silicon materials such as a mixture of germanium or carbon atoms, etc.) so that the first conductive region 107 has the first doping concentration distribution. Similarly, each of the lower portion 1091, the first upper portion 1092, and the second upper portion 1093 can also be deposited (or grown) by a different mechanism so that the second conductive region 109 has the second doping concentration distribution. In addition, in another embodiment of the present invention, laser-annealing technology (or rapid thermal annealing technology or other annealing technology) can be used to process the first conductive region 107 and the second conductive region 109 to increase the quality and stability of the first conductive region 107 and the second conductive region 109. In addition, how to design the shape of the first conductive region 107 and the shape of the second conductive region 109 depends on the desired resistance of the first conductive region 107 and the second conductive region 109 and the voltage/electric field distribution, wherein the shape/resistance of the first conductive region 107 or the shape/resistance of the second conductive region 109 can effectively control the on/off current of the transistor structure 100.

In addition, in another embodiment of the present invention, the first conductive region 107 and the second conductive region 109 may include a material having silicon (e.g., silicon, silicon carbide, or silicon germanium) to generate stress to improve the mobility of the channel region 105. In addition, as shown in FIG. 10A, when the first conductive region 107 and the second conductive region 109 include silicon carbide, the spacer 103 may be removed to improve the stress. However, in another embodiment of the present invention, as shown in FIG. 10B, a second dielectric layer 1003 (e.g., silicon nitride) may be formed on the spacer 103, the capping structure 115, and/or the first conductive region 107 and the second conductive region 109.

In step 214, as shown in FIG. 11, second insulating layers 121 and 129 are formed and etched back so that the second insulating layer 121 covers the lower portion 1071 and the first upper portion 1072 of the first conductive region 107, and the second insulating layer 129 covers the lower portion 1091 and the first upper portion 1092 of the second conductive region 109. In addition, the second insulating layers 121 and 129 can be thermally grown oxides, oxide and composite insulating materials, or other high dielectric constant materials. As shown in FIG. 11 , the second upper portion 1073 of the first conductive region 107 is not covered by the second insulating layer 121 , and the second upper portion 1093 of the second conductive region 109 is not covered by the second insulating layer 129 .

In step 216, n+ polysilicon material, p+ polysilicon material, metal, or other conductive materials are filled in the first groove 117 and the second groove 125 to form contact regions 123 and 131, respectively, wherein in one embodiment of the present invention, the top of the contact regions 123 and 131 is aligned with the top of the covering structure 115. Therefore, FIG. 12A shows the final structure of the transistor structure 100. However, in another embodiment of the present invention, the top of the contact regions 123 and 131 can be higher than the top of the covering structure 115. In addition, FIG. 12B is the final structure of the transistor structure 100 in the embodiment corresponding to FIG. 6B. As shown in FIG. 12B , because the spacer layer 103 is etched back to expose the portion 501 of the silicon surface 113 , the portion 501 of the silicon surface 113 can also be used as the silicon growth seed to vertically grow the first conductive region 107 and the second conductive region 109 above the portion 501 of the silicon surface 113 .

In another embodiment of the present invention, the formation of the first insulating layers 119 and 127 is not necessary, that is, step 208 can be omitted. In addition, as shown in FIG. 13, in another embodiment of the present invention, the portion of the first conductive region 107 below the silicon surface 113 can be completely formed in the first groove 117, and the portion of the second conductive region 109 below the silicon surface 113 can be completely formed in the second groove 125. In other words, the second insulating layers 121 and 129 can be omitted. In addition, the first doping concentration distribution of the first conductive region 107 and the second doping concentration distribution of the second conductive region 109 can be controlled in the above-mentioned manner.

In addition, as shown in FIG. 14, in another embodiment of the present invention, the second oxide layer 405 of the spacer layer 103 may be removed to expose a gap 1303, and a third oxide layer or insulating layer 1304 (as shown in FIG. 15) may be formed or regenerated in the gap 1303 to increase the interface quality between the first conductive region 107 and the spacer layer 103 and the interface quality between the second conductive region 109 and the spacer layer 103. In addition, the regeneration of the spacer layer shown in FIGS. 14 and 15 is not limited to the structure of the embodiment shown in FIG. 13, and the regeneration may also be used in the embodiment shown in FIG. 12A or 12B. In addition, in another embodiment of the present invention, the polysilicon layer 303 (corresponding to the gate 101) used for the gate-first process can be replaced by other materials or p+ doped polysilicon used for the gate-last process and having an appropriate work function (from 4.0 eV to 5.2 eV).

In addition, in another embodiment of the present invention, the first doping concentration distribution of the first conductive region 107 and the second doping concentration distribution of the second conductive region 109 can be intentionally made asymmetric to increase the turn-on current of the transistor structure 100. For example, please refer to FIG. 16, wherein FIG. 16 shows transistor structures 1600, 1601, 1602, and 1603 of four embodiments, and the transistor structures 1600, 1601, 1602, and 1603 correspond to a reference embodiment, an embodiment 1, an embodiment 2, and an embodiment 3, respectively. In addition, each of the transistor structures 1600, 1601, 1602, and 1603 includes a gate structure G, the transistor structure 1600 includes a source S0 and a drain D0, the transistor structure 1601 includes a source S1 and a drain D1, the transistor structure 1602 includes a source S2 and a drain D2, and the transistor structure 1603 includes a source S3 and a drain D3, wherein the sources S0-S3 are respectively the first conductive regions of the transistor structures 1600, 1601, 1602, and 1603, and the drains D0-D3 are respectively the second conductive regions of the transistor structures 1600, 1601, 1602, and 1603. To simplify the diagram, FIG. 16 only shows the gate structure G, source S0-S3, and drain D0-D3 of transistor structures 1600, 1601, 1602, and 1603. In addition, the source S0-S3 and the drain D0-D3 are respectively shown with different marks to represent different doping concentrations, wherein the design of the different doping concentrations depends on the trade-off between the requirements (or applications) of the turn-on current and/or the turn-off current. In particular, as shown in the reference embodiment and embodiments 1-3, the doping concentration distribution of the source S0 is the same as the doping concentration distribution of the drain D0, and the doping concentration distribution of the source S3 is the same as the doping concentration distribution of the drain D3. However, the doping concentration distribution of the source S0 (drain D0) is different from the doping concentration distribution of the source S3 (drain D3). For example, the doping concentration distribution of the source S0 includes light doping, normal doping, and heavy doping from bottom to top; while the doping concentration distribution of the source S3 includes only heavy doping. On the other hand, the doping concentration distribution of the source S1 (e.g., including light doping, normal doping, and heavy doping from bottom to top) is different from the doping concentration distribution of the drain D1 (e.g., including only heavy doping from bottom to top), and the doping concentration distribution of the source S2 (e.g., including only heavy doping from bottom to top) is different from the doping concentration distribution of the drain D2 (e.g., including light doping, normal doping, and heavy doping from bottom to top). The turn-on current of the embodiments 1 and 2 is higher than the turn-on current of the reference embodiment. In general, embodiments with asymmetric doping concentration distribution (i.e., embodiments 1 and 2) have higher turn-on currents compared to the reference embodiment. In addition, although the asymmetric doping concentration distribution may cause the turn-off current to increase slightly in some cases, the desired asymmetric doping concentration distribution can be selected to produce the desired turn-on current and an acceptable corresponding turn-off current.

As mentioned above, because the first conductive region 107 and/or the second conductive region 109 may include silicon, silicon carbide, or silicon germanium, the material of the first conductive region 107 may be different from the material of the second conductive region 109. Therefore, a transistor having the characteristic that the material of the first conductive region 107 is different from the material of the second conductive region 109 is an asymmetric transistor.

In addition, in another embodiment of the present invention, as shown in FIG. 17 , before completing the spacer 103, a lightly doped drain (LDD) region 135 can be formed below the silicon surface 113 and between the first conductive region 107 (e.g., the drain) and the gate 101 by using some diffusion sources (without the hazards of ion implantation) or implants (implants, which need to be subsequently removed by thermal annealing or laser annealing to remove the hazards of ion implantation). As shown in FIG. 17 , the lightly doped drain region 135 is formed below the silicon surface 113 of the substrate 112 or below a fin structure and below the gate 101 and/or the spacer 103. In this case, no lightly doped drain is formed between the gate 101 and the second conductive region 109 (e.g., the source). In addition, in another embodiment of the present invention, a lightly doped drain region is formed between the gate 101 and the source, instead of forming the lightly doped drain between the gate 101 and the drain. Therefore, at this time, the structure between the gate 101 and the source is different from the structure between the gate 101 and the drain, that is, the transistor structure including the characteristic that the structure between the gate 101 and the source is different from the structure between the gate 101 and the drain is an asymmetric transistor structure.

In addition, the thickness of the lower portion 1071 of the first conductive region 107 (i.e., the distance from the silicon surface 113 to the bottom of the lower portion 1071) may be different from the thickness of the lower portion 1091 of the second conductive region 109, so the width of one end of the channel region 105 may be different from the width of the other end of the channel region 105. In other words, the transistor structure including the characteristics that the thickness of the lower portion 1071 of the first conductive region 107 is different from the thickness of the lower portion 1091 of the second conductive region 109 and the width of one end of the channel region 105 is different from the width of the other end of the channel region 105 is also an asymmetric transistor structure.

Please refer to FIG. 1A again. The channel region 105, the first conductive region 107, and the second conductive region 109 are formed using a self-alignment technique. Therefore, the transistor structure 100 can be more accurately controlled, has a smaller form factor, and occupies less wafer plane area. In addition, because the steps of the manufacturing method of the transistor structure 100 can avoid using an ion-implantation technique to form a p-n junction between the first conductive region 107 (or the second conductive region 109) and the substrate 112, the damage caused by the ion-implantation technique in the p-n junction can be reduced. In addition, the position of the p-n junction, the thickness of the lower portion 1071 of the first conductive region 107 (or the thickness of the lower portion 1091 of the second conductive region 109), and the first doping concentration distribution and the second doping concentration distribution are better controlled.

In addition, the transistor structure provided by the present invention has a turn-on/turn-off current that depends on the parameters of the first conductive region 107 (e.g., the first doping concentration distribution, the material, the thickness of the lower portion 1071 of the first conductive region 107, and the thickness of the second upper portion 1073 of the first conductive region 107), the parameters of the second conductive region 109, the parameters of the channel region 105 (e.g., the length of the channel region 105), the asymmetric parameters of the transistor structure (e.g., the asymmetric structure mentioned above), and/or the presence of the first insulating layer/second insulating layer, etc. Therefore, the turn-on/turn-off current of the transistor structure can be adjusted by at least one of the above parameters.

In summary, the transistor structure provided by the present invention includes the gate, the spacer, the channel region, the first conductive region, and the second conductive region, wherein the first conductive region and the gate are separated by the spacer, and the second conductive region and the gate are also separated by the spacer. In addition, the first conductive region forms and contacts the sidewall of the first groove, and the second conductive region forms and contacts the sidewall of the second groove, wherein a portion of the sidewall of each of the first conductive region and the second conductive region is covered by an insulating layer, and another insulating layer can be formed on the bottom surface of the first groove, and the bottom surface of the second groove is also the same. Therefore, compared with the fin structure transistor provided by the prior art, the transistor structure provided by the present invention can reduce leakage current and adjust the turn-on/turn-off current of the transistor through the parameters of the transistor.

The above is only the preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the patent application of the present invention shall fall within the scope of the present invention.

100: transistor structure 101: gate 103: spacer 1031: first part 1032: second part 105: channel region 107: first conductive region 1071, 1091: lower part 1072, 1092: first upper part 1073, 1093: second upper part 109: second conductive region 110: shallow trench insulation structure 111: dielectric layer 112: substrate 113: silicon surface 115: cover structure 117: first groove 119, 127: first insulating layer 121, 129: second insulating layer 123, 131: contact region 125: second groove 133: conductive region

Claims (19)

A transistor structure includes: a gate located above a silicon surface of a substrate; a spacer covering a side wall of the gate; a channel region, wherein at least a portion of the channel region is located below the gate and the spacer; and a first conductive region formed between the spacer and a side insulating layer, wherein a portion of a side wall of the first conductive region is covered by the side insulating layer, a first portion of the bottom of the first conductive region is in contact with the substrate, and a second portion of the bottom of the first conductive region is not in contact with the substrate. A transistor structure as described in claim 1, wherein the first conductive region is partially formed in a first groove, and the side insulating layer is partially formed in the first groove. A transistor structure as described in claim 2, wherein a bottom insulating layer is formed in the first groove, the second portion of the bottom of the first conductive region is located above the bottom insulating layer, and the first portion of the bottom of the first conductive region is not located above the bottom insulating layer. A transistor structure as described in claim 3, wherein the first conductive region includes a first upper portion, a second upper portion, and a lower portion, the first upper portion and the second upper portion contact the spacer layer, and the lower portion contacts the channel region and is located above the bottom insulating layer. The transistor structure as described in claim 4 further includes: a contact region, at least partially formed in the first groove, wherein the second upper portion of the first conductive region contacts the contact region, and the side insulating layer separates the first upper portion and the lower portion of the first conductive region from the contact region. A transistor structure as described in claim 1, wherein the first conductive region comprises silicon, silicon carbide, or silicon germanium. The transistor structure as described in claim 1 further includes: a second conductive region, partially formed in a second groove; another side insulating layer, partially formed in the second groove; and another contact region, partially formed in the second groove; wherein the second conductive region includes a first upper portion, a second upper portion, and a lower portion, the lower portion of the second conductive region contacts the channel region, the second upper portion of the second conductive region contacts the other contact region, and the other side insulating layer separates the first upper portion and the lower portion of the second conductive region from the other contact region. The transistor structure as described in claim 1 further includes: another spacer layer, wherein the other spacer layer covers the other side wall of the gate, and the length of the channel region is not less than the sum of the length of the gate, the length of the spacer layer, and the length of the other spacer layer. A transistor structure as described in claim 8, wherein the spacer layer and the another spacer layer are regenerated spacer layers. The transistor structure as described in claim 8 further comprises: a lightly doped drain region located below the spacer layer. A transistor structure comprises: a substrate having a silicon surface; a gate located on the substrate; a spacer covering a side wall of the gate; a channel region, wherein at least a portion of the channel region is located below the gate and the spacer; a first conductive region and a second conductive region, wherein the bottom of the first conductive region is not flat; and a bottom insulating layer formed at the bottom of the first conductive region so that the bottom of the first conductive region does not contact the substrate; wherein the transistor structure is an asymmetric transistor structure. A transistor structure as described in claim 11, wherein a first doping concentration distribution of the first conductive region along a first extension direction is different from a second doping concentration distribution of the second conductive region along a second extension direction. A transistor structure as described in claim 11, wherein the structure between the gate and the first conductive region is different from the structure between the gate and the second conductive region. A transistor structure as described in claim 13, wherein a lightly doped drain region is formed between the gate and the first conductive region. A transistor structure as described in claim 13, wherein the first conductive region includes a first lower portion below the silicon surface, the second conductive region includes a second lower portion below the silicon surface, and the thickness of the first lower portion is different from the thickness of the second lower portion. A transistor structure as described in claim 13, wherein the width of one end of the channel region adjacent to the first conductive region is different from the width of the other end of the channel region adjacent to the second conductive region. A transistor structure as described in claim 11, wherein the material of the first conductive region is different from the material of the second conductive region. A transistor structure comprises: a gate located above a silicon surface; a spacer located above the silicon surface and covering a side wall of the gate; a channel region, wherein at least a portion of the channel region is located below the gate and the spacer; and a first conductive region and a second conductive region, wherein the first conductive region is electrically coupled to one end of the channel region and the second conductive region is electrically coupled to the other end of the channel region, wherein a portion of the bottom of the first conductive region is in contact with the substrate; wherein a turn-on current of the transistor structure depends on at least one of the parameters of the first conductive region, the parameters of the channel region, the asymmetric parameters of the transistor structure, and the presence of a second insulating layer covering the side wall of the first conductive region. A transistor structure as described in claim 18, wherein the off current of the transistor structure depends on at least one of the parameters of the first conductive region, the parameters of the channel region, the asymmetric parameters of the transistor structure, and a first insulating layer present below the first conductive region.

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