CN1523678A - A Thick Film SOI Field Effect Transistor - Google Patents

Abstract

The invention discloses a thick-film SOI field-effect transistor, the purpose of which is to provide a kind of transistor that can not only realize the full depletion of the silicon film, but also overcome the inherent Kink effect of the SOI device, and at the same time increase the driving current of the device, increase the speed, and improve the Thick-film SOI field-effect transistors with short-channel performance. The technical solution of the present invention is: a thick-film SOI field-effect transistor, which includes a thick-film SOI field including a source region, a drain region, a gate oxide layer, a buried oxide layer, a back gate, a silicon film, a substrate and a channel. The body of the effect transistor is provided with an oppositely doped heterogeneous silicon island near the interface of the back gate. The invention not only overcomes the inherent Kink effect of the thick film SOI field effect transistor, but also greatly increases the driving current of the device, so that the working speed of the device is greatly improved. The design of heterogeneous silicon islands allows large fluctuations in thickness, width, doping concentration, and position, providing a wider design space for thick-film SOI devices.

Description

A Thick Film SOI Field Effect Transistor

technical field

The invention relates to a semiconductor device, in particular to a thick film SOI field effect transistor.

Background technique

After more than 20 years of development, SOI (Silicon-on-Insulator) technology has become the preferred technology for high-speed, low-voltage and low-power integrated circuits. Compared with bulk silicon technology, SOI technology has incomparable advantages. SOI devices have the advantages of small parasitic junction capacitance, good radiation resistance, and anti-parasitic latch-up effect, etc., and have been widely used in today's industry (JPColing,, ^2nd Edition, Kluwer Academic Pub., 2000, KeithDiefendorff, Microprocessor Report, Vol.12, No.4, August 24, 1998). However, due to the partial exhaustion of the silicon film in thick-film SOI devices, there is a neutral body region. When the leakage voltage is high, the Kink effect will appear, which will rapidly increase the leakage current of the device and affect the performance of the device, which greatly limits the thickness of the thick-film SOI device. device application. In order to solve the influence of the Kink effect inherent in thick-film SOI devices on device performance, people try to reduce the thickness of the silicon film so that the silicon film is in a fully depleted state. Thin-film fully depleted (FD) SOI devices can eliminate the Kink effect, effectively suppress the short-channel effect (SCE) of the device, improve subthreshold characteristics, and increase the transconductance of the device (S.Maeda et al., IEDM Tech.Dig. , Page(s): 129-132, 1996, MJ Sheron et al., IEEE Electron Device Letter, Volume: 16, Issue: 3, March, 1995). However, the threshold voltage of thin-film FDSOI devices is very sensitive to changes in the thickness of the silicon film. As the silicon film becomes thinner, the requirements for the flatness of the silicon film become more and more stringent, which makes the material preparation of thin-film SOI devices very difficult. difficulty.

Contents of the invention

The purpose of the present invention is to provide a thick film SOI field effect transistor, which can not only realize the full depletion of the silicon film, but also overcome the inherent Kink effect of the SOI device, and at the same time increase the driving current of the device, increase the speed, and improve the short channel performance .

In order to achieve the above object, the present invention takes the following technical solutions: a thick film SOI field effect transistor, which includes a source region, a drain region, a gate oxide layer, a buried oxide layer, a back gate, a silicon film, a substrate and a channel The body of the thick film SOI field effect transistor is provided with an oppositely doped hetero-type silicon island near the interface of the back gate.

The optimized shaped silicon island should be located at the bottom center of the silicon film.

The optimization range of each parameter of the heterogeneous silicon island is: the width of the heterogeneous silicon island is about three-fifths of the length of the channel; the thickness is equal to half of the thickness of the silicon film; the doping concentration of the heterogeneous silicon island is higher than the The doping concentration of the silicon film.

A specific preferred solution for realizing the present invention is as follows: the special-shaped silicon island is located at the center of the bottom of the silicon film, the channel length L=1 μm, the silicon film thickness is t _si =0.4 μm, the gate oxide layer thickness t _ox =20nm, and the source The doping concentration of the drain region Nn ⁺ =1×10 ²⁰ cm ^-3 , the doping concentration of the silicon film is Filmdoping=1×10 ¹⁷ cm ^-3 , the thickness of the buried oxide layer t _box =0.2 μm, and the doping concentration of the substrate Np ^- = 5×10 ¹⁶ cm ^-3 , thickness t _sub =0.3 μm; the variation range of the doping concentration of heterogeneous silicon islands is between 1×10 ¹⁷ cm ^-3 -5×10 ¹⁸ cm ^-3 ; the design range of the thickness T of silicon islands between 0.18 μm and 0.28 μm; the half width W of the silicon island is between 0.25 μm and 0.3 μm.

So far, there is no literature report on how to fully deplete the silicon film of thick-film SOI devices to eliminate the Kink effect. The special-shaped silicon island SOI field effect transistor provided by the invention not only overcomes the inherent Kink effect of the thick film SOI field effect transistor, but also greatly increases the driving current of the device, so that the working speed of the device is greatly improved. The design of heterogeneous silicon islands allows large fluctuations in thickness, width, doping concentration, and position, providing a wider design and application space for thick-film SOI devices.

Description of drawings

Fig. 1 is the structure schematic diagram of thick film SOI field effect transistor of the present invention

Figure 2(a) shows the influence of the change of the half-width of the silicon island on the input and output characteristics of the heterogeneous silicon island SOI device

Figure 2(b) shows the effect of the change of the half-width of the silicon island on the transfer characteristics of the heterogeneous silicon island SOI device

Figure 3(a) shows the influence of silicon island thickness changes on the input and output characteristics of heterogeneous silicon island SOI devices

Figure 3(b) shows the effect of silicon island thickness changes on the transfer characteristics of heterogeneous silicon island SOI devices

Figure 4(a) shows the influence of the change of silicon island doping concentration on the input and output characteristics of heterogeneous silicon island SOI devices

Figure 4(b) shows the effect of silicon island doping concentration changes on the transfer characteristics of heterogeneous silicon island SOI devices

Figure 5(a) shows the influence of silicon island concentration changes on the input and output characteristics of heterogeneous silicon island SOI devices

Figure 5(b) shows the effect of silicon island concentration changes on the transfer characteristics of heterogeneous silicon island SOI devices

Figure 5(c) shows the effect of the change of silicon island concentration on the channel potential distribution of heterogeneous silicon island SOI devices

Figure 6(a) is the comparison result of the input and output characteristics of the optimized special-shaped silicon island SOI field effect transistor and the conventional thick film SOI field effect transistor

Figure 6(b) is the comparison result of the speed characteristics of the inverter of the optimized heterogeneous silicon island SOI field effect transistor and the conventional thick film SOI field effect transistor

Figure 6(c) is the comparison result of the short channel characteristics of the optimized special-shaped silicon island SOI field effect transistor and the conventional thick film SOI field effect transistor

Detailed ways

In order to illustrate the performance of the device provided by the present invention, the structural parameters of heterogeneous silicon island field effect transistors are optimized and analyzed by using the two-dimensional device simulation software DESSIS ISE (version 6.0). And compared with the conventional structure (that is, thick film partially depleted) field effect transistor characteristics. As shown in Figure 1, the thick film SOI field effect transistor of the present invention includes a source region 1, a drain region 2, a gate oxide layer 3, a buried oxide layer 4, a back gate 5, a silicon film 6, a substrate 7 and a channel 8. The body of the thick film SOI field effect transistor is provided with an oppositely doped hetero-type silicon island 9 at the interface close to the back gate. The parameters of the device in the simulation are as follows: channel length L = 1 μm, silicon film thickness t _si = 0.4 μm, gate oxide layer thickness t _ox = 20nm, source and drain region doping concentration Nn ⁺ = 1×10 ²⁰ cm ^-3 , The doping concentration of the silicon film is Filmdoping=1×10 ¹⁷ cm ^-3 , the thickness of the buried oxide layer t _box =0.2 μm, the substrate doping concentration Np ⁻ =5×10 ¹⁶ cm ^-3 , and the thickness t _sub =0.3 μm. Fluid dynamics and quantum effect models are used in the simulation; SRH, Auger, Band2band and Avalanche models are used for composite models; doping Dependence, High fieldsaturation, Enormal and PhuMob models are used for mobility models.

Example 1: Influence of the change of the half-width of the silicon island on the input and output characteristics and transfer characteristics of SOI devices with heterogeneous silicon islands (the silicon island is located in the center of the bottom of the channel)

Figure 2(a)(b) respectively shows the influence of the change of the half-width of the silicon island on the input and output characteristics and transfer characteristics of the heterogeneous silicon island SOI device. Wherein, the silicon island thickness T=0.2 μm, Doping=5×10 ¹⁷ cm ⁻³ . It can be seen from Figure 2(a) that when the silicon island half-width W=0.25 μm, the Kink effect of the thick-film SOI device is eliminated, the inside of the channel is fully depleted, and the driving current of the device increases; with the continuous increase of the silicon island half-width, The driving current is also continuously increasing; while the half-width of the silicon island W=0.3 μm is a relatively sensitive value, and when the half-width of the silicon island W>0.3 μm, the tube becomes very easy to break down. The reason can be explained from Figure 2(b). It can be seen that when the half-width of the silicon island W>0.3 μm, the threshold voltage of the device will shift significantly, and the junction depletion layer of the silicon island will completely deplete the inside of the channel, but when the width of the silicon island is too large, it will cause The source barrier of the device is reduced, the threshold voltage is reduced, the oversaturation voltage (V _G -V _T ) is increased, the tube becomes easier to turn on, and the saturation driving current is larger, so the device is easier to break down. Therefore, it can be seen that when the thickness of the silicon island is T=0.2 μm and Doping=5×10 ¹⁷ cm ⁻³ , the ideal half width W of the silicon island is between 0.25 μm and 0.3 μm. The SOI device with the half-width of the silicon island within this range can eliminate the Kink effect of the thick-film fully depleted device on the one hand, and on the other hand, the saturation drive current of the device increases, the leakage current is small, and the breakdown voltage of the tube is also high. .

Example 2: Effects of changes in the thickness of silicon islands on the input and output characteristics and transfer characteristics of SOI devices with heterogeneous silicon islands (silicon islands are located in the center of the bottom of the channel)

Figure 3(a)(b) respectively shows the influence of the change of the thickness of the silicon island on the input and output characteristics and transfer characteristics of the special-shaped silicon island SOI device (the silicon island is located in the center of the bottom of the channel). Wherein, the silicon island half width W=0.3 μm, Doping=5×10 ¹⁷ cm ⁻³ . It can be seen from Fig. 3(a) that when the thickness of the silicon island is T=0.2μm, that is, half of the thickness of the silicon film, the Kink phenomenon of the output curve is basically eliminated, and the inside of the channel is fully depleted. When the thickness of the silicon island increases further, the saturation driving current of the device increases further, especially when the thickness of the silicon island changes from T=0.3 μm to T=0.35 μm, the driving current of the device increases sharply. As the thickness of the silicon island increases, the voltage width between the saturation region and the breakdown region of the SOI device gradually decreases, and the tube becomes easy to break down. Figure 3.5(b) also shows that when the silicon island thickness T>0.25μm, the threshold voltage of the device drifts significantly. When the thickness of the silicon island is T>0.3μm, the leakage current cannot be ignored. At this time, the source barrier has become very low due to the influence of the special-shaped silicon island, and the tube can be turned on with a small gate voltage. Under the same gate voltage and drain voltage, the source barrier is reduced due to the increase of silicon island thickness, so that more source carriers can easily cross the barrier and enter the channel, thus forming a large output current. , which is the situation shown by the sixth curve in Figure 3(a). Therefore, when the half-width W of the heterogeneous silicon island is 0.3 μm and the doping concentration Doping is 5×10 ¹⁷ cm ⁻³ , the design range of the thickness T of the silicon island is between 0.18 μm and 0.28 μm. Within this thickness range, the special-shaped silicon island SOI device can not only eliminate the Kink effect of the thick-film SOI device, but also greatly improve the driving capability of the device while maintaining a small leakage current.

Example 3: Effects of changes in the doping concentration of silicon islands on the input-output characteristics and transfer characteristics of SOI devices with heterogeneous silicon islands (silicon islands are located in the center of the bottom of the channel)

Figure 4(a) and (b) respectively show the influence of the change of the doping concentration of the silicon island on the input and output characteristics and transfer characteristics of the heterogeneous silicon island SOI device (the silicon island is located in the center of the bottom of the channel). Wherein, the silicon island half-width W=0.3 μm, and the silicon island thickness T=0.2 μm. When the doping concentration Doping of the special-shaped silicon island is very low, the silicon island has basically no effect on the characteristics of the thick film device, and the low doping concentration of the silicon island makes the pn junction depletion layer between the silicon island and the channel mainly distributed in the silicon island side. But when the doping concentration of the silicon island can be compared with the doping concentration of the channel, the characteristics of the thick-film device change significantly, as shown in Figure 4(a). When the doping concentration Doping of the silicon island is greater than the impurity concentration Filmdoping of the silicon film (i.e. 1×10 ¹⁷ cm ^-3 ), it can be known from the pn junction principle that the higher the doping concentration of the n-type silicon island, the higher the consumption of the p-type channel region. The more the depletion layer is widened, the easier it is to achieve full depletion of the channel, thereby eliminating the Kink effect of thick-film SOI devices. At the same time, as the doping concentration of the silicon island increases, the driving current of the device also increases gradually. However, it can be seen from Figure 4(b) that due to the influence of threshold voltage drift and leakage current, the variation range of the doping concentration of heterogeneous silicon islands should be between 1×10 ¹⁷ cm ^-3 -5×10 ¹⁸ cm ^-3 .

Example 4: When the silicon island is located in the center of the top of the channel, the influence of the concentration change of the silicon island on the input and output characteristics, transfer characteristics and channel potential distribution of the device

Figure 5(a)(b)(c) respectively shows the influence of the change of silicon island concentration on the input and output characteristics, transfer characteristics and channel potential distribution of the device. Wherein, the silicon island half width W=0.3 μm, and the thickness T=0.2 μm. It can be seen from Figure 5(a) that when the doping concentration of the silicon island exceeds the doping concentration of the channel, although the inherent Kink effect of the thick film device can also be overcome, and the driving current also increases with the increase of the doping concentration of the silicon island However, it can be seen from Figure 5(b) that the threshold voltage of the device has greatly shifted, and the subthreshold slope of the device is very large, which greatly increases the leakage current of the device and seriously degrades the performance of the device. This is due to the large influence on the surface potential of the channel when the silicon island is located at the center of the top of the channel, as shown in Fig. 5(c). The figure compares the channel potential distribution when the silicon islands are located at the bottom of the channel and at the top of the channel respectively (other parameters of the device are the same). It can be seen that when the silicon island is at the center of the channel top (curve 2), the surface potential of the channel is about 200mV lower than that of the silicon island at the center of the channel bottom (curve 1), and it is more susceptible to the potential of the drain terminal. Therefore, the short channel effect of the device is more significant.

From the above, the optimized heterogeneous silicon island should be located at the center of the bottom of the silicon film, as shown in FIG. 1 . And the optimization range of each parameter of the silicon island is: the width is about three-fifths of the channel length, the thickness is about half the thickness of the silicon film, and the doping concentration only needs to be higher than that of the silicon film.

Embodiment 5: Comparison of the input and output characteristics of the optimized special-shaped silicon island SOI field effect transistor and the conventional thick film SOI field effect transistor, the speed characteristic of the inverter and the short channel characteristic of the device

Figure 6(a)(b)(c) respectively shows the input and output characteristics of the optimized special-shaped silicon island SOI field effect transistor and the conventional thick film SOI field effect transistor, the speed characteristics of the inverter and the short channel characteristics of the device comparison results. Among them, the channel length of the two structure devices is L=1μm, the silicon film thickness t _si =0.4μm, and the doping concentration Filmdoping=1×10 ¹⁷ cm ^-3 ; the silicon island half-width W of the special-shaped silicon island SOI field effect transistor is W= 0.3 μm, thickness T=0.2 μm, doping concentration Doping=5×10 ¹⁷ cm ^-3 . It can be seen from Figure 6(a) that the thick-film SOI device not only overcomes its inherent Kink effect due to the existence of heterogeneous silicon islands, but also greatly increases the driving current of the device. This also makes the device work faster, as shown in Figure 6(b). Under the same input waveform, the speed of the inverter composed of special-shaped silicon island SOI field effect transistors is faster than that of conventional SOI field effect transistors. Figure 6(c) compares the short channel effect of the devices with two structures. When the channel length is reduced from 1 μm to 0.1 μm, the threshold voltage shift of the heterogeneous silicon island SOI thick film fully depleted device is significantly smaller than that of the conventional structure. When the channel length L=0.1 μm, the threshold voltage shift of the special-shaped silicon island SOI field effect transistor is about 60 mV smaller than that of the conventional SOI device. Therefore, the special-shaped silicon island SOI field effect transistor is a better choice for small-sized SOI devices.

Claims (10)

1, a kind of thick film SOI field-effect transistor, it comprises source region, drain region, gate oxide, bury oxide layer, the body of the thick film SOI field-effect transistor of back of the body grid, silicon fiml, substrate and raceway groove, it is characterized by: the special-shaped silicon island that is provided with a phase contra-doping at the interface near described back of the body grid.

2, according to the described a kind of thick film SOI field-effect transistor of claim 1, it is characterized in that: described special-shaped silicon island is positioned at the bottom center place of silicon fiml.

3, according to claim 1 or 2 described a kind of thick film SOI field-effect transistors, it is characterized in that: described special-shaped silicon island width is about 3/5ths of described channel length.

4, according to claim 1 or 2 described a kind of thick film SOI field-effect transistors, it is characterized in that: described special-shaped silicon island thickness equals half of described silicon film thickness.

5, according to claim 1 or 2 described a kind of thick film SOI field-effect transistors, it is characterized in that: described special-shaped silicon island width is about 3/5ths of described channel length, and thickness equals half of described silicon film thickness.

6, according to claim 1 or 2 described a kind of thick film SOI field-effect transistors, it is characterized in that: described special-shaped silicon island doping content is higher than the doping content of described silicon fiml.

7, according to the described a kind of thick film SOI field-effect transistor of claim 2, it is characterized in that: described channel length L=1 μ m, silicon film thickness is t _Si=0.4 μ m, gate oxide thickness t _Ox=20nm, source-drain area doping content Nn ⁺=1 * 10 ²⁰Cm ^-3, the silicon fiml doping content is Filmdoping=1 * 10 ¹⁷Cm ^-3, bury oxidated layer thickness t _Box=0.2 μ m, substrate doping Np ^-=5 * 10 ¹⁶Cm ^-3, thickness t _Sub=0.3 μ m.

8, according to the described a kind of thick film SOI field-effect transistor of claim 7, it is characterized in that: the excursion of described special-shaped silicon island doping content is 1 * 10 ¹⁷Cm ^-3-5 * 10 ¹⁸Cm ^-3Between.

9, according to the described a kind of thick film SOI field-effect transistor of claim 7, it is characterized in that: the scope of design of described silicon island thickness T is between the 0.18 μ m-0.28 μ m;

10, a kind of thick film SOI field-effect transistor according to claim 7 is characterized in that: described silicon island half width W is between 0.25 μ m-0.3 μ m.

Images