CN104409409A - Method for improving SiC stress property of shallow trench isolation edge - Google Patents

Abstract

The invention provides a method for improving the stress performance of the shallow trench isolation edge SiC. The step of forming shallow trench isolation in the silicon substrate includes: sequentially depositing a pad layer silicon dioxide layer with a first thickness and a pad layer silicon nitride layer with a second thickness on the surface of the silicon substrate; wherein, for use The photolithography process, select the first thickness of the pad layer silicon dioxide layer to adjust the height of the shallow trench isolation to be formed, and select the first thickness of the pad layer silicon dioxide layer to meet the photolithography conditions; then the pad layer Active area photolithography and etching of the silicon dioxide layer, pad silicon nitride layer, and silicon substrate to form recesses in the silicon substrate; the recesses are then filled with silicon dioxide and the fill is chemical-mechanical polished The silicon dioxide is planarized to obtain shallow trench isolation; the pad silicon nitride layer is then stripped.

Description

Method for Improving Shallow Trench Isolation Edge SiC Stress Performance

technical field

The invention relates to the field of semiconductor manufacturing, and more specifically, the invention relates to a method for improving the stress performance of shallow trench isolation edge SiC by optimizing the pad layer silicon nitride layer process.

Background technique

With the rapid development of VLSI technology, the size of MOSFET devices is continuously reduced, which usually includes the reduction of the channel length of MOSFET devices, the thinning of gate oxide layer thickness, etc. to obtain faster device speed. However, with the development of VLSI technology to the ultra-deep submicron level, especially when the technology node is 90 nanometers and below, reducing the channel length will bring a series of problems. In order to control the short channel effect, it will be in the channel Doping with a higher concentration of impurities will reduce the mobility of carriers, resulting in a decrease in device performance. It is difficult to simply reduce the size of the device to meet the development of large-scale integrated circuit technology. Therefore, stress engineering has been extensively studied to enhance carrier mobility, thereby achieving faster device speeds and satisfying the rules of Moore's law.

From the 1980s to the 1990s, the academic community had already begun to realize heterostructure research based on silicon-based substrates, and it was not until the beginning of this century that commercial applications were realized. There are two representative stress applications, one is biaxial stress technology (Biaxial Technique); the other is uniaxial stress technology (Uniaxial Technique), namely stress memory technology (Stress Memorization Technology), nCESL and selective ( or embedded) epitaxially grown silicon-carbon SiC drain source (see literature "K.W.Ang et al., IEDM Tech.Dig., pp.1069, 2004" and literature "Y.C.Liu et al., VLSI, pp.44-45, 2007 ") Apply tensile stress to the channel of NMOSFET to increase the mobility of electrons, selectively (or embed) epitaxial growth of silicon germanium SiGe, pCESL to apply compressive stress to the channel of PMOSFET to improve the mobility of holes, thereby improving the performance of the device, see figure 2.

At present, the research on the SiC epitaxial growth process mainly focuses on how to increase the concentration of carbon in SiC. The higher the concentration of carbon, the greater the lattice mismatch, the greater the stress generated, and the more significant the increase in carrier mobility; In addition, due to the shape of SiC, the drain source of SiC is close to the edge of polysilicon, that is, close to the device channel, the more the stress acts on the carriers of the device channel directly, the better the performance of the device is.

All of the above research and development are based on silicon substrates, that is to say, silicon substrates provide the seeds for SiC growth, and SiC grows epitaxially along the crystal lattice of silicon. However, in the semiconductor process, devices are separated by shallow trenches. The process (STI) achieves electrical isolation, and silicon dioxide is used for filling in STI. Therefore, at the edge of STI and the active area, the SiC epitaxial process will be affected by STI. STI cannot provide enough silicon "seeds", and SiC will appear. The SiC growth on the left and right sides of the STI edge in the selective epitaxy process is low or even absent.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for improving the stress performance of shallow trench isolation edge SiC by optimizing the pad silicon nitride layer process in view of the above-mentioned defects in the prior art.

In order to achieve the above technical purpose, according to the present invention, a method for improving the stress performance of shallow trench isolation edge SiC is provided, including: forming shallow trench isolation in a silicon substrate; performing well implantation to form an N-type well and/or P-type well; make gate oxide layer, perform gate polysilicon material deposition, and perform gate polysilicon photolithography to form gate; silicon dioxide protective layer generated by atomic deposition; make first gate spacer Perform PMOS lightly doped implantation to form a PMOS device drain lightly doped structure; perform germanium silicon epitaxial growth process; perform NMOS lightly doped implantation to form an NMOS device drain lightly doped structure; make the second gate spacer, the second gate The side walls include SiO2 layer and SiN layer; forming NMOS source and drain SiC epitaxial regions.

Preferably, the step of forming shallow trench isolation in the silicon substrate includes: sequentially depositing a pad layer silicon dioxide layer with a first thickness and a pad layer silicon nitride layer with a second thickness on the surface of the silicon substrate; wherein, For the photolithography process used, the first thickness of the pad silicon dioxide layer is selected to adjust the height of the shallow trench isolation to be formed, and the first thickness of the pad silicon dioxide layer is selected to meet the photolithography conditions; and then Pad silicon dioxide layer, pad silicon nitride layer, and silicon substrate are subjected to active area lithography and etching to form recesses in the silicon substrate; the recesses are then filled with silicon dioxide and polished by chemical mechanical polishing The filled silicon dioxide is planarized to obtain shallow trench isolation; the pad silicon nitride layer is then stripped.

Preferably, the second thickness of the pad silicon nitride layer is selected as the maximum thickness satisfying the photolithographic conditions, thereby maximizing the height of the shallow trench isolation.

Preferably, the step of forming shallow trench isolation in the silicon substrate makes the upper surface of the shallow trench isolation higher than the upper surface of the silicon wafer substrate.

Preferably, the step of forming shallow trench isolation in the silicon substrate makes the upper surface of the shallow trench isolation not lower than the upper surface of the silicon wafer substrate.

Preferably, the step of forming the NMOS source-drain SiC epitaxial region includes: first depositing a silicon nitride layer as a SiC growth barrier layer, using the silicon nitride layer to perform photolithography to define the SiC region, and then performing embedded silicon stemming for the SiC region etched to form a U-shaped silicon groove.

The present invention rationally optimizes the thickness of the silicon nitride layer of the pad layer, thereby controlling the thickness from the surface of the shallow trench isolation silicon oxide layer to the silicon surface of the active region, so that a reasonable shallow trench can be obtained without affecting photolithography The height of the isolation controls the loss of the sidewall silicon in the shallow trench isolation by the embedded silicon etching process in the subsequent SiC process, enhances the SiC epitaxial growth capability, and improves the SiC semiconductor process capability.

Description of drawings

A more complete understanding of the invention, and its accompanying advantages and features, will be more readily understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 schematically shows the height difference between the STI silicon oxide layer and the silicon surface of the active region.

FIG. 2 schematically shows a flowchart of a method for improving stress performance of STI edge SiC according to a preferred embodiment of the present invention.

3 to 6 schematically illustrate various steps of a method for improving stress performance of STI edge SiC according to a preferred embodiment of the present invention.

7 to 10 schematically show different device structures obtained by pad silicon nitride layers with different thicknesses.

It should be noted that the accompanying drawings are used to illustrate the present invention, but not to limit the present invention. Note that drawings showing structures may not be drawn to scale. And, in the drawings, the same or similar elements are marked with the same or similar symbols.

detailed description

In order to make the content of the present invention clearer and easier to understand, the content of the present invention will be described in detail below in conjunction with specific embodiments and accompanying drawings.

Through research, the inventors advantageously found that the reason for the low or even missing SiGe growth on the left and right sides of the STI edge is due to the height difference between the shallow trench isolation (STI) silicon oxide layer and the silicon surface of the active region. When the STI height is lower than On the surface of silicon AA in the active area of the device, during the embedded silicon etching process, the silicon above the STI surface is etched away, which cannot provide silicon "seeds" for subsequent SiC growth, resulting in SiC on the left and right STI edges. Growth is reduced or even absent. Therefore, as shown in FIG. 1 , the height difference 12 between the STI silicon oxide layer 20 and the silicon surface of the active region 10 and the amount of silicon at the edge of the STI (shown by the dotted line in FIG. 1 ) are crucial to the SiC process.

In the present invention, by optimizing the pad silicon dioxide layer, the thickness of the STI silicon oxide layer to the silicon surface of the active region is controlled, thereby controlling the Si Recess Etch process (Si Recess Etch, also known as silicon groove etching) in the SiC process. etch) to the loss of silicon on the sidewall of the shallow trench isolation, enhance the selective epitaxial growth capability of SiC, and improve the process capability of SiC semiconductor process.

FIG. 2 schematically shows a flowchart of a method for improving stress performance of STI edge SiC according to a preferred embodiment of the present invention.

Specifically, as shown in FIG. 2, the method for improving the stress performance of STI edge SiC according to a preferred embodiment of the present invention includes:

First, step S10 is performed to form shallow trench isolation 20 in the silicon substrate 10 .

Step S10 may specifically include the following steps:

First, on the surface of the silicon substrate 10, a pad silicon dioxide layer 1 of a first thickness and a pad silicon nitride layer 2 of a second thickness are sequentially deposited (as shown in FIG. 3 ); wherein, for the photolithography process used, The first thickness of the pad layer silicon dioxide layer 1 is selected to adjust the height of the shallow trench isolation to be formed, and the first thickness of the pad layer silicon dioxide layer 1 is selected to meet the photolithographic conditions; for example, preferably, the pad layer The second thickness of the silicon nitride layer 2 is selected as the maximum thickness that satisfies the photolithographic conditions (thereby the height of the maximum shallow trench isolation in the current situation can be obtained);

Then carry out active area photolithography and etching to the pad silicon dioxide layer 1, the pad silicon nitride layer 2 and the silicon substrate 10 so as to form a groove 3 in the silicon substrate 10 (as shown in FIG. 4 );

Then fill the groove 3 with silicon dioxide and planarize the filled silicon dioxide by chemical mechanical polishing to obtain shallow trench isolation 20 (as shown in FIG. 5 );

Then the pad silicon nitride layer 2 is peeled off (as shown in FIG. 6 ).

As shown in FIGS. 7 to 10 , a thicker pad silicon nitride layer 2 results in a higher height of the STI oxide layer. Figure 7 and Figure 8 show the height of the STI oxide layer when the thickness of the pad silicon nitride layer 2 is relatively small (as shown by the double arrow in Figure 8), and Figures 9 and 10 show the height of the pad silicon nitride layer 2 The height of the STI oxide layer when the thickness is relatively large (shown by the double arrow in Figure 8).

Preferably, the step of forming the shallow trench isolation 20 in the silicon substrate 10 makes the upper surface of the shallow trench isolation 20 higher than the upper surface of the silicon substrate.

Next, step S11 is performed, performing well implantation to form an N-type well and/or a P-type well.

Then proceed to step S12 , forming a gate oxide layer, performing gate polysilicon material deposition, and performing gate polysilicon photolithography to form a gate.

Then continue to step S13, the silicon dioxide protective layer formed by atomic deposition is used to protect the silicon surface of the device and reduce the loss of surface silicon.

Next, step S14 is continued, optionally, lightly doped implantation is performed on the input-output device region to form a lightly doped drain structure of the peripheral input-output device.

Then continue to step S15 , forming the first gate spacer; for example, the material of the first gate spacer is SiN; specifically, for example, the step of forming the first gate spacer includes SiN deposition and etching.

Next, step S16 is continued, performing PMOS lightly doped implantation to form a lightly doped drain structure of the PMOS device.

Then continue to step S17 to perform a SiGe epitaxial growth process.

Next, step S18 is continued, performing NMOS lightly doped implantation to form a drain lightly doped structure of the NMOS device.

Then continue to step S19, forming a second gate spacer, the second gate spacer includes a _SiO2 layer and a SiN layer; for example, the formation of the second gate spacer includes deposition and etching of poly-SiO2 and SiN.

Next, step S20 is continued to form NMOS source and drain SiC epitaxial regions. Among them, first deposit a silicon nitride layer as a SiC growth barrier layer, use the silicon nitride layer to perform photolithography to define the SiC region, and then perform embedded silicon dry etching for the SiC region to form a U-shaped silicon groove.

When the upper surface of the STI is lower than the silicon surface of the active region, all the silicon above the upper surface of the STI will be etched, and SiC will grow low or even missing at the edge of the STI. When the upper surface of the STI is higher than the silicon surface of the active region, the STI oxide layer will protect the silicon on the edge sidewall, as shown in the range of the dotted circle in Figure 1, which reduces the loss of silicon on the sidewall of the STI and enhances the epitaxial growth capability of SiC , Improve the process capability of SiC semiconductor process.

Then continue to step S21, performing source and drain implantation to form source and drain.

Pre-metal dielectrics, vias, metal plugs and metal layers are then fabricated.

The present invention rationally optimizes the thickness of the silicon nitride layer of the pad layer, thereby controlling the thickness from the surface of the shallow trench isolation silicon oxide layer to the silicon surface of the active region, so that a reasonable shallow trench can be obtained without affecting photolithography The height of the isolation controls the loss of the sidewall silicon in the shallow trench isolation by the embedded silicon etching process in the subsequent SiC process, enhances the SiC epitaxial growth capability, and improves the SiC semiconductor process capability.

It can be understood that although the present invention has been disclosed above with preferred embodiments, the above embodiments are not intended to limit the present invention. For any person skilled in the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or be modified to be equivalent to equivalent changes. Example. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention, which do not deviate from the technical solution of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims (8)

1. A method for improving the stress performance of shallow trench isolation edge SiC, characterized in that it comprises: Form shallow trench isolation in the silicon substrate; performing well implantation to form N-type wells and/or P-type wells; Fabricate the gate oxide layer, perform gate polysilicon material deposition, and conduct gate polysilicon photolithography to form the gate; Silicon dioxide protective layer produced by atomic deposition. 2. The method for improving the stress performance of STI edge SiC according to claim 1, further comprising: making the first grid spacer; Perform PMOS lightly doped implantation to form a PMOS device drain lightly doped structure; Carry out epitaxial growth process of silicon germanium; Perform NMOS lightly doped implantation to form NMOS device drain lightly doped structure; making a second gate spacer, the second gate spacer includes a SiO2 layer and a SiN layer; NMOS source and drain SiC epitaxial regions are formed. 3. The method for improving the stress performance of STI edge SiC according to claim 1 or 2, wherein the step of forming STI in the silicon substrate comprises: On the surface of the silicon substrate, a pad silicon dioxide layer of a first thickness and a pad silicon nitride layer of a second thickness are sequentially deposited; wherein, for the photolithography process used, the first thickness of the pad silicon dioxide layer is selected To adjust the height of the shallow trench isolation to be formed, and select the first thickness of the pad silicon dioxide layer to meet the photolithographic conditions; Active area lithography and etching are then performed on the pad silicon dioxide layer, pad silicon nitride layer, and silicon substrate to form recesses in the silicon substrate; Then fill the groove with silicon dioxide and planarize the filled silicon dioxide by chemical mechanical polishing to obtain shallow trench isolation; The pad silicon nitride layer is then stripped off. 4. The method for improving the stress performance of SiC at the edge of shallow trench isolation according to claim 3, characterized in that, the second thickness of the pad silicon nitride layer is selected as the maximum thickness satisfying the photolithographic conditions, thereby making the shallow trench isolation The height of the trench isolation is maximized. 5. The method for improving the stress performance of STI edge SiC according to claim 1 or 2, characterized in that the step of forming STI in the silicon substrate makes the upper surface of STI higher than the upper surface of the silicon wafer substrate. 6. The method for improving the stress performance of SiC at the edge of shallow trench isolation according to claim 1 or 2, characterized in that, the step of forming shallow trench isolation in the silicon substrate makes the upper surface of the shallow trench isolation not lower on the top surface of the silicon wafer substrate. 7. The method for improving the stress performance of SiC at the edge of shallow trench isolation according to claim 1 or 2, characterized in that the step of forming the NMOS source-drain SiC epitaxial region comprises: first depositing silicon nitride as a SiC growth barrier layer layer, using a silicon nitride layer to perform photolithography to define a SiC region, and then perform embedded silicon dry etching for the SiC region to form a U-shaped silicon groove. 8. The method for improving the stress performance of STI edge SiC according to claim 1 or 2, characterized in that the method is used for manufacturing MOS transistors.