CN1834288A - Low temp chemical gaseous deposition for preparing silicon nitride thin film - Google Patents

Abstract

The invention relates to a method for preparing a silicon nitride (SiN _x ) film at low temperature by chemical vapor deposition, which belongs to the field of semiconductor films. It is characterized by using NH ₃ as the N source, and the organosilicon source precursor with the general formula (R ₁ R ₂ N) _n Si(R ₃ ) _4-n as the Si source (wherein R ₁ , R ₂ ＝H, CH ₃ , C ₂ H ₅ , C ₃ H ₇ , C ₄ H ₉ ; R ₃ =H, Cl; n=2, 3, 4), under optimized process conditions, through low-pressure chemical vapor deposition process, it can be Uniform, low H and C content, near-stoichiometric SiN _x films were prepared at low reaction temperature. The _SiNx (X=1.28-1.33) thin film prepared by the invention can be used in the semiconductor industry and silicon-based solar cells.

Description

A method for preparing silicon nitride film by low-temperature chemical vapor deposition

technical field

The present invention relates to a kind of method that adopts chemical vapor deposition (CVD) to prepare SiN _x thin film at low temperature, more precisely with _NH3 as nitrogen source, with organosilicon source precursor as silicon source, adopts low-pressure chemical vapor deposition ( The invention discloses a method for preparing _SiNx thin films by LPCVD) process at low temperature, belonging to the field of semiconductor thin films.

Background technique

In a semiconductor integrated circuit, an insulating film for electrical isolation between devices and between wirings is very important. In order to improve the stability and reliability of device performance, the device must be isolated from the surrounding environment to enhance the device's ability to block external ion contamination, control and stabilize the characteristics of the semiconductor surface, protect the internal interconnection of the device and prevent Devices are subject to mechanical and chemical damage. Due to the good interfacial compatibility with Si substrates and the characteristics of easy preparation, SiO ₂ thin films became the earliest surface protection materials used in integrated circuits. Compared with _SiO2 thin films, _SiNx thin films have obvious advantages in resistance to impurity diffusion (such as Na ⁺ ) and water vapor permeability, and at the same time have high breakdown strength, high chemical stability, and excellent mechanical properties, thus becoming a semiconductor The most excellent surface passivation material in integrated circuits. In addition, in silicon-based solar cells, SiN _x thin films can be used as anti-reflection films, which can simultaneously play the role of surface passivation and internal passivation, thereby improving the conversion efficiency of solar cells.

SiN _x thin films can usually be prepared by chemical vapor deposition (CVD) and plasma enhanced CVD (PECVD). Among them, the deposition temperature of PECVD is low, so it has been greatly developed in the past two decades. However, the _SiNx films deposited by PECVD are usually non-stoichiometric and often contain a large amount of impurity elements, so the electrical properties are not satisfactory. With the rapid development of microelectronics technology, higher requirements are put forward for the electrical properties of SiN _x thin films, so the preparation of SiN _x thin films by thermal CVD has been paid more attention. LPCVD is one of the thermal CVD methods widely used in the semiconductor industry. It is popular for its large loading capacity, low particle pollution, and high uniformity, and has become one of the main methods for preparing SiN _x thin films. At present, NH ₃ -SiH ₂ Cl ₂ system is commonly used in industry to prepare SiN _x thin films by LPCVD process, but the deposition reaction temperature is generally above 750°C. Excessively high reaction temperatures often cause the growth and spread of lattice defects and the redistribution of impurities in Si wafers, as well as severe warpage due to thermal stress. Therefore, it is very important to develop low-temperature thermal CVD processes to prepare SiN _x thin films. meaning.

Common silicon sources such as silane or silicon halide compounds are difficult to deposit SiN _x films at temperatures below 800°C, which greatly limits the application of thermal CVD in the field of microelectronics and semiconductors. The use of organic precursors can usually achieve the deposition of SiN _x thin films at relatively low temperatures, so the development of new Si source and N source precursors has attracted attention in recent years. RG Gordon et al. (RG Gordon, et al., Silicon dimethylamido complexes and ammonia as precursors for atmospheric pressure chemical vapor deposition of silicon nitride thin films, Chem. Mater., 1990, 2: 480-482.) Si[N(CH ₃ ) ₂ ] _n H _4-n (n=2-4) is the Si source, and a SiN _x film with a H content of about 8-10 at.% is prepared at 750° C. by using an atmospheric pressure CVD (APCVD) process. JMGrow et al. (JMGrow, et al., Grow kinetics and characterization of low pressure chemically vapor deposited Si ₃ N ₄ films from (C ₄ H ₉ ) ₂ SiH ₂ and NH ₃ , Maters Letters, 1995, 23: 187-193.) It is reported that using (C ₄ H ₉ ) ₂ SiH ₂ as Si source, using LPCVD process, at the reaction temperature of 600-700 ℃ to prepare SiN _x film. The prepared SiN _x film contains about 10 at.% C, In addition, the film also contains a certain amount of H element. Similarly, RALevy et al. (RALevy, et al., Lowpressure chemical vapor deposition of silicon nitride using the environmentally friendly tris(dimethylamino)silane precursor, J.Mater.Res., 1996, 11:1483-1488.) reported that [ (CH ₃ ) ₂ N] ₃ SiH as the Si source, using the LPCVD process to prepare SiN _x thin films at a reaction temperature of 650-800°C. The prepared SiN _x thin films contain about 5 at.% C. The SiN _x thin films prepared by these methods all contain different degrees of C or H contamination.

Contents of the invention

The object of the present invention is to provide a method for preparing SiN _x thin film at low temperature. The method for preparing _SiNx film provided by the present invention is to use _NH3 as N source, and organic silicon source precursor (R ₁ R ₂ N) _n Si(R ₃ ) _4-n as Si source (wherein R ₁ , R ₂ ＝H, CH ₃ , C ₂ H ₅ , C ₃ H ₇ or C ₄ H ₉ ; R ₃ ＝H or Cl; n=2, 3 or 4), using LPCVD process, the working pressure is 20-300Pa, basically Under the condition of sheet temperature of 600-900°C, through process optimization, SiN with uniform composition and thickness, low H and C content, and near-stoichiometric SiN can be prepared on the surface of Si substrate at a relatively low reaction temperature. _x film.

The object of the present invention is to be embodied through following technological process:

1. Device used

A hot-wall tubular diffusion furnace with a low-pressure reaction system, with a temperature control accuracy of ±1°C.

2. Raw materials used

Electronic grade NH ₃ is used as N source, organic silicon source precursor (R ₁ R ₂ N) _n Si(R ₃ ) _4-n is used as Si source (where R ₁ , R ₂ ＝H, CH ₃ , C ₂ H _5. C ₃ H ₇ or C ₄ H ₉ ; R ₃ =H, Cl; n=2, 3, 4), using high-purity N ₂ , H ₂ , Ar or He as the carrier gas to dilute the reaction raw materials, Adjust the total pressure of the reaction system.

3. Process conditions for preparing _SiNx thin films

Insert clean silicon wafers (single crystal silicon or polycrystalline silicon wafers) upright on the quartz boat, each time 50-100 silicon wafers can be loaded, placed at equal intervals, the distance between the wafers is 5-20mm, and the loaded quartz boat is placed on the The central position of the diffusion furnace is evacuated to below 0.5Pa by a vacuum pump, and the temperature is measured by a thermocouple, and the temperature of the substrate is controlled at 600-900°C, preferably 650-800°C. In order to ensure the uniformity of the deposited film, the diffusion furnace generates a temperature gradient along the radial direction, and the temperature gradient ranges from 10-30°C, preferably 15-25°C. The N and Si source materials are respectively introduced into the reaction system from the inlet end of the reactor, and the source bottle of the organosilicon source precursor and its transportation pipeline are insulated at 50-200°C, and the carrier gas (N ₂ , H ₂ , Ar or He) is introduced through the outlet port of the diffusion furnace to adjust the total pressure of the reaction system. The flow of all raw materials is regulated by mass flow meters, and the total pressure of the reaction system, that is, the diffusion furnace, is measured by a vacuum gauge. The total pressure of the reaction system is 20-300Pa, preferably 50-100Pa. The molar ratio of N and Si source materials is not less than 3:1, preferably 6-8:1.

Under optimized process conditions, after a period of deposition, a near-stoichiometric _SiNx thin film with uniform composition and thickness, low H and C content, and intra-chip and inter-chip can be obtained.

The method for preparing SiN _x thin films provided by the invention has very obvious advantages. Using a new organic Si source precursor as a raw material, through the LPCVD process, at a relatively low reaction temperature, a uniform composition and thickness (non-uniformity is not more than 10%) within the chip and between the chips can be prepared; the best , not more than 5%), low H content (H content is not more than 5 at.%; optimally, not more than 3.5%), low C content (C content is not more than 5 at.%; optimally, not more than 2%) 1. SiN _x thin film near stoichiometric (x=1.28~1.33; optimally, x=1.30~1.31). The prepared SiN _x film can be used for various surface passivation protective films, insulating layers, impurity diffusion masks and surface packaging of semiconductor components in the production of microelectronic materials and devices. In addition, it can be used as an anti-reflection film for silicon-based solar cells to improve the conversion efficiency of solar cells.

Description of drawings

Figure 1: The LPCVD device used in the present invention to prepare _SiNx thin films.

Fig. 2: FTIR spectrum of the _SiNx thin film prepared according to Example 1.

Fig. 3: AES depth component analysis spectrum of the _SiNx thin film prepared according to Example 1.

Fig. 4: Refractive index curve of the SiN _x film prepared according to Example 1.

Fig. 5: AFM surface topography photo of the _SiNx thin film prepared according to Example 1.

Detailed ways

The following examples are to further illustrate the present invention, but in no way limit the present invention.

Example 1

Insert clean 2-inch monocrystalline silicon wafers (p-type, 110) upright on the quartz boat, load 80 silicon wafers at a time, place them at equal intervals, and place the wafers at a distance of 8 mm. At the central position of the hot-wall tubular quartz reactor, turn on the vacuum pump and pump it down to below 0.5Pa. The temperature at the central position of the reactor, that is, the substrate temperature, is 700°C. In order to improve the uniformity of the deposited film, a resistance heating furnace (i.e. The temperature gradient between the inlet and outlet of the diffusion furnace) is 20°C, and the deposition can only start after the temperature is controlled to ±1°C. Use electronic grade high-purity NH ₃ as N source and [(C ₂ H ₅ ) ₂ N] ₃ SiCl as Si source, the flow rates of the two are 80 and 10 sccm respectively, and high-purity N ₂ (99.999%) is used as carrier gas After adjusting the system pressure, the total pressure of the reaction system is 80Pa. After the deposition is completed, the vacuum is continued to be below 0.5Pa, and the sample can be taken out by feeding _N2 to normal pressure. The thickness and refractive index of SiN _x film were measured by ellipsometer, and the deposition rate of SiN _x film could be calculated from the measured film thickness. The chemical composition of SiN _x films were analyzed by Fourier transform infrared (FTIR) and Auger photoelectron spectroscopy (AES). The surface morphology of SiN _x thin film was observed by atomic force microscope.

Under the above process conditions, the deposition rate of SiN _x film is about 12 Å/min. Film thickness measurements show that the deposited SiN _x thin film has an intra-sheet non-uniformity of <5% and an inter-chip non-uniformity of <8%. The FTIR spectra (Fig. 2) of the as-prepared SiN _x films only show very weak NH stretching vibration (3330cm ^-1 ) and Si-H stretching vibration absorption (2160cm ^-1 ), indicating that the H content in the film is very low. Further use the method of elastic recoil detection to measure the elastic recoil H atom energy spectrum of the film, collect the beam charge on the sample to normalize the energy spectrum, and take the standard sample (Si sheet with 2.7at% hydrogen) as the benchmark, the The content of H in the SiN _x film prepared under the process conditions is about 3.0at%. The strong absorption peak at 837cm ^-1 indicates the formation of Si-N bonds, and its broad peak shape indicates that the film is amorphous. AES (FIG. 3) depth analysis indicated that a near-stoichiometric _SiNx thin film (x=1.31) with uniform composition along the depth direction was prepared. There were no characteristic peaks of C and O in the AES spectra, indicating that the prepared SiN _x films did not contain C and O, or the contents of both were lower than the detection limit. The refractive index curve (FIG. 4) shows that the refractive index of the prepared SiN _x thin film is 1.935 at 632 nm. The AFM surface topography photos (Fig. 5) show that the prepared SiN _x film has a uniform and flat surface.

Example 2

Use high-purity NH ₃ as the N source and (C ₂ H ₅ NH) ₃ SiCl as the Si source. The flow rates of the two are 80 and 10 sccm respectively. The temperature at the center of the reactor is 680° C. The rest is the same as in Example 1. The content of H in the prepared SiN _x thin film is about 4.2 at%, and the nearly stoichiometric SiN _x thin film (x=1.30) does not contain C and O.

Example 3

Using high-purity NH ₃ as the N source and [(C ₃ H ₇ ) ₂ N] ₂ SiH ₂ as the Si source, the flow rates of the two are 80 and 10 sccm respectively, the temperature at the center of the reactor is 750°C, and the rest are the same as in Example 1 . The content of H in the prepared SiN _x thin film (x=1.28) is about 5.3 at%, and does not contain C and O.

Example 4

High-purity NH ₃ is used as N source, [(CH ₃ ) ₂ N] ₄ Si is used as Si source, the flow rates of the two are 70 and 10 sccm respectively, and the temperature at the center of the reactor is 720°C, and the rest are the same as in Example 1. The content of H in the prepared SiN _x thin film (x=1.31) is about 2.5 at%, and does not contain C and O.

Claims (10)

1, a kind of low temperature chemical vapor deposition prepares SiN _xThe method of film adopts the hot wall type tubular diffusion furnace with lp system, it is characterized in that with NH ₃For the N source, with (R ₁R ₂N) _nSi (R ₃) _4-nThe organosilicon presoma be the Si source, R in the formula ₁, R ₂=H, CH ₃, C ₂H ₅, C ₃H ₇, or C ₄H ₉, R ₃Be H or Cl, n=2,3 or 4, with N ₂, H ₂, a kind of as carrier gas among Ar and the He; Under 20-300pa work total pressure, substrate temperature is under the 600-900 ℃ of condition, prepares the SiN of nearly chemical dose at the Si substrate surface _xFilm.

2, prepare SiN by the described low temperature chemical vapor deposition of claim 1 _xThe method of film is characterized in that described Si substrate is a kind of in silicon single crystal or the polysilicon.

3, prepare SiN by claim 1 or 2 described low temperature chemical vapor depositions _xThe method of film is characterized in that the Si substrate uprightly is inserted on the quartz boat, equidistantly places, and a pitch of fins is 5-20mm, again quartz boat is positioned over the diffusion furnace middle position, and the silicon chip number is the 50-100 sheet.

4, prepare SiN by the described low temperature chemical vapor deposition of claim 1 _xThe method of film is characterized in that diffusion furnace radially produces one 10-30 ℃ temperature tonsure.

5, prepare SiN by the described low temperature chemical vapor deposition of claim 1 _xThe method of film is characterized in that the diffusion furnace total pressure is 50-100Pa.

6, prepare SiN by the described low temperature chemical vapor deposition of claim 1 _xThe method of film is characterized in that substrate temperature is 650-800 ℃.

7, prepare SiN by the described low temperature chemical vapor deposition of claim 4 _xThe method of film is characterized in that diffusion furnace thermograde radially is 15-25 ℃.

8, prepare SiN by the described low temperature chemical vapor deposition of claim 1 _xThe method of film is characterized in that the mol ratio in described N source and Si source is not less than 3: 1.

9, prepare SiN by the described low temperature chemical vapor deposition of claim 8 _xThe method of film, the mol ratio that it is characterized in that described N source and SSi source is 6～8: 1.

10, prepare SiN by the described low temperature chemical vapor deposition of claim 1 _xThe method of film is characterized in that prepared SiN _xFilm is near stoichiometric, x=1.28～1.33.

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