JPS6235266B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of forming a semiconductor nitride layer. The development of VLSI (Very Large Scale Integrated Circuits) is proceeding at a remarkable pace due to the reduction in the dimensional size of each device. The vertical size in VLSI must be considered in the same way as the horizontal size, but in the near future, the thickness of the gate insulating film of MOS transistors will be used to eliminate the short channel effect and stabilize _Vth. A value of about 100 Å is required for the purpose of increasing the However, when the SiO ₂ film as the gate oxide film is made thinner in this manner, the following disadvantages arise. (1) Since a 100 Å SiO ₂ film cannot be subjected to stabilization treatment such as phosphorus treatment, it has no masking effect to prevent contamination and is not useful as a protective film or a stabilizing film. (2) Since the film is thin, pinholes and non-uniformity in film thickness become noticeable, and problems in manufacturing technology remain. (3) The thickness of the gate oxide film further decreases due to the reaction between the SiO ₂ film and the gate electrode, and conduction occurs between the gate electrode and the semiconductor substrate due to the tunnel effect. Under these circumstances, the semiconductor industry is searching for a gate insulating film to replace the SiO ₂ film, but so far no suitable material has been found. On the other hand Si ₃ N ₄
The film is used as a memory transistor because it produces a memory effect when using the CVD method, but this is because the film quality is not good. In addition, there is a method of forming a Si ₃ N ₄ film by directly nitriding Si, but at practical temperatures and times, the thickness of the Si ₃ N ₄ film obtained is only about 50 Å at most, making it difficult to avoid the above-mentioned drawbacks. I can't. Silicon nitride (Si _x N _y ) such as Si ₃ N ₄ is a promising candidate as a gate insulating film to replace SiO ₂ film, but as mentioned above, there are difficulties in its manufacturing method, and it has not been put into practical use. has not been reached yet. The present invention provides a method for easily forming a silicon nitride film at a relatively low temperature and in a short time.
That is, the present invention includes a step of introducing iron ions into an oxide film on a semiconductor substrate, and a step of injecting the oxide film with a nitrogen-containing gas (here, "containing" means not only 100% nitrogen but also nitrogen as one component). (This also means a gas mixture of nitrogen compounds. The present invention relates to a method for forming a semiconductor nitride layer. Embodiments of the present invention will be described below with reference to the drawings. First, as shown in FIG. 1A, a SiO ₂ film 2 is formed on the surface of a silicon wafer 1 by thermal oxidation or CVD treatment.
It was grown to a thickness of 2000 Å. Next, as shown in FIG. 1B, 100 KeV Fe ⁺ ions 3 were implanted into the SiO ₂ film 2 at a dose of 1×10 ¹⁶ cm ⁻² . Under these implantation conditions, the range R _P of Fe ⁺ ions is
is 570 Å, and all of the ions are retained in the SiO ₂ film 2. Next, heat treatment was performed at 1200° C. for a predetermined time in an N ₂ gas atmosphere. Afterwards, when the wafer surface was analyzed using an X-ray microanalyzer, it was found that SiO ₂
It was found that the film 2 had been converted into a silicon nitride film 4 (FIG. 1C). Specific experimental data will be explained next. Five types of samples were created based on the above method. Sample 1: Annealed in N ₂ for 1 hour. Sample 2: Annealed in _N2 for 3 hours. Sample 3: Sample 1 etched with HF for 10 minutes. Sample 4: Sample 2 etched with HF for 10 minutes. Sample 5: After forming a thermally oxidized SiO ₂ film, it was annealed for 3 hours at 1200°C in N ₂ without implanting Fe ⁺ ions. As a result, the formation of white segregated substances was observed on the film surfaces of Samples 1 and 2, and it was found that these segregated substances still remained even after etching in Samples 3 and 2.
confirmed by. However, like sample 5
Even if annealing is performed without Fe ⁺ ion implantation,
It was confirmed that the SiO ₂ film surface did not change at all. Therefore, Fe, Si, O
When the concentration of these elements was measured using the electron probe microanalysis (EPMA) method, the data shown in Tables 1 and 2 below were obtained.

【table】

【table】

[Table] From these data, the following can be found. (1) The film surfaces of Samples 1 and 2 are almost entirely transformed into silicon nitride, but in Sample 5, in which Fe ions are not implanted, no transformation into silicon nitride occurs at all despite annealing in N ₂ . From this,
By implanting Fe ⁺ , the transformation point of SiO ₂ → silicon nitride (for example, Si ₃ N ₄ ) is lowered, and the transformation point is lowered to 1200
It is presumed that the nitriding reaction proceeds even at ℃.
Note that when annealing in N ₂ for 1 hour, silicon nitride grows thickly (Sample 1), but when annealing for 3 hours (Sample 2), an SiO ₂ film is formed on the silicon nitride film (this oxygen is mixed with O ₂ in N ₂ ). (by molecules) has grown. (2) If HF etching is performed as in Samples 3 and 4, the film is removed from the normal areas and the Si wafer surface is exposed, but the segregated substances still remain. All of these segregated substances are silicon nitride, with a trace amount of C.
(This is due to the carbon contained in the heat treatment furnace)
Contains O and Fe. However, since it can be considered that the composition is the same as Samples 1 and 2, it is considered that the film thickness was large in the segregated area and that it was not completely removed by etching and remained. As described above, it is fully possible to convert SiO ₂ to silicon nitride by implanting Fe ⁺ . Especially if you look at samples 3 and 4, where the Fe concentration in the segregated areas is about four times higher than in the normal areas,
It is thought that this Fe segregation promoted the reaction to silicon nitride. This is thought to be caused by the catalytic action of the nitriding reaction by the implanted Fe atoms, or by the formation of nitride film formation nuclei. As will be explained later, there is a correlation between the amount of Fe ⁺ implanted and the rate of nitride biofilm formation.
It was found that the nitriding reaction was significantly accelerated at a dose on the order of 10 ¹⁵ cm ^-2 or more. It is also known that the nitriding reaction proceeds very quickly when the crystal plane orientation of the Si wafer is (111). In the above example, the thickness of the silicon nitride film 4 is
The film thickness exceeded 1500 Å, but even if all SiO ₂ film 2 were converted to silicon nitride film, the film thickness would be 1250 Å.
Considering that the thickness is only about 250 Å, this means that the silicon 1 surface is directly nitrided by about 250 Å. This is surprising from the perspective of conventional concepts. To date, the nitride films obtained by directly nitriding the silicon surface are only 100 Å thick at most due to the limited diffusion rate of nitrogen radicals, but according to this example, the nitride films obtained by directly nitriding the silicon surface are only 100 Å thick. This means that the nitride film can be easily formed. In this case, the implanted region can be selectively formed by implanting Fe ⁺ 3 using a mask or by ion beam lithography. Therefore, any location can be selectively nitrided. As described above, since SiO ₂ can be effectively converted into silicon nitride, a silicon nitride film that can be substituted for SiO ₂ can be reliably formed. This silicon nitride film can be as thin as about 100 Å.
It can be formed as thick as about 1500 Å, has a good protection and stabilization effect, and has excellent pinhole and film thickness uniformity, making it suitable for VLSI gate insulating films and as an insulating film. Its general properties are also good. Furthermore, it is possible to provide a silicon nitride film that has good film quality and is easy to form. However, Fe ⁺ or Fe atoms usually have a harmful effect on semiconductor devices, but in this case, various gettering treatments have been considered (gettering by phosphorus doping on the back side of the wafer, chlorine-containing gas on the front side of the wafer, etc.). Fe can be removed at the final stage of the process by a method in which Fe is removed as iron chloride by flowing iron chloride. In the example above, nitrogen was used during annealing, but
Instead, a gas containing nitrogen as one component, such as NH ₃ or N ₂ H ₄ , may be used. Furthermore, if the SiO ₂ film is thin, for example about 100 Å, it is difficult to implant ^ions into this film even under low acceleration conditions. Fe ⁺ may be injected or doped into the SiO ₂ film by flowing nitrogen (containing nitrogen ₂ ). Furthermore, the semiconductor substrate that can be used may be other semiconductor substrates such as Ge wafers instead of Si wafers, and in short, SiO ₂ is added to the semiconductor substrate wafer.
Any material having an oxide film such as the like may be used. Next, in the process shown in FIG. 1, the above-mentioned ion species were implanted into the SiO ₂ film at various doses and then annealed. The results are shown in Table 3 below.

【table】

【table】 [Brief explanation of the drawing]

1A to 1C are cross-sectional views sequentially illustrating a method according to an embodiment of the present invention. In the symbols used in the drawings, 1...Si wafer, 2...SiO ₂ film, 3...Fe ⁺ , 4... silicon nitride film.

Claims (1)

[Claims] 1. A step of introducing iron ions into an oxide film on a semiconductor substrate, and a step of heat-treating the oxide film while bringing it into contact with a nitrogen-containing gas, thereby converting a predetermined region of the oxide film into nitride. A method for forming a semiconductor nitride layer, comprising: