JP3439657B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a nitrogen-containing dielectric layer formed on a surface of a semiconductor substrate. It is about the method. 2. Description of the Related Art A stable thermal oxide film is used as an insulating film for a gate dielectric layer of a MOS transistor. However, in order to increase the density and integration of an VLSI and to increase the operation speed, the thickness of the thin film is reduced. Is required. As the film becomes thinner, the initial withstand voltage (TZD
B), the amount of dielectric breakdown charge (Qbd), and the resistance to hot carriers are reduced. Therefore, it is important to improve these characteristics. Another important issue is the control of the threshold (Vth) shift due to boron penetration when using a P ⁺ gate. A nitrogen-containing dielectric layer grown using nitrous oxide (N ₂ O) has these characteristics better than a thermal oxide film, and the gate dielectric layer is formed in a nitrous oxide atmosphere. I have. However, it has been found that dielectric layers formed in a nitrous oxide atmosphere exhibit other undesirable characteristics. For example, it has been pointed out that a dielectric layer formed in a nitrous oxide atmosphere has a high interface state density. This characteristic causes a reduction in mobility and results in a reduction in drive current of the transistor element. [0005] It is considered that such characteristics are caused by the high concentration of nitrogen bonded to the interface between the nitrogen-containing dielectric layer and the semiconductor substrate. To obtain both the effective properties of a dielectric layer grown with nitrous oxide and the effective properties of a nitrogen-free dielectric layer formed by thermal oxidation, as shown in FIG. After forming the dielectric layer in an atmosphere, the substrate is re-oxidized in an oxidizing atmosphere, and a thermal oxide film is further grown between the substrate and nitrogen existing at the interface between the substrate and the dielectric layer. As a result, a dielectric layer having improved initial dielectric strength (TZDB), dielectric breakdown charge (Qbd), and hot carrier resistance and having a low interface state density can be obtained. FIG. 8 is a view showing a conventional process of forming an oxide film between a nitrogen-containing dielectric layer and a semiconductor substrate. However, reoxidation increases the thickness of the dielectric,
The capacitance of the dielectric layer decreases, and the drive current of the transistor decreases. As a method of reducing the interface state, there is a method of forming a silicon-halogen bond by performing a heat treatment in a halogen-containing atmosphere. This is not enough to reduce the level, and furthermore, there is a problem that the atmosphere containing halogen has an etching effect and conversely roughens the interface between the substrate and the oxide film. According to a first aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the step of forming a nitrogen-containing first dielectric layer on a semiconductor substrate. In the manufacturing method, a thermal oxide film is formed by oxidizing a semiconductor substrate in an atmosphere of oxygen and nitrogen, and after forming the nitrogen-containing first dielectric layer on the semiconductor substrate, an oxidizing atmosphere of oxygen and hydrochloric acid is formed. Wherein a second dielectric layer is formed between the semiconductor substrate and the first dielectric layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, based on one embodiment,
The present invention will be described in detail. FIG. 1 is a view showing a process of forming an oxide film between a nitrogen-containing dielectric layer of the present invention and a semiconductor substrate, and FIG. 2 is a diagram showing an oxide film formed between the nitrogen-containing dielectric layer and the semiconductor substrate. FIG. 3 is a cross-sectional view of the configuration when formed. Hereinafter, a manufacturing process of the semiconductor device of the present invention will be described with reference to FIGS. First, a silicon substrate 1 as a semiconductor substrate is loaded into a reactor in a first temperature state (room temperature to 900 ° C., for example, 700 ° C.). Next, the inside of the reactor is filled with a mixed atmosphere of oxygen and nitrogen (for example, oxygen 0.5%), the temperature is raised to a second temperature state (500 to 1000 ° C., for example, 750 ° C.), and the reactor is heated for a certain time (for example, 10 minutes). )Hold. Here, the holding at the second temperature state is to grow a thermal oxide film (not shown) slightly on the surface of the silicon substrate 1 and to prevent nitriding and roughening of the silicon substrate surface at the time of loading and at the time of temperature. is there. Specifically, a thermal oxide film having a thickness of 0.1 to 3.0 nm is formed. The interface level decreases as the thickness of the thermal oxide film increases, but the effect is saturated at a thickness of 3.0 nm or more. In this embodiment mode, a thermal oxide film having a thickness of 1.0 nm is formed. Next, the reactor is placed in a nitrogen atmosphere,
The temperature is raised to a temperature state (600 to 1200 ° C., for example, 900 ° C.). In the third temperature state, the inside of the reactor is kept in a nitrous oxide atmosphere for a certain period of time (for example, 10 minutes) to form the first dielectric layer 2 containing nitrogen. Although the thickness of the first dielectric layer 2 is preferably as small as possible, the holding time in nitrous oxide and the temperature are determined by the amount of nitrogen introduced necessary for the device to be applied. Specifically, the first dielectric layer 2 having a thickness of 1.0 to 20.0 nm, for example, 3.0 nm is formed (FIG. 2A). Thereafter, the interior of the reactor at the third temperature is set to a mixed atmosphere of oxygen and hydrochloric acid (for example, 3% of hydrochloric acid with respect to the whole mixed atmosphere), and an interface between the substrate and the first dielectric layer 2 is formed. 2) and a substrate, and a second dielectric layer 3 made of a silicon oxide film is grown (FIG. 2B). The thickness of the second dielectric layer 3 is determined from the amount of current in the channel of the transistor and the insulating characteristics. Here, for example, annealing is performed only in a hydrochloric acid atmosphere, and if the second dielectric layer 3 is not grown, the substrate is roughened by etching with chlorine, leading to deterioration of characteristics. Dielectric layer 3 is slightly (about 0.1 n
m or more), for example, annealing is performed while growing 0.6 nm. In order to reduce the interface state density, the thicker the second dielectric layer 3 is, the more effective it is. However, as the thickness of the second dielectric layer 3 is larger, the penetration of boron is more likely to occur, resulting in a threshold shift. Therefore, the optimum film thickness differs depending on the device used. At this time, in a hydrogen atmosphere, the substrate is not roughened and the film thickness does not increase. However, dissociation occurs at the same time as the silicon-hydrogen bond progresses, that is, an equilibrium state is established. The level cannot be reduced. Therefore,
In order to sufficiently reduce the interface state, it is effective to combine a method in which a silicon oxide film is further grown on the interface between the substrate and the dielectric layer and nitrogen is separated from the interface. Therefore, a mixed atmosphere of hydrogen and oxygen is effective. Alternatively, a wet oxidation atmosphere is desirable. Thereafter, the first dielectric layer and the second dielectric layer formed in the above steps are used as a gate insulating film,
A MOS transistor is manufactured using a conventional technique. The formation of the second dielectric layer in a wet oxidation atmosphere is performed under the following conditions. For example, when the volume of hydrogen is 1, the volume of oxygen is 1, water is generated in the apparatus, and wet oxidation is performed at 600 to 1200C, for example, 900C. Next, the inside of the reactor is cooled to a fourth temperature state (for example, 700 ° C.) in a nitrogen atmosphere, and the substrate is unloaded. FIGS. 3 and 4 show the results of the evaluation of the interface state density and the minority carrier lifetime with respect to the film thickness of the entire dielectric layer, respectively. 5 and 6 show the relationship between the breakdown charge amount and the failure rate. FIG. 7 shows the relationship between the reoxidation time, the overall thickness of the dielectric layer, and the thickness of the second dielectric layer. In FIGS. 3 and 4, the film thickness increased by the re-oxidation is shown in parentheses. From FIG. 3, the thickness of the dielectric layer is the same, and the oxygen atmosphere and the mixed atmosphere of oxygen and hydrochloric acid are used. Can be seen that the interface state density is lower in the mixed atmosphere method of oxygen and hydrochloric acid than in the oxygen atmosphere. FIG. 4 also shows that the minority carrier lifetime is longer in the mixed atmosphere of oxygen and hydrochloric acid than in the oxygen atmosphere. 3 and 4 show that the reoxidation atmosphere was changed from an oxygen atmosphere to a mixed atmosphere of oxygen and hydrochloric acid, so that defects in the substrate and at the interface between the substrate and the dielectric layer were terminated with hydrogen groups. Probably because it was done. Therefore, by adding a hydrogen-containing atmosphere at the time of oxidation, good characteristics can be obtained with a re-oxidized film thickness smaller than before, and it can be said that this is very effective for thinning the dielectric layer. FIG. 5 shows the evaluation results of Qbd. With the retention time in nitrous oxide kept constant, the thickness of the re-oxidized film and that of the sample not subjected to re-oxidation were controlled by controlling the thickness of the oxide film before exposure to nitrous oxide so that the total thickness of the dielectric layer was 4%. 0.5 nm. It can be seen that the Qbd value when the reoxidation atmosphere is a mixed atmosphere of oxygen and hydrochloric acid is slightly larger than that without reoxidation and with oxygen. This is because, in addition to the same reason as in FIGS. 3 and 4, oxidation in a hydrochloric acid mixed atmosphere is more insulative than in the case of oxidation with oxygen. The film that transitions to a film is thin, and the dielectric layer as a whole has better insulating properties than before. FIG. 6 shows the result of comparison of reoxidation between an oxygen atmosphere and a wet oxidation atmosphere. Although the thickness of the dielectric layer is thinner than that of FIG. 5, good results are obtained by wet oxidation. It can be seen that the oxide film structure is also improved and the same effect can be obtained by performing wet oxidation for re-oxidation. Therefore, by using this oxidation method, a dielectric layer having a lower interface state density while having better dielectric breakdown characteristics than conventional oxidation can be obtained. FIG. 7 shows the re-oxidation rate in oxygen and a mixed atmosphere of oxygen and hydrochloric acid. Compared with oxygen and a mixed atmosphere of oxygen and hydrochloric acid, the variation in film thickness within the substrate surface is almost the same, and the oxidation rate of the mixed atmosphere of oxygen and hydrochloric acid is faster than that of the oxygen atmosphere, and the processing time is shorter. Can be reduced. In FIG. 7, the solid line indicates the entire thickness of the dielectric layer, and the dotted line indicates the thickness of the second dielectric layer. As described in detail above, according to the present invention, a nitrogen-containing dielectric layer having a low interface state density and excellent insulating properties can be obtained, and the reliability of the device can be improved. And productivity can be improved. Further, the thermal oxide film is partially cut in an atmosphere of oxygen and nitrogen.
By oxidizing the conductive substrate, nitridation and roughening of the substrate surface before forming the first dielectric layer can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a step of forming an oxide film between a nitrogen-containing dielectric layer of the present invention and a semiconductor substrate. FIG. 2 is a cross-sectional view illustrating a configuration when an oxide film is formed between a nitrogen-containing dielectric layer and a semiconductor substrate. FIG. 3 is a diagram showing the results of evaluation of interface state density with respect to the thickness of the entire dielectric layer. FIG. 4 is a diagram showing a result of evaluating a minority carrier lifetime with respect to a film thickness of an entire dielectric layer. FIG. 5 is a diagram illustrating a relationship between a first breakdown charge amount and a failure rate. FIG. 6 is a diagram showing a relationship between a second breakdown charge amount and a failure rate. FIG. 7 is a diagram showing the relationship between the reoxidation time and the total thickness of a dielectric layer and the thickness of a second dielectric layer. FIG. 8 is a view showing a conventional process of forming an oxide film between a nitrogen-containing dielectric layer and a semiconductor substrate. [Description of Signs] 1 Silicon substrate 2 First dielectric layer 3 Second dielectric layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/318 H01L 29/78

Claims (1)

(57) A method of manufacturing a semiconductor device having a step of forming a nitrogen-containing first dielectric layer on a semiconductor substrate, wherein the semiconductor substrate is oxidized in an atmosphere of oxygen and nitrogen. After forming a thermal oxide film and forming the nitrogen-containing first dielectric layer on the semiconductor substrate, a thermal oxide film is formed between the semiconductor substrate and the first dielectric layer in an oxidizing atmosphere of oxygen and hydrochloric acid. Forming a second dielectric layer on the substrate.