JP2747556B2 - Method for manufacturing insulated gate field effect semiconductor memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a first dielectric film constituting a gate insulating film, a floating charge trapping central layer above the first dielectric film, and a second dielectric film. The present invention relates to a method for manufacturing an insulated gate field effect semiconductor memory device having the following. [Prior Art] When a non-volatile memory is to be manufactured using an insulated gate field effect semiconductor memory device, MNOS (gate electrode-silicon nitride-silicon oxide-silicon semiconductor substrate), MNCOS (gate electrode-silicon nitride film) -Semiconductor cluster or film-Silicon oxide film-Silicon semiconductor substrate), MNCNOS (Gate electrode-Silicon nitride film-Semiconductor cluster or film-Silicon nitride-
Many substrates such as a silicon oxide-silicon semiconductor substrate) are known. Further, a method is known in which a thin silicon oxide film is formed on the silicon semiconductor by a hydrochloric acid oxidation method with little deterioration. Typical examples thereof are the applicant's patent “Semiconductor memory device, Japanese Patent Publication No. Sho 50-36955”, and Ceramic Bulletin Vol64, No.
12 (1985) 1585-1589 "Metal-Insulator-Semiconduc
tor (Fulrath Award Paper). " [Problem to be Solved by the Invention] In such a nonvolatile memory, for the purpose of application to an IC card, an improvement in the number of times of rewriting has been demanded.
The number of times of rewriting of the IC card is from 1 × 10 ³ to 3 × 10 ³ times, and no means has been found so far. However, in the IC card or the like, has come to it is a strong demand it is possible to rewrite the more than 10 ⁶ times. Based on the criteria of “good” when the rate of change of rewriting is within 10% of the initial value, as a method of increasing the number of rewriting, a silicon oxide film closely contacting a semiconductor substrate is heated from 1150 ° C. to 1200 ° C. in ammonia. A method of transforming into silicon nitride at a high temperature of ° C. is known. Further, the semiconductor substrate itself is directly nitrided at a similar temperature to form a silicon nitride film 20 to
There is known a method of forming a thickness of 100 mm. Then
By using this silicon nitride, the structure of MNCNOS and MNCNS can be obtained. However, such high-temperature processing induces a stacking fault in a joint provided in the substrate, and promotes re-diffusion of impurities, resulting in deterioration of the substrate material, and
It must be said that it is insufficient in LSI. The present invention is intended to solve the above problems, and even if rewriting of a nonvolatile memory is repeated,
An object of the present invention is to provide an insulated gate field effect semiconductor memory device that does not deteriorate. Means for Solving the Problems In order to achieve the above object, a method for manufacturing an insulated gate field effect semiconductor memory device according to the present invention comprises the steps of:
And a channel forming region 10 formed in the semiconductor substrate 1.
And an N-type low-concentration impurity region (7-1) or (7'-1) formed in contact with the channel formation region 10, and an N-type high-concentration impurity region (7 -2) or (7'-2) a source region or a drain region, a first dielectric film, a floating charge trapping central layer, and a second dielectric film laminated on the channel formation region 10. And a silicon nitride film (3-D) formed on the channel formation region 10 by a photoreaction using ultraviolet light as a first dielectric film.
1) is formed. In the method for manufacturing an insulated gate field effect semiconductor memory device according to the present invention, a semiconductor substrate 1, a P-type channel formation region 10 formed on the semiconductor substrate 1, and a P-type channel formation region 10 are formed. N-type low concentration impurity region (7
-1) or (7'-1), and a source region or a drain region comprising an N-type high-concentration impurity region (7-2) or (7'-2) apart from the P-type channel formation region 10; A gate insulating film composed of a first dielectric film, a floating charge trapping central layer, and a second dielectric film laminated on the P-type channel formation region 10; A silicon nitride film is formed on the region 10 as a first dielectric film by a photoreaction using ultraviolet rays for 20 to 200.
It is characterized by being formed to a thickness of Å. In the present invention, the first dielectric film made of a silicon nitride film on the underlying silicon semiconductor substrate is formed as extremely thin as 10 ° to 50 °. Further, the source region or the drain region is provided with an N ^- low impurity concentration region in contact with the channel formation region to prevent deterioration due to rewriting. Further, a second layer is formed on a charge trapping central layer (also referred to as a trap layer) provided on the first dielectric film.
Is formed to obtain a MI ₂ TLI ₁ S (gate electrode−second dielectric film−charge trapping central layer−first dielectric film−semiconductor substrate) structure. is there. Then, a floating charge trapping center layer (floating trap layer) is obtained by a laminated structure of I ₁ TLI ₂ . The trap layer is formed of a cluster or thin film of a semiconductor such as a silicon semiconductor, or a layer having a dangling bond of the semiconductor. In particular, the first dielectric film is made of silicon nitride, and is formed on a semiconductor substrate or a blocking layer previously formed on the semiconductor, for example, on a silicon nitride film having a thickness of 5 to 20 degrees by a two-layer film. (I ₁ -TL). [Operation] The insulated gate field effect semiconductor memory device of the present invention is:
A source region or a drain region in contact with the P-type channel formation region was defined as an N-type low impurity concentration region, and an N ⁺ -type high impurity concentration region was formed further away from the channel formation region. For example, since the impurity concentration from the drain region to the junction surface with the channel formation region is reduced twice,
The electric field intensity in the reverse biased drain region is reduced. Therefore, the depletion layer formed between the P-type channel formation region and the vicinity of the N-type low impurity concentration region expands, and electrons flowing through the channel formation region collide with silicon in the depletion layer in this wide region and are stored in the floating trap layer. Hot carriers are generated. The present applicant has paid attention to the fact that the P-type channel formation region and the N ⁺ -type high impurity concentration region have a large difference in electric field strength, so that the depletion layer is narrow and the region where hot carriers are generated is also narrow. By adopting the structure of the present invention, the applicant widens the region where hot carriers are generated, and prevents local deterioration near the interface between the channel formation region and the source or drain region. In addition, the present inventors have found that it is possible to prevent a decrease in the number of rewrites due to the generation of a recombination portion for generating hot carriers in a region where stress concentration such as electron collision easily occurs. The present applicant has paid attention to the fact that when a silicon nitride film is formed by a photochemical reaction using ultraviolet light, a high-quality film without irregularities generated when the silicon nitride film is formed by a plasma CVD method can be obtained. In addition, the present applicant has proposed that when a high-quality silicon nitride film electrically rewrites information, even if a strong voltage is applied, the Si-N-
It has been found that the bonding of Si is stabilized. In other words, a silicon nitride film produced by a photochemical reaction using ultraviolet light is stable even at a high voltage because it has good film quality even when formed thin. As a result, the present invention, the number of times of rewriting of information has become possible to 10 ⁶ times. Furthermore, a silicon nitride film produced by a photochemical reaction using ultraviolet light is particularly effective even in a short channel MIS.FET having a channel length of 1 μm or less, and has no problem in patterning a super LSI. Can be processed. Embodiment 1 Embodiment 1 FIG. 1 is a longitudinal sectional view of an insulated gate field effect semiconductor memory device of the present invention. In FIG. 1, a P ⁻ type semiconductor substrate (1), a field insulating film (2), a first dielectric film (3-1), a trap layer (3-2), a second dielectric film (3) -3) a gate electrode (6) having a floating trap layer (3) as a gate insulator, a source region (7), a drain region (7 '), a channel cut (9), and a channel formation region (10). ing. FIG. 1 shows an N-channel insulated gate field effect semiconductor memory device having a P-type channel formation region (10) on a semiconductor substrate (1). Then, the channel formation region (1
The channel length in 0) is 1.5 μm and the channel width is 10 μm
And The gate electrode (6) was made of titanium silicide. The first dielectric film (3-1) is made of a silicon nitride film,
Its average thickness was 30 mm. Before forming the silicon nitride by the photo CVD method, the substrate (1) is heated to 300 to 500 ° C.
Furthermore, while irradiating ultraviolet light having a wavelength of 185 nm in an ammonia atmosphere to remove contaminants such as organic substances on the surface, an extremely thin silicon nitride film is formed by solid-phase oxidation or nitridation as a blocking layer. Is also good. Further, the trap layer (3-2) thereon was formed by photochemical reaction of a silicon semiconductor to have an average thickness of 30 ° to 2000 °, for example, 100 °. This silicon semiconductor may have an amorphous structure or a polycrystalline structure. In any case, it is preferable to have semiconductor characteristics and have a non-single-crystal structure in order to reduce stress strain. Further, as shown in Example 2, a second dielectric film (3) was formed on the upper surface to a thickness of 500 to 1000 mm by a photo-CVD method. The present invention focuses on the fact that the cause of the deterioration at the time of electrical rewriting occurs between the trap layer (3-2) and the silicon semiconductor. Silicon and its fabrication temperature is 700
C. or less. Next, a gate electrode (6) is formed, and thereafter, the source region (7) and the drain region (7 ') are divided into an N type low impurity concentration region (7-1) and an N ⁺ type high impurity concentration region (7- 2)
Were prepared by the self-alignment method. In such a structure, the gate voltage was ± 25 V, and the pulse width of 100 μs was repeatedly rewritten. Then, a threshold voltage of ± 7 V was obtained. Its value, 1 × 10 ⁶ times to about 7% of the rate of change only without of the initial value even if, the previous insulated gate field effect semiconductor memory device than 10 ² fold to 10 ³ times rewriting life It has grown. Embodiment 2 Hereinafter, the production of the silicon nitride film (Si ₃ N ₄ ) and the cluster or film of Si of the present invention will be described in detail with reference to the drawing shown in FIG. In FIG. 2, a silicon substrate (1) having a surface to be formed is held by a holder (1 ') and is close to a halogen heater (13) (upper surface is water-cooled (31)) in a reaction chamber (12). Is provided. The reaction chamber (12), the light source chamber (35) in which the ultraviolet light source is disposed, and the heating chamber (30) in which the heater (13) is disposed, maintain the respective pressures at approximately the same degree of vacuum of 10 torr or less. did. For this reason, a gas (nitrogen, argon, or ammonia) that does not hinder the reaction should be replaced with (3)
Fulfilled by supplying to (6) or exhausting from (36 '). The light source chamber (35) and the reaction chamber (12) are separated by a quartz window (40), which is a light-transmitting shielding plate. A nozzle (34) is provided above the window (40). The nozzle (34) is a nozzle for ammonia (NH ₃ ) used for the photo CVD method and a nozzle for nitrogen fluoride (NF ₃ ) used for the plasma etching method. (3
4 ″) faces the jet downward (toward the window) (32), and the nozzles (34 ′) for Si ₂ H ₆ , Si ₂ F ₆ and Si ₂ H ₈ used for producing Si ₃ N ₄ This nozzle (34) is provided with an upward facing (substrate facing) (33) This nozzle (34) uses a plasma etch method to remove unwanted substances formed on the window (40) after forming a film by the photo CVD method. High frequency power supply (15) for removal (frequency 13.56M
Hz). A heater (29) was provided to prevent the reactive gas from entering the light source chamber (35) due to backflow when exhausting the light source chamber (35). As a result, a component that becomes a solid after decomposition of the reactive gas was trapped, and only the gas was reversed. For the movement, a load lock method was used in which a pressure difference was not generated. First, in the preliminary chamber (14), the substrate (1), the holder (1 '), and the substrate holder (1 ")
(To efficiently conduct heat to the substrate) is inserted and arranged, and after evacuation, the gate valve (16) is opened and the reaction chamber (1) is opened.
Move to 2) and close the gate valve (16) to close the reaction chamber (1).
2) The spare room (14) was partitioned from each other. Doping system (37), valve (22), flow meter (21)
The reactive gas for forming a solid product after the reaction is from (23) and (24), and the gas product after the reaction is
(25) and (26) were supplied to the reaction chamber (12). The pressure in the reaction chamber (12) was evacuated through a control valve (17), a cock (20), a turbo molecular pump (using PG550 manufactured by Osaka Vacuum) (18), and a rotary pump (19). When the exhaust system (38) evacuates the spare chamber (14) by the cock (20), the spare chamber (14) side is opened and the reaction chamber (1) is opened.
2) Close the side. When the reaction chamber (12) was evacuated, the reaction chamber was opened and the spare chamber (14) side was closed. Thus, the substrate was inserted into the reaction chamber (12) as shown. The degree of vacuum in the reaction chamber (12) was set to 10 ⁻⁷ torr or less. Thereafter, nitrogen was introduced from (28), and a reactive gas was introduced into the reaction chamber from (37) to form a film. The reaction light source is a low-pressure mercury lamp (34) and water-cooled (31 ')
Was provided. The ultraviolet light source is a low-pressure mercury lamp (185 nm, 254 nm
The emission length is 40 cm, the irradiation intensity is 15 mW / cm ² , and the lamp power is 40 W. The number of lamps is 16. The ultraviolet light irradiates the surface of the reaction chamber (12) where the substrate (1) is to be formed, through the quartz window (40), which is a light-transmitting shielding plate. The heater (13) is of a "deposition up" type located above the reaction chamber to prevent flakes from adhering to the surface to be formed and causing pinholes. The reaction chamber is made of stainless steel, and both the light source chamber (35) and the heating chamber (30) are evacuated to reduce the pressure difference between them by 10 torr.
It was as follows. As a result, as shown in the conventional example, the present invention does not have a drawback that when the area of the quartz plate is increased for irradiation of a large area, the quartz plate cannot withstand pressure. That is, the ultraviolet light source is also held under vacuum in a stainless steel container surrounding the light source chamber (35) and the reaction chamber (12) held under vacuum. Therefore, a substrate having a size of 30 cm × 30 cm instead of a wafer having a size of 5 inches or 6 inches can be produced without any industrial problem. The effective area to be formed in the case of the drawing is 30 cm × 30 cm,
The structure is such that five substrates (1) having a diameter of 5 inches can be arranged in the holder (1 '), and the temperature of the substrate is controlled by the halogen heater (1).
Heating was performed according to 3) to a predetermined temperature from room temperature to 500 ° C. Hereinafter, an experimental example of the floating trap layer will be described. Experimental Example Si ₂ H ₆ , Si ₂ F ₆ or Si ₃ H ₈ was connected to (23) and supplied at 3 cc / min. From (25), ammonia was supplied at 30 cc / min. Then, they receive light of 185 nm from the ultraviolet light source (34) and are photolyzed without using mercury, react with ammonia, and form a Si ₃ N ₄ film on the surface of the substrate (1). Was. That is, after treating the underlying semiconductor as shown in FIG. 1 or such a semiconductor surface, silicon nitride is coated thereon with 20 to 200 °, typically 30 to 5 °.
It could be formed with a thickness of 0 °. Furthermore, to form a trap layer on this,
These were all evacuated. Next, Si ₂ H ₆ was supplied from (23) at a rate of 5 cc / min. Then, the Si ₂ H ₆ is decomposed without using mercury in the light source chamber (35), and the silicon semiconductor clusters (average film thickness of 30 mm or less)
At 100 °, silicon is formed in an island shape to form a cluster structure). Alternatively, a film having an average thickness of 200 to 2000 mm is formed. A mixed state of both 100 混合 and 200Å can be obtained. The semiconductor formation rate was 6 ° / min (pressure 3 torr, temperature 350 ° C.). Thus, the trap layer (Fig. 1 (3-2)
Was formed. In addition, since this semiconductor absorbs a large amount of ultraviolet light, it is necessary to further form a second dielectric film (FIG. 1 (3-2)) thereon continuously using the same reaction furnace. plasma
Must be formed by CVD. For this, NH ₃ / S
i ₂ H ₆ ≧ 50, and a high-frequency plasma of 13.56 MHz may be added to form a predetermined thickness. Thereafter, as shown in Example 1, an insulated gate field effect semiconductor memory device was manufactured using the floating trap layer. After the film is formed, the photo-CVD apparatus shown in FIG.
Plasma etching of the window (40) was performed by supplying NF ₃ from (26). Thus, the window (40) can be cleaned and the second operation of forming the floating trap layer can be performed. Even if the formation of the floating trap layer was repeated 10 times, the same film thickness could be obtained under the same conditions. As is clear from the above description, the present invention is one in which a trap layer and a first dielectric film therebelow (substrate side) are formed as a gate insulating film by photo-CVD.
As a result, damage to the substrate was small, and a trap layer could be formed at a predetermined distance from the semiconductor surface. In particular, despite the fact that such a silicon nitride film is formed at a temperature of 300 ° C. to 500 ° C., Si-N bonds are not broken, so that there is a great feature that deterioration due to rewriting hardly occurs. That is, a strong voltage is applied to the first dielectric film at the time of electrical rewriting. For this reason, Si-O-Si
Or, due to the presence of hydrogen, the bond is transformed into a bond of Si—OH + —Si, and the dangling bond of silicon causes deterioration. On the other hand, the bond of Si—N—Si is extremely stable, and its bond (Si—N bond) is not broken even by a strong electric field. In addition, it has a remarkable feature that even if hydrogen is present, hydrogen does not act as a catalyst that cuts off a bond which is observed in the case of silicon oxide. In the present invention, the channel formation region was silicon, and the gate insulator was a two-layer film of a silicon oxide and a nitride film. However, GaAs and InP
In the II-V compounds, since the with these semiconductor silicon oxide deteriorates react at a high temperature operation test, Si ₃ N ₄
It was better to have only. In other words, Si ₃ N
What is necessary is just to make ₄ directly adhere and make it the structure of a gate electrode. In the dielectric withstand voltage of the insulating film, 3.5 × 10 ⁶ V / cm of silicon nitride by the photo CVD method is 1 × of silicon nitride by the plasma CVD method.
The breakdown voltage was 3.5 times higher than × 10 ⁶ V / cm. Furthermore, even when a voltage corresponding to an electric field of ± 3 × 10 ⁶ V / cm was applied, the change in the threshold voltage drifted only within a range of ± 0.2 V or less. From this, if using such a silicon nitride film as the first dielectric film between the semiconductor substrate and the trap layer, it does not occur with the dangling bonds of information rewriting here, 10 ⁶ times Or more rewriting can be expected. The present invention utilizes the fact that such a high-quality silicon nitride film can be formed by a photo-CVD method. In addition, a trap layer on the silicon nitride film is formed by a photo-CVD method so as not to damage the silicon nitride film. Thus, according to the method of the present invention, 10
^Six or more rewrites are possible for the first time. In the above experimental example, an excimer laser (wavelength 100 to 400 n
m), it goes without saying that an argon laser, a nitrogen laser or the like may be used. [Effects of the Invention] According to the present invention, a source region or a drain region in contact with a channel formation region is an N-type low impurity concentration region, and further, an N ⁺ -type high impurity concentration region is formed apart from the channel formation region. Therefore, hot carriers can be generated in a wide area. For this reason, local deterioration is prevented near the interface with the source region or the drain region, and a decrease in the number of rewrites can be prevented. According to the present invention, as a result of forming a silicon nitride film on a trap layer as a gate insulating film and a first dielectric film thereunder (substrate side) by a photochemical reaction using ultraviolet light, the film surface is less damaged. In addition, a trap layer could be formed at a predetermined distance from the semiconductor surface. The silicon nitride film has a high voltage even when a high voltage is applied for rewriting information.
Since the Si-N bond is not broken, there is a feature that deterioration due to rewriting hardly occurs. That is, the bond of Si—N—Si in the silicon nitride film is
It is extremely stable and has a remarkable feature that it does not act as a catalyst for breaking a bond (Si-N bond) even when a strong electric field is applied or hydrogen is present. According to the present invention, since a high-quality silicon nitride film can be manufactured by a photochemical reaction using ultraviolet light, the silicon nitride film is not damaged, so that it has been impossible 10 ⁶ times or more. Rewriting became possible for the first time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of an insulated gate field effect semiconductor memory device of the present invention. FIG. 2 shows a CVD apparatus used in the embodiment. DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate 2 ... Field insulating film 3 ... Gate insulating film 4 ... Lead electrode 6 ... Gate electrode 7, 7 '... Source region or drain region 9 ... Char cut 10 ... Channel formation region

Claims (1)

(57) [Claims] A semiconductor substrate, a channel formation region formed in the semiconductor substrate, an N-type low concentration impurity region formed in contact with the channel formation region, and an N-type high concentration impurity region apart from the channel formation region. A source region or a drain region, and a first dielectric film laminated on the channel formation region;
A gate insulating film comprising a floating charge trapping center layer and a second dielectric film, comprising: a first dielectric film on the channel formation region; A method for manufacturing an insulated gate field effect semiconductor memory device, comprising forming a silicon nitride film as a body film by a photoreaction using ultraviolet light. 2. A semiconductor substrate, a P-type channel formation region formed in the semiconductor substrate, an N-type low-concentration impurity region formed in contact with the P-type channel formation region, and an N-type away from the P-type channel formation region A gate comprising a source region or a drain region comprising a high-concentration impurity region, a first dielectric film, a floating charge trapping central layer, and a second dielectric film laminated on the P-type channel formation region A method for manufacturing an insulated gate field effect semiconductor memory device, comprising: an insulating film; and a first dielectric film on the P-type channel formation region,
The silicon nitride film is exposed to a light
A method for manufacturing an insulated gate field effect semiconductor memory device, wherein the method is formed to a thickness of 0 °.