JP2634492B2 - Manufacturing method of nonvolatile semiconductor memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a nonvolatile semiconductor memory device.

[0002]

2. Description of the Related Art Electrically erasable EEPRO
As one of the M, a nonvolatile semiconductor memory device using a floating gate type field effect transistor is known. In this nonvolatile semiconductor memory device, a first gate insulating film is formed on a source region, a drain region, and a channel region sandwiched between both regions provided on a surface of a Si substrate,
The first gate insulating film on the drain region is partially removed by etching to partially expose the surface of the Si substrate, and the exposed S
i to form a thin second gate insulating film on the substrate surface, a floating gate, it is one obtained by successively forming an insulating film and a control gate over the first and <br/> second gate insulating film,
The principle is that charges are accumulated in the floating gate by injecting charges into the floating gate through a thin second gate insulating film on the drain region, and the threshold voltage of the transistor is changed to store information. (Eg Giora Yaron
et. al. ISSCC 82, P108).

FIGS. 12 and 13 are cross-sectional views illustrating a part of steps of a method for manufacturing a conventional nonvolatile semiconductor memory device.

In FIG. 12, reference numeral 201 denotes an Si substrate;
2b is a drain region which is an impurity diffusion layer, and 203 is a first region.
A gate insulating film 206 is a window for forming a second gate insulating film. As shown in the figure, when the first gate insulating film 203 is dry-etched to form the second gate insulating film forming window 206, the surface of the Si substrate 201 is over-etched to form a step 207. Even if wet etching is applied instead of dry etching, if cleaning is performed with an ammonia-based detergent such as NH ₄ OH after the etching, the Si substrate 201 is etched by the detergent and similar steps are formed. In addition, conventionally, both the plane orientation of the step bottom surface and the step side surface of the Si substrate 201 are (100). Next, through the second gate insulating film forming window 206, S
When the surface of the i-substrate 201 is oxidized, a second gate insulating film 208 is formed on the drain region 202b as shown in FIG. However, since the plane orientation of the step bottom surface and the plane orientation of the step side surface are the same on the surface of the Si substrate 201 as described above, the second gate insulating film 208
The relationship between the film thickness A of the step bottom surface portion and the film thickness B of the step side surface portion was A ≧ B. The reason why the film thickness B on the side surface of the step is small is that the thickness of the insulating film is reduced by thinning (thinni).
ng) The phenomenon occurs.

[0005]

Conventionally, as described above, in the over-etching step 207 of the Si substrate 201 formed when the first gate insulating film 203 is etched, both the plane orientation of the step bottom surface and the step side surface are ( 100), and the film thickness A at the step bottom surface portion of the second gate insulating film 208
On the other hand, the film thickness B of the step side portion was small, so that the dielectric strength of the step side portion of the second gate insulating film 208 was small. Therefore, when a repetitive electric field is applied to the second gate insulating film 208 for writing and erasing, there is a problem that a dielectric breakdown occurs early on the side surface of the step of the second gate insulating film 208.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a method of manufacturing a long-life nonvolatile semiconductor memory device having a second gate insulating film which is not easily broken down.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a method of manufacturing a nonvolatile semiconductor memory device according to the present invention has a step on a surface of a semiconductor substrate formed when a second gate insulating film forming window is formed. The thickness distribution of the second gate insulating film is improved by setting the plane direction of the step side surface to the plane direction in which the growth rate of the oxide film is higher than that of the bottom surface. More specifically, according to the first aspect of the present invention, the first gate insulating film is formed on the source region, the drain region provided on the surface of the semiconductor substrate having the first plane orientation, and the channel region sandwiched between the two regions. Forming a first gate insulating film, and partially removing the first gate insulating film on the drain region by etching to partially expose the semiconductor substrate surface; By forming the second gate insulating film forming window such that a step is formed, a step bottom having the same plane orientation as the first plane orientation and a second layer having a higher oxide film growth rate than the step bottom are formed. a second gate insulating film formed window creation step of exposing the step side having a plane orientation, the second gate insulating film by oxidizing the step bottom and step side through the second gate insulating film formed window A second gate insulating film forming step of forming the floating gate, and that a wiring sequentially forming an insulating film and a control gate over the first and second gate insulating film.

[0008] In order to form a second gate insulating film having a particularly high dielectric strength, in the invention of claim 2, RTP (Rapid Thermal Pro) is used in the second gate insulating film forming step.
ses) method to oxidize the surface of the semiconductor substrate and
A gate insulating film is formed.

[0009]

According to the first aspect of the present invention, in the over-etching step on the surface of the semiconductor substrate formed when the second gate insulating film forming window is formed, the side surface of the step is oxidized due to the difference in the plane orientation as compared with the bottom surface of the step. The film growth rate is faster
You. Therefore, in the next step, if the step bottom surface and the step side surface are simultaneously oxidized through the second gate insulating film forming window, the second gate insulating film grows thicker at the step side surface portion than at the step bottom portion portion. Thereby, the dielectric strength of the step side surface portion of the second gate insulating film is improved.

According to the second aspect of the present invention, when the RTP method is applied to the step of forming the second gate insulating film, the second gate insulating film grows in a short time. The phenomenon of thinning is smaller than in a normal electric furnace. Therefore, a second gate insulating film that is not easily broken down can be easily obtained.

[0011]

1 to 11 are process sectional views illustrating a method for manufacturing a nonvolatile semiconductor memory device according to an embodiment of the present invention.

First, as shown in FIG. 1, a semiconductor substrate Si
A source region 102 a provided on the surface of the substrate 101,
A first gate insulating film 103 serving as an oxide film on the drain region 102b and the channel region 102c sandwiched between the two regions;
To form As the Si substrate 101, the source region 10
2a, drain region 102b and channel region 102c
The plane orientation of the surface forming the transistor element made of
It is convenient to select a Si wafer whose orientation flat (orientation flat) is (110). A large number of transistor elements are formed on the Si substrate 101 by using a straight line parallel to the orientation flat and a straight line perpendicular to the orientation flat as vertical and horizontal reference lines.

Following the first gate insulating film forming step,
The step of forming the second gate insulating film forming window shown in FIGS. 2 to 4 is performed. First, a photoresist 104 having an etching window 105 is formed on the first gate insulating film 103 as shown in FIG. The etching window 105 is a rectangular window located on the drain region 102b. Next, the first gate insulating film 103 in the etching window 105 is removed by dry etching. FIG. 3 shows the result of this etching. The second gate insulating film forming window 106 is formed by the dry etching, so that not only the surface of the Si substrate 101 is partially exposed but also the Si
The surface of the substrate 101 is over-etched to
7 is formed. FIG. 4 shows a state in which the photoresist 104 has been removed after the second gate insulating film forming window 106 has been formed in this manner. Even if wet etching is applied instead of dry etching as described above, if cleaning is performed with an ammonia-based detergent such as NH ₄ OH after the etching, the Si substrate 101 is etched by the detergent and becomes similar to the Si substrate 101. Is formed.

FIGS. 5 and 6 are an enlarged sectional view and an enlarged perspective view of the second gate insulating film forming window 106 of FIG. 4, respectively. As shown in both figures, in the present embodiment, the plane orientation of the step bottom surface in the overetching step 107 of the Si substrate 101 is the same as the plane orientation of the transistor element formation surface (100).
And the plane direction of the step side is the same as the orientation flat (110)
become.

Next, the exposed surface of the Si substrate 101 is thermally oxidized through the second gate insulating film forming window 106. FIG. 7 shows an execution result of the second gate insulating film forming step, and FIG. 8 is an enlarged view thereof. Si has a higher growth rate of the oxide film in the plane orientation (110) than in the plane orientation (100).
The thickness B of the formed second gate insulating film 108 on the side surface of the step is larger than the film thickness A on the bottom surface of the step, unlike the related art.

[0016] Finally, as shown in FIGS. 9 to 11, the first gate
Floating gate 109 on the over gate insulating film 103 and the second gate insulating film 108, by executing the wire sequentially forming an insulating film 110 and the control gate 111 to complete the non-volatile semiconductor memory device.

As described above, according to the present embodiment, the film thickness B on the side surface of the step of the second gate insulating film 108 can be made larger than the film thickness A on the bottom surface, so that it was conventionally low. The dielectric strength of the step side part is improved. Therefore, even if a repetitive electric field is applied to the second gate insulating film 208 for writing and erasing, dielectric breakdown does not easily occur in the second gate insulating film 208, and the life of the nonvolatile semiconductor memory device is extended.

In the above embodiment, the plane orientation of the transistor element forming surface of the Si substrate 101 is (100),
The side face of the over-etched step of the substrate 101, that is, the second
The plane orientation of the side wall of the gate insulating film formation window 106 is (110)
However, the plane orientation of the element formation surface was set to (100) or (11).
In the case of 0), the same effect can be obtained even when the plane orientation of the side wall is set to (111). However, in the latter case, the side wall is not perpendicular to the element formation surface .

As a semiconductor substrate, an Si substrate 101 is used.
Alternatively, a compound semiconductor substrate such as GaAs may be used.

In the second gate insulating film forming step, RTP (Ra
When the pid thermal process is applied, the second gate insulating film 108 grows in a short time, so that the phenomenon of thinning due to the flow of the insulating film 108 is smaller than in a normal electric furnace. Therefore, the dielectric strength of the step side wall portion of the second gate insulating film 108 is improved, and it is possible to prevent dielectric breakdown particularly at a corner portion between the step bottom portion and the step side wall portion .

[0021]

As described above, according to the first aspect of the present invention, the side surface of the semiconductor substrate surface formed at the time of forming the second gate insulating film forming window is formed by the difference in plane orientation in the overetching step. Is oxidized compared to the bottom of the step
The growth rate of the film is increased, and the side surface of the step of the second gate insulating film formed in the next step is thicker than the bottom of the step. Therefore, in the nonvolatile semiconductor memory device manufactured by the method of the present invention, the dielectric strength of the second gate insulating film is improved and the reliability is greatly improved as compared with the related art. Moreover, this effect can be obtained only by considering the plane orientation of the semiconductor substrate.

In particular, in the second aspect of the present invention, the surface of the semiconductor substrate is oxidized by applying the RTP method to the second gate insulating film forming step.
By forming the second gate insulating film and a thin film phenomenon that occurs prior since grown out of the second gate insulating film short is reduced, the dielectric strength of the second gate insulating film is greatly improved .

[Brief description of the drawings]

FIG. 1 is a process cross-sectional view illustrating a method for manufacturing a nonvolatile semiconductor memory device according to an embodiment of the present invention.
This shows a state where the gate insulating film forming step has been completed.

FIG. 2 is a view showing a step of forming a second gate insulating film forming window in FIG.
FIG. 13 is a cross-sectional view showing a state after the step of forming a photoresist having an etching window on the first gate insulating film after the step of FIG.

FIG. 3 is a view showing a step of forming a second gate insulating film forming window in FIG.
FIG. 14 is a cross-sectional view showing a state where a step of forming a second gate insulating film formation window following the step of FIG.

FIG. 4 is a diagram showing a step of forming a second gate insulating film forming window in FIG.
FIG. 13 is a cross-sectional view showing a state in which the step of removing the photoresist subsequent to the step of FIG.

FIG. 5 is an enlarged view of a second gate insulating film forming window of FIG. 4;

FIG. 6 is a perspective view of a second gate insulating film forming window of FIG. 5;

FIG. 7 is a cross-sectional view showing a state where a second gate insulating film forming step following the step of FIG. 4 is completed.

FIG. 8 is an enlarged view of a second gate insulating film part of FIG. 7;

[9] The first Following out 7 step wiring process
And is a sectional view showing a state where the process has been completed for forming a floating gate on the second gate insulating film.

FIG. 10 is a cross-sectional view showing a state in which a step of forming an insulating film on the floating gate has been completed following the step of FIG. 9 in the wiring step;

FIG. 11 is a cross-sectional view showing a state in which a step of forming a control gate on an insulating film is completed following the step of FIG. 10 in the wiring step to complete a nonvolatile semiconductor memory device.

FIG. 12 is a process cross-sectional view illustrating a method for manufacturing a conventional nonvolatile semiconductor memory device, and shows a state where a process of forming a second gate insulating film formation window is completed.

FIG. 13 is a cross-sectional view showing a state where a step of forming a second gate insulating film subsequent to the step of FIG. 12 is completed.

[Explanation of symbols]

101, 201: Si substrate (semiconductor substrate) 102a: Source region 102b, 202b: Drain region 102c: Channel region 103, 203: First gate insulating film 104: Photoresist 105: Etching window 106, 206: Second gate insulating film Forming windows 107, 207: Over-etching steps on Si substrate surface 108, 208: Second gate insulating film 109: Floating gate 110: Insulating film 111: Control gate

Claims (2)

(57) [Claims] A first gate insulating film formed on a source region and a drain region provided on a surface of a semiconductor substrate having a first plane orientation and a channel region interposed between the source region and the drain region; A film forming step, by partially removing the first gate insulating film on the drain region by etching to partially expose the semiconductor substrate surface, and by overetching the exposed semiconductor substrate surface, By forming the second gate insulating film forming window so that a step is formed, a step bottom having the same plane orientation as the first plane orientation and a growth rate of an oxide film which is faster than the step bottom are formed. this oxidizing the second gate insulating film formed window creation step of exposing the step side, the stepped bottom surface and the step side through the second gate insulating film formed window having a second surface orientation The second gate insulating film forming step of forming a second gate insulating film, the floating gate on the first and second gate insulating film, further comprising a wiring step of successively forming an insulating film and a control gate A method for manufacturing a nonvolatile semiconductor memory device, characterized by: 2. The method according to claim 2, wherein the oxidation is performed based on an RTP method.
2. The method for manufacturing a nonvolatile semiconductor memory device according to claim 1, wherein a gate insulating film is formed.