JPS60113474A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the reliability of the nonvolatile semiconductor memory device by a method wherein a ferrodielectric polymer film is formed on a semiconductor substrate, and an electrode consisting of a conductive film is formed on the polymer film. CONSTITUTION:The ferrodielectric polymer film 11 is formed on the semiconductor substrate 1, and the gate electrode 7 consisting of a conductive film is formed thereon. The source 4 and the drain 5 are formed on both sides of the gate electrode. The polymer film 11 is polarized by an external electric field, and the direction of polarization is inverted. Further, the direction of polarization is maintained even after removal of the electric field by the ferrodielectric property of the polymer film.

Description

[Detailed Description of the Invention] (Industrial Application Field) The invention is based on ferroelectric properties that allow information to be electrically written, rewritten, and read, and that retains all information even after the power is turned off. The present invention relates to a semiconductor memory device using the material and a method for manufacturing the same.

(Prior art) In order to realize all the conventional devices of this kind, reference [1] (Y,
Higuma, Y, Matsui, M, Ok
uyama, T., Nakagawa and Y.
Hamakawa: Japanese Jour
nal of Applied Physics, vol.
, 17 (1978) Supplement 17-1.
A semiconductor device having the structure described in (pp. 209-214) has been proposed. FIG. 1 shows its manufacturing method 2 and structure, which will be explained below.

As shown in FIG. 1(4), a p-type layer 2 is formed on an n-type semiconductor substrate 1 by impurity diffusion. Next, in Figure 1)
As shown in FIG. 2, a source 4 and a drain 5 are formed by forming grooves 3 that reach the n-type substrate 1 using photolithography. Next, by high frequency sputtering method, P
By depositing an LZT (inorganic ferroelectric substance whose constituent elements are lead, lanthanum, zirconium, and titanium) film 6 and processing it using photolithography, the structure shown in FIG.
) obtain the structure shown. Next, a metal film is deposited and processed by photolithography to form the entire gate electrode 7 and source/drain wirings 8, thereby obtaining the entire structure shown in FIG. 1a.

The structure shown in FIG. 1a is an MIS type field effect transistor consisting of a gate electrode 7, a source 4, and a drain 5. As stated in the document [1], the PLZT film 6
has a ferroelectric association, so there is a gap between the gate electrode 7 and the n-type semiconductor substrate l in a certain direction! However, by applying an electric field whose absolute value is a certain value or more, the PLZT film 6 can be polarized. Furthermore, by applying an electric field having a direction opposite to that used for polarization and having an absolute value of a certain value or more between the gate electrode 7 and the n-type semiconductor substrate 10, the direction of polarization is completely reversed. be able to. Due to the ferroelectricity of the PLZT film 6, polarization is maintained even after the electric field is removed. n at 2 at the interface between the PLZT film 6 and the n-type semiconductor substrate 1
Since the surface potential of the type semiconductor substrate 1 has two values corresponding to the polarization direction of the PLZT film 6, the MIS type field effect transistor shown in FIG. 1 (0) has two threshold voltages corresponding to the polarization direction. . Therefore, there is information (“0”, “1”) in the two threshold voltages of the MIS field effect transistor.
If it is fully compatible, it is possible to write, rewrite, and read information, and even after the power is turned off, the information can be fully stored.

The conventionally proposed semiconductor devices described above have the following drawbacks and have not yet been put into practical use.

The first problem is that the difference between the two threshold voltages of MIS field effect transistors cannot be made sufficiently large. If the difference in threshold voltage is small, the probability of reading information incorrectly increases, making it impossible to ensure the reliability of the semiconductor device. The difference between the two threshold voltages is determined by the thickness of the PLZT film 6, the magnitude of residual polarization, and the dielectric constant.

Here, the film thickness of the PLZT film 6 is yt, the total residual polarization is Q, and the dielectric constant is 68. The permittivity of vacuum is ε. shall be.

At this time, the difference between the two threshold voltages of the MIS field effect transistor is 2 as described in reference [1].
・It can be expressed as QΦ1/(ε8·ε.). P.L.
As described in literature [1], the magnitude Q of the residual polarization of the ZT film is 7.7 uC/d, and the relative dielectric constant εS
is approximately 1000.

The magnitude Q of residual polarization and the dielectric constant ε8 are physical property values specific to the PLZT film, and therefore cannot be changed significantly.

Therefore, the thickness of the PLZT film 6? For example, when the thickness is 0.5 μm, the difference between the two threshold voltages of MIS field effect transistors is only 9 V according to the above calculation formula and numerical value. Moreover, in the actual electrical rewriting time of information, in order to shorten the rewriting time, the PLZT film 6 must be used in a state that is not completely polarized. Considering this, this threshold voltage difference is This cannot be said to be sufficient to ensure the reliability of semiconductor devices. Furthermore, if the thickness of the PLZT film 6 is made thinner in order to miniaturize semiconductor devices, the difference in threshold voltage will become smaller in proportion to t. The probability increases.

(Objective of the Invention) The present invention has been proposed to solve all of these drawbacks. Furthermore, by employing a structure in which this ferroelectric polymer film is sandwiched between two insulating films, it is possible to provide a highly reliable nonvolatile semiconductor memory device and its fabrication method. purpose.

(Structure of the Invention) In order to achieve the above object, the present invention comprises a ferroelectric polymer film formed on a semiconductor substrate and a conductive film formed on the ferroelectric polymer film. The gist of the invention is a semiconductor device characterized by comprising an electrode.

Furthermore, the present invention includes a first insulating film formed on a semiconductor substrate, a ferroelectric polymer film formed on the insulating film,
A semiconductor device comprising: a second insulating film formed on the ferroelectric polymer film; and an electrode made of a conductive film formed on the second insulating film. This is the gist of the invention.

Furthermore, the invention includes a step of completely forming a first insulating film on a semiconductor substrate, a step of dropping a ferroelectric polymer onto the insulating film to form a thin film of the ferroelectric polymer, and a step of forming a thin film of the ferroelectric polymer on the insulating film. A step of forming a second insulating film entirely on the dielectric polymer film, and a step of forming a conductive film on the second insulating film and then etching it to form an electrode. This is the gist of the entire invention, which is a characterized method for manufacturing a semiconductor device.

Next, embodiments of the present invention will be described with reference to all attached drawings. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

First, the present invention will be explained in detail.

FIG. 2 shows an embodiment of the semiconductor device of the present invention. As shown in FIG. 2, a ferroelectric polymer film 11 is formed on a semiconductor substrate 1, and a gate electrode 7 made of a conductive film is formed thereon.
1. It has a MIS type field effect transistor structure in which a source 4 and a drain 5 are formed on both sides of a gate electrode 7.

The MIS type field effect transistor having the structure shown in FIG. 2 basically uses the same principle as the semiconductor device shown in FIG. It is possible. That is, the ferroelectric polymer (7) film 11 can be polarized by an external electric field, and the direction of polarization can be completely reversed.
Due to the ferroelectric property of 1, the direction of polarization is maintained even after the electric field is removed. At the interface between semiconductor substrate 1 and ferroelectric polymer film 11? Since the surface potential of the semiconductor substrate 1 in which the ferroelectric polymer film 11 is polarized takes two values depending on the polarization direction of the ferroelectric polymer film 11, the MIS field effect transistor shown in FIG. have Therefore, if all the information ("0", "1#") corresponds to the magnitude of the threshold voltage,
It is possible to write, rewrite, and read information, and the information can be maintained in its entirety even after the telephone conversation ends.

The difference between the two threshold voltages of the MIS field effect transistor having the structure shown in FIG. 2 is determined by the thickness of the ferroelectric polymer film 11,
Determined by the magnitude of residual polarization and relative dielectric constant. As mentioned above, the film thickness of the ferroelectric polymer film 11 is t, and the magnitude of the residual polarization of the ferroelectric polymer film is Q5 and the dielectric constant t68.
, MIS type field effect (
8) The difference between the two dark value voltages of the transistor is 2・Q-t/(ε
8・ε. )It can be expressed as. Therefore, the difference in threshold voltage can be increased by increasing the residual polarization to the magnitude Q' or by decreasing the relative dielectric constant εsk. However, in general, the magnitude Q of residual polarization of a ferroelectric film cannot be changed significantly. Therefore, in the present invention, we focused on the fact that the dielectric constant of a ferroelectric polymer film is generally several hundred times lower than that of an inorganic ferroelectric film such as a PLZT film. By using a ferroelectric polymer film as the ferroelectric film 6, ε8 becomes small, so the difference between the two threshold voltages becomes significantly large.

For example, the magnitude of the residual polarization of polyvinylidene fluoride, a typical ferroelectric polymer material, is reported in Reference [2] (T,
Takahashi.

M, 1)ate, E, Fukuda: App
Lied physics 1etters.

vol, 37. p, 791. (1980), it is about 6 μC/-, and the dielectric constant is:
Reference [3] (H, Qhgashi and K, Ko
ga: Japanese Journal of A
pplied Physics vol, 21. T
), L455. 6.2, as described in (1982). Film thickness of ferroelectric film 'kO, 5μm
When polyvinyritine fluoride is used as the ferroelectric @11, the difference in threshold voltage between the two MIS field effect transistors is approximately 1100V.

In this way, by using a ferroelectric polymer film with an extremely low dielectric constant in place of an inorganic ferroelectric film, MIS
The calculated value of the difference in threshold voltage of type field effect transistor is P
Compared to a semiconductor device using an LZT film, it can be made more than 100 times larger, and all the drawbacks of conventionally proposed semiconductor devices can be solved.

In addition, even if the thickness of the ferroelectric film 11 is made thinner due to miniaturization of semiconductor devices, a practically large enough threshold voltage difference can be ensured.

As the material for the ferroelectric polymer film 11, polyvinylidene fluoride or vinylidene fluoride/trifluoroethylene copolymer is suitable because it has a small dielectric constant and is easy to manufacture.

The purpose of increasing the difference in threshold voltages of MIS field effect transistors is to reduce the probability of erroneously reading information, that is, to improve the reliability of the semiconductor device.

However, as shown in FIG.
If there is a structure in which the semiconductor substrate 1 and the gate electrode 7 are directly in contact with each other, when applying a full electric field to the ferroelectric polymer film 11 for writing or rewriting information, the ferroelectric polymer film 11
When electrons are injected into the film and captured in the film, the threshold voltage may fluctuate. Furthermore, it is generally believed that there are more electron capture levels in polymer films than in inorganic materials. Therefore, in order to use a ferroelectric polymer film and to realize a more reliable semiconductor device, it is necessary to create a structure that completely prevents electron injection into the ferroelectric polymer film.

FIG. 3 shows another embodiment of the semiconductor device of the present invention. In the figure, a first insulating film 9 is formed on a semiconductor substrate 1;
A ferroelectric polymer film 11 is formed on it, a second insulating film 12 is formed on it, a gate electrode 7 made of conductive material is formed on both sides of the gate electrode 7, and a source is formed on both sides of the gate electrode 7. 4 and a drain 5 are formed.

(11) That is, the semiconductor device according to the second embodiment of the present invention uses a structure in which a ferroelectric polymer film 11 is sandwiched between a first insulating film 9 and a second insulating film 12. These insulating films play the role of completely preventing electron injection into the ferroelectric polymer film 11 when an electric field is applied between the gate electrode 7 and the semiconductor substrate 10. This makes it possible to improve the fluctuation of the threshold voltage of the MIS field effect transistor. Note that even if either the first insulating film 9 or the second insulating film 12 is absent, electron injection into the ferroelectric polymer film 11 occurs. Therefore, both insulating films are indispensable in order to prevent deterioration of the ferroelectric polymer film.

A method for manufacturing a semiconductor device according to an embodiment of the present invention is shown in FIG. First, as shown in FIG. 4, a first insulating film 9 made of a silicon oxide film and having a thickness of 10 to 100 nm is formed on a p-type semiconductor substrate l by thermal oxidation. Next, resist pattern 1 is created using photolithography technology.
0 is formed, and using this as a mask, ions of phosphorus or arsenic are implanted (12) to form a source 4 and a drain 5.
The structure shown in Figure [F]) is obtained. Next, resist button 1
After removing 0, the p-type semiconductor substrate 1 is rotated at a speed of 300 revolutions per minute or more, and from thereon, polyvinylidene fluoride or vinylidene fluoride 03 fluorochemical tyrene copolymer is added to a solvent such as dimethylformamide. By dripping a solution dissolved in water and then continuing to rotate for 5 seconds or more, a ferroelectric polymer film 11' (j is formed, and the structure shown in FIG. 4 CC) is obtained. Next, it consists of a silicon oxide film with a film thickness of 10 to 1
A second insulating film 12 with a thickness of 0.00 nm is deposited as shown in FIG. 4(2).
We obtain the structure shown in Since the melting point of polyvinylidene fluoride and vinylidene fluoride/trifluoroethylene copolymer is approximately 150°C, the deposition of the second insulating film 12 is performed using high-frequency waves to prevent deformation of the ferroelectric polymer film 11. 150℃ such as sputtering method
The method must be such that the entire film can be deposited at a temperature below. Next, all metal films such as aluminum films are deposited, a gate electrode 7 is formed by photolithography technology, and then the second insulating film 12 and the ferroelectric polymer film 11 are etched, as shown in FIG. Obtain the structure shown. Next, 13 interlayer insulating films are deposited, one contact film is formed, a metal film is formed, and the source layer is etched using this metal film photolithography technology.
A drain wiring 8 and a gate electrode wiring 14 are formed, and finally the structure shown in the fourth drawing is obtained, and the semiconductor device is completely completed.

The coercive electric field values of polyvinylidene fluoride and vinylidene fluoride/trifluoro-modified tyrene copolymer are given in Reference [2] 2 and Reference [3].
K x n, approximately 40 MV/m ”'C6 Lua 7>
In the semiconductor device manufactured by the manufacturing method described above, information can be electrically written and rewritten by applying a voltage of 20 V or more in absolute value to the entire semiconductor substrate 1 and gate electrode 7K. In order to shorten the rewriting time, even if one ferroelectric polymer film is used in a state where it is not completely polarized, one of the two threshold voltages must be at least 100V or higher and the other 1-100V or lower. Therefore, there is no risk of reading information by mistake.

Note that this embodiment is merely an example, and various changes and improvements can be made without departing from the spirit of the invention.

For example, the first insulating film 9 and the second insulating film 12 may be films that can prevent electron injection into the ferroelectric polymer film 11. As the insulation@9, in addition to a silicon oxide film formed by a thermal oxidation method, a silicon nitride film formed by a thermal nitridation method, etc. can be used. When a semiconductor other than silicon is used as the semiconductor substrate 1, a silicon oxide film, a silicon nitride film, or the like deposited by a sputtering method can be used as the first insulating film 9. Further, as the second insulating film 12, a silicon nitride film or the like deposited by sputtering can also be used.

(Effects of the Invention) As explained above, the present invention has the advantage that it is possible to realize a nonvolatile semiconductor memory device with high reliability.

(15) As is clear from the above embodiments, the semiconductor device structure 2 and manufacturing method of the present invention are suitable for integrating a large number of semiconductor devices on all semiconductor substrates.

Therefore, if the entire semiconductor multiplication circuit device is manufactured as all the semiconductor device elements of the present invention, the above advantages can be more effectively utilized in one device. That is, by manufacturing a semiconductor integrated circuit device using the semiconductor device of the present invention as an element and using it in all-electronic computers and various terminal devices, it is possible to improve the reliability of these devices.

[Brief explanation of drawings]

FIG. 1 shows the manufacturing method and structure of a conventionally proposed semiconductor device. FIG. 2 shows the structure of a semiconductor device that is an embodiment of the present invention. FIG. 3 shows the structure of a semiconductor device according to another embodiment of the present invention. FIG. 4 shows a method for manufacturing a semiconductor device in one embodiment of the present invention. l...Semiconductor substrate 2...P-type layer 3...Groove (16) 4...Source 5 ......Drain 6...PLZT film 7...Gate electrode 8...Source/drain wiring 9 ...
......First insulating film 10...Resist baton 11...
...Ferroelectric polymer film 12...Second insulating film 13...Interlayer insulating film 14...Gate electrode wiring patent applicant
Nippon Telegraph and Telephone Public Corporation Figure 1 Figure 2 Figure 1/, Figure 3

Claims (4)

[Claims] (1) A ferroelectric polymer film formed on a semiconductor substrate,
A semiconductor device comprising: an electrode made of a conductive film formed on the ferroelectric polymer film; and gold. (2) A first insulating film formed on a semiconductor substrate, a ferroelectric polymer film formed on the insulating film, and a second insulating film formed on the ferroelectric polymer film. A semiconductor device comprising: an insulating film; and an electrode made of a conductive film formed on the second insulating film. (3) (a) A step of forming a first insulating film r on a semiconductor substrate; (b) A step of dropping a ferroelectric polymer onto the insulating film to form a thin film of ferroelectric polymer. (c) forming a second insulating film entirely on the ferroelectric polymer film; d) forming a conductive film on the second insulating film, and then etching it. 1. A method for manufacturing a semiconductor device, comprising a step of forming all electrodes. (4) The semiconductor device according to claim 1 or 2, wherein polyvinylidene fluoride or vinylidene fluoride/trifluoro-modified tyrene copolymer is used as the ferroelectric polymer film.