JP3034296B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

The present invention relates to a trench capacitor, a semiconductor device having a capacitor gate insulating film including a silicon nitride film, and a method of manufacturing the same, and particularly relates to a trench. It is used for the electrode of a capacitor.

(Prior Art) Conventionally, a semiconductor device having a trench capacitor and a capacitor gate insulating film including a silicon nitride film has a configuration as shown in FIG. 3, for example.

On the semiconductor substrate 31, a field oxide film 32 is formed. Also, by sandwiching the field oxide film 32,
Two trenches 33 are formed. A capacitor gate insulating film is formed on the surface of the substrate 31 in these two trenches 33. Capacitor gate insulating film is thermal oxide film 3.
4. It is composed of a silicon nitride film 35 and a thermal oxide film 36. A polysilicon film 37 is formed on the capacitor gate insulating film. This polysilicon film 37 becomes a capacitor electrode. On the polysilicon film 37, a thermal oxide film 38 is formed. Further, a polysilicon film 39 is formed so as to fill the trench 33. Further, a gate insulating film 40 of the transistor is formed in the transistor region.

However, it is known that various inconveniences occur in the manufacturing process of the semiconductor device having the above configuration. Hereinafter, the conventional manufacturing method will be described with reference to FIGS. 4 (a) to 4 (m) together with its disadvantages.

First, as shown in FIG. 1A, a field oxide film 2 having a thickness of about 8000 ° is formed on a semiconductor substrate 1 by using an element isolation technique. Further, as shown in FIG. 1B, a thermal oxide film 3 having a thickness of about 1000 ° is formed on the substrate 1. Thereafter, a silicon nitride film 4 having a thickness of about 1000 ° and an oxide film 5 having a thickness of about 5000 ° are sequentially deposited on the thermal oxide film 3. Further, a resist film 6 having a pattern for forming a trench is formed on oxide film 5 by using a lithography technique. Next, FIG.
As shown in FIG. 7, the oxide film 5, silicon nitride film 4, thermal oxide film 3, and field oxide film 2 are processed by performing anisotropic etching using the resist film 6 as a mask. After that, the resist film 6 is removed. Here, the cross-sectional shape of the field oxide film 2 is made square by the above processing. Next, as shown in FIG. 2D, the trench 1 is formed in the substrate 1 by processing the substrate 1 by anisotropic etching using the oxide film 5 as a mask. Thereafter, the oxide film 5 serving as a mask material is removed with a hydrofluoric acid-based treatment liquid. Next, as shown in FIG. 3E, a thermal oxide film 8 having a thickness of about 400 ° is formed on the surface of the substrate 1 in the trench 7 to protect the surface of the substrate 1 in the trench 7. Next, as shown in FIG. 4F, the chemical nitride is etched to remove the silicon nitride film 4 on condition that the selectivity to the thermal oxide films 3 and 8 is sufficiently large. Next, as shown in FIG. 1G, the thermal oxide films 3 and 8 are completely removed using a hydrofluoric acid-based treatment solution. Next, as shown in FIG. 1H, a thermal oxide film 9, a silicon nitride film 10, and a thermal oxide film 11 to be a capacitor gate insulating film are sequentially formed. On the thermal oxide film 11, a polysilicon film 12 doped with a dopant is deposited and formed. Further, a resist film 13 having a pattern for forming a gate electrode is formed. Next, as shown in FIG.
The polysilicon film 12 is patterned by performing chemical dry etching using the mask 13 as a mask. At this time, the pattern width of the resist film 13 for forming the gate electrode
L1 (see (h) in the figure) is governed by the trench edge,
It is designed to be longer than the length L2 from end to end of the adjacent trench. In addition, since the thermal oxide film 11 and the silicon nitride film 10 in the capacitor gate insulating film are generally formed to be thin, local pinholes (indicated by an arrow a) occur in these after chemical dry etching. There is. Next, as shown in FIG. 1J, a thermal oxide film 14 is formed through a thermal oxidation process. However, due to the etching during the patterning of the polysilicon film 12,
Local pinholes are generated in the silicon nitride film 10. For this reason, an oxidant may enter the pinhole, and the substrate 1 may be locally oxidized. Further, an oxidizing agent may enter between the patterned end portion of the polysilicon film 12 and the capacitor gate insulating film to form a wedge-shaped oxide film (indicated by an arrow b). Next, as shown in FIG. 2K, after the exposed silicon nitride film 10 is removed by chemical dry etching, a thermal oxide film 15 is formed, and a polysilicon film 16 is deposited and formed. Next, as shown in FIG. 1L, the polysilicon film 16 is etched back by chemical dry etching, so that the polysilicon film 16 remains only in the trench, and the other polysilicon film 16 is removed. Also,
A resist film 17 having a pattern covering a region other than the transistor region is formed. Next, as shown in FIG. 3 (m), the thermal oxide film 15 in the transistor region A is removed with a hydrofluoric acid-based treatment liquid, and the resist film 17 is further stripped. Thereafter, a gate insulating film 18 of the transistor is formed in the transistor region A by performing thermal oxidation.

In the manufacturing method as described above, as is apparent from FIG. 4 (m), a concave portion is formed in the substrate 1 in the transistor region A by a local thermal oxide film caused by the generation of a pinhole. I have. That is, since the gate insulating film 18 of the transistor is formed on the concave portion, the characteristics of the transistor are deteriorated. The wedge-shaped oxide film 14 formed between the patterned end portion of the polysilicon film 12 and the capacitor gate insulating film has stress on the trench. That is, this stress causes the reliability of the trench capacitor to deteriorate. Furthermore, the pattern width L1 of the resist film 13 for forming the gate electrode is determined by the trench edge, and needs to have at least a distance L2 from one end of the adjacent trench to the other. Further, when the polysilicon film 12 is shifted to one side due to a processing margin at the time of manufacturing, one end of the polysilicon film 12 may protrude from the trench 7 and may come out to the transistor region A. Note that this protrusion is not preferable because it reduces the design margin between the capacitor electrode and the gate electrode of the transistor when processing the transistor.

(Problems to be Solved by the Invention) As described above, conventionally, a pinhole is formed in a silicon nitride film serving as a mask in an oxidation step,
There is a disadvantage that a recess is formed in the substrate in the transistor region. In addition, a wedge-shaped oxide film is formed between the end of the polysilicon film serving as the capacitor electrode and the capacitor gate insulating film, which causes a problem that the reliability of the trench capacitor is deteriorated. Further, there is a disadvantage that the pattern width of the resist film for forming the gate electrode is increased, and a margin in design between the capacitor electrode and the gate electrode of the transistor is reduced due to a processing margin at the time of manufacturing.

The present invention has been made in order to solve the above-described drawbacks, and does not generate surface roughness such as a concave portion on a substrate in a transistor region, and a wedge-shaped thermal oxide film is formed at an end of a polysilicon film serving as a capacitor electrode. It is an object of the present invention to provide a semiconductor device which can be prevented from being formed, and can increase a design margin of a capacitor electrode and a gate electrode of a transistor, and a method for manufacturing the same.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a semiconductor device of the present invention comprises:
A semiconductor substrate having a trench, an insulating film formed on the surface of the semiconductor substrate inside the trench, a first conductive film embedded in the trench, and a contact hole reaching the first conductive film. An oxidation-resistant film formed on at least the first conductive film; and a second conductive film contacting the first conductive film through the contact hole.

In the method of manufacturing a semiconductor device according to the present invention, first, a trench is formed in a semiconductor substrate, and an insulating film is formed on the entire surface. Also,
A first conductive film is embedded in the trench, and an oxidation-resistant film is formed on the entire surface. Next, the first film is applied to the oxidation resistant film.
A contact hole reaching the conductive film is formed. Also,
Forming a second conductive film in contact with the first conductive film through the contact hole; Thereafter, thermal oxidation is performed to form a thermal oxide film on the surface of the second conductive film.

Further, after the step of forming a thermal oxide film on the surface of the second conductive film, the semiconductor substrate is exposed in the transistor region and thermal oxidation is performed, so that a thermal oxide film is formed on the semiconductor substrate in the transistor region. Is formed.

(Operation) According to such a configuration, the first conductive film is connected to the second conductive film serving as a wiring via the contact hole formed in the oxidation-resistant film. For this reason, the second conductive film can be processed without being restricted by the length of the trench edge, and the design margin between the second conductive film and the gate electrode in the transistor region can be increased.

According to such a method, an oxidation-resistant film having a sufficient thickness can be formed on the first conductive film embedded in the trench and the semiconductor substrate in the transistor region. Therefore, during thermal oxidation in a later step, an oxidizing agent does not enter between the first conductive film and the insulating film, and a pinhole is not formed.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In this description, portions corresponding to the conventional example are denoted by the same reference numerals as the conventional example.

FIG. 1 shows a basic configuration of a semiconductor device of the present invention.

On the semiconductor substrate 31, a field oxide film 32 is formed. Further, two trenches 33 are formed so as to sandwich field oxide film 32. These two trenches
A capacitor gate insulating film is formed on the surface of the substrate 31 in 33. The capacitor gate insulating film includes a thermal oxide film 34, a silicon nitride film 35, and a thermal oxide film 36. A polysilicon film 37 is formed to fill trench 33. This polysilicon film 37 becomes a capacitor electrode. On the polysilicon film 37, a silicon nitride film 41 as an interlayer insulating film is formed. Also, silicon nitride film
A contact hole 42 reaching each polysilicon film 37 in the trench 33 is opened in 41. further,
On the silicon nitride film 41, a polysilicon film 43 as a plate electrode connected to the polysilicon film 37 via the contact hole 42 is formed. On the polysilicon film 43, a thermal oxide film 44 is formed. Further, a gate insulating film 40 of the transistor is formed in the transistor region.

In the semiconductor device having the above configuration, the disadvantages of the related art can be solved by using the following manufacturing method. Hereinafter, the manufacturing method will be described in detail with reference to FIGS. 2 (a) to 2 (i).

First, the semiconductor substrate 1 is formed using the same method as in the prior art.
A field oxide film 2 having a thickness of about 8000 ° is formed thereon, and a trench 7 is formed so as to sandwich the field oxide film 2. In this state, a thermal oxide film 8 for protecting the surface of the substrate 1 in the trench 7 is formed in the trench 7, and a thermal oxide film 3 is formed on the substrate 1. FIG. 4 (f)). Thereafter, as shown in FIG. 3A, when etching is performed for a 600 ° equivalent amount using a hydrofluoric acid-based treatment solution, the thermal oxide film 8 is completely removed, and the thermal oxide film 3 is removed from about 1000 °. It becomes thin to about 400 ° and remains on the substrate 1 as a new thermal oxide film 19. Next, as shown in FIG. 2B, a thermal oxide film 9 is formed on the entire surface by 80.
About 80 mm of silicon nitride film 10 and thermal oxide film 11
It is formed sequentially about 40mm. The thermal oxide film 9, the silicon nitride film 10, and the thermal oxide film 11 form a three-layer capacitor gate insulating film. On the thermal oxide film 11, a polysilicon film 12 doped with a dopant is deposited to a thickness of about 6000Å. Next, as shown in FIG. 2C, the polysilicon film 12 is etched back by chemical dry etching, so that the polysilicon film 12 remains only in the trench, and the other polysilicon film 12 is removed. At this time, the thermal oxide film 11 on the substrate 1 is removed, and a part of the silicon nitride film 10 on the substrate 1 is etched.
A pinhole (indicated by arrow a) is formed. Therefore, thereafter, a silicon nitride film 20 is deposited and formed on the entire surface at a thickness of about 1000 °. Thereby, the pinhole is buried. further,
In order to form a contact hole reaching the polysilicon film 12 in the silicon nitride film 20, a resist film 21 having a predetermined pattern is formed using a photolithography technique.
Here, the resist film 21 has one pattern for forming a contact hole for every two adjacent trenches. Next, as shown in FIG. 1E, the silicon nitride film 20 is processed by anisotropic reactive ion etching to form a contact hole. After this, the resist film
21 is removed, and the polysilicon film 22 serving as a plate electrode is
Deposit about 00 °. Further, a resist film 23 having a pattern for forming a plate electrode is formed. here,
The plate electrode is formed independently of the capacitor electrode inside the trench. Therefore, the pattern width L3 of the resist film 23
Can be made shorter than the conventional pattern width L1 shown in FIG. 4 (h). Next, as shown in FIG. 3F, the polysilicon film 22 is processed by chemical dry etching. At this time, the silicon nitride film 20 is also slightly etched, but is not removed because the thickness is as large as about 1000 °. Thereafter, the resist film 23 is peeled off. Next, as shown in FIG. 2G, a thermal oxidation is performed to form a thermal oxide film 24 on the polysilicon film 22 by about 1000 °. At this time, since the sufficiently thick silicon nitride film 20 is used as a mask, local oxidation in the transistor region does not occur as in the prior art, and a wedge-shaped No thermal oxide film is formed. Thereafter, a resist film 25 having a pattern covering a region other than the transistor region is formed. Next, as shown in FIG. 1H, chemical dry etching is performed to remove the silicon nitride films 10 and 20 in the transistor region. In addition, with the hydrofluoric acid-based treatment liquid,
The thermal oxide films 9 and 14 in the transistor area are removed. Next, as shown in FIG. 1I, after the resist film 25 is peeled off, thermal oxidation is performed to form a gate insulating film 18 of the transistor in the transistor region A. At this time, a silicon nitride film 20 is formed on the polysilicon film 12 inside the trench.
, A wedge-shaped oxide film is not formed on the polysilicon film 12 at the end of the trench.

According to the semiconductor device having the above configuration and the method of manufacturing the same, when thermally oxidizing the polysilicon film 22 serving as the plate electrode, the silicon nitride film 20 is sufficiently thick on the transistor region and the polysilicon film 12 in the trench. . For this reason, a concave shape due to local oxidation in the transistor region A and a wedge-shaped thermal oxide film on the polysilicon film 12 at the trench end are not formed. Also, when forming the gate insulating film 18 of the transistor, since the silicon nitride film 20 is present on the polysilicon film 12, a wedge-shaped thermal oxide film is formed at the concave portion of the transistor region A and at the end of the trench. There is no. As described above, according to the present invention, a flat transistor region without unevenness and a capacitor electrode without a wedge-shaped oxide film can be obtained. Further, in the present invention, the plate electrode is formed independently of the capacitor electrode inside the trench.
Therefore, the pattern width L3 of the resist film 23 for forming the plate electrode can be made shorter than the conventional pattern width L1 shown in FIG. 4 (h). Therefore, since the plate electrode can be designed to be sufficiently small, the design margin with the gate electrode formed in the transistor region A can be increased.

In the above embodiment, the capacitor gate insulating film is composed of the three layers of the thermal oxide film 9, the silicon nitride film 10, and the thermal oxide film 11, but it goes without saying that the present invention can be applied to a single layer. No.

[Effects of the Invention] As described above, according to the semiconductor device of the present invention and the method of manufacturing the same, the following effects can be obtained.

A sufficiently thick silicon nitride film exists on the transistor region and the polysilicon film in the trench. The capacitor electrode embedded in the trench is electrically connected to the plate capacitor electrode via the silicon nitride film. Therefore, it is possible to prevent the formation of a roughened surface such as a concave portion in the transistor region, the formation of a wedge-shaped thermal oxide film at the end of the polysilicon film serving as the capacitor electrode, and the design of the capacitor electrode and the gate electrode of the transistor. A semiconductor device capable of increasing a margin and a manufacturing method thereof can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a semiconductor device according to one embodiment of the present invention, FIGS. 2A to 2I are sectional views showing a method of manufacturing a semiconductor device according to one embodiment of the present invention, and FIG. FIGS. 4A to 4M are cross-sectional views showing a conventional semiconductor device, and FIGS. 4A to 4M are cross-sectional views showing a method for manufacturing the conventional semiconductor device. 1,31 ... semiconductor substrate, 2,32 ... field oxide film, 3,8,
9,11,14,15,19,24,34,36,38,44 …… Thermal oxide film, 4,10,20,
35,41 ... silicon nitride film, 5 ... oxide film, 6, 13, 17, 21,
23,25 …… resist film, 7,33 …… trench, 12,16,22,3
7,39,43 …… Polysilicon film, 18,40 …… Gate insulating film,
42 ... Contact hole.

Continuation of front page (56) References JP-A-2-87571 (JP, A) JP-A-2-189968 (JP, A) JP-A-4-56166 (JP, A) JP-A-61-199657 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27 / 04,21 / 822 H01L 27 / 108,21 / 8242

Claims (3)

(57) [Claims] A plurality of trench capacitors formed in a plurality of trenches provided in a semiconductor substrate, the plurality of trench capacitors including a capacitor insulating film provided on an inner surface of each trench and a first conductive film filling each trench; An oxidation-resistant film formed to cover the first conductive film of the capacitor and having a contact hole reaching the first conductive film; and the first conductive film of each trench capacitor via the contact hole. And a second conductive film connected to each other. Forming a plurality of trench capacitors in the semiconductor substrate, forming a capacitor insulating film on the inner surface of each trench, and filling each trench with a first conductive film to form a plurality of trench capacitors; Covering the first conductive film of each trench capacitor with an oxidation-resistant film; forming a contact hole reaching the first conductive film of each trench capacitor in the oxidation-resistant film; Forming a second conductive film that connects the first conductive films of the trench capacitors to each other via a first conductive film, and performing a thermal oxidation to form a thermal oxide film on the surface of the second conductive film. A method for manufacturing a semiconductor device, comprising: 3. A step of exposing the semiconductor substrate in a transistor region adjacent to each trench capacitor after the step of forming a thermal oxide film on the surface of the second conductive film; Forming a gate insulating film of a transistor on the semiconductor substrate.