JPH02295151A - Manufacture of dielectric isolating substrate - Google Patents

Abstract

PURPOSE:To prevent isolated shallow islands from deforming by etching a region part in a desired thickness in a state that the side face of a shallow isolated island forming region part of a board is protected by an oxide film. CONSTITUTION:An SiO2 film 22 remains under a CVD SIN film 23 and at a deep isolated island forming region, and is removed from a V-shaped groove forming region part. Then, with the remaining films 22, 23 as masks an isolating V-shaped groove 23 is formed at a semiconductor substrate 21 by alkaline anisotropic etching. Thereafter, the film 22 is removed to expose a deep isolated island forming region part 25 of the substrate thereunder. Then, it is thermally oxidized with the film 23 as a mask, and a LOCOS oxide film 26 is formed on the front face of a first region 25 and the side face of a V-shaped groove 24. Then, the film 26 is used as a protective film of the substrate 21, the two layers of the films 23, 22 are removed by etching, and the front face of a shallow isolated island forming region part 27 of the substrate thereunder is exposed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a dielectrically isolated substrate, and more particularly to a method for manufacturing a dielectrically isolated substrate having isolation islands of different depths within the same substrate. It is. (Prior Art) FIGS. 2(a) to 2(e) show an example of a conventional manufacturing method of a dielectric isolation substrate having isolation islands with different island depths within the same substrate. This method is disclosed in Japanese Patent Application Laid-Open No. 63-36545. First, as shown in FIG. 2(a), a two-layer structure coating consisting of silicon dioxide 1!2 and silicon nitride film 3 is formed on one main surface side of a semiconductor substrate (single crystal silicon substrate) l having a (100) plane. is formed and patterned by photolithography to form a mask 4a consisting of a two-layer structure film only in the region where deep isolation islands are to be formed. Further, a mask 4b made only of the silicon dioxide film 2 is formed in a region where a shallow isolation island is to be formed. Next, as shown in FIG. 2(h), the substrate 1 is etched using an aqueous potassium hydroxide solution, and a required depth d. A trapezoidal groove 5 is formed. Next, Figure 2(c)
As shown in FIG.
At this time, the substrate 4a is not etched because its surface is the silicon nitride film 3. After this, the substrate 1 is removed with a potassium hydroxide aqueous solution.
The trapezoidal groove 5 is made into a V-groove 6 as shown in FIG. 2(c). At this time, in the shallow isolation island forming region portion 7 of the substrate (the portion covered by the mask 4b), the single crystal silicon of the crystal plane (100) is exposed on the surface, so the line changes from the dotted line to the solid line. The surface is dd. will be etched. On the other hand, since the side surface is a crystal plane (111),
The etching rate is extremely slow, and grooves 6 are formed. Next, after removing the mask 4a, as shown in FIG. 2(h), a silicon dioxide film 8 is formed on the main surface of the semiconductor substrate 1 including the above-mentioned V6, and a support layer is formed on this. A polycrystalline silicon layer 9 is deposited by CVD. After that, ■, the opposite main surface side of the semiconductor substrate 1 is
By polishing and removing the tip of the dielectric material until the tip thereof is exposed, a dielectric isolation substrate having a deep isolation island lO and a shallow isolation island 11 is completed as shown in FIG. 2 {e}. (Intelligence M to be solved by the invention) However, in the conventional method as described above, as shown in Fig. 2 (
When forming the V-groove 6 and at the same time forming the shallow isolation island forming region 7 in step c), as the etching with the potassium hydroxide aqueous solution progresses, the surface crystal plane of the shallow isolation island forming region 7 ( 100) as well as the part 7
(211). Higher-order crystal planes such as (311) are etched, and since these higher-order crystal planes have a faster etching rate than (111), when the shallow isolation island forming region 7 is made to the desired thickness, There was a problem that the shape of the portion 7 would be distorted. This deformation of the shallow isolation island formation region 7 leads to deformation of the shallow isolation island 11, which leads to the problem of deteriorating the characteristics of the element formed there. The present invention prevents deformation of the above-mentioned shallow isolation island forming region when etching it to a desired thickness, and forms deep isolation islands and shallow isolation islands on the same substrate without deformation. The purpose of this study is to provide a method for manufacturing dielectrically isolated substrates that can be used. (Means for Solving the Problems) In the present invention, after forming a V-groove for isolation in a semiconductor substrate, the side surface of the V-groove around a shallow isolation island forming region of the substrate is covered with an oxide film. The surface of the isolated island forming region is etched to give the shallow isolated island forming region a desired thickness. (Function) In the above method, the side surfaces of the shallow isolation island forming region, which are also the side surfaces of the trench, are protected by an oxide film, so etching is performed to obtain the desired thickness of the shallow isolation island forming region. When the etching rate is higher than that of the (111) plane, such as the (211) plane and the (31.1) plane, the plane with a higher-order index, which has a faster etching rate than the (111) plane, does not appear at the upper corner of the shallow isolation island forming region. , the deformation of the shallow isolation island forming region is prevented. (Example) An example of the present invention will be described below with reference to FIGS. 1(a) to (h). First, as shown in FIG. 1(a), does it have a (100) plane? A Stow film 22 and an oxidation-resistant film (:VD
The SiN film 23 is formed to have a two-layer structure. Here, the film thickness of the SIOt film 22 needs to be thick enough to serve as a mask material for forming a V groove by alkali anisotropic etching, which will be described later.
The thickness should be about 5,000 people to form a . That is, potassium hydroxide (κOH) was used as an alkaline etching solution.
) one isobrobyl alcohol (IPA) one water (0.0
) system at 80°C, the (100) crystal plane of Si
The etching rate is approximately 0. 7μ/IIIin,
Furthermore, the etching rate of the SiO* film is approximately 50 people/sin. To form a groove with a depth of 50Q, use 50/0.
It takes 7-70 minutes, and the SiO film requires 50 people x 70 = 3
500 people are etched. Therefore, approximately 5,000 people will need mask materials, taking into account +α. On the other hand, C
The thickness of the VD SiN film 23 of several hundred is sufficient as a mask material for alkaline anisotropic etching. this is,
Is this because the SIN film is hardly etched with the alkaline etching solution? It is. Next, a portion of the CVD SiN III 2 3 is removed by ordinary photolithography, leaving the CVD SiN 1g 2 3 only in the shallow isolation island forming region as shown in FIG. 1(b). Here, CVD
The SiN film 23 is made of, for example, CF. It can be easily removed by dry etching using +O■ gas. Next, stoxl [l
By patterning with I22, this Si(h film 22 is formed into the CVO SiN film 22 as shown in FIG. 1(c)).
It is left under the film 23 and in the deep separation island formation region, and is removed from the groove formation region. Next, the remaining Sing film 22 and the remaining CVD SiN film 23
Using as a mask, the substrate 2l is subjected to alkali anisotropic etching through the portion where the SiOglIi 22 has been removed, thereby forming a groove 24 for isolation in the semiconductor substrate 21, as shown in FIG. 1(h). Afterwards, the exposed SiO remained as a mask.
(1) By removing the film 22 as shown in FIG.
25 (called JlM) is exposed. And the first area 2
5 is exposed, next, as shown in FIG. 1(f), thermal oxidation is performed using the Cν SiN film 23 as a mask, resulting in so-called LQCQS oxidation II! 26 to 1st eM area 250
Formed on the surface and the sides of the V-groove 24. Here, the LOG
The thickness of the OS oxide film 26 is the same as that of the CVD SiN film 2, which will be described later.
3 and the SiJ film 22 are sufficiently protected from etching when the SiJ film 22 is removed, and the thickness is sufficient as a mask material for the alkali anisotropic etching described later, and the thickness is sufficient to achieve the desired shallow isolation island thickness. It depends on the number of people, but usually it is around 10,000 people. Next, using the LOCOS oxidized Wa 26 as a protective film for the semiconductor substrate 2l, the CVD SiN film 23 and stozll!
I 2 2 (7) The two layers are removed by etching as shown in Figure 1 (barrel), and the shallow isolation island forming region of the substrate below (
27 (hereinafter referred to as the second region) is exposed. After that, from the exposed surface, as shown in FIG.
The trl region 27 is anisotropically etched with alkali to form the second region 27 into a shallow isolation island with a required thickness. At this time,
First wI region 25 covered with LOCOS oxide film 26
The effect of etching does not appear at all. Also, ■Groove 2
The side surface of the second area 27, which is also the side surface of 4, is the same < LOG
Since the second region 27 is covered with the OS oxide film 26, a plane with a higher-order index having a faster etching rate than the (111) plane, such as a (211) plane and a (311) plane, appears at the upper corner of the second region 27. Therefore, the shape of the second region 27 (shallow isolated island) will not be deformed. Thereafter, the LOGOS oxide film 26 is removed as shown in FIG. 1(i), leaving the IGW region 25 exposed again and the second sJi region 27 completely exposed.

After that, in accordance with the usual manufacturing method of a dielectric isolation substrate, the first Si region 25 and the second
A buried layer 28 is formed in the surface layer portion of the entire surface of the region 27. Next, as shown in the figure, an isolation oxide film 29 is continuously formed over the entire surface of the first region 25 and second region 27, and a thick polycrystalline silicon layer 30 is deposited thereon as a support layer. after that,
The other main surface side of the semiconductor substrate 2l is polished away until the tips of the grooves 24 are exposed, and the first region 25 and the second fill region 27 are formed into deep isolation islands as shown in FIG. 1(9). By completely separating the isolation islands 25a and 27a, a dielectric substrate having isolation islands of different depths on the same substrate is completed. (Effects of the Invention) As described in detail above, according to the manufacturing method of the present invention, the shallow isolation island forming region of the base body is coated with a desired thickness while the side surface of the shallow isolation island forming region is protected with an oxide film. Since we performed etching to improve the
It is possible to prevent a surface having a high etching rate and a high-order index from appearing at the corner of the region, and it is possible to prevent deformation of the region and, by extension, deformation of the shallow isolated island. Therefore, it is possible to improve the characteristics of elements formed on this shallow isolation island.

[Brief explanation of the drawing]

Claims (1)

[Claims] (a) forming an oxide film on one main surface of a semiconductor substrate;
a step of forming an oxidation-resistant film thereon; (2) a step of patterning the oxidation-resistant film to leave the oxidation-resistant film only in the shallow isolation island formation region; (d) patterning the oxide film, leaving this oxide film under the oxidation-resistant film and in the deep isolation island formation region, and removing it from the V-groove formation area; (d) patterning the oxide film through the removed part; a step of etching the substrate to form an isolation V-groove in the substrate; (e) then removing the oxide film exposed and remaining in the deep isolation island formation region, and etching the deep isolation island formation region of the substrate below; (f) forming an oxide film as a protective film and mask material on the exposed surface of the deep isolation island forming region of the substrate and on the side surfaces of the V-groove; (g) then forming a shallow (h) removing the oxidation-resistant film remaining in the isolation island formation region and the oxide film thereunder, and exposing the surface of the shallow isolation island formation region portion of the substrate underneath; (h) the shallow isolation island formation region portion of the substrate; (i) Then, after removing the protective film and the oxide film as a mask material, the exposed substrate is removed by etching to a desired thickness using the protective film and the oxide film as a mask material as a mask; a step of continuously forming an isolation insulating film on the entire surface of the isolation island forming region and the entire surface of the shallow isolation island forming region of the substrate exposed to a desired thickness, and depositing a support layer thereon; ) Thereafter, the substrate is removed from the other main surface side of the semiconductor substrate until the tip of the V-groove is exposed.