JPH04124822A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce damage at the time of etching, to set the conditions of etching properly and to form a through-hole with a stepped section positively by leaving a resist on the bottom of the through-hole when a second resist mask with a second opening larger than a first opening is formed. CONSTITUTION:A process, in which a metallic electrode 2 is formed onto one main surface of a semiconductor substrate 1, a process, in which a first resist mask 3 with a first opening 3a is shaped onto the other main surface of said substrate 1, a process, in which the substrate 1 in the first opening 3a section is removed through etching by using said resist mask 3 and a through-hole 4, from which the underside of the metallic electrode 2 is exposed, is shaped, a process, in which said resist mask 3 is removed, a process, in which a second resist mask 5 with a second opening 5a larger than the first opening 3a is formed to the forming section of the through-hole 4 in the other main surface of said substrate 1 while leaving a resist 5b on the bottom of the through-hole 4, and a process, in which the substrate 1 in the second opening 5a section is removed through etching up to required depth by employing said second resist mask 5 and a stepped section 6 is formed around the through-hole 4, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a through hole having a step in a semiconductor substrate by an etching method.

[Prior Art] Generally, in the field of monolithic microwave integrated circuit devices used in microwave systems, semiconductor substrates are etched to improve heat dissipation using a metal layer on the back side of the substrate. A through hole connected to an electrode on the main surface of the substrate is formed, and the through hole is filled with metal by wet plating or the like, and the electrode on the main surface of the substrate and the metal layer on the back surface of the substrate are connected by the filled metal. At this time, one method for satisfactorily depositing metal in the through hole is to form a stepped portion around the through hole to widen the opening of the through hole.

As a conventional method for forming a stepped portion around such a through hole, there is a method as shown in FIG. 2, for example. A metal electrode 2 is formed on the entire surface of the semiconductor substrate 1 to serve as, for example, a source electrode of an FET element. A resist mask 7 having a first open lower a is formed on the other main surface of the semiconductor substrate 1 by photolithography using a positive resist (FIG. 2(a)). At this time, only exposure processing is performed in advance for a second opening for forming a step portion, which will be described later. 7b indicates the exposed resist portion (FIG. 2(b)). Using a resist mask 7, the semiconductor substrate 1 at the first open lower portion a is etched away by anisotropic dry etching to form a through hole 8 and expose the lower surface of the metal electrode 2 on the main surface of the semiconductor substrate 1 ( Figure 2 (c
)). Subsequently, the exposed resist b is developed and a second opening lower C is opened in the resist mask 7 (second
Figure (d)).

The semiconductor substrate 1 at the second open lower portion C is etched away to a required depth by anisotropic dry etching again to form a stepped portion 9 around the through hole 8 (FIG. 2(e)).

[Problems to be Solved by the Invention] In the conventional etching method of forming a step around the through hole, a second anisotropic dry etching is performed with the lower surface of the metal electrode exposed to form a step around the through hole. As a result, the damage during anisotropic dry etching that appears on the surface of the semiconductor substrate on which the FET elements and the like are formed becomes large, sometimes affecting the characteristics of the FET elements and the like. In order to avoid this, it is necessary to reduce the damage by lowering the RF power during anisotropic dry etching. Also, 1
In order to develop the exposed resist after the first anisotropic dry etching, etching conditions must be determined so that the resist is not damaged by the first anisotropic try etching. Therefore, in the conventional method, restrictions are imposed on the etching conditions in order to reduce etching damage, and a sufficient etching rate may not be obtained depending on the etching apparatus.

Therefore, the present invention reduces damage during etching to the whole surface side of a semiconductor substrate on which a semiconductor element is formed, and also enables the etching conditions to be appropriately set to reliably form a through hole having a stepped portion. It is an object of the present invention to provide a method for manufacturing a semiconductor device that can perform the following steps.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a step of (a) forming a metal electrode constituting a required semiconductor element on the entire surface of a semiconductor substrate; (b) a step of forming a metal electrode constituting a required semiconductor element; on the other main surface of
forming a first resist mask having an opening of
(c) etching away the semiconductor substrate in the first opening using the first resist mask to form a through hole through which the lower surface of the metal electrode is exposed; (d) the first resist (e) removing a mask, (e) applying a second resist mask having a second opening larger than the first opening in the formation portion of the through hole on the other main surface of the semiconductor substrate; (f) etching away the semiconductor substrate in the second opening to a required depth using the second resist mask to form a stepped portion around the through hole; The gist is that there is a process.

[Operation] After the through-hole is formed by the first etching, the first resist mask is removed, and a second resist mask having a second opening larger than the first opening in the first resist mask is formed. At this time, resist is left at the bottom of the through hole. As a result, the resist left at the bottom of the through-hole serves as a protective material during the second etching process using dry etching, etc., effectively preventing damage during etching to the entire surface of the semiconductor substrate on which semiconductor elements are formed. decreases to In addition, the first resist mask is not used as a mask for the second etching by opening the second opening through another development process.
There is no need to consider damage to the resist during the second etching. Therefore, the etching conditions for both the first and second etching can be appropriately set, and a through hole having a stepped portion can be reliably formed.

[Example] Hereinafter, an embodiment of the present invention will be described with reference to FIG.

In FIG. 1, parts that are the same as or equivalent to those in FIG. 2 are designated by the same reference numerals.

In this embodiment, a GaAs substrate is used as the semiconductor substrate.

On the whole surface of the GaAs substrate 1, a required semiconductor element such as an FET element whose constituent elements include a metal electrode 2 serving as a source electrode or the like is formed. The thickness of the GaAs substrate 1 is approximately 100 μm. A first resist mask 3 having a first opening 3a is formed using a positive resist on the other main surface of the GaAs substrate 1 by ordinary photolithography. 1st
The film thickness of the resist mask 3 is about 3 μm (FIG. 1(a)).
The portion a of the GaAs substrate] is selectively etched away to form a through hole 4 through which the lower surface of the metal electrode 2 is exposed. A parallel plate type reactive ion etching apparatus using S i C14 and C10 was used for etching. Gas ratio is 5iC14/C12-1~3, pressure is 10~50mTorr-, power is 400~800W
were set respectively. The through holes 4 were reliably formed by reactive ion etching under these conditions (
Figure 1(b)). After removing the first resist mask 3, a second opening 5a, which is larger than the first opening 3a, is formed by photolithography in the area where the through hole 4 is formed on the other main surface of the GaAs substrate 1. A resist mask 5 is formed. At this time, the resist 5b is left at the bottom of the through hole 4. During resist application, the resist is deposited thicker at the bottom of the through-hole 4 than in other areas, so the resist 5b can be easily left at the bottom of the through-hole 4 by controlling the exposure amount (see Fig. 1). c)). Using the second resist mask 5, the portion of the GaAs substrate 1 in the second opening 5a is selectively etched away to a required depth to form a stepped portion 6 around the through hole 4. As the etching method, reactive ion etching was used under almost the same conditions as above. Through this reactive ion etching, the stepped portion 6 is reliably formed around the through hole 4, and during this etching, the through hole 4 is
The resist 5b left at the bottom of the FE acts as a protective material.
Damage during etching to the full surface side of the GaAs substrate 1 on which T elements and the like are formed is effectively reduced (FIG. 1(d)).

As described above, according to this embodiment, there is less damage to the lifetime side of the GaAs substrate 1 on which FET elements and the like are formed, and there is a greater degree of freedom in the etching conditions during both the first and second etching. A through hole 4 having a stepped portion 6
It becomes possible to form reliably.

Note that in the above embodiment, the semiconductor substrate is made of GaAs.
was applied, but Si, InP, etc. can also be applied. Further, as the etching method, anisotropic dry etching consisting of reactive ion etching is applied, or other anisotropic dry etching such as reactive sputter etching or sputter etching can also be applied. Furthermore, the gas for etching the semiconductor substrate depends on the semiconductor substrate material; for example, for GaAs, 5iC14/C12, +:cc 12 F2102, CC12F2/inert gas, etc. are used.

[Effects of the Invention] As explained above, according to the present invention, after forming a through hole by the first etching using the first resist mask, the first resist mask is removed and the first resist mask is etched.
The second opening is larger than the first opening in the resist mask.
A second resist mask having an opening was formed, and at this time, the resist was left at the bottom of the through hole, so that the resist left at the bottom of the through hole was protected during the second etching by dry etching etc. Damage during etching to the entire surface of the semiconductor substrate on which semiconductor elements are formed is effectively reduced.

Further, since the first resist mask is not used as a mask for the second etching by subjecting it to another development process, there is no need to consider damage to the resist during the first etching. therefore,
Etching conditions for both the first and second etching can be appropriately set, and a through hole having a stepped portion can be reliably formed.

[Brief explanation of drawings]

FIG. 1 is a process diagram for explaining an embodiment of a method for manufacturing a semiconductor device according to the present invention, and FIG. 2 is a process diagram for explaining a conventional method for manufacturing a semiconductor device. 1: GaAs substrate (semiconductor substrate), 2: Metal electrode, 3: First resist mask, 3a:
1st opening, 41 through hole, 5, second resist mask, 5a: second opening, 5b = resist left at the bottom of through hole, 6: step portion.

Claims (1)

Scope of Claims: (a) a step of forming a metal electrode constituting a required semiconductor element on one main surface of the semiconductor substrate; (b) a step of forming a metal electrode constituting a required semiconductor element on one main surface of the semiconductor substrate; (c) forming the first resist mask; (c) forming the first resist mask;
etching away the semiconductor substrate in the first opening using a resist mask to form a through hole through which a lower surface of the metal electrode is exposed; (d) removing the first resist mask; (e
) A second resist mask having a second opening larger than the first opening is formed in the other main surface of the semiconductor substrate at a portion where the through hole is formed, leaving resist at the bottom of the through hole. (f) etching away the semiconductor substrate in the second opening to a required depth using the second resist mask to form a stepped portion around the through hole; A method for manufacturing a semiconductor device.