JPS633447B2 - - Google Patents

Description

Detailed Description of the Invention The present invention projects a high-energy laser beam onto a localized portion of the surface of a semiconductor substrate having a shallow PN junction on the substrate surface, heats the localized portion, and removes impurities present in the localized portion of the semiconductor substrate. The present invention relates to a method of manufacturing a semiconductor device in which a deep PN junction is formed in a portion corresponding to the local portion by diffusion inward.

Formation of a shallow PN junction on the surface of a semiconductor substrate, for example, a shallow PN junction with a depth of about 0.1 μm to 0.2 μm from the surface, is required for solar cells, high frequency transistors, and the like. Several methods have been developed to form this shallow PN junction, including an impurity coating and diffusion method and an impurity ion implantation method. A particular problem with this shallow PN junction is destruction of the PN junction during electrode formation. That is, when an electrode metal is formed by vapor deposition on a shallow P-type or N-type semiconductor layer of about 0.1 μm to 0.2 μm, melting and alloying occur at the interface between the semiconductor layer and the electrode metal layer, and as a result, the alloy layer As a result, the shallow PN junction is destroyed.

Conventionally, in order to solve the problems of shallow PN junctions mentioned above, deep P (or N) junctions were formed by selectively diffusing impurities, ion implantation, etc. into a part of the shallow P (or N) type layer.
The problem is solved by forming a mold layer, that is, forming a deep PN junction in a part of the shallow PN junction, and forming an electrode in this deep PN junction.

However, in the above conventional method, for example, in the case of selective diffusion of impurities, there is a SiO ₂ film formation process, a mask formation process by photoresist processing, a diffusion heat treatment process in an impurity gas atmosphere, and in the case of ion implantation, Processes such as a mask alignment process during implantation and a heat treatment process for activating the implanted ions after impurity ion implantation are required. Each of these processing steps takes a long time, and since they are precision processing, advanced manufacturing technology is required. especially deep
When ion implantation is used to form an electrode layer on a PN junction, it is difficult to distinguish the deep PN junction formed by ion implantation, and it is difficult to align the vapor deposition mask for forming the electrode metal layer. , the deposited metal layer for the electrode is shifted from the deep PN junction, and the shallow PN
Stretching over the joints often occurs. As mentioned above, this destroys the shallow PN junction and lowers the manufacturing yield.

As mentioned above, the conventional method involves many work steps and takes a considerable amount of time, resulting in poor productivity and low yield, resulting in an increase in the product unit price.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to propose a method for manufacturing a semiconductor device that easily forms a deep PN junction in a portion of a shallow PN junction in a short time.

Another object of the present invention is to provide a deep
The object of the present invention is to propose a method for manufacturing a semiconductor device in which a PN junction can be easily formed in a short time, and furthermore, an electrode metal layer can be precisely provided only on the deep PN junction surface.

Recently, after implanting impurities into the surface of a semiconductor substrate to a predetermined depth using the ion implantation method, high-energy laser light is applied to the surface of the substrate for a short period of time (1 to 2 J/cm ² , several
It has been reported that when the impurity ions are projected (nsec), the implanted impurity ions become electrically activated and act as conductivity type determining impurities on the semiconductor substrate.
(GA Kachurin, VA Bogatyriov, SI
Romanov and LSSmirnov, Proc. of Ion
Implantation of Semicon.
(p. 445 Colorado 1976) This reported technology began to be seen as a promising measure for improving productivity due to its advantages such as being able to complete annealing of a semiconductor substrate after ion implantation in a short time by laser beam projection.

The inventors are at the stage of further researching the above facts,
The following facts were confirmed. After forming an impurity-doped layer on the semiconductor surface region, if a high-energy laser beam is irradiated onto this doped layer for a short time, the impurities in the doped layer will diffuse into the semiconductor substrate, forming a PN junction at the interface between the doped layer and the semiconductor substrate. If there exists,
This is the fact that the above-mentioned PN junction advances deeper into the substrate by the projection of high-energy laser light. in this case,
The initial impurity-doped layer formation is not limited to impurity ion implantation methods, but there is no difference between impurity thermal diffusion methods and the like.

The above fact can be confirmed when the initial doped layer is shallow, for example, a layer with a depth of about 0.1 to 0.2 μm,
When a laser beam is projected onto this layer, the depth can be increased to about 0.3 to 0.5 μm.

The present invention has been invented focusing on the above-mentioned fact, and includes a method for manufacturing a semiconductor device in which a deep PN junction is formed in a part of a shallow PN junction, and an electrode is precisely placed on the surface of the formed deep PN junction. This is a method for manufacturing a semiconductor device in which metal is provided.

This invention involves forming a shallow doped layer of impurities of a second conductivity type in a desired surface region of the surface of a semiconductor substrate of a first conductivity type, and providing a mask having a window of a predetermined shape on the surface of the semiconductor substrate. implanting ions of a second conductivity type and irradiating laser light through the mask to introduce impurities of a second conductivity type into the semiconductor substrate surface region exposed in the window of the mask and introduce the impurities into the semiconductor substrate. After that, while the mask is fixed to the surface of the semiconductor substrate, an electrode metal is vapor-deposited on the surface of the semiconductor substrate, and an electrode metal vapor-deposited layer is formed on the surface portion of the semiconductor substrate exposed to the window of the mask. This is a method for manufacturing semiconductor devices.

Since the present invention has the above configuration, it has the following effects.

(1) It is easy to make a laser beam into a thin beam optically or using a mask, and by using this narrow beam laser beam, it is easy to create a deep PN junction in the desired part of a shallow PN junction. can.

(2) The projection time of the laser beam used on the semiconductor substrate varies somewhat depending on the intensity of the laser beam, but it is approximately several n.
The laser beam projection time is about seconds, which is an instantaneous processing time, and the manufacturing time of the product can be shortened accordingly.

(3) As mentioned above, laser beam projection is an instantaneous heat treatment, which eliminates the lateral impurity diffusion that is unavoidable with conventional heat treatment diffusion methods, which reduces the area of the semiconductor substrate for the product or allows for high density. make it possible to

(4) The mask used during ion implantation and laser beam projection can be used as a mask during subsequent electrode metal deposition without moving the relative position between the mask and the semiconductor substrate surface. The electrode metal layer can be formed accurately, and as a result, the yield of products can be increased.

Although the terms shallow PN junction and deep PN junction used in the present invention are relative, for example, shallow
A PN junction is a depth that is such that the PN junction is destroyed during electrode metal formation, and is usually 0.1 to 0.1 in the case of a Si substrate.
A deep PN junction is defined as a depth of about 0.2 μm, and a deep PN junction is a depth at which the PN junction is not destroyed even when electrode metal is formed, and in the case of a Si substrate, it is usually a depth of 0.3 μm or more.

In the present invention, the impurity-doped layer on the surface of the semiconductor substrate includes a state in which impurities are doped by ion implantation, a state after annealing after ion implantation, a state in which impurities are doped by diffusion from the substrate surface, etc. There is. Therefore, in the present invention, when referring to an impurity-doped layer, a case where a PN junction is formed at the interface with a semiconductor substrate or a case where a PN junction is not formed is included.

In the present invention, the depth at which some impurities in the impurity doped layer are further diffused into the semiconductor substrate by laser beam projection is related to the intensity of the laser beam and the projection time.
If a predetermined intensity or exposure time is exceeded, the semiconductor substrate may crack due to thermal strain.

Hereinafter, the present invention will be further explained with reference to Examples of the present invention.

Figures 1 to 6 show shallow depths formed on the surface of a Si substrate.
FIG. 3 is an explanatory diagram of an example in which a deep PN junction is formed in a part of the PN junction. P-type Si with specific resistance 0.1~10Ω・cm
Phosphorus ions are implanted into the surface of the substrate (FIG. 1) at a concentration of 1×10 ¹⁵ ions/cm ² at an energy of 100 eV to form an impurity doped layer 2 (FIG. 1). The thickness of the impurity doped layer is 0.1 μm. Next, a laser beam 3 (FIG. 2) with an intensity of 1.0 J/cm ² from a ruby laser is projected onto the surface of the impurity-doped layer 2 for 20 nsec. The phosphorus ions implanted into the surface of the Si substrate by the projection of this laser beam 3 (FIG. 2) are electrically activated, and the doped layer 2 becomes an n-type Si layer 4 (FIG. 2). The depth of this layer 4 is shallow, 0.1 μm from the surface.

Next, a 100 μm thick Mo mask 6 (FIG. 3) having a 150 μm×150 μm window 5 (FIG. 3) is placed on the surface of the semiconductor substrate 1. Thereafter, a laser beam 7 (FIG. 4) with increased energy of 2 J/cm ² is projected onto the surface of the Si substrate. As is clear from FIG. 4, the entire substrate surface is covered with the Mo mask 6 except for the mask window 5, so that the high-energy laser beam is projected only onto the n-type Si layer exposed at the mask window. strength
When a high-energy laser beam of 2 J/cm ² is projected for about 10 nsec, phosphorus in the area projected by the laser beam in the n-type Si layer 4 (Fig. 4) causes intra-solid diffusion, as shown in Fig. 4. 0.3μ deep into the board.
m) An n-type layer 8 (hereinafter also referred to as deep PN junction) is formed. This n-type layer 8 forms a deep PN junction in a part of the shallow PN junction. deep PN
The shape of the joint 8 is determined by the shape of the window 5 of the mask 6 since it has almost no lateral expansion.

To form an electrode on the surface of this deep PN junction 8, with the Mo mask 6 fixed on the Si substrate surface,
It is installed in a metal vapor deposition equipment (not shown), and first, Si
While heating the substrate to 300°C, titanium is evaporated to a thickness of 1000 Å to form a titanium layer 9 (Fig. 5), and on top of that, Ag is evaporated to a thickness of 3 μm to form an Ag layer 10 (Fig. 5).
form. After the vapor deposition is completed, apply Mo mask 6.
When removed from the Si substrate surface, deep PN junction 8 (sixth
Electrode 1 consisting of a titanium-Ag double layer on the surface of
1 can be formed.

This electrode 11 does not overlap the shallow PN junction because the mask 6 used when forming the deep PN junction 8 is not moved relative to the Si substrate and is used as a mask for electrode metal deposition. , the shallow PN junction will not be destroyed during electrode formation.

FIGS. 7 to 8 are diagrams for explaining other embodiments of the present invention. The feature of this embodiment is that a shallow PN junction and a deep PN junction can be formed by one laser beam projection.

FIG. 71 shows a P-type Si substrate, on the surface of which there is an impurity doped layer 2 with a depth of 0.1 μm formed by ion implantation of phosphorus. Since the impurity doped layer 2 remains in the state in which ions have been implanted, it has not yet shown the conductivity type due to the implanted ions. Next, a mask 12 is placed on the surface of this Si substrate. The mask used in this example has a structure in which a predetermined pattern of Al vapor deposited film (60 Å thick) 14 is provided on the surface of a glass plate 13 with a thickness of 1 mm. The portion of the Al deposited film 14 has a transmittance of about 50% to the laser beam. On the other hand, the transmittance of the laser beam in the portion of the glass plate where the Al vapor deposited film 15 is not provided is approximately 100% and there is no attenuation.

The mask 12 is placed on the Si substrate surface so that the Al deposited film 14 side faces the Si substrate surface side, and the mask 12 is
When the laser beam 7 (FIG. 8) of 2 J/cm ² is projected for 20 nsec, the impurity doped layer 2 directly under the Al deposited film 14 (FIG. 8) of the mask 12 is exposed to the transmitted laser beam of about 1 J/cm ² . The doped layer is then irradiated for about 20 nsec, and phosphorus in the doped layer is electrically activated to make the doped layer in that region N-type. On the other hand, the impurity doped layer 2 directly under the glass plate, where no Al deposited film is present, is projected for about 20 nsec by a transmitted laser beam of about 2 J/cm ² , and the ion-implanted phosphorus is electrically activated and the doped layer 2 is The layer is made N-type, and the phosphorus is further diffused deeply into the Si substrate to form a deep PN junction 8.

According to this embodiment, by using a semi-transparent film mask, the laser beam projection process that was previously required twice can be completed only once, and productivity can be further improved.

The transmittance of the mask used in the examples can be controlled by the thickness of the metal vapor deposited film such as Al.

Another embodiment of the invention will be described with reference to FIGS. 9 and 10. In a semiconductor device, reducing the connection resistance between an electrode layer and a semiconductor substrate is important for improving the characteristics of the semiconductor device. Conventionally, for this purpose, before forming the electrode metal layer, impurities were diffused at a high concentration into the electrode forming area on the surface of the semiconductor substrate to make it a low resistance area, and then the electrode metal layer was formed there. It is. The method of forming this low-resistance layer usually uses a selective impurity diffusion method, an ion implantation method, etc., but this increases the number of manufacturing steps and requires a long processing time, which poses problems in terms of productivity.

This example is a manufacturing method suitable for lowering electrode resistance.

In FIG. 9, a Mo mask 6 having a window 5 is placed on the surface of a substrate 1 having a shallow N-type layer 4 on the surface of the Si substrate, and in this state, 1×10 ¹⁶ phosphorus ions 15 are passed through the window 5 of the mask. Ion implantation was performed at a concentration of / ^cm2 ,
A state in which a layer 16 doped with high concentration impurities is formed is shown. Next, as shown in FIG. 10, the mask 6 is kept as it is and the laser beam ⁷ with an intensity of 1.4 J/cm
is projected for 22n sec. By this laser beam projection,
A deep PN junction 17 is formed. This deep PN
Since the impurity concentration in the junction portion 17 is high, the connection resistance between the electrode layer and the semiconductor layer formed in subsequent processing can be reduced.

FIGS. 11 to 15 show examples in which the present invention is applied to the production of solar cells.
P-type Si substrate 1 with a specific resistance of 0.5 to 10Ω・cm (Fig. 11)
An N-type layer 4 (FIG. 11) with a depth of 0.1 μm is formed on the surface. Next, as shown in FIG.
A Mo mask 21 having windows (which appear to be individual windows, but are actually all continuous windows) is placed. When a laser beam 7 (Fig. 13) with an intensity of 1.4 J/cm ² is projected for 20 ns onto this mask, the impurities in the layer 4 exposed at the window are diffused deeply into the Si substrate, and the N A mold layer 8 (FIG. 13) is formed.

Next, without moving the mask 20 from the semiconductor substrate, the Si substrate is heated to 300°C in a metal vapor deposition apparatus (not shown).
First, titanium was deposited to a thickness of 1000 Å, and then Ag was deposited to a thickness of 3 μm. Layer 9 (first
Figure 4) is the titanium vapor deposited layer, and layer 10 (Figure 14) is the titanium vapor deposited layer.
This is an Ag vapor deposited layer. When the Mo mask 20 (Fig. 14) is removed after the vapor deposition, an electrode 11 made of a titanium-Ag double layer is formed on the surface of the deep PN junction 8 (Fig. 15).
is formed.

Through the above steps, a solar cell structure is obtained.

This embodiment has the following effects. (1) Electrodes are reliably formed on deep PN junctions and do not extend over shallow PN junctions, increasing product yield. (2) Since the PN junction other than the electrode part is located at a shallow position from the surface of the semiconductor substrate, the photoelectric conversion efficiency for sunlight is increased. In particular, the photoelectric conversion efficiency for short wavelength light, which is extremely low in conventional solar cells, can be increased. (3) In addition, the deep PN junction under the electrode layer suppresses the leakage current that accompanies electrode formation (because local breakdown of the deep PN junction does not occur) and increases the open circuit voltage. (Four)
Productivity is improved because the mask for forming deep PN junctions can also be used as a deposition mask for electrode formation.

In this example, if a step of ion-implanting N-type impurities at a high concentration using a mask 21 is added as a pre-process to the laser beam projection shown in FIG. 13, the electrode resistance will be lowered, and the loss can be reduced accordingly. .

Although the present invention has been described above with reference to typical embodiments of the present invention, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various changes can be made within the scope of the technical idea of the present invention. For example, in the embodiments of the present invention, only Si was described as the semiconductor substrate, but it is not limited to Si, and other semiconductor substrates such as Ge,
Compound semiconductor substrates such as GaAs and CdSe can also be used. Further, as for the electrode metal, not only the Ti-Ag double layer but also an electrode metal suitable for the semiconductor substrate used can be used.

[Brief explanation of the drawing]

1 to 6 are enlarged vertical cross-sectional views of main parts for explaining an embodiment of the present invention, FIGS. 7 to 8 are enlarged longitudinal cross-sectional views of main parts for explaining other embodiments of the present invention, and FIG. 10 to 10 are enlarged longitudinal cross-sectional views of main parts for explaining other embodiments of the present invention, and FIGS. 11 to 15 are enlarged longitudinal cross-sectional views for main parts for explaining other embodiments of the present invention. 1: P-type Si substrate, 2: impurity doped layer, 3,
7: Laser light, 4: N-type layer, 5, 18, 19, 2
0: Mask window, 6, 21: Metal mask, 8, 1
7: Deep PN junction, 9: Titanium vapor deposition layer, 10:
Ag vapor deposition layer, 11: electrode layer, 12: glass mask,
13: glass plate, 14: Al deposited film, 15: ion beam, 16: high concentration ion implantation region.

Claims (1)

[Claims] 1. A step of forming a shallow second conductivity type impurity layer in a surface region of a semiconductor substrate having a first conductivity type; a step of placing a mask having a window of a desired shape on the surface of the semiconductor substrate; a step of implanting ions of a second conductivity type through a window to form a region containing a large amount of ions of the second conductivity type in a surface region of the semiconductor substrate; and a step of applying a laser beam to the semiconductor substrate through the window of the mask. irradiating and diffusing second conductivity type ions in the region containing a large amount of second conductivity type ions into the semiconductor substrate to form a deep Pn junction; and exposing the exposed surface of the semiconductor substrate through the window. 1. A method for manufacturing a semiconductor device, comprising the step of depositing an electrode metal on the substrate to form an electrode metal layer.