JPS6247251B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor sensor that utilizes an electric field effect, and particularly to a method for manufacturing a semiconductor sensor characterized in that its sensitive film is formed from an alcohol solution (alkoxide solution) of an organometallic compound.

Conventionally, as a sensitive film for semiconductor sensors, e.g.
Proposals have been made so far, such as that valinomycin fixed on PVC can be used for K ions. For example, in Japanese Patent Application Laid-Open No. 52-26292, there is a possibility that "...the glass composition can be formed by a coating method of an alkoxide solution", but the specific content thereof is completely unknown.

When forming a sensor-sensitive film using an alkoxide solution, special attention must be paid to the problem of contamination of the transistor (FET) by metal ions contained in the solution.

Alkoxide solutions often contain alkali and alkaline earth metals, and it is well known in the FET manufacturing process that ions such as Na ⁺ can cause device instability if they enter the FET. It is a fact that Therefore, when forming a sensitive film, it is important to pay sufficient attention to the contamination of the metal ions and prevent this from occurring.

The present invention provides a method for manufacturing a field-effect semiconductor sensor that effectively prevents contamination from the contact portion, which is often a problem, in the process of forming an alkoxide solution film on the gate insulating film of the sensor and the subsequent heat treatment process. This is what we provide.

Hereinafter, a method for manufacturing a sensor according to the present invention will be explained with reference to the drawings.

For example, the manufacturing process of field effect transistors before forming the sensitive film of the sensor is disclosed in Japanese Patent Application No. 1973-
96602 (Japanese Unexamined Patent Publication No. 55-24603). Briefly explained according to the drawings: (1) A P-type silicon (100) surface with a resistivity of about 10 Ωcm is used as the substrate, and the thickness is reduced by chemical etching.
The diameter shall be 200μm.

(2) Both sides are oxidized and covered with _two layers of SiO. (3) The _two SiO layers in the areas indicated by hatches in Figure 2a are removed by photo-etching, and at the same time, silicon is etched on the back side of the device. Mark it for removal.

Although FIGS. 2a to 2e are plan views of one element for explaining each process, in reality, as shown in FIG. 1, a large number of the same elements are formed on the silicon substrate 1. To briefly explain Figure 1 here,
FIG. 1 is a diagram for explaining the manufacturing process according to the present invention in which a large number of sensing elements are simultaneously formed on a single silicon substrate 1. In FIG. The manufacturing process according to the present invention is characterized in that the surface stabilization of the vicinity of the sensitive portion of each element including its side surfaces is completed before separating the elements formed at the same time.
For this purpose, the front part 3 containing the sensitive part of the element is made thin, the rear part 4 of the element is made wide, and the parts where the rear parts 4 are adjacent to each other, that is, the parts 5 with cross hatches, are made not to be separated and are finally scribed. Only a scribe line for cutting is formed, and only the portion 6 shown with a hatch is completely removed. Hereinafter, portion 6 will be referred to as the removed portion. By doing so, the side surface of the element front section 3 is exposed at this stage, so that the process can proceed at this time, including surface stabilization of this side surface.
Incidentally, since the etching of the removed portion 6 is carried out simultaneously from the front and back sides, the mark on the back side provided in step (3) is necessary at this time.

(4) Next, phosphorus is diffused to a density of 10 ¹⁸ cm ^-3 to form a source region and a drain region in the portion where the SiO ₂ layer was removed in step (3). The depth of this diffusion is from several μm to more than ten μm, and the source region 11
The distance 13 between and the drain region 12 is 10 to 50 μm.
It is as follows. Of course, these values can be changed as appropriate depending on the overall size of the element.

(5) Remove the SiO ₂ layer in the hatched region in FIG. 2b, and diffuse boron into this region to form the P ⁺ channel stopper region 14. The channel stopper region 14 is for preventing a channel from being formed between the source region 11 and the drain region 12 except near the sensitive part at the tip of the element, and has a depth of 0.1 to 3 μm. As a result, a channel is formed only in the crosshatch portion 15 of FIG. 2b. Hereinafter, this channel area will also be represented by the reference numeral 15.

(6) Photo-etch the portion of the SiO ₂ layer indicated by hatching in FIG. 2c, and diffuse phosphorus into this portion to form contact n ⁺ regions 16 and 17. After this, the removed portion 6 and scribe line 5 shown in FIG. 1 are etched. That is, (7) by photo-etching, the two SiO layers on the front and back sides of the removed portion ₆ shown by hatches in FIG. 1 and the front side of scribe line 5 shown by cross hatches are removed.
Remove the _SiO2 layer.

(8) When selective etching is performed on these parts, grooves formed by etching progressing from both the front and back surfaces of the removed portion 6 are connected, and the side surface of the element front portion 3 is completely exposed. On the other hand, in the scribe line 5, a groove with a depth of only about 50 μm is formed because the etching progresses only from the front side and the width of the etched portion is narrow.

(9) After drying the wafer, the exposed sides of the device front 3 are oxidized and coated with a layer of SiO ₂ . this
The thickness of the SiO ₂ layer is, for example, 6000 Å or less.

(10) The SiO ₂ layer above the device sensitive area 19, drain contact region 16, and source contact region 17 shown by hatching in FIG. Dry oxidation is performed to form a SiO ₂ layer with a thickness of several hundred to several thousand Å, for example 1000 Å. As a result, a gate oxide film is formed above the channel region 15.

The above is an example of the manufacturing process of a field effect transistor before forming a sensitive film. After this, in order to form a sensitive film from an alkoxide solution, the device surface must be stabilized immediately after the gate oxidation process. There is a need. The reason for this is that the alkoxide solution contains alkali (or alkaline earth) metal ions as one of its components, and if these enter the gate oxide film (SiO ₂ ), they can cause device instability. It is from.

For example, the method of surface stabilization is disclosed in Japanese Patent Application No. 1983-96602.
As disclosed in , Si ₃ N ₄ is deposited over the entire surface of the device by high temperature CVD at 900-1000°C. Furthermore, the surface stabilizing film is not limited to the Si ₃ N ₄ film, but any insulating material with excellent water resistance, denseness, and ion impermeability may be used, for example,
Films such as tantalum pentoxide (Ta ₂ O ₅ ), tantalum nitride (TaN), silicon oxynitride (SiOxNy), aluminum oxynitride (AlOxNy), and tantalum oxynitride (TaOxNy) can be used.

After the surface stabilizing film is deposited, a sensitive film is formed on the gate insulating film (stabilizing film) of the sensor, and source and train contacts are formed to complete the sensor. When forming contact areas, care must be taken in handling the contact portions, especially during the alkoxide solution film formation process and heat treatment process. Regarding the handling of the contact portion in order to prevent contamination of the FET from the alkoxide solution, the present invention specifically proposes the method described below.

In this method, a film of an alkoxide solution is formed on the gate insulating film of the sensor while the surface stabilizing film is still deposited so as to cover the entire surface of the device including the contact portion, and then heat-treated and multilayered. This is a method of forming a component-based oxide film (sensitive film).

A specific example of forming the sensitive film will be described later. The structure of the contact portion in this case is shown in FIG. FIG. 3 shows a cross-sectional view at the drain contact part 35 of the sensor according to the invention, which is completely covered with an oxide film (SiO ₂ ) 36 and a surface stabilizing film 37 thereon. In addition, contamination by NA ⁺ ions and the like released during the formation of the sensitive membrane can be prevented. This situation also applies to the source contact portion. After forming the sensitive film,
The surface stabilizing film 37 of the drain and source contact portions 16 and 17 shown by hatching in FIG. By this method, the sensor is completed by forming the drain and source contact portions 21 and 22 shown in FIG. 2f.

FIG. 4 is for explaining an example of an ion sensor to which the present invention can be applied, and shows a cross-sectional view at a channel portion 15 of the element. here 4
1 is a P-type silicon substrate, 42 and 43 are source/drain diffusion regions, 44 is a gate oxide film (SiO ₂ ), 45 is an oxide film (SiO ₂ ), 46 is a surface stabilizing film, and 51 is a sensitive film. . In Fig. 4, the sensitive film is formed only on the sensor surface, but there is no problem even if the sensitive film extends to the side or back surface of the sensor by the forming method (spray method, spin coating method, dipping method, etc.). do not have.

Hereinafter, a method for forming a sensitive film will be specifically explained based on some examples.

Example 1 Formation of a glass sensitive membrane for H ⁺ ions.

The alkoxide compounds used are as follows.

Si(OC ₂ H ₅ ) ₄・Ca(OCH ₃ ) ₂ 16mole% solution and
_NaOCH3 16mole% solution. Here, the above Ca
(OCH ₃ ) ₂ and NaOCH ₃ 16mole% solutions are each metal
It was prepared by dissolving Ca and Na in methanol (CH ₃ OH). The alkoxide solution was prepared as follows. While introducing dry nitrogen gas into a flask on a stirred hot plate equipped with a selective flow condenser, add 100 c.c. of methanol (3.03 cc) of Ca (OCH ³ ) ₂ 16 mole% solution and bring to a boil while stirring. , add the following in sequence:

NaOCH ₃ 16mole%...11.1cc Si(OC ₂ H ₅ ) ₄ ...16.1cc This was heated under reflux until the solution became transparent.
Stir. The alkoxide solution thus prepared contains oxides in the following proportions:

Na ₂ O: 22 mole% CaO: 6〃 SiO ₂ : 72〃 The oxide composition is not limited to the above ratio, and H ⁺
As the sensitive membrane of the ion sensor, any composition within the following range can be selected.

Na ₂ O: 15-30 mole% CaO: 4-10 SiO ₂ : 60-81 A method for forming a sensitive film on the sensor surface from the above alkoxide solution will be described below.

A uniform coating of the alkoxide solution is formed on the sensor surface, preferably on the front part 3 in FIG. 1, by a spraying method, a spin coating method using a spinner, dipping, or the like. The thickness of this film can be arbitrarily adjusted by adjusting the content of alcohol (methanol) in the alkoxide solution, but it is preferably in the range of 500 Å to 10,000 Å. This coating is then fully hydrolyzed in the presence of moisture. If the film is thin, moisture in the air is sufficient, but it is generally better to carry out hydrolysis in air that contains sufficient water vapor. If this hydrolysis is insufficient, the remaining alkyl groups left in the film will be carbonized in the next heating step, which is undesirable due to the presence of carbon in the sensitive film. After hydrolysis, in an inert gas (e.g. nitrogen gas) 2-3
Raise the temperature to 500-800℃ over time and leave it at this temperature for several hours. This completes the sensitive film.

After forming the ion-sensitive film by the method described above, the drain and source contact portions 21 and 22 shown by hatching in FIG. 2f are formed.
Complete the PH sensor.

Example 2 Formation of glass sensitive membrane for Na ⁺ ions.

The alkoxide compounds used are as follows.

Si( _OC2H5 ) ₄ , Al(i- _OC4H9 ) ₃ and _{NaOCH3 16 mole} % solution. here
A 16 mole% NaOCH ₃ solution was prepared by dissolving metallic Na in methanol (CH ₃ OH). To prepare the alkoxide solution, add 8.86 g of methanol (100 c.c. Ai(i-OC ₄ H ₉ ) ₃ ) and stir while introducing dry nitrogen gas into a flask on a stirring hot plate equipped with a reflux condenser. Bring to a boil, then add the following in order:

NaOCH ₃ 16mole% solution...5.55cc Si(OC ₂ H ₅ ) ₄ ...15.8cc This was heated under reflux until the solution became transparent.
Stir. The alkoxide solution thus prepared contains oxides in the following proportions:

Na ₂ O: 11mole% Al ₂ O ₃ : 18〃 SiO ₂ : 71〃 The oxide composition is not limited to the above ratio, and Na ⁺
As the sensitive membrane of the ion sensor, any composition within the following range can be selected.

Na ₂ O or Li ₂ O: 10 to 25 mole% Al ₂ O ₃ : 10 to 25〃 SiO ₂ : 50 to 80〃 However, like Na _{2 O, Li 2 O} is prepared by dissolving metal Li in methanol. The prepared LiOCH ₃ 16 mole% solution was used.

The method for forming a sensitive film on the sensor surface from the alkoxide solution is as shown in Example 1. This completes a pNa sensor with excellent characteristics.

Example 3 Formation of glass sensitive membrane for K ⁺ ions.

The alkoxide compound used was the same as in Example 2. To prepare the alkoxide solution, introduce dry nitrogen gas into a flask on a stirred hot plate equipped with a reflux condenser, add 100 c.c. of methanol and 1.97 g of Al(i-OC ₄ H ₉ ) ₃ and stir. Bring to a boil, then add the following in order:

NaOCH ₃ 16mole% solution...13.6cc Si(OC ₂ H ₅ ) ₄ ...15.4cc This was heated under reflux until the solution became transparent.
Stir. The alkoxide solution thus prepared contains oxides in the following proportions:

Na ₂ O: 27 mole% Al ₂ O ₃ : 4〃 SiO ₂ : 69〃 The oxide composition is not limited to the above ratio, and K ⁺
As the sensitive membrane of the ion sensor, any composition within the following range can be selected.

Na ₂ O: 25 to 30 mole% Al ₂ O ₃ : 2 to 7 SiO ₂ : 63 to 73 The method for forming a sensitive film on the sensor surface from the above alkoxide solution is as shown in Example 1. This completes a pK sensor with excellent characteristics.

Note that the alcohol used as a solvent is not limited to methanol, and the alkyl group of the alkoxide compound may be the methyl group (-OCH ₃ ) described in the example,
Needless to say _, it is not limited to the ethyl group ( _-OC2H5 ) and _the butyl group ( _-OC4H9 ). Furthermore, it goes without saying that the method for forming a sensitive film described here can be applied not only to cations such as H ⁺ , Na ⁺ , and K ⁺ , but also to semiconductor sensors for negative ions and certain gases. It is.

As described above, in the method of forming a sensitive film from an alkoxide solution on the gate insulating film of a field effect semiconductor sensor, the process of forming the sensitive film is carried out with the contact portion covered with a surface stabilizing film. This makes it possible to prevent the problem of FET contamination due to alkali metal ions such as Na ⁺ ions, and to realize a stable sensor.

[Brief explanation of the drawing]

Figure 1 is a plan view showing a large number of semiconductor sensors formed on one wafer, Figures 2 a to f
is a plan view showing the parts processed in each process,
FIGS. 3 and 4 are cross-sectional views of a sensor for explaining an embodiment of the present invention. 31, 41...P-type silicon substrate, 32, 42...
Source diffusion region, 33, 43... Drain diffusion region, 34... Channel stopper, 35... Contact portion, 36, 45... Oxide film (SiO ₂ ), 37,
46...Surface stabilization film, 44...Gate oxide film ( _SiO2 ), 51...Multi-component oxide sensitive film.

Claims (1)

[Claims] 1 In a method of forming a sensitive film of a semiconductor sensor using an electric field effect from an inorganic film, an alkoxide solution is applied to the gate insulating film of a field effect transistor whose entire surface including the contact area is covered with silicon nitride. A method for manufacturing a field-effect semiconductor sensor, which comprises heat-treating the film to form a sensitive film, and then removing silicon nitride from the contact portion to form an electrode at the contact portion.