JPS58130528A - Semiconductor etching method - Google Patents

Abstract

PURPOSE:To enable a deep etching having a high pattern accuracy in simple processes, by selectively etching a semiconductor substrate by a microwave plasma etching using a gas not containing carbon. CONSTITUTION:An Si substrate is prepared whereon a sensor region is formed at the fixed part of the main surface 12, and an SiO2 film is selectively formed on the main surface 11 of this substrate. As the SiO2 film selectively formed on the main surface 11, the part corresponded to a recess 14 and pelletizing grooves 13 is opened window. Next, a microwave plasma etching is applied to this Si substrate. In this case, a gas selected from gasses not containing carbon e.g. SF6, NF3, F2, XeF2 is used as the atmosphere gas. Thereby, the Si substrate 1 for a semiconductor pressure sensor is obtained which has deep and high pattern accuracy recess 14 and grooves 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for etching semiconductors, a method for etching silicon substrates using a micro-ridge plasma qtz.

The manufacture of semiconductor devices often involves processing a silicon plate into a desired shape by etching.

In addition, this etching liquid machine is required to have a simple etching process, a short processing time, a high temperature of 11 degrees, and a flat etching surface.
Etching, which is used in the manufacture of semiconductor devices such as semiconductor pressure sensors, in which most of the semiconductor substrate in the sensor part is removed by etching, and the sensitivity and strength are determined by the thickness and shape of the remaining semiconductor substrate, is particularly difficult. High precision processing is required.

Semiconductor etching methods include wet etching using a liquid atmosphere and gas atmosphere I! ! Dry etching is known. The former method is widely used because if etching conditions are appropriately selected, the associated etched shape can be obtained relatively well with ffJ[, and the etched surface is also flat. However, this wet etching process is complicated because (1) the semiconductor substrate is immersed in an etching solution, and the narrow surfaces that will not be etched are coated with a corrosion-resistant film, which must be removed after etching is completed. (4) When using an etching solution whose etching speed is not affected by the shadow 11 of crystal planes, that is, isotropic etching, the pattern quality is poor due to side etching, and this becomes more pronounced as the etching depth increases. (3) When using an etching solution that has different etching rates depending on the crystal plane, that is, an anisotropic etching solution, there is little side etching, and a straight pattern has a relatively high degree of +lib etching, but a curved pattern (4) No matter what kind of etching solution is used, the pattern n1 degree will be bad in the pattern of
It is not possible to obtain an etched surface with a single surface, but the @ surface is inclined so that the irr#J surface, which is parallel to the royal surface, becomes smaller in the depth direction. The latter method has a simple process and a short processing time, and in the case of shallow etching, the pattern density decreases. Recently, the etching depth has been used in the LSI field, but most of them have an etching depth of 1 to 2βm, and the etching depth is from several μm to several 10 μm, and even 111 μm.
It is not used for etching as deep as 00 μm.

The reason for this is inferred as follows based on six experiments conducted by the inventors. The reason for Ml is thought to be that deep etching causes ions to be physically ejected from the etched surface, making the etched surface uneven. For example, coat At on 5i01, use 9 masks, and CF
When a silicon substrate was etched to a depth of 100 μm using a parallel plate electrode with a 4T atmosphere gas, the etched surface (bottom of the recess) had irregularities of up to 30 μm and was round.The second reason is that it is the most suitable as a mask. There it is! 3
Selectivity when using 10m (etching speed of St/
Most of the etching speeds (5ill etching speed) are below 10, and the maximum reported is 3o, so the depth that can be reliably etched is about 10 times the mask thickness. Considering the difference in thermal expansion coefficient with the silicon substrate and the curvature of the substrate, the etching depth must be 1 μm or less, and the etching depth that allows highly reliable etching using a SiO mask is 104 m@
This is thought to be because it is limited to [. In order to increase the selectivity, it is possible to stack 9-hole metal of A/, on 5ins, but in this case, the etching gas tl-2
Not only does the process become more complicated due to the use of soybeans, but also S
There is a drawback that the iOx and At windows do not match due to differences in resist film thickness, insufficient alignment, etc. when forming T, resulting in a drop in the pattern/tlff.

As described above, in the semiconductor etching methods known so far, deep etching with a high pattern thickness nIIt using a simple process has not been possible.

It is an object of the present invention to provide a method for etching a modified semiconductor, which eliminates the above-mentioned drawbacks. A specific object of the present invention is to provide a semiconductor etching method that allows deep etching with simple steps.

The semiconductor etching method of the present invention that achieves the above purpose is characterized by selectively etching the silicon substrate using a silicon oxide film as a mask by microwave plasma etching using a gas excluding carbon-containing gas as an atmospheric gas. Focus on what you want to do.

Microwave plasma etching is a process in which atmospheric gas at a predetermined pressure is excited by a micrometer to generate plasma, and the chemical reaction between excited atoms and molecules (positive ions and radicals) in the plasma and solid material increases volatile or vapor pressure The basic principle is known for etching solid materials in the gas phase using reactions that produce high φ reaction products.

There are two types of microwave plasma etching: one that causes the above reaction without a magnetic field, and one that causes the above reaction in a magnetic field.The former is isotropic etching, while the latter is anisotropic etching. is somewhat superior in terms of pattern accuracy. Also, the latter has high fI even at low gas pressure! jg
iL plasma can be obtained, which has the advantage of increasing the etching rate when the gas pressure is the same.1 Although the present invention can be applied to both non-magnetic field and magnetic field, the latter, magnetic field microwave plasma etching The effect is huge.

The atmospheric gas for microwave plasma etching is
Fluorine-based gases, which have a small atomic radius and a large electrical cathodity, are conveniently used. The fluorine-based gases that have been used in the LSI field so far are mainly CF4, and other fluorine gases such as CF, , CF'
s, CF2Cl, CFfuClx.

There are CCjsF* CFsBr, etc. In the case of such a gas containing C, the etching speed is low, so if it is applied to deep etching, the escape time will be long, and as the etching depth increases, the etching surface will become more uneven. be.

In the present invention, to eliminate the above-mentioned drawbacks, gases not included in C', such as SFg, NFs * Fs, XeFs
Use at least one type of gas T-conveyor selected from the following.

According to the magnetic field microwave plasma etching IIC using such an atmospheric gas, even if deep etching of 30 to 100 m is performed, the unevenness of the etched surface can be reduced to less than m.

Among these gases, those that do not contain S are preferred from the viewpoint of workability and pollution.

Next, the ψ center is etched by the pressure of the atmospheric gas, which exceeds 3011 mi using 5 ins as a mask]
lKi! 'Demeru. Figure 1 shows the results of measuring the relationship between the pressure of the atmospheric gas and the etching thirst of 3i (*il) and 810m (dotted line) in magnetic field microwave plasma etching using SF as the atmospheric gas. . Based on this result, the relationship between the atmospheric gas and the selectivity (Si etching rate !21/S i Os etching rate) is shown in FIG. According to this figure, when the atmospheric gas pressure is below 5 x 10-'Torr, the selection ratio is small, and even if the gas pressure changes, the selection ratio changes only slightly.
It can be seen that when the value exceeds 5×10 Torr1, the selection ratio exceeds 30 tons, and the change in the selection ratio with respect to a change in gas pressure becomes large. Also, the gas pressure is 3 × 1 G-”Torr
When reaching , the selection ratio exceeds 100i, and the selection ratio becomes 3
It can also be seen that when r is exceeded, a selectivity of 100 or more is always obtained. Is it possible to obtain a selectivity t of 100 or more and close to 200 even when the gas pressure exceeds 10" Torr? If we pre-empt the etching process by evacuating the chamber and supplying atmospheric gas, we can obtain the desired etching ratio. It is preferable to perform etching at the lowest possible gas pressure at which the selectivity can be obtained.The relationship between the atmospheric gas pressure and the selectivity is almost the same even when N k's # Ft mXeFsk* other than 8Fs is used. 19. The results shown in Figures 1 and 2 are for micro-temporal plasma etching in a magnetic field, but in the case of microwave plasma etching in a non-magnetic field, the etching rate of Sl and 5 ins in a magnetic field. Although the ratio softened and decreased somewhat, the relationship between gas pressure and selectivity was approximately the same as in FIG. 2.

The present invention will be explained in detail below with reference to Examples.

FIG. 3 shows a silicon substrate for a semiconductor pressure sensor formed using the present invention. In the figure, a silicon substrate having a pair of major surfaces 11.12 and -10,000 major surfaces 1
On the first side, there are formed pelletizing holes 13 formed in a grid pattern and a circular recess s14 formed in a rectangular portion surrounded by the pelletizing holes 13. A sensor region (not shown) having a conductivity type opposite to that of the silicon substrate (M) is previously formed in a portion of the other main surface 12 of the silicon substrate 1 corresponding to the recess 14 by, for example, selective diffusion.

This silicon deposited plate 1 is divided by a pelletizing die 13 to form a semiconductor pressure sensor.

A#i4 is a method for manufacturing such a cryocon board for use in body pressure cassettes. First 1. A silicon substrate is prepared in which seven regions are formed at predetermined locations on the other main surface, and 810sllI is selectively formed on the -1 main surface 11 of this substrate. Specifically: A 5LQs film is formed on both main surfaces of a ti silicon substrate by a thermal oxidation method, and then selectively removed by a photoetching method.

The 810m film on the other main surface is used as a mask for diffusion when forming a sensor region.

-9Sin selectively formed on the main surface of 10,000, as a film,
The recess 14 and the portion corresponding to the pelletizing hole 13 are opened and left as a memorial. Next, the solid silicon substrate is etched in a chamber of a microwave plasma five-chip/dry apparatus.

As a result, a silicon substrate 1 for a semiconductor pressure sensor having the shape shown in FIG. 8 is obtained.

This is illustrated using a keft example as follows.

A disk-shaped single-crystal silicon wafer with a thickness of 200 μm and a diameter of 40 μm is used as the silicon substrate.
A circular window with a diameter of 1.6 m was formed on a medium flame in a grid-shaped window spaced at intervals of 20 square meters and a portion surrounded by the grid pattern. This silicon substrate was heated under atmospheric gas SF- and gas pressure lXl0-2T.
orr, -r cum o[2,45GH! 4kl'
! Magnetic field microwave plasma etching was carried out at F for 50 minutes. As a result, a grid-like pelletizing groove having a width of 50 .mu.m and a depth of 60 .mu.m and a circular recess having a diameter of 1.6 .mu.m and a depth of 150 .mu.m were formed on the -1 main surface of the silicon substrate. The circular recess has the same shape as the window formed in the Sin and section, the side surfaces of the recess are flat heads perpendicular to the main surface, and the bottom is formed with a plane approximately parallel to the main surface, and the uniformity is a constant curve. It was a slow curved surface with a single semipolar curve. Each surface of the l'c circular concave portion was approximately fitted with a mirror l with a maximum unevenness α of 5 μm. Note that 0.05 μm of sio and g as a mask remained after etching. As described above, it can be seen that according to the present invention, extremely deep dry etching of 150 .mu.m can be performed as a 3i01 film t mask, and etching with high pattern accuracy can be performed for a single tablet based on the mask shape. Further, according to the present invention, the etching depth can be changed by changing the area of the window (particularly the window) formed in the mask, so that recesses of different depths can be formed at the same time.

Next, as a comparative example, a case in which a similar silicon substrate for a semiconductor pressure sensor is manufactured by wet etching and conventional dry etching will be described.

First, as an example of wet etching, a resist layer is used as a mask and a KOHt-etching solution is used.

After etching with liquid m'toc for 6 hours, JllI
A recess and a pelletizing groove as shown by the dot in Figure 3 can be obtained, that is, the recess has a hexagonal opening along the crystal plane, and the 111 plane has an inclination tki of about 471'' with respect to the main surface. M
The etching direction has locally uneven protrusions and depressions, and the maximum unevenness is 10 μm.

As an example of dry etching, parallel plate electrodes with uck'at-atmosphere gas were used. When only the mask tSins film (1/Am) was used, the etching solution was lθ~2
When the VC reached 0 μm, the S10 film disappeared, and deeper etching could not be performed. if, 3
When a mask 'tR with Atf formed on i (h) was used, a recess of 150.4 m was obtained after one hour of etching. However, the maximum unevenness of the recess was 30 μm, and a practical recess could not be obtained.

The above description has focused on the case where the present invention is applied to a conductor pressure sensor, but the present invention is not limited to this, and in other words, it can be applied to groove formation for isolation of MOS-IC, dielectric material, etc. # Separate board! When manufacturing, the present invention can be applied to the formation of annular groups of power semiconductor devices.

[Brief explanation of the drawing]

Figure 1 is a diagram of the relationship between atmospheric gas pressure and etching speed when etching 9i and 3iQ1 by microwave plasma etching, and Figure #L2 is a diagram of the relationship between atmospheric gas pressure and etching selectivity in i microwave plasma etching. FIG. 3 is a schematic diagram showing a substrate for a cow conductor pressure sensor manufactured according to the present invention. l... Silicon substrate, 13... Pelletizing groove, 1
4 Figure 1 □ Atmospheric force (human pressure (Torr)) Figure 2

Claims (1)

[Claims] 1. Selection of the six main directions n 11i! A semiconductor etching method characterized in that a selected portion of a silicon substrate coated with a silicon oxide film is subjected to micro-plasma etching, and the etching method is characterized in that a gas other than a carbon-rich gas is used as an atmospheric gas. . 2. A semiconductor etching method according to claim s1, characterized in that at least one gas selected from NFs #Fm + XeFs is used as the atmospheric gas.