JPS62210618A - Manufacture of semiconductor element - Google Patents

Abstract

PURPOSE:To perform a diffusion process at lower temperature, by utilizing a difference in a thermal expansion factor among SiN or SiO2 and a substrate so that diffusion of impurities is promoted in a silicon thin film. CONSTITUTION:An amorphous silicon thin film 2 is formed on a substrate 1 of quarz glass, and glow discharge is generated with SiH4 and impurities serving as raw material gases to form an a-Si:H film containing impurities. A silicon nitride film 4 is formed by glow discharge with SiH4 and NH3 or N2 serving as raw material gas thereon, and the whole element is heated at about 450 deg.C to make boron in the a-Si:H film 3 be diffused into the silicon thin film 2. After selectively etching the silicon thin film 2, a silicon nitride film 6 is formed thereon, and the whole element is heated at about 450 deg.C to make oxygen in an oxidizing silicon film 5 be shallowly diffused into the silicon thin film 2. Diffusion of oxygen is promoted by stress due to difference in a thermal expansion factor among the silicon nitride film 6 and the substrate 1 and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing semiconductor elements integrated on a substrate. Furthermore, the present invention relates to a manufacturing method that lowers the manufacturing temperature of a semiconductor element.

BACKGROUND ART Conventional Example 1. There is a technique of oxidizing SL in steam at 50 to 100 atmospheres. The substrate temperature was 600 to 1000°C, the oxidation rate was increased, and the oxidation temperature was lowered. However, since the pressure is extremely high at 50 to 100 atmospheres, and the entire substrate must be under high pressure, it is expected that the manufacturing equipment will be large-scale. Difficulties increase as wafer diameters increase. Or increase the pressure too much?
If the temperature is raised too high, the S s 02 film will melt.

Conventional example 2. A conventional method is to dissolve P2O5, B2O3, etc. in a solvent and apply it. However, in order to diffuse impurities, a high temperature of 900'C or higher has conventionally been required.

Conventional example 3. There is a conventional technology for diffusing impurities by molding phosphorus into a disk shape with silicon oxide and an organic binder, and fixing the disk containing phosphorus on one side of the boron and the disk containing boron on the other side. . This diffuses p-type and n-type at the same time. However, in this case, only the same impurity could be diffused over the entire surface of one side of the wafer. In addition, high temperatures were required for diffusion.

Problems to be Solved by the Invention As the integration of semiconductor circuits progresses, high temperature processing must be avoided in the process. This is because impurities interdiffuse. A low-temperature process is absolutely necessary for miniaturization.

Means for Solving the Problems The present invention uses an impurity-containing a-8i:H (hydrogenated amorphous silicon) film as a diffusion source, selectively etches it to leave only the necessary portions, and then Tinated silicon (Si)
The S102 film is covered with a silicon oxide (SiC2) film or a silicon oxide (SiC2) film.

By using such a method, the present invention promotes the diffusion of impurities into a silicon thin film, making it possible to lower the temperature of the diffusion process that requires the highest temperature among semiconductor processes.

Example Hereinafter, some embodiments according to the present invention will be described.

Example 1 Here, a thin film transistor (T
The manufacturing method of PT) will be described. The steps of the manufacturing method will be described in Figure 1.

A silicon wafer or quartz glass with an oxidized surface is used as a substrate 1, and an amorphous silicon thin film 2 is formed thereon by LPGVD. The raw material gas is S I H4-bound,
Vacuum level approximately 0.5 Torr and substrate temperature 600-630'C
deposited in The deposition rate was about 18 seconds. (1st
(Figure (a)) Next, a glow discharge is generated using SiH4 and impurities as source gases with a high frequency of 13.56 MHz and maintained at about I Torr to form an a-8i:H film containing impurities. B2H6 or BF3 was used as an impurity. A volume ratio of about 10 ppm to 10% was used with respect to SiH4. The concentration and a-3i:H film thickness were varied depending on the amount of boron doped into the silicon thin film 2. The threshold voltage of TPT could be controlled by the doping amount. a-3
The thickness of t:H film was 300 to 10,000. A silicon nitride film 4 was formed thereon by glow discharge using S I H4, NH3, and N2 as raw material gases. The degree of vacuum was approximately ITorr, and the substrate temperature was 180 to 300°C. After forming the silicon nitride film 4, the entire device is heated by 450'
The temperature was raised to about 50°C, and boron in the a-3t:H film 3 was diffused into the silicon thin film 2. The heat treatment time is 5 to 100 minutes. (Figure 1(b)).

Next, the silicon tinide film 4 was etched with phosphoric acid heated to 160'C, and a-Si:Hs containing impurities was removed by etching while measuring the surface resistance. After selectively etching the silicon thin film 2, a silicon oxide film 5 was formed by glow discharge. A mixed gas of SiH and No, CO2, H2O, or 02 was used as the raw material gas. Conventionally, a silicon oxide film 5 is formed on a silicon thin film 2.
If only the silicon oxide film 5 was formed, these interface properties would be poor (adversely affecting the TPT operation. In the present invention, the silicon oxide film 5
A silicon nitride film 6 is formed on top of the silicon nitride film 6 in the same process as in FIG.
The entire device is heated to about 450° C. to shallowly diffuse oxygen in the silicon oxide film 5 into the silicon thin film 2.

The stress caused by the difference in thermal expansion coefficient between the silicon nitride film 6 and the substrate 1 promoted the diffusion of oxygen. (FIG. 1(C)) The silicon nitride film 8 is etched again with phosphoric acid to form a contact hole 20. Silicon oxide film 5
was etched using a mixture of ammonium fluoride and fluoride. On top of this, S 1% and PH
a-S using a gas mixed with 3 or A s H3
i: H film 7 is formed. n-type impurity a-3i:H film 7
The purpose of doping is to make it easier to establish ohmic contact. The silicon nitride film 8 is formed again, and the thickness of about 4
Heat treated at 50°C. (FIG. 1(d)) When the silicon nitride film 8, a-8t:H film 7 is etched, the contact hole 2 is formed by phosphorus diffused in the previous process.
A diffusion layer 9 is formed under 0. The TPT is completed by forming metal vapor deposition film wiring 1o. The metal of the wiring 10 includes Al, T
i, Cr, Ni, Ta, W, Cr, etc. were used.

Example 2 In the above-mentioned Example 1, a silicon nitride film was used as the material to apply stress, but a silicon carbide film may also be used.
A mixed gas of carbides such as 2H4 and C2H2 was used.

Example 3 Although a silicon oxide film was used as the gate oxide film of the 'l' F T, a TPT could also be created using a silicon carbide film created by mixing carbide gas with S I H4.

Example 4 SIH4 and N20 are added to the TPT gate insulating film.
TPT could also be created using a silicon oxide film using a mixed gas of .

Example 5 A p-type impurity doped with B2H6, BF3, etc. is used instead of an n-type impurity as an impurity for ohmic contact under the contact hole, and a TP is also used as a p-channel.
I was able to create T.

Example 6 In order to promote the diffusion of impurities, stress due to the difference in thermal expansion coefficient between the silicon nitride film, silicon carbide film, silicon oxide film and the substrate was used, but impurities could also be diffused by applying mechanical pressure. was able to promote the spread of As for mechanical pressure, the present invention was carried out using, for example, a device as shown in FIG.

That is, the half-manufactured semiconductor elements 30 shown in FIG. 3 are stacked one on top of the other, and graphite 31 is placed above and below the stacked semiconductor elements 30 to reduce shock. Place these on the substrate stand 32 and place the top plate 33 on top as shown in the figure. Semiconductor element 3
A weight 35 is placed on the shaft 34 in order to apply pressure to the shaft 34, and it is fixed to the top plate 33 with a screw 36. The entire body is covered with a quartz tube 37, a lid 38 is attached, and the tube is introduced into an electric furnace (not shown).

An inert gas such as N2 is supplied from the pipe 39 of the lid 38. H2
Heat treatment is carried out by flowing ゜8r, f(e, etc.).The temperature of the electric furnace is set at 300 to 700℃.In order to effectively apply pressure to the area to be diffused, as shown in Figure 3, the area to be diffused is heated. An a-8i:H film 50 containing impurities was formed by etching, leaving the a-3i:H%aO portion.When the substrates 3o thus formed were stacked as shown in FIG. pressure will be added.

Although the magnitude of the pressure can be easily calculated using the area left after etching and the load, a large error occurred due to the elastic deformation of the substrate. The optimum value must be found for each jig that applies the load.

In this example, when a 5α×10 quartz substrate was used and the portion left after etching was about 0.1%, impurity diffusion was promoted when a load of 5001 to 59 was applied.

Effects of the Invention As mentioned above, by applying mechanical pressure to the polycrystalline silicon on the substrate and accelerating the diffusion of impurities such as phosphorus, boron, arsenic, etc., low temperatures can create ohmic contact between the polycrystalline silicon and the metal. It can be done selectively. Further impurities include oxygen and carbon.

By using nitrogen, an insulating film can be formed on the polycrystalline silicon surface at a low temperature, and by these, TP
Semiconductor elements such as T can be formed at low temperatures.

[Brief explanation of drawings]

FIG. 1 is a process cross-sectional view showing a method for manufacturing a thin film transistor according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a semiconductor device manufacturing apparatus according to another embodiment of the present invention, and FIG. FIG. 3 is a cross-sectional view showing an example of how to add layers. 1...Substrate, 2...Silicon thin film, 3.
Completed, 50... a-8i containing impurities: H14,6
, 8... Silicon nitride film, 9... Diffusion layer, 1o... Metal vapor deposition film wiring, 20...
・Contact hole, 3o... Semiconductor element in the process of being manufactured, 31... Graphite, 33... Top plate,
35... Weight. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 1 Figure 2 q Diffusion layer Figure 2

Claims (3)

[Claims] (1) A silicon thin film made of polycrystalline silicon or amorphous silicon is formed on a substrate using a low-pressure vapor phase epitaxy method, hydrogenated amorphous silicon containing impurities is formed using a glow discharge method, and then a silicon film is formed using a glow discharge method. silicon oxide silicon carbide or silicon oxide, and by heating the silicon thin film while applying mechanical pressure, hydrogen-containing impurities present in the hydrogenated amorphous silicon are diffused into the silicon thin film. Features: A method for manufacturing semiconductor devices. (2) When forming hydrogenated amorphous silicon by glow discharge method, B_2H_6, BF_3, PH_3, AsH_3,
O_2, N_2O, CO_2, H_2O, CH_4, C
2. The method of manufacturing a semiconductor device according to claim 1, wherein at least one of _2H_4, C_2H_2, NH_3, and N_2 is used as an impurity source. (3) The method for manufacturing a semiconductor device according to claim 1, characterized in that after forming hydrogenated amorphous silicon containing impurities, selectively etches only the portion where the impurities are desired to be diffused.